How to optimize the recovery and reuse of steam condensate
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Dear experts, let me first explain the situation: Our factory has 3 production lines whose products need to be dried, and steam heat exchange is used for heating. The steam condensate from these three drying lines is collected in a common system and sent to a flash tank for flashing. The hot water resulting from this process is collected, while the steam generated is used to heat cold water via plate heat exchangers. The condensate from this secondary steam is also collected. Due to the varying temperatures required for drying, our factory has restricted the opening degree of the valves that feed the dryers. For the two drying lines with similar drying temperatures, there are no issues with the discharge of their condensate, but the condensate from the line with a lower temperature often suffers from interference from the other two lines. We are currently looking for ways to solve this problem. Due to the old age of our factory, pressure gauges and thermometers are not installed in many areas. As far as we know, the steam supplied to us by the thermal power plant has a pressure of 8 kilograms and a temperature of 180 degrees after being cooled and depressurized; the pressure in the flash tank ranges between 1 and 3 kilograms. Method 1 that comes to mind for now: add a buffer tank and a centrifugal pump after the steam trap on the affected production line, in order to increase the pressure of the steam condensate before feeding it back into the system ； Method 2: Install a pumpless automatic steam trap pressurizer after the hydrostatic trap on the disturbed production line to increase the pressure of the steam condensate before connecting it to the network ； Method 3: Connect another pipe from the flash tank, install a pressure control valve to maintain the pressure in the flash tank at around 1 kilogram, thereby reducing the backpressure in the condensate piping network. I would like to ask the experts here: I have discussed Methods 1 and 2 with my colleagues, and they think they are feasible. What do you all think? For Method 3, I’m concerned that reducing the pressure in the flash tank might lead to an increase in the amount of steam generated through flashing, as well as a drop in temperature and pressure. I’m not sure if this will have a negative impact on the heat exchange efficiency. Additionally, with an increased amount of steam, I wonder whether the pipes leading to the heat exchanger will still be suitable for use A beginner is asking questions; I hope experts will kindly offer their guidance
Pipelines with low temperature and pressure cause poor discharge during the waste discharge process; will increasing pressure at the rear cause the condensate from the other two tanks to be discharged as well? Because the relative back pressure has increased.
Plan 1 proposed by the original poster is feasible, but since the condensate is still under pressure, adding a buffer tank will still lead to flashing problems, as well as issues with the discharge of secondary steam; heat waste thus remains a problem. For centrifugal pumps, heat-resistant cavitation-resistant pumps should be selected; otherwise, cavitation may occur. Both Option 1 and Option 2 involve increasing the drainage pressure of the low-pressure steam equipment and connecting it to the network; it is necessary to control the degree of pressure increase carefully, as otherwise it may lead to an excessively high overall backpressure, which in turn can affect the proper drainage function of the two drainage devices. In Option 3, the flashing pressure is reduced, which certainly increases the amount of steam generated; however, if the requirements regarding the heat exchange temperature are not high, this has no impact on the heat exchange process. I see you said it’s for heating cold water; it depends on how high you want the temperature of the cold water to rise. There should be no major problem; at a pressure of 3 kilograms, the temperature of steam is around 130 degrees. Water can vaporize even at atmospheric pressure. I have a question: you use the steam generated by the flashing of the condensate from the heat exchanger to heat cold water. How much water do you need for this purpose? Why not directly pour the condensate into cold water? Do we need to add a flash tank + heat exchanger or something else? Also, I notice that the pressures in your flash tanks are not all the same; there is clearly a pressure difference in the steam used. Why not reuse the flash vapor in the heat exchangers at the front end? This can also save a significant amount of steam usage in power plants. If you want to optimize the waste heat from steam (flash vapor, high-temperature condensate), feel free to contact me; we can discuss it in detail.
The response on the second floor was quite comprehensive. As a supplementary point, Option 2 is only suitable for boosting voltage in situations with low traffic; the specific approach to be taken still depends on the actual circumstances and requirements. It seems that there is room for process optimization
First, the new steam from the power plant enters the heat-consuming equipment after being depressurized, resulting in a decline in the quality of the steam. This pressure reduction process can be replaced by a steam injection heat pump; by using the fresh steam from the power plant to eject the flashed waste steam, it is possible to reduce the backpressure of the condensate water, while also allowing the waste steam to be pressurized and reused in heating equipment, thereby directly reducing the consumption of fresh steam. If you need it, feel free to reach out to me to discuss it.
This problem is quite common and occurs in many heat exchangers equipped with temperature control valves; we call it flow loss. The main cause is too low an inlet pressure of the steam, and too high a pressure in the condensate recovery pipeline behind the steam trap. This causes the condensate to flow slowly or not at all in front of the steam trap, resulting in the accumulation of condensate inside the heat exchanger; it cannot be fully forced into the steam trap and discharged. There are two solutions: 1) increase the inlet steam pressure, 2) reduce or eliminate the backpressure on the steam trap. Increasing the inlet pressure is generally limited by production conditions and is not very feasible; therefore, eliminating backpressure is the preferred option. Among the several solutions you proposed, options 1 and 2 are quite similar; it is recommended to use a mechanical condensate recovery pump that relies on steam as the driving force for closed-loop recovery. For Option 3, it is still unclear whether it is feasible to reduce the back pressure by 1 kilogram when the steam inlet pressure is not determined. Moreover, the flash volume is usually around 10%, and pressure drops do not result in significant changes in this value.
Method 1 should be the most feasible. The pump used does not have to be a centrifugal pump; the mechanical type mentioned on floor 6, driven by steam, can be used – this is the type of pump we employ