28-08-2012, 11:21 AM
Pulverized Coal-Fired Subcritical Plant 400 MWe
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PULVERIZED COAL
The market-based pulverized coal power plant design is based on the utilization of pulverized coal
feeding a conventional steam boiler and steam turbine. The plant configuration is based on
current state-of-the-art technology, commercially available components, and current industry
trends. The traditional pulverized coal power plant of the 1970s and 1980s contained reliable
equipment with built-in redundancy and several levels of safeguards against unplanned downtime.
During the 1980s, the level of redundancy and the design margins were decreased in an effort to
reduce cost, yet maintain availabilities in the 82 to 86 percent range. During the 1990s,
construction schedules were shortened, design time was decreased by use of “reference plants,”
and equipment design margins were reduced, all in an effort to enhance the pulverized coal power
plant’s competitive position. “Reference plants,” or modular plant designs, are standard packaged
component designs developed by the design firms to enable owners to pick and choose the plant
configuration from these pre-designed modules with minimal engineering time.
Design Basis
The design basis of this pulverized coal plant is a nominal 400 MWe subcritical cycle. Support
facilities are all encompassing, including rail spur (within the plant fence line), coal handling,
(including receiving, crushing, storing, and drying), limestone handling (including receiving,
crushing, storing, and feeding), solid waste disposal, flue gas desulfurization, wastewater
treatment and equipment necessary for an efficient, available, and completely operable facility.
The plant is designed using components suitable for a 30-year life, with provision for periodic
maintenance and replacement of critical parts. The plant design and cost estimate are based on
equipment manufactured in industrialized nations (United States, Germany, England, etc.) with
the standard manufacturer’s warranties. The design is based on a referenced design approach to
engineering and construction. All equipment is designed and procured in accordance with the
latest applicable codes and standards. ASME, ANSI, IEEE, NFPA, CAA, state regulations, and
OSHA codes are all adhered to in the design.
Heat and Mass Balance
The steam power cycle is shown schematically in the 100 percent load Heat and Mass Balance
diagram (Figure 3.1-1). The diagram shows state points at each of the major components for the
conventional plant. Overall performance is summarized in Table 3.1-1, which includes auxiliary
power requirements.
The plant uses a 2400 psig/1000°F/1000°F single reheat steam power cycle. The high-pressure
(HP) turbine uses 2,734,000 lb/h steam at 2415 psia and 1000°F. The cold reheat flow is
2,425,653 lb/h of steam at 604 psia and 635°F, which is reheated to 1000°F before entering the
intermediate-pressure (IP) turbine section.
Ash Removal
The furnace bottom comprises several hoppers, with a clinker grinder under each hopper. The
hoppers are of welded steel construction, lined with 9-inch-thick refractory. The hopper design
incorporates a water-filled seal trough around the upper periphery for cooling and sealing.
Water and ash discharged from the hopper pass through the clinker grinder to an ash sluice
system for conveyance to the ash pond. The description of the balance of the bottom ash handling
system is presented in Section 3.1.9. The steam generator incorporates fly ash hoppers under the
economizer outlet and air heater outlet.
Burners
A boiler of this capacity will employ approximately 30 coal nozzles arranged in three elevations,
divided between the front and rear walls of the furnace. Each burner is designed as a low-NOx
configuration, with staging of the coal combustion to minimize NOx formation. In addition, at
least one elevation of overfire air nozzles is provided to introduce additional air to cool the rising
combustion products to inhibit NOx formation.
Steam Turbine Generator and Auxiliaries
The turbine is tandem compound type, comprised of HP - IP - two LP (double flow) sections, and
30-inch last-stage buckets. The turbine drives a hydrogen-cooled generator. The turbine has DC
motor-operated lube oil pumps, and main lube oil pumps, which are driven off the turbine shaft.
The turbine is designed for 434,500 kW at generator terminals. The throttle pressure at the
design point is 2400 psig at a throttle flow of 2,734,000 lb/h. The exhaust pressure is 2.0/2.4 inch
Hg in the dual pressure condenser. There are seven extraction points.
Precipitator
The flue gas discharged from the boiler (air preheater) is directed through an electrostatic
precipitator array comprised of two rigid frame single-stage units. Each precipitator unit is
divided into five field sections, each in turn containing three cells. Each cell contains a number of
gas passages comprised of discharge electrodes, collecting plates, and ash hoppers supported by a
rigid steel casing. Each cell and ash hopper is provided with a rapping system, which periodically
provides a mechanical shock to the unit to cause the fly ash particles to drop into the hopper, and
then out into the collection piping. The precipitators are provided with necessary electrical power
and control devices, inlet gas distribution devices, insulators, inlet and outlet nozzles, expansion
joints, and other items as required.