Dynamic Reliability Model And Simulation Of Heat Supply Network

Since 1980 s, it has been seen that the heating penetration rate and the size and complexity of heating network have experienced a fast growh with unprecedented development of heating industry. However, because of high failure rates of heating network, the safe operation and guarantation of heating supplies have plagued heating enterprises and the government, as well as the normal production and lifes of residents. As the reliability design of heat supply neatwork is relatively backward, the structure of heating system in China is complex and diverse, and the lack of equipment and the outdated management lead to imperfect operation regulation of heating system. In face of complex and diverse existing heating system, traditional reliability evaluation mathods are no longer suitable. So the research of dynamic reliability of heating system can not only meet the requirements of reliability assessment of complex heating system, but also meet the need of safe operation of heating system. Dynamic reliability of heat supply network is assessed with changes over time and outdoor temperature. Different from the traditional static reliability study, dynamic accident criteria of heat supply network is redefined with changes of outdoor temperature. And dynamic reliability model of heat supply network is built base on Stochastic Petri Nets(SPN) to discrible the dynamic transfer process between the normal state and accident state of heat supply network. Operator semigroup approximation theory and numerical simulation are used to analyze changes of instantaneous probability reliability indexes of heat supply network during heating period respectively, and based on the instantaneous probability reliability indexes functional reliability indexes of repairable heat supply network considering the changes of time and outdoor temperature are proposed to build a whole dynamic reliability evaluation methods and indexes. With the proposed methods and indexes, dynamic reliability indexes of some heating pipe network are analyzed to vertify the correctness and practicality of dynamic reliability evaluation methods.Firstly, in order to build dynamic reliability model of heating network, the failure and accident critera of repairable heating network is redefined considering the effects of heat storage capacity on building’s indoor temperature during fault conditions, and the involved features of repairable heating network including failure rate and maintenance rateare are analyzed as well. According to the dynamic failure ctiteras, SPN dynamic reliability model of repairable heating network is built to describe the dynamic transfer process of state, and the steadystate availability of network is analysed quantitatively.Secondly, instantaneous availability of heating network is calculated by operator semigroup approximation theory and numerical simulation respectively concluding that the instantaneous availability of heating network remains stable with small fluctuation during heating period. By comparing the results of analytical method and simulation method, it can be found that within a certain error range, numerical simulation method is more suitable to heating network with many accident elements. According to transient state probability, the functional reliability evaluation methods and inesxes of heating network are proposed to evaluation amd analyze dynamnic reliability of heati ng network comprehensively, which is different from unrepairable heating network, and the indexes include no accident probability index, no failure probability index, mean failure or accident index, indoor temperature during accident condition and so on. Finally, during the heating period, the variation of dynamic reliability indexes of some heating pipe network is summarized with the proposed methods. It can be found that the availability and reliability of pipe network are stepped increased with the increasing of outdoor temperature during heating period and the availability of pipe network is higner than the reliability of network overally; no accident probability is also stepped growing with changes of outdoor temperature, while no failure probability changes linearly; mean failure time is higher than mean accident time of heating network; to pipe network indoor temperature of users in accident conditions is not only related to failure repair time, but also associated with the maximum heating rate of pipe network. With analyzing the variation of reliability of heating network during heating period, it can provide the necessary advice and gudilines to improve reliability of heat supply network in China.