Issues related to the turbine extraction check valve
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Our turbines are multi-stage extraction condensing type (ENK40/45/60) manufactured by Hangzhou Steam Turbine Co., with an extraction pressure of 1.2 MPa and an extraction rate of 45–80 t/h. During operation, a fault occurred in the extraction steam check valve (it was possible that the valve core had fallen off; the on-site indicator showed that the valve was fully open), which resulted in the extraction steam flow dropping to 0. The extraction steam pressure became extremely high, causing the safety valve to activate; this safety valve failed to return to its normal position. I wonder if anyone has encountered this situation before – and how did they handle it? I also have a question: for a extraction-condensing steam turbine, if no extraction is performed, that is, when the low-pressure control valve is fully open, what should the extraction pressure not exceed?
Generally speaking, the extraction check valve is oil-controlled: it functions as a check valve when oil is supplied, and as a shut-off valve when no oil is supplied.
The only option is to shut down the unit for maintenance; if it operates at full capacity without exhaust ventilation, the pressure at the exhaust port is proportional to the air intake volume. In a pure condensation mode, as long as the unit does not operate beyond its capacity limits, it’s fine. The exhaust pressure serves only as a reference value, as well as for monitoring the pressure in that section