Analysis Of Thermal Hydraulic Characteristics Of Steam Pipe Network System Based On Modelica

As China's industrialization and urbanization continue to accelerate,China 's demand for heating has gradually increased.Combined heat and power units with high thermal efficiency,energy conservation and environmental protection are the main development directions of urban industrial heating technology.Large-scale district heating boilers will become centralized As an important supplement for heating,decentralized heating boilers will be eliminated,and gradually formed a "coal-fired combined heat and power and large-scale boiler room centralized heating-based,decentralized coal-fired boilers and other clean or renewable energy heating supplemented" Heating pattern.In order to further improve the energy utilization rate of the combined heat and power central heating system,make better use of the system's characteristics of improving enterprise productivity and low production costs,and also take into account the heat storage and energy storage facilities of thermal power units to participate in peak and frequency regulation of the power grid This requires the use of computer technology to model and simulate the steam heating system,understand the movement state of steam in the pipe network,and know the thermal and hydraulic dynamic characteristics of the pipe network.This paper presents a dynamic simulation model of a steam heating network based on Modelica,which comprehensively considers the effects of various factors such as steam parameter fluctuations,compressibility,state changes,friction,and heat transfer during the steam flow process.Simple,topological structure is more practical,and the model is fast to solve.Based on engineering thermodynamics,heat transfer,fluid mechanics and other theories,through the calculation of steam thermal properties,steam pipe network heat loss analysis,hydraulic and thermodynamic calculation theory,a thermal-hydraulic dynamic coupling model considering the state of the steam medium is proposed.In order to establish the heating pipe network`s hydraulic calculation model,must base on the network graph theory and Kirchhoff's law;based on the heat dissipation process of the pipeline,a thermal calculation model of the heating pipe network was established;based on three major conservation equations,resistance loss equations,and heat dissipation The loss equation and the equation of state of the medium are used to derive the thermal-hydraulic coupled dynamic model of the steam heating pipeline.The language features of Modelica and the simulation environment of OpenModelica are described in detail,and the advantages of modeling and simulation of Modelica in steam heating system are determined.In view of the steam heating system modeling and simulation,each equipment components in the heating system in the research of physical behavior,establish a mathematical equation to describe the dynamic pipelines,valves,pumps,heat sources and heat users,media,and to describe the equipment such as heat transfer process,on the basis of the physical behavior of which adopts the object-oriented representation type physical modeling language Modelica to the dynamic behavior of the system in as much detail as possible.The corresponding unit equipment model was compiled based on Modelica language,and then combined with the Modelica standard library to form a district heating system model library applicable to steam pipe network heating,and a set of unified DistrictHeatingSystem Modelica model library was established.Then,the model library is used to build the actual pipe network system and carry out simulation verification under the platform of OpenModelica simulation.The collected data at the source end were used as the input of the simulation model,and the steam heating system under the set condition was simulated and verified.By comparing the simulation data at the end with the measured data,the overall error between the simulation data and the measured data was less than 2%,which could greatly meet the requirements of engineering calculation.Furthermore,the dynamic response process of steam heating pipe network is simulated and analyzed,the characteristics of transition process and transient process system are analyzed,and the dynamic characteristics such as lag and attenuation of pipe network are quantified.Finally,the dynamic analysis of the heating pipe,heat storage and release characteristics of the steam pipe network system was simulated and analyzed.A solution for intermittent operation of the steam network is proposed.The heat storage and heat storage characteristics of the pipe network were obtained,and the corresponding calculation formulas for heat storage and heat release capacity and the evaluation indexes of heat storage and heat release were given.