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This project is in progress -- Check back here frequently for updates!

Contents:

• GFBCC Repowering Project Summary
• Key Features
• Site Layout
• Performance
• Environmental Characteristics
• Cost

Other Combustion Systems Repowering Study Links:

A related study is underway that would repower Sheldon Unit 1 and
Unit 2 with advanced circulating pressurized fluidized-bed combustion
combined cycle technology (APFBC). CLICK HERE to find out more
about repowering the Sheldon Station with APFBC instead.

GFBCC Repowering Project Summary

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Gasification fluidized-bed combined cycle systems (GFBCC) are hybrid systems with a pressurized circulating pressurized fluidized-bed PCFB partial gasifier and an atmospheric-pressure circulating fluidized-bed combustor (CFB).  Coal is used as fuel.  In this concept, the PCFB partial gasifier and CFB are supplied by Foster Wheeler.  

The Sheldon Steam Plant.   The host site for this repowering concept evaluation is Nebraska Public Power District’s Sheldon steam generating station.  The Sheldon station is a coal-fired electric generating station located near Hallam, Nebraska, about 25 miles south of Lincoln.  The plant was constructed between 1958 and 1963 as an experimental nuclear power plant for the Atomic Energy Commission.  After the Commission (today known as the Nuclear Regulatory Commission) acquired the information it needed, the nuclear portion of the facility was decommissioned and the equipment and parts were sent to other nuclear plants or disposal sites.  What could not be moved was sealed and buried in large vaults beneath the earth's surface at the plant.

Today, Sheldon station's two boilers can generate 225,000 kilowatts of electricity.  There are two coal-fired steam units at this site:

• Unit 1, commissioned in 1961, is a 108,800 kW output reheat unit.
• Unit 2, commissioned in 1965, is a 119,000 kW output reheat unit.

GFBCC repowering increases the amount of electric output from the plant.  The efficient new equipment continues the use of coal there, but lowers electricity production costs.  The method significantly reduces the amount of wasted energy, so more electricity is produced from each ton of coal, with much less pollution.  These studies show that GFBCC has attractive characteristics, and that it appears easily customized to match the steam demands of the existing plant equipment.   This is important compared to many other ways of repowering a plant, since it means that with GFBCC more of the existing equipment at the plant can be re-used, keeping costs low.

GFBCC is under development by industry and the DOE.  A commercial demonstration plant is in the planning stages.  When that demonstration occurs, GFBCC should be ready for commercial orders soon, so a number of electric companies are looking at the technology to see whether GFBCC repowering makes sense for them.

The Nebraska Public Power District volunteered its evaluation support for the study, getting no government funding.

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Key Features

PCFB Partial Gasifier.   The PCFB partial gasifier operates at elevated pressure (10 to 15 times atmospheric pressure) in a mild gasification process that produces a syngas, which fuels a gas turbine topping combustor.  The syngas is quenched to moderate temperature before it passes through sintered metal filters to remove dust from the syngas before it enters the gas turbine topping combustor.  Removing the dust avoids corrosion and erosion damage to the combustor and gas turbine. 

Atmospheric-Pressure CFB.  The PCFB partial gasifier leaves some of the coal's remaining energy in the char and ash.  The char and ash solids from the PCFB partial gasifier are dropped in pressure, and transferred to an atmospheric-pressure CFB, where the char is burned.  This releases the rest of the coal's energy.  Limestone is added to the CFB to capture and remove sulfur pollutants.  The gas turbine exhaust has excess air, which is used as combustion air for the CFB.  This is a convenient way to recover the heat energy from the gas turbine's exhaust, so the power cycle becomes very energy efficient.  Steam tubes in the CFB bed generate steam for a steam turbine bottoming cycle, which in a plant repowering uses the existing Sheldon steam turbine. 

The combination of the gas turbine and steam turbine provides combined cycle plant efficiency from coal, making these types of GFBCC plants among the cleanest, most efficient ways of using coal for electric power generation.  More steam is needed to match the existing Sheldon station steam requirement than can be developed from the char alone, so coal is added to the CFB to supplement the char energy. 

NOx Control.  The fluid beds in the PCFB partial gasifier and CFB produce low levels of NOx compared to conventional furnaces:  some NOx is developed in the gas turbine topping combustor.  To make the NOx emissions exemplary, an SNCR is employed within the CFB to provide low-NOx environmental emissions. 

Baghouse and ID Fan.  A baghouse removes dust from the CFB exhaust, with an induced draft fan to draw down the pressure to overcome CFB, SNCR, and baghouse pressure drops so the gas turbine operates at normal atmospheric back-pressure.

Combustion Turbine.  In this concept, two near-identical single trains are employed.  Each uses a GE 6FA gas turbine and topping combustor, modified for GFBCC service, to add output to the plant.  The existing Sheldon station Unit 1 and Unit 2 steam turbines are retained as the steam bottoming cycle.   A single GFBCC/gas turbine train supplies Unit 1, while a second independent train supplies Unit 2.  These trains are near identical, except for the differences in steam pressure and flow demands of the two trains.  Once the GFBCC system is put in place and tested, the existing Unit 1 and Unit 2 boilers will no longer be needed and can be demolished, or kept in standby condition if added reliability states are desired. 

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Site Layout

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Performance

Unit 1 output would increase about 90 percent with this repowering, while excellent energy efficiency of GFBCC would reduce the amount of coal needed to produce each kilowatt of power by about 14.5 percent.

§ these are the conditions used as baseline for the comparisons, not the rated output of the units. 
Unit 1 rated output is 109,000 kWe

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Environmental Characteristics

This study is underway and not yet available.  Check back soon.

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Cost

This study is underway and not yet available.  Check back soon.