It's like a genset, but it does the job better—continuously and with minimal emissions. A microturbine is a gas-turbine engine—small, as its name implies. It drives a generator, and like those familiar gensets, it provides power directly to your facility. Housed inside or outside your plant, retail establishment, or general office building, the microturbine has few moving parts and offers long maintenance intervals; you can expect a microturbine to last considerably longer than a traditional genset in its operating life. The Ingersoll-Rand PowerWorks system will provide extended operation of 8,000 hours between scheduled service and an operating life as much as 10 times longer than that of a conventional genset. In typical, working-all-the-time operating conditions, an Ingersoll-Rand PowerWorks microturbine system is designed to provide the user with a practical life of 80,000 hours, or about 10 years. "Microturbines are a distributed-energy technology, suitable for small projects," explain Benny Benson and Jeffrey Pierce, experts at SCS Energy, a division of SCS Engineers. "As a point of reference, a 70-kilowatt microturbine produces enough power to satisfy the requirements of a 100-horsepower electric motor, or the equivalent of about 100 homes." How quiet is a microturbine? At 1 m, the noise levels are below 73 dBA.

The cleanliness of any direct-power system is important. With NOx emissions below 5 ppm, it is almost 20 times cleaner than a typical genset and quite like the low emissions produced by the most modern central power plants with special exhaust treatments. Some states (Texas, for example) have proposed dramatically lowering permitted NOx emissions over the next few years, and others, including New York and California, would like to set similar emissions standards for distributed generation (DG) equipment. Facilities now using generators powered by reciprocating engines might encounter a practical problem. It is probably possible to improve the emissions technologies for reciprocating engines, but the cost of doing so could be prohibitive. Diesel engines—and nobody can deny the good service they have given over the last few decades—might be the most difficult to improve beyond their currently accepted levels. Some communities have already forbidden the use of reciprocating gensets. Ingersoll-Rand's PowerWorks microturbines easily meet California's stringent standards for emissions. In fact, at some locations where they operate on such fuels as landfill gas (LFG), they actually help the environment by practical use of potential pollutants.

Before You Install the Equipment
Perhaps this paragraph should have been put at the beginning. There is a condition called islanding about which potential users of any microturbine power or cogeneration system should be aware. It is a potential threat to workers who are trying to restore power during an outage when a source of DG electric power (like a microturbine) remains connected to the electric grid and keeps the distribution lines energized during the outage. Simply, it means the worker up the electric pole can be injured or killed if electricity goes in a reverse direction from the facility. If the workers do not know that a source of power is keeping part of the grid live, they might start repairs and suffer electrocution. The electric distribution company should be informed of all sources of electric power that are connected (or will be connected) to the grid. Islanding is not deliberate; it is caused by ignorance or lack of proper caution.

"People who are considering onsite microturbine power and cogeneration systems should address all the local compliance issues before installing the equipment and turning it on," asserts Jim Watts, director of product strategy for Ingersoll-Rand's PowerWorks systems. "The permitting requirements for installer and property owner vary with local jurisdictions. To deal with what can seem like a labyrinth of permitting requirements, the installer or property owner should be able to seek efficient help from the manufacturer of the microturbine. Ingersoll-Rand has application engineers available to assist with the permitting process and to ensure that every PowerWorks microturbine installation complies with industry standards, as well as local, state, and federal codes and regulations."

Simple-System Cogenerated Heat
Air is drawn into the PowerWorks microturbine, then compressed. It passes through a patented recuperator that captures heat from escaping exhaust gases to preheat the incoming air. (This stage boosts the efficiency of the unit significantly.) The preheated, compressed air then enters the combustion chamber, where it is mixed with fuel, typically natural gas. This air/fuel mixture is ignited to produce hot, rapidly expanding gases. The gases flow through the blades of a turbine to drive the compressor and then through a second turbine, called the free-power turbine. The latter rotates at some 44,000 rpm and drives the rotating generator that produces electric power. The gases leaving the free-power turbine pass through the hot side of the recuperator, and the hot-water heat exchanger captures even more of the heat from those escaping exhaust gases. The PowerWorks system thus demonstrates an efficiency that is indisputably high.

The ambient air temperature will affect the power output of a microturbine (as it will affect that of all combustion turbines). When a manufacturer lists the unit's capacities, it is usually those capacities at ISO conditions (at sea level at 59°F). At temperatures above that, output decreases; below 59°F, output increases. "Output in excess of the ISO output is possible only if the microturbine has reserve capacity in excess of its rated output," explains Benson. "The Ingersoll-Rand 70-kilowatt microturbine has an actual maximum output of 92 kilowatts. When the microturbine has an actual capacity in excess of its ISO capacity, it is possible to offset power production lost in warm weather with extra power production during cold weather."

Since the emissions of the PowerWorks engine are low, exhaust heat can be used directly to regenerate the desiccant wheel of a dehumidifier by expelling the captured moisture. It also can reduce the fuel required by a manufacturing facility or an industrial process, lowering some of that facility's original fuel costs. Such uses within the PowerWorks system are cogeneration applications; they increase the total energy savings for the user by taking advantage of 70% of the fuel energy consumed. For example, cogenerated heat can reduce or replace the amount of fuel needed by a boiler for domestic hot water, or it can heat the water provided by a furnace for space heating. As the PowerWorks recovery system is rated for potable service, the hot water may also be used directly for cooking or washing.

Ingersoll-Rand's history goes back to 1871. Since then the company has established a global network of engineers and technicians to provide customers with readily available, reliable service for all products sold. In the creation of the PowerWorks system, engineers from several divisions within the company contributed to the design and production of components, the refinement of critical subsystems, and the maintenance of high quality at all stages of manufacture.

Who Would Use Microturbines?
"The competition for microturbine technologies is the transmission-and-distribution companies—the Grid, as they are known," explains Watts. "In those states where electricity is especially expensive, our systems will give customers significant savings." The sheer cost of power, then, has become a factor in decisions to purchase alternative sources. Prolonged power outages, such as the one in the Northeast in the summer of 2003, make people at home and at work understand how much they rely on a constant source of electricity. Some estimates for the loss of perishable goods (simply because the refrigeration was not working) in New York were as high as $250 million, and that was only one sector of the region affected. In states where natural threats like hurricanes have a regular season, companies that rely on electricity to keep their products in marketable conditions (cold-storage plants, for example) have understood for some years the value of uninterrupted power. They are now considering a system like PowerWorks as their total and constant source.

"One of our 70-kilowatt microturbines installed at a 60,000-square-foot community center and skilled nursing facility in New York was perceived as a source complementary to the center's use of electricity from the public grid," notes Holly Emerson, marketing specialist at Ingersoll-Rand. "The current savings are significant on both the electric utility costs and the hot-water energy costs." In Colorado at a commercial greenhouse, a 70-kW microturbine not only provides base-load electricity, but the PowerWorks cogeneration heat-recovery system preheats the water used for the plants. (Plants grow more quickly if the water is warmed to between 60°F and 70°F, studies have shown.) The facility uses at least 90,000 gal. of groundwater every day, and the PowerWorks microturbine helps considerably in heating the water to reduce the amount of natural gas used by the boilers.

Could there be economical benefits to replacing an existing reciprocating genset with a microturbine? "Reciprocating gensets used for emergency backup power typically remain off until needed," replies Watts. "Then they are only intended to start and run for relatively short periods, to cover planned or unplanned outages. For older or undercapacity reciprocating gensets that need replacement, a running backup microturbine is a more practical and economical investment. The PowerWorks microturbine is designed to run continuously, supplying the facility with economical energy while offering clean electricity that maintains power to priority loads if the utility grid fails."

Ski resorts benefit from microturbine power and cogenerated heat because large amounts of electricity are required to operate snowmaking compressors (a sector of equipment in which Ingersoll-Rand has long been a leader). Operation of the guest facilities also demands hot water, heat, and electricity. In the summer months demand is less, though some resorts have extended their season beyond the traditional November to March to include summer resort facilities in their offerings. PowerWorks will suit those with the traditional ski season or those with the year-round program because it can be operated 365 days a year to offset utility grid charges, or it can be used only during the skiing season when the thermal energy is most needed and energy savings might be the greatest.

	70-kW Microturbine Engine Cycle & 250-kW Microturbine Engine Cycle.

Successful Sites
Microturbines have proved their worth at closed landfills for electric power generation. One such site is Jamacha Landfill in Spring Valley, CA. It was a small municipal solid waste landfill that operated from 1960 to 1978; it accepted 1.8 million tons of waste. A gas collection and control system was installed in 1995. A year later, SCS Field Services, another division of SCS Engineers, assumed responsibility for routine operation of the LFG collection system and flare station. In late 2000, SCS Engineers recommended that seven supplemental vertical extraction wells be installed—there were already 40 at the site—to correct deficiencies in well-field coverage. In that same period of late 2000 and early 2001, there was an electric power crisis in California, with rolling blackouts imposed.

The customers of San Diego Gas and Electric Company were not protected by a general retail price freeze. San Diego County (where Jamacha Landfill is located) watched the cost of electric power usage rise from less than $0.10/kWh to more than double that. In October 2000, San Diego County asked SCS Engineers to evaluate the feasibility of electric power generation at all of their small closed landfills. Jamacha Landfill was perceived as most appropriate for the development of a small power project. A plant capacity of 300 kW (gross) was selected; this was based on the anticipated LFG availability over the next decade. This capacity was also compatible with the microturbine sizes (not Ingersoll-Rand) available at the time. About a year after installation, the manufacturer of the original microturbines withdrew from that sector of its business, and SCS Energy and San Diego County determined that the landfill should continue to use microturbines because of the benefits they had demonstrated; the net cost of the changeover from one manufacturer to another should be eliminated or minimized; and the change-out should be accomplished as quickly as possible to permit the project to restart its generation of revenue. Ingersoll-Rand microturbines were the chosen replacements.

The owners expected the Ingersoll-Rand microturbines to have a gross power output of 70 kW at ISO conditions with a heat rate of 13,500 Btu/kWh (higher heating value) and—most importantly—offer NOx emissions less than 9 ppmv (0.035 lb./mmBtu). The parasitic load of the plant was anticipated to be approximately 20% or 60 kW; the resulting net power output would be 220 kW. "The Ingersoll-Rand microturbine includes an onboard compressor that reduces the required inlet pressure from 80 to 7 pounds per square inch gauge, so the need to continue using the existing compressor skid at this particular site meant there was some inefficiency in satisfying the overall compression requirement," comments Benson of SCS Energy. "Informal testing showed that the gross power output and heat-rate expectations were met." The Jamacha project operates with no operator present. By June 2002, the plant was producing power 100% of the time. There was a minor setback when one of the microturbines was off-line for a few hours, but including that lapse, the combined machine-by-machine availability has been 97.5%.

Success at a Superfund Site
OII (Operating Industries Inc.) Landfill is bigger. It covers a 190-ac. site about 12 mi. east of downtown Los Angeles, by the cities of Monterey Park and Montebello. The site was used for disposal from 1948 until 1984 (when an estimated 30 million tons had been placed there). Two years later OII Landfill became a Superfund site, and its remediation continues. The LFG collection system for this landfill includes 40,000 lin. ft. of above-grade PVC collection tubing, the same length of above-grade HDPE liquid- and air-conveyance piping, 100 in-soil and 250 in-refuse vertical extraction wells, a booster blower station (2,000 scfm) to permit maintaining a higher vacuum on the in-soil wells, 150 in-well dewatering pumps, and two LFG flares (60 ft. tall and 10 ft. in diameter). Fans supply combustion air to the flares, and those flares have a 99.99% destruction efficiency. There is a leachate treatment plant with a capacity of 20,000 gpd. Recovery of LFG is about 5,600 scfm, with a methane content of 25%.

That 99.99% figure has great significance. When there was an evaluation of the feasibility of having a large LFG-fired power plant at the OII site, it was the United States Environmental Protection Agency (EPA) requirement that there be 99.99% destruction efficiency that contributed to a negative decision. In 2001, however, when the California Public Utilities Commission lifted the retail rate freeze from Southern California Edison, this landfill's power cost rose from $0.10/kWh to more than $0.14/kWh. The annual power cost went up to more than $450,000. Late that year, SCS Energy suggested that a power project to serve the onsite power requirements might now be economically and technically feasible.

Microturbines can yield destruction efficiency better than 98%, but that still falls short of EPA's 99.99%. SCS Energy proposed, for OII Landfill, that a combustion turbine exhaust into the flare as a solution to this problem. EPA agreed. There is an oxygen content of about 15% and a temperature of 500°F in combustion turbine exhaust; this is mixed with combustion air entering the flare's combustion air fans.

After a review of the onsite electrical loads (averaging about 300 kW with a peak demand of 400 kW), it was decided that capacity of the proposed plant should be 420 kW (gross). "We selected Ingersoll-Rand as the microturbine supplier for this important project for several reasons," explains Benson. "We'd had a favorable experience with the company at Jamacha Landfill, and piping and installation cost for Ingersoll-Rand microturbines would be less, with six units versus 14 for an alternative source. Ingersoll-Rand was also willing to offer a five-year fixed-price maintenance contract of 1.4 per kilowatt-hour." It also was decided not to install siloxane-removal equipment in the first installation at OII, but project funds have been put aside to install the equipment at a later date if it becomes necessary. The siloxane level at OII is relatively low (0.0690 ppmv), and Ingersoll-Rand was willing to accept operation without siloxane removal to determine the impact that lack of siloxane treatment might have on long-term cost and maintenance. At Jamacha Landfill, there seemed to be no identifiable problems with having no siloxane treatment.

Availability and Development
The number of manufacturers capable of satisfying the needs of today's power generation via microturbines is small. We have already seen how the original supplier to Jamacha Landfill in San Diego County withdrew from the business. Ingersoll-Rand is a leader among today's manufacturers, with plans to continue improvements in capacities and performance. The 70L and 70S Series microturbines have already earned praise from users nationwide. (All of the projects for microturbines are not in California.) The 70L offers 70-kW grid-parallel electrical power, and the 70S offers 70-kW continuous electrical power; remember that these models actually have maximum electrical power of 92 kW at 0°F. Both models have a frequency of 60 Hz with three-phase, wye, four-wire ungrounded service. They are designed for 80,000-hour life.

The Ingersoll-Rand PowerWorks 250 Series microturbine provides 250 kW of continuous electrical power and gives grid-isolated or grid-parallel electrical generation. During grid outages there are closed transitions to grid-isolated mode. Like the smaller models, the 250 Series microturbine produces low emissions (9 ppmv at 15% O₂ for both NOx and CO). It has the integrated, variable-output waste-heat recovery system and an optional internal, process industry-qualified fuel-gas booster. Its product design life is that impressive 80,000 hours, and the maintenance interval is 8,000 hours. Complete specifications (that help with permitting regulations) are readily available from Ingersoll-Rand PowerWorks.

Author PAUL HULL writes on construction and environmental topics for several international magazines.

DE - Jan/Feb 2004