Reboiler heat exchange
Thread Content
Typically, the temperature difference between the inlet and outlet of a bottom reboiler is only a few degrees; for example, the temperature at the inlet to the reboiler is 137 degrees, while the temperature of the fluid returning to the tower from the reboiler is 138 degrees. But here, the inlet temperature of the reboiler is 108 degrees, and it rises to 196 degrees when the reflux height increases. The designed temperature at the bottom of the tower is 137 degrees, but it’s not possible to raise it no matter what; the pressure in the tower is also controlled at the designed level. Moreover, it’s difficult to regulate the pressure of the steam coming from the reboiler – it fluctuates constantly, sometimes reaching 2.3 megapascals, which causes the safety valve to activate. Even when the steam control valve is closed, the steam pressure doesn’t drop. But sometimes the pressure suddenly drops, all the way down to 0.3 MPa or even lower. Then the pressure will rise very slowly on its own until it triggers the safety valve. Could some expert help analyze this?
Let’s analyze each specific issue; what you’re saying is too general, making it difficult to determine the cause
Based on your description, the possible reasons are as follows: 1. There is a significant deviation between the components at the bottom of the tower and those specified in the design; an excess of light components results in a lower temperature at the bottom of the tower compared to the designed temperature. 2. Large fluctuations in steam pressure may be caused by fluctuations in the load on the heat exchanger. When temperature-based cascade control is used for condensate discharge, high temperatures cause the condensate valves to close, resulting in an increase in pressure inside the heat exchanger. 3. Another reason is severe scaling of the heat exchanger, which leads to poor heat transfer; the high pressure on the steam side of the heat exchanger causes the safety valve to activate. Each issue should be analyzed on a case-by-case basis; your description lacks clarity. It would be better to include a flowchart if possible, as it would help explain the matter more clearly
It is necessary to first be able to properly control the pressure of the entire distillation tower before it is possible to assess the extent of pressure fluctuations. There are several factors that contribute to these fluctuations: 1. Steam fluctuations at the bottom of the tower (including temperature/pressure); 2. Significant changes in the composition of the feed material (with the composition of the light boiling fractions being the most important factor); 3. Fluctuations in the flow rate of the cold reflux at the top of the tower; 4. Stability of the pressure at the top of the tower (including whether there are any blockages in the pipelines); 5. Blockages in the packing inside the tower (when there are such blockages, a high enough pressure at the bottom of the tower is required for gases to rise, which can cause the pressure at the top of the tower to become abnormally high); 6. Blockages in the heat exchanger at the bottom of the tower... Logically, this leads to a decrease in the efficiency of heat exchange... As a result, the temperature at the bottom of the tower may not reach the ideal operating temperature
Stable pressure control and high outlet temperature indicate that the gasification rate is too high; should we try increasing the circulation rate?