Again within the early 2000s, some controversy emerged concerning the observe of spraying massive quantities of fog instantly into the compressor. Some claimed that this led to blade erosion, pitting, and scaling. So, is it secure to make use of moist compression on fuel generators by pumping water droplets into the compressor inlet? The reply is sure—supplied the system produces small droplets, is from a good provider, that demineralized water is employed, and that it’s operated and maintained appropriately.
What Is Moist Compression?
Moist compression or overspray consists of injecting demineralized water within the type of tiny fog droplets into the inlet of a fuel turbine to enhance output and warmth fee (Determine 1). These droplets evaporate contained in the compressor, which lowers the temperature and the work of compression. In consequence, extra energy is offered on the output shaft. Estimates of its effectiveness fluctuate from 5% to 10% energy enhance for every 1% of water injected into the compressor inlet air mass circulation. Some moist compression adopters have put in programs that spray as a lot as 2.5% of the air mass circulation.
There have been many agency advocates of moist compression over time. Steve Ingistov, principal engineer at Tesoro Corp.’s Watson Cogeneration Plant in Carson, California, has been utilizing it efficiently for the reason that Nineteen Nineties. The plant has 4 pure fuel–fired GE 7EA generators rated at 83.5 MW every (ISO), in addition to two Siemens Vitality steam generators and a duct-fired warmth restoration steam generator (HRSG) for a complete of 385 MW. Ingistov is understood for introducing a collection of enhancements, improvements, and upgrades to the ability that boosted output to 425 MW. Fogging and moist compression account for about 10 MW of that acquire, he estimated.
First-row blade erosion was found at Watson Cogen in 2000. An in depth investigation traced it to the web water washing system and an getting old evaporative cooler that was releasing very massive droplets into the airflow. These massive droplets agglomerated and have been carried into the compressor.
The evaporative cooling system has since been changed with fogging. Compressor blades have been upgraded to Carpenter 450 at the moment to keep away from erosion resulting from water washing. Since then, Watson Cogen has amassed 20 years of liberal utilization of moist compression with out problem.
“Throughout greater than twenty years of operation, the MeeFog moist compression system has not triggered blade erosion,” mentioned Ingistov. “We run the system across the clock in the course of the peak interval of electrical energy technology from June to September and anytime the ambient temperature is above 50F.”
Supportive Moist Compression Customers
Many different vegetation have deployed moist compression with out problem, each in North America and internationally. The majority of those have been designed and put in by Mee Industries Inc. One other instance is Eagle Level Energy Technology (EPPG) in Westville, New Jersey. This 225-MW mixed cycle facility consists of two GE Body 7EA turbine turbines, two Nooter/Eriksen HRSGs, and a single 50-MW Alstom condensing steam turbine. The power started working in 1991.
It had been utilizing inlet air fogging for evaporative cooling for a few years earlier than a Rockland Capital affiliate bought the producing facility in April 2012. That signaled an entire vary of steps to spice up the output, together with upgrading the unique inlet fogging system and including moist compression.
“Relying on ambient circumstances, EPPG will get an extra 12 MW whole from the GE 7EAs, and there might also be an extra MW from the steam turbine,” mentioned Jeff Zelik, EPPG’s plant supervisor. “This enhance is from each the inlet fogging and the moist compression. The compressor inlet temperature will drop greater than 20F in heat climate. Borescope inspections present that moist compression retains the compressor clear so intervals between water washes will be prolonged.”
He added that the MeeFog system has carried out effectively with no erosion, however cautioned others concerning the significance of protecting the filters clear and guaranteeing there’s a good fogging sample. With these factors taken care of, operating each inlet fogging and overspray is a dependable and secure approach to get extra worth out of current tools, he added.
Like Ingistov, EPPG’s Plant Undertaking Supervisor Dan Turley discovered on-line water washing to be the offender for blade erosion discovered many years in the past on its two GE Body 7FAs. “Fogging is an integral a part of our plant economics,” mentioned Turley. “Having a correctly designed and functioning fogging system on each items has made us an amazing amount of cash in comparison with the price of the system.”
One other Current Moist Compression Instance
The Mesquite Block 2 plant, owned by Onward Vitality, carried out moist compression about three years in the past (Determine 2). The primary objective was to extend energy output all year long, particularly in the course of the Arizona summer time when each day highs can common higher than 100F for 4 straight months. Block 2 consists of two GE 7FA.03 fuel generators, a D11 steam turbine, and Nooter/Eriksen HRSGs. The fuel turbine’s most score is 180 MW and the steam turbine supplies 321 MW. Block 2 operates in baseload many of the yr.
Onward put in a MeeFog moist compression system in every turbine within the spring of 2021, simply in time for the new summer time months. Every unit can spray as much as 35 gallons per minute with 90% of the circulation being in droplets of 20 microns or much less. The spray nozzle arrays are positioned within the vertical part of the inlet, downstream of evaporative coolers that proceed to function. The moist compression system makes use of a single high-pressure pump with a variable frequency drive to offer two phases of demineralized water spray.
After operating the system for 3 years, Todd Hart, director of Fuel Engineering at Onward Vitality, gave the blades a clear invoice of well being. That is based mostly on inspection of its blades each summer time to make sure they continue to be in tiptop situation. The latest inspection included digital R0 scans (the ahead rotor blade in a fuel turbine’s compressor) and nondestructive examination (NDE) testing.
“Our moist compression system produces 7 MW per 7F.03 unit inside two to a few minutes. We’ve got not had any points with erosion or scaling,” mentioned Hart.
Good Design Ensures Moist Compression Success
Mee Industries is the foremost proponent of moist compression. It has put in fog programs in additional than 1,000 generators. A couple of third included moist compression functionality. During the last 5 years, the corporate has observed an upsurge of shoppers requesting moist compression. They view it as a cheap various to main turbine upgrades or changing older items with the newest technology of machines.
“As with every know-how, inlet fogging should be finished correctly to supply the specified outcome,” mentioned Thomas Mee III, CEO of Mee Industries. “We’ve got greater than 25 years of discipline expertise with moist compression and our programs are designed to function safely and successfully.”
Mee laid out the important thing components that maintain compressor blades free from erosion, corrosion, scaling, and pitting.
Droplet Measurement. Properly-designed fogging nozzles produce billions of tiny droplets per second. This exposes extra floor space of water to the air in order that they evaporate quicker than bigger droplets and supply more practical cooling. A given quantity of spray consisting of 40-micron droplets exposes solely one-fourth the floor space as in comparison with the identical quantity of spray consisting of 20-micron droplets.
“Analysis and expertise present that inlet fogging droplets needs to be about 20 microns or much less,” mentioned Mee. “Our impaction pin nozzles supplied droplets with 90% of the circulation being in droplets of 20 microns or much less.”
The next chart (Determine 3) was developed based mostly on analysis finished at Mee Industries. It may be used to estimate the droplet dimension produced by a proposed moist compression system.
Demineralized Water. Untreated water comprises minerals that may result in blade fouling and hot-gas-path corrosion. Due to this fact, utilizing Demineralized water is essential for fogging and moist compression programs.
Good Drainage. Compressor blade erosion can happen if flowing or pooled water is sucked into the compressor inlet. This may occasionally trigger erosion of compressor blades over prolonged durations of time. Due to this fact, it is very important make the most of correctly designed drainage programs to take away water from the inlet duct. Water diverters needs to be utilized to direct water to drainage factors. Moreover, a false flooring above drain factors can enable water to circulation to the drain and never be drawn into the compressor.
Droplet Distribution. Inlet fogging programs should evenly distribute droplets within the airflow. That is greatest achieved with a bigger amount of fog nozzles, every with a decrease flowrate, somewhat than fewer, high-flowrate nozzles. Such a system will even have nominal accumulation of flowing or pooling water within the inlet ducts, and at a given working stress, low-flow nozzles usually produce smaller droplets than high-flow nozzles.
Grime and Rust. Inlet surfaces, together with the compressor inlet, needs to be completely cleaned earlier than working a fogging system. Grime that has amassed on duct surfaces or the compressor inlet will be carried to the compressor and trigger fouling. Areas of rust or compromised coating also needs to be cleaned and recoated earlier than working a moist compression fogging system.
“Whereas some early moist compression programs from inexperienced distributors might have contributed to blade erosion, MeeFog programs have recorded a whole bunch of 1000’s of hours of problem-free moist compression operation over greater than 1 / 4 of a century,” mentioned Mee.
—Drew Robb ([email protected]) has been a full-time freelance author for greater than 25 years specializing in engineering and know-how.
