【 Weak current College 】 speed pump and motor pumps for water analysis---Power By 【 China power house network 】

Certain speed pump and motor pump works and characteristics

When the pump is installed in a certain pipe work, actual work status depends not only on the pump performance curve itself, it also depends on the characteristic curve of the entire pipeline. The intersection point of 2 curve determines the pump to the pipeline system operating conditions. In the same pipe characteristic curve devices system, for a different pump, its work is different. Constant speed pump and motor pump points vary greatly, so that the flow rate, head, efficiency.

Constant speed to pump the water supply system in General as centrifugal, its working principle is to use rotating centrifugal force generated by the fluid access to energy. It is through a certain power of motor-driven pump to a certain speed rotation so that fluids could be a certain pressure and kinetic energy. Variable speed pump (in YT62 fluid couplings for example) have a special pieces — hydraulic coupling. It is installed on the original motive (motor, etc.) and rotate between the pump for liquids of kinetic energy to pass dynamic hydraulic drive unit. Its working principle is: the driving shaft end with 1 pump wheel, in a driven axle and drive shaft relative end one turbine, pump wheel and maintain a clearance between the turbines, both forming one Chamber, known as the torus. When the original motivation driving the drive shaft rotates, the working liquid in the pump wheel, and gain energy to a certain speed from the pump wheel thrown, rushed to the turbine, the energy transfer to the turbine, which drives the passive axis of rotation, enabling dynamic delivery.

Oil circulating round the work cycles in the pump and turbine at different speeds (existence slip) that exist when the centrifugal force in order to keep the circulation. The rated operating conditions of slip ≤ 3%, as long as the change in the circulation of oil in the circle, that is, change the oil quantity, you can adjust the speedof the driven shaft and transfer power to realize stepless speed regulation.

2-speed pump, variable speed pump technical and economical comparison

Hebei Electric Co., Ltd. Technical conversion project of eight stage 2 200MW dual pumping supply unit and 4 410t/h cycle fluid bed boiler, furnace 1 2 convert is 1 unit, each unit nameplate output set to 440t/h, the lift is 1400m of 2-speed pump and 1 single-speed pumps. The following comparison when the constant speed pumps in the system (or speed pump) separate run, 2-speed pump (or 2-speed pump) parallel operation, 1-speed pump and 1 single-speed pumps in parallel operation.

2.1 speed pump (or speed pump) separate run

Change the pump performance curve of the method itself has a variable speed control, regulation, and cavitation blade. Change line characteristic curve of the method main export import throttle control, throttle control, but the most common regulation is the outlet port throttle modulation, which is used to change the valve to open degree to be adjusted. General speed pump is the outlet port throttle control, variable speed pump is speed adjustment.

Boiler start-up time is longer, but will also bring to the boiler load 410t/h for the entire reference pressure process press machine side requirement is to achieve, that is to say in this process if you use speed pump can only rely on changes in the rotational speed to meet demands of startup boiler. From speed pump performance curve can be seen, the flow is 120 ~ 450t/h when the corresponding head according to the furnace of gradually step-up from 800m (or lower) to 1400m, without the need for regulation of water supply control valve. So with constant speed pump, long time saving water supply control valve to meet the required flow and therefore consume high to head.

2.2 parallel operation of the pump

Pumps connected in parallel is the same as in the head, thus increasing the flow and then draw the common lineb and pump performance curve of the intersection of the parallel characteristic curve, i.e. the parallel C work working point, at which point the flow for QC, head for the HC. Parallel work characteristics: head equal to each other, the mass per 1 pump (with performance pump) conveying flow, i.e., QC = 2QA. The phase 2 furnace 1 mechanism, when 2 boiler ignition with load-time, you need to start the second stage pump. Following on the 2-speed pumps in parallel and 1 for 1 and 2 of the transfer of the to do a comparison.

2.2.12 single speed pump in water supply systems in parallel operation

Constant speed pumps in parallel at run time by changing the line characteristics curve of the methods that adjust boiler water supply control valve to open degree to achieve the purpose of regulating the flow. This work is with the flow of change, the lift is changed. General design point is in the water supply control valve fully open in design to the pump flow rate, head, efficiency, this is the economic conditions and method of adjustment by throttling is simple and convenient, but the resulting high-lift consumed by water supply control valve, cause energy loss, low load-time economy even worse. Especially for heat and power co., Ltd. Hebei heat, heat load by industrial heat users and heating load of a large, frequent changes in the main water supply flow, long-term water supply control valve by adjusting the aperture to adjust the flow rate will result in better than ernergy greater economic waste and water supply control valve erosion damage.

When the system is rated load (2Q0) run time, head to feed pump rated lift H0, flow for 2 units to the rated flow of the pump and 2Q0, tube resistance curve for b, i.e. water supply control valve is fully open; when the system is 0.75 rated load (1.5Q0) run time, as the pipeline performance curve becomes b '', i.e. water supply control valve for throttling state, so that the work of the parallel pump from A pointinto A ', then flow to 1.5Q0, head for H1, corresponds to a single pump of point B from B to that flow of '' 0.75Q0, head for H1, i.e., the lift from the original H1-H0 H0, increased.

2.2.21 single-speed pumps with 1 speed pumps in parallel operation

If each unit for 2-speed pump, then add 1 single-speed pumps. Normal operation by speed pump to regulate the unit required water flow, it can be overcome to jellyfish pipe pressure too high. This operation requires speed control pump outlet pressure remains constant-speed pump rated outlet pressure and flow rate in 30% ~ 100% change in between, this requires at the same time adjusting to the pump performance curve (by adjusting the pump speed) and tube resistance characteristic curve (by adjusting the water supply control valve to open degree). The operating point falls on the lift h line segments.

Parallel operation, running under full load operating condition to A point, flow, pressure head to 2Q0 H0, constant-speed pump and motor pumps are run from point b. When the load is reduced to 1.5Q0, lowering the speed pump speed, the pump performance curve into a2, so feed pump set total lift curve to a2 '. At the same time changing the water supply control valve to open degree, so that the tube resistance curve-b '. At this point the operating point to A0, constant-speed-pump is still running in point b (i.e. pump rated operating point), speed pump run to B0, flow 0.5Q0, head for H0, so in the flow, 1.5Q0 than said pure speed pump system saves H1-H0 head of energy consumption.

If you do not adjust the tube resistance curve, the original pipe resistance curve downward extension of the original single-speed pump performance curve intersect, will find constant speed pump load too high speed pump only with fewer loads, this results in a constant-speed pump overload and speed pump load too small and fever, vibration or even negative phenomena of vaporization, when speed pump should be taken at the same time adjusting to the pump performance curve and tube resistance curve methods to achieve the purpose of regulating the flow.

2.2.32 single-speed pumps in parallel operation

Run-time speed pumps in parallel by changing the speed of the pump speed so that the head and flow are to meet the requirements of the boiler, so that both avoid a 2-speed pumps in parallel, the pump at a relatively low flow (rated flow following) run-time, high lift the waste; overcome when 1 single boiler band full load another boiler ignition or with a small load, 1 set 1-parallel operation enables constant speed pump overload, speed pump load too small on pump damage. Guarantees affordability and security unit.

Three conclusions

To sum up, speed pump, constant-speed pumps in parallel systems than all-speed pump system saves initial investment, and full-speed pump system than water consumption, in particular as a heating unit, in Hebei thermoelectricity co., Ltd. of eight issues technical conversion project of water supply system sets the 2-speed pump technology economy good for 1-speed pump as the fallback is more reasonable.