By Lars van Pomp, Sales and Marketing Manager, Resolute Research
First, the attractiveness of natural gas
The attractiveness of natural gas has been much discussed over the past several years, and will be briefly summarized here. The shale-gas development in the US has been the major headline grabber and with ample justification. The industry has spawned expansive new gas supplies, driving prices down and creating opportunities for state-of-the-art power generation plants that are re-writing the textbooks on thermal efficiencies and favorable environmental protection. Other attractive features of gas include:
• Suitability for development of highly reliable gas turbine base-load power plants, important in the “fleet restructuring” that is in progress in many electric utility markets today
• Suitability for the rapid-start performance required as backup to other power sources, including intermittent solar or wind power
• Suitability for non-utility, industrial co-generation and combined heat and power (CHP) power plants
• Cleaner combustion than is possible with other fossil fuels
• Relatively easy transport by pipeline to widely separated markets
• Compatibility with enhanced bulk transportation methods in over-the-road vehicles and ocean-going carriers in the form of compressed natural gas (CNG) or liquefied natural gas (LNG)
• Combustion capabilities supportive of relatively low-cost thermal power plants, most significantly combined cycle gas turbine plants
Although the list of attractive features goes well beyond this, the last point provides a convenient segue into the heart of the pump opportunity, which is the combined cycle gas turbine (CCGT) power plant.
The attractiveness of the CCGT power
Very high on the list for attractiveness of CCGT power plants would be the easier permitting process, the compressed build-cycle time, the significantly lower capital cost and the significantly lower operating cost of CCGT plants relative to coal or nuclear power plants. Those metrics alone are likely sufficient to drive the market. However, beyond that there are additional drivers related to improved thermal efficiency.
While the thermal efficiency of a simple cycle turbine-only power plant is relatively low (about 35 percent) because of lost energy resident in the high-temperature exhaust gas, the thermal efficiency of the combined cycle plants is among the highest for thermal power generators. As an example, a traditional coal-fired power plant will have a thermal efficiency in the range of approximately 42 percent or so (a nuclear power plant may have a thermal efficiency even slightly less than that). State-of-the-art supercritical and ultra-supercritical coal power plants operating at higher steam temperatures and pressures will have an efficiency in the range of 48 percent, possibly approaching 50 percent. In contrast to that, state-of-the-art combined cycle gas turbine power plants are now available with thermal efficiencies of 60 percent and higher. The practical benefits of that are lower-cost electric power and increased protection of the environment. Both are powerful drivers of the technology and the industry.
The core of this higher efficiency – and many of the pump opportunities – is the heat recovery steam generator (HRSG). The HRSG captures the heat energy that would otherwise be lost in the turbine exhaust. This captured heat is used to create steam for operating a secondary steam turbine and electric generator, which is added to the power generated by the gas turbine. In a typical plant, the ratio of total nameplate capacity will be 2/3rds from the gas turbine(s) and 1/3rd from the steam turbine. A CCGT plant is sometimes described as a “2 X 1”, which means that it includes two gas turbines and one steam turbine. The exhaust gas from the CCGT plant is very low, reflective of the energy capture provided by the HRSG.
A specific look at pump opportunities
Pump opportunities can be suitably presented by taking a plant “walk about”, starting with the front-end processes. Water pumps: Gas turbine power output and efficiency are affected by inlet air density. The denser the air, the higher the turbine output. Cooler air is denser than hot air and so “inlet air coolers” and misting systems are sometimes employed to boost turbine output, particularly in hot and arid climates. These systems often include water tanks, pumps and valves for introducing an atomized mist of water into the inlet air stream. Equipment cooling will be discussed later.
As mentioned earlier, the HRSG is home to most of the pumps in a CCGT power plant. These pump systems bear many similarities to a conventional power plant. Typical pump and valve equipment would include (but is not limited to) the following:
• High-pressure, high flow HRSG feed water pumps
• HRSG feed water valves (recirculation valve and feed control valve)
• Super heat and re-heat safety valves
• Pressure reducing de-superheater valves
• Main steam control valves
• Turbine bypass and vent valves
• Seal steam valves and many more
Condensate and condenser cooling systems
Similar to a conventional power plant, CCGT power plants include condensate and cooling water systems with equipment that includes but is not limited to the following:
• Condensate extraction pumps
• Cooling water circulation pumps and makeup water pumps
• Condensate recirculation and control valves
• Heater drain valves and more
To read the full article by Lars van Pomp, please email Deirdre Morgan.