Control method and system for preventing fuel-water ratio imbalance of once-through boilers in thermal power plants

Abstract

The invention relates to a control method and a control system for preventing a fuel-water ratio of a once-through boiler of a heat-engine plant from imbalance. The control method comprises the following steps: obtaining outlet steam pressure, an intermediate point steam temperature and all-level thermoreduction spray flow of a steam-water separator of the once-through boiler; controlling water flow of the once-through boiler according to the outlet steam pressure and the intermediate point steam temperature of the steam-water separator; and controlling a coal feed rate of the once-through boiler according to the intermediate point steam temperature and the all-level thermoreduction spray flow. The control method for preventing the fuel-water ratio of the once-through boiler of the heat-engine plant from imbalance, according to the outlet steam pressure, the intermediate point steam temperature and the all-level thermoreduction spray flow of the team-water separator during operation of the once-through boiler, controls the water flow of the once-through boiler and the coal feed rate of the once-through boiler, so that on one hand, the fuel-water ratio of the once-through boiler of the heat-engine plant can be prevented from imbalance, on the other hand, damages caused by a too high intermediate point temperature due to imbalance of the fuel-water ratio of the once-through boiler of the heat-engine plant are prevented, and therefore, stable operation of the once-through boiler is guaranteed.

Description

technical field [0001] The invention relates to the field of boiler control in thermal power plants, in particular to a control method and system for preventing the imbalance of the fuel-water ratio of once-through boilers in thermal power plants. Background technique [0002] Since the once-through boiler adopts forced circulation and there is no fixed limit for the heating section, each disturbance of the input quantity will have an effect on each output quantity. Therefore, the once-through boiler in the power station adopts ratio control. The key to boiler adjustment is to control the outlet of the steam-water separator. The degree of superheat of the steam temperature (intermediate point temperature) ensures an appropriate fuel-water ratio. At present, the fuel-water ratio control system of domestic super (super) critical units is divided into two typical control schemes of "water and coal" and "coal and water". When the "water and coal" control scheme is adopted, the ...

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Problems solved by technology

Judging from the current domestic application situation, both the "water and coal" control method and the "coal and water" control method have been widely used and have achieved good control effects. Basically, they all need to participate in power grid peak shaving, and even participate in deep peak shaving, which makes the load of the unit change very frequently. In addition, the coal quality of the boiler is variable, and the frequent start / stop of the pulverizing system, etc. It makes it difficult for the control of the boiler fuel-water ratio to meet the variable working conditions of the unit, resulting in large fluctuations in the temperature of the intermediate point and the temperature of the main steam, endangering the safe operation of the unit

In the process of changing working conditions of the unit, it is often necessary for operators to manually intervene in water or coal supply continuously, resulting in high labor intensity for operators, and the operation level of different operators is uneven, and it is impossible to completely suppress the middle point temperature and main steam Temperature fluctuations, and misoperations are prone to occur during manual intervention, which endangers the safe operation of the unit. At present, incidents of unit tripping due to boiler-to-water ratio imbalance still occur from time to time

[0004] Once-through boilers are more harmful to the imbalance of fuel-water ratio. When the temperature at the middle point is too high, it is easy to cause hazards such as boiler water-cooled wall tube bursting and other hazards, and it will also cause overheating of the main steam temperature. When the unit is running normally, the main steam temperature is already high. Close to the limit value of the metal material, the fluctuation of the main steam temperature will not only affect the stability of the control system and the economy of the unit operation, but also pose a threat to the safe operation of the unit and shorten the service life of the equipment, etc.

When the temperature of the middle point rises further, it will trigger the high temperature protection of the boiler middle point and MFT, causing the unit to trip; when the temperature of the middle point is too low, it will cause the temperature of the main steam to drop sharply, causing the steam to carry water, causing water shock to the turbine other hazards

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