Thermal system with double reheat

Abstract

The invention relates to the field of thermal power generation and discloses a double reheat thermodynamic system. The double reheat thermodynamic system comprises a steam turbine, a condenser, a by-pass turbine, a combination drive turbine, a high pressure heater; the steam turbine comprises an ultrahigh pressure cylinder, a high pressure cylinder, a medium pressure cylinder and a low pressure cylinder; an exhaust port of the ultrahigh pressure cylinder is respectively connected with the combination drive turbine and the high pressure heater; an extraction port is arranged on the combinationdrive turbine and the extraction port is connected with the high pressure heater; an exhaust port of the medium pressure cylinder is respectively connected with the low pressure cylinder and the by-pass turbine; and an exhaust port of the by-pass turbine is connected with the condenser. According to the thermodynamic system, the economy of an electric generating set can be greatly improved by thegradient utilization of energy; meanwhile, when the load of the electric generating set changes, it can be guaranteed that the high pressure cylinder, the medium pressure cylinder and the low pressurecylinder all work within a high efficiency working condition range, the station service power consumption rate can be reduced and the overall working performance of double reheat can be improved.

Description

technical field [0001] The invention relates to the field of thermal power generation, in particular to a thermal system for secondary reheating. Background technique [0002] Intermediate reheating means that the steam expanded and done in the high-pressure cylinder of the steam turbine is sent to the reheater of the boiler for reheating, so that its temperature reaches or approaches the temperature of the main steam, and then sent back to the medium and low-pressure cylinders of the steam turbine for further expansion. achievement. Reheating technology can increase the work enthalpy drop of steam and reduce the humidity at the end of steam expansion, thereby improving the work ability of steam and the power generation efficiency of the unit. Intermediate reheating can be divided into primary reheating and secondary reheating. Under the same steam pressure and temperature parameters, the thermal efficiency of the secondary reheating unit is 2% higher than that of the prima...

AI Technical Summary

Problems solved by technology

The biggest problem of this scheme is the application of BESD turbine power generation. Since the turbine operates at a fixed frequency, the efficiency is very low under variable working conditions, and a high-power frequency converter is required when the electric energy generated by it is used to drive the feed water pump. Not only the equipment investment is large, but also cause further energy loss

In addition, since the pressure at the extraction point of the deaerator cannot be kept constant under variable working conditions, throttling is required to meet the requirements of the deaerator, and the exergy loss is also very large

[0003] In addition to the above-mentioned problems, when a high-power steam turbine operates under high-load conditions, there is also the problem of insufficient expansion of the final stage of the low-pressure cylinder, which seriously affects the economy of the unit

This is because, limited by the strength of the blade material, the flow area of ​​the final stage of the steam turbine is difficult to reach the optimum value under high load, resulting in a decrease in the efficiency of the low-pressure cylinder as the load increases, and limits the further reduction of the exhaust back pressure

Adding a set of low-pressure cylinders can solve the problem of insufficient flow area of ​​the final stage, but not only the cost is too high, but also the complexity of the rotor shaft system will lead to a decrease in work reliability

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