When electricity is generated in diesel or gas engine-based power plants, waste heat is produced. This heat can be used to generate more electricity and also for a wide range of thermal applications. The engine exhaust gases – which may be as hot as 380°C – are ideal for producing steam, for example, which can be used to heat production processes in nearby industrial plants. Applications like these are found in the textiles, food, paper and chemicals industries, to name a few examples. The steam or hot water produced with exhaust gas can also be used to heat people’s houses on a district heating network.
On the other hand, if the steam is used to heat an absorption refrigeration system, it is possible to produce cold water of around 4°C - 6°C, which can be used to run central air conditioning systems in hospitals, hotels and office blocks. This combination of power, heat and refrigeration is already an established technology in smaller diesel and gas engines, and is equally viable for larger engines too.
As well as the heat from the exhaust gases, usable heat is also produced in the engine cooling circuits. There are cooling circuits at two temperature levels: the high-temperature circuit with outlet temperatures of around 80°C - 90 °C, and the low-temperature circuit with outlet temperatures of around 30°C - 40°C. The heat from the high-temperature cooling water can be channelled straight to heating systems, while the heat from the low-temperature circuits is frequently used to preheat process water.
If all available heat sources in a MAN Diesel engine-based power plant are used, it is possible to achieve an overall efficiency of almost 90%.