Scholarly article on topic 'Capture of CO2 from medium-scale emission sources'

Capture of CO2 from medium-scale emission sources Academic research paper on "Environmental engineering"

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Energy Procedia
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{"CO2 capture" / "Medium-scale combustion" / "Coal boiler" / "Oxygen conducting membranes"}

Abstract of research paper on Environmental engineering, author of scientific article — Chris Hendriks, Erika de Visser, Daan Jansen, Michiel Carbo, Gerrit Jan Ruijg, et al.

Abstract Until now, the work done on capture and storage of CO2 has mainly focused on capture and storage of CO2 from fossil fuel fired power plants and other large point sources. Although medium-scale sources of CO2 account for a smaller proportion, their contribution to global CO2 emissions is still substantial and in the range of 10–15% of total global energy related CO2 emissions. The study identifies possible combinations of capture technologies and medium scale combustion installations and assesses these in terms of potential and costs. Although medium-scale capture of CO2 is expected to be more expensive than large-scale capture, it may nevertheless be competitive with alternative methods of abating CO2 from medium-scale sources in some circumstances.

Academic research paper on topic "Capture of CO2 from medium-scale emission sources"

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Energy Procedía

Energy Procedía 1 (2009) 1 4097-1504


Capture of CO2 from Medium-scale Emission Sources

Chris Hendriksa*, Erika de Vissera Daan Jansenb, Michiel Carbob, Gerrit Jan Ruijgb, John


Until now, the work done on capture and storage of CO2 has mainly focused on capture and storage of CO2 from fossil fuel fired power plants and other large point sources. Although medium-scale sources of CO2 account for a smaller proportion, their contribution to global CO2 emissions is still substantial and in the range of 10 - 15% of total global energy related CO2 emissions. The study identifies possible combinations of capture technologies and medium scale combustion installations and assesses these in terms of potential and costs. Although medium-scale capture of CO2 is expected to be more expensive than large-scale capture, it may nevertheless be competitive with alternative methods of abating CO2 from medium-scale sources in some circumstances.

© 2009 Elsevier Ltd. All rights reserved.

Keywords: CO2 capture, medium-scale combustion, coal boiler, oxygen conducting membranes

1. Introduction

The main focus of existing work on CO2 capture has been on capture and storage of CO2 from fossil fuel fired plants power plants and other large point sources. Usually, CO2 capture from medium scale sources has not received much attention, because of expected high costs and concerns about the safety of CO2 transportation from populated areas where medium scale sources are often located. Although these medium-scale sources of CO2 account for a smaller contribution to global CO2 emissions compared to large point sources their proportion is still substantial (about 10-15%). In order to comply with (inter)national targets, carbon capture and storage from these small and medium scale sources might be necessary in the future.

Ecofys and the Energy research Centre of the Netherlands (ECN) therefore carried out this study for the IEA Greenhouse Gas R&D Programme to identify suitable combinations of medium scale sources and capture

aEcofys,P.O. Box 8408, Utrecht NL-3503 RK, the Netherlands bECN, P.O. Box 1, Petten NL-1755 ZG, the Netherlands cIEA, Greenhouse Gas R&D Programme, Stoke Orchard, Cheltenham GL52 7RP, United Kingdom


* Corresponding author. Tel.: +31(0)30 -662- 3393; fax: +31(0)30-280-8301 E-mail address:


technologies in terms of applicability, costs and emission reduction potential,. This conference paper is based on the content of the report 'CO2 capture from medium scale combustion installations' [1]. The second part of the report covers the case study on oxyfuel coal boilers with oxygen conducting membranes and is included in another conference paper by Carbo et al. (2008) [2].

2. Scope

For the purpose of this study a medium-scale installation is defined as a combustion installation with size between 1 and 100 MWth, which is at the scale of district heating plants, industrial installations and large commercial buildings. The corresponding amount of CO2 produced depends on the size of the installation and the type of fuel used. Because of higher carbon content a 100 MWth coal-fired installation produces about 250 ktonne CO2 per year whereas a 100 MWth gas-fired installation produces only 150 ktonne CO2 per year. This equals to 33 and 20 kg/h assuming a load factor of 7500 hours.

3. Methodology

The study starts with the characterization of typical medium-scale combustion installations and is followed by a market analysis of these technologies. The characterization focuses on aspects such as typical size, fuel use, efficiency and flue gas characteristics of the combustion installations. The market analysis gives an indication of the current and future market for carbon dioxide equipment and the emission reduction potential that can be obtained by applying the different capture technologies. It concentrates on the current most important medium-sized power and heat generating installations: reciprocating engines, gas turbines and boilers. The study reviews publicly available information on the market size of medium scale sources of CO2, with emphasis on the USA, the Netherlands and China.

The second part of this study involves the technical characterization of capture technologies for medium-scale combustion plants. A long list is created with potential feasible combinations of combustion installation with capture technology. Six cases that represent a combination of technology, fuel and capture technology are selected for in-depth analysis on the technical aspects, the potential for application and an indication of the energy requirements and cost performance.

4. Characterization and market analysis of medium scale combustion installations

A commonly used categorization for power and heat production units, which is also used throughout this study, is furnaces (including boilers), steam turbines, reciprocating engines, large gas turbines, micro gas turbines and fuel cells. Typically, these medium-sized installations are placed close to the location where the energy is used (distributed), for example at industrial sites.

Devices that produce only heat are furnaces. They either supply heat to the processes directly or indirectly through the generation of hot water or steam (then called boilers). Furnaces which supply heat directly are used in the iron and steel industry, ceramic industry, cement and limestone industry and glass industry and furnaces which supply heat indirectly are used in a wide range of other applications. The scale of furnaces covers a wide range -from small domestic heaters (smaller than 30 kWth) to large boilers for coal-fired plants (larger than 1000 MWth). Steam from boilers is either used for industrial purposes or used in steam cycles to produce electricity and/or heat.

The power generation technologies identified are steam turbines, reciprocating engines, gas turbines and fuel cells.

Table I summarizes the most important characteristics of the distributed power generation technologies. In general, steam turbines are optimized to heat production and generate electricity as a by-product. The capacity of steam turbines covers the largest range from 50 kWe to several hundreds of MWe for large utility power plants, followed by gas turbines that are found in the 0.5 to 50 MWe class. Fuel cells are included because of their expected future importance in electricity generation and their anticipated potential for economically capturing CO2.

Table I Characteristics of power generation technologies

Steam turbine Reciprocating engine Gas turbine Fuel cell

Large gas turbine Micro turbine

Applicable Institutional buildings, Commercial buildings, Large commercial, Commercial Residential,

market sectors Industry, Waste fuels Light industry, Grid, Industry, Grid, Waste buildings, Light Commercial buildings,

Waste fuels fuels industry, Waste fuels Light industry

Technology Commercial Commercial Commercial Early entry Early entry,

status development

Size (MWe) 0.5 - 100 0.05- 20 0.5 - 50 0.03 - 0.25 0.005 - 2

Electrical <10% - 40% 20% - 30% 40% 25% 25% - 35% (PEMFC)

efficiency 35% - 43% (SOFC) > 40% (PAFC) 45% - 47% (MCFC)

Fuels All Natural gas, biogas, liquid fuels Natural gas, biogas, distillate oil Natural gas, biogas Hydrogen, natural gas

Uses for heat LP and HP steam, Hot water, LP-steam, Direct heat, hot water, Direct heat, hot Hot water, LP steam

recovery district heating district heating LP and HP steam, district heating water, LP steam

Typical CO2 8-15% (boiler) 9- 14% 3-4% 2-4% 8-10%

flue gas concentration 3-4% (gas turbine HRSG)

□ # of boilers □ Average capacity

Food industry Paper and pulp industry

Primary metals Other Non-

manufacturing manufacturing industry

Figure I Number of boilers in industry (red bar) and average capacity of the boilers (blue bar) in the United States [3]

Of the above discussed technologies, boilers, reciprocating engines and gas turbines are represented well in the medium-scale segment. A 2005 US market survey on industrial and commercial boilers shows that 97% of the industrial boilers has capacities below 73 MWth (250 MMBtu/h) [3]. The highest number of both industrial and commercial boilers is found in the capacity range below 3 MWth. The most important steam-intensive industries are pulp and paper, chemical industry, refineries and primary metals. These industries have installed 82% of the total industrial boiler capacity in the United States. The average capacity of the boilers in industry is highest in refineries (42 MWth) and the paper and pulp industry (32 MWth), smaller capacities are found in primary metals (10 MWth) and the chemical industry (10 MWth) [3]. Figure I shows the average capacity in the major steam intensive industries in the United States.

Diesel and gas-fired reciprocating engines are dominant in the segment of capacities below 3.5 MWe. Gas turbines are the dominant technology above 20 MWe. The mid-range is equally shared between the technologies, although we see a trend that smaller gas turbines become more available in the low capacity ranges. The market for reciprocating engines expands rapidly. Most reciprocating engines are found in the 1.0-2.0 MWe class, representing 22% of the total sales of gas engine and turbines in 2004 (see Figure II). Over 50% of the total gas turbine and engine capacity ordered in 2004 (26 GWe) is to be found in the capacity range 120 MWe and above [4]. Medium-scale gas turbines from 1 to 40 MWe are 15% of the total ordered gas turbine capacity in 2004. An example from the United States shows that the largest capacity of gas turbines with sizes below 40 MWe is installed in the oil recovery and chemical industry [5].

Fuel cells, currently in the pilot phase, are potentially well suited for distributed power generation and CHP markets in the future.

□ gas turbine □ gas engine

- ■ 1 - -

1.0 - 2.0 2.0 - 3.5 3.5 - 5.0 5.0 - 7.5 7.5 - 10 10 - 15 15 - 20 20 - 30 30 - 60 60 - 120 120 - 180 > 180

Capacity (MW)

Figure II Share of ordered gas engines and turbines in 2004 [4]

5. Medium scale capture technologies

Among the CO2 capture methods for medium-scale combustion installations are post-combustion, pre-combustion and oxy-fuel conversion technologies. The capture processes are further classified according to the

separation technology used - liquid phase absorption, solid absorption, membranes and cryogenic absorption (see Table II).

Table II Overview of processes for power generation with CO2 capture

Separation technology Capture method

Post-combustion decarbonisation Pre-combustion decarbonisation Oxy-fuel conversion

(O2/N2- separation) (C O2/H2-s eparation) (O2/N2-separation)

Liquid phase absorption • Mono Ethanol Amine (MEA) absorber • Selexol CO2 absorber

Solid sorption • Flue gas CO2 adsorption • Pressure Swing Absoprtion (PSA) or • Temperature Swing Adsorption (TSA) • Sorption enhanced reforming • Sorption enhanced shift • In situ CO2 separation • PSA for CO2 separation • Chemical Looping Combustion (CLC)

Membranes • Membrane assisted absorption • Membrane reformer • Shift membrane reactor • OCM combustor (AZEP) • SOFC (GT) with afterburner • Boiler with integrated OCM • Membrane oxygen production

Cryogenic • Oxyfuel conversion with CO2 recycle • Oxy fuel boiler • Matiant cycle • Water cycle

5.1. Furnaces and boilers

For coal-fired furnaces and boilers oxyfuel combustion with cryogenic air separation is a suitable capture option. For natural gas and oil fired furnaces and boilers, post-combustion MEA, PSA or TSA seems to be the more appropriate technology. Pre-combustion and oxyfuel would require relatively high oxygen demand for the capture of one tonne of CO2, because oil and natural gas contain relatively high ratios of the element hydrogen. This drawback might be partly circumvented by using an Oxygen Conducting Membrane (OCM) to supply the oxygen.

5.2. Reciprocating engines

Reciprocating engines can be equipped with post-combustion technologies without any major technical problems foreseen. It is assumed that sufficiently low concentrations of SOx and NO2 can be reached to avoid MEA degradation. Also all pre-combustion technologies presented in Table II are applicable to reciprocating engines. The fuel processor can be a natural gas reformer as well as a coal gasifier. However, the latter can suffer from economy of scale problems, especially concerning the cleaning of the fuel gas. Oxyfuel capture is applicable to reciprocating engines, but is less preferred in case of natural gas-fuelled applications. For solid fuels, gasifiers with pre-combustion or oxyfuel combustion, are the preferred options e.g. the combination of a coal gasifier with a reciprocating engine.

5.3. Gas turbines

In principle, all types of carbon capture technologies can be applied to gas turbines. From all studies published so far it can be concluded that SOx and NOx levels are sufficiently low for the application of MEA technology. Gas

turbines can also easily be modified for the use of hydrogen as a fuel, which makes gas turbines suitable for pre-combustion technologies. In case of oxyfuel with oxygen from cryogenic distillation or membrane separation, a recycle of cooled flue gas is necessary, to prevent high turbine inlet temperatures. This flue gas has high CO2 concentrations. The use of CO2 instead of air as the working fluid for the gas turbine requires drastic modifications of the gas turbine. These modifications are necessary due to the difference in physical and chemical properties between air and CO2 and require significant massive upfront R&D investments.

5.4. Solid Oxide Fuel Cells (SOFC)

In Solid Oxide Fuel Cells the fuel remains completely separated from the air. Only oxygen passes through the electrolyte, which makes the SOFC in principle an oxyfuel option. The maximum fuel utilisation however is about 85%. After-combustion will be necessary to avoid large energy losses. If some form of oxyfuel combustion is applied here, e.g. by supplying liquid oxygen from a storage facility, or through the use of an OCM, CO2 can be captured by cooling with water knock-out.

6. Selection

Based on all possible combinations of combustion technologies with capture technologies a short list of six combinations has been composed for in-depth evaluation of potential carbon dioxide emission reductions and its costs. The cases cover a broad range of options, whilst complying with reasonable economic prospects and potential future markets. The six selected combinations of combustion installation and capture technology for the short list are:

• 1.5 MWe diesel engine with membrane assisted liquid absorption

• 1.5 MWe gas engine with membrane assisted liquid absorption

• 5 MWe gas turbine with pre-combustion PSA capture

• 50 MWth oxyfuel coal boiler with oxygen conducting membranes

• 5 MWth oxyfuel natural gas boiler with oxygen conducting membranes

• 500 kWe natural gas SOFC with oxygen conducting membrane afterburner

7. Results

For all selected options a first estimate has been made of the CO2 avoidance costs (€/tCO2) and the potential for application (Mt CO2). In general, CO2 capture from smaller combustion installations results in higher specific energy consumption and higher specific costs.

7.1. Cost

The estimated CO2 avoidance cost including compression range between 27 and 112 € per tonne of CO2 at typical operational hours for the six selected combinations (marked with red bullets in Figure III). The highest costs are estimated for post-combustion applied to relatively small reciprocating engines (both diesel and gas). Coal-fired boilers offer the cheapest option in terms of cost per tonne CO2 avoided. Even if fuel prices would double or triple the economic advantage of the coal boiler is maintained. This option is currently not commercially applicable, because the OCM technology is still in an early stage of development. Pre-combustion capture in combination with industrial gas turbines is expected to be promising within the near future. The natural gas-fired SOFC offers an inexpensive option with respect to the costs per tonne of CO2 avoided, namely 9 € per tonne CO2 for typical load hours. Currently, there is no SOFC market and it is expected that a substantial market share can develop only within 10 to 20 years. If the SOFC market develops and fuel cell capital expenditures reduce it is very likely that this technology will offer an economically viable method to capture CO2.

Under certain circumstances CO2 does not need to be compressed directly after capture but might be collected from different medium and small scale capture plants in pipelines operating at low or even sub-atmospheric pressure. Compression will then take place at nodes in the collection grid. When compression is not included the CO2 avoidance costs are 9 to 92 € per tonne of CO2, with the lowest avoidance cost for natural gas-fuelled SOFC.

Table III Costs per tonne of CO2 avoided at various fuel prices

Fuel price [€/GJ] 2 4 6 8 CO2 emission [t/h] Operation Time [h]

Diesel Engine 1.5 MWe 106 108 110 112 0.9 4000

Gas Engine 1.5 MWe 109 112 114 117 0.8 4000

Gas turbine 5 MWe 42 47 53 58 3.4 6000

Coal-frred boiler @18bar, 50 MW, 25 27 29 32 20.3 8000

NG boiler @1bar, 5 MWth 107 108 110 111 1.1 2000

Natural Gas SOFC, 500 kWe 33 34 36 37 0.2 6000

■o a ■o

o _ 13 ä

a O c " c

m m o O

Diesel engine Coal boiler

Gas engine Natural gas boiler

Gas turbine Natural gas SOFC

160 140 120 100 80 60 40 20 0

4000 6000

Full load hours (h/y)

Figure III Costs per tonne of CO2 avoided with compression (fuel price is set to 4 €/GJ). Avoidance costs for typical operation times

of the technology are marked with a red bullet

7.2. Potential for application

For all cases introduced we estimated the potential for application in terms of CO2 emissions in Mt per year. Based on global market statistics of reciprocating engines sold in 2004 the total emissions of CO2 for the 1-20 MWe capacity class are estimated at 600 - 700 Mt per year. For gas turbines in the capacity range of 1 to 60 MWe, the global CO2 emissions are estimated at 350 - 400 Mt per year.

Estimation of global CO2 emissions (excluding China) from medium scale coal-fired boilers (with capacities below 75 MWth) is based on 2002 US data from [3]. Carbon dioxide emissions from US industrial and commercial medium scale coal boilers have been calculated at 80 Mt, which is only 1.5% of the total US energy related CO2. When we assume the US situation as typical for the rest of the world (excluding China) global CO2 emissions from medium scale coal fired boilers amount to 300 Mt. A rough estimate of global CO2 emissions from medium scale coal fired boilers including China is about 1500 Mt. For China, it is estimated that 480,000 coal-fired boilers in the industrial and residential sector consume about 12 EJ annually and emit about 1200 Mt CO2.

Summed, approximately between 10 and 15% of the worldwide energy related CO2 emissions can be attributed to medium-size installations. A subdivision of emission and shares to the various distinguished types of combustion installations is presented in Figure IV.

/ 100% = 27 GtCO2 "6%/ / \ on/ 3% □ Diesel engines □ Gas engines

87% 13% □ Gas turbines

1% □ Coal-fired boilers

□ Natural Gas boilers

World wide emissions Medium scale emissions

Figure IV Overview of CO2 emission volumes of medium scale combustion installations

8. Discussion and conclusion

The main focus of capture of carbon dioxide has been on large combustion plants, notably fossil fuel power plants. However, to achieve reductions in CO2 emissions that are expected to be necessary, substantial reductions in emissions from medium scale sources may be required. This study shows that a wide range of capture options is in principle applicable for medium scale combustion installations. Although not commercially available at the moment specific combinations of prime movers with capture equipment have good future prospects. For coal-fired boilers with integrated capture using oxygen conducting membranes for example CO2 avoidance cost of between 25 and 32 €/tCO2 are calculated. The proposed technology, however, still needs considerable development and full-scale application can not be expected within the next 10 to 15 years.

Comparable systems for natural gas fired boilers do not look favourable. This is mainly due to the higher hydrogen content of the natural gas compared to coal. Typical capture costs are estimated at above 100 €/tCO2.

Solid oxide fuel cells offer also an attractive low-costs emission reduction. However, it is not expected that these SOFC will obtain a substantial market share within the next 20 years.


[1] IEA Greenhouse Gas R&D Programme GHG (IEA GHG) (2007) CO2 capture from medium scale combustion installations, 2007/7, July

[2] Carbo, M.C., D. Jansena, C. Hendriks, E. de Visser, Gerrit Jan Ruijg, J. Davison (2008) Opportunities for CO2 Capture through Oxygen

Conducting Membranes at Medium-scale Oxyfuel Coal Boilers, paper prepared for the GHGT-9.

[3] ORNL - Oak Ridge National Laboratory (2005) Characterization of the United States Industrial Commercial Boiler Population, Energy and

Environmental Analysis, Inc., Virginia, May 2005.

[4] Diesel & Gas Turbine Worldwide (2005) Power Generation Order Survey, 2005

[5] NREL - National Renewable Energy Laboratory (2003) Gas-fired distributed energy resource technology characterizations, NREL/TP-620-34783, November 2003.