Cooling systems for gas-fired cogeneration units (part 1/2)

Operation of cogeneration systems (CHP)

Cogeneration systems (CHP, combined heat and power) generate both electricity and heat. The cogeneration units in question use spark-ignition internal combustion piston engines to convert the chemical energy of gaseous fuel into thermal energy and ultimately mechanical energy. The mechanical energy generated in the internal combustion engine is transferred by the coupling (usually with a flexible coupling element attached to the pin of the dynamo) and is used to produce electricity in the dynamo (synchronous dynamos are the most common). Depending on the specifics of the industrial plants where the CHP unit is installed and the voltage of the grid with which the unit is to operate, various dynamo voltage ratings are used. For example, a CG-170 series cogeneration unit manufactured by Caterpillar scan be equipped with dynamos with the following voltage ratings: 400V, 415V, 690V, 6000V, 6300V, 6600V, 10 000V, 10 500V, 11 000V, 15 000V. In the case of transmitting electricity to the distribution network, with the rated voltage of the dynamo different from that of the transmission network, a transformer is installed between the CHP unit and the transmission network.

Cooling of the engine block of the cogeneration system

The heat that is generated during the combustion of the gas mixture and the physical phenomena occurring during the operation of a given cogeneration system is collected by cooling systems and discharged from the gas-fired cogeneration unit to the outside. Thermal imaging on figure 1 illustrates the engine block’s emergency cooler during operation; this cooler operates at a lower heat demand than the CHP unit’s current output.

The obvious elements from which heat should be collected and removed are the engine block and cylinder heads. The heat in the engine block comes mainly from cooling the cylinder liners, while the heat from the cylinder heads comes from cooling the combustion chambers and exhaust ducts. In addition to the aforementioned areas of heat generation in the engine, the engine oil, for example, should also be cooled. Engine oil has several functions, and one of them is precisely to cool engine components.

Cooling of the engine oil of the cogeneration system

In addition to cooling, i.e. dissipating heat from components that work together by friction, such as:

– crankshaft and camshaft pins,

– pistons and cylinder liners,

– turbocharger shaft bearings,

– timing gears and others,

Engine oil also takes heat away from the hottest engine components. The most well-known example is the removal of heat from the bottoms of pistons. For this purpose, special spray nozzles are used, which spray engine oil into the pistons from underneath, from the engine crankcase. It is common knowledge that heat must be removed from hot engine oil and the engine oil must be brought to the appropriate temperature (and therefore viscosity) before being reused for engine lubrication and engine cooling. For this purpose, engine oil coolers are used. They are most often mounted in the most advantageous place, i.e. enabling the best heat dissipation. In CG-132 and CG-170 Caterpillar engines as well as in the following models: MWM TCG 2016, MWM TCG 3016, and MWM TCG 2020 engine oil cooler is mounted at the coolant (usually glycol solution) inlet to the engine block. This is illustrated in thermal image no. 2.

mail: promanski@eneria.pl

Written by: Piotr ROMAŃSKI

CAT Industrial Engines Service Expert