| At present,the power centralized system is widely used in China’s central heating industry,but it has shortcomings such as large ineffective system energy consumption,poor pipe network stability,and uneven cooling and heating of users.The design concept of the power distributed multi-stage pump transmission and distribution system is"pump instead of valve,distribution on demand",which can effectively solve the existing problems of power centralized system,has become the focus of current research.This paper takes the power distributed multi-stage pump transmission and distribution system as the research object.By adopting the method of theoretical analysis,theoretical calculation and simulation with engineering case,the applicability,pipe network characteristics,pump characteristics and engineering application are studied.Firstly,the power centralized system is compared with the power distributed multi-stage pump transmission and distribution system.On this basis,the influence of zero pressure point and back pressure on the power distributed multi-stage pump transmission and distribution system is studied,and the design methods of the power distributed multi-stage pump transmission and distribution system when it is applied to heating engineering are summarized.Secondly,five types of user distribution pipe network models are established,and the application scope of power distributed multi-stage pump transmission and distribution system is studied by taking heating radius and average economic specific friction as variables.Thirdly,the simulation software Flowmaster is used to establish the power distributed multi-stage pump transmission and distribution system pipe network model with evenly distributed users,and the pipe network characteristics and pump frequency conversion are studied.Fourthly,taking the heating project as the background,three heating schemes are drawn up,and the economic and environmental benefits of each scheme are calculated and analyzed,and the best scheme of this project is obtained,then the simulation software Flowmaster is utilized to study the pipe network characteristics and pump characteristics of the scheme by using quantity regulation in the project(for power distributed multi-stage pump transmission and distribution system).Finally,the problem that water pump frequency conversion does not meet the similarity law is studied.The results show that:the back pressure has great influence on the pump performance in the power distributed multi-stage pump transmission and distribution system.The increase of energy saving rate of power distributed multi-stage pump transmission and distribution system decreases with the increase of heating radius and average economic specific friction.For projects with heating radius less than 6.25km,the power distributed two-stage pump transmission and distribution system is preferred.The relationship between the hysteresis time(y)and the distance from the zero pressure difference point(k≥1200)of the power distributed multi-stage pump transmission and distribution system in the qualitative regulation condition is y=1.0316k-350.64 and R~2=0.9932.Under the condition of quantity regulation,the middle and rear users of the power distributed multi-stage pump transmission and distribution system do not meet the requirements of hydraulic stability,and the fluctuation of flow and pressure is large,but the stability of the power distributed three-stage pump transmission and distribution system is better than that of the power distributed two-stage pump transmission and distribution system.In addition,there is no clear relation between the flow fluctuation amplitude and the distance to uniform pressure pipe.Both power distributed transmission and distribution system can maintain strong uninterruptible operation capability in fault condition.In the engineering design of power distributed multi-stage pump transmission and distribution system,the design working condition of pump should be set to the right of its maximum efficiency point.The energy saving rate,economy and environmental benefit of power distributed transmission and distribution system with quality and quantity control are the best.In the power distributed multi-stage pump transmission and distribution system,the relationship between the speed and flow rate of the variable frequency pump is a quadratic function in its adjustable range.In the high efficiency frequency conversion range,the pump flow and speed,head and speed square,power and speed cube are all linear,but does not satisfy the similarity law. |
