Sunday, August 10, 2008


IGCC - "A Promising Technology" for Future Coal Power Plants

The following link appeared on my radar screen recently. Even though the article was published by a competitor, I felt that it merits repetition here just in case it didn't come to you via your own Google Alert, or whatever system you use to bring such items regarding Gasification and IGCC news to your attention.

Link: Coal Gasification - A promising technology


In case you would rather read the article by Kentucky chemical engineering consultant John Colebrook right here, I'm providing you with a copy. It comes with proper credit to author and publisher, but sans advertisement.

Let me know what you thought of it. Although, in my opinion, it doesn't give adequate credit to IGCC as being a commercially proven technology, it does highlight the important benefits of gasification when it comes to resolving permitting issues for new coal-fired power plants.


Posted by:

Harry Jaeger
Gasification Editor
Gas Turbine World Magazine

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Coal Gasification, a Promising Technology

Support for IGCC is resolving permitting challenges and enhancing performance.

Electric Light & Power July, 2008
Author: John Colebrook

In 2007, more than 50 percent of the electricity in the U.S. was generated from coal-fired power plants, and according to estimates by the Energy Information Administration, coal-based power generation will continue to be the largest single source of the nation's electricity production through 2030 and beyond. Coal gasification is considered an emerging technology that could replace many of the aging conventional pulverized coal boilers currently used to supply the majority of coal-based electricity in the U.S.




Utility companies, however, have been reluctant to make gasification a major component of their generation portfolios due to high capital costs and the lack of large-scale commercial applications. In an effort to resolve the most pressing challenges preventing the widespread implementation of integrated gasification combined cycle technology (IGCC), the U.S. government, mainly through the Department of Energy, has supported research and development efforts focused on advanced gasification technologies to improve the efficiency and environmental performance of IGCC plants while reducing capital costs.


Utility companies, however, have been reluctant to make gasification a major component of their generation portfolios due to high capital costs and the lack of large-scale commercial applications. In an effort to resolve the most pressing challenges preventing the widespread implementation of integrated gasification combined cycle technology (IGCC), the U.S. government, mainly through the Department of Energy, has supported research and development efforts focused on advanced gasification technologies to improve the efficiency and environmental performance of IGCC plants while reducing capital costs.
Emissions reduced with IGCC

The current state of IGCC technology already offers significant reductions in emissions of the major criteria air pollutants—nitrogen oxides, sulfur dioxide, particulate matter and carbon monoxide—when compared to pulverized coal plants (see sidebar and chart) but the DOE program seeks to achieve near-zero emissions of these pollutants by 2020 and to simultaneously develop carbon dioxide sequestration technologies that can be readily commercialized.
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The IGCC process. Source: National Energy Technology Laboratory

In a July 2006 EPA report comparing the environmental impacts and capital costs associated with IGCC to pulverized coal technologies, EPA joined the DOE in endorsing IGCC technology, stating "the EPA considers IGCC as one of the most promising technologies in reducing the environmental consequences of generating electricity from coal."

IGCC air permitting challenges

With only two commercialized IGCC facilities in operation (Wabash River, ConocoPhillips E-gas gasifiers, and Polk Station, GE Energy gasifiers) and only a few next-generation high-availability multi-train facilities that have recently received air permits, the air permitting arena for IGCC technology is relatively undeveloped.

However, the DOE's National Energy Technology Laboratory (NETL) identifies more than 30 IGCC projects as of October 2007 that are in various phases of development or that have recently been announced. Consequently, the quantity of air permit applications and air permits available for consideration and comparison when developing the required components of a New Source Review (NSR) permit application for a new IGCC plant is rapidly expanding. (Tracking New Coal Fired Power Plants, Office of Systems Analyses and Planning, DOE National Energy Technology Laboratory, Oct. 10, 2007.)

Further, despite the limited air permitting history for IGCC technology, several key challenges have been identified in the permitting process for a new IGCC plant.

Balancing the pressure to submit air permit applications early in the project against the need to obtain a representative permit on the first submittal of the application. Since state and federal approval processes for IGCC plants can span years, and the participation of environmental groups, the general public and federal land managers in the air permitting process is common in the coal-fired power generation industry, the typical strategy is to submit an air permit application very early in the design process. However, significant design changes after the submittal of an air permit application can lead to multiple revisions of the permit application, the reopening of public comment periods, and substantial delays in obtaining a complete and representative air permit for such a large-scale industrial facility. Successfully striking a balance between securing a timely air permit and ensuring the air permit is representative can alleviate much of the friction between the developer, regulatory agencies, and other interested stakeholders.

Ensuring that the appropriate basis is used for establishing emission limits. The Energy Policy Act of 2005 and New Source Performance Standards (NSPS) Subpart Da require that IGCC emission limits are established on either a power output basis, or a combustion turbine heat input basis. One of these two methodologies needs to be utilized when determining project emission rates and establishing emission limitations; the gasifier heat input should not be used as the basis for emissions calculations.

Representing accurate estimates for the frequency, duration, process flows, and emissions for each type of startup, shutdown, and maintenance (SSM) event in the permit application. Due to gasifier maintenance and the tendency for process upsets, SSM events for IGCC plants are relatively frequent and are often subject to explicit emission limitations in air permits. Therefore, it is important to represent accurate estimates for the frequency, duration, process flows, and emissions for each type of SSM event in the permit application so that acceptable permit limits can be established and accurate air dispersion modeling impacts can be predicted.

Accurately characterizing unique emission sources that require careful consideration in BACT evaluations. Several unique emission sources are associated with IGCC processes that require careful consideration in BACT evaluations under the Prevention of Significant Deterioration (PSD) program. For example, flares can be used during startups, shutdowns, and upsets to combust pure or mixed streams of raw syngas, sweet gas and various other process streams. With such varied inlet exhaust conditions, sources should estimate flare emissions under all scenarios prior to establishing BACT limits to ensure that continuous compliance is attainable. The composition of the vent streams from the acid gas removal system and sulfur recovery unit are often a function of the technology supplier, so selection of a vendor and establishing design specifications is a prerequisite for evaluating BACT for these sources.

Assessing the applicability of Maximum Achievable Control Technology (MACT) standards for Hazardous Air Pollutant (HAP) emissions. Emissions of hazardous air pollutants (HAP) from the acid gas recovery system and combustion by-products at IGCC plants can be above major source thresholds, requiring implementation of MACT for HAP emissions. While certain emission units at IGCC facilities fit into affected MACT source categories under 40 CFR Part 63, the provisions of 40 CFR Part 63 Subpart B can apply to sources not covered by an existing source category. A case-by-case MACT analysis for a new major source must establish an emission limitation that is achieved in practice by the "best-controlled" similar source. Determining the best-controlled similar source for IGCC processes can require technology reviews in a variety of similar industries and can lead to new control installations and increased monitoring, recordkeeping and reporting requirements.

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An increasingly complex regulatory environment for conventional coal-fired power plants bodes well for the future of IGCC technology. IGCC has distinct advantages over conventional coal-fired power plants because of its fuel flexibility and capacity for producing high levels of CO2 capture and sequestration. As with the commercialization of any new type of industrial facility, regulatory challenges will certainly play a key role in the development and implementation process of IGCC technology.

Author

John Colebrook is an air quality consultant for Trinity Consultants, based in the northern Kentucky office, where he helps clients in various industrial sectors successfully navigate the complexities of air quality permitting. Colebrook, a chemical engineer, is in the process of becoming a registered professional engineer to serve clients in Kentucky, Indiana, and Ohio.


A Detailed Look at Emissions from IGCC

In the gasification process, carbon-based feedstocks such as coal, petcoke, biomass or heavy oil residue are converted to synthesis gas, or "syngas," a mixture of primarily carbon monoxide and hydrogen with smaller amounts of CO2, methane and water. Combined with steam and either air or nearly pure oxygen from a cryogenic air separation unit, the preprocessed coal undergoes exothermic gasification reactions in the refractory-lined pressurized gasifier.

With a reduced chemical environment in the gasifier, sulfur compounds in the feedstocks are converted primarily to hydrogen sulfide with smaller amounts of carbonyl sulfide. Nitrogen bound to carbon is liberated primarily as gaseous nitrogen with smaller amounts of ammonia and hydrogen cyanide, and chlorides are converted primarily to gaseous hydrogen chloride. Depending on the gasification technology, ash or slag is recovered from the bottom of the gasifier and can be landfilled or sold.

Syngas leaving the overhead of the gasifier is routed to a filtering and cooling process. High temperature filters and cyclones remove entrained particulate matter while scrubbing systems remove chlorides and ammonia. The cooled raw syngas is then routed to an acid gas removal process where a physical absorption system using an organic solvent separates the raw syngas into a hydrogen sulfide-laden acid-gas stream and a sweetened syngas stream ready for combustion in gas turbines. The acid gas is routed to a sulfur recovery unit that produces salable sulfuric acid or elemental sulfur from the hydrogen sulfide in the acid gas stream.

The acid gas removal system can also produce a nearly pure sequestration-ready CO2 stream. The gas turbines, heat recovery steam generators and steam turbines generate power in the conventional combined cycle arrangement.

The acid gas removal system/sulfur recovery unit is capable of achieving lower SO2 emissions than flue gas desulfurization units at supercritical pulverized coal (PC) plants. Removing particulate matter in the syngas using high temperature filters or cyclones and/or wet scrubbing systems can achieve greater reductions than the use of electrostatic precipitators or baghouses downstream of the boilers at PC plants. Finally, IGCC and PC plants both use activated carbon absorption for mercury removal to achieve comparable emissions rates.

By separating elemental nitrogen from the coal during the gasification process and combining the syngas with diluents prior to combustion in the gas turbine, NOx emissions can be reduced to levels below those achieved at PC plants utilizing low NOx burners and selective catalytic reduction.

Electric Light & Power July, 2008
Author(s) : John Colebrook