Techno-economic and Environmental Analysis of Calcium Carbonate Looping for CO2 Capture from a Pulverised Coal-Fired Power Plant

A. Rolfe [a], Y. Huang* [a], M. Haaf [b], S. Rezvani[a], A. Dave[a] and N.J. Hewitt [a]

a CST, Ulster University, Northern Ireland, UKb Institute for Energy Systems and Technology, Technische Universität Darmstadt,

Germany

Abstract

Pulverised coal-fired (PC) power plants are among the major technologies used to

generate electricity for power generation around the world. Coal-fired systems are

generally considered to have high greenhouse gas emission intensities, apart from power

plants that employ CO2 capture and storage (CCS) technology. As a technology option,

calcium carbonate looping can be employed to remove carbon dioxide from the PC flue

gas streams. Calcium carbonate looping is an attractive technology due to relatively low

efficiency penalties. To better understand the performance characteristics and benefits of

such a system integration, the ECLIPSE modelling software is used to perform a techno-

economic analysis of the calcium carbonate looping system integrated in to an existing

hard coal power plant. The overall system efficiency and the CO2 capture rate is evaluated

based on a mass and energy balance calculation as part of the modelling. The capital costs,

and maintenance and operating costs are estimated according to a bottom-up approach

using the information gained through a mass and energy balance. The SimaPro software is

used to perform a life cycle analysis of the capture technology to determine its

environmental impact. The calcium carbonate looping system is also compared to other

CCS solutions.

*Corresponding author: Tel.: +0-2890368483.

email address: y.huang@ulster.ac.uk

Keywords: Coal-fired power plant; calcium carbonate looping; carbon capture; life cycle

analysis; techno-economic analysis;

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1. Introduction

Globally, fossil fuels remain a major primary energy source. The transition to

cleaner and more sustainable energy system is still very slow. Around 81.1% of the

world’s total energy supply is based on coal, oil and natural gas. Electricity

generation from fossil fuels also remains high (66.7%) with coal being the

dominant fuel at 40.8% [1]. However, burning fossil fuels produces large amounts

of CO2 emissions. Coal contributes to more than 40% of the world’s CO2

emissions. Over 70% of CO2 emissions from electricity production comes from

coal combustion [2]. CO2 emissions are a major contributor to anthropogenic

climate change and as such, there has been a focus on efforts to decarbonize the

fossil-based electricity generation. These include replacing aging and inefficient

power plants by pursuing state of the art technologies with more efficient energy

conversion rates, increasing renewable energy supply and adopting of carbon

capture and sequestration (CCS) technologies [3, 4].

This study focuses on the technical, economic and environmental analysis of a

supercritical Pulverized coal (PC) power plant with post combustion CO2 capture.

CCS comprises of a range of technologies that can be divided into pre-combustion,

post-combustion and oxyfuel. Pre-combustion capture uses the process of

gasification or reforming to split fuel into hydrogen and CO2. Post-combustion

capture uses a suitable solvent to capture CO2 from exhaust gases. In oxyfuel

combustion, fuel is ignited with almost pure oxygen mixed with flue gases rather

than air. This results in flue gases that mainly consists of CO2 and water which

produces exhaust gas with higher CO2 concentrations and enables easier

purification [5]

The calcium carbonate looping (CCL) process is a post combustion carbon capture

technology that utilizes solid CaO based sorbents to remove CO2 from flue gases

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e.g. from a power plant, producing a concentrated CO2 stream (over 90%) suitable

for storage or utilization. The CCL carbon capture process is based on the

reversible, exothermic reaction that occurs in the carbonator at a temperature of

650oC where CO2 in the flue gas is absorbed by CaO to form solid CaCO3. The

resulting CaCO3 is directed to the calciner, where it is regenerated at high

temperature, producing a concentrated CO2 stream. After regeneration, the sorbent

is transferred back to the carbonator. The captured CO2 is subsequently treated and

stored permanently. A CO2 depleted flue gas is emitted from the carbonator to

atmosphere [6] Sensible heat recovered from the CO2 depleted flue gas steam and

concentrated CO2 stream, along with the heat rejected from the carbonator is used

in a secondary steam cycle to produce electricity. The principle of the CCL process

is depicted in Figure 1.

Figure 1 Schematic diagram of the CCL process

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2. Technical evaluation of CCL for the selected PC power plant

The selected power plant is a 600 MWe supercritical PC power plant, which is

fitted with flue gas desulphurisation (FGD) and selective catalytic reduction (SCR)

for reduction of SOx and NOx respectively.

For the base case without CO2 capture, the PC plant had a net electricity generation

of 588.6 MWe, which led to an efficiency of 39.1% (LHV). The flow of flue gases

was 3244 t/h with a CO2 concentration of 10.1% (v/v), equivalent to 860 g

CO2/kWh of net electricity generated.

For the integrated system with the CCL plant, the output of the PC plant was

increased to 1,186 MWe. Due to the air separation unit (ASU) and CO2

compression duties, the integrated PC plant had a significant increase in the

auxiliary power consumption to 262.1 MWe. The net plant efficiency was 32.1%

(LHV). The efficiency penalty for the CCL CO2 capture was therefore 7

percentage points. The flow of CO2 gas from the CCL plant was 73 t/h, equivalent

to 88 g CO2/kWh. Table 1 summarizes the results of the technical evaluation.

Table 1: Technical evaluation summary

600 MW Plant Without CCL With CCL

Thermal Input (MW) 1504 2875

Gross Power Production (MW) 637 1186

Auxiliary Power Usage (MW) 49 183

Air Separation Unit (MW) - 79

Net Electricity (MW) 588 924

Net Efficiency, % (LHV) 39.1 32.1

CO2 Emission Factor (kg/MWh) 898 88

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CO2 Captured (kg/s) - 260

Efficiency Penalty, % - 7.0

3. Economic evaluation of CCL for a hard coal power plant

The ECLIPSE software has been used to estimate the capital investment and

operational and maintenance costs for the CCL unit to calculate the levelized cost

of electricity (LCOE), CO2 capture cost and CO2 avoidance cost. The CCL

technology has also been compared with other CO2 capture solutions.

Carbonator, 15%

Calciner, 7%

Air Separation Unit22%

CO2 Compression14%

Steam/FW sys-tem11%

Cooling Water System

7%

Steam Turbine, 19%

ESP and waste treatment, 4% BoP, 3%

Figure 2: Breakdown of the Capital Costs for the CCL

The calculation of capital costs has been determined using two approaches. Firstly,

if the selected component (and its size/capacity) was standard equipment, then

manufacturers’ quotes, prices published in literature and historical project data,

would be used. If a similar component of different size or capacity the capital cost

would be scaled up or down. Secondly, if the component was a non-standard

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equipment, a seamless cost estimation within ECLIPSE simulation was adopted.

This method is based on the design data generated by the mass and energy balance

calculation.

The most significant component of the direct cost for integration of a CCL process

with a PC coal power plant for CO2 capture is the CCL unit capital cost. A bottom-

up approach was used to estimate the overall unit cost for this study. To get the

basic information about the system with CO2 capture, mass and energy balances

(including utility calculations) were generated. A detailed cost model for the CCL

plant including main equipment, design and installation was developed for the

CCL integration. A breakdown of the capital cost is shown in Figure 2.

For the selected 600 MW PC power plant, the CCL plant capital cost was

estimated to be about 669 million euros.

The total capital cost for the base PC power plant was estimated to be 906.3

million euros, resulting in a specific capital investment of €1540 per kW e (net). If

the reference coal price of €84.9/t and annual operating hours of 7446 were

assumed, a LCOE of €66.9/MWh was required.

For the PC power plant integrated with the CCL plant, the total capital cost

increased to 1719.4 million euros due to additional CCL plant and secondary steam

cycle being introduced, which was equivalent to a specific capital investment of

€1861 per kWe (net), excluding CO2 transport, storage and monitoring costs. With

the same fuel price and load factor a LCOE of €82.4/MWh was calculated.

In this study, the amount of CO2 avoided was 771.9 g/kWh. The CO2 capture cost

and CO2 avoidance cost relative to the corresponding reference plant were €15.4/t

CO2 captured and €20.2/t CO2 avoided, respectively. Table 2 summarizes the

results of the economic analysis.

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Table 2: Summary economic results of PC power plant with and without CCL

600 MW Plant Without CCL With CCL

Total EPC (M€) 788.09 1495.19

Owner Cost (M€) 118.21 224.27

Total Capital Cost (M€) 906.30 1719.46

The CCL cost (M€) - 813.16

Specific Cost (€/kWe) 1540 1861

LCOE €/MWh 66.9 82.4

Cost of CO2 captured €/t CO2 15.31

Cost of CO2 avoided €/t CO2 20.08

Based on a detailed literature review a comparison of different CO2 capture options

was performed. In terms of the efficiency penalty from carbon capture, the

comparison results show that either the MEA post-combustion option is around

8.9% or the oxyfuel combustion option is about 8.4% is higher than the CCL

technology in PC power plants [7]. In comparison to either MEA post-combustion

or oxyfuel combustion, the CCL option indicates the lowest avoidance cost at

€20.2/t CO2 (in the cases of MEA post-combustion and oxyfuel combustion these

costs are around €43.0/t CO2 and €38.5/t CO2, respectively) [8].

4. Life cycle analysis of hard coal plant with CCL

A Life cycle analysis (LCA) was completed to evaluate the environmental impact

of (CCL) technology integrated with a hard coal power plant. The study is a

comparison between the hard coal power plant with and without CCL. The

environmental impacts of the plant technology and its potential hazards to human,

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wildlife, and bio-systems are considered. The LCA was carried out using the

ReCiPe [9] methodology and both the midpoint and endpoint were considered.

4.1. Goal and Scope

The goal is to evaluate the environmental impact of generating electricity at an

existing full-scale hard coal plant, while capturing CO2 via a retrofitted CCL

process. The intended application is to appraise whether the CCL technology could

lower the environmental burden of electricity generation from hard coal without

introducing any adverse environmental impacts.

The function of the process is to generate electricity for grid delivery. In agreement

with other similar studies, the functional unit is the production of 1 kWh of net

electricity delivered to the grid [10]. The reference flow is 1kWh of net electricity.

The study assumes that the 600MW power plant is operating at full load. It is a

cradle-to-gate LCA and capital goods are not included.

The electricity retains 100% of the environmental burden. This is because the CCL

is a cleaning system. Its resultant product; CO2, has no value.

This study does not consider the capital costs for the CO2 transportation and

storage facility or the alternate disposal options of spent sorbent (CaO) [11]. The

environmental impact study is only concerned with substances that cross the

boundary to and from the environment.

4.2. Life Cycle Inventory

The life cycle inventory (LCI) is shown in Table 3. It shows the inputs and outputs

to the PC power plant and CCL system. The increase in electricity output is due to

the secondary steam cycle in the CCL process that utilizes the excess heat. The

negative numbers for SO2 and CO2 indicates the amount of substance removed by

the CCL.

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Table 3: LCI HCPP with CCL

  Component Units PC Plant

without

Capture

CCL

Plant

PC Plant

with CCL

 

 Inputs

 

 

Coal kg/s 59.18 52.644 111.824

Air kg/s 748.7 524.890 1273.590

Water kg/s 277.8 0.000 277.800

CaCO3 kg/s 3.72 55.556 59.276

Wastes Nitrogen, N2 kg/s 629.661 398.361 1028.022

Sulphur dioxide, SO2 kg/s 0.090 -0.089 0.001

Carbon Dioxide, CO2 kg/s 140.426 -112.480 27.945

Oxygen, O2 kg/s 66.788 0.000 66.788

Water, H2O kg/s 64.354 0.000 64.354

Coal Ash kg/s 8.007 9.306 17.313

CaCO3 kg/s 1.860 1.745 3.605

CaO kg/s 0.000 25.397 25.397

CaSO4 kg/s 1.860 2.326 4.186

Outputs Gross Electrical

Power

MWe 623 641 1264

Net Electrical Power MWe 588 436 1024

CO2 for Processing kg/s 0 260.344 260.344

4.3. Impact Assessment

The impact assessment was carried out using the SimaPro v8.3 software. In the life

cycle impact assessment (LCIA) the results are sorted and assigned to the various

impact categories. This is known as classification. The relationship between an

environmental event and its potential effect is determined via a cause-effect

pathway. There are two stages in the pathway; endpoint and midpoint. Endpoint

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methods look at the environmental impacts at the end of the cause-effect pathway,

while the midpoint method does the same at an earlier point in the pathway. Figure

3 shows the midpoint results for the LCA and Figure 4 the endpoint results.

The endpoint analysis indicates that generating electricity has a lower

environmental impact with the employment of CCL as a de-carbonization tool then

without CCL. The damage assessment results indicate a 60% and 68% reduction in

potential impact for the human health and ecosystems indicators respectively. This

is achieved via a 9% increase in the resource indicator.

Figure 3 Comparing PC Plant without/or with CCL; Method: ReCiPe Midpoint (H) V1.13 / Europe ReCiPe H/A / Characterisation

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Figure 4 Comparing PC Plant without/or with CCL; Method: ReCiPe Endpoint (H) V1.13 / Europe ReCiPe H/A / Damage assessment

The midpoint analysis indicates that some impact categories are lowered by the

integration of CCL and others are raised. This is to be expected as the CCL plant

consumes resources to function. An increase use of resource will have an

environmental impact. However, this must be balanced against a 72% reduction in

the climate change impact category. Impact categories that were reduced by the

retrofit of the CCL technology are those that are normally affected by the flue gas

emissions; climate change, terrestrial acidification, particulate matter formation

and natural land transformation.

Overall, the results indicate that the power plant with CCL has a lower

environmental burden than the base hard coal power plant. The increased resource

use be justified by the reduction in the climate change impact.

5. Conclusions

A techno-economic analysis was performed using the ECLIPSE software to

estimate the increased capital and O&M costs of integrating CCL into a PC power

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plant. In this study, the amount of CO2 avoided is 771.9 g/kWh. In terms of

economics, the reference case has a specific capital investment of €1540 per kWe

(net) and the capture case €1861 per kWe (net). The CO2 capture cost and CO2

avoidance cost relative to the corresponding reference plant were €15.4/t CO2

captured and €20.2/t CO2 avoided, respectively.

Using SimaPro software an LCA analysis was performed to determine the

environmental impact of the CCL technology and HCPP. The endpoint analysis

indicates a reduction of 60% and 68% in the human health and ecosystem impacts

with a 9% increase in the resource impact. While some impacts increase, others

decrease in the midpoint analysis. However, the climate change impact is reduced

by 72% with CCL carbon capture.

Acknowledgements

This research work was carried out as part of the FP7 project SCARLET (Scale-up

of Calcium Carbonate Looping Technology for Efficient CO2 Capture from Power

and Industrial Plants) funded by the European Union (GA608578).

(http://www.project-scarlet.eu/.)

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