On fig. 4.3 shows a simplified flow diagram for the production of electricity and heat at a CHP.
The technology for generating electricity at a condensing thermal power plant and a thermal power plant is practically the same, therefore, in this part of Fig . 3.1 and 4.3 match. Moreover, when the CHPP does not release heat (for example, in the summer or immediately after commissioning, when the heating networks are not yet ready), it simply works as a condensing CHP.
The main difference between a CHP and a CHP is the presence of a water-heating (cogeneration) network installation at the CHP. The return network water cooled in the heat receivers of the heating network enters the network pumps I of the CH-I lift. Pumps increase the pressure of network water, eliminating its boiling when heated in network heaters and ensuring its pumping through network heaters. From the mains pump CH-I, the mains water passes through the pipe system of the mains heaters SP-1 and SP-2 in series. The heating of network water in them is carried out by the heat of condensation of the steam taken from the two selections of the steam turbine.
Steam extraction is carried out at such pressures that the temperature of its condensation in the network heater is sufficient to heat the network water.
The network water heated in SP-1 and SP-2 goes to the network pumps of the second rise, which supply it to the peak water boiler of the PVC and ensure its pumping through all or part (to the heat pump station) of the heating network. To heat the network water in the PVK, gas is supplied to it from the gas distribution unit, and air is supplied from the blower fan. The network water (direct) heated to the required temperature is supplied to the direct network water line and from it to heat consumers.
The second significant difference between the turbine plant of a heating CHP plant and a thermal power plant is the use of not a condensing, but a heating steam turbine – a turbine that allows large controlled steam extractions to network heaters, regulating their pressure (i.e., heating network water and its flow rate).
CHPPs use heat-and-power turbines with intermediate heat-and-power extractions of steam and back-pressure turbines .
CHP with backpressure turbines (Fig. 4.4) is characterized by the fact that the production of electricity here is strictly connected with the release of thermal energy, the operation of such a station is advisable only if there are large consumers of heat with a constant consumption of it throughout the year, for example, enterprises of the chemical or oil refining industry.
CHP plants with combined heat and power turbines (Fig. 4.5) can operate equally efficiently over a wide range of heat loads. The thermal circuit has a condenser, and steam for heating water is released from the intermediate stages of the turbine. The amount of steam and its parameters are regulated, such extractions are called cogeneration extractions, in contrast to the extractions used for regenerative heating of feed water.
Figure 4.3 – Simplified technological scheme for the production of electricity and heat at a CHP.
Figure 4.4 – Thermal scheme of CHPP with backpressure turbines
where: 1 – steam boiler, 2 – steam turbine, 3 – electric generator, 4 – heat consumer, 5 – condensate pump, 6 – deaerator, 7 – feed pump.
Figure 4.5 – Thermal scheme of CHP with heat-extraction turbines
where 1, 2, 3, 4- correspond to the designations in Fig. 4.4; 5 – network pump, 6 – condenser, 7 – condensate pump, 8 – deaerator, 9 – feed pump.