Simulation For The Switch Of Steam Source In Feed Water Pump Turbine

Boiler feed pump is one of the most important auxiliary equipments in the powerplant. Its power is about2%~4%of the unit rated power. Compare with using themotor-driven feed water pump, use the steam-driven feed water pump in the powerplants which rated power is higher than300MW, have more profits. Using thesteam-driven feed water pump, can not only raise the Unit thermal efficiency, controlthe feed water flow easier, can also keep the running more stable. So, using the steamturbine drive the feed water pump become the general way in the high-power units.In our northern region, where is rich in coal and poor in water, In order to save thewater in the power generation, the units would choose the air-cooled condenser. It takesan important part to ensure the local economic growth. In the direct air-cooled unit, theeffect of back pressure cannot be ignored. To keep the running steady, we must considerthat how to satisfy the boiler feed water requirement under the special workingcondition, like the quickly rise of the back pressure.In the normal working condition, when the working low pressure steam cannotsatisfy the power consume of the turbine driving the feed water pump, the source of thedriven-turbine working steam will switch to the high pressure.As a result, the way howto switch the working steam from low pressure source to high pressure source, having asignificant Impact on the performance of the feed water system under special workingcondition. In this paper, according to the simulation purposes, and on the basis ofassumptions and simplified, the model of water-steam system of turbine and boilersystem for600MW direct air-cooled units is established in the modular platformprovides by MMS. With the model, this paper takes some simulation under the specialworking condition, like the back pressure suddenly rise up or the low pressure steaminlet`s valve quickly closed by faults. In such conditions, we take a compare betweeninner steam source switch and external steam source switch, and also take a comparebetween two adjustment methods in the feed water pump driven-turbine which use theexternal steam source switch. Simulation results shows that:In the condition which theback pressure changes a little, the inner steam source switch is a better way to keep therunning steady, but under the condition which back pressure changes a lot, the externalsteam source switch way is better; In the working condition which the back pressuresuddenly rise and the low pressure steam inlet valve be quickly closed by faults, the adjustment method which use the high pressure steam to control the pressure of the lowpressure steam inlet valve has a faster response to the external interference.