LCA Biomas Combustion

Capítulo 7: Análisis ambiental de la combustión de biomasa.

Capítulo Capítulo 7: 7: Análisis Análisis ambiental ambiental de de la combustión combustión de biomasa.

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Table of content 1.

Introduction to bioenergy ....................................................................................... 3

2.

LCA assessment of biomass energy...................................................................... 5 2.1.

Goal and scope definition ............................................................................... 6

2.2.

Inventory analysis........................................................................................... 9

2.3.

Impact assessment....................................................................................... 10

2.4.

Results ......................................................................................................... 11

3.

Carbon footprint................................................................................................... 14

4.

Energy Pay Back Time ........................................................................................ 14

5.

Conclusions ......................................................................................................... 14

6.

References .......................................................................................................... 15

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1. Introduction to bioenergy Bioenergy: The conversion of biomass into useful forms of energy such as heat, electricity and liquid fuels.

The modern biomass energy represents the heat, electricity, and/or transport fuels that are produced from biomass-fueled technologies other than those using “traditional biomass.” Technologies include combustion, gasification, pyrolysis, cogeneration of power and heat, and anaerobic digestion to produce biogas and landfill gas. Liquid biofuel also is a form of modern biomass [Renewables 2011, Global Status Report]. The traditional biomass refers to all the unprocessed solid biomass that it burned to provide heat energy, mostly used in rural areas of developing countries. Biomass is derived from different types of organic matter: energy plants (oilseeds, plants containing sugar) and forestry, agricultural or urban waste including wood and household waste. Biomass can be used for heating, for producing electricity and for transport biofuels. Biomass can be solid (plants, wood, straw and other plants), gaseous (from organic waste, landfill waste) or liquid (derived from crops such as wheat, rapeseed, soy, or from lignocellulose material). [http://ec.europa.eu/energy/renewables/bioenergy/bioenergy_en.htm] A schematic presentation of the different types of biomass fuels and their utilization is presented in Figure 1-1.

Figure 1-1 Types of biomass fuels and their utilization Source: Ecoinvent database, “Life Cycle Inventory of Bioenergy”

Bioenergy in the world Biomass is widely used in developing countries because it is cheap and easily available. Biomass energy annual usage represents approximately 8–14% of the world final energy consumption (2010) [A. Williams and co., 2011].

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Biomass supplies an increasing share of electricity and heat and continues to provide the majority of heating produced with renewable sources. An estimated 62 GW of biomass power capacity was in operation by the end of 2010. The United States is the world leader in terms of biomass power generation in 2010, followed by EU countries (Germany, Sweden, United Kingdom), Brazil, Japan, China [Renewables 2011, Global Status Report]. Table 1-1 Bioenergy in the world in 2010

Country

Biomass power capacity [GW]

Energy generated [TWh]

Comments

US

10,4

48

mostly derived from wood, agricultural residues and black liquor burned as fuel for cogeneration in the industrial sector 62,2 TWh from solid biomass. About half of Europe’s biomass power production came from electric-only facilities and half came from combined heat and power (CHP) plants, but the breakdown varies by country.

EU states

7,1

87,4 (in 2009)

Germany

4,9

28,7

Brazil

7,8

28

most generated in CHP plants

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excluding co-firing with coal combination of sugarcane bagasse, solid biomass, organic waste, and biogas (including from livestock wastes

Japan China

4

-

India

3

-

Thailand 1,3 Source: Renewables 2011, Global Status Report

Bioenergy price The power generation from biomass, considering plants between 1-20 MW, has a typical cost of 0,04 – 0,10 €/kWhel [Renewables 2011, Global Status Report]. The electricity generation costs of biomass CHP technologies, based on biomass combustion, is between 0,13 and 0,22 €/kWhel [I. Obernberger and G. Thek, 2008], depending on size, fuel price and operating hours.

Technologies to use biomass The methods available for the biomass utilization are open fires (up to 3kWth), simple stoves, Patsari cookers and household heating (1–10 kW th), fixed bed combustors (up to 5 MWth), moving or travelling grate (up to 100 MWth), fluid bed (up to 500 MWth) and pf/suspension firing/and co-firing (up to 900 MWth) [A. Williams and co., 2011]. Direct combustion power plants have a much lower capital investment than solar power, and equipment is widely available. By using high yielding, the cost of electricity is much cheaper than solar electricity. Furthermore, biomass can produce low carbon electricity 24 hours a day which is needed for "base power" applications. [http://www.viaspacegreenenergy.com/direct-combustion.php]

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Depending the technology used, the biomass size is reduced to: 10 μm–1000 μm for PF (pulverized fuel) systems, 2-5 mm or larger for the fluidized bed systems and 5-100 mm (up to 50 cm) for the packed-beds, in order to ensure the complete a high combustion rate [A. Williams and co., 2011]. Combined heat and power (CHP) technologies based on biomass combustion have been developed intensively over the past ten years. For large-scale CHP plants (>2000 kWel) the steam turbine process (Figure 1-2) is economically and technically feasible [I. Obernberger and G. Thek, 2008]. The biomass is stored in the plant, and then passes to the preparation building (depending on the size, is redirected to the proper store) and after that is burned in a boiler. The steam that is produced here is used to produce electricity, through a steam turbine which is connected to an electric generator. Steam-turbine power boilers designed to work primarily with bark can be added to sawmill as an alternative to beehive burners or other apparatus to dispose of waste [Warren and co., 2007]. Direct combustion boiler/steam turbine technology involves the oxidation of biomass with excess air, giving hot flue gases that produce steam in the heat exchange sections of boilers. The average size of the power plants is tens of MW and the electrical energy produced varies in the interval 20 to 25% [ A. D’Ovidio and co., 2008], although some other studies showed an efficiency up to 40% [Warren and co., 2007].

Figure 1-2 Steam turbine system scheme Source: http://www1.eere.energy.gov/tribalenergy/guide/biomass_biopower.html

2. LCA assessment of biomass energy While biomass possesses the advantage of CO 2 neutrality, there are potential problems concerned with the environmental pollution that it causes. All the combustion technologies have a potential of air pollution, releasing: VOC (volatile organic compounds), NOx, SOx, HCl, PAH (polyaromatic hydrocarbons), furans and dioxins etc. These emissions are affecting the air quality as well as human health. In this respect, a life cycle analyses is helpful. Life Cycle Assessment aims at evaluating all environmental impacts associated with a given product or service at all stages of its lifetime from “cradle to grave”: fr om resource

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extraction and processing, through construction, manufacturing and retail, distribution and use, repair and maintenance, disposal/decommissioning and reuse/recycling. LCA procedures are usually based on environmental management standards ISO 14040:2006 and 14044:2006 and are carried out in four steps: 1. 2. 3. 4.

Goal and scope definition Life Cycle Inventory (LCI) Life Cycle Impact Assessment (LCIA) Interpretation

2.1.

Goal and scope definition

The goal of this study is to gain a solid understanding of the environmental issues associated with the energy generated from the biomass combustion. Additionally, the study has one more goal, and that is to analyse 4 categories of impact, the most representative for this renewable energy. The results of the LCA assessment will be used to compare the bioenergy with other renewable energies, in order to establish which one have the major negative impact over environment.

Assumptions and limitation Since no specific case was analysed, the data were extracted from literature (other studies, master thesis etc), journal papers, LCA database, and internet sites. All the data used in this paper were adapted to our functional unit, as no information was found to match. Because no study that will analyse the entire cycle (from the biomass culture to biomass combustion) was found, we collected the data from different studies. In this respect we have collected data regarding the biomass production and biomass transport from one paper [Siyu Chen, 2009], when the data regarding the biomass combustion from a different study [S. Caserini and co., 2010]. Therefore, the LCA comprise the biomass production, the biomass transport and the biomass combustion, even though the process includes also the biomass processing.

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LCA diagram

Plant nursing

Inputs:     

Diesel Electricity Gasoline Tree seeds Fertilizer

Soil preparation

Emissions: 

Planting

 

Clearing (of young forest)

 

Thinning of forest area

 

Fertilizing



Dust (PM10) CO2 CO N2O NOx HC SO2 CH4

Final felling (harvesting)

Biomass transport

Emissions to air: CO2, CO, NOx, HC, SO2, PM, HC, CH4, SO2, N2O;

Energy use Diesel Natural gas

Biomass preparation (eg. into sawmill)

Emissions to air: CO2, CO, NOx, HC, SO2, particles; Emissions to water: N-tot

Air flow Electricity Diesel

Biomass combustion in a CHP plant (100 MW)

Emissions: CO, VOC, NOx, PAH, PM10, SO2,

Diesel

Electricity

Phases analysed in the LCA

Each plantation includes several steps, as stated bellow. The inventory data for each step were extracted from literature [Siyu Chen, 2009; Berg and Lindholm, 2005; Aldentum 2002] and is shown in the Table 2-1. Therefore, for a biomass culture the following steps were needed: 





Plant nursing: to prepare seedlings. In this process, two machines with 6kW and 50% utilization is used for peat handling and sowing. 1000 plants are kept in 5 plastic cases, which can be used for 4 times. Tractors (60kW and 50% utilization) are used for transporting plants to greenhouse, where diesel oil is used to supply heat. Soil preparation: to prepare the soil for growing trees. It is assumed that 22.5 liters diesel/ha is used to prepare 0.5 ha/h, which equal to 45 l diesel/ha resulting in 1602 MJ/ha (assuming 35.6 MJ/l diesel). Planting: to plant tree seedlings. Trucks, with capacity of 40000 seedlings per truckload, are used to carry the seedlings from the seedling nursery to the 7








 

forest. Tractors (30kW) are used in the forest. Fertilizer is assumed to be the same as it is used in the forest with 27.2% nitrogen content. Clearing: to clear some plants in order to limit the competition and protect the best plants, by using a portable clearing saw. Thinning: to conduct by using forest processor in order to raise the productivity of the remaining forest. Fertilizing: to increase the growth rate of the plants. This is done one to three times by using tractors (14%) and helicopters (86%). Fertilizer in this study is considered as N-fertilizer with nitrogen content 27.2% (SKOG-CAN). Final felling: to harvest the woods. Forwarding: to transport the felled wood from felling area to the road side [Siyu Chen, 2009].

The biomass must be transported and prepared into a bioenergy fuel to be burned easily. For the transport was assumed that average distance was 10 km. The biomass will be transported by heavy Lorries, Euro 5. For the biomass combustion was chosen to be analyzed a CHP plant of 100 MW, with an electric efficiency of 17%. The plant uses as fuel wood wastes with a moisture content of 35% study. The plant uses abatement devices typical of waste-to energy plants: bag filters for dust removal, a selective noncatalytic reduction (SNCR) system fed with ammonia in the combustion chamber for NOx control, lime addition to remove acid gases and activated carbon for adsorption of micropollutants such as heavy metals and trace organics [S. Caserini and co., 2010]. All the inputs and outputs are presented in the LCA diagram. As showed in [Siyu Chen, 2009]., the phases of this process that have the highest impact on environment, considering all the phases from the culture to pellet combustion, are the biomass production, biomass transport and the biomass combustion. Therefore, in this paper the phases analyzed will be the three ones mentioned above, as being the less environmental friendly.

Functional unit

The FU for the entire system was defined as 1.0 MWh el. Impact categories The four categories of impact that would be analyzed:    

Global warming; Acidification; Eutrophication; Human toxicity

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2.2.

Inventory analysis

Table 2-1 Inventory analysis Biomass culture

Transport

Use of resources

Unit

Forest land

ha

0.00009452

Tree seeds

kg

0.00004726

Thinned forest area

ha

0.00009452

copper ore

g

0.0037808

iron ore

g

0.00014178

lead ore

g

4.2534E-05

bauxite

g

2.363E-07

uranium ore

g

0.002363

coal

kWh

9.452E-06

oil

kWh

0.00004726

natural gas

kWh

2.363E-06

Energy use

Value

Use of resources

Unit

Energy use*

MJ/ton***

Combustion

Emission factor**

Value

0.43676

Use of resources

Unit

Value

4.3676

0

Electricity

kWh

0.004726

diesel

MJ

6.1438

gasoline

MJ

0.037808

kerosene biofuel

MJ

0.042534

Emissions to air

Emissions to air

CO2

g

499.500392

CO2

g

0.085068

NOx

g

0.9452

HC

g

N2O

Emissions to air

CO2

g/ton

32.3

274.55

PM10

g

0.0556

CO

g/ton

0.0348

0.2958

NOx

g

9.452

NOx

g/ton

0.0852

0.7242

VOC

g

0.113424

PM

g/ton

0.00118

0.01003

SO2

g

2.0016

g

0.033082

HC

g/ton

0.0155

0.13175

CO

g

3.336

SO2

g

2.43389

CH4

g/ton

0.000371

0.00315

PAH

mgTEF

CH4

g

0.042534

SO2

g/ton

0.000163

0.00139

Particles

g

0.18904

N20

g/ton

0.000224

0.0019

g

4.726E-06

Highly active radioactive waste

g

0.00009452

Low active radioactive waste

µg

0.0491504

Building waste

g

Emissions to water

N-tot

Waste

0.00014178

*Was assumed a distance of 10 km; **Emission factors for transportation based on euro engine class (NTM, Bäckström, 2007).

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0.0008

Capítulo 7: Análisis ambiental de la combustión de biomasa. ***For an energy content of 18 GJ/ton of biomass, are necessary 0,85 tons of biomass to produce 1 MWhe. The emissions therefore calculated for 0,85 tons of biomass. Source : [Siyu Chen, 2009], [NTM, Bäckström, 2007] and [S. Caserini and co., 2010]

All the emissions were calculated for the FU of 1 MWhe.

2.3.

Impact assessment

The methodology used to quantify the impact for the chosen impact categories is the ReCiPe Midpoint (E) versión 1.05., with the European normalization. Therefore, to fill the tables bellow were used factors of characterization, normalization and weghting. As stated above, the following categories of impact were analysed: Climate change, terrestrial acidifcation, human toxicity and photochemical oxidation. Table 2-2 Inventory table for the bioenergy from biomass combustion Impact category

Climate change Terrestrial acidification Human Toxicity Photochemical oxidation

CO2 CH4 N2O SO2 NOx PAH CO CH4 NOx SO2

Biomass culture

Biomass transport

Biomass combustion

499.500392 0.042534 0.033082 2.43389 0.9452 0.085068 0.042534 0.9452 2.43389

274.55 0.0031535 0.001904 0.0013855 0.7242 0.2958 0.0031535 0.7242 0.0013855

* 2.0016 9.452 0.000834 3.336 9.452 2.0016

*the biomass combustion is considered to be CO2

neutral.

Impact characterization is a quantitative step to translate the environmental load into impact. This translation can be realized by introducing equivalency factors, which are determined by the contribution of different substances to the different impact categories according to the physico-chemical mechanisms of the substances. Table 2-3 Characterized impacts values for bioenergy from biomass combustion

Impact category Climate change

Terrestrial acidification Human Toxicity Photochemical oxidation

Unit kg eq CO2 kg eq SO2 Kg eq 1,4-DB Kg NMVOC

Biomass culture

Biomass transport

Biomass combustion

TOTAL

0.50961592

0.27513755

0

0.784753473

0.00310498 0 0.0011469

0.00051557 0 0.00073783

0.008713 1.71E-08 0.009766

0.01233307 1.7097E-08 0.011651181

Many methods allow the impact category indicator results to be compared by a reference (or normal) value. This means, the impact category is divided by the reference. A commonly used reference is the average yearly environmental load in a country or continent, divided by the number of inhabitants. In our case, with the methods used, we compare the results with the European reference.

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Capítulo 7: Análisis ambiental de la combustión de biomasa. Table 2-4 Normalized impacts values for bioenergy from biomass combustion Impact category Climate change


Normalization factor

Biomass culture

Biomass transport

Biomass combustion

TOTAL

1.04E-04

5.27E-05

2.85E-05

0.00E+00

8.12E-05

2.60E-02 kg eq SO2 Kg eq 1,42.26E-04 DB Kg 1.88E-02 NMVOC

8.08E-05

1.34E-05

2.27E-04

3.21E-04

0.00E+00

0

3.86E-12

3.86E-12

2.16E-05

1.39E-05

1.84E-04

2.19E-04

Unit kg CO2

eq

The environmental impacts need to be weighed against one to another to see which one is the most important. Therefore this process is a qualitative and quantitative process, and it’s meant to measure the severity of the environmental impacts. The reason we use the weighted factors is to express the contribution of each impact category for the global impact of this renewable energy production. Table 2-5 Weighted impacts values for bioenergy from biomass combustion Impact category Climate change


2.4.

Unit kg CO2

eq

Weighting factor

Biomass culture

Biomass transport

Biomass combustion

TOTAL

10

5.27E-04

2.85E-04

0.00E+00

8.12E-04

5.66E-04

9.39E-05

1.59E-03

2.25E-03

0.00E+00

0.00E+00

2.31E-11

2.31E-11

1.30E-04

8.33E-05

1.10E-03

1.32E-03

7 kg eq SO2 Kg eq 1,46 DB Kg 6 NMVOC

Results

By following the characterization factors, the environmental load has been translated into specific environmental impacts. The results show that the main activities with the main environmental impact are the biomass culture and the biomass combustion. Although, by the lack of information, and the method used in this paper to quantify the impact, the results may mislead: in the case of human toxicity impact category, the only emission that contribute to the impact analysis was from biomass combustion. Though other studies [Sara González-García and co., 2011] show a clear and important contribution of biomass culture (harvesting, mechanical weed control, nitrogen fertilization and biomass collection). The production of biomass present a carbon sink, due to the CO 2 absorbed from the atmosphere. But even so, are other emissions associated to the culture activities, such as fertilizer application. In case of the climate change impact category, the activities with the higher impact remains the biomass culture and biomass transport, as the biomass combustion is CO 2 neutral, CO2 having the highest contribution on this impact category.

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For the photochemical oxidation, the main responsible of this result, in the case of biomass production, are the oxidant emissions from diesel combustion (thus all the activities that involve machinery use). Although the biomass combustion remains the most import activity in this case, with high emissions of NOx, SO 2 and CO. Again, the biomass culture contributes to the terrestrial acidification impact category, with diffuse emissions from N-fertilizers and NOx emissions from diesel combustion. Even so, the biomass combustion has a higher impact, due to all the emission.

Figure 2-1 Environmental impact of bioenergy for different impact categories

After normalizing the values for each impact category, we can observe that the most impacting activity is the biomass combustion, followed by the biomass culture.

Figure 2-2 Environmental impact profile for bioenergy normalized for each phase of the LCA

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The terrestrial acidification, according to the ReCiPe Midpoint (E) versión 1.05. method, is the most significant parameter, followed by the photochemical oxidation, climate change and human toxicity. This is due primarily to the combustion emission of NOx and SO2. This method weights the the terrestrial acidification and photocchemical oxidation mush nore then the climate change or human toxicity.

Figure 2-3 Environmental impact profile for bioenergy normalized for different impact categories

At the end, after weighting all the impacts, it is clear that the terrestrial acidification is the most important impact in the global impact of this technology, followed by the photochemical oxidation.

Figure 2-4 Environmental impact normalized and weighted for bioenergy

There would be some other impact categories that were not analyzed in this study, but that could be important for this bioenergy production, such as: natural land transformation, agricultural land occupation, freshwater eutrophication or fossil depletion.

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3. Carbon footprint The carbon footprint is defined as the total amount of greenhouse gases produced to directly and indirectly support human activities, usually expressed in equivalent tons of carbon dioxide (CO2). Although we considered in this study that biomass combustion is CO2 neutral, as most of the studies presume, it is recognized increasingly that this is incorrect. Indeed, is more carbon positive that fossil fuels, but not neutral. Some references presume that bio-based products are carbon neutral: European Union Emissions Trading Scheme; UK Standard Assessment Procedure for Energy Rating of Dwellings, 2005; PAS 2050 — Specification for GHG emissions of goods and services [Eric Johnson, (2009)]. Therefore, in our case the carbon foot-print has this value: 0.78 kg CO2 eq. most of this is given by the biomass culture, though in some others studies [Sara González-García and co., 2011], this value might be negative (in the case of biomass culture), as it was considered all the CO2 that the culture absorbs during its growth.

4. Energy Pay Back Time Energy payback is the ratio of total energy produced during a system’s normal lifespan, divided by the energy required to build, maintain and fuel it. A high ratio indicates good environmental performance. If a system has a payback ratio between 1 and 1.5, it consumes nearly as much energy as it generates, so it should never be developed Biomass performs well (ratio of 27) when power is produced from forestry wastes. But when trees are planted for the purpose of producing electricity, the ratio is much lower (about 3 to 5), because biomass plantations require high energy inputs. For all biomass options, the distance between the source of biomass and the power plant must be short, otherwise the energy payback ratio drops to very low values [http://www.hydroquebec.com/sustainable-development/]. The payback time for the biomass combustion varies between 0.9 (for a steam production system [B. Prasit and co., 2011]) to 6 years, depending on the applied technology.

5. Conclusions The bioenergy is more and more used in all the countries along the world, being available and cheap. The most impacting activity in the production of bioenergy is the biomass combustion, although a high impact has also the biomass culture. The LCA analysis showed, after weighting all the impacts, that the terrestrial acidification is the most important impact in the global impact of this technology, followed by the photochemical oxidation. The environmental impact is due to the diffuse emission form biomass culture, diesel combustion from the machinery and transport camions and biomass combustion. 14


6. References 1. A. D’Ovidio, M.Pagano, (2009), Probabilistic multicriteria analyses for optimal biomass power plant design , Electric Power System Research; 2. A. Williams, J.M. Jones, L. Ma and M. Pourkashanian, (2011), Pollutants from the combustion of solid biomass fuels , Energy and Resources Research Institute/CFD Centre, University of Leeds, Leeds LS2 9JT, UK; 3. Aldentun, Y. (2002), Life cycle inventory of forest seedling production -- from seed to regeneration site , Journal of Cleaner Production 10(1): 47-55. 4. B. Prasit, P. Maneechot, S. Ladpala, S. Vaivudh (2011), Optimization and payback period of steam production by biomass combustor for Agro-industry , Energy Procedia, Vol 9; 5. Berg, S. and E.-L. Lindholm (2005). Energy use and environmental impacts of forest operations in Sweden, Journal of Cleaner Production 13(1): 33-42. 6. Bäckström, S. (2007). NTM-Environmental Data For International Cargo Transport , The Network for Transport and the Environment. 7. Eric Johnson, (2009), Goodbye to carbon neutral: Getting biomass footprints ,

right , Environmental Impact Assessment review 8. Obernberger and G. Thek, (April, 2008), Combustion and gasification of solid biomass for heat and power production in Europe – state-of-the-art and relevant future developments ; Editor CENERTEC, Portugal; 9. Sara González-García a,*, Jacopo Bacenetti b, Richard J. Murphy a, Marco Fiala b, (2012), Present and future environmental impact of poplar cultivation in the Po Valley (Italy) under different crop management systems , Journal of Cleaner Production; 10. S. Caserini, S. Livio, M. Giugliano, M. Grosso, L. Rigamonti LCA of domestic and centralized biomass combustion: The case of Lombardy (Italy), Biomass and Bioenergy 34, pag. 474-482; 11. Siyu Chen, (2009), Life cycle assessment of wood pellet , Chalmers University of Technology, Göteborg, Sweden; 12. Warren E. Mabee, John N. Saddler, (2007), Forests and energy in OECD Editor: Food and agriculture organization of the United Nations countries , (FAO); 13. Ecoinvent database, “Life Cycle Inventory of Bioenergy” 14. Renewables 2011, Global Status Report. 15. http://www.hydroquebec.com/sustainable-development 16. http://ec.europa.eu/energy/renewables/bioenergy/bioenergy_en.htm 17. http://www.viaspacegreenenergy.com/direct-combustion.php 18. http://www1.eere.energy.gov/tribalenergy/guide/biomass_biopower.html ,

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LCA Biomas Combustion

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