carbon capture & storage
Post-combustion capture: aiming to be commercial by 20151 December 2010
Alstom’s efforts in the field of post-combustion capture are focused on two technologies, chilled ammonia and advanced amine. Initial results from pilot and validation facilities are encouraging.
With the world’s population and economy growing fast, any significant reduction in CO2 emissions will require considerable investment in three areas: energy efficiency; a shift to non CO2 sources of energy (renewable and nuclear); and carbon capture & storage (CCS).
Since 41% of the total emissions are contributed by the electricity production sector alone, capturing CO2 at power plants fired by fossil fuels will make a huge difference. Emerging legislation is also demanding that all new fossil fuelled plants are ‘CCS ready’. The challenge for power plant owners and operators is to limit emissions while still maintaining power plant economics. Alstom’s development activities are concentrated on a dual approach: providing reliable and cost-effective technology; and delivering an integrated approach that optimises operation and reliability at every step of the CO2 capture value chain.
Alstom’s R&D programmes are concentrated primarily on post-combustion and oxycombustion technology. Post-combustion technologies, such as amine or ammonia scrubbing, will be available as early as 2015 for full commercial deployment, owing to the fact that they can be fully tested at a smaller scale and flexibly deployed in single or multiple trains in any power generation unit.
Post-combustion is the most mature CO2 capture technology today. It consists of separating CO2 from exhaust gases using a solvent. Alstom is developing two post-combustion technologies, using either chilled ammonia or advanced amines as solvents. Early development work, supported by results from field pilot and validation facilities, shows that these technologies can remove 90% or more of the CO2 from combustion gases. They can be applied to both coal-fired and combined cycle gas-fired power plants and are equally suitable for greenfield projects, as well as the installed fleet.
Chilled ammonia process
In the chilled ammonia process (CAP), flue gas from the boiler is conditioned to condense water and capture residual emissions, improving CO2 absorption and reducing the volume of gas to be treated and the size of the downstream equipment. The conditioned gas then passes through a column where the CO2 is absorbed from the flue gas through contact with an ammonia based scrubbing solution containing ammonium carbonate. The absorbed CO2 reacts in solution to form ammonium bicarbonate. The treated flue gas then passes through additional columns to recover ammonia vapour and to heat the gas prior to venting a CO2-lean flue gas to the stack. The ‘rich’ ammonium bicarbonate solution (rich in CO2) is pressurised and pumped to a regenerator column where heat is applied to separate CO2 from the solution. The CO2 is further compressed and treated to produce CO2 of the desired customer specifications needed to facilitate transport and storage. The ‘lean’ ammonium carbonate solution (lean in CO2) leaves the bottom of the regenerator column and is returned to the CO2 absorber.
The chilled ammonia process is expected to provide significant energy savings when compared to other CO2 capture technologies because it requires less low-pressure steam for absorbent regeneration. This is due to the lower heat of reaction, higher pressure regeneration resulting in very low levels of water in the vapour phase corresponding to reduced moisture vaporisation energy requirements, and less sensible heat loss due to higher CO2 net loading in the solvent and hence lower circulation rate. Significant electrical power savings can be achieved through the use of a smaller CO2 compressor, which is possible because the CAP regeneration stage occurs at higher pressure (above 150-300 psi (10-20 bar)), thus eliminating the largest and least efficient compression stage.
The process does of course require additional power for the flue gas cooling (down to around 20 ºC or less), with the actual power consumption dependent upon ambient conditions, allowing reduced energy requirements for sites located in cooler climates.
Other features of the chilled ammonia process include:
• Use of a globally available, low-cost reagent (ammonia), tolerant to oxygen and flue gas impurities, resulting in low reagent consumption costs.
• Ammonium sulphate byproduct stream that can be used commercially as fertiliser, disposed of within the existing power plant infrastructure, or cost-effectively treated for non-hazardous disposal.
• Ability to utilise local access to cold water to further offset mechanical chilling and further reduce auxiliary power consumption.
• High-purity CO2 product stream containing low moisture and ammonia at elevated pressure, resulting in reduced costs and energy consumption for CO2 compression.
• Flexible process that can be retrofitted to units with conventional air quality control systems (AQCS), without the need for additional flue gas treatment.
The R&D process for advancing a new technology from the laboratory to commercial scale involves a series of progressively larger demonstration projects, culminating in a commercial offering that includes guarantees for typical performance parameters. This process applies to CO2 control technologies as much as it does to any other new technology.
For the chilled ammonia CO2 capture process, bench scale laboratory tests were conducted in 2005/2006 at SRI International, Palo Alto. Based on the results of the bench scale tests, a pilot facility was constructed at SRI International with sufficient size to demonstrate the CO2 absorption, ammonia capture, and rich solution regeneration unit operations. Tests run on this pilot facility provided the basis for scaling the process for the field demonstration units. Once the initial phase of testing was complete, the pilot facility was re-located to Alstom’s Växjö laboratory where process development experiments could be conducted to improve the chilled ammonia process efficiency and economics (ongoing).
As the next step, Alstom planned a series of field demonstration projects to test the technology. The first such project was installed at the We Energies Pleasant Prairie power plant. This unit, which was designed to capture approximately 38 metric tonnes of carbon dioxide each day, was started in early 2008 and completed operations in Oct 2009, with over 8000 hours of operation.
This project was jointly developed by EPRI and Alstom. The Alstom and EPRI team first conducted a comprehensive screening process of several candidate sites to select a plant suitable to host the field pilot. The We Energies’ Pleasant Prairie power plant, a state-of-the-art facility that operates with extremely high environmental performance, was determined to be the desired location for the pilot. The Pleasant Prairie units 1 and 2 were recently retrofitted with selective catalytic reduction (SCR) and wet flue gas desulphurisation (WFGD) systems to control emissions of NOx and SO2, respectively. These air pollution control retrofit projects also included the construction of a new stack. The chilled ammonia process pilot system extracts approximately 1% of the flue gas from the outlets of either the unit 1 or unit 2 WFGD systems located upstream of the stack.
On-line gas measurements are made to determine the amount of CO2 captured and the quality of the CO2 product stream leaving the chilled ammonia process. The CO2 product stream from the CAP pilot plant is combined with the treated flue gas prior to discharge from the pilot. The entire extracted gas volume is reintroduced back into the WFGD outlet transition duct and mixed with the WFGD exhaust gas.
The pilot system has been designed to capture more than 1600 kg CO2/hour (over 14 000 tonnes/year with continuous operation). The project achieved most of its operational objectives and all of its fundamental research objectives.
It has demonstrated full system operation on flue gas from a coal-fired boiler, including: flue-gas cooling using heat recovery/exchange and chilling; removal of residual pollutants; CO2 absorption; and CO2 regeneration. Over time, pilot performance steadily improved to the point that stable absorber operation at 100% of design flue gas flow was established, in April 2009.
The project has also demonstrated high-efficiency removal of CO2 (> 90%) at design conditions, minimised ammonia slip (during operation at design gas flow consistent measurements of less than 10 parts per million (ppmv) and normally less than 5 ppmv ammonia slip to the atmosphere) and produced high-purity CO2 with low ammonia (< 10 ppmv) and water content (< 2500 ppmv). The pilot has operated for more than 8000 hours and, since September 2008; it has been operated 24 hours per day, 7 days per week. The experience in operating the field pilot has been invaluable, as the Alstom operations and project validation teams have refined startup and shutdown procedures and gained experience troubleshooting issues with process operation.
The We Energies’ Pleasant Prairie pilot plant has confirmed the technical viability of operating a chilled ammonia carbon capture system at an operating power plant and demonstrated thermodynamic properties that were consistent with Alstom’s process design tools. Another similarly sized CAP pilot plant located at E.On’s Karlshamn power plant in Sweden has also provided valuable operating data and experience needed in the development of the technology. In particular, the Karlshamn pilot is installed on an oil-fired auxiliary boiler that burns higher sulphur fuel resulting in higher SOx levels at the CAP inlet. This pilot has been in operation since April, 2009 and is designed to capture approximately 15 000 metric tonnes per year.
Product validation testing
As the next step, key questions around energy consumption – a key driver of cost – and other important technical issues are to be addressed in a larger scale, next generation, installation which we call a product validation facility (PVF).
A PVF, at AEP’s Mountaineer site, located on the Ohio River near New Haven, West Virginia, was started up in September 2009 (see panel, p 15).
This joint Alstom and American Electric Power installation will capture and store approximately 100 000 metric tons of CO2 annually.
The project is the first to capture CO2 from a pulverised-coal-fired power plant and inject it into a permanent storage site, which is more than 2400 m underground. The data collected and analysed from the operation of the PVF will support efforts to advance CCS technologies to commercial scale and provide information to the public and industry on future advanced coal generation options.
AEP’s Mountaineer plant complex consists of a 1300 MWe net supercritical coal-fired unit that began service in 1980. The facility is presently equipped with an air quality control system (AQCS) consisting of low NOx burners, SCR, and WFGD.
The Mountaineer chilled ammonia product validation facility is designed to remove CO2 from a slipstream of flue gas taken downstream of the existing WFGD system. The PVF is designed to treat approximately 80 000 Nm3/h of flue gas, or 1.5% of the total plant flue gas flow.
A second chilled ammonia product validation facility is currently under construction, at Statoil’s Mongstad refinery in Norway. This PVF will be designed to capture 80 000 metric tonnes of CO2 per year and will form part of a multi-process test facility that will evaluate several post-combustion technologies (including amines). The multiprocess test facility is being developed by a consortium of companies that includes Statoil, Shell and Gassnova and will be known as the European CO2 Technology Centre Mongstad or “TCM” for short.
The chilled ammonia PVF is being designed to treat exhaust gases with a CO2 concentration of around 12%, coming from a fluid catalytic cracker unit. Additionally, the validation pilot will be designed to treat exhaust gases from a natural gas fired combined heat and power (CHP) unit that contains around 3-4% CO2.
The pilot also benefits from the availability of cold seawater that offsets the need for mechanical chilling. This validation pilot is scheduled to commence testing before the end of 2011.
Advanced amine process
As well as chilled ammonia, Alstom is also working with The Dow Chemical Company (Dow) on advanced amines. The two companies are jointly developing an advanced amine process technology that utilises UCARSOLTM FGC 3000, a new advanced amine solvent from Dow*, in combination with advanced flow schemes, to provide cost-effective post combustion carbon capture technology.
The advanced amine process is based on the chemistry of the amine CO2–H2O system and the ability of the amine solution to absorb CO2 at low temperatures and release it at moderately elevated temperatures. CO2 and water produce carbonic acid that reacts with the amine solution in the absorption column.
The diagram above shows a simplified schematic of the process currently being tested by Dow and Alstom.
In February 2008 Alstom and Dow announced a joint development and commercialisation agreement on advanced amine scrubbing technology for the removal of CO2 from low pressure flue gases particular to fossil fuel fired power plants and other major industries.
Amongst the advantages of collaboration with Dow is their proven industrial track record in gas cleaning and separation, as well as their global capabilities to support advanced amine supply and provide amine solvent management programmes and technical services to the marketplace. Combined with Alstom’s capabilities in plant integration, power plant OEM supply, EPC capabilities and global service capabilities, this collaboration with Dow supports our plans to offer product to
market, including performance guarantees, for commercial-scale units by 2015.
One of the main areas of Alstom’s focus on the development of the advanced amine process is to quantify and maximise the amount of savings, both in CAPEX and energy, relative to standard amines. Initial results show significant energy savings over the MEA process.
While Dow will provide innovative solvents, Alstom’s integration know-how promises substantial additional savings in applying the technology. Several improvements to the process are currently being considered that will further reduce solvent consumption and overall energy requirements.
To help obtain amine solvent and process system operating experience, Dow and Alstom agreed to jointly construct and operate a small pilot plant facility. This facility is now operating and capturing carbon dioxide from industrial coal-fired boiler flue gas at a nominal rate of 1800 metric tonnes per year.
This facility has been developed with several objectives in mind: it has been applied to an operating coal-fired boiler; it has been designed, using both Alstom’s and Dow’s knowledge of amine systems; and it has been designed to operate using the UCARSOLTM FGC-3000 advanced amine solvent from Dow.
The pilot plant unit is located at the Dow owned South Charleston Facility in West Virginia, USA. Dow and several other companies produce a wide variety of specialty chemicals at this facility. Three boilers including one coal-fired boiler, Boiler 25, provide steam to the site. Boiler 25 is a Riley PC boiler originally rated at 130 000 kg/h of 40 bar steam. This boiler’s current output is nominally 70 000 kg/h steam while firing coal supplied from a local source. The boiler is equipped with an electrostatic precipitator to control particulate emissions but does not feature any other post-combustion air pollution control equipment. The exhaust gas stream produced by the boiler is nominally 175ºC and it contains approximately 9% CO2 and 200 ppm NOx.
The pilot plant is designed to capture 1800 tonnes/year of CO2 from the flue gas exiting the coal-fired boiler. A nominal 2000 m3/h slipstream of exhaust gas is withdrawn from the boiler exhaust stack and directed to the nearby amine pilot plant. The exhaust gas is routed through a fabric filter unit and a sodium-based desulphurisation unit that reduces the SOx content below 50 mg/Nm3 prior to introduction to the amine CO2 treatment pilot. A gas blower precedes the flue gas treatment portion of the amine pilot system.
The balance of the pilot plant is skid-mounted and modular in nature. The configuration, established in 2009, consists of a conventional flow scheme.
The pilot plant was placed into operation during the autumn of 2009 and will run in its initial configuration until the end of 2009. Then it will be modified to test and validate an advanced process configuration jointly developed by Dow and Alstom, with the test programme continuing over a two-year period, into 2011.
In its current configuration the plant consists of an absorber column equipped with structured packing, and a water wash section that minimises amine emissions in the exiting flue gas. The absorber is designed to remove 90% of the incoming CO2 from the inlet flue gas stream using the UCARSOLTM FGC-3000 solvent. It also includes a regeneration column containing structured packing, a steam driven reboiler unit, and a water-cooled condenser to dry the exiting CO2 gas stream. The CO2 gas stream will be discharged directly to the atmosphere so no further treatment or compression will be performed. Plate-and-frame heat exchangers are used to exchange heat between the rich and lean amine streams and to cool the lean amine stream entering the absorber. The pilot plant also features a variety of mechanical filters, an activated carbon filter, and an electro-dialysis reclaimer unit, to manage the content of heat stable salts in the amine solvent.
Site preparation for the South Charleston amine pilot plant began in February 2009 and construction was completed in July 2009.
A potential further key step for advanced amines is a planned large scale demonstration to be located at the 858 MWe lignite-fired Belchatow plant in Poland. An MOU was executed between Alstom and PGE Elektrownia Belchatow in December 2008 for the development of a feasibility study for carbon capture on this unit, which is currently under construction. This feasibility study was completed in June 2009, confirming that a carbon capture facility was capable of being incorporated into the plant.
The MOU was modified in June 2009 to include the development of a 260 MWe advanced amine CCS facility at the 858 MW site. This capture facility is proposed for EU funding and will be designed to capture CO2 emissions from 30% of the 858 MW plant’s total flue gas flow with a 90% capture rate, equivalent to over 1.8 million tonnes per year.
Currently Alstom is performing preliminary engineering for this 260-MWe-equivalent facility, supporting PGE Elektrownia Belchatow’s EU funding application and providing the necessary engineering details for the preparation of the construction permit for the unit. Detailed engineering is expected to start in the first quarter of 2010, with the capture facility to be operational in 2014/15.
Retrofittable CO2 capture technologies, post-combustion and oxy-combustion, show a lot of promise and Alstom’s technology development programme continues on schedule. Initial data from the chilled ammonia field pilot and validation facilities are very encouraging and suggest the concept will be commercially viable. We expect similar success with advanced amine in the coming months, with initial results from the pilots Alstom is developing with The Dow Chemical Company.
Alstom is currently working with different partners to develop the next phase, commercial scale demonstration of both chilled ammonia and advanced amine, and has already announced planned projects with AEP and TransAlta (chilled ammonia) and PGE (advanced amine).
Alstom is also simultaneously investing in capabilities to offer a complete integrated CCS system to its customers. Through a recent acquisition of the former Lummus Global unit in Wiesbaden, Alstom can now draw on extensive experience in numerous fields of chemical processing, especially in gas cleaning technologies. The Wiesbaden unit, which consists of 113 employees has the full set of skills and capabilities required for the design and turnkey delivery of CO2 capture plants based on considerable relevant experience gained in its traditional markets. This acquisition will enable Alstom to make its CO2 capture technologies available to its customers with greater responsiveness and efficiency.
Alstom has also entered into an agreement with Schlumberger for mutual collaboration in the joint offering of CCS-Ready studies. While Alstom will bring its know-how in post-combustion and oxy-combustion capture technologies as well as its power plant integration experience, Schlumberger Carbon Services will contribute expertise, technology and project management in the geological storage of carbon dioxide. The collaboration will support Alstom’s aim to provide full CCS support to its customers – from the flue gas tie-in to underground storage.