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Reprinted From Dec-Jan 2001 Issue of Energy-Tech Magazine
Cogeneration Industry, Latest Trends and Future Developments
With Jim Spencer, Lipten Company General Manager
 
Two For the Price of One: Latest trends in cogeneration
What does UCLA have in common with the Grand Old Opry? Both have discovered the benefits of combined heating and power (CHP), or cogeneration as the process is known . The Opryland Hotel in Nashville Tennessee built a 5 MW combined heat and power plant with an 80,000 pound per hour heat recovery steam generator, an 80 pound per hour gas/oil standby boiler and 9,000 tons of chilled water capacity. A 1,000-ton absorption chilled water generator is used for laundry and heating. The hotel also has a 23.9 KV and 5 KV primary electrical distribution system. The system was installed in 1994 and so far the energy savings have resulted in a five-year payback on installation costs. In the same year, UCLA completed construction of a CHP system utilizing landfill and natural gas. The exhaust from two 14.5 MW combustion turbine generators goes to a pair of heat recovery steam generators which in turn drive a condensing steam-turbine electric generator to produce 48 MW of electricity. Thermal energy from the CHP unit is used for heating and cooling. As a result, UCLA cut its electricity purchase by 85%. Cogeneration, or CHP, is the production of two forms of energy from the same source. In its most typical application, heat from energy production is utilized for heating and/or cooling operations as in the Opryland and UCLA examples. The benefits are obvious. When fuels are converted to energy, as much as two thirds of the energy input can be lost. By capturing the lost energy, efficiency of the plant can be as high as 70% to 80% while emissions are cut drastically. At UCLA, emissions were cut by 50%, with the NOx emissions meeting the 6 parts per million standard. By its very nature, combined systems imply close proximity between the power source and end user. Cogeneration then becomes closely aligned with another trend in the energy industry, namely distributed generation (DG), which is the onsite production of power. Not surprisingly, some the most recent advances in DG technology are also the same as the innovations in CHP

Advanced Turbines and Controls
While the idea of cogeneration seems completely logical, the actual process of designing systems can be tricky. The emphasis is on the word system, according to Abby Layne, project manager for advanced turbines at the National Energy Technology Laboratory. "In designing a combined heat and power system, engineers need to look at the whole system and how the components interrelate. We naturally strive for efficiency and low emissions, but there is always the possibility we will make the system too efficient. In other words, we may make a system where there is not enough heat produced to be useful. Looking at the whole system, you can reduce emissions and yet raise the heat produced." The NETL Advanced Turbine Program is currently looking at combined cycle combustion turbines where a steam turbine is added to a natural-gas fired combustion turbine. One advantage of this type of system is its ability to adjust to differing demands for electricity or heat. For instance, as heat requirements shift depending on time of day or season, a turbine may become underutilized. In a combined cycle system, the heat from the combustion turbine fuels the steam turbine to produce electricity. When electrical demand rises, more steam can be routed to the steam turbine while at other times the steam can be used to meet increased heating needs. Naturally, such systems require advanced controls. According to James Spencer of the Lipten Company in Wixom, Michigan, the control side of the energy industry as a whole has changed dramatically in the past decade. "Ten years ago, there were only a few proprietary software systems in the industry. Now, with the need for more data and feedback from the system, a whole host of non-proprietary systems have sprung up, particularly Programmable Logic Control systems. Cogeneration systems are the same way except we sometimes split the controls between the energy and heating systems." Spencer also sees CHP systems as being under the same financial constraints as the entire industry; cost savings are basically determining capital outlays. People simply are not buying unless they can see a relatively quick pay back on the investment, sometimes in time frames measured by months rather than years. In this context, CHP systems have an edge since savings can be gained not only on the energy side, but also the heating and/or cooling side. Fuel Cells and Hybrids Fuel cells produce energy by directly generating electricity from hydrogen-rich fuels through a catalytic reaction, i.e. a chemical process rather than combustion. As such, the process results in very few emissions. In addition, the process is efficient and requires low maintenance. Along with electricity, the process produces heat and this fact makes fuel cells a potential candidate for future CHP applications. For instance, the Department of Defense installed 30 phosphoric acid fuel cells at department sites across the country in a demonstration project. The fuel cells were the Onsi PC25"C. Each fuel cell is rated to deliver 200 kW/235 K VA of electricity at 480/277 V (3 phase) and deliver >700,000 Btu/hr of thermal energy at 140fF or 350,000 Btu/hr at 250fF. At Edwards Air Force Base, the fuel cells were used for domestic hot water and space heat in the base hospital. It was thermally connected to a steam heat exchanger serving the building's space heating loop. Fluid from the space heating return loop is passed through the fuel cell's high-grade heat exchanger before reentering the steam heat exchanger. This configuration allows the steam system to operate when either the fuel cell is unavailable or unable to generate high enough temperatures to meet heating needs. As a result, the cost savings were estimated at $96,000 from 1997 to 1999. At the moment, fuel cell technology is still too expensive for widespread commercial applications. However, competition and technological designs are rapidly bringing down the cost per kilowatt for fuel cells. In addition, some interesting projects are underway. For instance, International Fuel Cells is installing a 200kw system at the Pool and Park Recreational Center in Woking, England. The system will provide heat, light, air conditioning cooling and dehumidification. The fuel cell is part of a larger CHP system that will include a 1.35 megawatt reciprocating engine and solar photovoltaic cells. The Woking Borough Council is the only local authority in the UK to supply electricity directly to customers on a private wire network. This system allows a maximization of green technology potentials rather than selling electricity to the grid at lower prices. Work by Edison Technology Solutions and Siemens Westinghouse, sponsored by the Department of Energy, resulted in the first hybrid system, combing a fuel cell with a microturbine. Siemens developed the hybrid and utilizes the discovery that pressurizing a solid oxide fuel cell increases voltage and improves electrical efficiency. When a pressurized fuel cell is combined with a gas turbine, efficiency increases even more dramatically. High-pressure air is produced by the microturbine and delivered to the fuel cell where it reacts with natural gas to produce electricity and heat. The exhaust from the fuel cell is returned to the microturbine to produce more electricity. The solid oxide fuel cell is comprised of 1152 tubular ceramic cells with the capability of generating 200 kilowatts. The microturbine generates an additional 20 kilowatts. First testing of the hybrid is currently underway at the Fuel Cell Research Center at the University of California-Irvine. Currently, work is underway on a 1-megawatt hybrid, scheduled for completion in late 2002. Internal Combustion Of course, these are advanced demonstration projects. What happens in the real world? Engineers are faced with designing systems based on cost and finding the right-size turbines. While advanced turbine design tends to concentrate on natural gas as a fuel, the internal combustion engine has made a comeback in the energy industry. The traditional noisy and dirty reciprocating internal combustion engine (IC) has given way to highly efficient and environmentally friendly mechanisms. In the small size category (1 to 10 MW) IC engines are outselling turbines by a large margin. For one thing, they are among the least costly and yet most efficient systems in the size category. In addition, they afford easy maintenance and a very broad service infrastructure. In a different variation on the combined cycle principle, DTE Energy Technologies in Michigan is looking at combining gas-fired turbines with IC engines. "Our belief is that more and more people are looking at the benefits of having their own power facilities," said Mark Fallek, vice president of sales and marketing at DTE Energy. "We believe the trend is towards a microgrid concept where a variety of generating technologies are used depending on the situation. For instance, we are developing a package system where a turbine will handle the base load while an IC engine handles the load follow. In a theoretical application, a facility might generate 800 kw all the time, but at peak times jump to 1200 kw. The turbine would handle the constant 800kw, then the IC engine would kick in to handle the additional load." Again depending on the customer's needs, these technologies can be combined with heat recovery systems, absorption chillers, etc to serve all the customer's power and heating needs. When used in a CHP environment, i.e. with a heat recovery system, IC engines can produce up to a 79% total useful energy output. Emissions have been reduced in large part because of exhaust catalysts. They can handle hot water needs up to 250 F. In another example, Caterpillar, usually associated with heavy machinery, offers engines and generators to the power industry. Last year, the company installed a cogeneration system in the Concorde Lafayette Hotel in Paris, Europe's largest hotel and convention center. The system powers the entire complex independent of the grid. The system includes a gasoline engine delivering 1165 ekW at a power rating of .8, a generator, a heat recovery system and the necessary pipework, controls and interconnections. The system complies with all environmental regulations. Two themes run through all these technical trends: economic constraints place a great emphasis on saving money wherever possible while at the same time the need for reliable energy leads to solutions independent of the grid. Combined heating and power systems meet both needs. They offer the means to save money on two fronts simultaneously while utilizing the independence of distributed generation. Indeed, Abby Layne from NETL, considers combined heating and power as a subset of distributed generation. In the future, there may be no need to make the distinction

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