-ABSTRACT This project on packed absorption column was designed to remove 95 percent of ammonia from a gaseous mixture of 8% ammonia and 92% air by volume. The flow rate of the gaseous mixture entering the tower at 293k and 1.013 x 105 N/m2 is 2.5kmol/hr. pure water, flowing at the rate of 30% above the minimum, is used as solvent. While One inch ceramics Berl saddle was used as the packing materials. The aim is to determine the total height, the diameter, and costing of the tower. The design was successful using carbon molybdenum steel (SA – 135 Grade B) as materials of construction with thickness and hemispherical head of 6.25mm The tower height was estimated to be 1.922m, with diameter of 0.1405m and the column operating at 293k and 1atm costs approximately N380000.
TABLE OF CONTENTS APPROVAL/CERTIFICATION DEDICATION ACKNOWLEDGMENTS ABSTRACT TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES CHAPTER ONE INTRODUCTION 1.1 application of gas absorption work 1.2 Aims and objectives of the design
CHAPTER TWO LITERATURE REVIEW 2.1 Packed absorption tower 2.2 System efficiencies and performance 2.3 Absorber system configuration 2.4 Process description 2.5 Types of absorber equipment 2.6 plate or Tray tower 2.7 Venturi scrubbers 2.8 Spray tower 2.9 Welted wall tower 2.10 Packed tower internals
2.11 A liquid distributor 2.12 Packing materials 2.13 Supporting plates 2.14 A packed restrainer 2.15 Tower shell 2.16 Packed tower 2.17 Random packing 2.18 Regular packings 2.19 Choice of solvent for absorption 2.20 Types of solvent for gas absorption 2.21 – 2.25 Ammonia; properties, uses an health effect
CHAPTER THREE DESIGN PROCEDURES 3.1 Equilibrium data 3.2 Determination of gas and liquid stream property 3.3 Physical properties 3.4 Determination of absorption factor 3.5 Column (Tower) diameter 3.6 Determination of tower height 3.7 Mechanical design 3.8 Costing of the tower
CHAPTER FOUR RESULTS ANALYSIS, DISCUSSION, CONCLUSION AND RECOMMENDATION
4.1 Results analysis 4.2 Discussion, concision and recommendation REFERENCES APPENDIX 1 APPENDIX 2 APPENDIX 3 APPENDIX 4 APPENDIX 5
Nomenclature LIST OF TABLES Table 1 Table 1.1, Equilibrium data Table 1.1 Equilibrium solubility data for NH3 in air Fig. 2.1
A schematic diagram of packed tower
Fig 2.6
A sketch of tray tower
Fig. 2.7
A sketch of venture scrubber
Fig. 2.9
A sketch of wetted wall tower
Fig. 2.11
A sketch of inadequate and adequate distributor
Fig. 2.17
various sketch of packing materials
Fig. (A-1)
A Schematic diagram of packed absorber
Fig. (D -1)
Single V Buff joint with 600C level and roof opening Of 1/16 inch
Fig. (D-2)
A Sketch of packed absorption tower
Fig. (D-3)
A sketch of the hemispherical Head.
CHAPTER ONE INTRODUCTION Packed column (tower) is an equipment used for gas absorption and
other operations. It is a cylindrical column with a gas inlet and distributing space at the bottom, liquid inlet and distribution at the top. It consists of liquid and gas exists at bottom and top respectively. Packing tower is used for gas absorption operation in which a gaseous mixture is allowed to contact with the liquid in a counter-current manner for the intention of preferentially dissolving one or more component from the gas to form a solution of them in the liquid. The liquid which consist of pure solvent is pumped into the column at the top and flows downward. The gaseous mixture is pumped into the tower at the bottom and flow upward through the space in the packing. It flows counter currently to the flow of the liquid. The arrangements of the packings provide a large surface for contact between the liquid and the gas which help the contact between the two phases. The solute in the gas mixture is absorbed by the two phases. The solute in the gas mixture is absorbed by the fresh liquid flowing down while the dilute gas or lean gas leaves at the top of the tower. The liquid is enriched with the solute gas it flows down the tower and concentrated liquid called strong liquid leaves at the bottom of the tower through the liquid exit. The project is required to design a packed column which will remove 95% of ammonia from the gaseous mixture of 8% and 92% air by volume. The flow at 293k and 1.013 x 105 N/m2 is 2.5kmol/hr and pure water flowing at the rate of 30% above the minimum is required to be used as solvent while 1 inch ceramic Berl Saddle would serve as the packing materials. The design parameters will be solved for by applying liquid and gas condition along with the associated physical properties to estimate the diameter of the tower and height of the packing required. The tower mechanical design would be based on the diameter while the overall costing will be the function of the overall height and material of the constructions of the tower. APPLICATION OF GAS ABSORPTION Gas absorption is applied for the separation and purification of dirty air. Gas absorption is the removal of gases from the air by a liquid. The undesirable gas dissolves in the scrubbing liquid while other gasses do not, the pollutants gas can be scrubbed out. The most efficient gas scrubber is the packed tower, which is also used for capturing particulates. The packings material, supported by plates or screens, provides many channels for the air and scrubbing liquid to come into close contact. The packing materials used
are ceramic or plastic pieces, wood slates, stones, marble ping pong ball. Gas absorber is an instrument used widely in industry for separation and cleanliness of gaseous mixture as product recovery device. It is used for pollution abatement on gas streams which have a pollutant concentration ranging from 250- 10,000ppmv. It can be apply for removal of water solution of inorganic contaminant from air stream. AIMS AND OBJECTIVES OF THE DESIGN The objective of the design of the packed tower is to remove 95% of ammonia from a gaseous mixture of 8% and 92% air by volume. This has a flow rate at 293k and 1.013 x 105N/m2 as 2.5kmol/hr. The solvent is pure water and 1inch ceramic Berl saddle is used while the liquid flow at 30 percent above the minimum. It is required to determine the following: Equilibrium data Diameter of the column The material balance of the column Height of the column The mechanical design of the column The cost of the tower The design drawing of the column.
CHAPTER TWO LITERATURE 2.1 PACKED ABSORPTION TOWER Absorption is the act by which one or more components of a gaseous mixture are dissolved in a liquid (that is, a solvent). The gas exits as byproduct of coke oven when washed with water to remove NH3, and also with oil to remove benzene and toluene vapors. When mass transfer occurs from the liquid to the gas, the operation is called “adsorption” or “stripping”. For instance, benzene and toluene are removed from the absorption oil by contacting the liquid solution with steam. If the gas steam enters the liquid in the absorption tower, it is called “absorption”. The operations are used only for solute recovery or solute removal. The absorption process can be classified into two ways, such as physical and chemical absorption in the solvent. Chemical absorption occurs when the components and the solvent are chemically combined together. The fluid (liquid) commonly used as solvent include water, mineral oil, and aqueous solution etc. Gas absorbers is the apparatus used widely in industry for separation and purification of gaseous mixtures as product recovery devices. This chapter focuses on the use of absorption for pollution abatement on gas streams which have a pollutant concentrations ranging from 250 to 10,000ppmv. Gas absorbers are commonly used to remove water solution of inorganic contaminant from air stream.
Fig. 2.1 Packed Tower 2.2 SYSTEM EFFICIENCIES AND PERFORMANCE The efficiency of gas absorber depends on the type of pollutant solvent system and also based on the gas absorber used. Most absorbers have removal efficiencies in excess of 90% while packed tower absorbers in some solvent system achieve efficiencies as high as 99.9%. The acceptable gas absorption for pollution abatement method is justified by the following factors - Desired removal efficiency - Pollutant concentration in the inlet vapor - Capacity required for controlling waste gas - Recovery value of the solute. Physical absorption is used on properties of the gas stream and solvent, such as viscosity and density as well as specific characteristics of the pollutant in the gas and the liquid stream (e.g. equilibrium solubility, diffusivity). These parameters are based on temperature, and lower temperature generally favor absorption of gases by the solvent. Absorption is facilitated by larger contacting surface, higher liquid gas ratios, and greater concentrations in the gas stream. The considered solvent to remove the pollutant(s) should have a higher solubility for the gas, must have low vapor pressure, low viscosity, and should be relatively inexpensive. The most common solvent is water, to remove inorganic contaminant, and also used to absorb organic compounds having relatively high water solubility. Some organic compound that have low water solubility, solvent such as hydrocarbon oil are used, through only industries where large quantities of these oil are available (e.g. petroleum refineries sand petrochemical plants). Solute removal can also be facilitated by forming the chemistry of the absorbing solution to react with the pollutant (e.g. caustic solution for acidgas absorption versus pure water sued as solvent). Chemical absorption may
be limited by the range of reaction, although the rate limiting step is typically the physical absorption rate then the chemical reaction rate.
2.3
ABSORBER SYSTEM CONFIGURATION
The flow of gas and liquid in the absorber may be counter current, concurrent or cross-current. The most usefully installed designs are countercurrent, where the waste gas stream flow is at the bottom of absorber tower and exit at the top. The solvent stream flows in, at the top and exit at the bottom. Counter current design provide the highest theoretical removal efficiency, due to the gas with the lowest pollutant concentration contact liquid with the lowest pollutant concentration in the column. His increases the average driving force for absorption through the column (Mc Innes et al 1990). Sometime, counter current designs usually required lower liquid to gas ratios than concurrent and very suitable when the pollutant loading is higher (Josel, 1992). For cross current, the waste gas flows horizontally across the column while the solvent flows vertically down the column. Cross current design have lower pressure drop and required lower liquid to gas ratios than concurrent and counter current design. They are mainly used when gases are highly suitable, since they offer less contact time for absorption (Mc Innes et al, 1990). For concurrent tower, the waste gas and the solvent flow sin at the bottom. Concurrent design have lower pressure drops, are not subject to flooding limitation and more efficient for the (that is submicron) mist removal. Concurrent designs are efficient where large absorption driven forces are available. The removal efficiency reduces since the gas-liquid system approaches equilibrium at the bottom of the column (Mc Innes et al, 1990).
2.4 PROCESS DESCRIPTION Gas absorption is a mass transfer operation in which one or more component of the gaseous mixture are dissolved in a liquid that has lower
volatility under the process condition. The solute diffuses from the gaseous phase into the liquid phase; when the liquid state is below the equilibrium concentrations while the equilibrium. Concentration supply the driving force fro absorption. A well designed a gas absorber will provide large contact between the gas and the solvent in order to facilitate diffusion of the pollutant(s). It performs much better than a poorly designed absorber (Raymond, 1992). The rate of mass transfer between two phases is largely based on the surface are and period of contact. the factor guiding the absorption rate, such as solubility of the gas in a particular solvent and the degree of the chemical reaction are characteristics of the constituent involved and relatively base don’t eh apparatus used.
2.5 TYPES OF ABSORBER EQUIPMENT Absorbers are classified based on absorption principles which include packed tower, spray lower, venture scrubbers, tray (plate) columns and wetted wall tower.
This chapter focuses more on packed tower or column, which is the given design and the most commonly used gas absorber for pollution abatement. Packed absorption tower are column filled with packing material which provide enough surface area to facilitate the contact between the liquid and gas. Packed with higher liquid range, and water consumption is low compared to other type of gas absorbers. Packed column may have high system pressure drops, high clogging and fouling potential and extensive maintenance cost, as a result of the presence of packing material. Installation operation and waste water disposal cost are higher for packed bed absorber that for other absorbers. In addition to pump and fan power requirement and solvent cost, packed tower have operating cost associated with replacing damage packing (Mc Innes et al, 1990).
2.6
PLATE OR TRAY TOWER
Tray tower are vertical cylinder in which the liquid and gas are contacted in stage wise fashion on tray (plate). Liquid enter at the top of the
column and flow through a down spout (down corner) to plate, below. Gs moves upwards though openings in the plate, bubbles into the liquid, and passes to the plate above. They are easier to clean and tend to handle substantial temperature fluctuation properly than packed lower do. However, at high gas flow rate plate tower exhibit larger pressure drops and have larger liquid holdup. Plate tower are generally made of materials such as stainless steel. This make sit to withstand the force of liquid on the plate and facilitate corrosion protection. Packed tower are considered better when acid and other design can be of fiberglass, polyvinylchloride, or other less cost corrosive resistant materials. Packed tower are preferred to column smaller than two feet in diameter and when pressure drop in important consideration (Perry, 1984).
Fig. 2.6: A socket of tray tower 2.7 VENTURI SCRUBBERS Venture scrubbers are generally applied for controlling a particular
matter and sulfur dioxide. They are designs for application of submicron particle of range 0.5 - 5.0 micrometers in diameter (Treybal 1980). Venturi scrubber employs a gradually converging and then diverging section called the throat as shown in the diagram below, to clean the inflow gas stream. Liquid is introduced to the venture upstream of the throat. It can be infected directly into the throat where it is atomized by the gaseous stream. If liquid is atomized, it dissolves particles from the venture. The high pressure drop through this system result in high energy used, and relatively short gas liquid contact time restricts their application to highly soluble gases. Therefore, they are frequently employed for control of volatile organic compound emission in dilute concentration (Mc Innes et al, 1990).
Fig. 2.7: Venturi scrubber
2.8 SPRAY TOWER Spray tower works by delivering a liquid droplet through a spray distribution system. The droplet fall through a counter current gas stream under influence of gravity and contact the pollutant(s) in the gas (Perry and Chillon, 1984). Spray towers are simple to operate and maintain, it have relatively low energy requirement. However, they have the least effective mass transfer capacity of absorbers described and they are usually restricted to particulate removal and control of highly soluble and ammonia. They need high water recirculation rate and are inefficient at removing small particle (Jack, 1992).
2.9 WETTED WALL TOWER A thin film of liquid running down the inside of a vertical pipe, with gas flowing either concurrently or counter currently, constitute a wetted wall tower. A flow of liquids through soluble pipe, a volatile pure liquid is permitted to flow down the inside surface of permitted to flow down the inside surface of a circular pipe while a gas is blown upward or downward through the central core. Industrially, they have been used as absorber for hydrochloric acid, where absorption involves a large evolution of heat. The wetted wall tower is surrounded by a rapidly flowing of cooling water. Gas pressure drop is lower than any other gas liquid contacting design.
Fig. 2.9: A sketch of a wetted wall tower
2.10 PACKED TOWER INTERNALS A packed absorption tower is made up of column shell, mist eliminator, liquid distributor packing support. Corrosion resistant alloy or plastic material such as polypropylene are required for column internals when highly corrosive solvent or gases are used. The absorption tower packing is more expensive than design of one section (Kack, 1992). The tower shell may be made of plastic or steel or a combination of these materials depending on the corrosiveness of the gas and liquid streams, and the process operating considerations. The shell is sometimes lined with a protective membrane often made from a corrosion resistant polymer. For absorption involving acid gases, an interior layer of acid resistant brick provide additional chemical and temperature resistance (Crowe and Cooper, 1988). At high gas velocities, the gas existing in the top of the column may carry off droplets of liquid as a mist. To prevent this, eliminator in the form of corrugated sheets or layer of mesh and be installed at the top of the column to collect the liquid droplets which coalesce and fall back into the lower.
2.11 A LIQUID DISTRIBUTOR A distributor is designed to distribute the liquid evenly at the surface of the packings to facilitate the uniform contact of the liquid and the gaseous mixture in the tower. The liquid distributor must spread the liquid uniformly, resist plugging and fouling, provide free space for gas flow and permit operational flexibility. A substantial lower have re-distributor which divert the movement of liquid from the wall shell to the center of the tower for proper spreading of the liquid and enhance contact in the lower section of the packing. Redistributors are incorporated with tower of 8-20 feet of random packing depth (Coker, 1991).
Fig. 2.11:
(A) INADEQUATE DISTRIBUTOR
(B) ADEQAUTE DISTRIBUTOR
2.12 PACKING MATERIALS Packing materials provide a large wetted surface for the gas stream maximizing the area available fro mass transfer operation. Packing materials are available in variety of forms each having specific characteristics with
respect to surface area, pressure drop, weight, corrosion resistance, and cost. Packing life varies, depending on the application. In ideal circumstance, packing will last as long as the tower itself in adverse environments, parking life may be as short as 1-5 years due to corrosion, fouling and brakeage (Roy 1992).
2.13 SUPPORTING PLATES To ensure the waste is properly distributed, an open space between the bottom of the tower and the packing is necessary. The support plates hold the parking above the open space. The support plate must be strong enough to carry the weight of the ceramic Berl Saddle (packings) to allow the gas and solvent flow with minimum restriction (Trey Bal 1980).
2.14 PACKED RESTRAINER The packings are fluidized at high velocities son top of a bed. The packings may be emitted to the distributor, become unevenly, or be damage (Harrison and John, 1989). A parked restrainer may be installed at the packing. To avoid the restrainer from being dislocated, it should be secured at the wall and also not to “float”, unattached weight plate may be placed on top of the packings so that it can settle with the bed. The later is often used for fragile ceramic packings. 2.15 TOWER SHELL The tower shell may be metal, wood, chemical stone ware, acid, proof brick, glass, plastic or glass linked metal or other material depending on the corrosion condition. They are usually circular in cross section for ease of construction and strength.
2.16 PACKED TOWER Packed tower, which is applied continuous contact of liquid and gas in both concurrent and counter current flow, are vertical, column that have
been filed with packing of large surfaces. Packings are of two major types such as random and regular packing.
2.17 RANDOM PACKINGS This is a packing dumped into the tower during the time of installation and deposited at random. Sometimes ago materials as broken stone, gravel or lumps of coke were used and are not expensive. They are not needed for small surface and poor fluid flow. The random packing is produced and effective. The common types are Rashing ring, which have the hollow cylinders with diameter ranging from 6 – 100mm (1/4 to 4 inch0 or more. It can be made of chemical stone ware or porcelain for contacting of most liquid except alkaline and hydrofluoric acid, of carbon which is useful except in strongly oxidizing atmosphere; of metals; or plastics. Plastics should be chosen, since they may deteriorate rapidly with certain organic solvents. The plastic offers the advantage of lightness in weight. The Lessing rings and others with internal partition are frequently used. Berl and intalox saddles and variant of them are available in size from 6-75mm (1/4 to 3 inch) made of chemical stone were or plastic. Pall rings which are called “Flexi ring”, cascade rings, hy-pack is available in metal and plastic. They offer large specific surface (and large gas pressure drop) in the small size and cost less per unit volume in larger sizes. To avid breakage during pouring, water is first filled in the tower before releasing the packing.
(A) Rashing Ring
(c) Partition Ring
(b) Lessing Ring
(d) Metal
(e) Ceramics
2.18 REGULAR PACKINGS The regular packing have the advantages of lower pressure drop for gas and greater possible fluid flow rates, usually at the expense of more costly installation than random packing. Stacked Rashing rings are economically practical only in very large sizes. A lot of medication of the expanded metal packings. Wood grids, or hurdles re inexpensive and frequently adopted where large void volume are required as in thecae of far-
bearing gases from coke oven or liquid that carry solid particles.
2.19 CHOICE OF SOLVENT FOR ABSORPTION The choice of solvent for absorption is very significant in the process industries. The solvent is specified by the nature of the product. If the principal purpose is to remove some constituent from the gas, some choices are considered. They are: GAS SOLUBILITY: The gas solubility should be high, thus increasing the rate of absorption and decreasing the quantity of solvent required. Generally, solvent of a chemical nature similar to that of the solute to be absorbed will
provide good solubility. Thus, hydrocarbon oils are used to remove benzene from coke oven gas. For some cases, where the solution formed is ideal, the solubility of the gas is the same in terms of model fraction for all solvent. A chemical reaction of solvent with the solute will frequently result in very high gas solubility but if the solvent is to be recovered for reuse, the reaction must be reversible. VOLATILITY: The solvent should have a low vapor pressure, since the gas leaving an absorption operation is ordinarily saturated with the solvent and much may be lost. If necessary, a second less volatile liquid can be use to recover the evaporated portion of the first, CORROSIVENESS: the solvent chosen must not corrode the absorption lower or introduce any act of pollutant to the mixture to be separated. COST: The solvent should be inexpensive, so that losses are not costly and should be readily available. VISCOSITY: low viscosity is preferred for reason of raid absorption rates, improved flooding characteristics in absorption towers. Low pressure drops on pumping and good heat transfer characteristics. Miscellaneous: The solvent should not be toxic, flammable and chemical unstable and have a low freezing point.
2.20 TYPES OF SOLVENT FOR GAS ABSORPTION WATER: Is often used to absorb ammonia. CAUSTIC SODA: Is often employed to absorb hydrogen sulphide ETHANOLAMINE SOLUTION: Is some time employed to remove hydrogen sulphide also HYDROCARBON OILS: Is also used to remove benzene from the coke-oven gas.
2.21 AMMONIA-PROPERTIES, SUES AND HEALTH EFFECTS Ammonia is largely produced for commercially by the use of HaberBosech process, which is also sometime referred to as the Harber-Ammonia
process or synthetic ammonia process. First Haber, the German physical chemist, created the process in 1909, and it was further developed by Carl Bosch to make it economically viable. The production of ammonia is achieved by the direct combination of hydrogen and nitrogen over an iron or aluminum catalyst. Hydrogen is obtained from the decomposition of methane by heating. Nitrogen is obtained from the distillation of liquefied air. It was the first chemical process to use high pressure conditions. The reaction is shown below.
N2
(g)
+ 3H2
(g)
> 2NH3 (g)
The process is highly exothermic with a ΔH value of 92.2kgt per mol. The solubility of ammonia at 200C and 1alm is given by Henry’s law. That is
P = HX Where, P is the partial pressure H is the Henry’s constant X is the mass function The solubility has been found experimentally to be 33.1% (w.w)
2.22 PROPERTIES OF AMMONIA The physical properties of ammonia include; Ammonia is the most soluble gas. That is why it cannot be collected over water. The solubility can be demonstrated with the fountain experiment. Anhydrous ammonia gas is considerably lighter than air and will rise in dry air. Liquid and gas ammonia expand and contract with change sin pressure and temperature Anhydrous ammonia is a clear liquid boils at a temperature of 280f. Ammonia is a colorless gas with a choking smell.
2.23 CHEMICAL PROPERTIES OF AMMONIA Anhydrous ammonia is an alkali. Anhydrous ammonia is easily absorbed by water. Anhydrous ammonia is non flammable Anhydrous ammonia in the presence of moisture reacts and corrodes copper, zinc, and many other alloys.
2.24 USES OF AMMONIA Ammonia is used as a fertilizer, which improves the growth and productiveness of plant by enhancing the fertility of the soil. Ammonia is also found in household detergent and cleaner sand for pH control. In the solvent process: it is one of the most important compounds for manufacture of washing soda. Ammonia is used as a refrigerant, since it is easily liquefied by compression and when heated back into its gas page, absorbers much heat. Ammonia is also used in the manufacture of nylon; the dying of cotton wool and silk, Ammonia is used for the production of paint.
2.25 HEALTH EFFECT Ammonia has some detrimental effect to some part of human body. Small concentration of ammonia in the air causes initiating to the eyes, throat, and breathing passages. The anhydrous ammonia primary affects the lungs, skin and eyes.
CHAPTER THREE DESIGN PROCEDURES The design of packed tower absorber for purification of gaseous mixture pollutant and air depend son knowledge of the following characteristics: Required removal efficiency Waste gas flow rate Waste gas composition and concentration of gas streams. Equilibrium relationship between the pollutant and solvent, and Properties of the pollutant(s) waste gas and solvent, diffusivity, viscosity, density and molecular weight. Packed absorption tower (column) is design to determine the parameters
below: To find the equilibrium data The material balance The diameter of the lower To calculate the height of packing The mechanical design calculation To find the costing of the packed absorption tower.
3.1 EQUILIBRIUM DATA Table 1: Equilibrium data S/N
Mass of NH3/mass of H20
NH3 partial pressure (NH3) mmHg
1
100.0
-
2
90.0
-
3
80.0
1450
4
70.0
1170
5
60.0
945.0
6
50.0
686.0
7
40.0
470.0
8
30.0
298.0
9
25.0
227.0
10
20.0
166.0
11
15.0
114.0
12
10.0
69.6
13
7.5
50.0
14
5.0
31.7
15
4
24.9
16
3
18.2
17
2
12.0
1
-
3.2 DETERMINATIONS OF GAS AND LIQUID STREAM PROPERTY Gas absorption column is designed on the ratio of liquid togas entering the column (Ls /Gs) which is the slope of the equilibrium curve (M). All these parameters are calculated from the inlet and outlet gas and liquid streams variables. Wastes gas flow rate, actual meter cube per minute (m3/min) entering and exiting column (G1 and G2 respectively). Pollutant concentration (1kg mole pollutant/kg mol of pollutant free gas) entering and exiting the column in the waste (Y1 and Y2 respectively). Solvent flow rate entering and exiting the column (L1 and L2) respectively and Pollutant concentration entering and exiting the column in the solvent (X1 and X2). Then the exit pollutant concentration Y2 = Y1 (1- ŋ/100) ……………………………………………………… (3.2.1) The liquid flow rate entering the absorber, 1, is then calculated using a graphical method. The equilibrium curve indicates that relationship between the concentration of pollutant in the waste gas and the concentration of pollutant in the solvent at a specified temperature and pressure. The slope of the operating line intersecting the equilibrium curve is the minimum L/G ratio on moles of pollutant free gas basis Gs. The slope is calculated using
Slope (m) = Ls /Gs= ΔY/ ΔX = (Y2 –Y1)/ (X2 – X1)………………………..(3.2) The value of X2 is taken from the equilibrium curve. To calculate the actual L/G ratio Ls /Gs= Ls/Gs x (adjustment factor)
To estimate Gs Gs = G1 (1-Y1) ………………………………………………………… (3.2.3) Where G1 = Gas flow rate The variables Ls Ls (min) = Gs (Y1 – Y2) ……………………………………………….(3.2.4) X1(min) – X2
Ls (actual) = 1.3 Ls (min) ………………………………………………… (3.2.5) The total molar flow rate of the gas and liquid entering the absorber (G2 and L2) are evaluated using the following equation.
Gs = Gs or G2 = Gs (1+Y2) ………………………………………… (3.2.6) 1-Y2
L2 = Ls 1-x2
or L2 = Ls (1 + X2) ………………………………………… (3.2.7)
3.3 PHYSICAL PROPERTIES The physical properties are gas density, surface tension, of the mature Gas density (ρG) ρG = P.M (axg) ………………………………………………………….(3.3.1) RT
Surface tension (σ) σ= Pch (ρ1 - ρv)
4
x 10-12 ………………………………………………..(3.3.2)
M
3.4 MATERIAL BALANCE G1 + L2 = G2 + L1 ………………………………………………………(3.4.1)
3.5 DETERMINATION OF ABSORPTION FACTOR The absorption factor (AF) value is frequently used to describe the relationship between the equilibrium lien and liquid t gas ratio. AF = L. mol, i …………………………………………………………………. (3.5.1) M. Gmol, i
M = ΔY = Y2 – Y1 ………………………………………………………….(3.5.2) ΔX = X2 – X1
Where Y2 and Y1 are the mole fractions of the pollutants in the vapor phase in equilibrium with mole fraction of the absorber in the liquid X1 and X2 respectively.
X1
=
X1 …………………………………………………… (3.5.3) 1+X1
X2
=
X2 …………………………………………………….. (3.5.4) 1 + X2
Y1
=
Y1 ……………………………………………………... (3.5.5) 1+Y1
Y2
=
Y2 ……………………………………………….. (3.5.6) 1+Y2
The absorption factor is used to evaluate the theoretical number or transfer unit and the theoretical height of a transfer unit.
3.6 COLUMN (TOWER) DIAMETER From Eckert’s modification to the generalized correlation for randomly packed lower, the abscissa value (X-axis) in the graph is Abscissa = L’ (ρG)
1/2
………………………………………………. (3.6.1)
G’ (ρL-ρG)
The ordinate value (Y-axis) in the graph is expressed as Ordinate = G2sfr, 1CFµl0.1J ……………………………………… (3.6.2) ρG (ρL - ρG) gc
Where Cf = correlation factor µL = Ratio of the density of the scrubbing liquid. But G2sfr, I = Ordinate ρG (ρL - ρG) ……………………………… (3.6.3) Cfµi 0.1J
The cross sectional area of the tower
A = Gmi …………………………………………….. (3.6.4) Gsfr, i
Then, the diameter of the column D = 4A …………………………………………………………. (3.6.5) π
3.7 DETERMINATION OF TOWER HEIGHT The tower height is primarily a function of packing depth. The required depth of packing (H pack) is determined from the theoretical number of overall transfer unit (N10G) needed to achieve a height of the overall transfer unit (HtoG) H pack = NtoG HtoG For NtoG
NtoG = in
………………… (3.7.1)
For HtoG HtoG = HtG = Htl ………………………………………………….. (3.7.2) AF
To estimate HtG and HtL HtoG = G ………………………………………………………….. (3.7.3) FGα
HIL = L ……………………………………………………………… (3.7.4) FLα
α = α Aw QLO …………………………………………… (3.7.5) QLow
Overall total height of the column Htower = 1.40 Hpack + 1.02 (D) + 2.81 …………………….. (3.7.6) 3.7 Mechanical design Estimation of wall thickness(tm) tm = PR+ CA …………………………………… (3.8.1) SE – 0.6P Where tm = wall thickness of the tower P = design pressure S = stress value
R = radius of the tower E = welded joint factor CA = Corrosion allowance Hemispherical head (t) t=
PR + CA …………………………………………(3.8.2) 2SE – 0.2p
3.9 COSTING OF THE TOWER Installed equipment cost = installed equipment cost x overall height in feet For molybdenum steel, the relative cost is
Cost of carbon molybdenum steel = 1.065 Cost of carbon steel
Installed cost for carbon molybdenum = 1.065 x Cost of carbon steel..(3.9.2 Using cost index method. Installed cost for 2010 = Cost index for 2010 /cost index for 2000………………… (3.9.2)
CHAPTER FOUR RESULT ANALYSIS, DISCUSSION, CONCLUSION AND RECOMMENDATION 4.1 RESULT ANALYSIS The successful design drawing has been sketched, based on the value obtained from the parameters calculated and attached at the back cover of this report. The qualitative and quantities material flow is illustrated in chapter two (literature review) of this report. The flowing of material in and out, tower diameter, the packing height, the total height of the tower, the mechanical design and the installed equipment cost, are calculated in the appendices and the following values were obtained: A.
Material flow in and out Gas in (G1)
=
0.000694kmol/sec
Gas out (G2) Air in (Gs) Liquid in (L2) Liquid out (L1)
= =
0.000641kmol/sec
0.0006385kmol/sec =
0.001306097kmol/sec =
0.001359kmol/sec
NH3 removed
=
0.000897kg/sec
B.
Diameter of the tower (D) =0.1405m
D.
Height of the packing
=0.6589m
D.
overall Height (Htower)
=1.9223m
E. The construction material used is carbon molybdenum steel (SA – 135) Grad B ii.
Corrosion allowance (C)
iii.
Wall thickness (lm)
IV
Hemispherical head (f)
F.
installed equipment cost
= = =
4mm 6.25mm
6.25mm =
N, 380,000
4.2 DISCUSSION, CONCLUSION AND RECOMMENDATION The required design of a packed absorption tower to remove 95% of ammonia (NH3) from a gaseous mixture of 8% NH3 and 92% air by volume has been completed. The rate of the solvent (water) required was found to be 0.001306097kmol/sec. While the diameter of the tower or column was calculated to be 0.1405m and the height of the towers packings is 1.9223m. Their values in ft are 0.460958ft and 6.3067585ft respectively. The material used for the construction from American society of mechanical engineering (ASME) is carbon molybdenum steel (SA – 135 Grade B); has been recommended as the material of construction. Comparing the cost and high corrosion allowance of 4mm is recommended. According to the recommendation, the joints of the equipment should be totally radio graphed.
The designed equipment will meet up the required specification, if all the condition recommended are put into consideration and adhered to
properly during design and operation of the tower.
REFERENCES 1.
Coullson and Richardson (1973) “Chemical Engineering Design: Vol. 6, Perganon Press Oxford, page 294.
2.
Control technologies for hazardous air pollution, office of Research And Development, Us Environmental protection Agency, Research Triangle per, North carling Publication N. EPN 625/6-91014.
3.
Churse, R. (`977). Pressure vessel the ASME code. Simplified 6th Edition (McGraw-hill).
4.
Coker A.K
(1991) “Understanding the basics of Packed Column
Design”, Chemical Engineering progress. Pp. 93-94.
5.
6.
Robert E.
Treybal. (1970) “mass transfer operation” 3rd edition, Mc Graw-hill international book company (Pp. 301–310)
Charles R, and cooper, D. (1988). “Brick/membrane linings pass the Acid test”, chemical engineering. (Pg 83–86).
7.
Fouls et al. principles of unit operation 2nd edition
8.
Danwerks
9.
Holland C.D (175) “fundamental of modeling of separation process”. Principle– hall Englewood Chiffs, New Jersey.
P.V (1970) “gas– liquid reaction” MC Graw-Hill book company, New York.
10.
Harrison, Mark E, and john France J. (1989) “distillation column troubles– shooting, part 2. Packed column”. Chemical Engineering. (Pg. 121– 128)
11.
Letter from jack. D Broby of Anderson 2000, Inc; to Willian M. Vatavuk, U.S environment protection agency, June 9, 1992.
12.
Letter from Jose L. Bravo of Jaeger product, inc., to Willian M. Vatavuk, U.S environmental protection agency, June, 8,
1992.
13.
Mc Inness. R. Jameson K. and Austin D. (1990) “Scrubbing toxic inorganic: chemical engineering. (Pp. 116 – 121).
14. Letter from S. Raymond will of air product, inc. to Willian M. vatavuk, June 25, 1992,
15.
Moss D.F (1987): pressure Vessel Design Manual (Hemisphere).
16. Jerry R. H and Clinton C.H (1984): “Chemical engineering Hand Book”. 6th Edition, Mc Graw–Hill Book Company. (Pg. 3–252)
17.
Peter M.S and timmerhous K.D (1970) “Plant design and economists for chemical engineering. 3rd edition. Mc Graw hill Siky Aliyu. Book Company, New York. Pg. 671, 723, and 770.
18.
(1987): Separation processes vol. 1, Warri Refinery, Nigeria.
19. Telephone conversation between Roy Commem, Radian Corporation and Geraldnealon, Norton processes equipment, April 4, 1992.
20.
Sherwood, T. K; and Holloway F.A.L (1940): Trans AICHE, 36, 39.
21. Ronald V. Gills (1976). “Fluid Mechanics and Hydraulics” 2nd Edition. Mc Graw hill book company, New York. (Pg 294).
APPENDIX 1 STEADY STATE MATERIAL BALANCE Temperature of the gaseous mixtures in 293k 293 – 273 = 200C According to cousin and Richardson (1973) “Chemical Engineering Design vol. 6. Page 294, chemical engineering design in based on K mole.
The pressure of the gaseous mixture in 1atm which is equivalent to 1.013 X 105N/M2 = 760 mmHg.
Percentage of ammonia (NH3) in the gas mixture is 8% = 0.08 mole fraction of NH3 and also equivalent to y :. Y1 = 0.08 kmole The liquid is pure H20 with respect to NH3, which is equal to zero for X2. Gas flow rate (G1) = 2.5 kmole/hr.
BASIS: 1 sec G1=2.5 Kmol=0.000694kmol/sec (60 X60) sec
GENERAL SOLUTION From mass transfer operation by Robert E treybal (page 283):
X2 = X2 1–X
…………………………………………….1
Where X2 =0
:. X2 = 0 = 0 kmol of NH3 /Kmol of H2O 1–0 For y1 Y 1 = y1
……………………… 2
1-y1
Where y1 = 0.08 K mole of NH3 Y1
= 0.08 =0.08696 1- 0.08
Kmol of NH3 k mol of Air
Since 95% removal of NH3 is desired, this is equal to 0.95 The removal efficiency η = 0.95 From Robert E treybal Y2 = y1 (1– η) …………………………3 Y2 = 0.8696 (1 – 0.95) Y2 = 0.00435 Kmol of NH3/Kmol of air For gas (gs) Gs = G1 (1-Y1) ……………………….. 4 : .Gs = 0.002695 (1 – 0.08) Gs = 6.385 X 10-4 Kmol dry Air /sec
EQUILIBRIUM DATA From reference table 2-123 Robert it Perry (chemical engineering handbook), the equilibrium data is given below: S/N
Mass of NH3/ 100 weight Partial pressure of of H2O NH3 in mmHg
1.
100
–––––
2.
90
–––––
3.
80
1450
4.
70
1170
5.
60
945
6.
50
686
7.
40
470
8.
30
298
9.
25
227
10.
15
166
11.
20
114
12.
7.5
69.6
13.
5
50.0
14.
4
31.7
15.
3
24.9
16.
2
18.2
17.
1
12.0
The table above is used to plot the graph of mole fraction of solute in gaseous phase Y against mole fraction of solute in liquid phase X. Recall:
From mass transfer operation by Robert E Treybal (page 279): XA
= PA
……………………………….. 5a
Pt
YB
= PB ………………………………….. 5b Pt
But Y = YA
=
YB
Y
PA
=
PB
PA pt – PA
= PA
……………………………. 6
Pt – PA Where: PA = partial pressure of NH3 at 200C Pt = standard pressure of 760 mmHg Y = mole ratio By applying equation (6) we have: Y1
=
0
=
0
760 – 0
Y2
=
0
=
760 –0
Y3 = 1450
= -2.101
760 – 1450
0
Y4 = 1170
= -2.854
760 – 1170
Y5 = 945
= -5.108
760 – 945
Y6 = 686
= 9.270
760 – 686
Y7=
470
= 1.620
760 – 470
Y8 = 298
= 0.645
760 – 298
Y9 = 227
= 0.425
760 – 227
Y10= 166
= 0.280
760 – 166
Y11 = 114
= 0.176
760 – 114
Y12 = 69.6
= 0.101
760 – 69.6
Y13 = 50
= 0.070
760 – 50
Y14 = 31.7
= 0.044
760 – 31.7
Y15 = 24.9
= 0.034
760 – 24.9
Y16= 18.2
= 0.024
760 – 18.2
Y17 = 12
= 0.016
760 – 12
Calculating the value of X from the equilibrium data, we have: Mole (n)
= Mass (m) Molar mass (M)
Thus M = nm
……………………. 7
mA
=nA mA
mB
nB mB
…………………………….. 8
Therefore, X
= nA = mA/MA nB
= mA
mB/MB
X
MA
MB
…………….. 9
mB
Molar mass of H2O, MA=18kg mol-1
Molar mass of gaseous mixture (NH3) MB=17Kg/mol-1
X1 = 100
X
18
X2 = 90
X
0.944
17
=
0.850
100
X
18
X4 = 70
=
100
18
X3 = 80
17
17
=
0.756
100
X
17
=
0.661
18
X5 = 60
100
X
18
X6 = 50
X
X
X
X
18
0.472
17
=
0.378
17
=
0.283
17
=
0.236
100
X
18
X11 = 10
=
100
18
X10 = 15
17
100
18
X9 = 25
0.561
100
18
X8 = 30
=
100
18
X7 = 40
17
17
=
0.142
100
X
17
=
100
0.094
X12 = 7.5
X
18
X13 = 5 18
18
18
18
0.047
17
=
0.038
17
=
0.028
17
=
0.019
100
X
18
=
100 X
X17 = 1
17
100
X
X16 = 2
0.071
100
X
X15 = 3
=
100
X
X14 = 4
17
17
=
0.009
100
TABLE FOR THE GRAPH OF Y AGAINST X S/N
Mass of NH3/100 mass of H2O
1
100
2.
Partial Pressure NH3 mmHg
Y
X
––––
0
0.944
90
––––
0
0.850
3.
80
1450
-2.101
0.756
4.
70
1170
-2.854
0.661
5.
60
945
-5.108
0.561
6.
50
686
9.270
0.472
7.
40
470
1.620
0.378
8.
30
298
0.645
0.283
9.
25
227
0.425
0.236
10.
15
166
0.280
0.142
11.
10
114
0.176
0.094
12.
7.5
69.6
0.101
0.071
13.
5
50.0
0.070
0.047
14.
4
31.7
0.044
0.038
15.
3
24.9
0.034
0.028
16.
2
18.2
0.024
0.019
17.
1
12.0
0.016
0.009
For Graph
Plotting of Y against X
X1 = 0.0525
Kmol NH3 K mol H2O
X2 = 0
Kmol NH3 K mol H2O
Y1 = 0.8696 Kmol NH3 K mol H2O
Y2 = 0.00435
Kmol NH3 K mol H2O
The X1 value shows that the amount of NH3 that is per amount of H2O To get the corresponding LS (min), we apply: Ls (min) (X1 – X2)
= Gs (Y1 – Y2)
Thus: Ls (min) = Gs (Y1 – Y2) X1 – X2 = 6.385 X 10-4 (0.08696 – 0.00435) 0.0525 – 0
= 5.27464850 X10-5
0.0525
Ls (min) = 1.00469 X 10-3 kmol H2O Minimum liquid flow rate for actual liquid flow rate is above 30% Therefore, Ls (actual) = 1.3 X Ls (min) =
1.3 X (1.00469 X 10-3)
=
1.306097 X 10-3 kmol
For X1 (actual)
=
Gs (Y1 – Y2) + X2
Ls (actual)
= 6.385 X 10 -4 (0.08696 – 000435) + 0 1.30697 x 10-3
= 5.27464850 X 10-5 1.306097 X 10-3
X1 (actual) = 0.0404
Kmol NH3 K mol H2O
Thus, L2 = Ls (1+X2) Where Ls = Ls (actual) L2 = 1.306097 X 10-3 (1+0)
L2 = 1.306097 X 10-3 kmol/sec For, L1 L1= L2 (1 + X1 (actual)) L1 = 1.306097 X 10-3 (1 + 0.0404) L1 = 0.001359 Kmol/sec Therefore, G2 = Gs (1 + Y2) G2 = 6.385 X 10-4 (1+0.00435) G2 = 0.000641 Kmol/ sec Overall material balance Input = output G1 + L2 = G2 + L1 0.000694 + 1.306097 X 10-3 = 0.000641 + 0.001359 0.00200 = 0.00200
DIAGRAM OF COUNTER CURRENT PACKED BED OPERATION
For Y2 Y2
=
Y2 1–Y2
0.00435 = Y2 1–Y2
Y2 = 0.00435 (1-Y2) Y2 = 0.00435 – 0.00435 Y2 Y2 + 0.00435y2=0.00435 1.00435y2=0.00435 :. Y2 = 0.00435 1.00435
Y2 = 0.00433 Kmol For X1 X1
= X1 1–X1
0.0525 = x1 1-x1 X1 = 0.0525 (1–X1) X1 = 0.0525 – 0.0525 X1 X1 + 0.0525 X1 = 0.0525
:. X1 = 0.0525 1.0525
X1 = 0.04988 Kmol
TOWER DIAMETER ESTIMATION Area can be calculated by the formula given below: A
= π D2 4
D2
= 4A π
Thus, D =√ 4A π
To Estimate for Area Average molecular weight of the gas M
(avg)
:
M avg = ∑ Y1 M1 + Y2 M2 M
avg
= (mole of fraction of NH3) in the gas X molecular weight of NH3) +
(mole fraction of air by volume X molecular weight of air).
Using Bottom Conditions M
avg
= (0.08 X 17) + (0.92 X 29)
= 1.36 + 26.68 = 28.04 kg/Kmol Gas flow rate (Gm1) at the bottom Gm1 = molar flow rate of gas (G1) X M avg = 0.00694 X 28.04 Gm1
= 0.01946 Kg/sec
Density of gas mixture, ρ a ρ a= P1 M avg RT
P1 = 1.013 X 105 N/M2 Mavg = 28.04 Kg/kmol R = 8314 Nm/mol k T =293 K Therefore, ρ G = 1.013 X105 X 28.04 8314 X 293 ρ G = 1.6603 kg/m3 From reference (1), density of H20 at 200C and 1atm is equal to 100 kg/m3 and viscosity at the same condition is 1.0076 X10-3 kg/m.s the liquid mass flow rate at top (LM2): Lm2 = liquid flow rate at top (L2) X molecular Weight of the liquid Thus, Lm2 = 1.306097 X10-3 X 18 =0.023510 Kg/sec
NH3 removed from the gas mixture = Gas mixture flow rate X % NH3 in the mixture X removal efficiency (η ) X molecular weight of NH3. = 0.000694 X 0.08 X 0.95 X 17 = 0.00897 Kg/sec Liquid mass flow rate, Lm, at the Bottom, Lm1 = liquid flow rate at the top, (Lm2) + amount of NH3 removed. = 0.023510 + 0.000897 = 0.032480 Kg/sec. Pressure drop at the depth of the packed tower is taken to be 400 KN/M2 per meter of packed height for 1 inch of ceramic Berl saddle packing. For Abscissa, using the Eckert modification for generalized correlation for random packed tower. From reference (1); Abscissa = Ll (ρ G)
1/2
Gl ( ρ L –ρ G)
Where Ll = Lml = 0.032480 Kg/ sec Gl = Gmi = 0.01946 kg/sec Thus, Abscissa = 0.032480 (1.16603)1/2 0.01946
(1000-1.16603)
= 1.669065 (0.001167) ½ 1.669065 X 0.034167 = 0.0570 From figure 6.34 in references (1), the ordinates corresponding to 0.0570 = 0.075
Ordinate = (G1)2 CFµ L
0.1
ρ G (ρ L – ρ G) gc From table 6.3 in references (1). CF for 1inch ceramic berl saddle = 110 :. (Gl)2 = ordinate ρ G (ρ L –ρ G) gc CF µ L 0.1 j
(Gl)2 = 0.075 X 16603 (1000 – 1.16603) 110 X (1.0076 X 10-3)0.1 X 1.0
Gl =/ 0.075 X 1.16603 (1000 – 1.16603)1/2 110 X (1.0076 X 10 -3)
Gl =
/ 0.0875 X 998.83 110 X 0.5016 X 1.0
Gl = / 1.584
Gl = 1.259 Kg/ M2 sec Therefore, area will be: A = Gml Gl = 0.01946 1.259
A = 0.0155 M2
0.1
X 1.0
Diameter D = 4A/π Where π = 3.142
D = / 4X 0.0155 3.142
D = / 0.0620 3.142
D = / 0.01973
D = 0.1405 m Therefore, Area (A) = πD2 4
= 3.142 X (0.1405)2 4
= 0.0620 4 A = 0.0155m2
THE HEIGHT OF TOWER
From references (1) Height of packing = HtoG NtoG ……………….1 Where HtoG = overall height of transfer unit NtoG = overall number of the transfer unit But HtoG = HtG + MG HTL + HTG + HTL ……………. 2 L
AF
Where AF = absorption factor M = slope of the equilibrium curve HtG = G …………………………………………. 3 FG aA
From reference (1): FG SCG
2/3
= 1.195 (ds Gl)
………………….. 4
µ G (1–∑L0)
G
Then ScG = µ
G
ρ G DG
Where
…………………………….. 5
The subscript G denotes gas Density of Gas mixture ρ a = 1.16603 Kg/M3 Viscosity of gas, µ
G
= 1X 10-5 Kg /Ms
Diffusivity of the gas = DNH3 – Air or DG Pressure (Pt) = 1.013 X105 N/M2
MA = 17kg/ Kmol MB = 29 Kg /Kmol rΑ Β = rA + rB …………………. 6 2 From reference (1), table 2.2 pages 33, the molecular separation at
Collision (r
r
AB
) for air and NH3 is 0.3711 and 0.29 respectively
AB
= 0.3711 + 0.29 2 = 0.33
The normal boiling point Tb, A = 351.4 K
∑ = 1.21 Tb ………………………………..7 K
For air
∑A = 1.21 x 351.4 K
= 425.2
∑AB =/ 425.2 x 78.6 K Where ∑B = 78.6 K Thus: ∑AB = 182.8 K :. KT = 293 Σ
AB
= 1.60
182.8
F (KT)
= F (1.60) = 0.58
(∑AB)
Therefore, DAB = 10-4 1.084 – 0.249
/1/mA + 1/mB) T3/2 / 1/mA + 1/mB Pt (rAB) 2 F (KT / ∑AB)
DAB = 10-4 (1.084 – 0.249
/ 1/17 + 1/29) 2931.5
/ 1/17 + 1/29
1.013 x 105 (0.33)2 x 0.58
= 0.0001 (1.008) 5015.4 x 0.304 6398.3
= 0.154 6398.3
DAB = 0.000024m2/s = DG
From equation (5)
ScG = µ ρ
G
G
D
G
= 0.00001 1.16603 x 0.000024 = 0.357
From the material balance, Gl = molar gas flow rate Gl = GMl A
= 0.01946 0.0155
= 1.255 kg 1m2s
Converting to kmol /m2s
Gl = 1.255 kg x m2s
kmol 28.04kg
= 0.0448 kmol1m2s
From reference (1), table 6.3/6.5
∑ω - ∑ -φ
LT
∑ = 0.69 for ceramic berl saddle. j = 0.0320 φ
LT
= φ ω + φ Ls ……………………….11
φ
Ls
= 4.23 x10-3 µ L ds
1.56
ρ L
Where
µ L = 0.002kg/ms
0.04
0.37
σ
0.55
………………12
σ = 0.07475 ρ L = 1000kg/m3 Thus φ
= 4.23x10-3 x 0.002
Ls
0.0320
1.56
0.04
x 1000
x 0.07475 0.55 0.37
= 0.00 423 x 0.7799 x 0.2402 0.0047 x 12.88 = 0.000796 0.061
φ
Ls
= 0.01305
For φ
low
φ low = φ Ltw -φ Lsw ………………………………13 From reference (1) table 6.5 φ Lsw = 5.014 x 10-5 ds
1.56
Where ds = 0.0472m :. φ lsw = 5.014 x10-5 0.047 = 0.107m3/m3 For φ φ
Ltw
LtW
= (2.32 x 10-6) (73 7.5Ll) β ds2
Where
β = 1.508 ds0.376 = 1508 x (0.0320)0.376 = 1.508 x 0.2741 = 0.413 Ll = 0.03248 kg/sec φ
= (2.32 x 10-6) (737.5 x 0.03248)0.413
Ltw
(0.0320)2
=
2.32 x 10-6 x 3.7126 (0.0320)2
= 8.6133 x 10-6 0.001024 φ
Ltw
= 0.00841 m3/m3
Therefore φ
Low
= φ Ltw - φ
Lsw
= 0.00841 – 0.0107 = 0.00229 m3/m3 But: φ
Lo
=φ
Low
H ……………………. 14
Calculating for Hs we have H=
1404L ρ L
0.84
0.57
(3.24L
µ L
(σ )
0.2187-0.262logi
-1) (0.073)
0.413
Where H =correlation factor (holding packed tower)
σ = surface tension
s From reference (2) table 3.317, page 294;
σ = (Pch (ρ L -ρ L)
4
x 10-12)
M
Where Pch = sagolin’s parachor M = molecular weight Grant
contribution
H
17 x 2
34.2
0
20.0 X1
20.0 54.20
Considering the surface tension of the liquid ammonia to be zero (0) for pure water: Let: Density of pure water at 200c = 1000 Density of water vapor at 20oc = 1.16603
molecular weight of pure water = 18.0kmol/secs
σ
L
= 54-20 (1000 – 1.16603)4 18.0
x10-12
= 0.08125.N/M
But: ∑m = σ NH3 x NH3 σ H20 x H20 Since y1 + y2 = 1.0 y2 = 1 – y1 y2 = 1 – 0.08 = 0.92 :. σ = 0 (0.08) + 0.08125 (0.92) = 0.07485 N/M Then: H = 1404 x (0.032480) 1000
0.84
0.57
(3.24 x 0.032480
x 0.002 0.413
-1)
0.13
(0.07485) (0.073)
Where A = 0. 2187 – 0.262 log (0.032480) H = (88. 74055467)
1.01535
(70.61030734)
H = (1.25676)1.01535 H = 1.2612 Therefore, φ Lo
= φ low H = 0.00229 x 1.2612
A
= 0.0029 Thus, from the equation, φ Lt
= φ Lo + φ Ls = 0.0029 + 0.01305 φ Lt = 0.01595
But ∑ω
= ∑ - φ Lt …………………………16 = 0.69 – 0.01595 = 0.67405
Estimating for FG FG (SCG)
⅔
= 1.195 (ds Gl)- 0.36 µ
Gl
FG (0.357) 0.0448
⅔
G
(1-∑ω ) ……………17
= 1.195(0.0320 x 0.0448) 0.00001 (1-0.67405)
FG (0.5032) = 1.195(0.00143)
-036
0.0448 0.0000033
FG (0.5032) = 1.195 (433.333)-0.36 0.0448
-036
FG (0.5032) = 1.195 (0.11239) 0.0448
FG (0.5032) =
:. FG
=
0.006017
0.006017 0.5032
FG = 0.01196
Estimating for a a= aAW
φ Lo φ Low
Where: a = specific interfacial surface for adsorption area/vol (1.2/1.3) From reference [1] table 6.4s the interfacial area in given by: aAw = Μ ( 808Gl)
n
x Llρ ………………….18
(ρ G0.5)
Where M = 52.14 n = 0.0506Ll – 0.1029 p=0 Ll = 0.032480 :. n = 0.0506 x 0.32480 – 0.1029
= - 0.10126 aAw = (52.14 808 x 0.0448) (1.16603)0.5
= 52.14
(36.1984)-0.10126 (1.07983)
= 52.14 (33.5223)
-0.10126
aAw = 36.536 Therefore a = 36.536 (0.0029) (0.00229)
= 36.536 x 1.26638 = 46.2683
:. FG a = 0.01196 x 46.2683 = 0.5534 For HtG = Gl FGa
= 0.0448 0.5534 HtG = 0.08095m For
x1
-0.10126
HtL
= Ll/ FLa
Where FL = KL x c
To estimate for KL (liquid phase mass transfer coefficient). KL ds = 25.1 (dsLl ∆L
)-0.45
x SCL0.5 ……………………19
( µ L)
Where: ds = 0.0320 µ L = 0.002 And DL = (117.3 x 10-8) (φ MB) 0.5T ............................20 µ VA0.6 Where VA = molar volume of NH3 = 0.0267 m3/kmol φ = Association factor for solvent (for water as solvent = 2.26) µ
L
= viscosity of liquid = 1.055 x 10-3 kg/m.s
MB = molar mass of H20 = 18.02 kg/kmol DL = Diffusivity of the liquid = DNH3O – H20 Thus DNH3 – H20 =
(117.3x10)-18 (2.26 x 18.02)0.5 x 293 1.055 x 10-3 x (0.0267)0.6
= 2.19 x 10-13
0.000114
DL = 1.92 x 10-9 m2 Therefore SCL = µ ρ
L
L
x DL
SCL = 1.055 x 10-3 1000 x 1.92 x 10-9
SCL=527.5 From the material balance Ll = 0.032480 kg/m2s Then using equation (19) KL x 0.0320 = 25.1 (0.0320 x 0.032480) 1-92 x 10-9
-0.45
x 527.5
0.002
KL x 0.0320 = 25.1 (0.03936 x 10-3)
-0.45
x 527.5
1-92 x 10-9 0.002
kL 0.0320/1.92 x 10-9 = 25.1 (0.51968
kL x 0.0320 = 25.1 x 1.3425 x 527.5
) 52.75
-0.45
1-92 x 10-9
KL x 0.0.320 = 3.4128 x 10-5
kL = 3.4128 x 10-5 0.00320
kL = 0.001067
Recall, that
FL = KL x C
Where: FL = liquid mass transfer coefficient C = molar density of the solvent liquid Where C = density of liquid AV. mol wt
ρ
L
= 1000kg/m2 (density of the liquid)
Average molecular wt. for liquid = 18.02
C= 1000 = 55.49 8.02
FL = 0.001067 x 55.49 = 0.05921
Therefore
HtL = Ll FLa
HtL = 0.032480 0.05921 X 46.2683 HtL = 0.01186
DETERMINING THE ABSORPTION FACTOR (Af)
Af = L mol, i
or
M.G mol, I
Ls MGS
Where, M = slope of the equilibrium curve Ls = 1.306097 x 10-3kg/sec Gs = 6.385 x 10-4 kg/sec But M = ∆ y = Y2 – Y1 ∆x
X2 – X1
:. M = 0.08696 – 0.00435 0.0525 - 0 M = 1.574 Then Af =
1.306097 x 10-3 1.574 x 6.385 x 10-4
Af = 1.2996
To get HtG, we use the formula HtoG= HtG + HtL Af HtoG= 0.08095+ 0.01186 1.2996 HtoG = 0.08095 + 0.009126 HtoG = 0.90076
From reference [1], page 309:
NtoG = ln (Y1 – mx2/Y2-mX2 (1 – 1/Af) + 1/Af) 1 – 1/Af Where Af = 1.2996 Y1 = 0.08696
m = 1.574 Y2 = 0.00435 1 + 0.00435 Y2 = 0.00433 X2 = 0
Thus NtoG = In (0.08696 – 1.574 (0))
(1 – 1)
(0.00433 – 1.5740 (0)) (1.2996) 1–1 1.2996
NtoG = ln (20.0831) (0.2305) + 0.76947) 0.2305
= ln (5.398625) 0.2305
NtoG = 1.686144 0.2305 = 7.3152
Therefore,
+ (1) (1.2996)
Hpack = HtoG NtoG
= 7.3152 x 0.090076
Hpack = 0.6589m
TO ESTIMATE THE TOTAL HEIGHT OF THE TOWER
The total height is calculated from the equation below: Htower = 1.40Hpack + 1.02 (D) + 2.81 ……………….. 23
Converting 0.6589m packing to Ft 1 inch = ½ Ft = 25.4mm 1ft = 12 x 254mm = 304.8mm = 0.3048m :. 1ft = 0.3048m Now: 0.304m = 1ft 0.6589m =x :. x = 1ft 0.3048m x = 2.16175Ft.
x 0.6589m
For diameter, D = 0.1405m 0.3048m = 1ft 0.1405m = x :. x = 0.1405m x 1ft 0.3048m x = 0.46095Ft
Therefore, Htower = 1.40 (2.16175) + 1.02 (0.46095) + 2.81 = 3.02645 + 0.470169 + 2.81 = 6.30662 Ft Converting to Ft 1Ft = 0.3048m 6.30062ft = x :. x = 0.3048m x 6.30662 ft 1ft x = 1.9223m
MECHANICAL DESIGN CALCULATION The material desired for the construction was made using the American society of mechanical engineering (ASME) specification code for boiler and pressure vessel. A low alloy steel given SA – 202 (Grade B), for the construction. We considered the following factors while making the choice. 1) Physical and mechanical properties of construction material to withstand the operating condition.
2)
Resistant to corrosion with respect to ammonia air system.
3)
The material should be relatively cheep in terms of cost
DESIGN CONDITION From reference [2], table 13.2, page 812: Maximum allowable temperature = O0c to 50oc Maximum operating pressure = 15psig Corrosion allowable = 4mm = 0.004m = 0.16inch Design stress for SA 202 (Grade B) construction material is 135 N/mm2 Welding method is used for the joining of the construction material. A single wedded buff/groove joint should be fully radio graphed.
Fig 4.1 single V buff joint 60oc level and roof opening of 1/16 inch. In the welded buff joint where, the stress tending to share the join apart is given by T= F/hl Where h = weld threat = wall thickness L = length of weld from reference [2] , table 13.3 page/813, the welding efficiency for a completely radiography of single buff wielded joint with backing strip in shown in fig A is ∑ = 0.90
The wall thickness, according to ASME, the formula of wall thickness. tm =
PR
+
CA
……………….. 1
Sε - 0.6ρ Where: Tm = thickness of the tower P = design pressure S = stress value R = Radius of the tower ∑ = wedded joint factor or joined sufficiency CA = corrosion allowance According to ASME recommendation, the design pressure in between 5 to 10% above the normal working pressure. Design pressure = 1 atm + 10% of atm =1 + 0.1 = 1.1 atm But 1 atm =m 15 Psig 1.1 atm = x :. x = 15 psig x 1.1 atm 1atm = 16.5 psig Design stress value for grade B material is = 135 N/mm2 = 135 x 102 N/mm2 x (100)2 mm2 /m2 = 1.35 x 108 N/mm2 = 1.35 x 108 Pa
But: 10atm = 1.013 x 105 psig x = atm = 1.35 x 108 psig x = 1.35 x 10-8 psig x 1atm 1.013 x 105 psig x = 1332.7 atm
Recall that: 1atm = 15psig 1332.7 atm = x :. x = 15psig x 1332.7 atm 1 atm
x = 19990.5 psig But, D = 0.1405m
R = D = 0.1405m 2
2
R = 0.07025m
Then, 1 inch = 25.4mm = 0.0254m
0.0254m = 1 inch 0.07025m = x
:. x = 1 inch x 0.07025m 0.0254m
x = 2.7657 inch
Therefore,
c = 4mm = 0.004m 0.0254m =1inch 0.004m = x
:. X =1inch x 0.004m 0.0254 x = 0.1575 inch
Where ε = 0.90
Using equation 1
tm = PR
+ CA
Sε - 0.6ρ
tm =
16.5 psig x 2.7657 inch
+ 0.1575
19990. S psig x 0.90 -0.6x16.5psig
tm =
4.63405
+ 0.1575
17981.55
tm = 0.002538 + 0.1575 = 0.1600038 inch
¼ inch = 0.25 inch For 1 inch = 25.4mm 0.16038 inch = x x = 25.4mm x 0.160038 inch 1 inch x = 4.06496mm use 6.25mm
HEMISPHERICAL HEAD The head is hemispherical head which is given according to ASME recommendation t=
PR
+CA ……………. 2
2Sε - 0.2ρ
Where t= the head t=
16.5 x 2.7657 2 x 1990. 5 x 0 .9 – 0.2 (16.5)
+0.1575
= 45.63405
+ 0.1575
35979.60
= 0.001268 + 0.1575 t = 0.158768 inch. Using ¼ inch
Recall: ¼ inch = 0.25inch Converting to mm 1 inch = 25mm
0.158768 inch = x
:. x = 25.4mm x 0.158768 1 inch
x = 4.032716mm. Using 6.25mm
a = 2b ……………………. 3
Where: a = radius of the diameter b = hemispherical height D = diameter.
D = 2R R=D 2
R= 0.1405 2
R = 0.07025 But a = 2b b=a 2
b = 0.07025 2
b = 0.03513m
COSTING OF THE TOWER The costing of the purchasing and installation of equipment depend on the total height of the equipment. The cost of eternal packings, plate support and distribution cost of hemispherical head nuzzle and mandible and cost of ladder etc. With reference to figure 16.28 peter and timmernans fourth edition, the cost of tower including the installation and auxiliary can be estimated directly for 23 to 27 inches material diameter tower, the January 2000 cost data in given by installed equipment per height as $640 For diameter
D = 0.1405m Converting to inch 1 inch = 25.5 = 0.0254m x = 0.1405m x = 0.1405m 0.0254 Thus, x = 5.53150 inch The hemispherical head is 0.03513 deep. Since there is equal hemispherical height at bottom, them we have the total hemispherical height as (2 x 0.03513) m = 0.070260m The packed height is equal to 0.6589m converting to ft, we multiply by 3.290 That is; 0.6589 x 3.290 = 2.16778 ft The total height = Hpack + Hemispherical head height + top and bottom space height. = 0.6589 + 0.070260 + 12 inch = 0.6589 + 0.070260 + 0.3048 = 1.03396m Converting to Ft, we multiply by 3.290 = 1.03396 x 3.290 = 3.401728 ft Installed equipment cost = $ 640 x 3.401728
= $ 2177.106 For carbon molybdenum steel, the relative cost is given by 1.065 The installation cost, using carbon molybdenum steel is: 1.065 x $ 2177.106 = $ 2318.61789 Using cost index method, Installed cost for 2008 = installed cost for installed cost for 2000 x cost index for 2008 / cost index for 2000. That is; installed for 2008 = installation costs for 2000 X cost index for 2008 Cost index for 2000 From SYSSEX university England 2008 cost index = 987 2000 cost index = 904 Installed cost for 2008 = $ 2318.61789 X 987 904 = $ 2531. 4998 The current exchange rate as at 23rd march 2010 $ 1.00 was equivalent to N150 :. N150 X 2531.4998 = N379, 724.976 say N380, 000
