Study On Key Technologies Of The Gas-Solid Flow In Large-Scale CFB Boilers

Circulating fluidized bed (CFB) boiler has been more rapidly developed in recent years because of its comparative combusting efficiency with pulverized-coal (PC) boiler, cheaper desulfurization cost, lower NOx emission and wide fuel applicability. CFB with larger capacity can enhance the power generation efficiency of existing CFB technology, combine low cost pollution control of coal combustion with high power electricity generation and promote the application of CFB in power generation industry.However, there are some problems during the course of the large scale of CFB boiler, such as the problem of the bigger furnace's volume with the secondary air jetting distance, the problem of the bigger cyclone separator's capacity with the lower separating efficiency, the problems of the disposing ability and dependability of ash slag cooler with the increasing of the ash's quantity, etc. Moreover, several problems of them in the existing CFB boilers have not been well solved.In the present work, we set up a set of visual cold experimental apparatus with Plexiglas according to a commercial 410t/h CFB boiler with a scale of 1:10. Experimental and simulating study on the characteristics of the secondary air (SA) injection and the cyclone separator are carried out in the set-up. Based on study of the performances of the flow and the slag discharge of selective fluidized bed ash cooler, we developed a novel mixing-type fluidized ash cooler. Furthermore, a preparatory investigation on the heat balance and the material balance of a introduced 300MWe CFB boiler is performed. The main works and innovations in this paper include as following:(1) Systemic cold study on the secondary air injection in CFB boilerBased on measuring the solid concentration in the riser cross-section at the SA injection level, we have explored the trend of solid concentration changing with the primary velocity and the effect of secondary air on the solid concentration. Besides, the influences of primary air velocity, secondary air velocity, solid concentration and jetting ports'diameter on the SA injection distance are investigated in detailed, and a dimensionless equation relation about secondary air jetting distance for general cases is obtained by the regression of experimental data.(2) Study on the effect of the bottom-contracted and edge-sloped vent-pipe on the performance of cyclone separators The cold tests and simulations on the separation efficiency and pressure drop of a modified cyclone with a bottom-contracted and edge-sloped vent-pipe are researched in detailed. The changing rules of the separation efficiency and the pressure drop are obtained under the different directions of the cut, and the results are also compared with those of the traditional linear-pipe-shaped cyclone separators. Inaddtion, we evaluated the performance of the novel separation cyclone.(3) Systemic study on the characteristics of material flow and ash discharge in a type selective fluidized bed bottom ash cooler and having developed of a novel mixing flow fluidized bed ash coolerA systemic study on the characteristics of material flow and ash discharge in a type selective fluidized bed bottom ash cooler is carried out. The influence rules of the pressure distribution characteristics of the"ash cooler– furnace"system on the pressure drop of the chambers and bed material flow is first described in this paper. Besides, based on analyzing and summarizing the characteristics of the existing fluidized bed ash coolers, we developed a novel mixing flow fluidized bed ash cooler. This mixing flow fluidized bed ash cooler has a better selective action on wide screen sized bed material. And it can make full use of the advantages of the existing fluidized bed ash coolers, avoid these abnormal phenomena of the clogging of bigger slag and no slag discharging from main slag discharged hole, which can result in decreasing the possibility of agglomeration in the fluidized bed ash cooler.(4) Study on the heat balance and the material balance of a introduced 300MWe CFB boilerBased on the operating data of the first anthracite-fired 300MW CFB boiler in the world, a preparatory study on the heat balance and material balance of the boiler under different boiler's loads (290MW, 300MW and 320MW) were carried out by use of Visual Basic. In addition, the total heat balance and the circulated ash flux of every part of the boiler are all obtained through calculation. The results may provide a base for our further test.