Carbon Dioxide - Developing oxyfuel capture as a retrofit technology
Backfittable technologies have a number of advantages for carbon abatement at fossil fired power plants, not least of which is that it will probably be necessary to build new power plants before carbon dioxide capture storage is commercially proven. Also, retrofits on existing plants will allow the new technologies to be introduced more quickly, at lower cost and at less risk, while avoiding the planning problems that arise with new build. Oxyfuel combustion appears to be a promising potentially backfittable capture technology, with pilot scale trials and large scale demonstrations planned.
The International Energy Agency (IEA) in its World Energy Outlook 2004 predicts that world primary energy use will grow by 60% during the period from 2002 to 2030, with almost 90% of this growth coming from fossil fuels (see Figure 1). More than 60% of the growth in primary energy demand is from the developing countries, with the resultant carbon dioxide emissions in these countries predicted to overtake those of the OECD countries in the 2020s.
Carbon dioxide emissions from electrical power generation and transport amount to around one-half and one-quarter of the total respectively.
Coal, with more than 200 years of reserves, is, with nuclear fission, an essential bridge to a future of sustainable energy from renewable sources and, potentially, nuclear fusion. Increasing use of gas for power generation, often urged for environmental reasons, would be at the expense of proportionately quicker depletion of the remaining 66 years of reserves.
Against the background of growing demand and the need to cut emissions of carbon dioxide, carbon abatement technologies (CATs) for coal-fired generation are essential. The available technologies include efficiency improvement, biomass co-firing and carbon dioxide capture and permanent underground storage (CCS). If CCS was applied to 800 coal-fired power plants the saving would be 1 billion t carbon/year, one-seventh of the reductions needed by 2050. Reductions of around half this magnitude can be achieved by combining efficiency improvements (-20 to 25%) and biomass co-firing (-20%).
The scale of the problem and the key issue of reducing carbon dioxide emissions in the developing world as well as the developed world whilst energy demand grows rapidly, are now well understood and have led to many national and international programmes on carbon abatement technologies, including CCS.
At the Gleneagles G8 summit in July 2005, the G8 leaders agreed a five point action plan to accelerate the development and commercialisation of CCS technology.
Capture technology options
Mitsui Babcock is particularly interested in the carbon dioxide capture technologies that can be retrofitted to existing plant and plant currently being built (for example in China) as well as being used with new plant.
Two technologies - amine scrubbing and oxyfuel firing - are being explored in many projects around the world and both are realistically expected to be available on the scale required and at an acceptable cost by 2012-15 (see Figures 2 and 3).
Mitsui Babcock has deliberately focused on technologies for carbon abatement of coal-fired generation which are suitable for progressive retrofit to existing plants and plants under construction as well as being suitable for completely new plants. The reasons for this focus are:
- If global targets for CO2 reduction are to be met as well as global needs for energy security, CATs will be needed on existing plant, plants under construction (in the period 2006-15) as well as future plants (from 2015 to 2030). Many new plants will be built or committed before carbon dioxide storage is commercial.
- In developed countries, including the UK, opposition is strong to new plant at the planning stage. Re-use of existing sites is therefore preferred, allowing continuity of employment and maximising use of existing infrastructure (grid connections, coal and ash handling, road and rail links).
- Retrofits allow CATs to be introduced more quickly and at much less cost than new build.
- Retrofits allow innovative technologies to be proven in shorter timescales and at less risk and cost than on complete new plants, making demonstrations more affordable and more valuable within a national CAT development strategy.
Developing oxyfuel firing
Oxyfuel combustion for pulverised coal was demonstrated by Mitsui Babcock (and others) in the European Community sponsored project "Pulverised Coal Combustion System for CO2 Capture" within the JOULE 2 programme.
Testing was undertaken in Mitsui Babcock's 160 kWt clean coal combustion test facility in Renfrew during 1994/5. The test facility (Figure 4) comprises a refractory lined furnace, arranged vertically, with a low NOx burner firing downwards. The furnace exit gases are cooled in a convective tube bank before being recycled or exhausted to atmosphere.
Two coals (UK and Polish) were fired. The tests demonstrated a flue gas high in CO2 can be produced that is amenable to subsequent separation and capture, that the combustion process was stable and sustainable over a wide range of operating conditions (ie flue gas recycle rates from 60% to 90%), and that there was no detrimental impact on the combustion process as a whole. While there is scope for maximising the system performance, there are no technical reasons to prevent the uptake of oxyfuel combustion technology.
It was found that NOx emissions fell with increasing flue gas recycle rate. At higher recycle rates the NOx emission (expressed in terms of mg/MJ) was lower than for air firing. This NOx reduction arises from dilution effects and the reaction of NOx in the recycle gas with hydrocarbon radicals from the fuel (the "reburning" mechanism).
The testing included unique studies into the impact of oxyfuel firing on slagging and fouling. Slagging propensity was assessed by means of a deposition probe inserted into the furnace; the temperature decay of the metal coupon being indicative of deposit build-up. The test data showed that the rate of deposition was slightly faster for oxyfuel firing compared with conventional combustion in air, but was largely independent of oxyfuel operating parameters such as recycle rate. Convective pass fouling was studied by monitoring the thermal performance of an air cooled tube bank (designed to achieve typical metal temperatures in a realistic geometry) and determining the fouling resistance. Results indicated that the rate of fouling was worse for oxyfuel conditions, possibly due to the lower gas velocities during the tests; however, the impact was small, and the deposits were easily cleaned.
Testing of the pozzolanic activity of the flyash showed that it was unaffected by the oxyfuel process; the ashes arising from oxyfuel combustion are equally acceptable for cement manufacture as those arising from conventional air firing.
The oxyfuel process largely comprises existing basic technologies (air separation, combustion, CO2 separation) combined in an innovative way. Studies have shown that a boiler designed for conventional air firing can be operated under oxyfuel firing conditions without excessive penalty. This gives rise to the possibility of retrofitting the process to existing plant and the concept of capture ready generating capacity. Both approaches aim to protect the considerable investment already made in conventional plant, and provide a measure of future-proofing. Here the term capture ready can mean as little as ensuring that there is adequate space on site to subsequently install air separation and CO2 capture plant, and a potential route to a CO2 disposal/sequestration site.
A number of studies have been carried out recently to compare the economics of the pulverised fuel (PF) based capture technologies with the alternative approach of IGCC (integrated gasification combined cycle).
The most significant of these are probably the three studies commissioned and reported by the International Energy Agency and the work that is currently ongoing within the Vattenfall led EU funded project ENCAP. The output from these studies has been taken and normalised to a common base of owners' costs and exchange rates to produce the following summary:
Technology specific Net
IGCC (Shell) 2035 - 2261 34.5 - 35.5
IGCC (GE/Texaco) 1720 - 1818 31.5 - 34.1
PF + amine 1990 - 2070 34.8 - 36.1
PF + oxyfuel 1996 - 2104 35.4 - 36.2
In the absence of any clear economic advantage the take up of capture technology may well be determined by risk and the ability to hedge against risk. This is where PF based capture technologies and oxyfuel in particular with the potential to retrofit and operate with either air or oxyfuel have a clear advantage.
Mitsui Babcock is leading an industry collaborative project (Project 407), supported by the UK DTI, to evaluate how retrofits can be accomplished on the UK fleet of coal-fired power plants and how thay can be optimised. The partners in the project are Mitsui Babcock, E.On, Alstom, Air Products and Imperial College. Sponsors, in addition to the DTI, are E.On, Drax Power, EDF, Scottish and Southern and RWE npower.
The company is also leading another major project, DTI Project 366 - "Future CO2 Capture Technology Options for the Canadian Market" - in collaboration with the Canadian Clean Power Coalition (CCPC) and Alstom Power, Air Products, Imperial College, with MHI as subcontractor. This project aims to carry out techno-economic assessments for new build green field coal-fired PF advanced supercritical power plants for oxyfuel and amine scrubbing CO2 technologies (with capture installed, as well as capture ready). Canada is currently targeting commercial operation of a such a plant, with CO2 capture, by 2012.
Mitsui Babcock is also a key participant in the ENCAP project, which is led by Vattenfall under the EU Sixth Framework Programme. ENCAP aims to further develop pre-combustion CO2-capture technologies and process concepts for power generation based on fossil fuels; mainly hard coal, lignite and natural gas. Within "SP3, Oxyfuel Boiler Technologies", Mitsui Babcock is work package leader for "WP 3.3, OxyFuel Greenfield Coal Pulverised Fuel Definition", collaborating with Alstom Power Boilers (Germany), Siemens, Air Liquide, Vattenfall, PPC, E2, RWE and the University of Ulster.
Oxyfuel firing for carbon dioxide capture is sufficiently well understood to allow the design of the rest of a power plant to be made capture-ready.
A combination of pilot scale trials currently underway and large scale demonstrations - anticipated between 2007 and 2012 - are needed to prove the technologies.
In parallel, governments, with the UK playing a leading role, are developing the criteria for choice, approval, validation and monitoring of CO2 storage sites.
To optimise the technology, further R&D is necessary leading up to and in parallel with the large scale demonstrations. This R&D includes gaining a deeper understanding of coal combustion, heat transfer and corrosion in oxyfuel conditions, which we and our partners hope to execute as part of the UK Carbon Abatement Technologies R&D programme.
Russian, German foreign ministers discuss bilateral relations, G8
BBC Monitoring Former Soviet Union, Apr 5
Text of report by Russian news agency ITAR-TASS
Berlin, 5 April, The Russian and German foreign ministers, Sergey Lavrov and Frank Walter Steinmeier, today discussed preparations for the eighth round of interstate consultations. "The consultations will take place in Tomsk at the end of April," Lavrov told reporters after today's talks.
"We are cooperating in the G8 and appreciate Germany's constructive contribution to preparations for the [forthcoming G8] summit in St Petersburg, especially given that Germany will be presiding over the club of the industrially advanced nations next year," he said.
The ministers "considered the rather intensive schedule of political contacts for this year". "Russia appreciates Germany's role in the development of partnership between the EU and Russia, and relations between NATO and Russia," Lavrov said.
[ITAR-TASS news agency, Moscow, in Russian 1758 gmt 5 Apr 06 quoted Lavrov as saying that the results of recent elections in Ukraine and Belarus should be recognized. "Russia and Germany are interested in united Europe," he said. "Issues should be resolved through dialogue and involvement in cooperation rather than through isolation," Lavrov said. "Our views with Germany differ but Russia respects Germany's position and Germany respects the position of the Russian Federation," he said.
ITAR-TASS news agency, Moscow, in Russian 1735 gmt 5 Apr 06 quoted Lavrov as saying that dialogue is also important in the Middle East. "We are encouraged that statements have been made following the Palestinian and Israeli parliamentary elections, in which the Palestinians and the Israeli, using different formulas, are sending a signal that they are ready for a dialogue," he said after the talks with his German counterpart.]