| Municipal solid waste(MSW)incineration techniques are developing rapidly due to the primary advantages of hygienic control,volume reduction,and energy recovery.The circulating fluidized bed(CFB)incineration method is one of main waste incineration technologies has very wide popularization and application prospects in China.With the continuous improvement of the standardization,environmental protection standards and supervision of the waste incineration industry,CFB waste incinerators are faced with the requirements of economy and environmental protection during the production process,Part of CFB waste incinerators cannot operate normally and continuously because of CO emission and the temperature in the upper and middle parts of the furnace cannot reach the standard continuously and stably.At present,there are still a large number of CFB incinerators in operation in China,how to improve the environmental and economical performance of CFB incinerators operation through technological optimization and improvement has become an important topic for the sustainable development of CFB incineration technologies.The following research works have been carried out for domestic CFB waste incinerators from the perspective of combustion optimization and with the goal of improving the environmental and economical performance in this paper:(1)The CFB waste incineration process and the composition of CFB incinerators are introduced in detail,therefore the research object of this paper is understood more clearly and intuitively.Analyzing and summarizing the fluid dynamics,heat transfer model,combustion mechanism,formation and combustion mechanism of CO,the main characteristics of CFB combustion technology and thermal properties of combustion system,and then the operation control objectives of CFB waste incineration system and significance of this paper are expounded.(2)A systematic,comprehensive and detailed investigation has been carried out on CFB waste incinerator,On this basis,the emission characteristics of flue gas pollutants from CFB incinerators are analyzed comprehensively.Tracking and understanding of boiler CO emission status,operation stability in-depth.The results show that,due to the overall design of the system and the lack of attention to waste pretreatment and other factors,the early CFB waste incineration boilers are faced with problems such as excessive CO emission and short boiler operation cycle.The CO emission concentration of most boilers without systematic improvement and optimization often exceeds the emission concentration of more than350mg/m~3,abnormal conditions such as feeding blockage and slagging blockage often occur in the process of boiler operation,leading to a short operation cycle less than 7000h.(3)The characteristics of the CO emission and the reasons that affect the CO emission are deeply studied by experimental research in order to cope with excessive CO emissions of CFB incinerators.The systematic solutions are put forward from the aspects of waste pretreatment,waste feeding,adding refractory boards to the membrane wall of the in the dilute flow region,modification of secondary air and adding secondary combustion chamber.The practice results show that the CO emission concentration of CFB incinerators can continuously and stably meet the national emission standard after the overall transformation,the average hourly concentration of CO can be controlled below 50 mg/m~3,the average daily concentration of CO can be controlled below 20 mg/m~3,and the boiler operation cycle has been greatly improved,which can reach about 7500h.(4)However,the heating values change widely and frequently,while there is no reliable real-time instrument to measure heating values in the process of incinerating municipal solid waste.A rapid,cost-effective,and comparative methodology was proposed to evaluate the heating values of burning MSW online based on prior knowledge,expert experience,and data-mining techniques.First,selecting the input variables of the model by analyzing the operational mechanism of circulating fluidized bed incinerators,and the corresponding heating value was classified into one of nine fuzzy expressions according to expert advice.Development of prediction models by employing four different nonlinear models was undertaken,including a multilayer perceptron neural network,a support vector machine,an adaptive neuro-fuzzy inference system,and a random forest;a series of optimization schemes were implemented simultaneously in order to improve the performance of each model.Finally,a comprehensive comparison study was carried out to evaluate the performance of the models.Results indicate that the adaptive neuro fuzzy inference system model outperforms the other three models,with the random forest model performing second-best,and the multilayer perceptron model performing at the worst level.A model with sufficient accuracy would contribute adequately to the control of circulating fluidized bed incinerator operation and provide reliable heating value signals for an automatic combustion control system.In addition,intelligent modeling algorithm is also utilized to model the parameters of boiler bed temperature,NOx,drum water level,etc.,and the prediction error can be controlled within±2%.(5)The fly ash rate of CBF incinerators is generally between 10%and 15%,the higher fly ash rate leads to lower boiler efficiency,shorter operating cycle and higher cost of fly ash disposal.Flay ash reduction control methods are studied for CFB incinerators,especially those which burn rural garbage and landfill stale waste boiler regularly.The bottom ash collection and reduction system,circulating ash collection and reduction system and fly ash reburning system are designed and applied to reduce the fly ash rate of CFB incinerators by many ways.Practice results show that the bottom ash collecting system of U-type chamber of tail flue can reduce the fly ash rate more than 4%,circulating ash collecting system can reduce the fly ash rate more than 5%,the fly ash reburning system contributes to CO emission control and can reduce the fly ash rate by about 1.5%and the calcium hydroxide consumption about 2kg per ton of waste. |
PDF Full Text Request