Fuel-water ratio control method for supercritical and ultra supercritical unit

Abstract

The invention discloses a fuel-water ratio control method for a supercritical and ultra supercritical unit, and provides a novel fuel-water ratio control method in which fuel quantity and feed water flow simultaneously play parts in intermediate point temperature correction. The method comprises the following steps of: defining a fuel-water ratio distribution coefficient; correspondingly adjusting the magnitude of the fuel-water ratio distribution coefficient according to intermediate point temperature difference and deviation variation of the temperature difference; and determining instruction values of the fuel quantity and the feed water flow to keep control overall gain of an entire fuel-water ratio adjusting system unchanged and keep the system stability not influenced. Meanwhile, a decoupling loop from a water feed side correcting value to a fuel side is further added in a control logic, so that the load on the unit and the disturbance of steam pressure brought by adjustment of the fuel-water ratio by the feed water flow can be greatly eliminated. Actual system application shows that the supercritical (ultra supercritical) unit using the control method can more effectively adjust the fuel-water ratio during running of the unit, and has more stable variation in main steam temperature and main steam pressure while loading rate quickly varies.

Description

technical field [0001] The invention relates to an improved method for controlling the fuel-water ratio in a coordinated control system of a super (super) critical unit, belonging to the fields of thermal power engineering and automatic control. Background technique [0002] The fuel-water ratio control of super (super) critical units is an important part of the coordinated control of the machine and boiler in the DCS (distributed control system) of the unit. The control performance of this part directly affects the stability of the main steam temperature, main steam pressure and variable load ability. At present, domestic and foreign super (super) critical units generally use the deviation of the intermediate point temperature (usually the outlet temperature of the boiler steam-water separator) to correct the unit fuel quantity command or feed water flow command in the fuel-water ratio control, so as to re-match the fuel-water ratio and stabilize For the purpose of main st...

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Problems solved by technology

However, for the unit adopting Scheme 2, although the feedwater flow can adjust the steam temperature faster, it also has a greater impact on the load and pressure of the unit. When there is a deviation in the middle point temperature, the correction effect on the feedwater side will often be coupled with the coordinated control, affecting Unit stability

Therefore, the coordinated control system of the unit adopting the second scheme can usually only be designed as a TF (turbine following) mode in which the boiler adjusts the load and the steam turbine adjusts the main steam pressure. Due to the large inertia of the boiler, the variable load rate of this type of unit is difficult to reach 1%. Pe / min, and the load response delay is usually above 90s

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