Application examples of cascade control in petrochemical processes
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I would like to ask everyone: what are some examples of the application of temperature zoning control in petrochemical processes? Specific small process tasks can be used as teaching examples. Similar to the following schematic. Preheat before the reaction, and remove heat once the reaction temperature is reached. I earnestly request the expertise of all experts.
When the reaction vessel needs to be heated, valve A is closed and valve B is opened. When the reaction vessel needs to be cooled, valve A opens and valve B closes.
0%-50%-100% step control
1. In the diagram, valve A is air-locked (opens in case of failure), while valve B is air-operated (closes in case of failure). When valve A loses its air pressure signal due to a fault, it opens to its maximum degree, resulting in the maximum cold water flow rate； When the pressure signal is lost due to fault in valve B, it closes and the steam flow becomes zero, thereby ensuring the safety of the reactor (since it is an exothermic reaction, heat must be removed). 2. The temperature controller TC is a feedback controller. 3. Material is injected into the reactor, but no reaction has yet occurred; the temperature inside the reactor is low (at ambient temperature). Since it is a feedback controller, its output is high. Under this high output, valve A is opened to a small degree while valve B is opened to a large degree. At this point, hot water from the water pump is used to heat the reactants. 4. As the reaction progresses, the heat release increases, causing the temperature inside the reactor to rise. The controller then reduces its output, which results in an increase in the opening degree of valve A and a decrease in the opening degree of valve B. This leads to a lower temperature of the water pumped out, thereby reducing the amount of heating required. When the temperature inside the reactor rises to a certain level, valve B closes completely, while the opening degree of valve A continues to increase. At this point, the water pumped out is unheated cold water. 5. The operating ranges of the two valves overlap to a certain extent; for example, valve A operates at 0–70%, while valve B operates at 50–100%. Thus, between 50% and 70%, both valves are open. It is not possible for valve A to be completely closed before valve B starts to open, as this would result in no water being pumped out.
Pressure control of the nitrogen-protected tank: nitrogen is introduced when pressure is low, and gas is released when pressure is high
Where does this cooling water from the utility systems go? Is it recycled? I haven’t come into contact with it; I hope you can offer some guidance.
It depends on the specific situation; usually, the cooling circulating water goes to the cooling tower, where fans are used to blow air to reduce the temperature.
As shown in the diagram, it’s a funnel-shaped receiver; there’s no pressure to push the fluid back, and instead, the pressure in the return pipe might force the cooling water out from here