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#BoilerManual #Ramping #Section8 #Page15

increased flow would drop PSH outlet temperature, so the 207 valve is driven closed a proportionate amount in an effort to maintain a constant flow and therefore temperature though the PSH. The amount of 207 valve closure is based on the ratio of 201 to 207 valve port areas. As the total 201valve port area increases, the 207 valve port area must be decreased an equal amount. The initial opening of the 201 and closing of the 207 should provide an even flow exchange. The 202 valve should not have to move significantly to maintain boiler pressure.

Between points B and C, the 201 and 207 valves should stabilize in partially open positions (the 207 valve opening will vary slightly depending on firing rate).

At point C, as the 201 valves are ramped open, the 207 will begin to close entirely. As flow to the turbine is increased, the 202 will close off gradually. Flow to the flashtank will decrease as it maintains boiler pressure. The 202 valves will close entirely with the opening of the 200 valves, taking the entire system off of the bypass.

While the 205 valve has not been shown in Figure 6C, its operation should be mentioned. The 205 valve is a non-return valve. When throttle pressure increases above flashtank pressure, shortly after point C, the 205 valve will close and all steam flow willl be through the 201 valves. Flow to the flashtank through the 202 will he distributed to the feedwater heaters, deaerator and condenser.

STEAM TEMPERATURE CONTROL DURING RAMP

So far we have discussed the bypass system valve operation and the controll of pressure and flow during the ramp. The other major area of concern is the control of steam temperatures. Steam temperature control is achieved by adjustment of the firing rate. The adjustment is

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