Feedwater pump recirculation valve state-based feedwater feedforward control system and method

Abstract

The invention discloses a feedwater pump recirculation valve state-based feedwater feedforward control system and method. The system comprises a deaerator, a feedwater pump, a feedwater pump outlet flow sensor, a feedwater pump adjusting device, a feedwater pump small steam turbine, a variable-speed feedwater pump, a rotation speed measuring instrument, a minimum feedwater flow calculation module,a recirculation controller, a feedwater recirculation valve and a recirculation state-based feedwater feedforward module. According to the system and method, under the premise of protecting the low-load operation safety of the feedwater pump, the opening speed and opening curve of the feedwater recirculation valve are limited to avoid the low-opening operation of the feedwater recirculation valveand decrease the abrasion of the feedwater recirculation valve; at the moment of opening or closing the feedwater recirculation valve, water yield feedforward compensation is carried out on a feedwater system to decrease the control disturbance caused to the feedwater system by the large motion of the feedwater recirculation valve under the low load of the unit, thereby realizing the comprehensive goals of ensuring the safety and energy saving of the feedwater system under the low load and enhancing the control stability.

Description

technical field [0001] The invention belongs to the field of automatic control of thermal power plants, relates to a water feed control system of a boiler, in particular to a feed water feedforward control system and method based on the state of a recirculation valve of a feed water pump, and is applicable to the opening and closing process of the minimum flow valve of the feed water pump. Background technique [0002] With the upgrading of my country's power industry institutions and the rapid development of renewable energy, thermal power units will assume the functional role of deep peak regulation of the power grid, with flexible adjustment from low load to medium and high load as the main operating mode, and frequent low load The operating conditions put forward higher requirements on the furnace equipment and control system. The conventional feed water control logic sets the minimum feed water flow protection system to ensure the safe operation of the feed water pump un...

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Problems solved by technology

[0003] Under the deep peak-shaving operation condition, the load of the unit frequently touches the load point below 30% Pe, and the low flow rate of the feedwater pump continues to exist, which makes the protection action of the minimum flow recirculation valve frequent, resulting in large fluctuations in the feedwater flow, minimum Severe flow valve wear and other problems:

Under long-term low-load operation, the feedwater pump often works near the minimum flow rate, and the overshoot phenomenon in the PID control process will frequently trigger the switch of the minimum flow valve, which is not conducive to the stable operation of the water supply system and the safe operation of the feedwater pump.

[0006] (2) The minimum flow recirculation valve equipment of the feed water pump is easy to wear

Therefore, the working fluid after valve throttling is prone to flashing and cavitation, especially under low load, the valve is prone to wear during frequent opening

In actual operation, it should be considered to avoid the recirculation valve working at a small opening, otherwise it will seriously accelerate the wear of the equipment and sacrifice the life of the equipment

[0008] (3) Increase the disturbance of the water supply control circuit under low load

However, due to the weak stability of the unit under low load, when the opening of the recirculation valve is opened or closed instantaneously, the sudden change of the water supply flow will bring inevitable control disturbance to the water supply system, and even cause the system to oscillate and diverge

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