Regarding the exhaust steam issue of backpressure steam turbines
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Hello, seniors. I recently took on a project for a heating heat exchange station, and for the circulation pump of the water in that station, it was required to be driven by a small back-pressure industrial steam turbine. The heat source is 0.7 MPa (g) and 300°C. According to calculations by the turbine manufacturer, the exhaust pressure of the turbine is 0.15 MPa (g) at 190°C, and the steam requirement for the turbine is 10 t/h. The steam exhaust from the turbine needs to enter a heat exchanger for heat exchange. However, in order for the heat exchanger to meet the heat supply requirements, it needs nearly 20 t/h of steam, which necessitates mixing the main steam with the turbine’s exhaust steam. The pressure of the main steam is much higher than that of the turbine’s exhaust steam; will mixing them and sending them into the heat exchanger affect the turbine’s exhaust? Will increasing the exhaust resistance of the turbine affect its operation? If there is an impact, what are some better solutions? Looking forward to everyone's advice! I am extremely grateful. This post was last edited by qiwu9981 on 2008-5-18 21:14.]
I’ve heard of such an exhaust head for the first time. I hope experts can provide an answer
In fact, many large heating companies, including cogeneration power plants, are now adopting turbines to replace motors in driving the circulation water pumps. By doing so, it will bring significant economic benefits to the enterprise in terms of economics, environmental protection, and equipment maintenance. However, if the pressure of the steam from the heat source itself is not very high, the utilization of low-pressure exhaust steam becomes an important issue. Low-pressure exhaust seems to have no other use besides going into the heat exchanger. Of course, it is possible to install a separate heat exchanger to make full use of the turbine’s exhaust steam; however, this will result in higher initial investment. I was thinking about whether a single heat exchanger would work. A heat exchanger requires a large amount of steam input; main steam must be supplied. I wonder if simply adding a control valve would work
1. The turbine is a model with 80% efficiency and a power output of 530 KW. 2. If I understand correctly, the exhaust gas from the turbine is used as a heat source? Here are several suggestions: 1) Use a turbine with a high back pressure; if the back pressure is increased from 0.15 MPa(g) to 0.30 MPa(g), 15.8 tons of steam per hour will be required, the exhaust steam temperature will rise to 230°C, and the superheat will increase from 61°C to 86.5°C. Under such conditions, 20 tons of steam per hour may not be necessary for heat exchange – 15 tons per hour might suffice (of course, detailed calculations are required), with all of the turbine’s exhaust steam being used as a heat source for heat exchange. 2) Keep using a turbine with a low back pressure, and supplement the insufficient amount of heat source steam by integrating the primary heat source into the exhaust steam network through a temperature-reducing pressure regulator. 3) Also keep using a turbine with a low back pressure, and reduce the resistance of the heat exchanger as well as the steam pressure at its outlet to sufficient levels, so that the addition of supplementary steam does not affect the turbine’s exhaust steam pressure
The expert upstairs explained it really well; he truly deserves to be called an engineer. That’s indeed the proper way to do it.
Generally, there is a low-pressure steam network throughout the plant; the exhaust steam from the turbines has a pressure of 0.15 MPA, and even when it enters the heat exchanger, it remains part of this network. Piping systems all have pressure control valves to regulate pressure. So when the main steam enters the heat exchanger, and the pressure in the pipeline system rises, control valves should be used to adjust the system pressure balance.
We need to find ways to make use of heat sources; energy is currently in short supply, but it cannot be wasted. I wonder what kind of company the original poster works for.
For 0.7MP, mixing should be done at the turbine outlet; a pressure reducing valve can be installed before mixing.
That’s right; it is to save energy that steam turbines are used instead of electric motors to drive the circulation water pumps. This approach is both environmentally friendly and energy-saving, and it also allows for the full utilization of the exhaust steam. My company is Shandong Huayu Power. Mainly engaged in pressure vessels; key products include: Class I and Class II pressure vessels, as well as custom chemical products ； Shell-and-tube heat exchangers, plate heat exchangers, power plant auxiliary equipment, water treatment equipment, water supply equipment, etc.
Thank you to the engineer on floor 4. That’s correct – it’s a turbine with 530 KW of power and an efficiency of 80%. However, if the exhaust pressure of the turbine is increased, the cost of the turbine will rise, which is somewhat difficult for the client to accept. Moreover, it is quite challenging for turbine manufacturers to produce turbines under such conditions. Then, if a pressure reducing valve is installed, I’ve considered that option as well, but I still don’t understand how it works. They say that a pressure reducing valve causes some loss of energy, and I wonder whether it can ensure that the steam flow meets the required levels after its installation (I really don’t know much about pressure relief valves; it seems I should do some research on them.) Furthermore, if the pressure at the steam outlet of the heat exchanger is reduced to a low enough level, it means that the temperature of the condensate will be very high. In such cases, the condensate produced by ordinary power companies is of little use, and it ends up being wasted needlessly. The best solution seems to be to install a pressure regulator, but the price of pressure regulators appears to be quite high. Would it be possible to use an ordinary control valve instead? Thank you for the advice, engineer. Thank you.
A ejector can be installed, using the main steam as the driving gas and the turbine exhaust as the gas to be drawn in; this way, the exhaust pressure is not affected or even reduced, thereby improving the efficiency of the turbine.