How to address excessive fluctuations in the liquid level of the medium-pressure drum
Thread Content
Dear teachers, the liquid level in the medium-pressure drum has been fluctuating for 14 years now, and we want to resolve this issue. The process flow is as follows: the material reacts with hydrogen in R2001, which contains a powdered catalyst; hot soft water is circulated directly from the medium-pressure drum to the fluidized bed using pumps, and the steam generated is sent to the steam distribution network. R2001 displays the temperature as the reaction temperature, not the temperature of the hot soft water; since no thermometer is installed in the medium-pressure drum, the exact temperature of the hot soft water is unknown. The pressure of the medium-pressure drum is automatically controlled at 1.6 Mpa, maintaining stability. The liquid level in the medium-pressure steam drum is currently being adjusted manually. Why is the level of the medium-pressure steam drum fluctuating so sharply, and how can this problem be resolved? Here at the steam drum, a gurgling sound can be heard and vibrations can be felt (not too strong). 2205
Is it entering the steam drum through the pipe for mixing air and liquid, as shown in your control diagram?
Is the distributor inside the medium-pressure drum damaged?
Yes, there are 4 tubes at the bottom of the drum; gas and liquid enter the drum from the bottom through these 4 tubes, with an insertion depth of 700 mm, and baffles are present at the tube openings
Based on my personal experience, the reasons for fluctuations in liquid level are generally as follows: 1. Problems with the measurement function of the level gauge itself, or intense agitation of the liquid level in the area where the gauge is located; 2. An unstable matching between the inlet and outlet flow rates; 3. False liquid levels in the drum caused by pressure fluctuations (but you said the pressure is stable); 4. An unstable control system. In your case, the flow control for the drum’s exhaust pipe relies solely on pressure control, and pressure is a very sensitive parameter. It is recommended to check the following parameters: 1. The flow rate of hot water at the inlet and the steam flow rate at the outlet, to see if there are any significant fluctuations, and whether these fluctuations are related to changes in liquid level. 2. Whether there are significant fluctuations in the temperature of the hot water at the inlet. If both the inlet and outlet flow rates are stable, it is likely that there is a problem with the instruments or their installation location. If the inlet flow rate is stable while the outlet flow rate is not, and if there is a certain relationship between the outlet flow rate and the liquid level, then considerations should be given from a control perspective, to determine whether the opening degree of the control valve changes frequently; if so, a temperature parameter is usually added as an auxiliary for regulation. If the inlet flow rate is stable but the inlet temperature is not, then the operating conditions of the reactor need to be checked. It might be possible to install a bypass valve on the pipes carrying hot water into and out of the reactor, so that when the temperature in the outlet pipe is high, the control valve on the bypass can be used to regulate the temperature of the incoming water. As shown in the figure below. In this way, although the exhaust volume may fluctuate, the inlet water temperature can be controlled. The liquid level fluctuations will not be very large either. One last question: is it hot water or hot steam that enters the steam drum? I see that the color of the medium in the inlet and outlet pipes is the same.
Question: 1, Is the bed temperature stable? 2. Is there any fluctuation in the pressure of the main steam pipeline network? 3. Is there any fluctuation in the gas volume?
1. The circulation volume of the heated soft water remains stable. 2. The pressure in the steam drum is automatically controlled stably (although the control valve on the steam drum is set at 100%, there is another control valve that regulates the pressure in the steam drum); the steam generation rate is fairly constant, and the water inflow volume is roughly equal to the steam generation volume. 3. Since the water inflow is controlled manually, it is affected by the operator, resulting in fluctuations in the water inflow volume of around 3 m3/h. 4. The water used for inflow comes from the deaerator, and its temperature is approximately 100°C. 5. The feed to the reactor is stable. 6. It is not a problem with the instruments, as both level sensors show significant fluctuations. 7. The temperature of the hot soft water entering the steam drum is around 200°C, while the temperature of the water exiting the steam drum is around 195–200°C. The temperature of the steam generated in the steam drum is also about 200°C (as measured by an infrared thermometer, with fairly accurate results). The pressure in the steam drum remains stable at 1.6 Mpa; values between 1.25 and 1.9 Mpa were tried as well, but the liquid level did not change much, with significant fluctuations occurring in all cases. Isn’t 1.6 Mpa at 200°C superheated steam?
1\ The steam pressure is not stable. What is the pressure in the steam main? It is not possible to see the condition of the self-regulating valve at the back, so based on this alone, it can be inferred that the drum pressure should be increased, and the self-regulating valve at the front should also function. 2. Check the separator inside the steam drum; keep the liquid level at the middle of the separator. 3. Do not open a liquid level gauge valve completely – check for any fluctuations again
It’s strange; the saturation temperature at 1.6 MPa (A) is 201°C. But what you’re showing here is a gauge reading, so it should be 1.6 MPa (G), which corresponds to 1.7 MPa (A) and a saturation temperature of 204°C. But you mentioned a steam temperature of 200°C – what is the inlet pressure? Are there any initial process design calculation documents available?
Is there an issue with the selection of the level gauge?
Is the liquid level you are controlling causing these 700mm outlets to be submerged? If so, you can try keeping the liquid level even lower than that of the return outlet and see what happens