Benefiting from large-scale CHP

Tognum subsidiary MTU makes engines at two plants in Friedrichshafen, Germany, that draw power from an on-site natural gas fired cogeneration station that supplies over 1.8 MWe and 2 MWth. What are the advantages of using combined heat and power on such a large scale?

By: Dirk Naujokat, MDE Dezentrale Energiesysteme GmbH, Germany

Generating heat and power from your own plant happens not only on a small-scale at farms or bio-energy villages, for example. It is also an economically attractive form of energy provision for large consumers who have a constant, high demand for heat.

As well as the classic examples such as hospitals and swimming baths, large industrial facilities also use the technology to generate energy efficiently. MTU’s two facilities in Germany, for example, have the energy requirements of a small town. The factories produce around 8000 diesel and gas engines a year and employ roughly 5200 people.

The 16-cylinder 16V 4000 L61 natural gas engine enables the CHP plant to output 18858 kWe of electricity and 2000 kWth of heat
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MTU has invested in combined heat and power (CHP) generation to produce this large quantity of energy efficiently and ecologically. The cogeneration plant’s electrical output almost covers the needs of Plant 1 for electricity. Considering consumption over a year, it covers about 25 per cent of MTU’s total electricity needs and about 30 per cent of its total heating needs.

Christof von Branconi, head of the Tognum division Energy Systems and Components, says: “The technology for gas-to-energy systems is one of Tognum’s key future markets. We see a worldwide boom for cogeneration and decentralized power generation with bio-gas and natural gas.” He adds: “With plants for decentralized power generation on a diesel, gas and fuel-cell basis, Tognum is well positioned in both traditional and future-oriented energy markets.”

CHP’s efficiency

When electricity is generated, heat is produced as a byproduct that can be put to direct use. MTU’s Plant 1 uses 8800 MWh of this heat for space heating and other purposes such as heating engine test benches. The result is that the effective use of the fuel energy in the natural gas is as high as 87 per cent, or as much as 40 per cent higher than the figure for conventional large-scale power stations that supply electricity to the German power grid.

Operating principle of decentralized CHP plants, which can result in an overall efficiency level of up to 87 per cent
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While operating economically, the CHP plant also reduces its environmental impact by virtue of its low emissions. Compared with the separate generation of heat and power, MTU’s CHP plant saves 1700 tonnes of carbon dioxide (CO2) a year.

Fast investment pay-off

The investment is worthwhile for MTU in several respects. The new plant covers the baseload electricity demand of Plant 1 and generates around 25 per cent of the annual electricity requirement and around 30 per cent of the heat needs. Dieter Sautter, in charge of energy provision at MTU, neatly explains the benefits of the installation: “We lose only 13 per cent of the energy we use. For a lignite fuelled power plant, that figure is nearly 50 per cent. That high efficiency level means that for every hour the plant is in operation, we are saving €600 ($852) compared with having to pay for the electricity and produce the heat separately. This is paying off now and will continue to do so in the future when the divide between electricity and gas prices is expected to widen.”

CHP and the EU climate target

The CHP plant operates for 7000 hours a year to produce 13 900 MWh of electricity. It is primarily used at times when the electricity and heat can be used simultaneously. This allows MTU to use 8800 MWh of the heat produced as a byproduct of electricity generation. That spin-off is responsible for the high efficiency. The investment will have paid for itself in just five years.

Gas engines offer high continuous-duty output and low exhaust emissions
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Today, 12 per cent of the electricity generated in Germany comes from CHP installations. According to a study by the Bremen Energy Institute, it should be possible to raise that figure to 57 per cent. Rapid realization of that potential would prevent immense quantities of CO2 being emitted into the environment. The combination of increasing energy efficiency in that way and simultaneously reducing energy resource use could make a substantial contribution to achieving the EU climate change targets for Europe.

CHP plants are environmentally friendly in other respects apart from their energy efficiency. Natural gas combustion produces very low levels of sulphure dioxide (SO2) and virtually zero particulates and soot. In addition, internal improvements to gas engines by MTU have reduced CO2 and nitrogen oxides (NOx) emissions even further. When running on natural gas, emissions can be as low as 50 per cent of the pollutant maximum limits required by German clean air regulations.

Heating and cooling in industry

By using absorption refrigeration plants, the heat from CHP installations can also be used for cooling, again with high efficiency. The cooling effect of evaporation of a fluid in a sealed system can be used for process refrigeration in production facilities, in the chemical industry, for freezing food products or for air conditioning in workplaces, conference centres or theatres.

Combined cooling, heat and power production (CCHP) is also possible in combination with fuel cells. In that way, specialized customer requirements can be met. For example, telecommunications provider T-Systems uses a CCHP plant at one of its data centres for cooling that simultaneously provides a localized, and therefore uninterruptible, electricity supply. By individual adaptation to heat and cooling needs, therefore, optimum solutions for customers’ requirements can be found that also offer outstanding efficiency.

Complete system from one provider

Tognum subsidiary MDE Dezentrale Energiesysteme, based in Augsburg, Germany, built the MTU plant in a new annex to the boiler house. The central component is an enhanced-power MTU Series 4000 gas engine. Other important constituents are the generator, baseframe, control systems, heat exchanger, silencers, exhaust treatment, oil supply and air temperature control system. The entire power plant is controlled from a single touch-screen monitor.

The MTU engine management electronics signal numerous engine operating parameters to the plant control system, which makes the installation very easy to control. Convenience can be further enhanced by options such as remote diagnosis. The next generation of the MTU gas engines will use the same engine management hardware and sensor systems as the company’s diesel engines. That will reduce costs and make servicing quicker and easier. The enhanced-power gas engine has a larger cylinder capacity than its predecessor as well as optimized combustion with an open combustion chamber. As a result, the engine has a higher per-cylinder output and greater efficiency.

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The baseload demand of the factory is 2-3 MW at all times of the day or night. This means that the output of the modular CHP plant can be fully utilized at any time. The plant also covers demand peaks between 9 am and 12 noon. Electricity and heat are fed directly into the factory, which means that distribution losses are very small.

An exhaust/water heat exchanger recovers 912 kW by raising water to a temperature of 120 à‚°C. This can be used 24/7 virtually all year round. It is used for a variety of purposes, such as simulating extreme outside temperatures on the engine test benches. A second heat exchanger recovers 1112 kW of heat from the engine coolant and oil, allowing water to be heated to 90 à‚°C to heat the factory sheds and offices.

That energy can be used for 2550 hours a year. The more fully the heat can be used, the greater the efficiency. The determining factor at Friedrichshafen in that regard is the length of the heating period during which heat can be fully used for heating the offices and factory sheds.

The design of the power plant is focused on minimizing noise pollution. The technology of the new cogneration plant can be seen through a 5 m2 window in the heating building. After all, technology should be seen, not heard.

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