Method for controlling system under steam protection mode after MFT of secondary reheat unit boiler

Abstract

A method for controlling a system under a steam protection mode after master fuel trip (MFT) of a secondary reheat unit boiler. The method includes the following steps that (1) a control target of thesteam protection mode is specified; (2) judging conditions of automatic triggering and automatic exit of the steam protection mode are set; (3) automatic control over high-pressure, medium-pressure and low-pressure three-stage bypasses and attemperation water thereof under the steam protection mode are explicitly described; (4) the control logic of a feed pump small machine and an induced draft fan small machine under the steam protection mode is described in detail; (5) pressure control of an auxiliary steam header and action conditions of a steam trap group under the steam protection modeare further described; and (6) supply of a shaft seal is preferentially considered under the steam protection mode, and meanwhile, control over a condensed water system and an auxiliary steam system is taken into consideration. The entire control process becomes accurate automatic adjustment from coarse manual control. The method has great significance in achieving energy conservation and consumption reduction of a thermal power generating unit, rapid recovery of accident shutdown and improvement of the automation degree of a unit.

Description

technical field [0001] The invention relates to the technical field of large-scale thermal power generating sets, in particular to a system control method in the "steam preservation mode" after the MFT of the boiler of the double reheating unit. Background technique [0002] The ultra-supercritical 660-1000MW double reheat unit (hereinafter referred to as the double reheat unit) usually adopts three-stage bypass and four-stage desuperheater arrangement, which are high, medium and low pressure three-stage large bypasses. The unit is routinely equipped with one 100% steam-driven feed water pump (or two 50% steam-driven water feed pumps), one electric feed water pump, two 50% steam-driven induced draft fans, and each small machine has five-stage steam extraction and auxiliary Steam dual steam source. The auxiliary steam main pipe is supplied by the five pumps of the machine under normal working conditions, and the secondary reheating and cooling section is used as a backup ste...

AI Technical Summary

Problems solved by technology

The auxiliary steam main pipe is supplied by the five pumps of the machine under normal working conditions, and the secondary reheating and cooling section is used as a backup steam source. When the machine is started, the temporary machine or the starting boiler can be used to supply steam. Under normal accident conditions, the starting boiler cannot replenish the steam source in time

[0003] For the above-mentioned double reheat unit equipped with a steam-driven feedwater pump and a steam-driven induced draft fan, when MFT (main fuel trip) occurs in the boiler, the steam-driven feedwater pump and the steam-driven induced draft fan in the conventional design are all due to the loss of steam source And jumping off the plane, this will cause adverse effects in four aspects

One is that it takes more time to restart the unit; the other is that after the boiler MFT, the furnace cannot be purged because the induced draft fan trips, the incompletely combusted pulverized coal and combustible coal accumulated in the furnace, flue, air preheater, etc. The gas may deflagrate when it is ignited next time; the third is that there is a large amount of high-quality hot steam stored in the system pipeline of the large-scale double reheating unit, which is not properly utilized, resulting in waste; After MFT, there is no hot spare auxiliary steam, which brings a high risk to the reliable supply of the shaft seal of the unit

[0004] In the existing transformation and optimization, after MFT occurs in the unit, most of them use the secondary reheating and cooling section to supply auxiliary steam, and then use the auxiliary steam to supply the steam source of the shaft seal, while for the steam-driven induced draft fan and the steam-driven feed water pump, it is directly selected to trip , did not perform deceleration to maintain operation

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