Comparing Different Biogas Upgrading Techniques

Comparing different biogas upgrading techniques Final report 

J. de Hullu J.I.W. Maassen P.A. van Meel S. Shazad J.M.P. Vaessen L. Bini, M.Sc. (tutor) dr. ir. J.C. Reijenga (coordinator) Eindhoven University of Technology, July 3, 2008

Abstract

This report is the result of a multidisciplinary project at the technical university of Eindhoven commissioned by Dirkse Milieutechniek BV. The goal of the project was to research and compare the currently availabl availablee techniques to upgrade biogas. Upgrading of biogas comprises the removal of C of  C O2 , H 2 S  and other possibl p ossiblee pollutan p ollutants ts from biogas. This increases increases the concentration concentration of  C H 4 which gives the biogas a higher calorific value allowing for injection in the gas grid or to use as a fuel. H 2 S  has to be removed because of its corrosiveness. Five Five techniques techniques have been investigat investigated. ed. Chemical Chemical absorption absorption of H  of H 2 S  and C O2 into iron-chelated iron-chelated cq. amine solutions offers a highly efficient efficient removal removal of  H 2 S  from a gaseous gaseous biogas biogas stream. stream. The catalyst catalyst solutio solutions ns function function as a pseudopseudo-cata catalys lystt which which can be regenera regenerated. ted. The H 2 S  is removed almost completely and converted to elemental sulphur. The C O2 is removed and is treated as a waste stream. High pressure water scrubbing is based on the physical physical effect of dissolving dissolving gases gases in liquids liquids.. In a scrubber, scrubber, CO 2 as well as the H 2 S , dissolve into the water while C H 4 does not, because because of their their differen difference ce in solubi solubilit lity y. This This makes water scrubbing a very simple process. Pressure swing adsorption separates certain gas species from a mixture of  biogas under pressure, according to the species molecular characteristics and affinit affinity y for an adsorpti adsorption on materia material. l. The adsorptio adsorption n material material adsorbs adsorbs H 2 S  either irreversibl irreversibly y or reversible. reversible. Therefore Therefore a complex H 2 S  removal step or regeneration phase is needed for this process. The fourth process pro cess separates the components components cryogenically cryogenically.. The different chemicals in biogas liquefy at different temperature-pressure domains allowing for distillation. Typically a temperature of -100 C  and a pressure of 40 bars is used. Finally, it is possible to separate C O2 and H 2 S  from C H 4 using a membrane. Because of selectiv selectivee permeation, C O2 and H 2 S  will pass through a certain membrane while C H 4 does not. This is also a very simple technique since only a compressor and a membrane are needed. Each technique is compared on financial feasibility, impact on the environment and ease of operating the process. Furthermore, each technique has its own unique advantages advantages and disadvantage disadvantages. s. Table 1 gives an overview of  the costs, yield and purity of each technique. ◦

Table 1: Comparison of prices, yield and purity of the different techniques

Price p er N m3 of biog biogas as Yiel Yield d %  Chemical Absorption 0.28 90 High Pressure Water Scrubbing 0.15 94 Pressure Swing Adsorption 0.26 91 Cryogenic separation 0.40 98 Membrane separation 0.22 78 Technique

Puri Puritty % 98 98 98 91 89

Financial Feasibility

Table 1 shows that high pressure water scrubbing seems to be the cheapest techniqu techniquee to upgrade upgrade biogas. biogas. Also Also this this techni technique que gives gives quite quite high high yield yield and purity. Cryogenics is the most expensive way of upgrading biogas but it gives the highest possible yield. Impact on the environment

Chemical absorption has several waste streams, one containing C O2 and two different streams containing amines or Fe/EDTA complexes.Thes complexes.Thesee are the catalysts catalysts used in the absorpti absorption on processes. processes. All streams streams need to be disdisposed posed as chem chemic ical al wa waste ste.. High High press pressur uree water ater scrub scrubbi bing ng has has two two wa wast stee streams. The water waste stream contains such a low concentration of H  of H 2 S  and C O2 that it does not need further treatment. treatment. The second waste waste stream is a gas stream which also contains H 2 S  and C O2 but also some C H 4 . Because H 2 S  is rather poisonous, this stream should be treated and the C H 4 should be burned. Pressure Pressure swing adsorption and membrane membrane separation both have one waste stream that mostly contains C H 4 and and has to be burned burned.. Cryo Cryo-genics has also one waste stream containing mostly C O2 and some traces of  H 2 S  and C H 4. This waste stream needs treatment. Ease of operation

The operation of the pressure swing adsorption and chemical absorption process is quite simple. However, the plant needs to shut down several times per year because the catalyst has to be replaced. Membrane separation and high pressure water scrubbing are the simplest processes to operate because they do not need special chemicals or equipment to run. Cryogenics is difficult to operate because it works on high pressure and really low temperatures and therefore need good checking of the insulation. But for scaling up cryogenics seems to be the most suitable technique.

Conclusion

It can be concluded that high pressure water scrubbing is performing the best. With With the low cost cost pric price, e, high high puri purity ty and yiel yield d it is a promi promisi sing ng upgra upgradi ding ng techn techniq ique. ue. Thou Though gh one waste waste strea stream m needs needs treat treatmen ment, t, it is a continuous process which operates almost on it self.

Preface This report presents the results of a multidisciplinary project executed at the Eindhoven University of Technology commissioned by Dirkse Milieutechniek BV (DMT). The results are also presented on a poster and a website //students.chem.tue.nl/ifp24 24//). (http : //students.chem.tue.nl/ifp The aim of such a project is to teach students, by means of real problems, to combine and apply professional knowledge and skills and to integrate these into non-technical aspects of importance and new technical knowledge. The main goals are learning to communicate with colleagues from various fields, and to gain experience in working as a team, executing a research project. DMT solves environmental problems with tailor made solutions and is always seeking new possibilities to do so. DMT offers a wide range of products and services varying from research, development, consultancy and design sign to rental rental of equipm equipmen ent, t, instal installati lations ons service service and maintenan maintenance. ce. DMT supplies equipment and systems for air treatment, odor abatement, (bio)gas desulphurization, groundwater purification, soil remediation and waste water treatment. This This project wa wass focused on the upgradin upgradingg of biogas. biogas. Biogas Biogas is a result result of anaerobic digestion of organic material, resulting in methane and carbon dioxid dioxidee gas and some pollutan pollutants. ts. The methane methane gas can be used as a green green energy source by upgrading the biogas to natural gas and injecting it into the existing gas grid. Upgrading Upgrading of biogas signifies removal removal of the C O2 and pollutants such as H 2 S . Current Currently ly,, several several processes processes are avail availabl ablee for the upgrading. Project descripti description on

DMT has developed a biogas upgrading technology based on high pressure water wa ter scrubbi scrubbing. ng. To get get a leadi leading ng posit positio ion n in the mark market, it is of most importance to know the advantages and disadvantages of all the different processes available for upgrading biogas and their cost.

1

A literature study was conducted to create a clear overview of the present upgrading techniques allowing for an objective comparison. The comparison of the different options was focused on: •

chemical absorption

•

high pressure water scrubbing

•

pressure swing adsorption

•

cryogenic separation

•

membrane separation

Firstly, each technique is described shortly including a cost estimate of the cost price price per cubic cubic meter meter of upgraded upgraded biogas biogas.. Thereaf Thereafter, ter, a compari comparison son of  the advantages and disadvantages of the different techniques is given. These results will help Dirkse Milieutechniek decide which option to upgrade biogas best fits their customers demands.

2

Contents 1 In Introd troduct uction ion to Bio Biogas gas

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2 Upg Upgrad rading ing tec techni hnique quess

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2.1 2.2 2.3 2.4 2.5

Chemicall abso Chemica absorpti rption on . . . . . High Hig h press pressure ure wa water ter scru scrubbi bbing ng Pressu Pre ssure re swi swing ng ads adsorpt orption ion . . Cryogen Cry ogenic ic sep separat aration ion . . . . . Membran Mem branee sepa separati ration on . . . . .

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3 Co Comp mpar aris ison on

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4 Co Conc nclu lusi sion onss

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Acknowledgement

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Bibliography

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A Alte Alternate rnate cost cost estimation estimation PSA

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B Cry Cryogeni ogenic c equipmen equipmentt

44

C C O2 footprint

46

D Vis Visit it to SM SMB B Stortgas Stortgas BV in Tilburg Tilburg

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E Vis Visit it to Carbio Carbiogas gas BV in Nuene Nuenen n

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Chapter 1 Introduction to Biogas The current use of fossil fuels is rapidly depleting the natural reserves. The natural formation of coal and oil however, is a very slow process which takes ages. ages. Therefo Therefore, re, a lot of researc research h effort effort is put into into finding renewabl renewablee fuels fuels nowa nowada days ys to replace replace fossil fossil fuels. fuels. Renewa Renewable ble fuels are in balance balance with the environment and contribute to a far lesser extent to the greenhouse effect. Biogas is a renewable fuel, an energy source that can be applied in many different settings. It is defined as a combustible gas mixture produced by the anaerobic fermentation of biomass by bacteria and takes only a relatively short short time to form. form. In nature nature,, the fermen fermentat tatio ion n proces processs occurs occurs in plac places es where biological material is fermented in an oxygen deprived environment such as swamps and waterbeds. The two main sources of biogas from human activities are domestic garbage landfills and fermentation of manure and raw sewage. sewage. The advan advantage tage of processin processingg these these wa waste ste products products anaerobi anaerobical cally ly,, compared to aerobically, is the larger decrease in volume of waste product. For this this reason, reason, the industry industry nowa nowada days ys prefers prefers anaerobi anaerobicc fermen fermentati tation on to process waste streams. Biogas mainly consists of combustible methane (C (C H 4) and non-combustible carbon dioxide (C (C O2). Besi Beside dess C H 4 and CO 2 , biogas also contains small amounts of hydrogen sulphide (H  (H 2 S ) and some some other pollutant pollutants. s. The composition position of biogas biogas strongly strongly depends on its source. source. Table able 1.1 [1] shows the composition of biogas from various sources. It can be seen that biogas from a garbage landfill also contains some nitrogen (N  (N 2 ). C H 4 combusts very cleanly with hardly any soot particles or other pollutan lutants, ts, making making it a clean clean fuel. But C O2 , the non-combustible part of the biogas, lowers lowers the calorific calorific value of the biogas. Biogas containing containing 60% C H 4 has a calorific value of 21.5 MJ/N MJ/N m3 while pure C H 4 has a calorific value of  35.8 MJ/N MJ/N m3 .

4

Table 1.1: Overview of compositions of biogas from different sources

Compone Component nt Bioga Biogass facto factory ry Sewer Sewer factor factory y C H 4 (%) 60-70 55-65 C O2 (%) 30-40 35-45 N 2 (%) <1 <1 H 2 S  (ppm) 10-2000 10-40

Garb Garbage age land landfil filll 45-55 30-40 5 -1 5 5 0 -3 0 0

Besides C O2 , biogas also contains small amounts of  H 2 S . H 2S  is poisonous when inhaled. Furthermore, urthermore, when water water is present, present, H 2S  forms sulphuric acid (H  (H 2 SO 4 ), which is highly corrosive, resulting in extra costs for maintenance when using the biogas. Depending on the source of the biogas, it can contain other pollutants. Common pollutants are water vapor, ammonia (N (N H 3) and siloxanes. Water vapor in biogas biogas forms, forms, combin combined ed with with N H 3 or H 2 S , a corrosi corrosive ve solve solvent nt.. Siloxanes are silicate compounds that have oxygen groups replaced by organic groups like C H 3 . When this this compound compound is burned, burned, it will form SiO 2 (sand) which can cause severe damage to equipment. There are a number of uses for biogas. Currently, biogas which has been stripped of  H 2 S  is mainly used in gas turbines turbines to produce electricity electricity. HowHowever, most energy is lost as heat in this process, which results in a low overall efficiency efficiency.. But biogas biogas can also be used used for injecti injection on in the gas grid or as a car fuel. The requirements for the end product depend on the final use of the biogas. The average composition of gas in the gas grid for low calorific gas, used in The Netherlands, and high calorific gas, used for example in Canada, are shown in table 1.2 [2]. All of the values mentioned in table 1.2 are averages, except for the Wobbe index. index. The Wobbe Wobbe index of the gas should should always always be in between between the menmentioned tioned boundaries. boundaries. To reach reach the calorific calorific value value of Dutch Dutch natural natural gas the methane purity should be increased to a value of 88%. But if Canadian standards must be achieved, as shown in table 1.2 1.2,, the calorific value of biogas should be increased above the calorific value of methane. This of course can never be reached by increasing the purity of  C H 4 . Therefo Therefore, re, the purity purity of  C H 4 should be as high as possible and some higher alkanes are added to the gas to obtain the required calorific value. For injection of biogas into the gas grid grid there there are some additio additional nal requireme requirement nts. s. These These are shown in table table 1.3 [2].

5

Table 1.2: Average compositions of gas used in the commercial gas grid in The Nether-

lands and Canada Dutc utch natur atural al gas gas

Cana Canadi dian an natu natur ral gas gas

(Source: (Source: Dutch Dutch Gas union) union) (Source: (Source: Uniongas Uniongas Canad Canada) a) Volume % Volume % Methane 81.30 94.9 Ethane 2.85 2.5 Propane 0.37 0.2 Butane 0.14 0.06 Pentane 0.04 0.02 Hexane 0.05 0.01 Nitrogen 14.35 1.6 Carb on Dioxide 0.89 0.7 Oxygen 0.01 0.02 Water vapor Unknown Unknown Hydrogen Unknown Traces 3 Density (kg/m (kg/m ) 0.833 0.7525 3 Wobbe index (MJ/m (MJ/m ) 43.1-44.6 50.5-52.5 Calorific value (MJ/m (MJ/m3 ) 31.669 37.8 Component

The minimum amount of C of  C H 4 required as well as the maximum amount of  N 2 depends on the Wobbe index. The Wobbe index is defined as follows: calorific value( value(MJ/m3 ) √ Wobbe index = relative density

(1.1)

The Wobbe index is a measurement for the combustion behavior. If this value is too high or too low, the combustion behavior will be disturbed. The values may not deviate from the desired range. Biogas Biogas can also be used as a car fuel. fuel. Howe Howeve ver, r, because of the low low enbars. Also ergy per volume the biogas must be compressed up to 200 bars. Also,, the

Table 1.3: Requirements for injection of biogas into the gas grid

Compon Comp onen entt Requ Requir irem emen entt < 8 vol % C O2 Water dewp oint < -10 C  Oxygen < 0.5 vol % H 2 S  < 5 mg/Nm3 ◦

6

calorific value of the biogas should be at least the value of low calorific gas. Furthermore, there may be no water or heavier alkanes than propane in the biogas because it will form condensate at such a high pressure. Removing C O2 and H 2 S  from the biogas is not easy. easy. Howe Howeve ver, r, the upgrading technology is rapidly evolving, bringing biogas as a reliable energy source in sight. To produce large amounts of upgraded biogas, it is necessary to examine different upgrading methods to see which method might be implemented plemented in the industry industry. Calculating Calculating the so called C O2 footprint of each technique is valuable to determine the durability [3 [3] [4].

7

Chapter 2 Upgrading techniques In this chapter, the five investigated upgrading techniques are explained. For each technique, a short description including a process flow diagram (PFD) is given and the distinctive advantages and disadvantages of each technique are discussed. discussed. The environm environment ental al impact of the upgrading upgrading processes processes is an important factor to compare the different techniques, so this is discussed for each technique. In order to compare the different techniques, the cost price of the produced produced upgrade upgraded d gas must must also also be taken taken into into accoun account. t. The cost 3 price per N m biogas are calculated using the following formula, in which the interest rate on the investment is taken to be 6%:

3

P rice rice per per N m =

investment depreciation depreciation period

+ investment · interest rate + annual cost

N m3  produced upgraded gas per year

(2.1) For each technique the input flow is taken to be 250 N m /h containing 60 % of C of  C H 4 . The output is calculated as follows: 3

Output = input · % C H 4 · yield

(2.2)

The total running costs are determined by the operating costs, the electricity and the water costs. The current electricity price is about  0.10 per kW h [13 13]. ]. The The price price of water water is  0.92 per m3 [14 14]. ]. The The servi service ce costs costs are  50,000 per year.

2.1 2.1

Chem Ch emic ical al abso absorp rpti tion on

Both the chemical absorption of C of  C O2 and H 2 S  were investigated.

8

2.1. 2.1.1 1

Chemi Chemica call abso absorpt rptio ion n of  C O2

Multiple theories exist about the removal of C of  C O2 in gas streams. However, However, these theories are often contradictive. In the following text, C O2 absorption using aqueous amino acid salt solutions will be discussed. Cooler 

Biogas out CO2

Absorption column Regeneration column Heat exchanger  Gas stream in

Figure 2.1: Process flow diagram for chemical absorption of  CO 2

An amino acid dissolved dissolved in water water exists as a zwitter ion. A zwitter ion can have a positive and a negative charge depending on the pH of the solution. The amino group has to be deprotonated before it reacts with C O2 . This This deprotonation is mostly done by addition of an equimolar amount of base, according to the following mechanism [5]: HOOC  − R1 − N H 3+



OOC  − R2 − N H 3+  OOC  − R3 − N H 2 (2.3)

These aqueous solutions react with C O2 to absorb absorb this componen component. t. In open literature about chemical absorption of  C O2, no reliable information about the reaction reaction mechani mechanism sm and kinetics kinetics is avail available able.. Therefor Therefore, e, the assumption is made that the reaction mechanism occurs according to the experimental studies of Kumar, Hogendoorn, Feron and Versteegh, 2002. The main reactions occurring during the absorption of CO of  CO 2 are the following: 2 RN H 2 + C O2



RNHCOO + RN H 3+ −

9

(2.4)

CO 2 + OH  RN H 3+ H 2 O −

  

H C O3 RN H 2 + H + H + + OH  −

−

(2.5) (2.6) (2.7)

In reaction 2.4 2.4,, the reaction of C of  C O2 with with an amino amino acid can be seen. The contribution of reaction 2.5 to the conversion of C of C O2 is not significant, significant, while not much OH  ions are present in the solution because the pH is very low. Since the OH  ions are in equilibrium with the amine molecules, reactions 2.6 and 2.7 have to be taken into account. This study also discusses the Membrane Gas Absorption (MGA) investigated by TNO [6]. Resear Research ch has been done by TNO at the the membra membrane ne absorpti absorption on techni technique. que. Accord According ing to TNO, TNO, this this is a techni technique que which which makes use of porous, water-repelling membranes for transport of components. Currently, new absorption liquids, called CORAL, are developed, which show a stable operation with cheap olefin membranes. membranes. According According to P.S. Kumar et al. the MGA technique is economically not very attractive in comparison to conventional absorption processes, because of the limited availability of the fibres. The process flow diagram of the C O2 absorption process is shown in figure 2.1 2.1.. −

−

2.1. 2.1.2 2

Chemi Chemica call abso absorpt rptio ion n of  H 2 S 

In the literature [7] [8] several processes are presented which discuss the removal of  H 2S . Many Many of these processes processes remove remove this pollutan pollutantt only only from the gaseous stream, but do not convert H 2 S  into a more stable or valuable product, or convert it into the elemental form sulphur (S  (S ). ). The conversion of  H 2 S  into S  or a valuable compound is an advantage of chemical absorption with respect to other methods. The process of chemical absorption of  H 2 S  into iron-chelated solutions offers a highly efficient H 2 S -removal, -removal, a selective removal of  H 2 S  and a low consumption of chemicals, because the iron-chelated solutions function as a pseudo-catalyst that can be regenerated. The overall reaction of this purification process is expressed as follows [9 [9] 1 H 2 S + S  + O2 (g ) → S + S  + H 2 O (2.8) 2 In the reaction described above, H 2 S  is first absorbed into water and then undergoes the dissociation as follows: H 2S (g) + H 2O



10

H 2 S (aq) aq)

(2.9)

H 2 S (aq) aq) H S  −

 

H + + H S  H + + S 2

(2.10) (2.11)

−

−

The formation of S  of  S  occurs according to the reaction mechanism is described here: S 2 + 2F 2F e3+  S + S  + 2F 2F e2+

(2.12)

−

By means of oxygenation the aqueous iron-chelated solution will be regenerated. generated. This oxygenation oxygenation is followed followed by conversion conversion of the pseudo-catalyst pseudo-catalyst 3+ into its active form F e . This This mechani mechanism sm is shown shown in the followin followingg equaequations: 1 O2 (g ) + H 2 O(l) 2 1 O2 (aq) aq) + 2F 2 F e2+ 2

→ →

1 O2(aq) aq) 2

(2.13)

2F e3+ + 2OH  2OH 

−

(2.14)

In this mechanism, several chelate agents can be used for the specific proposal of the overall reaction, with the EDTA being the most used common chelate [10 [10]]. In this process, the sulphur sulphur produced can be removed easily easily from the slurry by sedimentation or filtration operations. Next to that, the whole process can be carried out at ambient temperature.

Figure 2.2: Process flow diagram for chemical absorption of  H 2 S 

11

Figure 2.2 shows an overview of the units that are used to remove the H 2 S  from the biogas stream. stream. The complete complete system consist consistss of an absorber absorber column, column, a particl particlee separator separator or filter, filter, and a regenerati regeneration on column. column. Under Under continuous operating conditions, the biogas is introduced as small bubbles at the bottom bottom of the absorber absorber of the column. column. These These bubbles bubbles pass through through the Fe/EDTA soluti solution on flowin flowingg down downwa wards rds to the particle particle separator. separator. In the absorber column the H 2 S  will be absorbed and transformed into S. The mechanism of this transformation can be seen in the equations in the former section section.. In the particle particle separato separator, r, the small particles particles of S that have have formed formed are separated separated from the product product stream. stream. After After this separatio separation, n, the outgoing outgoing 2+ 3+ product stream is regenerated from F e /EDTA into F e /EDTA in a bubbling air column. The last step in this purification is washing the treated biogas with water in a packed column to remove residual traces of H  of  H 2 S . The advantages of this absorption process are the almost complete removal of  H 2S  from the biogas. biogas. The remove removed d H 2 S  is also converted into its elemen elemental tal form, so it can be sold sold to other companies companies.. A big disadv disadvan antage tage is that after the absorption process a scrubber is still needed to remove the C O2 . It is not possible with this absorption process to remove the C O2 .

Waste streams Chemical absorption of  C O2

The only process stream next to biogas needed in the absorption process is a liquid water phase in which amines are dissolved. As can be seen in figure 2.1 the biogas flows through a column filled with the amine solution. In this column, the C O2 is split from the biogas and the biogas leaves the absorption column. The amine solution including including the captured C O2 leaves the column and will be generate generated d in the generati generation on column. column. During During this process, process, the split off and is emit emitted ted in the atmos atmosphe phere re as a wa waste ste stream stream.. The The C O2 is split amine solution will be regenerated and flows back into the column to capture C O2 again. again. This This solution solution must be replaced replaced a few times times a year year and then it becomes becomes a wa waste ste stream stream too. This This solution solution can be b e separated separated into a wa water ter phase phase and the amines using using a membran membrane. e. The clean water water phase can then be purged purged to a river. river. The only real waste waste streams streams are the C O2 stream and the amines. Chemical absorption of  H 2 S 

S  absorption process only the removal of H  S  is taken into account. For the H 2 S absorption of H 2 S is In figure 2.2 a scrubber is also shown, but since this process is discussed in 12

another part of the report, we will focus only on the H 2 S  removal. removal. Figure 2.2 show showss the process process flow diagram diagram.. The The bioga biogass strea stream m can be seen seen and and in the regeneration part also some other streams are added to the process. The biogas flows through the absorption column and the H 2 S  is captured in the liquid phase. The liquid phase consists of water in which Fe/EDTA is dissolved. dissolved. The biogas leaves leaves the column containing containing almost no H 2 S . The Fe/EDTA solution flows to the regeneration part in which the sulphur is separ separate ated d from from the soluti solution. on. After After this step, step, the F e is regenerated from 2+ 3+ F e to F e . This This aqueous aqueous solution solution is again used in the absorber absorber column column to capture H 2 S . The separated separated elemental elemental sulphur sulphur is collected collected and because because it is pure it can be sold sold to other other compani companies. es. Howe Howeve ver, r, the amount amount is small and to sell a reasonable amount would take quite a long time to collect. Because of these circumstances, the sulphur is mostly treated as a waste stream and has to be put away as chemical waste. Another waste stream is the Fe/EDTA solution. This solution has to be replaced a few times a year. The solution can be filtered using a membrane, to separate the water phase and the Fe/EDTA complexes. These components are another waste stream of the absorption process and need to be disposed of as chemical waste. The purity of the obtained biogas is approximately 98%. In both processes the yield for C H 4 is 90%. The C H 4 waste stream is best handled by sending the stream to to a flare. BurningC Burning C H 4 is better for the atmosphere than emitting the gas. Looking at the two absorption absorption processes the absorption absorption of C O2 seems to have less waste streams than the absorption of H  of H 2 S , at least less harmful waste waste streams.

Cost estimation for chemical absorption For the absorption absorption process, two two cost prices of upgraded biogas are calculated, calculated, one for the absorption of C of  C O2 and one for the absorption of H  of  H 2 S . The price for biogas using both methods at the same time is calculated in the end. Cost estimation chemical absorption of  C O2

· · · · ·

one time per year general inspection in- and outside one time per year general inspection outside if necessary, cleaning of internals maintenance of recirculation pump calibration of instrumentation

/h, 1,127,000 N m3 per year Output: 137 N m3 /h, 90% C H 4 yield, purity output: 98% C H 4 13

Investment costs

Absorber column2 Additional costs6 Pump 3 Heat exchanger exchanger4 Cooler1 Regeneration Regeneration column1

     

125,000 100,000 5,000 15,000 18,000 90,000

Total investment costs   353,000 Depreciation period of equipment is 10 years. Running costs

Energy costs6 Catalyst costs5 Operator Maintenance6





30,000 50,000 50,000 4,500

Total running costs 



134,500

 

Costs per N m3 biogas without H 2 S  removal:



0.17

After the absorption of C of  C O2, an amount of 3% H 2 S  is still present in the biogas. biogas. For excelle excellent nt cleaning cleaning of biogas biogas,, also also the H 2 S  has to be removed, because the requirements are less than 5 mg/Nm3 biogas. Cost estimation chemical absorption of  H 2 S 

· · · · ·

one time per year general inspection in- and outside one time per year general inspection outside if necessary, cleaning of internals maintenance of recirculation pump calibration of instrumentation

Investment costs

Absorber column2 Additional costs6 2 Pumps3 Regeneration Regeneration column1 Particle separator1





125,000 100,000 10,000 90,000 100,000

Total investment costs 



516,000

  

14

Depreciation period of equipment is 10 years. Running costs

Energy costs6 Catalyst costs5 Operator Maintenance6





30,000 15,000 50,000 4,500

Total running costs 



99,500

 

The costs per N m3 produced are calculated according to formula 2.1 2.1.. 3 Costs per N m biogas:  0.16 When the price of the complete upgrading process, including both C O2 and H 2 S  absorption, is calculated, we obtain a price of   0.28 per N m3 upgraded biogas. This price is based on the following values: Investment costs Running costs 1 2 3 4 5 6

 

869,000 179,500

costs from Aspen Icarus Project Evaluator costs from offer of Rootselaar costs from offer of Grundfoss costs from calculation of Mauri costs from excursion to Cirmac costs from offer of E-kwadraat

2.2 2.2

High High pr pres essu sure re wat water er scr scrub ubbi bing ng

Water scrubbing is a technique based on the physical effect of gases dissolving in liquid liquids. s. Water ater scrubb scrubbin ingg can be used used to remov remove C O2 and H 2 S  from biogas since these components are more soluble in water than in C H 4 . This absorption process is a fully physical process. The main parts of the process are shown in figure 2.3 2.3.. In high pressure water scrubbing, gas enters the scrubber scrubber at high high pressur pressure. e. This This high high pressure pressure increases increases the dissol dissolubi ubilit lity y of  gases gases in water. water. Then, Then, wa water ter is spray sprayed ed from the top of the column column so that it flows down countercounter-curr curren entt to the gas. To ensure ensure a high high transfe transferr surface surface for gas liquid contact, the column is usually filled with a packing material. 15

Figure 2.3: PFD for high pressure water scrubbing

In the flash vessel the pressure is decreased and some traces of C of  C H 4 will be regenerated. In the stripper the washing water is regenerated. C O2 and H 2 S  are strippe stripped d by air in this vessel essel.. After After a dryin dryingg step, step, the the obtai obtaine ned d C H 4 purity can reach 98% using this process and yields can achieved up to 94%. There are two types of water scrubbing [2 [2]: Single pass scrubbing  In singl singlee pass pass scrubb scrubbin ing, g, the washi washing ng water ater is used used only only once. once. The The advantage of this type of scrubbing is that no contamination in the water occurs like traces of  H 2 S  and C O2 . This This gives gives that that the total total amount of C of  C O2 and H 2S  is at its maximum. The disadvantage of this techni technique que is that it require requiress a large large amount amount of wa water. ter. This This techni technique que is only feasible when working near a sewer water cleaning plant from which water can be used. Regenerative absorption  In regenerative absorption, the washing water is regenerated after washing the biogas. The main advantage of this technique is that the total amount of water required is much lower compared to single pass scrubbing. Water scrubbin scrubbingg require requiress a large large amoun amountt of wa water. ter. For example, example, the regenerative absorption process from DMT that washes 330 N m3 /h biogas

16

requires approximately 50 l/h of water. water. So single single pass scrubbin scrubbingg is practipractically impossible in The Netherlands because water is too expensive and the government will have objections against the usage of such large amounts of  water. Therefore, the main focus will be on regenerative absorption. When working at high pressure, there are two advantages compared to worki wo rking ng at atmosph atmospheric eric pressure. pressure. The main advan advantage tage is that the dissol dissoluubility increases when the pressure is higher. This results in a lower required amount of water per amount of biogas. The total amount of water required will will thus thus be b e a lot lower. lower. Also, Also, the washing washing water water is oversat oversaturat urated ed at atmospheric pressure so regenerating will be a lot faster. The driving force behind the regenerating process is the concentration difference between the oversaturated concentration and the equilibrium concentration. With this being as high as possible, the speed of the process will be highest. For the design of a water scrubber it is rather important to know how much H 2 S  and C O2 can be dissol dissolve ved. d. The increasing increasing dissolubi dissolubilit lity y of H  of  H 2 S  and C O2 with increasing pressure is described by Henry’s Law: P i = H  · C max max C max max H  P i

(2.15)

Saturation concentration of the component [mol/m [mol/m3 ] /mol] Henry’s coefficient [P [P a · m3 /mol] Partial pressure of the component [P [P a]

According to Dalton’s law, the total pressure is the sum of all partial pressures. So if the total pressure is increased, the partial pressure increases by the same factor. This means the saturation concentration rises as well. However, However, when higher pressures pressures are reached, reached, the dissolubilit dissolubility y of the components will no longer linearly increase increase with the pressure. pressure. At higher pressures the increase increase of dissol dissolubi ubilit lity y becomes becomes lower. lower. Up to a pressure pressure of 20 bars the dissolubility can be described according to Henry’s law [11 11]. ]. These These calculacalculations are based on the ideal situation so non idealities should be taken into account in the design of a scrubber. Another important factor for the dissolubility of the components in water is the pH [2 [2]. Furthermore, the pH depends on the amount of H  of  H 2 S  and C O2 that has been dissolved into water. Water becomes more acid when more H 2 S  and C O2 are absorbed. When the pH is decreased, C O2 will dissolve less and the H 2 S  will dissolve less. At a pH of 1, the dissolubility of  H 2S  is only half  of the dissolubility at a pH of 7. Therefore, a low pH is not feasible because the H 2 S  removal is important; the stripping process becomes more difficult and acid wa water ter damages damages equipm equipmen ent. t. Working orking at a high high pH is unfeasi unfeasible ble as well well because sulphur sulphur and carbonate carbonate ions will precipit precipitate. ate. It is best to wo work rk at a pH of 7. 17

The mass transfer of components from the gas phase to the water phase and vice versa is important important to know. know. When it is known, the dimensions dimensions of the reactor reactor can be calcula calculated. ted. Mass Mass transfer transfer occurs when a high high concent concentrati ration on difference difference between two two phases is realized. The mass transfer can be described using the double film model. This model is shown in figure 2.4 2.4.. When two layers with different concentration profiles intersect, the following equations are valid: N AG AG = kG · a · (C AG AG − C AG AG ) N AL AL = kL · a · (C AL AL − C AL AL ) i

i

(2.16) (2.17)

Figure 2.4: Concentration profile in double film model

The mass mass transfe transferr coefficien coefficients, ts, kL and kG , are dependent on a lot of  parameters. It is difficult to get a precise measurement of these values. But a rough estimate of these values suffices to design the dimensions of the scrubber. Water scrubbing is a simple process because it only requires water and an absor absorpti ption on colu column mn to upgrad upgradee the the bioga biogas. s. Scrub Scrubbers bers also have have some some advantages [12 [12]] compare compared d to other other devices devices.. Wet scrubbers scrubbers are capable capable of  handling high temperatures and moisture. The inlet gases are cooled so the overall overall size of the equipment can be reduced. Wet scrubbers can remove both gases and particulate matter and can neutralize corrosive gases. Furthermore, water scrubbing can be used for selective removal of H  of  H 2 S  because this is more soluble in water than C O2 . The water water which which exits the column with the absorbed components, can be regenerated and recirculated 18

back to the absorption column. This regeneration can be done by depressurizing izing or by strippi stripping ng with air in a simila similarr column. column. When levels levels of H  of  H 2 S  are high it is not recommended to strip with air because the water can become contaminated contaminated with elemental elemental sulfur which causes operational problems. problems. Also at high levels of H  of  H 2 S  the dissolubility is limited because of decreasing pH.

Waste streams The water scrubbin scrubbingg process process contain containss two two main main wa waste ste streams. streams. The first waste stream is the exhaust of air which was used to strip the regenerated water. This stream mainly consists of air and a high percentage of C of  C O2 but also contains traces of  H 2 S . Becau Because se H 2 S  is rather poisonous this stream needs to be treated. Also the stream contains small amounts of C of C H 4 . Because C H 4 is far more damaging to the environmental than C O2 the C H 4 in this stream should be burned. The second waste waste stream stream is a purge purge of water. water. To keep keep the dissol dissolubil ubilit ity y as high as possible a part of the washed water is purged and replaced with clean clean water. water. In this way the concentrat concentration ion of C of  C O2 and H 2 S  in the water stream to the scrubber will remain as low as possible and C O2 and H 2 S  will not accumulate. Because most of the C O2 and H 2 S  will be absorbed in the gas phase in the stripper the purge stream does not have to be treated.

Cost estimation for high pressure water scrubbing /h, 1,215,200 N m3 per year Output: 144 N m3 /h, 94% C H 4 yield, purity output: 98% C H 4 bars, 250 N m3 /h biogas)  110,000 Compressor (10 bars, Columns />  140.000  5,000 Heat exchangers Pumps and blowers  10,000 Total investment costs   265,000 Depreciation period of equipment is 10 years. Running costs

Energy costs Operator

 

60,000 50,000

Total running costs 



110,000

Costs per N m3 biogas:



0.13

19

This cost price is in close accordance to the costs in Tilburg at the biogas upgrading plant, SMB Stortgas BV. At this upgrading plant the cost price was approximately  0.11 to  0.12 per N m3 .

2.3 2.3

Pres Pressu sure re swin swing g adso adsorp rpti tion on

Pressure swing adsorption (PSA) is another possible technique for the upgrading of biogas. PSA is a technology used to separate certain components from a mixture of gases under pressure according to the species’ molecular characteristics and affinity for an adsorption material. Figure 2.5 shows how the adsorption material material selects the different gas molecules. The adsorption material adsorbs H 2 S  irreversibly and is thus poisoned by H 2 S  [15 15]. ]. For this reason, an H 2 S  removal removal step is often included in the PSA-process. DisturDisturbances have been caused by dust from the adsorption material getting stuck in the valves. alves. Special adsorption adsorption materials are used as molecular sieves, sieves, preferentially adsorbing the target gas species at high pressure. Aside from their ability to discriminate between different gases, adsorbents for PSA-systems are usually very porous materials chosen because of their large surface areas (for instance activated activated carbon, silica gel, alumina and zeolite). The process then swings to low pressure to desorb the adsorbent material [16 16]. ]. Desorbing the adsorbent material leads to a waste stream, containing concentrations of  impurities. The upgrading system consists of four adsorber vessels filled with adsorption material, as can be seen in figure 2.6 2.6.. During normal operation, each adsorber operates in an alternating cycle of adsorption, regeneration and pressure build-up. During the adsorption phase, biogas enters from the bottom bottom into into one of the adsorbers adsorbers.. When When passin passingg the adsorber adsorber vesse vessel, l, C O2 , O2 and N 2 are adsorbed adsorbed on the the adsorb adsorben entt materi material al surface surface.. This This can be seen in figure 2.5 where N 2 , O2, H 2O , H 2 S  and C O2 are adsorbed in the adsorber. The gas leaving the top of the adsorber vessel contains more than 97% C H 4 . This methane-rich methane-rich stream is substantially substantially free from siloxane siloxane components, volatile organic compounds (VOCs), water and has a reduced level of  C O2 . Before the adsorbent material is completely saturated with the adsorbed feed gas components, the adsorption phase is stopped and another adsorber vessel that has been regenerated is switched into adsorption mode to achiev achievee contin continuous uous operation. operation. Regenera Regeneratio tion n of the saturat saturated ed adsorben adsorbentt material is performed by a stepwise depressurization of the adsorber vessel to atmospheric pressure and finally to near vacuum conditions. Initially, the pressure is reduced by a pressure balance with an already regenerated adsorber sorber vesse vessel. l. This This is followe followed d by a second second depress depressuriz urizati ation on step to almost almost 20

Figure 2.5: The principle of pressure swing adsorption, picture taken from [ 17 17]]

atmosphe atmospheric ric pressure. pressure. The gas leavin leavingg the vessel vessel during during this step contai contains ns significant amounts of C of  C H 4 and is recycled to the gas inlet. These significant amounts of  C H 4 were trapped within the voids of the adsorbent particles. Before the adsorption phase starts again, the adsorber vessel is repressurized stepwis stepwisee to the final adsorpti adsorption on pressure pressure.. After After a pressure pressure balance balance with with an adsorber that has been in adsorption mode before, the final pressure build-up is achieve achieved d with with feed gas. A complete complete cycle is complet completed ed in approx approxima imately tely 3-5 minutes [20 20]]. The The advan advantag tages es of the PSAPSA-proc process ess are the high high C H 4 enrichment of more than 97%, the low power demand and the low level of  emission. The waste stream of the PSA-plant consists of N  of  N 2 , O2 , H 2 O , H 2 S  and C O2 . The main disadv disadvantage antage is the H 2 S -remov -removal step. This is a complex step in the process, which is necessary.

Waste streams The PSA-plant has a final product stream, the upgraded biogas, which contains more than 97% C H 4 . Next Next to the product product stream, stream, a wa waste ste stream stream is produced. produced. The waste waste stream stream leave leavess the adsorber vessel vesselss at the bottom and contai contains ns all the adsorbed adsorbed material material from the carbon molecul molecular ar sieve sieves. s. Also, Also, some significant amounts of C of C H 4 are found in this waste stream (among other 21

Figure 2.6: PFD for pressure swing adsorption [17 [ 17]]

things the remaining 3% C H 4 ). C H 4 is more damaging than C O2, so it is of  most importance to make sure that C H 4 is not emitted into the air. Burning the C H 4 is less harmful to the environment in comparison with emitting C H 4 directly into the air. Therefore, the waste stream can be led to a gas engine linked to a generator. Increasing the yield of C of C H 4 in the product stream can be achieved by recycling the waste stream. This has also a positive effect on the amount of C of  C H 4 in the waste stream, which will decrease.

Cost estimation for PSA Using the process flow diagram of the PSA-process, gives the following cost estimation. The costs for the removal of H  of  H 2 S  are included in the investment costs costs as well ell as in the runnin runningg costs costs.. The The costs costs of the the press pressure ure swing swing adadsorption depend on which type of adsorbent material is used in the columns and the number number of units used. The operational operational costs costs are influenced influenced by the operating pressure, which which on its turn is dependent on the adsorbent adsorbent material. The compressor needed in the beginning in order to compress the incoming biogas is the last element which contributes to the cost of the whole plant signifi significan cantly tly.. Compres Compressio sion n is expensiv expensivee and in order order to make make it profitabl profitable, e, it is needed needed to recover recover the required required pressure. pressure. The pressure pressure recovery recovery can be enabled by several pressure valves. The type of adsorbent material used in the PSA is a carbon molecular 22

sieve. The choice for this adsorbent material can be explained by the ability of  removing N 2 and O2 from the biogas. The lifetime of the adsorbent material is taken taken to be 3 to 4 years years.. Furthe urtherm rmore ore,, there there are are four four adsorbe adsorberr vessel esselss needed needed in the plant. plant. Figure Figure 2.6 shows the overall scheme of the PSA-plant. The compressor, the four adsorber vessels, the vacuum pump and the H 2 S remov removal step are included included in the cost estimatio estimation. n. Appendix Appendix A shows an alternate way of estimating the cost of a PSA-plant. The equations used, are found in [18 [18,, 19 19]. ]. In this chapter, the cost estimation is adjusted to the cost estimations of the other techniques which are investigated. /h, 1,176,000 N m3 per year Output: 139 N m3 /h, 91% C H 4 yield, purity output: 98% C H 4 Investment costs

C O2 adsorber columns (4) 4  500,000  70,000 Additional costs6 3 Pumps (2)  10,000  100,000 Compressors Compressors (2) Total investment costs   680,000 Depreciation period of equipment is 10 years. Running costs

Energy costs Catalyst costs Operator Maintenance





33,500 100,000 50,000 3,750

Total running costs 



187,250

 

The costs per N m3 produced are calculated as explained at the beginning of  this chapter. chapter. Costs per N m3 biogas:

2.4 2.4



0.25

Cry Cryogen ogenic ic sepa separa rati tion on

The name cryogenic separation already reveals the fact that this technique makes use of low temperatures, close to -90 C , and high pressure, approxibars. Because C O2 , C H 4 and all other biogas contaminants liquefy mately 40 bars. ◦

23

at different temperature-pressure domains, it is possible to obtain CH 4 from biogas by cooling and compressing the crude biogas to liquefy C O2 which is then easily separated from the remaining gas. Among the existing techniques for biogas upgrading, cryogenic separation of impurities from biogas is still in the early stages of research and development. ment. In order to inve investi stigate gate the feasibi feasibilit lity y of this this techni technique que,, in the first first designing steps, the focus has been only on the separation under low temperature and high pressure. When the desired purity of the upgraded gas is achieved, the designing of the cooling and compressing unit in this technique can be contin continued. ued. Finall Finally y these these two two models, models, for compressi compressing ng and separatseparating of biogas, is put together to achieve the final separation model which is shown in figure 2.9 2.9.. Figu Figure re 2.7 shows this primary model for the cryogenic separation of biogas. The calculations for this model are based on the crude /h. The inlet inlet biogas with an inlet gas flow of 250 N m3 /h. inlet gas is assumed assumed to be dried, under atmospheric pressure and has an ambient temperature. The composition of the inlet gas is given in table 2.1 2.1.. 2

1

3

Distillation Column

simple model of cryoge cryogenic nic separat separation ion of biogas. biogas. Stream Streamss 1, 2 en Figure 2.7: A simple 3 respectively are the crude biogas (inlet gas), the upgraded biogas (product) (product) and the impurities impurities..

The model in figure 2.7 has been created by using the Aspen Plus software package. In this model, the impurities from crude biogas are separated using C  and a pressure a distillation column which operates at a temperature of -90 C and bars. The results of the modeling are summarized in table 2.2 of 40 bars. 2.2.. As can be seen in table 2.2 the product stream, upgraded biogas (stream 2), has a C H 4 purity purity of 91%. Again Again it should be mentio mentioned ned here that this purity purity is based on the model made in Aspen Plus. However However,, according to [31 [31]] it should be possible to upgrade biogas to a higher purity of C of C H 4 . Another demand for the upgrading of biogas is the reduction of H  of  H 2 S  quality with a ◦

24

21]] Table 2.1: The average biogas composition assumed for use in the model [21

Biogas Biogas componen componentt C H 4 C O2 CO N 2 H 2 H 2 S  Oxyg Oxygen en,, Silo Silox xane ane

Volume olume % 60 35 0.15 3 1.55 0.3 trac traces es

Table 2.2: The results of the modeling for the cryogenic separation

Stream Temperature ( C ) Pressure (bar (bar)) Vap or Fraction Mole Flow (kmol/h (kmol/h)) Mass Flow (kg/h (kg/h)) /h) Volume Flow (m (m3 /h) Enthalpy (MMkcal/h (MMkcal/h)) Mass Fractions C H 4 C O2 CO N 2 H 2 H 2 S  ◦

1 25 1 1 10.11 263.42 25 0 -0.44

2 -91 40 1 6.48 10 105.63 1.26 -0.11

3 1.4 40 0 3.63 157.78 0.17 -0.34

0.369 0.591 0.001 0.032 0.001 0.004

0.91 0.006 0.00014 0.98 0.004 1.91E-09 0.08 2.29E-08 0.003 4.23E-15 Trace 0.006

factor 1000 which is achieved as well. Knowing these demands are achieved, the second step in the process design will be designing of the cooling and compressing units. Figure 2.8 shows these process units. In these process units the crude inlet biogas goes through the first heat exchanger in which it is cooled down to -70 C . This heat exchanger uses the product stream as a cooling medium, which has the advantage of preheating the upgraded biogas before leaving the plant as well as the energy efficiency benefit benefit of the the process process.. The The first first cooli cooling ng step is foll follow owed ed by a casca cascade de of  compressors compressors and heat exchangers exchangers which cool the inlet gas down to -10 C  and compress up to 40 bars before entering the distillation distillation column. To defrost ◦

◦

25

Biogas

1

2

Cooler 

Compressor

3

Cooler

4

Compressor  

5

Cooler 

Figure 2.8: Cooling and compressing units in cryogenic separation

frozen water each heat exchanger needs a parallel heat exchanger. Table 2.3 shows the stream conditions through this process unit. Table 2.3: Stream conditions through the cooling and compressing process units

Stream Temperature ( C ) Pressure (bar (bar)) Vapor Fractions Mass Flow (kg/h (kg/h)) /h) Volume Flow (m (m3 /h) Enthalpy (MMkcal/h (MMkcal/h)) ◦

Inlet gas 1 2 3 4 5 25 -70 20 7 -10 54 -10 1 1 21 20 40 40 1 1 1 1 1 1 177.70 177.70 17 177.70 17 1 77.70 17 1 77.70 17 177.70 168.64 114.21 12.89 6.81 4.27 3.07 -0.29 -0.30 0.28 -0.30 -0.29 -0.30

Figure 2.9 shows the complete PFD for the cryogenic separation process

Waste streams The fact cryogenic separation uses no chemicals makes of this separation an environme environmenta ntall friendl friendly y techniq technique. ue. The only waste waste stream stream is stream stream 8 shown in figure 2.9 2.9.. (The same as stream 3 in figure 2.7 2.7)) This stream mainly consists of a high percentage of  C O2 but also contains traces of  H 2 S  and C H 4 . Becau Because se H 2S  is rather poisonous and C H 4 is more damaging to the environment comparing C O2 , this stream needs to be treated.

Cost estimation for cryogenic separation The cost analysis for the final designed process is estimated using quotations from DMT, the Matches process, a cost engineering website (appendix B) and Aspen Icarus process evaluator. /h, 1,228,500 N m3 per year Output: 161 N m3 /h, 98% C H 4 yield, purity output: 91% C H 4

26

Biogas 25 oC 1 bar  37 % CH4 58 % CO2 5 % other 

Recirculation Recirculation of product stream as cooling agent

-70 oC 1 bar 

207 oC 21 bar 

-10 oC 21 bar 

54 oC 40 bar 

-10 oC 40 bar 

-90 oC 40 bar 

Cooler  Compressor

Cooler

Compressor

Cooler   Distillation Column

Waste 0.6 % CH4 98 % CO2

Product 91 % CH4 8 % N2 1% other 

Figure 2.9: PFD of the cryogenic separation of biogas

Investment costs

Heat Exchanger 1 Heat Exchanger 2 Heat Exchanger 3 Compressor1 Compressor2 Separation Separation train

     

10,300 26,500 21,700 200,000 250,000 400,000

Total investment costs   908,500 Depreciation period of equipment is 10 years. Running costs

Energy costs Operator Maintenance Total running costs  Costs per N m3 biogas:

   



343,000 50,000 4,500 397,500

0.44

27

2.5 2.5

Mem Membr bran ane e sepa separa rati tion on

C H 4 and C O2 can also be separated using a membrane. Because of the difference in particle size or affinity, certain molecules pass through a membrane whilst others do not. The driving force behind this process is a difference in partial pressure pressure betw b etween een gases. The properties of this separation separation technique are highly highly dependen dependentt on the type type of membrane membrane used. Many Many differen differentt memmembranes are available each with its particular specifications [26 26]. ]. The general general principle however is basically the same and is explained below on the basis of a membrane from the Natcogroup [22 [22]. ]. The Natcogroup use membrane gas separation modules which operate on the basis of selective permeation [22 [22]. ]. The technol technology ogy takes takes advan advantage tage of  the fact that gases dissolv dissolvee and diffuse diffuse into into poly p olymeri mericc materia materials. ls. If a prespressure differential is set up on opposing sides of a polymeric film, a membrane, transport transport across across the film (permeatio (permeation) n) will occur. The rate of permeati permeation on is determined by the product of a solubility coefficient and a diffusion coefficient efficient.. Very small small molecul molecules es and highly highly soluble soluble molecul molecules es (such (such as H e, H 2 , C O2 and H 2 S ), ), permeate faster than large molecules (such as N 2 , C 1 , C 2 and heavier hydrocarbons including C H 4 ). When When a biog biogas as stream stream containing C O2 is fed to a membrane, the C O2 will permeate the membrane at a faster faster rate than the natural natural gas componen components. ts. Thus, Thus, the pressuri pressurized zed feed stream (coming from below in picture 2.10 2.10)) is separated into a C O2 rich, low pressure permeate stream on the right hand side and a C O2-depleted, high pressure C H 4 gas stream.

Figure 2.10: Schematic representation of membrane separation

Any polymeric material will separate gases to some extent. Proper selection of the polymeric material comprising the membrane is extremely impor28

tant. It determines the ultimate performance of the gas separation module. Membranes made of polymers and copolymers in the form of a flat film or a hollow fibre have been used for gas separation. Several different membranes have have been found in literat literature. ure. The Natcogrou Natcogroup p use cellulo cellulose se acetate as a base membrane material [22 22]. ]. Cellul Cellulose ose acetate acetate is very very inert and stable stable in C O2 /hydrocarbon /hydrocarbon environments. environments. Application Application of polyim p olyimide ide membranes membranes has also been found [23 23]. ]. For this type of membran membranee a single single stage unit is sufficient to achieve 94% enrichment from gas with a common concentration of  C H 4 . Using Using a liquid liquid as a membran membranee is also also possible possible making it possible possible to replace the membrane in situ by circulating the liquid [24 [24]]. The permeation of  H 2 S  depend dependss on the choic choicee of membra membrane. ne. If H  If  H 2 S  permeates permeates only partly partly both exit exit streams streams contai contain n H 2 S . Eith Either er the the inpu inputt strea stream m or the outpu outputt stream streamss can be clean cleaned. ed. Since Since the C O2 rich stream still contains a relatively high concentration of  C H 4 ( 10-15%) this stream is best used used in a gas engin enginee to produce produce elect electri rici city ty or heat. heat. For that, the does not not have have to be remov removed ed.. This This will will resul resultt in more wear wear of the the H 2 S  does engine but maintaining an engine is cheaper than the removal of H  of  H 2 S . The cheapest option therefore is only cleaning the C H 4 stream which constitutes constitutes a signific significan antly tly smaller smaller amount amount of gas than the input. A membran membranee which which fully removes the H 2 S  from the biogas would be a great improvement. The need for other pre-treatment such as drying or heating is fully dependent on the membran membranee used. A higher pressure pressure gives gives a higher higher gas flux through the membrane. However, the maximum pressure is determined again by the membrane. membrane. For this reason, high strength hollow fibre membranes membranes have have been developed. Overall, the efficiency of the entire process mainly depends on the membrane brane used. used. Its selectivi selectivity ty towards towards the gases gases havin havingg to be separate separated, d, memmembrane flux or permeability, lifetime, operational temperature and humidity range, maintenance and replacement costs are all factors that determine the overal overalll performan performance ce of such a biogas biogas upgrading upgrading techni technique que.. It is therefore therefore difficul difficultt to judge this this techni technique que in total. total. Some main characte characteris ristics tics can be given; given; it is a proven proven technology technology.. It has been b een applied for many years to extract nitrogen from ambient air. It has also already been used to upgrade biogas; experimentally [27 [27]] as well as commercially commercially.. Membranes, Membranes, especially hollow hollow fibre membranes, are very compact, light weight and allow for a modular design making expansion and replacement very easy. However, well maintained membranes hardly need any maintenance and can last as long as 10 to 15 years. Other equipment such as the compressor and pumps do need maintenance nance but this is also also true for the other other techniq techniques. ues. The total energy energy needs needs are very low since the membran membranee itself itself is passiv passive. e. Because Because the membran membranee is passive the entire process is easy to operate and simple to understand. 29

Membranes however can be expensive and also very fragile. Certain solvents or fine colloidal solids such as graphite can permanently destroy or foul the membrane.

Waste streams A major disadvantage of this technique is the low methane yield. The waste gas still contains C H 4 which which is highly highly poll p olluti uting. ng. Pa Part rt of it can be b e fed back back into the inlet or, as mentioned above, the waste gas can be burnt in a gas engine engine linked linked to a generato generator. r. Using Using a multi multistag stagee setup setup also also increas increases es the yield. Positive results have been found using an internally staged permeator [25 25], ], depicted in figure 2.11 2.11.. Electrical costs are low since only a compressor has to be powered powered.. The generator generator can power power the compres compressor sor which which results results in an even higher C H 4 efficiency. The C O2 stream is then of no further use. If the waste stream is not burned in an engine it is very polluting since C H 4 is far more harmful than just C O2 . CH4 + CO2

mainly CO2 + small amount of CH4

mainly CH4 + small amount of CO 2

Figure 2.11: Schematic representation of an internally staged membrane separa-

tor

Cost estimation membrane separation To prevent damage to the membrane, intensive pre-treatment might be necessary. This could be quite expensive. However, it is not taken into account in this report.

· · ·

Without H 2 S  removal 150 hours of maintenance per year Flare recommended (especially during start-up)

30

/h, 1,002,400 N m3 per year Output: 130 N m3 /h, 78% C H 4 yield, purity output: 89.5% C H 4 Investment costs

Additional costs Pumps (2) Compressor (5-10 bar) Membrane2

   

100,000 10,000 100,000 23,000

Total investment costs   233,000 Depreciation period of equipment is 10 years. Running costs

Energy costs (41 kW h) Operator Maintenance1

 

28,000 50,000 3,750

Total running costs 



81,750



The costs per N m3 produced are calculated as explained at the beginning of  this chapter. chapter. Costs per N m3 biogas without H 2 S  removal:



0.12

To remove H 2 S  the process described in 2.1.2 is added to these costs. This results in a total cost price for upgraded biogas of   0.22. This price is calculated from the following values: Investment costs  749,000 Running costs  126,750 1 2

Estimate E-kwadraat Estimate from Cirmac

31

Chapter 3 Comparison This chapter will compare the five different techniques which are investigated for biogas biogas upgradi upgrading. ng. The techniq techniques ues will be compare compared d on a couple couple of factors. Of course, every technique technique has its own advantag advantages es and disadvantage disadvantages, s, but there is more than that. The techniq techniques ues will be compared compared on the price price 3 per N m upgrad upgraded ed bioga biogas; s; how how easy easy or hard hard the process process runs runs looki looking ng at maintenance and scale up; and the impact on the environment by examining the waste waste streams. streams. The cost estimate estimate is used to calcul calculate ate the price of  3 one N m of upgraded upgraded biogas. biogas. Also, Also, there are the costs of investm investmen entt and the operating operating costs. The considera consideration tion to be made is the best combina combinatio tion n of advantages and disadvantages, the cost for operating and investment and finally, the price which has to be paid for the upgraded biogas, the waste strea streams ms and main mainten tenanc ance. e. The table table at the end of this this chapter chapter gives gives an overview of this comparison. Furthermore, appendix ?? gives the advantages and disadvantages of each technique in the current opinion of DMT [29 [29]. ]. These are compared to the findings presented in this report. Finances

Looking at the price of the upgraded biogas, it can be seen that high pressure pressure water water scrubbi scrubbing ng is the cheapes cheapest. t. This This can be linke linked d to the investinvestment costs which also are the lowest. Cryogenic separation sticks out of the list with the highest investment cost and also the cost price is with  0.44 the highest. While the investmen investmentt costs of pressure swing absorption are also quite high, the cost price is the average compared to the other four techniques. Impact on the environment

Looking at the amount of waste streams, it can be easily seen that pressure swing adsorption and membrane membrane separation have only one waste waste stream, where chemical absorption and high pressure water scrubbing have two waste 32

streams. But it does not automatically automatically mean that chemical absorption absorption and high pressure water scrubbing are a bad technique. Not only the amount of  waste waste streams has to be noticed, noticed, also the content content of the waste streams have have to be determined. The waste stream produced with pressure swing absorption and membrane separation both will be led to a gas engine linked to a generator. This is the best solution, because C H 4 is more harmful when emitted into air compared to burning a waste stream containing C H 4 . Chemical absorption has two real waste streams, namely a stream containing C O2 and a stream periodically catalyst catalyst stream. High pressure pressure water scrubbing has a waste stream containing C O2 and some traces of H  of H 2 S . The last component is poisonous, which result in the fact that this waste stream needs waste treatment. The second waste stream is a water stream containing C O2 and H 2 S . Because the amount of  C O2 and H 2 S  is rather small, this stream does not need any treatment. treatment. Cryogenic Cryogenic separation has one waste stream containing a high percentage of C of C O2 and some traces of H  of H 2 S  and C H 4. This waste stream needs treatment. treatment. High pressure water water scrubbing and membrane membrane separation are the only two techniques that don’t produce pure CO 2 . Ease of operation

Not each technique requires the same amount of maintenance, materials, catalyst catalyst and operators. Therefore, Therefore, a distinction distinction between between this has to be made. Looking at chemical absorption, an expensive catalyst is used in order to absorb C O2 and H 2 S . This This catalyst catalyst has to be changed changed twice twice a year, year, which which leads to a shut down. The same is partly true for pressure swing adsorption. High High pressure pressure water water scrubbin scrubbingg howe howeve verr is a very very simple simple process. process. The only separation parameter is the pressure of the water scrubber and this can be easily easily kept under the desired desired condition. condition. Because Because of this easines easiness, s, there there is still an operator needed to check if everything goes well, which is there all the time. Another Another advant advantage age is the absence absence of using using special chemic chemicals als or a catalyst, which makes that the process can run continuously without a periodic shut down. Since membrane membrane separation only needs few equipment equipment and makes no use of chemicals, no operator is needed which is constantly at the plant. plant. Howe Howeve ver, r, in order to chec check k the running running process, one operator is needed. Another consequence is the simple process, which makes it an easy running running process. process. At last, last, cryogen cryogenic ic separation separation is looked looked at. Because Because of the large amount amount of equipment equipment needed, it is a complex process. Furthermore, urthermore, the high pressure and very low temperature makes it a dangerous process, which has to be controlled. Operators are certainly needed therefore.

33

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Chapter 4 Conclusions Comparing the five techniques for the upgrading of biogas with the goal of  injecting injecting it into the commercial commercial gas grid is done in the previous section. From that, it can be concluded that looking only at the cost price, high pressure water wa ter scrubbin scrubbingg is the best option. option. But there is more than only cost price to make a process succeed or fail. Therefore, some other criteria are set up. The waste stream inventory gives another picture. Pressure swing adsorption and membrane separation are the only two techniques which have only one waste stream, which can be cleverly used by driving a generator. The other techniques techniques have waste streams which which need some waste waste treatment, treatment, which which also have have to be taken into account looking from an environmental environmental and economical economical point of view. Furthermore, urthermore, the yield and purity is of great importance. The purity of  the upgraded biogas is comparable for most of the techniques, but membrane separation has the lowest purity of 89.5% C H 4 . The other techniques have a purity of 98% C H 4 . The yield of methane achieved achieved with chemical chemical absorption is the highest with 98%. Pressure Pressure swing adsorption, chemical chemical absorption and cryogenic separation are at average, where membrane separation is the lowest with 78% C H 4 yield. Membranes in series increase the yield, but this results also in an increase in costs. Considering the ease of operation of each process, membrane separation and high pressure pressure wa water ter scrubbing scrubbing are the easiest easiest processes processes to operate. operate. No catalysts catalysts or chemicals chemicals are needed. Cryogenic Cryogenic separation separation has the problem of  the need to wo work rk at very very low temperatures temperatures and high pressur pressures. es. Therefor Therefore, e, it needs to be controlled by an operator and some safety restrictions have to be set, because of the high possibil possibilit ity y of explos explosion ion.. Chemica Chemicall absorpti absorption on and pressure swing adsorption both need a catalyst in order to upgrade the biogas. biogas. This This catalys catalystt has to be change changed d twice twice a year year which which leads leads to a shut shut down. 35

From this all, it can be concluded that high pressure water scrubbing perfor performs ms the best. best. With With the low low cost cost pric price, e, high high purity purity and yield yield it is a promising upgrading technique. Though one waste stream needs treatment, it is a continuous process which operates almost on it self.

Recommendations

For further investigation we recommend the following subjects: •

•

•

•

•

•

The waste stream treatment is not considered in our investigation and can influence the price of the upgraded biogas. For a better cost investigation more quotations should be acquired and mass balances should be made. Then, a more precise estimation of the cost per N m3 biogas can be made. The C O2 footprint footprint is mentioned in the report but not calculated. calculated. When mass balances are made the CO 2 footprint can also be calculated. For chemical absorption it could be useful to look for more types of  catalyst. The performance of the membrane separation is highly dependent on the type of membran membranee used. used. An investi investigati gation on of more types types of membranes can be useful. Cryogenics Cryogenics is only investigated investigated at one pressure pressure and temperature. We do not know if this is the optimal condition and therefore the cryogenics process should be investigated on a range of temperatures and pressures.

36

Acknowledgement During our Multi Disciplinary Project we received help from may people. Without their help we would not have been able to successfully finish this project. Therefore our gratitude goes out to the following people. First First of all we want to thank thank Laura, Laura, our tutor. tutor. We greatly greatly appreciat appreciated ed Laura’s presence during our weekly meetings. Her input was always insightful. ful. Altho Although ugh she was rathe ratherr quie quiet, t, the things things she said said were well well worth orth listening to. We would like to thank the people at Dirkse Milieutechnology, in particular Robert Lems, Déborah Felisoni and Pieter-Durk van Jaarsveld for making this this project possible possible and receiving receiving us at DMT in Joure. Joure. We gathered gathered lots of useful information and had some good fun during our overnight stay in Joure. Furthermore we thank René van den Kieboom for making the excursion to Tilburg possible and thank Maarten van der Heuvel and Olivier Kuijer for arranging the excursion to Nuenen. Both excursions were a real addition to our project and gave us a good understanding of the reality of upgrading biogas. Also, we would like to thank Jetse Reijenga, our project coordinator, for alway alwayss being attentiv attentivee to our wo work rk and his interes interestt in our progress progress.. The short introduction into building websites was quite helpful and resulted in an awesome website for our project.

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Bibliography [1] R. Lems, Lems, Biogasopwaardering: Het DMT-TS-PWS systeem , februari 2006 [2] Harry Benning, Benning, Opwerken van biogas naar aardgas kwaliteit , maart 2005 [3] Wahyudin, ahyudin, W., Biogas upgrading installation unit , 2007. [4] Information Information collected collected from DMT [5] TNO Environmen Environment, t, Energy and Process Innovation, Innovation, C O2-recovery using membrane gas absorption, brochure [6] P.S. Kumar, J.A. Hogendoorn, P.H.M. .H.M. Feron, G.F. Versteegh, Versteegh, New absorption liquids for the removal of  C O2 from dilute gas streams using  membrane contactors , Chem. Eng. 57, 2002, 1639 - 1651 [7] Horikaw Horikawa, a, M.S., M.S., Rossi, Rossi, F., Gimenes Gimenes,, M.L., M.L., Costa Costa C.M.M. C.M.M.,, Da Silv Silva, M.G.C., Chemical absorption of  H 2 S  for biogas biogas purification  purification , UniversiUniversidade Estaldual de Maringá, 2001 [8] Astarita, Astarita, G., Gioia, Gioia, F., Hydrogen sulphide chemical absorption , Chemical Engineering Science, 1964, vol. 19, pp. 963 - 971 [9] OBrien, OBrien, M., M., Catalytic Oxidation of Sulfides in Biogas, Ventilation Air and  Wastewater Streams from Anaerobic Digesters , Proceedings 1991 Food Industry Environmental Environmental Conference, USA, 1991 [10] Wubs, H.J.and Beenackers, Beenackers, A.A.C.M., Kinetics of the Oxidation of Ferrous Chelates of EDTA and HEDTA into Aqueous Solutions , Ind. Eng. Chem. Res., 1993, vol.32, pp2580 - 2594 [11] Perry, Perry, R.H. en D. Green, Perry’s chemical engineers handbook , McGrawHill Book Company, USA, 6th print. //en.wikipedia.org/wiki/Wet_ [12] Wikipedia, Wikipedia, http : //en.wikipedia.org/wiki/Wet _scrubber

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[13] [13] Eneco, Eneco, http : //mkb.eneco.nl/producten e nt arieven/tarieven/ tarieven.asp [14] [14] WMD, WMD, http : //www.wmd.nl/MijnWMD/TariefNota/ TarievenGrootverbruik.html [15] http://www. http://www.biotec biotech-ind. h-ind.co.uk/M co.uk/Methane-R ethane-RGP-P GP-Process.h rocess.htm, tm, visited visited at th the 24 of February 2008 [16] O. Jönsson, Jönsson, M. Persson, Persson, Biogas as transportation fuel , Swedish Gas Centre, 2003 [17] Dr. Alfons Schulte-Sc Schulte-Schulze hulze Berndt, Intelligent Utilization of Biogas Upgrading and Adding to the Grid , Jonköping, May 2006 [18] O. Smith, A. Westerberg, Westerberg, The optimal design of pressure swing adsorption systems , Chemical engineering science, Vol. 45, No. 12, pp. 2967 2976, 1991 [19] [19] P. Cruz, Cruz, J. Santos, Santos, F. Magalh Magalhães, ães, A. Mendes, Mendes, Cyclic adsorption separation processes : analysis strategy and optimization procedure , Chemical engineering science, 58 (2003) 3143 - 3158 [20] Information Information from excursion to Cirmac in Nuenen [21] http://www.kolumbus.fi/suomen.biokaasukeskus/en/enperus.html, http://www.kolumbus.fi/suomen.biokaasukeskus/en/enperus.html, visited at the 8th of May 2008 [22] Natcogroup, Natcogroup, Acid Gas ( C O2 ) Separation Systems with Cynara Membranes , July 2007. [23] M. Harasimowicz, P. P. Orluk, G. Zakrzewska-Trznadel, Zakrzewska-Trznadel, A.G. Chmielewski, Application of polyimide membranes for biogas purification and enrichment , Journal of Hazardous Materials 144 (2007) 698-702. [24] [24] Asim Asim K. Guha, Guha, Sudipto Sudipto Majumdar Majumdar and Kamalesh Kamalesh K. Sirk Sirkar, A largerscale study of gas separation by hollow-fiber-contained liquid membrane  permeator , Journal of Membrane Science 62 (1991) 293-307 [25] K. Li and W.K. Teo, Use of an internally staged permeator in the enrichment of methane from biogas , Journal of Membrane Membrane Science 78 (1993) 181-190 [26] Danial L. Ellig, Joseph B. Althouse Althouse and F.P. F.P. McCandless, Concentration of methane from mixtures with carbon dioxide by permeation through  polymeric films , Journal of Membrane Science 6 (1980) 259-263 39

[27] S.A. Stern, B. Krishnakumar, Krishnakumar, S.G. Charati, W.S. Amato, A.A. FriedFriedman, D.J. Fuess, Performance of a bench-scale membrane pilot plant for  the upgrading of biogas in a wastewater treatment plant , Journal of Membrane Science 151 (1998) 63-74 [28] Carbon Trust, Trust, Carbon footprint measurement methodology , version 1.3, march 2007 [29] [29] R. Lems, Lems, Upgrading Upgrading biogas , 2008 [30] Brochure Brochure Biogas CHP, CHP, The use of biogas in Tilburg The Netherlands , 2000 [31] Myken Myken A., Jensen J., Dahli A., Final report, Adding Gas from Biomass  to the Gas Grid , Contract Contract No: XVII/4.1030/Z/99XVII/4.1030/Z/99-412; 412; Danish Gas TechTechnology centre a/s, Swedish Gas Center

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Appendix A Alternate cost estimation PSA The costs of the pressure swing adsorption depend on which type of adsorbent bent mater materia iall is used in the colum columns ns and the number number of units units used. used. The The operational costs are influenced by the operating pressure, which on its turn is dependent dependent on the adsorbent adsorbent material material.. The compresso compressorr needed needed in the beginning in order to compress the incoming biogas is the last element which contributes contributes to the cost of the whole plant significantly significantly.. Compression Compression is expensive and in order to make it profitable, it is needed to recover the required pressure. The pressure recovery can be enabled by several pressure valves. Now, some assumptions are made to be able to make a cost estimation. The type of adsorbent material used in the PSA is a carbon molecular sieve. The choice for this adsorbent material can be explained by the ability of  removing N 2 and O2 from the biogas. The lifetime of the adsorbent material is taken taken to be 3 to 4 years years.. Furthe urtherm rmore ore,, there there are are four four adsorbe adsorberr vessel esselss needed needed in the plant. plant. Figure Figure 2.6 shows the overall scheme of the PSA-plant. The compressor, the four adsorber vessels, the vacuum pump and the H 2 S removal step are included in the cost estimation. The several pressure valves which are required are included in the equations by the modular factor in it. The costs of the PSA-plant are divided in two parts: operational costs and capital costs. First, the operational costs will be calculated. The operational costs depend on the operating pressure, the flow rate, and the dimensions of  the adsorber vessels. Therefore, first those parameters are determined. The operating pressure of the PSA-plant is 1 bar at the inlet and the product strea stream m is at 5 bar. bar. The The bed length length is set at 6 m with a diam diamete eterr of 1,5 1,5 m /h. assuming cyclic steady state. The inlet flow is assumed to be 250 N m3 /h.

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The following equation from [19 [19]] determines the operational costs: OC  = Qin · W  · EC 

(A.1)

Where: OC  Qin W  EC 

Operating costs [E/year [E/year]] /year] Average inlet flow [N [N m3 /year] Theoretical work [J/m [J/m33] Energy costs [E/J  [E/J ]]

The energy input amounts to 1,875 kW h. The The energ energy y price price per kW h amounts to  0.10. The operational costs become  35,721-. The other part, the capital capital costs, costs, can now now be calcula calculated. ted. These These are divided divided in three parts. parts. The bed metal shell which includes the adsorber vessels, abbreviated with C Shell Shell ; the costs of the compressor, C Comp Comp ; and finally, the costs of the driver for the compressor, C Driver 18]. ]. Driver . The following equations are taken from [18 0.584 C Shell 3.74 · d2 + 739 · 4.93 · d · l + 3. Shell = P 





(A.2)

Where: P  d l

Pressure [P [P a] Bed diameter [m [m] Bed length [m [m]

The costs for the shell become  425.500,0.435 C Comp 14.020 · Qin Comp = 14.

Qin

(A.3)

/min] Volumetric flow rate at the inlet [f [f t3 /min]

The costs for the compressors become  79,423-. 1.61 0.32 C Driver 11.68 · hpComp + 2. 2.470 · hpComp Driver = 11.

hpComp

(A.4)

hp. Horse power of compressor [hp [hp]; ]; assumed to be 5 hp.

The costs for the driver of the compressor become  2,771-. In order to calculate the cost of the PSA-plant, also the investment costs for the H 2S -removal -removal part has to be taken into account, therefore, the costs used for H 2 S -absorption -absorption is included which amount to  516.000,-. 42

The total capital costs are the cost of the bed metal shell summed up with the costs of the compressor, the costs of the driver of the compressor and the costs of the H 2S -removing -removing part. The total capital costs become  1.023.694,The total running costs of the PSA can also be calculated by: C Annual Annual = C Cap Cap τ  pb tax C op op dr

C Cap Cap + (1 − tax) tax) · C op op + dr · tax · C Cap Cap τ  pb

(A.5)

Capital cost [E  [E ] Pay back time [s [s] Tax rate [s [s] Operating cost [E  [E ] Depreciation rate [−]

The pay back time is set at 3 years, which is equal to 94.608.000 seconds. The tax rate is assumed to be 0,6 and the depreciation rate 0,125. The total running costs of the PSA-plant become  282.616,-. The final cost price per N m3 biogas become:

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

0,23.

Appendix B Cryogenic equipment Compressor 1

Manufacturer: Vilter (http (http : //www.vilter.com ) Compressor type: oil flooded single screw compressor Motor power: 180Kw Price for complete package ready to work: 200,000

Compressor 2

Manufacturer: Vilter (http (http : //www.vilter.com ) Compressor type: oil flooded single screw compressor Motor power: 200Kw Price for complete package ready to work:  250,000 Heat exchanger 1

Price is calculated by http : //www.matche.com/EquipCost/Exchanger.htm Heat exchanger type: Condenser, vertical tube Area: 70 f t2 Internal pressure: 150 psi Material: Carbon Steel Heat exchanger 2

Price is calculated by http : //www.matche.com/EquipCost/Exchanger.htm Heat exchanger type: Condenser, vertical tube Area: 150 f t2 Internal pressure: 300 psi Material: Carbon Steel

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Heat exchanger 3

Price is calculated by http : //www.matche.com/EquipCost/Exchanger.htm Heat exchanger type: Condenser, vertical tube Area: 100 f t2 Internal pressure: 150 psi Material: Carbon Steel

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Appendix C

C O2 footprint The carbon footprint is a method to measure the effect of a certain process on the environment in terms of the amount of green house gases produced during the entire process. The process encompasses the whole life cycle of a product, thus from the production of the raw material to disposal of the final product. product. This This makes it a very very extensiv extensivee method. In order to produce produce such a carbon carbon footprin footprint, t, a certain certain path needs to be follo followe wed. d. This This methodolo methodology gy will will be b e explained explained in the follow following ing text. Because Because of the method method being that extensive, the carbon footprint is not calculated for every biogas upgrading technique separately. Making a carbon footprint of a process will follow five major steps in order to calculate the green house gases produced during the supply chain. Table C.1 gives a schematic overview of the methodology. Step 1 Step 2 Step 3 Step 4 Step 5

Analyz Analyzee inte internal rnal product product data data Build Build suppl supply y chai chain n process process map Define Define boundary boundary condition conditionss and identif identify y data requireme requirements nts Collec Collectt primar primary y and secondar secondary y data data Calcul Calculate ate carbon carbon emission emissionss by supply supply chain chain process process steps steps

Table C.1: The overview of the five major steps in order to calculate the carbon

footprint

These steps always have to be followed one by one and boundaries have to be b e set. For instance, instance, the carbon carbon footprin footprintt can cover cover all the supply supply chain chain steps from raw material to disposal, but this can be adjusted. Step 3 in the methodology takes care of that.

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Figure C.1: The steps used in order to produce the whole supply chain process map,

picture taken from [28 28]]

Step 1: Analyze internal product data  The main goal of this first step is to develop a deeper understanding of the product. This implies implies determining determining what raw materials the product is made of and which actions or process are needed to convert the raw material into the desired final product. Next to that, the waste streams and the produced co-products have to be known. It is necessary carefully evaluate each step in the entire process. Step 2: Build supply chain process map The objective of the second step is to produce the whole supply chain process map, which can be visualized using figure C.1 C.1.. Step 3: Define boundary boundary conditions conditions and identify identify data requir requirement ements  s  The third step has two sub-objectives. First, the boundaries need to be set which have to be followed for the product. After that, the required data is needed in order to set up the mass balances and the carbon footprint. Step 4: Collect primary and secondary data  From the data collected in the third step of the methodology, the required data is found. found. This This data can be used used in order to develop develop the mass mass balance balance

47

and also to calculate the GreenHouse Gas emissions (GHG emissions) for each step in the process. Step 5: Calculate GHG emissions by supply chain process steps  Now all the required data is collected, a model can be designed to actually calculate the mass balance and the GHG emissions of each step in the process. After the five steps, the carbon footprint is ready. It gives insight in the GHG emissions emissions produced in the process. Then it is necessary to take a critical look at the environmental performance of your process. When the emissions are too large or harmful, the carbon footprint can help to design a solution in order to reduce and control the produced greenhouse gas emissions.

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Appendix D Visit to SMB Stortgas BV in Tilburg Since 1987, DMT has grown to be a multidisciplinary international and leading compan company y with importan importantt referenc referencee projects projects within within the environ environmen mental tal sector. DMT is expert in: air treatment and odor abatement systems, desulphurization unit (both biological and chemical), ground water purification and soil soil remedia remediatio tion n plant plants, s, wa water ter treatme treatment nt plants plants and aeratio aeration n systems systems and water management. management. At this moment moment DMT is developing developing its biogas upgrading technology. For SMB stortgas BV in Tilburg, a high pressure water scrubbing plant is installed. In Tilburg, a municipal association initiated a complex, including a landfill gas installation, a biogas plant, and an upgrading plant which has been running running since 1994. The upgraded upgraded gas, which which has natural gas quality quality,, is injecte injected d into into the natural natural gas netwo network. rk. An association association has been created created involving volving 9 municipal municipalities, ities, of which Tilburg is the largest. The name is SMB (Samenwerkingsverband Midden Brabant) and the objective is to solve the waste waste problem in the cities. In total, the 9 municipalities municipalities have have 480,000 inhabitants, who yearly produce 40,000 tons of organic waste. As a landfill biogas treatment plant was already present in Tilburg, SMB chose anaerobic digestion of the organic waste, which means Vegetable, Fruit and Garden waste, (VFG) [30 [30]. ]. In order to obtain more detailed information about the upgrading processes of biogas and also to get answers to our questions regarding this upgrading technique, we visited the SMB high pressure water scrubbing plant in Tilburg. Our visit took place on the 9th of April 2008. We arranged a meeti meeting ng with with René van den den Kieboo Kieboom. m. The The visi visitt starte started d with with a genera generall presentation about the upgrading plant in Tilburg, which was followed with a detaile detailed d explan explanatio ation n about each separati separation on unit. unit. After After this this presen presentati tation on there was the opportunity for asking our questions. Since this excursion was 49

Figure D.1: The HPWS plant in Tilburg

planned in the middle of our project we had many questions, both about the technique of biogas upgrading as well as the treating method of the waste streams streams and a cost estimati estimation on accordin accordingg to this this techni technique. que. The questions questions were extensively answered. Finally we went to the site to have a closer look at different units of the plant, where the given presentation was coupled to more detailed information information about each separation separation unit of the plant. We talked further about the different theoretical features of the process and how they turn out to behave during operation. The picture shows the plant we visited. Address

Vloeiveldweg 10 5048 TD Tilburg Telephone: 013-4556163

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Appendix E Visit to Carbiogas BV in Nuenen Cirmac International BV is a world-wide operating company, specialized in gas treatment systems for the petrochemical and chemical industry, refineries and other industries. Cirmac is part of the Rosscor Group of companies. In order to obtain more detailed information about the upgrading processes of biogas, we visited an installation build by Cirmac on the 20th of  May 2008 in Tilburg at a site of Carbiogas BV. We arranged a meeting with Ing. Olivier Kuijer and Ing. Maarten van den Heuvel in Nuenen.

Figure E.1: The VPSA plant in Nuenen

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The visit started with a presentation about the plant in Nuenen, in which we got insight in the processes of pressure swing adsorption and membrane separati separation. on. At that moment moment we still still missed some informat information ion about the cost estimation estimation of a few upgrading processes. processes. Our questions were were answered extensively, which gave us the opportunity to fill the gaps in our theories. After the presentation, we went outside to take a look at the upgrading instal installati lation. on. The installa installatio tion n we viewed viewed can be seen in the picture, picture, it is a vacuum pressure swing adsorption adsorption (VPSA) installation. installation. We discussed the different theoretical features of the process and how these turn out to behave during operation. Furthermore, we spoke about the waste streams, how they are kept as low as possible and how they are disposed. Finally, we walked to the top of a landfill, to have a look at the biogas wells and to see how a landfill is operated to obtain a large amount biogas with the right conditions.

Address

Gulberg 7 5674 TE Nuenen Telephone: 040-839683

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