Research And Application Of Safe,Low-Nitrogen,High-Efficient And Intelligent Control System For Gas-fired Heating Boilers

With the implementation of China’s atmospheric pollution controlling and Blue Sky Action Plan,natural gas has become an important heating energy in large and medium-scale cities.Gas-fired heating boilers are the main utilizers of natural gas and large emitters of nitrogen oxides.Gas-fired boilers possess the merits of safety,low-nitrogen,high-efficiency and intelligent controlling for heating boilers.It relates to the peoples’ livelihood and national energy safety,and it is the hot topic in the field of energy environment and architectural energy saving.The paper aims at flash-explosion,vibration,condensate corrosion,low-efficiency in the nitrogen-oxides reducing retrofitting of gas-fired boilers,combines theoretical and practical engineering measurement,and studies safety,low-nitrogen oxides,high-efficiency and intelligent controlling for heating supply technologies.It can provide technical support for improving the natural gas utilization level and safety,saving energy,reducing emissions,improving air environment of heating operation managers,the level of intelligent controlling of heating and reducing heating costs.The paper surveyed 137 gas boiler rooms,which contains 567 gas boilers and 2097 steam tons in Beijing.The results showed that 567 gas-fired boilers have been retrofitted with low nitrogen-oxides technologies,adopted 17 sorts of low nitrogen combustion equipment,four kinds of low nitrogen combustion technology: staged combustion combining with flue gas outer circulation(FGR)technology,lean combustion premixing metal-surface combustion technology,water cooled premixing combustion technology and flue gas internal circulation(FIR)technology.The ratio of each combustion technologies are 80.6%,17.81%,1.41%,0.18%,respectively.The concentration of NOx emission are all below 80 mg/m3.However,the concentration of uncompleted CO in some boiler combustion are more than 76 ppm,thermal efficiency and power output are reduced by 1%~3%,and some boiler systems occurs the problems of condensate corrosion and vibration.The flue gas/air mixing parameters and safe control of nitrogen-reducing boilers were studied.Based on the analysis of nitrogen-reducing mechanism and technology of gas-fired boilers and the causes of the problems in the retrofitting project,the paper studied the variation of mixing temperature between reflux flue gas and combustion-supporting air under different operation load,excess air coefficient,flue gas recirculation ratio and interface position of flue gas recirculation pipe for flue gas outer circulation(FGR)boilers.Further,the safe,low-nitrogen,high-efficient and intelligent controlling for heating logic were proposed,which can supply theoretical reference for the low-nitrogen,completed combustion,corrosion and CO reduction.Then,this paper analyzed the effects of boiler retrofitting on the thermal efficiency and heat loss of gas-fired boilers,analyzed the energy saving potential of deep recovery of flue gas waste heat.The heat recovery of exhausted flue gas can make up for the thermal efficiency loss of low nitrogen retrofitting boilers.Also,the safe,nitrogen-reducing,heat-efficiency enhancing scheme was proposed combined condensation heat recovery and indoor atmospheric quality improvement.Finally,aiming at the low-nitrogen retrofit project of gas boilers in Beijing district,the intelligent controlling scheme for safe,low-nitrogen and efficient operation of gas-fired boilers is established.Through the project implementation and the 2019-2020 heating season tracking measurement,the results can be obtained: the boiler load rates are 10%~90%,flue gas recirculation ratio is 20%~25%,NOx emissions are 28~50 mg/m3,CO emissions are17~35 ppm,boiler thermal efficiency are 9.9%~10.6% higher than before boiler transformation,and boiler system thermal efficiency of 103.38%~104.30%.The boilers have stable operation,no vibration,no condensation corrosion,and the indoor atmospheric quality of boiler room has been improved.The safe,low nitrogen oxides,high-efficiency and intelligent heating controlling of gas boiler system was realized.