Research On Water Hammer Of Long-Distance District Heating Pipeline With Multi-Stage Pump Stations

Nowadays,due to the environmental problems in China,northern China is facing the lack of clean heat source for district heating.Based on the Co-ah system,long-distance DH(district heating)systems can solve the problem effectively.Long-distance pipeline always involves large elevation difference and multi-stage pump stations.Therefore,security of long-distance pipeline is an intractable problem in DH systems.Existing researches on water hammer focus on water conservancy engineering,few of them is about DH systems.Therefore,the paper conducts theoretical and experimental studies on water hammer problems in long-distance DH systems.Different from the method of characteristics(MOC),which is widely used in water hammer simulation,the paper proposes a kind of local analysis method to analysis water hammer in DH systems.Water hammer problems can be divided into a series of local problems.Theses local problems fall into three categories: generation,propagation and interaction with different boundaries.Hence,the method focuses on this three subproblems,and according to these local property,primal water hammer problem can be solved.According to these local property,pump station design,pump starting,water tank usage and pressure vessel usage in long-distance DH pipeline are analyzed in the paper.The analysis provides a basis for application and promotion of long-distance DH systems.According to the theoretical analysis,the similitude criterions are put forward in the paper.Quasi-similitude is found in the system in which pumps are with the same speed variable frequency.Based on the taiyuan-gujiao long-distance DH demonstration project,a scared model experiment is introduced to verify the similitude criterions.At the last of the paper,apply the novel method to taiyuan-gujiao long-distance DH demonstration project.The system design,operation condition and pressure curve of pump failure are introduced.The theory is also verified by the demonstration project.