Operation of gas engine power plant
The principle of operation of a gas engine power plant is similar to that of any four-stroke engine in a motorcar. Its fuel, however, is natural gas. The natural gas is kept under pressure according to the demand of engine and it is supplied to the cylinder mixed with air necessary for combustion.
This is done by the turbo compressor. Unlike engines in car, the gas engine works at constant speed after the ignition. To increase the power output does not need change in speed; the additional output comes from the growing amount of gas-air mixture fed to the cylinders. The operator sets the necessary capacity; the gas-mixture amount is set by the control automatics. The generator connected to the axis of the engine produces the electricity, which then gets to the outer electric network through an appropriate transformer. There is special control equipment to synchronise the generator and network, to protect, check and regulate the generator and engine. This equipment also allows the operator to have different data and possibilities of interference. While providing the necessary capacity for producing power, the engine also warms up (just like the engines in cars). In addition to this, the systems necessary for the operation of the engine also produce “waste heat”. Such “heat sources” are the hot lubricating oil, the heat generated when the gas mixture is produced and, most of all, the exhaust gas. This heat energy cannot be used for power generation, but it can be used through heat exchangers to produce district heating. When using this leftover heat, the overall efficiency of gas engines surpass 80 % while the efficiency of the condensing power plants does not exceed 50-55 % even in the most modern gas-steam cycle units. This difference explains the lower consumer price of heat produced with gas engines.
CHP Gas Engine Central Heating Plants in Miskolc
MVM Rt. won the tender in the city of Miskolc in late 2001. The project was launched to equip three central heating plants with CHP production. The call for tender contained the modernisation of the following central heating plants: the Tatár street plant with a heat demand of nearly 170 MW, Diósgyőr with 23 MW and Bulgárföld with 8 MW heat demand. The accepted MVM Rt. tender of gas engine contained the establishment of the Tatár street central heating plant consisting of small gas engines with an aggregate capacity of 20 MWe.
Based on the evaluation of tenders invited for the supply of gas engines, MVM Rt. signed a contract with DEUTZ for their delivery. In Tatár street 5 pieces of engine-generator units of type TBG632V16F with 3.9 MWe power and about 4.2 MWh heat capacity for each piece were installed. In Diósgyőr 1 piece of the same type and in Bulgárföld also 1 piece of engine generator of type TBG620V12K with 1 MWe power and about 1.1MWh heat capacity was installed. The 5 engines in Tatár street provide heat to two heat-districts: 2 engines permanently operate for the Avas district and 2 engines for the City Centre while the fifth engine can be connected to any of them according to the heat demand.
Measures taken in the course of pilot operation and the data obtained during the actual operation since then has shown that the gas engines have met the requirements of the contract in terms of power, heat and aggregate efficiency, availability and also in terms of the smoke gas emission parameters.
The measures have evidenced that all gas engines have reached more than 40 % of power efficiency. But taking into account the leftover heat, the overall efficiency of gas engine units was between 85.75 and 89.9 %, while the aggregate availability of engines reached 96 %. The pollutant emission of the engines is also lower than the limit value required in the environmental provisions.
Commercial operation started at all three sites at the end of 2003.
Gas engine generates electric power with great efficiency and, at the same time, the generated heat can also be used to a significant extent.
The water returning from the pipes of the district heating systems gets to the engine where the control system adjusts its temperature to nearly 70 Co by admixture from the supply side. The temperature of the water in the district heating is increased by the released heat from the oil cooler, the mixture cooler and from the very engine through a radiator. Water temperature can be further increased by the discharged smoke gas below 120 Co. This water heated to nearly 90 Co is mixed with the water flow of the district heating system. The gas engines that operate transitionally and in summer, are also equipped with air cooler heat exchangers (so called forced coolers), so the surplus heat can leave.
The gas mixed with the preheated combustion air is compressed to the required pressure by the turbo compressor driven from the smoke gas side. The heated gas compound cools to the optimal temperature for the gas engine operation in the two-stage mixture cooler. The gas/air mixture burnt in the four-stroke gas engine drives the main axis and the generator as well. After driving the turbo compressor the smoke gas gets outside through the catalyst, the primary silencer, the smoke gas/water heat exchanger and through two other silencers and the chimney. The NOx content of the evolved smoke gas does not exceed the 500 mg/Nm3 value (according to ISO).
To start gas engines with higher capacity compressed air is used, while small gas engines are started starter with a starter motor. The lubrication of gas engines and the continuous supply of lubricating oil are automatically controlled and the oil quality is regularly checked.
The gas engine power plants are operated by the Miskolc Central Heating Plant Ltd., which is 75 % in MVM Rt. ownership. Maintenance and developments are the responsibility of MVM Rt. Power Plant Subdivision.