What are the advantages and disadvantages of single-impulse water level adjustment and three-impulse water level adjustment?

The single-impulse water level automatic adjustment system is the simplest adjustment method. It adjusts the opening of the feed water control valve according to the water level deviation of the steam drum.The advantage is that the adjustment is simple, and only one water level signal is used as the adjustment amount.The main disadvantage of the single-impulse water level adjustment method is that when the evaporation or steam pressure changes suddenly, the steam content in the boiler water will change rapidly, resulting in a false water level in the boiler drum, resulting in misadjustment of the feed water control valve.Therefore, single-impulse regulation is generally used for small-capacity boilers with relatively stable loads.
The three-impulse water level automatic adjustment system is a relatively complete adjustment method. In addition to the drum water level signal, the system also includes steam flow and feed water flow.The water level of the steam drum is the main signal; the steam flow rate is the feedforward signal. Due to the existence of the feedforward signal, it can effectively prevent the malfunction of the regulator caused by "false water level", and improve the adjustment quality under the disturbance of evaporation or steam pressure. ; The feed water flow signal is the feedback signal of the medium, which can overcome the change of the feed water volume caused by the change of the feed water pressure, and keep the feed water flow stable.The three-impulse automatic adjustment system comprehensively considers the principle of balance between steam flow and feed water flow, and also considers the size of the water level deviation. It can not only overcome the influence of "false water level", but also solve the problem of disturbance of feed water flow. Drum water level adjustment system commonly used in capacity boilers.