(1) Minimum flow system After the high-pressure feed pump is started (or in operation) and the outlet valve is not opened (or closed), most of the work done by the prime mover is converted to heat and the feed water temperature at the pump inlet will increase. The temperature exceeds the permissible temperature of the saturated vapor pressure of the water in the deaerator tank, vaporization will occur. To prevent this phenomenon from damaging the feed pump, a part of the flow of feedwater is led out before the outlet valve of the feed pump, The heat generated so that the feed pump does not occur in the low-flow operation of the vaporization. Lead to the part of the flow that the so-called pump minimum flow (or recirculation flow). The recirculation system including the minimum flow valve is called the minimum flow system. Search Keyword: More Pump Technology Articles Petg Jars,Plastic Petg Jars,Cosmetic Cream Petg Jar,15Ml Petg Jar Zhejiang Xinlei Packaging.Co.Ltd.(China) , https://www.xinleipack.com
The minimum flow range is determined by calculation and in combination with the test. Domestic and foreign information shows, and hydraulic, NPSHr, speed, water temperature, operating clearance and structure design. The general minimum flow rate is 20% ~ 30% of the pump design point flow. For supercritical units (above 600MW), the minimum flow rate of the feed water pump is continuously adjusted instead of the two-point switch, so as to avoid large fluctuations in the system when the minimum flow rate is running. Practice has proved that the minimum flow valve to determine the parameters and system layout, related to the safe and stable operation of the pump.
(2) Warm pump system From theory and design point of view, the correct operating procedure is that the high pressure boiler feed pump should be warm pump before start-up, especially for the pneumatic feed pump group which should be used for low-speed crank before starting, It is particularly important to avoid jamming and grinding as a result of thermal deformation in the pump body where hot water enters the cold state and thereby damaging parts of the pump. Of course, in an emergency, too late to start the pump that is not entirely impossible pump. From the experience of pneumatic pumps used by many power plants in our country, there are many cases of jamming and grinding in the segmented pump core without heating pump, and it is forced to execute the start-up procedure of directing the small steam engine. Internal pump is a volute type feed pump, to adapt to low-speed crankshaft and cold start features much better.
The supercritical unit uses the inner pump to axially split the warm pump system of the volute-type high-pressure feed water pump. The system is simple and easy to operate (Figure 1-15). The current domestic subcritical unit of the pump system is also changed to this method.
(3) high controllability of the pump group Large-capacity units, the controllability of the water supply pump group is getting higher and higher. In addition to the normal temperature, pressure and flow rate to be monitored, the vibration (including shaft vibration, axial force, speed, noise and fault) should be monitored and input into the computer for analysis and report at any time to improve the controllable Sexual, easy to fault analysis, to ensure safe and reliable pump operation, in order to meet the requirements of the unit full of hair stable,
(4) Configuration of pump capacity For supercritical units, there are two ways to configure the capacity at home and abroad at present: Generally, a unit-based thermal power unit is configured as a 2 × 50% air pump group and a 1 × 30% standby standby electric pump group. 2 × 50% pneumatic pump + 1 × 30% starting electric pump. After the way the electric pump only as a starter pump, and then as a backup pump, so electric pump head can be greatly reduced, with the configuration of the motor, gear (gearbox or fluid coupling) capacity can also be reduced, Thus reducing the project cost accordingly. At present, foreign large-scale supercritical units have adopted l × 100% pneumatic pump + 1 × 30% start-up pump, and stable operation in the million-kilowatt-class units, the premise is l00% capacity high-pressure feed water pump must be safe and reliable.