Diversion station

A diversion station (full name of a steam turbine diversion station , also called a bypass station ) is a group of fittings in a steam power plant that is used to guide the live steam from the steam generator ( boiler ) around the steam turbine (hence the name). This is necessary - at least temporarily - because the steam generator (steam boiler) can only be adapted slowly to changes in consumption. The redirection is done either directly in the condenser , or if the boiler through a reheat (CP) has, in two steps, first from the high pressure (HD) to the cold side of the reheater, and then from the hot reheat to the condenser.

The diversion station usually consists of a fast-acting shut -off valve and a pressure reducing valve with integrated water injection as well as a downstream section for evaporation of the water and, at the inlet to the condenser, one or more pinhole diaphragms.

functionality

In order to temporarily generate too much steam from the steam generator, e.g. B. when starting up and shutting down or in the event of malfunctions, not having to blow off into the open via the steam generator safety valves (steam / condensate loss), large steam turbines have a device with which this more generated steam is discharged to the condenser via HP and MD bypass stations can be. The diversion stations serve as starting, HP reducing and often as safety devices.

Your job is:

• To ensure flow and thus protection of the reheater,
• enable independent operation of the steam generator with the turbine inlet valves closed,
• to take over the live steam pressure control during start-up and shutdown processes in both fixed pressure and sliding pressure operation, in the event of load disturbances and load shedding
• to prevent exceeding the maximum permissible operating pressure,
• to avoid charging the superheater up to the maximum permissible operating pressure in sliding pressure operation even with reduced live steam pressure.

If the steam pressure ratio HD to ZÜ is disturbed, the pressure ratio controller lowers its control pulse for the medium pressure control valves. This falling control oil pressure is converted by a reversing converter into an increasing control oil pressure for the bypass device. If a lock to protect the condenser does not block the bypass device, the bypass valves open before the medium pressure control valves would close. The rise in the control oil pressure for the bypass device causes the water control valves to open for the injection of condensate into the bypass steam. Such a control is necessary so that the reheater in the boiler always has a sufficient passage of cooling steam without the ZÜ safety valves responding. The valuable condensate is retained in the cycle. The diversion device is very important to avoid noise emission when starting up and shutting down the steam generator system. The criteria for blocking the bypass device are the condenser pressure and the injection water pressure. In addition, some systems also have temperature measuring points at the inflow point in the condenser to protect against clogged injection points.