Combo Technical tour

Nigel Blackaby, Associate Editor, Power Engineering International magazine

A party of 30 intrepid POWER-GEN International delegates left the Las Vegas Convention Centre at 8:30 am on Monday, headed for the Nevada desert and the chance to see two very contrasting power generation facilities, the Walter M. Higgins combined-cycle generating station and the Goodsprings Waste Heat Recovery plant.

Both plants are owned and operated by NV Energy, a public utility with power generating facilities spanning gas, wind, coal and waste to energy in Nevada. The two plants that they were opening up to POWER-GEN were located around 30 miles southeast of Las Vegas, almost on the California state border. Our guide at the Walter M. Higgins facility and our co-host on the second part of the tour was NV Energy’s Production Manager, Jeff Smith.

Walter M. Higgins Generating Station

We approached the Walter M. Higgins Generating Station after turning off highway 161 and passing through the small casino resort at Pimm. The plant went into service in 2004 and was originally built as an IPP by Reliant Energy before being sold to NV Energy. The plant, which has a peak generating capacity of 530 MW, is a clean burning natural gas fired plant featuring two Westinghouse 501FD combustion turbines. Exhaust gas from the gas turbines is recycled to produce steam to power an Alstom STF30C steam turbine.

The remote desert location of the plant means that water is scarce and the plant has been designed without conventional cooling towers that would consume large amounts of water. Instead, the Higgins station uses a six-story-high dry cooling system. Similar to a car radiator, 40 massive fans (34 feet in diameter) are used to condense the steam and cool plant equipment. The water that the plant does use to produce steam is derived from the nearby casino and a sophisticated water treatment plant conditions the grey water from Pimm for use in the plant. Grey water refers to water from sinks, showers, tubs, washing machines etc.

One of the main challenges for the water treatment is the number of bugs that have to be removed otherwise they risk blocking the membranes in the system. The Aquatech water treatment system includes two RO membranes, an evaporation tank, UV filters, chlorine removal and injection of sulphuric acid to lower PH levels.

The plant can produce enough electricity to serve approximately 320 000 Nevada households and has performed in the top ten per cent for combined cycle plants in the US, based on its high customer availability rate of 99 per cent. Average load capacity is running at 95 per cent and typically runs at 500 MW during the day, dropping to 300 MW at night. On arrival at the plant the facility was producing 510 MW but, upon receiving instructions from NV Energy’s Reno HQ, the operator shut off firing ducts and lowered capacity to 465 MW – a process that took around 20 minutes. Most of the power produced is consumed by customers in Nevada although a proportion is exported into the Californian power grid through the nearby Eldorado sub station.

Gas is supplied to the plant by the Kern River Gas Transmission Company and usage is around 78 145 cubic feet/day. Gas is received at 1400 PSI and is dropped down to 500 PSU for use in the plant.

The Higgins plant operates comfortably within current emissions regulations and features a dry low NOx system. According to Jeff Smith, keeping pace with environmental regulation is a challenge and the plant is regularly inspected and audited for emissions, including ground water and ammonia.

The impression was of a well organised and maintained plant that is run by a staff of just 17 personnel. “Future expansion of the plant is a possibility”, said Smith. He and his colleagues took pride in showing delegates the plant and answered many questions from their very inquisitive guests.

Goodsprings Waste Heat Recovery Plant

Part two of the combo tour required the coach travelling the ten miles across the Nevada desert to the Goodsprings Waste Heat Recovery Plant. Nestled in the foothills of the reddish brown Spring Mountains, we approached the plant by way of a mile-long dirt track that was a surrounded by mile after miles of stony desert, interspersed by yucca trees and the occasional cactus that was a protected habitat for tortoises. Here the air was thinner and the air much colder and wit the temperature dropping by the minute, the visit to Goodsprings was of shorter duration.

Goodsprings is located 35 miles southwest of Las Vegas and generates 7.5 MW from the waste heat produced by the large adjacent natural gas compression station that is used to pump natural gas through Nevada to California. In the normal operation of the compressor station, some waste heat is released and this can be captured and converted to electricity by the installation of an energy converter, similar to those used in geothermal electricity generation. The Goodsprings project uses three heat exchangers to capture the heat from each of the existing compressors, and then uses that heat to turn a separte generator to produce electricity. A schematic diagram (below?) illustrates the process.

The plant is a three-way partnership between geothermal specialists Format Technologies, Kern River Transmission Co. and NV Energy. Ormat, the technology provider, also served as the project’s engineering, procurement and construction partner. Colin Duncan, Manager, Recovered Energy at Ormat’s Reno base, served as the guide to the facility and explained that, while Ormat has been operating the plant for three years, the plan was to turn it over to NV Energy who will become the plant operator.

Goodsprings is classed under Nevada law as a renewable energy facility. The resulting green credits that it thus qualifies for has made the project viable and contributes to NV Energy’s renewable obligations. Unlike some renewable energy sources, the waste heat is not an intermittent energy source. The compressor station is expected to operate around 90 per cent of the time and will provide a more consistent energy source, capable of serving approximately 4500 Nevada homes.

 Eventually, the cold drove the visitors back to the coach. There was no sign of the tortoises who were wisely hibernating, so we headed back to Las Vegas with the prospect of three days of indoor POWER-GEN to look forward to. The two very different plants made for an interesting tour and POWER-GEN extends its grateful thanks to all who took part and to our host NV Energy.

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