For flow control in chemical plant design, is it better to use variable-frequency pumps or instrument control?

Flow control in chemical processing units can be achieved using variable-frequency pumps or instrument control. When using a variable-frequency pump to control flow, the pump’s speed can be adjusted according to actual needs in order to regulate the flow rate. However, this method may cause a certain response delay for measurement points that require high control responsiveness, as it takes some time to adjust the pump speed. Another option is to use instrument control, that is, to install flow meters to measure the flow rate, and adjust it by controlling devices such as valves and pumps. This method offers higher precision and faster control response, but it requires consideration of the location and quantity of flow meters to be installed during design, which increases investment and maintenance costs. In short, the choice of method depends on the specific process design and product requirements, requiring a comprehensive technical and economic evaluation. .

Do you mean that the variable-frequency pump is a metering pump? This should respond faster than using a flow meter. Another reason for not using a flow meter is perhaps that the metering pump is a pulse pump, making it difficult to measure the real-time flow rate.

It’s not a variable-frequency pump; it’s a pump whose frequency is adjusted by an inverter

It’s a pump with variable frequency control; no pump can adjust its frequency on its own

Oh, it’s not a metering pump or a pulse pump

Is pump wear not taken into account in the design? Estimate the flow rate only based on the pump’s flow characteristics and the corresponding frequency? Also, the flow rate curve of pumps generally isn’t linear, so it can’t be simply treated using linear equations. The impellers in pumps wear out over time. If the requirements regarding flow rate aren’t very high, controlling the frequency is sufficient to regulate the flow rate

First, it is necessary to understand what control is and what measurement is. A variable-frequency pump is a control device that can directly control the flow rate; it is capable of controlling only the flow rate ； A flow meter is a measuring device that can measure flow rate; it is capable of measuring nothing other than flow rate. Well, then it’s clear from now on. For flow control, variable-frequency pumps and flow meters are two different concepts. Our conventional flow meter control also involves detecting the flow rate using a flow meter, and then adjusting this flow rate through valves, pumps, etc., to achieve the desired flow value. The variable-frequency pump control mentioned in the building’s topic is commonly used in applications with low flow rates (where pulse metering pumps are employed), or in applications with high flow rates where the flow requirements are not very strict. No matter what the actual amount is, I use the pump to deliver the desired volume based on the theoretical value, and then I don’t worry about it anymore. It’s all fine; choose based on the operating conditions.

Everyone, what I mean is not a metering pump, but using frequency conversion to regulate the flow rate. And the consideration of installing a flow meter to control the control valve was not given. Does this affect the precise control of the entire device?

If you are a regular pump, the parameter that needs to be controlled is not flow rate; even without a flow meter, the requirements can still be met through fuzzy control. I guess what you want to ask is whether it’s better to use a pump itself to control the flow rate or a control valve So, whether it’s the device itself or its installation location, control valves generally respond more quickly; it depends on how much this delay affects your control system.