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Contents:

• Summary
• Existing Units Considered for Repowering
• Dresser-Rand Turbomachinery Considered
• Phased-Construction Approach
• Plant Layout
• Performance
• Environmental Characteristics
• Cost

Click on picture to enlarge

The host site for this repowering evaluation is the Arizona Public Service Company's Four Corners steam generating station, shown in the photo to the right.

The Four Corners station is a mine-mouth, low-sulfur subbituminous coal-fired electric generating station located near Fruitland, New Mexico, about 15 miles southwest of Farmington, New Mexico.

Today, the Four Corners station's five coal-fired units can generate a combined output of 2.23 million kilowatts of electricity. The three older units at the site are the target of this APFBC repowering assessment, as follows:

• Scrubber-equipped Units 1 and 2, both commissioned in 1963, each
  rated at 190,100 kW output.

• Scrubber-equipped Unit 3, commissioned in 1964, which is a
  253,400 kW output unit.

Unit 4 and Unit 5, constructed in 1969 and 1970, respectively, are not part of the APFBC repowering evaluation.  These are large scrubber-equipped supercritical units, rated at 818,100 kW output each.

Summary

This concept assessment evaluated a new way to get more electricity from an existing electric plant.  The method would evaluate how the Arizona Public Service Company might add new equipment to its Four Corners generating station.  The efficient new equipment continues the use of coal there, but lowers electricity costs.  The method significantly reduces the amount of wasted energy, so more electricity is produced from each ton of coal, with much less pollution.  DOE emphasizes that this is only a feasibility study; no actual construction is planned at the Fruitland, New Mexico site, which is located about 15 miles southwest of Farmington.

The new way of getting more electricity from an existing generating station has a long technical name that goes by the abbreviation "APFBC."  This stands for "advanced circulating pressurized fluidized-bed combustion combined cycle." APFBC adds equipment that allows jet engines to run safely on coal. The jets are added to the site, giving more electricity, which reduces the amount of energy wasted. This study evaluated a phased construction approach to installing APFBC at the site.  It begins with the installation of 1st-generation pressurized fluidized-bed combustion (PFBC) technology in the initial project phases, then in later phases, upgrades the repowering to APFBC. 

APFBC is under development by industry and the DOE, and is now being tested at DOE’s Power System Development Facility in Wilsonville, Alabama.

The Arizona Public Service feasibility evaluation is one of five assessments of FBC, APFBC, and GFBCC repowering.  The studies, which can be reached from the hyperlinks at the top of this page,  show the improvements in added power, reduced waste of energy, and lower electricity costs of these combustion-based technologies.  These studies show that PFBC, GFBCC, and APFBC technologies have attractive characteristics for repowering existing units, and that each of them is easily customized to match existing steam plant equipment.  This is important compared to many other ways of "repowering" a plant, since it means that with these combustion technologies, more of the existing equipment at the plant can be re-used, keeping costs low.

APFBC should soon be ready for commercial orders, so a number of electric companies are looking at the technology to see whether APFBC repowering makes sense for them.  The Arizona Public Service Company joins the other participating companies in learning more about PFBC, GFBCC, and APFBC technologies.   Each company volunteered its evaluation support for the study, getting no government funding.  The APFBC equipment evaluated in the Four Corners station evaluation was from Foster Wheeler, the high-temperature filters from Siemens Westinghouse Power Corporation, and the jet engines from Dresser-Rand.  Parsons Corporation provided the engineering support for the DOE study.

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Existing Units Considered for Repowering

• Unit 1: 190 MW, 1800 psig / 1000ºF / 1000ºF

• Unit 2: 190 MW, 1800 psig / 1000ºF / 1000ºF

• Unit 3: 253 MW, 2000 psig / 1000ºF / 1000ºF

• Each unit is equipped with a lime venturi scrubber for particulate and sulfur control.

• The Four Corners station is a mine-mouth plant located adjacent to the BHP Navajo Coal Company (BNCC), with sufficient reserve of low-cost coal for many years of operations.

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Dresser-Rand Turbomachinery Considered

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The APFBC repowering major equipment is from Foster Wheeler, with ceramic filters from Siemens Westinghouse, and turbomachinery (jet engines) from Dresser-Rand.  In this application, Dresser-Rand turbomachinery modified for APFBC operations from their compressed air energy storage system (CAES) designs is employed.

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Phased Construction Approach

Phase I

• Design a 1720ºF-capable rotor inlet temperature (RIT) Dresser-Rand turbomachinery and Foster Wheeler APFBC system for Unit 1, but do not install the APFBC carbonizer until Phase V.

• Install the 1720ºF-capable topping combustor.

• Install only the 1^st-generation equipment, with filters, pipes, topping combustor, and Dresser-Rand gas turbine.

• The gas turbine unit would be 1720ºF-capable, but initially operated on coal with the topping combustor unfired in 1^st-generation PFBC mode, at 1550ºF RIT.

• The Unit 1 gas turbine heat recovery unit (HRU) develops feedwater for the PFBC steam generation.

Phase II

• Demolish the Unit 1 boiler.

• Build similar 1720ºF-capable, but 1550ºF-enabled APFBC system for Unit 2 as was installed for Unit 1 during Phase I.

• Build in the space formerly occupied by the Unit 1 boiler.

• In Phase II, Unit 2 would be like Unit 1, 1720ºF-capable, but initially operated on coal with the topping combustor unfired in 1^st-generation PFBC mode, at 1550ºF RIT.

• The Unit 2 HRU develops feedwater for the PFBC steam generation.

Phase III

• Demolish the Unit 2 boiler.

• Install 1950ºF-capable Dresser-Rand turbomachinery with Foster Wheeler APFBC system for Unit 3 Train A.  This will be installed as an APFBC-capable repowering system from the start, with topping combustor capable of delivering 1950ºF rotor inlet temperature, but operated unfired, as a 1^st-generation unit.

• A single Unit 3 HRU develops feedwater for the PFBC steam generation from combined exhaust of Train A and Train B; blank off Train B ducting connection until Train B is built.

• The single train develops partial steam output for the Unit 3 steam turbine.

• Build the equipment in former Unit 2 boiler space.

• Demolish the Unit 3 boiler, and wet scrubber and scrubber control systems formerly used for Units 1, 2, and 3.

• Install 1950ºF-capable Dresser-Rand turbomachinery with Foster Wheeler APFBC system for Unit 3 Train B.  This will be installed as an APFBC-capable repowering system from the start, with topping combustor capable of delivering 1950ºF rotor inlet temperature, but operated unfired, as a 1^st-generation unit.

• The Train B exhaust is now connected to the single Unit 3 HRU, so now both Train A and Train B exhaust heat is recovered, and the combined steam generation from the Train A and Train B PFBCs now develop full steam output for the Unit 3 steam turbine.

• Build the equipment in former Unit 3 boiler space, leaving space between Train A and Train B for the carbonizer.

• Build the Unit 3 carbonizer in the space between Train A and Train B. Install pipes to and from these two trains.

• The carbonizer is to be oversized; this one carbonizer eventually, in Phase V, supplies the syngas for all the four APFBC-repowered trains: Unit 1, Unit 2, Unit 3 Train A, and Unit 3 Train B.

• Unit 3 APFBC compressors supply all of the air for Unit 3 syngas production, and later --in Phases IV and V-- for the Unit 1 and Unit 2 syngas production as well.

• Install Train B topping combustor, begin 1950ºF RIT 2^nd-generation operations.

• Install Train A topping combustor, begin 1950ºF RIT 2^nd-generation operations.

Phase IV

• Install the piping from the Unit 3 APFBC carbonizer to the Unit 2 topping combustor in the space reserved.

• The added equipment will convert the 1^st-generation PFBC repowering into a 1720ºF capable 2^nd-generation APFBC repowering, adding topping combustor.

• Operate APFBC-repowered Unit 2 in 2^nd-generation 1720ºF PFBC mode, with syngas from the Unit 3 carbonizer.

Phase V

• Install the piping from the Unit 3 APFBC carbonizer to the Unit 1 topping combustor in the space reserved.

• The added equipment will convert the 1^st-generation PFBC repowering into a 1720ºF-capable 2^nd-generation APFBC repowering, adding topping combustor.

• Operate APFBC-repowered Unit 1 in 2^nd-generation 1720ºF PFBC mode, with syngas from the Unit 3 carbonizer.

• Phase V completes the project.

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After Phase V is completed:

• Units 1 and 2 each retain the ability to operate as coal-fueled 1550ºF RIT unfired topping combustor 1^st-generation units if the Unit 3 carbonizer is out of service.

• Units 1 and 2 are coal-fueled 1720ºF RIT 2^nd-generation APFBC units, with syngas imported from the Unit 3 carbonizer.

• Unit 3 Train A and Train B each retain the ability to operate as coal-fueled 1550ºF RIT unfired topping combustor 1^st-generation units if the Unit 3 carbonizer is out of service.

• Unit 3 is a coal-fueled 1950ºF RIT 2^nd-generation twin-train APFBC unit, with syngas from its own single carbonizer.

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Plant Layout

Project construction would begin in Phase I by building a PFBC island to the north (left in the photo below) of Unit 1.  In later project phases, this would be converted to APFBC operations.  After the tie-in and operation of the Unit 1 PFBC, the project would proceed with a series of demolitions and constructions, until PFBC repowered Unit 2, and Train A and Train B of Unit 3 were constructed.  The project would end in the later project phases with the completion of upgrade of all four trains feeding the three units to APFBC operations.  The illustrations below show where this construction would occur at the site.

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Photo and Plan Layout Before the Project
The aerial photo and sketch below show the location of Units 1, 2, and 3, and illustrate the general area planned for the construction of the APFBC equipment.

Plan Layout at the End of All Project Phases

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Performance

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Repowering Units 1, 2, and 3 with APFBC would increase the output from these units by 60 percent.  The energy efficiency of these units would improve from 34.9 percent on an HHV basis to 38.1 percent with the proposed APFBC repowering upgrades.  The resulting fuel savings would result in a significant reduction in production costs. 

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Environmental Characteristics
APFBC is an exceptionally clean technology, one of the principal benefits of an APFBC repowering project.  Enlarge the image below to see the benefits to the station.

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Cost

• Estimated total plant cost for the APFBC project is about $994,465,000 or $1,100 per combined kW.

• APFBC production cost is about $13.50 per MWh.

• APFBC levelized busbar cost is about $43.60 per MWh.