Steam drum level control

Code? You mean the configuration in DCS?

https://wenku.baidu.com/view/8bba2c25ccbff121dd36831b.html?sxts=1588385832103 Take a look; is this what you’re looking for?

This is a design concept; in our project, it involves automatic water addition for the boiler’s drum. Based on thermal calculations, it is determined how much water is required when the boiler is in operation. A liquid level value is calculated, and this value is used as a set point; the feed water pump then adds water according to this liquid level value

I roughly understand what you mean and your goal; you are writing a technical paper and need relevant design concepts and calculation formulas. I’ll help you switch to the instrumentation and control version; it’s more professional there!

Oh, the previous three impulse methods were all feedback control schemes. Your approach is similar to material balance: other parameters are used to calculate the water consumption per hour, and this value is then used as a setpoint to control the inlet control valve?

Hello, thank you for the explanation~ Our three-element control for the drum liquid level works by calculating, as you mentioned, how much water is needed in the drum during boiler operation; from this, the corresponding drum liquid level is determined, and this value is used as the set liquid level. Then, the value of the feedwater flow rate that needs to be supplied to the pump is calculated based on three factors: the coefficient representing the difference between the actual liquid level in the drum and the set liquid level, the ratio of the gas flow rate out of the drum to the amount of gas exiting and the amount of water entering the drum. The opening degree of the pneumatic valve is then controlled using PID control – roughly that’s the idea. I’m not sure whether this type of control can be considered as material balance or feedback control; could you explain that? I really don’t understand this part

This post was last edited by sdlyml on 2020-5-8 at 10:40. The three impulses are such that the drum liquid level serves as the main control parameter, the make-up water flow rate acts as the secondary control parameter, and the steam flow rate functions as a feedforward element. In other words, the PID module compares the current level of liquid in the drum with the set value, and adjusts the valve opening based on the difference ； Your approach is a material balance approach. I calculate how much water needs to be added, and determine how much water the valve should allow in; typically, theoretical or empirical values are used as the setpoint for the water addition flow rate, in order to control the opening degree of the valve. It involves converting the complex three-pulse circuit into a single-loop control using material balance. Personally, I think it’s tricky, because the three impulses are mainly used to prevent false liquid levels. In your case, you still need to calculate the difference between this value and the actual liquid level in the drum. If a false liquid level occurs, the amount of water that needs to be added should be less; could this lead to the boiler drying out?

The feedwater flow rate is calculated using the formula: W=αWmax*D/Dmax. W: Feedwater flow rate； α: Water supply consumption coefficient, generally taken as 1.1~1.3 ； Wmax: Maximum feedwater flow rate (upper limit of the feedwater flow transmitter range) ； D: Steam flow rate ； Dmax: Maximum steam flow rate (upper limit of the steam flow transmitter range). This formula represents the feedwater flow rate derived from the principle of mass balance.

No, the level control algorithm for our project was developed by Germans. It works perfectly during boiler operation – the level control is excellent. Apart from occasional situations where manual intervention is required, everything is controlled automatically