ghg emissions evaluation from fossil fuel with ccs

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The study shows that life cycle GHG emissions from fossil fuel power stations with carbon capture and storage (CCS) can be reduced by 75-84% relative to the ...
Environmental Engineering and Management Journal

January/February 2009, Vo/.8, No.1, 81-89

http:llomicron.ch.tuiasi.ro!EEMJ/

"Gheorghe Asachi" Technical University of lasi, Romania



'

GHG EMISSIONS EVALUATION FROM FOSSIL FUEL WITH CCS Cristian Dinca*, Adrian-Alexandro Badea, Tiberiu Apostol, Gheorghe Lazaroiu University POLITEHNICA of Bucharest, Power Plant Department, 313 Splaiul Independente, 060042, Bucharest, Romania

Abstract A present challenge for research is to determine how to use the combination of oil, gas and coal most efficiently with the minimum environmental damage. In this paper the authors have compared technologies to produce the electricity using natural gas and coal. The objective of this paper consists in evaluation of the life cycle assessment of the natural gas and coal in order to compare their greenhouse gases (GHG) emissions. In this way, three systems with and without CCS were examined: one using the natural gas combined cycle (NGCC) and two using the coal: pulverized coal with sub-critical and super-critical parameters and integrated gasification combined cycle (IGCC). The study shows that life cycle GHG emissions from fossil fuel power stations with carbon capture and storage (CCS) can be reduced by 75-84% relative to the reference case. IGCC is found to be favorable with a reduction of GHG emissions to less than 160 g/k:Wh. For NGCC power plants, the amount of methane leakage from natural gas extraction and transport has a significant effect on life cycle GHG emissions.

Key words: CCS, coal, energy, life cycle assessment, natural gas.

1. Introduction

Coal and natural gas have the largest share of utility power generation in the UE, accounting for approximately 55 % of all utility-produced electricity (Gavrilescu, 2008). In Romania, the share of fossil fuel in order to produce the electricity is 63 %. Therefore, understanding the environmental implications of producing electricity from this fuel is an important component of any plan to reduce total emissions and resource consumption. A life cycle assessment (LCA) on the production of electricity from coal and natural gas was performed in order to examine the environmental aspects of pulverized coal boiler systems with sub-critical and super-critical parameters (PC), integrated gasification combined cycle (IGCC) and natural gas combined-cycle (NGCC), (Pislaru et al., 2008). All energy systems emit greenhouse gases (GHGs) and contribute to anthropogenic climate change. It is now widely recognized that GHG emissions resulting from the use of a particular energy technology need to be quantified over all stages of the technology and its fuel life-cycle. While accurate calculation of GHG emissions per kilo-Watt-

hour (kWh) is often difficult, sound knowledge of life-cycle GHG emissions can be an important indicator for mitigation strategies in the power sector. In the section 2 the boundaries and methodology adopted for the present life cycle assessment has presented. Section 3 outlines the life cycle assumptions, while Section 4 gives a detailed description of the power generation technologies considered. Finally, Sections 5 and 6 give a summary of the results and conclusions for the different CCS and non-CCS systems. The results are given for life cycle GHG emissions, resource consumption and net energy ratio. A sensitivity analysis is then undertaken to investigate the effect of some key parameters on the total GHG emissions for each of the systems. Therefore, the current paper examines life cycle emissions from three types of fossil-fuel-based power plants, namely supercritical pulverized coal (super-PC), natural gas combined cycle (NGCC) and integrated gasification combined cycle (IGCC). The PC power plants studies (both sub-PC and super-PC) are equipped with NOx, particulates and S0 2 removal processes (i.e. selective catalytic reduction, SCR, electrostatic precipitation, ESP and flue gas

·Author to whom all correspondence should be addressed: e-mail: [email protected], Phone: +40-722-466-980,

Dinca et al./Environmental Engineering and Management Journal 8 (2009) , J, 8 1-89

Process changes, material substitution, and recycling possibilities are explored. The third component, impact assessment, is the least developed and most controversial of the three. Several options for describing the possible impacts on the environment as a result of the system exist.

desulfurization, FGD). The NGCC power plant on the other hand, is equipped with NOx control. 2. Methodology Generally, a life cycle study consists of four (Munteanu, 2007): goal and scope definition, inventory analysis, impact assessment and improvement assessment In the first two steps, boundaries of the analysis are defined and impacts of the different processes of the system are calculated. The third and fourth steps examine the actual environmental and human health effects from the use of resources (energy and materials) and environmental releases and give recommendations for reducing these effects. The current study focuses on the first two steps. The methodology used in conducting this LCA is based on the standard three-component model set forth by the Society of Environmental Toxicology and Chemistry (Dinca et al., 2007). The first component, inventory, consists of material and energy balances for each process within the system. These flows are added to give the total em1ss1ons, resource consumption, and energy use for the system. In performing the second component, improvement, the results of the inventory step are assessed to identify opportunities to reduce the effects the system has on the environment.

steps • • • •

2.1. The boundaries of the systems The limits for the systems analysed in the paper are shown in Figs. 1-3 for PC, NGCC and IGCC technologies with and without CCS. In theses figures, is represented the life cycle of coal and natural gas and the life cycle for the technologies choosed tacking into account the power plant construction, power generation and the power plant decommissioning. It has been studied the life cycle of the technologies in two cases: with and without carbon capture storage. In this context, the life cycle for the capture plant is represented by discontinuous contur. In the Figs. 1-3 is indicated the input and the output: energy and/or materials as inputs and emissions as output. In addition to accounting for direct emissions from fuel combustion in the power plant, other emissions arising from upstream (e.g. production and transport of limestone, ammonia, catalyst, etc.) and downstream (e.g. waste transport and disposal) processes, as well as emissions from power plant construction and decommissioning, are also included.

,-----------------------------------------------, :

Material transport (SteeL concrete, aluminum and iron)

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By-products: C O:;i captured, gypsum, ash Pollutant Removal (i.e. SCR, ESP, FGD, Sulphur remov~ etc .)

Material transport (Air, water, limestone, ammonia, SCR catalyst, MEA, NaOH)

Air emissions: CO:;i,H:;iO, SOx, NOx. NH3, HCL dust

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Fig. 1. Life cycle boundaries for PC power plants without and with CCS

Solid waste : SCR catalyst, sludge, boiler slag. MEA waste

GHG emissions evaluation from fossil fuel with CCS

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Electricity Extraction of coal

Treatment of coal

Transport of coal

Power generation

By-products: C02, ash, sulphur

Pollutant Removal (i.e. SCR, ESP, FGD, Sulphur removal, etc.)

Material transport (Air, water, Selexol, Claus Plant catalyst)

Air emissions: C02, H20, SOx, NOx, NH3, HCL dust

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Power/Capture plant Decommissioning Fig. 3. Life cycle boundaries for IGCC power plants without and with CCS

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Dinca et a/./Environmental Engineering and Management Journal 8 (2009) , 1, 81-89

Extracting the materials used for constructing the power plant are also accounted for. For downstream processes, waste transport and disposal in a near-by landfill are considered. In PC coal power plants, for example, waste is generated by the boiler and ESP process as bottom ash and by the FGD process as gypsum and calcium chloride (Rubin et al. , 1991). For coal-based power plants, emissions arising from mining activities such as methane leakage and machinery operation are included. For natural gas fuel cycle systems, on the other hand, upstream emissions include those from gas exploration, extraction, processing and compression as well as from methane leakage during extraction and transport. Emissions from pipeline construction (and associated steel requirements for constructing the pipeline) are also accounted for. Extracting the materials used for constructing the power plant, the capture plant and the C0 2 transport pipeline are also accounted for. For downstream processes, waste transport and disposal in a near-by landfill are considered. In PC coal power plants, for example, waste is generated by the boiler and ESP process as bottom ash and by the FGD process as gypsum and calcium chloride (Rubin et al., 1991). For CCS systems where the capture process is MEA-based, waste is generated in the re-claimer where NaOH is used to reclaim MEA from salts resulting from MEA oxidation. For coal-based power plants, emissions arising from mining activities such as methane leakage and machinery operation are included. For natural gas fuel cycle systems, on the other hand, upstream emissions include those from gas exploration, extraction, processing and compression as well as from methane leakage during extraction and transport. Emissions from pipeline construction (and associated steel requirements for constructing the pipeline) are also accounted for.

2.2. Life cy cle data and methods ofGHG analysis Two methods for life cycle GHG assessment of power plants can be employed as shown in Fig. 4. A power plant techno-economic model is used to estimate material and energy requirements and costs. The input parameters for the model are discussed in Section 4. Data of GHG content (kgC0 2/kg material produced) and energy content (MJ/kg material produced) are obtained as described by Dey and Lenzen (2000) from process chain analysis (PCA), while data of GHG intensity (kgC02/€ material produced) and energy intensity (MJ/€ material produced) are obtained from an input/output analysis (IOA). Process chain analysis is usually based on data obtained from previous studies, from stakeholders or from available software packages. The Ecolnvent database of the software SimaPro (by Pre 'Consultants), which contains data applicable for Western Europe in general, has been

used in the current study. Input/output (I/O) analysis is bas1;;d on data obtained from European Commission study - 1/0 tables (Zaharia and Surpateanu, 2006). In order to obtain annual emissions from operation, the results from PCA and IOA are multiplied by the material requirements and costs obtained from the techno-economic model as shown in Fig. 4. Annual emissions are multiplied by the power plant lifetime to obtain total emissions from operation. The procedure is repeated for all GHG gases within a given process and then for all processes within a life cycle system. For emissions from construction, the material requirements (for example kg of steel or concrete) or the total costs of construction (€) are multiplied by GHG content or GHG intensity as applicable. For emissions from transportation, quantities of transport fuel (e.g. m3 or kg heavy oil) or costs of transport (€) are multiplied by available factors in units of ''kg COrelm 3 heavy oil" or " €/m3 heavy oil". Alternatively, factors in the form of " kg COr e/ton.km " or "kg COre/€ worth of transport' ' (which can be obtained from VO tables for different means of transport) can be multiplied by transport distances and amount of material transported. Total emissions from construction and decommissioning are added to total emissions from operation (production, transport and waste disposal) and the sum is divided by the power plant output over its lifetime. Normalized values of total GWP from the two methods showed that the cost-based IOA provides a more complete accounting of emissions incurred during construction thus resulting in larger estimates of emissions. The authors stated that for plant construction, the material-based PCA resulted in emissions that approximate a subset of emissions computed via the cost-based IOA method. For plant operation, however, only emissions due to mining and consumption of coal at the plant are significant, and both methods of analysis give essentially equivalent results.

2.3. Energy considerations Life cycle efficiency is the energy output throughout the lifetime of the power plant divided by all sources of energy input from the life cycle of the system over the same period of time. The energy input includes energy contained in the fuel in addition to embodied energy added to the power plant (for example the energy used for construction of the power plant, the energy used to produce limestone and transport it to the power plant etc.). The percentage reduction of life cycle efficiency from actual power plant efficiency (i.e. the efficiency calculated by dividing the electrical output of the power plant by the energy content of the fuel over the life time of the power plant) is an indication of how significant energy use in upstream, downstream and construction processes.

GHG emissions evaluation from fossil fuel with CCS

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Pu w t:I I-' 1~.tL t: mi::; ::;ium foi.; Lux (klfkVV11) Fig. 4. Life cycle analysis by two methods: process chain analysis and 1/0 analysis

In Table 1, the technologies are evaluated according to the C0 2 emissions and the total cost in the both cases: with and without carbon capture. The data were collected from different sources and it has been established the represented value for each energy technology. It has been found that the NGCC technology presents the smallest cost comparative to the coal technology. According to the C0 2 emissions generated by the combustion stage, the NGCC technology has the smallest amount of carbon dioxide but the cost of net C02 captured without transport and storage is the bigger than the other technologies. Table 2 presents the basic data for all technologies analyzed in this study.

3. Life cycle assessment assumption For the coal life cycle, it is assumed that coal and other necessary materials (including limestone and ammonia) are produced locally in the Romania and according to local technologies. A transport distance of 100 km was assumed for transport of coal as well as other materials. The assumption that all coal used by a Romanian power plant is locally mined may not be realistic. A pipeline length of 250 km was assumed between the power plant and the gas field. A diameter of 80 cm, which is typical for natural gas transport, is assumed.

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Dinca et al./Environmental Engineering and Management Journal 8 (2009) , 1, 81-89

Table 1. The evaluation of C0 2 emissions and costs for a differe1,t power plant with and without CCS

Performance and cost measures

NGCCplant Report:d Range value

PColant Report:d Range value

Total capital requirement without capture 1 172-1 495 612 - 835 696 (€/kW) Total capital requirement with capture (€/kW) 1086-1393 1 212 1 903 - 2 612 44 - 71 Emission factor with capture (kg COzfMWh) 103-155 63 Emission factor without capture (kg CO,/MWh) 744-812 373 - 412 385 Percentage net C0 2 reduction per kWh (%) 83-88 84 81-86 Cost of net C0 2 captured, without transport and 51 - 96 78 35-59 ~torage (€/kW) - Reported value - the value which has been taken mto account m the curent study

IGCColant Report:d Range value

1 315

1 169-1 565

1 326

2 107 120 768 84

1432-2285 65-152 688-853 82-91

1 866 108 781 86

51

15-46

28

Table 2. The basic data for the technologies

Parameter

NGCCplant

PC plant

IGCCplant

Reference

Capture

Reference

Capture

Reference

Capture

612 - 835

696

1 172-1 495

1 315

1 169-1 565

1 326

Gross plant size (MW)

1 086 -1 393

1 212

1 903 - 2 612

2 107

1432-2285

1 866

Net plant output (MW)

44 - 71

63

103-155

120

65-152

108

373 - 412

385

744-812

768

688-853

781

C0 2 capture system

83-88

84

81-86

84

82-91

86

C02 capture efficiency

51 - 96

78

35-59

51

15-46

28

Fuel used

Net plant efficiency, HHV (%)

Emissions for producing the steel required to construct the pipeline were taken into account. The effect of importing all or a some part of natural gas required by the power station from Russia is investigated in Section 5.3 as part of a sensitivity analysis. However, due to lack of data, emissions from digging and laying the pipeline were ignored. A 1% methane leakage is assumed for the reference case. However, a sensitivity analysis is undertaken in Section 5 .3 to investigate the effect of natural gas loss on total GHG emissions. The current analysis assumes that natural gas is transported from the extraction platform where it is sweetened and flared. Onshore processing includes gas compression and delivery to the power plant. In general, the LCA of CCS systems accounts for emissions arising from the construction of the capture plant and C0 2 pipeline, those arising from the production and transport of chemicals necessary for running the capture plant, as well as those arising from the energy requirements for the transport and injection processes. It is assumed that the captured C02 is compressed to 13.5 Mpa and transported via a 300-km pipeline where it is injected in gas fields. In addition, the current analysis considers electricity requirements for C02 re-compression along the pipeline. An energy requirement of 3 kW of electricity per km of C02 pipeline was used based on a calculation from Spath and Mann (2004). Due to lack of data, C0 2 leakage from the pipeline and emissions and energy requirements for the injection

of C0 2 were roughly estimated based on experience in the natural gas and oil industries. Furthermore, it was assumed that leakage from the reservoir over the lifetime of the power plant is negligible.

4. Description of technologies considered The following technologies are considered for analysis: •



A reference case (reference), which comprises a non-CCS subcritical PC power plant equipped with pollution control processes including SCR for NOx removal, ESP for particulates removal and FGD for S02 removal. The current study compares LCEs and efficiencies from each of the following technologies to this sub-PC reference plant. Two supercritical PC technologies without (Casela) and with (Caselb) CCS. Both cases are equipped with SCR, ESP and FGD. A third case (Caselc), which consists of a supercritical PC power plant with CCS but without FGD is considered for life cycle assessment. The reason for including this case is to quantify the effect of including or excluding the FGD process on life cycle GHG emissions from the CCS system. While the effect of excluding FGD on the costs of C02 capture has been previously reported (Rao et al., 2004 ), the effect on LCEs has not been quantified before. The current analysis investigates the effect of removing FGD on LCEs.



Two NGCC technologies without (Case2a) and with (Case2b) CCS. • Two IGCC technologies without (Case3a) and with (Case3b) CCS. The capture technology considered for PC and NGCC is post-combustion MBA-based absorption. For IGCC, on the other hand, a pre-combustion physical absorption with Selexol solvent is considered. The power generation capacity for all non-CCS cases was kept constant at 500 MW with a 75% load factor. A power plant lifetime of 30 years was considered. For CCS plants, a capture efficiency of 90 % is considered. Other process-specific parameters are based on typical values from the literature. These output parameters are then entered into an Excel spreadsheet (Fig. 6) where they are used in combination with a built-in database of GHG content and GHG intensity data as shown in Fig. 4 under the box 1/0 analysis to estimate production and transport emissions and, consequently, the GWP (emissions in mass COre per kWh of electricity produced) can be determined. The life cycle efficiency defined in Section 2.3 can be calculated by repeating the calculation procedure shown in Fig. 4 with energy content and energy intensity data instead of GHG data. The steam used for regenerating MEA is taken from the main power plant and so no auxiliary natural gas power plant was considered. The calculated emissions per kWh were based on the net power produced from the plant and so the plant with CCS used the same amount of fuel as in the case without CCS. 5. Results and discussion 5.1. Power plant performance results

The net power and corresponding efficiency for each of the technologies is shown in Table 3. For the reference power plant, a 25MW reduction (475 instead of 500MW) is caused by the air blower, coal pulverizes and the steam cycle pumps and cooling system. Table 3. Net power and power plant thermal efficiency

Case

Net power,

MW Reference la lb 2a 2b 3a 3b

475 453 335 500 432 500 471

Pow er plan t efflcien cy, %

35.3 39.6 30 50.1 42.8 37.2 32

LCA efficiency %

32.9 36.3 27.7 41 36.5 35 30.2

%

Reduction in efficiencv 6.8 8.3 7.7 18.2 14.7 5.9 5.6

For the super-critical PC system, additional energy penalties are caused by the SCR (3 MW), ESP (lMW) and FGD (18MW) processes. The addition of CCS to super-PC imposes an energy penalty of 118MW (26%). Corresponding energy penalties for

NGCC and IGCC due to CCS are 15% and 7%, respectively. Table 3 reveals that for NGCC systems, life cycle efficiency is much lower than power plant efficiency. This reflects the fact that upstream processes in the natural gas cycle are more energy intensive in comparison to upstream emissions from the coal fuel cycle. Fuel and other material consumption for each of the technologies are shown in Table 4. For all power plants, the inclusion of CCS increases fuel consumption by 15-30% on a g/kWh of electricity-produced basis. Table 4. Resource consumption

Case Reference la lb 2a 2b 3a 3b

Fuef'b 329.7 294.9 390.1 130.1 151.9 314.9 365.9

Limestoni 19 16.9 27.2

-

NH/ MEAb Selexof 0.68 0.61 0.8 3.6 0.2 0.23 1.33 0.02 0.03 -

-

-

-

•Fuel consumption as coal for cases 1a, 1b, 3a, 3b and natural gas for cases 2a and 2b b All values in these columns are in units of g/kWh

The large increase in fuel consumption for PC is an indication of the high energy penalties associated with CCS when used with PC. The increase in limestone consumption shown in Table 4 for PC power plants with CCS is due to the fact that the model increases the SOx removal efficiency from 90% to 98% when CCS is considered (Rao et al. , 2004). This is necessary in order to avoid significant MEA losses due to the strong reaction of MEA solvent with S02 . MEA is very reactive with acid gases (S0 2 , S0 3 , N0 2 and HCl in addition to C0 2). As a result, it is seen from Table 4 that MEA consumption is higher for PC than for NGCC because more acid gases are associated with the coal technology. 5.2. Life cycle GHG emissions

LCEs for each of the non-CCS and CCS technologies are compared in Table 5. All systems with CCS show a large reduction in life cycle GHG emissions. The highest reductions from the reference case are obtained with IGCC followed by NGCC. The contribution of different sections of the life cycle to GHG emissions is shown in Fig. 5. It is evident that emissions from the construction phase are negligible both for CCS and non-CCS systems when compared with other LCEs. LCEs from super-critical PC power plants without CCS are 10,6 % less than LCEs from the reference subcritical case. This difference is a reflection of the higher efficiency and consequent lower fuel consumption by the supercritical power plant. For IGCC without CCS, LCEs are only 2% lower than LCEs from supercritical PC.

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Dinca et a/./Environmental Engineering and Management Journal 8 (2009) , 1, 81-89

only requirements for the power plant are those of coal in addition to water. Ruether et al. (2004) reported that IGCC with 90% C02 capture exhibits lower life cycle GHG emissions than NGCC, which agrees with results from the current study. An important conclusion can be drawn from Fig. 5 regarding Caselc (super-PC with CCS and without FGD). It is recognized that S02 reacts strongly with MEA and so, if FGD is not included upstream of CCS, large quantities of MEA will be needed to remove C0 2. Tzimas et al. (2007) state that SOx emissions from coal power plants should be decreased to avoid significant losses of the chemicals that are used to capture C02. The present study also reveals that life cycle C02 emissions double if FGD was not included prior to the MEA process. This is caused by the emissions arising from the production (and transport) of chemicals (including MEA) necessary for running the MEA process.

Moreover, LCEs from NGCC without CCS are, as expected, 50% less than emissions from the reference case For NGCC, upstream GHG emissions from gas extraction and transport constitute 26% of all LCEs emissions. For the coal life cycle on the other hand, upstream emissions constitute 6-10% of all GHG emissions (depending on whether the technology is PC or IGCC) For the super-critical PC power plant with CCS, LCEs are 74% less than emissions from the reference case. Emissions attributed to CCS (capture, transport, injection and construction of power plant and C0 2 pipeline) account for 10% of all LCEs. For Case2b (NGCC with CCS), LCEs are 79% lower than the reference case and only 22 % lower than the supercritical PC with CCS case. This is because upstream emissions for the natural-gas fuel cycle are more significant than they are for the coal fuel cycle. Finally, for Case3b (IGCC with CCS), LCEs are 83% less than for the reference case. Emissions from Case 3 b are lower than those from Case 2b due to the low operations and maintenance costs of the Selexol process in comparison to the MEA process. Moreover, the modeling of the IGCC process does not account for limestone requirements for S0 2 removal because S0 2 removal is performed with a Selexol system instead of an FGD system and so the

5.3. Sensitivity analysis of GHG emissions

A sensitivity analysis was undertaken to determine the effect of several parameters on the total life cycle GHG emissions. The parameters considered in the sensitivity analysis and their corresponding effects are shown in Table 6.

Table 5. Life cycle emissions (g C0 2 - e/kWh) and fuel consumption (MJ/kWh)

Case

Life cycle emissions, gCOi-elkWh

Fuel consumption MJ/kWh

984 879 255 488 200 861 167

8.4 8.4 10 6.4 7.8 8.2 9.5

Reference

la lb 2a 2b 3a 3b

-

·PC

-

-PC• CCS

--PC• CCS-

Comf}aring with reference case Reduction of GWP, Reduction offossil % energy consumf}tion, %

-

-

-11

0 19 -24.6 -7.2 -3 12.1

-74 -50

-79 -13

-83

NGCC+CCS

NoFGD

~· - :

l"' ,.,.,.,Mri