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Hot Times for Turbine Cooling
American Moistening Co.’s inlet air cooling systems are designed to raise gas turbine output and efficiency
By Mike Mercer
Inlet Air Cooling
As the demand for electricity rises with the ambient air temperatures of the summer months,electric power producers whose plants use gas turbine engines are pressed to raise their output and efficiency. A way to achieve the increases is through the cooling of inlet air cooling system packages such as those produced by American Moistening Company (AMCO), of Pineville, North Carolina, U.S.A.
“Over the past decade, the face of the power generation industry has undergone some substantial changes,” said Elliott Smith gas turbine marketing manager for American Moistening. “Deregulation, the increased demand for electricity to power computers and factories, compliance with environmental regulations and a growing population, have been responsible for the increased demand for clean, efficient energy.“This is especially true in the hot summer months when demand for power is even higher to operate air conditioning and other electric powered items. It is also during the summer that gas turbine power plants lose a large percentage of their rated power due to the summer heat.”
Since 1997, AMCO has been a manufacturer of direct spray inlet air cooling systems for gas turbine engines. The company has gained extensive experience in humidification systems since its beginnings in Providence,
Rhode Island, U.S.A., in 1888. Origi- nally, the company provided industrial cooling and plant humidifying systems for the textile industry. In 1929, it relocated to North Carolina along with the heart of the textile industry. Early products used compressed air atomization of water and conventional air washers. In the 1970’s AMCO broke into other markets with the demand for a more economical means of humidifying process air. In response to customer needs,AMCO developed its direct spray, high-pressure water system. Since the introduction of this system, AMCO has installed thousands in the textile, wood-working, printing, automotive, and industrial HVAC markets. The company has applied all this experience and knowledge of high pressure systems to gas turbine inlet air cooling applications.
The company produces a wide variety of auxiliary equipment for the gas turbine industry, including gas turbine inlet fogging systems, enclosures, inlet air filter housings, mist eliminators, water forwarding skids, demineralized water systems, control panels, mechanical cooling and direct evaporative cooling for heat exchangers. Evaporative media coolers have been available for years, helping to recover some of the capacity and revenue lost to the effects of reduced mass flow and efficiency of gas turbines in warm, dry or even humid conditions. Until a few years ago, media type coolers had been the most prevalent within the marketplace. “There were solid power gains realized by using these ‘passive evaporation’ systems to cool the inlet air to the turbines,” said Smith. “The primary goal is to cool the inlet air, making it more dense, allowing the engines to process higher mass air flows. The result is a recovery of some of the lost power.”
These systems were a step in the right direction. However, the largest hurdles to overcome, according to Smith, are the constant inlet pressure losses and often-limited life of the cooling media.“Teaming up with Fern Engineering in the mid 1990’s was key to the growth and success of AMCO in the turbine market,” said Smith. “Fern provided us over 30 years of design consulting and research expertise in the gas turbine industry, and played a key role in the development of our first direct spray coolers to enter the market.
“As with any technology, there is always the quest to develop the next stage in evolution,” said Smith. “Many advances were made in the past few years to improve evaporative efficiency of media coolers and that is what lead us to the advent of direct spray inlet cooling or gas turbine inlet fogging. This has pushed us to the level of 100% evaporative efficiency, producing significant gain in power via an ‘active’ evaporative process with essentially no inlet pressure loss.” Years of research and development have gone into the pursuit of perfection, reviewing turbine design parameters, modeling and testing of nozzle technologies, building databases of performance information, and working to develop the trust of long-term repeat customers through service and full support.
“Inlet fogging has rapidly grown in acceptance by end users of gas turbines and in the past few years it has also gained the acceptance of gas turbine OEM’s as well,” said Smith. “This is due to the desire to gain a competitive edge, coupled with a push by large power producers to maximize capacity of new unit installations.”
AMCO now has over 100 units in operation with over 70 new OEM plant system orders to date. New OEM orders for Siemens Westinghouse W501FD turbines include inlet fogging systems for large end users such as Calpine and Dynegy. With over 100 new advanced-class turbine units currently installing foggers industry wide, it is expected that the retrofit market for this low cost upgrade alternative will grow more and more over the next few years. In addition, inlet fogging can easily be installed into virtually any existing plant configuration, according to Smith.
The AMCO inlet air fogging systems operate at high pressures to minimize the number of nozzles required, thereby minimizing the chances for recombination (agglomeration). This helps to improve evaporative efficiency and reduce the risk of having free moisture enter into the compressor. The AMCO systems operate at 207 bar to ensure maximum distribution of fog while minimizing any risk of compressor blade erosion and wear. Laboratory testing has confirmed that the AMCO nozzles, when operating at 207 bar, can produce a droplet size distribution with at least 90% of the mass being composed of droplets less than 20 ?m in diameter, according to AMCO.
“Our gas turbine inlet air cooling systems are custom-designed to achieve maximum evaporation in varying ambient conditions,” said Smith. “This is accomplished via a ‘closed loop’ control approach which allows us to control the compressor inlet air temperature to within a 1 °F approach to the wet bulb temperature.”The central part of every AMCO system is the pump and controls skid. The primary components of which include heavy-duty ceramic plunger pumps with stainless steel heads, premium TEFC electric motors, high efficiency water filters, motor control center and an overall system control.
The system control uses an advanced PLC logic capable of managing multiple cooling zones — a zone consists of one or more nozzle manifold lines. Optimum cooling is achieved through a highly developed algorithm that selects a flow stage, which is a single zone or combination of zones. When reviewing inlet fogging systems, many factors must be considered to ensure that the design utilized is engineered for gas turbine use. In particular, it is important to follow industry codes and standards such as B31.1 for piping and welding. “Our systems are never soldered and they utilize industry approved locking mechanisms to secure components completely, minimizing the risk of foreign object damage,” said Smith.
Inlet air fogging systems can be set up in different configurations. The most typical application is a design where the nozzles are placed downstream of the high efficiency air filters in the clean air plenum. With the nozzles in this location, the pressure drop across the nozzle manifolds is less and can extend the life of the final filters.
The direct spray cooler system consists of one or more positive displacement pumps that pressurize demineralized water to 207 bar. The water is fed into a series of seamless stainless steel headers connected to stainless steel nozzle manifolds. The specialized AMCO nozzles atomize the pressured water into ultra-fine droplets that evaporate quickly and efficiently even in the most humid conditions. The pressure drop across the nozzle manifolds of an AMCO system is close to zero, according to the company. This is compared to 1.27 cm of water across media coolers and 2.54 cm of water across cooling coils. The result is a higher increase in power output.The AMCO system is designed for a quick and easy installation into existing inlet air ducts. The systems can be installed during a regular planned maintenance outage or as part of a brand new project . AMCO also offers turnkey installation services.
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