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Stationary point sources of CO2

A stationary point source of CO2 is any source that is a single localized emitter, such as fossil fuel power plants, oil refineries, industrial process plants and other heavy industrial sources. Stationary point sources can be distinguished from mobile sources, such as automobiles, ships, aircraft and other non-stationary sources.

In theory, all point sources of CO2 may be captured and stored, but current technology suggests that capturing and storing CO2 from mobile sources would be significantly less practical than simply changing to a renewable or zero emission fuel.

Economy of scale also makes capture and storage of CO2 more practical and cost efficient when the source of emission is relatively large. However, introduction and maturation of new technology better suited for small scale emissions (such as membrane technology), and development of distributed pipeline systems for CO2 transport may make CCS viable also for small, localized emissions, particularly where a large number of smaller sources are clustered within a limited geographical area. 

While there are millions of stationary point sources of CO2 in the world, total emissions are dominated by a limited number of large point sources. A survey conducted by IEA showed that out of more than 14 thousand identified emission sources, the 7500 largest of these accounted for 99 percent of the total emissions, with the top 25 percent of this fraction accounting for 85 percent of the emissions. (IEA GHG, 2000)

Contents

1. Profile of worldwide large stationary sources of CO2

2. Fossil fuel power plants

3. Industrial sources

4. Alternative energy carriers and CO2 source implications

5. Geographical relationship between sources and storage opportunities

 

Profile of worldwide large stationary sources of CO2

The power and industry sectors combined account for about 60 percent of total global CO2 emissions. While future projections indicate that this share will decline, these sectors will still account for around 50 percent of all CO2 emissions 2050 (IEA, 2008). Coal is currently the dominant fuel in the power sector, accounting for 38% of electricity generated in 2000, with hydro power accounting for 17.5%, natural gas for 17.3%, nuclear for 16.8%, oil for 9.8% and other renewables for 1.6%. Coal is projected to still be dominant fuel for power generation in 2020, whilst natural gas generation will surpass hydro to be the second largest.

Fuel selection in the industrial sector is largely sector-specific, with coal and coke being the fuel of choice in blast furnace steel production and oil and gas the dominate fuel in refining and the chemical sectors. Globally, biomass is not a significant fuel source in the the large manufacturing industries, but biomass use can  be significant in certain regions, like Brazil and Scandinavia (IPCC, 2005).

Apart from combustion, large scale industrial emissions of CO2 can be found in various industrial processes, including petrochemical processes, carbon reduction in the production metal ores, calcination of limestone in cement production and biomass fermentation (IPCC, 2005).

The following table provides a profile of global CO2 emissions and flue gas properties of selected large stationary sources in the power and industry sectors:

 

Process CO2 concentration
in gas stream %
by vol.
Pressure of gas stream
(MPa)
CO2 partial pressure
(MPa)
% of total CO2
emissions
Average emissions/
source
(MtCO2 per source)
CO2 from fossil
fuels or minerals
 



 
 Power  

 
   Coal boiler
12 to 14
0.1
0.012 - 0.014
56.69
3.94
   Natural gas turbine
 3 to 4
0.1
0.003 - 0.004
 5.68 0.77
   Natural gas boiler
 7 to 10
0.1
0.007 - 0.010
 5.62 1.01
   Fuel oil boiler
 8 0.1
0.008
NA 1.27
   IGCC
12 to 14
0.1
0.012 - 0.014
NA
NA
   Other fuels  NA NA
NA
 0.45 0.77
Natural gas sweetening  

 
  2 - 65
0.9 - 8
0.05 - 4.4
 0.37 NA
Cement production  

 
   14 -33
0.1
0.014 -0.033
 6.97 0.79
Refineries  

 
   3 to 13
NA
NA
 5.97 1.25
Iron and steel industry  

 
   Integrated steel mills  15 0.1
0.015
 4.71 3.50
   Other processes  NA NA
NA
 0.12 0.17
Petrochemical industry  

 
   Ethylene  8 2.5
0.2
 1.93 1.08
   Ammonia production
18
2.8
0.5
 0.84 0.58
   Hydrogen production
15 - 20
2.2 - 2.7
0.3 - 0.5
NA
NA
   Methanol production
10
2.7
0.27
NA
NA
Other sources  

 
   Non-specified  NA NA
NA
 0.25 0.37





1.76

Table 1: Profile of worldwide large stationary sources of CO2 (Source: IPCC, 2005)


Several factors determine the suitability of a particular type of emission for CO2 capture. Overall size of the emission is, as mentioned, a significant factor. At refineries and other large industrial complexes emissions may come from multiple exhaust stacks, adding challenges in CCS integration. Properties of the flue gas streams are also significant factors. Higher concentrations of CO2 in the flue and higher partial pressure of CO2 generally makes capture easier and more cost efficient (IPCC, 2005).

Fossil fuel power plants

Main articles: How does a gas power plant work, How does a coal power plant work

Representation of a typical combined cycle natural gas power plant

Representation of a typical combined cycle natural gas power plant. Source: Siemens.

35% of global fossil energy consumption comes from electric power generation. This accounts for 26% of total global CO2 emissions. 73% of fossil fuel power generation comes from coal, 19% from natural gas and 8% from oil (IEA, 2008). Traditional thermal power plants, using single cycle steam turbine technology,  is the dominant power plant design in the world, but gas turbine designs using natural gas, or sometimes fuel oil, have a wide use in niche operations (such as peak power generation or mobile generator units), and combined cycle gas turbine power plants are becoming a more prominent alternative in areas of the world where natural gas is a relatively abundant resource. Natural gas is expected to account for a larger fraction of total power generation in the future (IEA, 2008).

In a traditional thermal power plant, coal, gas, oil or other fuels are used to boil water to generate steam. The steam is then superheated to increase energy, and then expanded through a steam turbine, which generates rotary work that can be converted to electric power in a generator. A single cycle gas turbine works by compressing air, and then heating it to very high temperature using gas or diffused oil. The hot air is expanded through a turbine, creating work to drive the compressor, and excess work that can be used to drive an electric generator.

Combined cycle power plants (CCPP) use both the above cycles by first expanding hot air through a gas turbine, and then using the excess heat of the exhaust to generate steam that drives a steam turbine. The advantage of this is a higher overall efficiency in the unit, reaching as high as 58%.

Combined cycle power plants require gas or liquid fuels, but coal and other solid fuels may be used if they are first transformed to syngas, a mixture of hydrogen and CO gas, through a process called gasification. Designs have been developed where gasification is integrated in the power plant design, called Integrated Gasification Combined Cycle (IGCC) plants. In the future this design may be used to increase efficiency in coal power plants. An added advantage to this design is that it facilitates pre-combustion CO2 capture.

Industrial sources

A number of different industrial processes produce CO2 as a waste gas. Globally, the largest industrial process emission source is cement production. Cement is produced by heating calcium carbonates (CaCO3) , such as chalk or limestone, decomposing them into lime (CaO) and CO2. Nearly 900 kg of CO2 is released for every 1000 kg of cement produced.

Refineries are usually large industrial complexes where emissions come from a large number of different sources. Gas-fired process heaters and steam boilers are usually the largest emitters of CO2, but emissions also include process waste gas from the production of hydrogen used in reforming heavy hydrocarbons and some process waste emissions from other processes.

In the primary steel-making process, melted iron ore (iron oxide, Fe2O3) is deoxidized by reacting it with CO gas. This produces pure iron and CO2. Additional CO2 is released from combustion of fossil fuels for heating. Typical concentrations of CO2 in the waste gas stream is about 20%. There are several ways of achieving high CO2 capture rates from steel mills.

Many petrochemical industrial processes have potential for CO2 capture. The production ethylene and ammonia are large sources of CO2 emissions. The ammonia process is particularly suited for CO2 capture, as the process produces a waste gas stream of almost pure CO2. CO2 produced in this way is currently in use in several EOR projects in the United States.

Alternative transport fuels and CCS

Alternative energy carriers in the transport sector may have implications for the role of CCS as a future climate change mitigation measure. The combustion of fossil energy carriers in the transport sector account for about 14% of global greenhouse gas emissions (IEA, 2008). There is no practical way of capturing and storing these emissions directly.

However, if a major migration happens from fossil fuels to electricity or hydrogen, CCS may have a role in reducing transport emissions. In the case of electricity, the positive climate effect of switching from fossil fuels to battery electricity depends on the source of the energy used. If the power comes from renewable energy or nuclear energy, CO2 emissions are removed. Fossil energy is unlikely to be replaced by non-fossil alternatives within a short time-span. Increased demand for electricity to power vehicles will therefore likely also increase demand for electricity from fossil power sources. Capturing CO2 from fossil fuel power plants may therefore serve as an indirect measure to cut emissions from the transport sector.

If hydrogen can be successfully established in the market as a transport fuel, a consequence could be that more hydrogen is produced by decarbonization of fossil fuels. This is currently the most economic way of producing hydrogen on a large scale, and at least in parts of the world it is likely to remain less costly than renewable production also in the future. If a large portion of the hydrogen used in a developed hydrogen economy comes from fossil fuel decarbonization, CCS is a necessary prerequisite to achieve large greenhouse gas emission reductions. 

Geographical distribution and capacity

Emission sources

Regional emission clusters with a 300 km buffer relative to world geological storage prospectivity (IPCC, 2005)

Not all sedimentary basins are suitable for CO2 storage; some are too shallow and others are dominated by rocks with low permeability or poor confining characteristics. Basins suitable for CO2 storage have characteristics such as thick accumulations of sediments, permeable rock formations saturated with saline water (saline formations), extensive covers of low porosity rocks (acting as seals) and structural simplicity. 

The IPCC special report on CCS estimates the worldwide technical potential for storage in geological formations to be at least 2,000 GtCO2. This is only the lower bound, and the IPCC believes the capacity may be many times higher, but the upper limit estimates are uncertain due to insufficient charting and disagreements on methodology. The capacity for storing CO2 in depleted petroleum reservoirs is known with much greater certainty.

 

Storage option Global capacity, lowest estimate (Gt CO2) Global capaity, highest estimate (Gt CO2)
Depleted oil and gas reservoirs 675* 900*
Deep saline aquifers 1000 Uncertain, but possibly 10,000
Deep unmineable coal seams 3-15 200

* These estimates may increase by 25 per cent, when undiscovered oil and gas fields are included (IPCC 2005b).

 

Potential storage sites are likely to be broadly distributed in many of the world’s sedimentary basins, located in the same regions as many of the world’s greatest emission sources.


References

IEA GHG, 2000: Greenhouse Gas Emissions from Major Industrial Sources III

IEA, 2008: World Energy Outlook 2008

IPCC, 2005: IPCC Special Report on Carbon Dioxide Capture and Storage

 

 





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