The Modern Coal-Fired Power Plant
When coal is combusted in the furnace boiler the resultant flue gas contains pollutants that must be removed. Today’s coal plants achieve regulatory using commercially available technology. The following table shows removal of regulated pollutants.
|Sulfur Dioxide (SO2)||90 - 98 %|
|Oxides Nitrogen (NOx)||80 – 90 %|
|Mercury (Hg)||50 – 90 %|
Air Pollution Control Technology
Electrostatic Precipitator (ESP) -- The fluegas laden with flyash is sent through pipes having negatively charged plates which give the particles a negative charge. The particles are then routed past positively charged plates, or grounded plates, which attract the now negatively-charged ash particles. The particles stick to the positive plates until they are collected. This ash is used in various construction materials e.g. additive to cement forming improved concrete.
Flue Gas Desulfurization (FGD) -- SO2 is an acid gas and thus the typical sorbent slurries or other materials used to remove the SO2 from the flue gases are alkaline. The reaction taking place in wet scrubbing using a CaCO3 (limestone) slurry produces CaSO3 (calcium sulfite). When FGD were first introduced this so called ‘FGD sludge’ was ponded. But some FGD systems go a step further and oxidize the CaSO3 (calcium sulphite) to produce marketable CaSO4 • 2H2O or gypsum1.
Selective Catalytic Reduction (SCR) -- SCR achieves NOX reduction by introducing Ammonia (NH3) with proprietary catalysts upstream of the ESP. The resultant material exists with the ash. Increasing the auxiliary or over-fire air also aids in removing NOX .
Mercury (Hg) -- Activated carbon is introduced in the flue gas upstream of the ESP – adsorbing the solid-phase Hg. The resultant material is contained in the ash.
New Coal-Fired Power Plants and Global Warming Greenhouse Gas
During the last several months, thousands of megawatts of new coal-fired power plants have been delayed or cancelled (e.g. Texas, Florida, Oklahoma, and Idaho). These cancellations are attributable to the issue of GHG or control of Carbon Dioxide (CO2) – an unregulated gas but product of coal combustion. Recently, Citigroup, JPMorgan Chase and Morgan Stanley formed The Carbon Principles, which are climate change guidelines for advisers and lenders to power companies. These investment banks are more likely to finance proposed coal-fired power plants that capture greenhouse gas (GHG) and bury (sequester) them. An often-cited, recent Kansas decision denied an air permit to Sunflower Electric Power due to the absence of CO2 removal. Such policies prod developers of proposed coal-fired plants to commit to controlling GHG emissions – most notably CO2.
Integrated Gasification Combined Cycle (IGCC)
IGCC consists of Gasification, Syngas Cleanup, Gas Turbine Combined Cycle and Cryogenic Air Separation: Gasification or partial oxidation of the feedstock with pure oxygen inside a reactor. The carbon and hydrogen from the feedstock are converted into a mixture composed primarily of hydrogen and carbon monoxide. This mixture is commonly called synthetic gas, or syngas. The syngas from the reactor must be cleaned before it can be used as a gas turbine fuel. The cleanup process typically involves removing sulphur compounds, ammonia, metals, alkalytes, ash and particulates to meet the gas turbine's fuel gas specifications. IGCC potentially yields marketable products e.g. methanol, ammonia, fertilizers. The cleaned syngas is combusted in the gas turbine. A cryogenic air separation unit provides pure oxygen to the gasification reactor, often using or supplemented with post-compression air bleed from the gas turbine.
IGCC has demonstrated CO2 capture for several years (TECO Polk 5 Station) and is commercially available for grass-root units (e.g. Bechtel/GE) and under demonstration study as retrofit approach (e.g. Alstom, American Electric Power, WE Energies). Carbon disposal (Sequestration - geological burial) has not been commercially demonstrated and represents a significant cost unknown. Whether or not federal or state (e.g. Kansas) regulators can arbitrarily mandate that electric utilities incorporate undemonstrated technology into their proposed plant designs is unanswered. Even so, the public and media arena requires electric utilities to consider carbon capture in their siting considerations.
IGCC and Using Captured CO2 for Enhanced Oil Recovery
Integrated gasification combined-cycle (IGCC), a commercially demonstrated technology for Carbon (CO2) capture is marketed as turnkey approach via Bechtel and General Electric's long-term alliance. The recent alliance with Schlumberger addresses the outstanding question of what to do with captured CO2. The alliance of Bechtel, GE and Schlumberger offers Electric Utilities a turn-key option to address Green House Gas Issues Carbon Capture and Sequestration (Storage) - promoting coal-fired power plants.
Integrated gasification combined-cycle (IGCC) has been operating commercially for several years at Tampa Electric's Polk Unit No. 5. IGGC was proposed, but aborted, for TECO's Polk Unit 6, a 630-megawatt coal-fired new plant.
GE Energy has signed a carbon sequestration alliance agreement with Schlumberger Carbon Services to accelerate the use of "cleaner coal" technology. The agreement aligns GE's experience in integrated gasification combined-cycle (IGCC) systems with proven carbon capture capabilities and Schlumberger's geologic storage expertise and capabilities for site selection, characterization and qualification.
This alliance offers electric utilities with a turn-key approach to implement IGCC technology. GE and Bechtel worked together to offer a packaged approach for IGCC implementation including: Engineering, Procurement, Construction, Equipment, Technology. The Schlumberger Alliance offers a solution to the disposition of captured CO2. Given suitable geological formation and known oil reserves, captured CO2 can be injected to achieve Enhanced Oil Recovery.
While the new arrangement provides technical and commercial expertise for moving forward with coal-based power generation, clear regulations and policies are needed for large-scale implementation. GE's IGCC plants can be built with CCS from the beginning or designed to be retrofit when clear policy and regulations create an appropriate environment.
Carbon Capture Does Not Ensure Siting Coal-Fired Power Plants
Among the 26 coal-fired projects cancelled since March 2006, at least two included carbon capture. Tampa Electric’s (TECO) abandoned its Polk 6 630-megawatt Integrated Gasification Combined Cycle (IGCC). TECO has been operating IGCC (technology designed to remove and capture CO2) for several years. TECO would have received a $250 million tax credit from the US Dept. of Energy (DOE). Southern Company’s Orlando Utilities Commission (OUC) also cancelled plans to build a 285 MW IGCC unit – foregoing a $ 235 million USDOE grant. Although these plants had received regulatory approval, the economics of carbon sequestration may have played a part in their cancellation.
Factoring in Carbon Capture and disposal (sequestration - geological burial) increases the cost from 20% to 30 – 40 %. Upon realizing, that Florida’s governor and appointed Public Service Commission would not have sanctioned increased electrical rates (for sequestration); plans for these IGCC plants were abandoned2.
The U.S. Department of Energy’s (USDOE) recent cancellation, of the 275-megawatt, $1.8 Billion FutureGen Industrial Alliance Inc.’s demonstration project (funded by private-public consortium and includes gasification, CO2 capture and sequestration), slated for Mattoon, Illinois, was due to excessive cost. The USDOE intends a restructuring to convert the $1.8 Billion prototype – demonstrating Carbon (CO2) Capture and Sequestration (CCS) – to a series of CCS demonstrations on operating facilities. USDOE will invest $648 million in advanced coal research much of it focused on CO2 disposal – the least technically demonstrated and highest cost unknown. Developers of proposed coal-fired plants could commit to incorporate demonstrated sequestration technology when commercially available (2015-2016 using the USDOE timetable) – satisfying environmental concerns. To avoid Global Warming Threat (i.e. excessive GHG), scientific consensus determined that US should achieve 80% CO2 (Carbon) reductions by 2050.
Incorporating Carbon Sequestration in Siting Future Coal Fired Power Plants
The USDOE will replace its original FutureGen with a structured approach. A multi-plant approach will be employed to demonstrate carbon capture and storage (CCS) technology at multiple commercial-scale IGCC clean coal power plants. Forty IGCC plants (totaling 23,000 MW) have been proposed. Besides the restructured FutureGen, the Southwest Regional Partnership for Carbon Sequestration has conducted field research beginning in 2003 and a new project involving large-scale sequestration, to be based near Price Utah, has $67 million in federal funds and $21 million from private partners like ConocoPhillips. Such programs should yield demonstrated technology with reliable costs. Developers of proposed coal-fired plants could commit to incorporate demonstrated sequestration technology when commercially available. For example, Alliant (developer of 650-megawatt coal plant Sutherland 4, Marshalltown Iowa) proposes to address environmental concerns by designing the plant for future incorporation of carbon sequestration equipment if needed. Electric utilities could adopt this posture provided that the costs of CO2 capture and burial can be recovered.
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