Questions regarding turbine steam seal pressure
Thread Content
If the steam seal pressure is indicated on the turbine’s DCS monitoring system, then what exactly does this steam seal pressure refer to? Is it the steam pressure leaking from the shaft seal? If this steam seal pressure has gradually increased from 30 KPa half a year ago to 53 KPa now, what problem does this indicate? I saw online that there are vapor seal pressure regulation devices – does this mean that external gas such as nitrogen needs to be fed into the vapor seal through pipes? The books describe steam seals as mechanisms that use multiple rows of closely spaced and spaced teeth to prevent communication between the inside and outside of the turbine, but they don’t mention anything about pressure regulation. Please advise
Such gas seals usually consist of sealing gas, leakage gas, and mixed gas, which act on this set of sealers respectively. The mixer pressure is slightly lower than that of the leaking gas, thereby suppressing the sealing of the leaking gas. The pressure of the mixture must be lower than the pressure of the sealing gas. This is a comb-tooth seal assembly; it is recommended to examine its physical structure when installing or disassembling it, and similar views can be found on Baidu Images.
I’ve seen the picture, but I still don’t quite understand it
Based on your description, I assume you are referring to a condensing steam turbine. 1. In the case of a condensing steam turbine, the exhaust cylinder is under negative pressure during normal operation. To prevent outside air from entering the turbine, low-pressure steam is provided at the shaft seals before and after the turbine. Generally, there are no special requirements regarding this pressure; as long as steam is coming out of the steam seals at the front and back and the steam pressure does not drop, that’s sufficient. 2. Once the unit is operating normally under load, the air supply for the shaft seals can usually be stopped.
During startup, the steam for the turbine shaft seal air is supplied by the shaft seal air main; it generally enters the high-pressure side first, and then proceeds to the low-pressure side as well as the signal pipes. Once it reaches the low-pressure side, some of it goes into the signal pipes while another portion goes into the condensate system. As the air intake to the turbine increases, the amount of air leaking through the labyrinth at the high-pressure shaft end inside the machine also increases, causing the pressure in the seal air main to rise. At this point, the seal air control valve will close to a predetermined pressure level in order to maintain the pressure in the main. The pressure of your seal gas is high or above the design pressure; this could be due to a fault in the seal gas control valve, or the bypass valve may be partially open.
Understood, thank you all for your answers
It should be controlled by a regulating valve; as long as air comes out, that’s fine
After the unit is in operation, a negative pressure should also be maintained inside the condenser. So, won’t stopping the shaft seal air supply affect the vacuum? I see that our engine unit continues to emit steam from its exhaust pipe, both when it just starts up and while it is running. Looking forward to your advice! Thank you.
What he meant is that under high load, the turbine achieves self-sealing, but the shaft seal control valve still needs to be opened – perhaps at a lower setting
It only indicates that the gas seal is worn, which has caused the pressure to rise； Simply increase the shaft seal air pressure appropriately.