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Wednesday, May 14, 2008:

Reliant Cheswick Coal Plant Tour

Program Description:

Join the Pittsburgh Sections of ASME for a tour of the Cheswick Power Station in Springdale.

The Cheswick Power Station is located along the Allegheny River in Springdale, Pennsylvania, approximately 10 miles North-East of Pittsburgh. The station achieved commercial operation in 1970. The plant consists of one coal-fired 588 MW (net) steam unit and employs 85 full-time power station professionals.

The boiler is a Combustion Engineering tangentially fired, split furnace, balanced draft, controlled circulation, drum-type unit delivering 4,000,000 Lbs/Hr of 1005° main steam at 2,620 Psi (SH outlet) and reheating 3,650,000 Lbs/Hr of reheat steam to 1005°, at 550 Psi. Forced/assisted circulation is provided by four, 700 HP, boiler circulating water pumps. The boiler firing system has a total of 40 burners at 5 elevations supplied by five, bowl-type coal pulverizer mills. Natural gas is used as startup fuel and flame stabilization during upsets. Two Lungstrom 30.5' diameter, vertical-shaft airheaters preheat the combustion air delivered by two 2,250 HP Forced Draft fans and two 1,250 HP Primary Air fans. A B&W Selective Catalytic Reduction (SCR) system removes 90% of the NOx emissions. Cold side, 24-section, Hamon Research Cottrell electro-static precipitators remove 99.8% of the fly ash from the flue gas, prior to the two 7,500 HP, 1,200,000 CFM Induced Draft fans which discharge into a single, 755' tall concrete shell, steel lined stack.

The steam performs its work in a 20 stage General Electric tandem compound steam turbine generator of the "G2" series. A combined HP/IP dense pack turbine and two, double flow LP turbines directly drive the two-pole generator at 3,600 Rpm. The HP turbine consists of 8 stages and is straight full-arc admission using four control valves. The IP turbine has 5 stages and the two double-flow LP turbines each consist of 7 double flow stages with 30" last-stage blades.

LP turbine exhaust steam is condensed in a single pass, two-zone 210,000 Ft^2 surface condenser, supplied with once-through river water from three circulating water pumps, each rated 1,000 HP and 82,000 GPM. Seven stages of extraction steam are taken off at various points on the HP, IP and LP turbines for feedwater heating and to drive the two 50% steam turbine-driven boiler feedwater pumps. The hydrogen cooled generator has a nameplate capacity of 700 MVA at 23,000 Volts and is connected via a dedicated iso-phase bus duct to two 350 MVA step-up transformers which raise the voltage to 138,000 Volts for connection to the Pittsburgh control area grid. Station service power is provided by five, 4,160-Volt station service busses fed from three 25 MVA, 138 kV to 4,160 V station service transformers. A fuel-oil-fired auxiliary boiler provides building heat and critical system protection during extended outages.

The condensate system consists of two 50%, 350 HP, 4,040 GPM, 120 Psi, vertical-type hotwell pumps, discharging in to the air-ejector condensers, steam packing exhausters and finally through the three-vessel condensate polisher. Two 1,250 HP, 4,900 GPM condensate booster pumps take suction from the polishers and raise the condensate pressure to 550 Psi and discharge to the LP heater train. The last LP heater is an open, tray-type deaerating heater of 55,000 gallons capacity located on the 10th floor of the plant to provide adequate suction head for the feed pumps.

Two 50% steam turbine driven feed pumps each rated 10,000 HP, 5,000 GPM, 3,500 Psi take suction from the dearator and discharge feedwater to the two vertical high-pressure feedwater heaters and then to the finned tube economizer in the boiler backpass which completes the feedwater heating, delivering 4,000,000 Lbs/hr of 585°F feedwater to the boiler drum. The steam turbines driving the boiler feed pumps exhaust their steam directly to the main unit condenser.

Complete automatic plant control is provided by a Westinghouse WDPF DCS system. 15 separate, dual-controller DCS drops, each fed by two redundant UPS power supplies provide complete coordination and control of the main plant systems. A Westinghouse Ovation DCS system provides control of the SCR NOx removal system. Nearly all plant functions other than bus switching and large motor starting are performed on the various DCS computer workstation screens. A fully implemented OSI-PI data historian and trending package complement the Westinghouse DCS historian, providing thorough and complete data trending, history and sequence of events information seamlessly.

Coal is delivered via barge with truck delivery available for frozen river conditions. The plant maintains two active sections of the coal storage pile for both high and low sulfur coal. The two coals are then blended to meet an SO2 emission limit of 2.8#/Mmbtu and the as-fired blend typically has a heating value of 11,800 BTUs/Lb and an ash content of ~ 8%. The plant consumes roughly 5,500 tons of coal per day at full load. Ammonia for the SCR system is delivered via rail car and stored in four 60,000-gallon storage tanks. Bottom ash is sluiced from the dry-bottom boiler, submerged ash hoppers to the nearby hydrobins where it is dewatered and hauled by truck to the plant owned landfill or sold for beneficial use. Fly ash is pulled from the precipitator hoppers with a dry vacuum system, stored in the onsite ash silo and also hauled via truck to the same landfill or beneficial use site. The plant can operate in load-following automatic control from full rated 590 MW down to 145 MW without firing supplemental fuel, and at typical controlled ramp rates of 7 MW's per minute. At full load the demonstrated net station heat rate is 9,750 BTU/kWH.

*Cancellation within 24 hours of event will require event payment unless a replacement can be found to attend.

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