June 15, 2008
PG&E Repowering Project Set to Begin
By Wagman, David
Wartsila North America Inc. began detailed engineering and manufacturing on a 163 MWe gas-fired power plant for Pacific Gas and Electric Co. (PG&E). Plant construction could begin later this year and be completed in the fall of 2009. Construction cost is estimated at $250 million, or around $1,500/kW. Coming to PG&E: A Wartsila 18V50DF dual-fuel engine.
The plant will be in Humboldt County near Eureka in northern California and is expected to enter commercial operation by mid- 2010. When compared to the existing 50-year-old PG&E plant at the site, the new facility will be 33 percent more efficient with 85 percent fewer ozone forming compounds and a 34 percent reduction of greenhouse gas emissions production.
The new facility will consist of 10 Wartsila 18V50DF lean-burn dual-fuel engines delivered on an engineering, procurement and construction basis. The engines will be fueled by natural gas and will be capable of using ultra-low sulphur diesel as a back-up during times of natural gas curtailment.
The plant is designed as a loadfollowing and daily cycling facility to meet electric generation load and reliability requirements in PG&E's transmission constrained Humboldt service area. The project replaces existing Units 1 and 2 (105 MW combined capacity) consisting of natural gas- and oil-fired steam turbine- generating units. Two diesel-fired mobile emergency power plants rated at 15 MW each also will be replaced.
The service area relies extensively on local generation resources due to power import constraints and service interruptions in the 115 kV transmission system.
The reciprocating engines being installed are similar to a conventional automobile engine, containing 18 cylinders in a V- formation. During normal operation, the engines use natural gas as fuel, with a small amount of diesel fuel injected through a micropilot system to ignite the natural gas in the cylinders. During times of natural gas disruption or curtailment, the engines use diesel fuel supplied through a separate, conventional injection system. The dual-fuel technology is capable of operating at up to 48 percent efficiency. Auxiliary equipment includes inlet air filters, oxidation filters, gas exhaust silencer stacks, air radiator cooling array, generator step-up and auxiliary transformers and emergency diesel fuel storage tanks.
Air emissions from the proposed facility would be controlled using best available control technology applied to each engine's exhaust. Each system would consist of a selective catalytic reduction unit for oxides of nitrogen (NO^sub x^) control and an oxidation catalyst unit for carbon monoxide (CO) and volatile organic compound (VOC) control.
The plant would be connected to PG&E's existing switchyard via 13.8 kV cables and bus work from the generator circuit breakers to new stepup transformers and then via two 60 kV tie lines and one 115 kV tie line into the switchyard. Normally, four of the units would feed into the 115-kV line. The remaining six units would feed into the 60 kV lines. Switchyard improvements would include replacing the existing 60 kV and 115 kV circuit breakers and replacing a 115 kV steel lattice tower with three steel poles.
Natural gas would be supplied via an onsite 10-inch-diameter, high pressure natural gas pipeline owned and operated by PG&E. The natural gas would flow through gas scrubber/filter equipment, a gas pressure control station and a flow regulating station prior to entering the reciprocating engines.
The plant proposes using around 2,400 gallons of water per day (2.7 acrefeet/year) on average for cooling or other industrial purposes. The engines would use an air radiator cooling system in a closed loop system (similar to automobiles). Raw water for industrial processes and site landscape irrigation would be supplied from PG&E's existing ground water well via a direct connection to an onsite six-inch-diameter water pipeline.
The project is expected to take about 18 months for construction and startup testing and could begin commercial operation as early as fall 2009, if there are no delays.
The power plant would be capable of operating both in load following mode to meet local system demand and reliability requirements and in daily cycling mode, where the plant could operate up to maximum capacity during the day and totally shut down at night or on weekends. The planned life of the generating facility is 30 years, but could be extended if the plant is still economically viable. -David Wagman
Copyright PennWell Publishing Company May 2008
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