Analysis of abnormal operation of the drain valve after the heat exchanger; steam superheating is suspected to be the cause
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Background: The reboiler is heated using 2.0 MPa steam, and after heating, a double-seat lever float trap is used for water drainage, with a back pressure of 1.0； The original design called for the use of \"saturated steam\" at 2.0 Mpa (with a saturation temperature of 212°C); however, due to a malfunction in the pressure reducing valve, the steam became superheated to around 260°C. Question: The drain valve was originally designed to handle a drainage rate of around 7800 Kg/h (at 100% load), but during actual operation at 70% load, if only the drain valve is used, the flow rate is only about 2000 Kg/h, and the float ball of the drain valve has broken several times ； If the drain is opened after the steam trap (which is equivalent to setting the back pressure to zero), the flow rate can reach up to 5000 ； Currently, to achieve the heating effect, the drain valves before and after the steam trap are both opened (at a low setting), with a flow rate of around 5600. Analysis: Two possible reasons are suspected: 1. No reference data sheet was used in the manufacturing of the drain valve, resulting in an undersized drainage capacity; however, this cannot explain the breakdown of the float ball. 2. The superheat of the steam is too high, resulting in poor heat exchange efficiency of the superheated steam. The original design took advantage of the latent heat of saturated steam; now, it is necessary to release the sensible heat of the superheated steam first before releasing its latent heat. This leads to a decrease in the amount of water discharged per unit time, and since no new steam can enter, the heat exchange efficiency deteriorates ； Furthermore, flash vaporization occurs in the check valve chamber, causing the float to fluctuate significantly and making it prone to rupture. I’m a beginner in the chemical industry; my descriptions might not be clear enough. Please forgive me ； I respectfully seek the guidance of experts from all fields.
There is an abnormality with the temperature reduction regulator. I have encountered this situation before, but it’s the first time I’ve seen such a large difference in temperature. You can start by checking whether the thermocouple is still functioning properly. In this case, it is an abnormal condition if the demineralized water valve of the temperature and pressure reducer opens fully automatically. I wonder if handling things this way will meet the production requirements?
“The float ball broke, probably pushed by the steam.
It can just barely be achieved; actually, the problem with the temperature reducer has been identified – it’s indeed the installation location of the thermometer that causes inaccurate temperature readings. Now it is gradually turning into saturated vapor
“The “Zhongli” drain valve only drains water, not air! It has nothing to do with the gas source! The temperature of the discharged water is no higher than 100 degrees! Backpressure available!
Is there a flowchart? Take a screenshot – I don’t think it’s that simple. Is the reheater heated by controlling the steam flow? Is there a condensate tank?
Have you considered the issue of poor heat transfer efficiency in the reboiler?
1. Due to issues with the pressure and temperature reduction systems of your equipment, the saturation temperature of steam at 2MPa, which was originally 211 degrees, has increased to 260 degrees. →There is heat at 50 degrees above normal. 2. The original design used saturated steam, but now superheated steam is being used; therefore, the heating section functions as described in your second point... 3. Due to problems with the temperature and pressure reduction system, the steam temperature is too high. Is there a thermometer for controlling it? Or has it been determined that the temperature is 50 degrees higher than the set value in steady state? In that case, can water be added manually to bring the temperature closer to the designed value? ； Observe again whether the operation of the hydrophobic valve is abnormal. The suggestions above are for reference only