home: success stories:

Polk IGCC Power Plant

Tampa Electric's successful 250 MW coal gasification power plant project near Tampa, Florida.

Project Objective
To demonstrate IGCC technology in a greenfield commercial electric utility application at the 250 MW size using an entrained-flow, oxygen-blown gasifier with full heat recovery, conventional cold-gas cleanup, and an advanced gas turbine with nitrogen injection for power augmentation and NOx control.

Technology and Project Description
Coal/water slurry and oxygen are reacted at high temperature and pressure to produce a medium-Btu syngas in a Texaco gasifier. Molten ash flows out of the bottom of the gasifier into a water-filled sump where it is forms a solid slag. The syngas moves from the gasifier to a high-temperature heat-recovery unit, which cools the syngas while generating high-pressure steam. The cooled gases flow to a water wash for particulate removal. Next, a COS hydrolysis reactor converts one of the sulfur species in the gas to a form that is more easily removed. The syngas is then further cooled before entering a conventional amine sulfur removal system. The amine system keeps SO2 emissions below 0.15 lb/106 Btu (97% capture). The cleaned gases are then reheated and routed to a combined-cycle system for power generation.

A GE MS 7001FA gas turbine generates 192 MWe. Thermal NOx is controlled to below 0.27 lb/106 Btu by injecting nitrogen. A steam turbine uses steam produced by cooling the syngas and superheated with the combustion turbine exhaust gases in the HRSG to produce an additional 124 MWe. The plant heat rate is 9,350 Btu/kWh (HHV).

Results Summary: Environmental

• The Polk Plant is one of the cleanest coal-based power generation facilities in the world.
   

• Emissions of SO2, NOx, and particulates are well below the regulatory limits set for the Polk plant site.
   

• SO2 reduction of 95% achieved.
   

Results Summary: Operational

• The gasifier operated more than 29,000 hours and processed coal at a rate of 2,300 tons/day, while the combustion turbine operated over 28,000 hours to produce over 8.6 million MWh of electricity on syngas.
   

• Power production met the target goal of 250 MWe at a high stream factor and plant availability.
   

• Carbon burnout exceeds 95%.
   

• During the fourth and fifth year of operation, the gasifier capacity factor was 75% and 66%, respectively. For these same years, the gasifier availability was 88.7% and 84.2%, respectively.
   

• For the fourth and fifth year of operation, the air separation unit had an availability of 93.9% and 90.5%, respectively, and the power block had an availability of 86.6% and 93.9%, respectively.

Results Summary: Economic

• The total cost of the Tampa Electric IGCC Project is $303 million, or $1,213/kW. The total project cost includes the cost of operating the unit throughout the demonstration period as well as experimental work on hot gas cleanup. The investment for a commercial unit would be significantly lower than that of the Tampa project.

Project Summary
The Tampa Electric IGCC project conducted at Polk Power Station has successfully demonstrated the commercial application of Texaco coal gasification in conjunction with electric power generation. Power production met the target goal of 250 MWe at a high stream factor and plant availability. The gasifier operated more than 29,000 hours and processed coal at a rate of 2,300 tons/day, while the combustion turbine operated over 28,000 hours to produce over 8.6 million MWh of electricity on syngas. Carbon burnout exceeds 95%, and emissions of SO2, NOx, and particulates are well below the regulatory limits set for the Polk plant site. Along with other IGCC demonstrations in the CCT Program, the Polk Plant is one of the cleanest coal-based power generation facilities in the world.

Environmental Performance
The Tampa Electric IGCC Project has very low pollution impacts. Environmental considerations have been a major driving force from the inception of the project. The site was selected by an independent Community Siting Task Force commissioned by Tampa Electric. Members included environmentalists, educators, economists, and community leaders. Economic factors were also considered. The Task Force evaluated 35 sites in six counties and recommended three in south western Polk County that had previously been mined for phosphate.

About one-third of the site is used for power generation facilities. Another third, about 1500 acres, is used to enhance the environment by creation of public fishing lakes for the Florida Fish and Game Commission. This area was converted from phosphate mining spoils to wetlands and uplands, thereby providing habitat for native plants and animals, and was transferred to the Commission in 1997. The final third of the site is used primarily for access and to provide a visual buffer. The site contains an 850-acre cooling reservoir.

The permitted stack emissions are shown in Exhibit 33. The plant achieved SO2 reduction of 95%. A COS hydrolysis unit was installed in 1999 to reduce SO2 emissions, enabling the station to meet recent, more stringent restrictions. Injecting nitrogen into the gas turbine is used to control NOx emissions. The use of nitrogen that would otherwise be vented represents a novel approach in oxygen-blown gasification technology.

A brine concentration unit processes "grey" water discharged from the gas cleanup systems, recovering a reusable water stream for slurry preparation and a land-fillable solid waste stream. There is no liquid effluent. Makeup water for the power plant is provided from on-site wells. All process water is recycled.

Operational Performance
As originally envisioned, the overall process scheme was to have incorporated hot gas cleanup on a portion of the raw syngas stream. After some initial test work, support for this option was discontinued. The cleaned syngas is sent to the General Electric model MS 7001FA gas combustion turbine. Nitrogen from the air separation unit (at 98% purity) is mixed with the syngas at the combustor inlet. Nitrogen addition has important benefits to the power plant: (1) the increased mass flow through the gas turbine produces more power than without the nitrogen; (2) the overall efficiency of the system is enhanced; (3) NOx emissions are reduced; and (4) the need for steam or water injection is eliminated.

During the fourth and fifth year of operation, the gasifier capacity factor was 75% and 66%, respectively. For these same years, the gasifier availability was 88.7% and 84.2%, respectively. For the fourth and fifth year of operation, the air separation unit (ASU) had an availability of 93.9% and 90.5%, respectively, and the power block had an availability of 86.6% and 93.9%, respectively. The lower availability of the gasifier in the fifth year of operation reflects the longer planned outage in that year to replace the refractory liner. Also, there was a
28-day forced outage to weld repair the main compressor in the ASU.

Several modifications to the original design and procedures were required to achieve the high availability that has been demonstrated. Soon after initial startup, ash plugging caused failure of some exchangers in the high-temperature heat recovery system. This led to serious damage to the combustion turbine. The exchangers were removed in 1997, and compensating adjustments were made in the rest of the heat recovery system. Additional particulate removal was provided to protect the turbine.

Pluggage in another bank of exchangers in the high-temperature heat recovery system was arrested by a design modification in 1999. In late 1997, hot restart procedures were implemented. These eliminated the need to change burners and reheat the gasifier every time it shut down, reducing gasifier restart time by over 18 hours.

Initially, there were problems with the gasifier, which is 50% larger than any previous Texaco gasifier. Carbon conversion in this larger gasifier was lower than expected, and refractory life has been identified as a significant issue. Liner replacement is expensive and requires considerable downtime. To achieve the target life of two years, the gasifier is being operated at a lower temperature than design, which in turn results in a further decrease in carbon conversion efficiency. This caused load restrictions due to capacity limitations in the fines handling system. A slag crusher and a duplicate fines handling system installed in 1998 solved this problem.

Thermocouple replacement in the gasifier also presents a problem. Replacement is relatively expensive. Thermocouple failure by shearing is attributed to expansion of dissimilar materials. In early 1998, revised operating procedures were developed to handle high shell temperatures in the dome of the radiant syngas cooler. This problem had caused two extended outages.

Numerous short forced outages occurred in 1997 and 1998 due to erosion and corrosion in the process water and coal/water slurry piping systems, pumps, and valves. Various changes have virtually eliminated these problems, and no such outages occurred in 1999. Some of the corrective actions taken to solve operating and maintenance problems in this project have resulted in patent applications.

The overall heat rate of the plant is 9,350 Btu/kWh (36.5% efficiency, HHV). The efficiency is somewhat lower than design because of removal of the high-temperature exchangers, lower than excepted carbon conversion, and a compressor failure in the brine concentration unit which necessitates its operation as a single effect evaporator. In the second half of 2000, a slag recovery system was commissioned to recover and use the unconverted carbon, and the brine concentration unit will be restored to its original more efficient vapor compression cycle. Ways are being evaluated to use the heat available as a result of removing the high temperature exchangers. Together, these projects are expected to increase the efficiency to 38% (9,000 Btu/kWh), consistent with the original design value.

The IGCC's oxygen plant requires 11.5 x 106 scfm of air to produce enough oxygen for full load operation on a variety of fuels over the normal ambient temperature range and to simultaneously reprocess enough fines to generate a slag product suitable for the cement industry. This air requirement is 8.5% above the ASU design values. The main air compressor (MAC) could almost meet this air requirement when the compressor was new, the MAC output has deteriorated at a rate of about 2% per year. At the end of the demonstration period. The MAC is 15% deficient on a normal Florida summer day. About 30% of the deficiency is attributable to pluggage of the MAC aftercooler and resulting backpressure. The after- cooler bundle will be replaced and all carbon steel parts coated to prevent further deterioration. The remaining 70% of the loss is distributed throughout the compressor system and there are no obvious ways to resolve the deficiency.

Ten coals and blends were tested in the three years of operation to determine the impact of feedstock properties on system performance. These coals included Kentucky No. 9, Kentucky No. 11, two Illinois No. 6 coals, and three Pittsburgh No. 8 coals. Four areas were evaluated for each coal: (1) feasibility of processing into a high concentration slurry, (2) carbon conversion, (3) aggressiveness of the slag to the gasifier's refractory liner, and (4) tendency toward fouling of the syngas coolers. All of the coals were found to be suitable with some design modifications. Lower cost petroleum coke blends were also tested.

Economic Performance
The total cost of the Tampa Electric IGCC Project is $303 million, or $1,213/kW. The total project cost includes the cost of operating the unit throughout the demonstration period as well as experimental work on hot gas cleanup. The investment for a commercial unit would be significantly lower than that of the Tampa project.

The Department of Energy estimates that future IGCC power plants, based on mature and improved technology, will cost in the range of $900–1,250/kW (1999$) depending on the degree to which existing equipment and infra- structure can be utilized. Heat rate ultimately is expected to be in the range of 7,000–7,500 Btu/kWh (46–49%; HHV).

Commercial Applications
The project was presented the 1997 Powerplant Award by Power magazine. In 1996 the project received the Association of Builders and Contractors award for construction quality. Several awards were presented for using an innovative siting process: 1993 Ecological Society of America Corporate Award, 1993 Timer Powers Conflict Resolution Award from the State of Florida, and the 1991 Florida Audubon Society Corporate Award.

As a result of the Polk Power Station demonstration, Texaco-based IGCC can be considered commercially and environmentally suitable for electric power generation utilizing a wide variety of feedstocks. Sulfur capture for the project is greater than 98%, while NOx emissions reductions are 90% those of a conventional pulverized coal-fired power plant. The integration and control approaches utilized at Polk can also be applied in IGCC projects using different gasification technologies.

TECO Energy is not only actively working with Texaco to commercialize the technology in the United States but also has been contacted by European power producers to discuss possible technical assistance on using the gasifier technology.

Contacts

Mark Hornick
General Manager, Polk Power Station
TECO Energy
P.O. Box 111
Tampa, FL 33601-0111
(813) 228-1111 ext. 39988
(863) 428-5927 (fax)
mjhornick@tecoenergy.com

George Lynch, DOE/HQ
(301) 903-9434
george.lynch@hq.doe.gov

Copyright Notice

Unless otherwise indicated, this information has been authored by an employee or employees of the University of California, operator of the Los Alamos National Laboratory under Contract No. W-7405-ENG-36 with the U.S. Department of Energy. The U.S. Government has rights to use, reproduce, and distribute this information. The public may copy and use this information without charge, provided that this Notice and any statement of authorship are reproduced on all copies. Neither the Government nor the University makes any warranty, express or implied, or assumes any liability or responsibility for the use of this information.

top of page