600MW unit extraction steam

Should the extraction steam be adjusted or not? If a condensing unit is to be modified for external heating, it is necessary to adjust the extraction steam; such modification is feasible. Steam at a pressure of 0.3–0.5 MPa is generally extracted from the pipe connecting the medium-pressure cylinder to the low-pressure cylinder, and a butterfly valve is installed behind the extraction port to regulate the extraction pressure. For domestic 600MW heating units, the rated steam extraction rate is 600 t/h, with a maximum of up to 900 t/h. However, your unit is a condensing unit, and 600 kg/h is far too low – it’s less than 1 ton per hour. This amount of steam can be obtained directly from the low-pressure auxiliary steam header, as its pressure remains stable. There is no need to modify a condensing unit to use such a small amount of steam; making modifications to the unit itself would have an impact on its economic efficiency. Of course, you can use steam drawn without adjustment, but as the unit’s load changes, the pressure also changes accordingly; in other words, the steam supply pressure becomes unstable. Otherwise, a temperature and pressure reduction device must be installed, and throttling losses will occur during operation. Therefore, it is recommended that you use the steam from the plant’s low-pressure auxiliary steam header; its pressure remains stable at around 0.5 MPa. This low-pressure auxiliary steam comes from the fifth stage of steam extraction after being depressurized, and this approach requires the least investment. Otherwise, it would be necessary to purchase temperature and pressure reduction devices as well as related systems.

Thank you! It’s 600 t/h; what impact would drawing 600 t/h have on the power generation capacity? Over 10%?

This post was last edited by gjn1970 on 2015-9-1 at 16:55. A load exceeding 10% is certain; the 600 t/h of steam does not undergo work in the low-pressure cylinder. By multiplying this flow rate by the enthalpy drop from the exhaust gas in the medium-pressure cylinder to the condenser (i.e., the enthalpy drop in the low-pressure cylinder), the amount of electricity that is not generated can be determined (generator losses and mechanical transmission losses are ignored here). Make sure to use the International System of Units for all measurements.

Thank you! How can a pure condensing unit achieve such a high amount of extraction steam? What is the maximum impact on power generation? Can it exceed 20%?

I would also like to ask: What is the maximum size of the largest low-pressure saturated steam boilers available in China? Is 100tph okay?

This post was last edited by gjn1970 on 2015-9-8 at 14:03. In fact, after converting it into a extraction unit, it is easy to achieve such a high level of steam extraction. The method involves adjusting the opening degree of the extraction butterfly valve located on the pipe connecting the medium-pressure and low-pressure cylinders; reducing the opening of this valve increases the amount of steam extracted. At the same time, the amount of steam supplied to the turbine can also be adjusted (with the aim of regulating both the power generation load and the steam extraction volume). Of course, the power generation load cannot reach its original maximum value. This approach allows for the regulation of the extraction pressure, thereby meeting the requirements regarding the steam extraction volume. Of course, when the extraction butterfly valve is fully closed, there is still some leakage, which is necessary to remove the heat generated due to friction in the low-pressure cylinder (this amount is greater than the minimum amount of cooling steam required). Therefore, the extraction butterfly valve functions differently from ordinary butterfly valves. The above is also achieved through the turbine control system; therefore, the turbine control system is also modified accordingly. Based on my estimates, a 600 t/h extraction rate will result in the turbine generating approximately 110,000 kilowatts less power at its rated load compared to before the modification, which is about 18% of the unit’s rated output prior to the modification, nearing 20%.

Although I haven’t conducted any research on this myself, the pressure of low-pressure saturated steam boilers is below 1.3 MPa. In the past, the maximum capacity of low-pressure saturated steam boilers in China was 35 t/h, and even today it does not exceed 100 t/h. This is because operating at such flow rates with low-pressure parameters is not economically viable