Co2 Capture

Anthropogenic carbon dioxide emissions arise mainly from combustion of fossil fuels (and biomass) in the power generation, industrial, buildings and transport sectors. CO2 is also emitted from non-combustion sources in certain industrial processes such as cement manufacture, natural gas processing and hydrogen production.

CO2 capture produces a concentrated stream of CO2 at high pressure that can be transported to a storage site and stored. In these Guidelines, the systems boundary for capture includes compression and any dehydration or other conditioning of the CO2 that takes place before transportation.

Electric power plants and other large industrial facilities are the primary candidates for CO2 capture, although it is the high purity streams of CO2 separated from natural gas in the gas processing industry that have been captured and stored to date. Available technology is generally deployed in a way that captures around 85-95 percent of the CO2 processed in a capture plant IPCC (2005). Figure 5.2, taken from the SRCCS provides an overview of the relevant processes. The main techniques are briefly described below. Further detail is available in Chapter 3 of the SRCCS:

• Post-combustion capture: CO2 can be separated from the flue gases of the combustion plant or from natural gas streams and fed into a compression and dehydration unit to deliver a relatively clean and dry CO2 stream to a transportation system. These systems normally use a liquid solvent to capture the CO2.

• Pre-combustion capture: This involves reacting a fuel with oxygen or air, and/or steam to produce a 'synthesis gas' or 'fuel gas' composed mainly of carbon monoxide and hydrogen. The carbon monoxide is reacted with steam in a catalytic reactor, called a shift converter, to give CO2 and more hydrogen. CO2 is then separated from the gas mixture, usually by a physical or chemical absorption process, resulting in a hydrogen-rich fuel which can be used in many applications, such as boilers, furnaces, gas turbines and fuel cells. This technology is widely used in hydrogen production, which is used mainly for ammonia and fertilizer manufacture, and in petroleum refining operations. Guidance on how to estimate and report emissions from this process is provided in Chapter 2, section 2.3.4 of this Volume.

• Oxy-fuel capture: In oxy-fuel combustion, nearly pure oxygen is used for combustion instead of air, resulting in a flue gas that is mainly CO2 and H2O. This flue gas stream can directly be fed into a CO2 compression and dehydration unit. This technology is at the demonstration stage. Guidance on how to estimate and report emissions from this process is provided in Chapter 2, section 2.3.4 of this volume.

Table 5.1 Source categories for ccs

1

C

Carbon dioxide Transport and Storage

Carbon dioxide (CO2) capture and storage (CCS) involves the capture of CO2, its transport to a storage location and its long-term isolation from the atmosphere. Emissions associated with CO2 transport, injection and storage are covered under category 1C. Emissions (and reductions) associated with CO2 capture should be reported under the IPCC sector in which capture takes place (e.g. Stationary Combustion or Industrial Activities).

1

C

1

Transport of CO2

Fugitive emissions from the systems used to transport captured CO2 from the source to the injection site. These emissions may comprise fugitive losses due to equipment leaks, venting and releases due to pipeline ruptures or other accidental releases (e.g. temporary storage).

1

C

1

a

Pipelines

Fugitive emissions from the pipeline system used to transport CO2 to the injection site.

1

C

1

b

Ships

Fugitive emissions from the ships used to transport CO2 to the injection site.

1

C

1

c

Other (please specify)

Fugitive emissions from other systems used to transport CO2 to the injection site and temporary storage.

1

C

2

Injection and Storage

Fugitive emissions from activities and equipment at the injection site and those from the end containment once the CO2 is placed in storage.

1

C

2

a

Injection

Fugitive emissions from activities and equipment at the injection site.

1

C

2

b

Storage

Fugitive emissions from the end containment once the CO2 is placed in storage.

1

C

3

Other

Any other emissions from CCS not reported elsewhere.

Figure 5.2 CO2 capture systems (After the SRCCS):

Figure 5.2 CO2 capture systems (After the SRCCS):

Factors 102
Raw material Gas, Ammonia, Steel

As already mentioned in a number of industrial processes, chemical reactions lead to the formation of CO2 in quantities and concentrations that allow for direct capture or separation of the CO2 from their off gases, for example: ammonia production, cement manufacture, ethanol manufacture, hydrogen manufacture, iron and steel manufacture, and natural gas processing plant.

The location of guidelines for compiling inventories of emissions from the CO2 capture and compression system depends on the nature of the CO2 source:

• Stationary combustion systems (mainly electric power and heat production plants): Volume 2, Chapter 2, Section 2.3.4.

• Natural gas processing plants: Volume 2, Section 4.2.1.

• Hydrogen production plants: Volume 2, Section 4.2.1.

• Capture from other industrial processes: Volume 3 (IPPU) Chapter 1, Section 1.2.2, and specifically for

(i) Cement manufacture: IPPU Volume, Section 2.2

(ii) Methanol manufacture: IPPU Volume, Section 3.9

(iii) Ammonia production: IPPU Volume, Section 3.2

(iv) Iron and steel manufacture: IPPU Volume section 4.2

Negative emissions may arise from the capture and compression system if CO2 generated by biomass combustion is captured. This is a correct procedure and negative emissions should be reported as such.

Although many of the potential emissions pathways are common to all types of geological storage, some of the emission pathways in enhanced hydrocarbon recovery operations differ from those for geological CO2 storage without enhanced hydrocarbon recovery. In EOR operations, CO2 is injected into the oil reservoir, but a proportion of the amount injected is commonly produced along with oil, hydrocarbon gas and water at the production wells. The CO2-hydrocaibon gas mixture is separated from the crude oil and may be reinjected into the oil reservoir, used as fuel gas on site or sent to a gas processing plant for separation into CO2 and hydrocarbon gas, depending upon its hydrocarbon content. EGR and ECBM processes attempt to avoid CO2 production because it is costly to separate the CO2 from a produced gas mixture. CO2 separated from the hydrocarbon gas may be recycled and re-injected in the EOR operation, or vented; depending on the economics of recycling versus injecting imported CO2. CO2-rich gas is also released from the crude oil storage tanks at the EOR operation. This vapour may be vented, flared or used as fuel gas depending upon its hydrocarbon content. Thus there are possibilities for additional sources of fugitive emissions from the venting of CO2 and the flaring or combustion of CO2-rich hydrocarbon gas, and also from any injected CO2 exported with the incremental hydrocarbons. These emissions along with fugitive emissions from surface operations at EOR, and EGR and ECBM sites (from the injection of CO2, and/or the production, recycling, venting, flaring or combustion of CO2-rich hydrocarbon gas), and including any injected CO2 exported with the incremental hydrocarbons, can be estimated and reported using the higher methods described guidance given in Volume 2 Chapter 4.

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