Design And Optimization Of A New Type Of Small Vertical Natural Circulation Steam Generator

With the increasing demand for steam generators for field operations such as camping and bathing vehicles and troop camping and stationing,there is a growing interest in small steam generators.The calculation and software preparation for industrial-grade large steam generators,etc.,are quite mature,but are not applicable to the design and calculation of small steam generators.Based on this,this paper has carried out research work in the following areas:First,based on a summary of the current status of research on steam generator structures at home and abroad,a compact nested small vertical natural circulation oil-fired steam generator is designed with an overview of its structure and an introduction to the workflow of the flue gas and water flow channels,taking into account usage scenarios and basic design parameters.Then,based on the structural characteristics of the designed steam generator,the basic thermal calculations such as fuel combustion and heat balance are analyzed,and the thermal calculation methods are explored from the nature of heat transfer,especially the liquid and gas-liquid phases in the steam generator need to be segmented according to the phase state.After determining the heat transfer area through thermal calculations,the size of the generator is initially determined based on the specifications of the selected steel pipe.Then,the formula for calculating the flue flow resistance of the steam generator was derived by combining the structure of the steam generator,and MATLAB was used for programming to further calculate and analyze the flue flow resistance of the abovementioned steam generator with multiple size specifications that meet the thermal calculation error.The results show that the flue resistance is gradually increasing with the increase of the flue height,while the percentage of the outer flue resistance is also gradually increasing.After that,the steam generator hydrodynamic calculation model is established,and based on the basic calculation equations such as single-phase flow and two-phase flow pressure drop in the tube,combined with the principle of summed flow and equal pressure difference,the steam generator hydrodynamic calculation equation set can be obtained.MATLAB is used to program the hydrodynamic calculations.The appropriate structural values are determined according to the circulation multiplier and circulation water velocity of the hydrodynamic calculation.Further analysis of the trends of the hydrodynamic characteristics parameters of the steam generator under different specifications and operating conditions revealed that the designed 100 kg/h oil-fired steam generator gradually decreases in operating conditions,the circulation multiplier and operating differential pressure gradually increase,and the circulation flow rate gradually decreases.In the case of steam generator rising tube height of 2.5 m,for example,this type of steam evaporator is suitable for safe operation at 50% to 110% operating conditions.If the circulating flow rate and circulating multiplier both meet the recommended value range,as the overall height increases,the starting boiling point of this type of steam generator at the same load gradually rises,and the lower limit of safe operating conditions gradually decreases and the upper limit gradually increases.Ends with stagnation and backflow calculations,and the results show that the designed steam generator has been tested,and the stagnation and backflow coefficients of the weakest heated water pipe are greater than1.1,which is in line with the safety design specifications.Again,the designed steam generator was compiled using QT Creator,the programming language C++,and the ".m" file for thermal,smoke resistance,and hydrodynamic calculations written in MATLAB software above was compiled into a dynamic database that can be called directly by QT Creator.The ".dll" file is compiled into a dynamic database that can be called directly by the software QT Creator,and the composition of the small steam generator design software and the design and code implementation process of each module are described.The chapter concludes with an example of the design process of a 100 kg/h small vertical natural cycle oil-fired steam generator,and describes the processes and operations related to the design software interface from the user’s perspective.Finally,the designed natural cycle steam generator is optimized and analyzed in terms of both efficiency and economy,and the effects of structural changes,feed water temperature,flue gas inlet and outlet temperatures,and variable operating conditions on the efficiency of the steam generator are investigated.The calculation results show that the increase in the height of the rising pipe(water pipe)and evaporation volume,and the decrease in feed water temperature,flue gas inlet temperature,and exhaust temperature all bring about an increase in efficiency,and the The deep-seated reasons for the efficiency change.In terms of economics,the main steel price of the steam generator under different specifications is calculated;the trend of fuel consumption under different structures and variable working conditions is studied;for example,with a steam generator rising pipe height of 2.5 m,the feed water temperature of 35 ℃ is about 37,000 yuan/year more than the annual output gain of 15 ℃,and the exhaust smoke temperature of 105 ℃ is about148,800 yuan/year more than the annual output gain of 85 ℃.