Cold-state Model Experimental Research On The Selective Slag Discharge Device In Cfb Boilers

With the rapid development of the national economy, the coal supply is becoming tighter. The circulating fluidized bed (CFB) combustion technology is getting more and more popular because of its better coal adaptability and excellent environmental performance. However, there are some problems such as serious abrasion in the furnace, insufficient fine particles and large heat loss of the bottom ash etc., when burning the low quality coal by the CFB combustion technology. In view of this phenomenon, a kind of bottom ash separation slag-discharge technology was first proposed in this paper. The furnace heating surface abrasion might be decreased effectively by reducing the fine particle discharge proportion. It might prevent the slagging pipe from coking and reduce the requirement on the cooling capacity of bottom ash coolers by reducing the slagging temperature, and also recover some bottom ash heat to the furnace to improve the CFB boiler's economy and reliability when burning low quality coal.In order to verify the technical feasibility of the slag discharge device, a cold-state model bench for the fluidized bed selective slag discharge device had been designed, manufactured and installed. After the scientific research on the gas-solid flow characteristics of this new type device, some rules that impact the bottom ash separation performance and slag discharge characteristics had been concluded using the important parameters defined, such as separating effect factor, demarcation particle size etc.. Some main conclusions were expressed as following:①The separation characteristics parameters defined could correctly estimate the particles'separation effect, and also determine whether the slag discharge device was in a normal separating state;②With time increasing, the sorting process would eventually get to a relatively stable state, and the increase of selective air velocity could effectively reduce the time of this processs;.③The increase of selective air velocity was beneficial for the fine particles'separation and recuperation, but also resulted in the increase of demarcation particle size. The augment of furnace air velocity had a negative impact on the separation effect of the slag discharge device;④The increase of fine particles'proportion in the bed materials and the height difference between the top of the bed and the bottom of the fine-particle outlet was conducive to the fine particles'separation and recuperation, but also resulted in the increase of demarcation particle size.⑤The separating effect of the slag discharge device would begin to deteriorate when the demarcation particle size was more than the design critical particle size. Some conclusions were obtained under the pre-set particle sizeφs= 1mm: 1) Within the test range, the slag discharge device was in a normal separating state when the dimensionless air velocity ratioωs> 1.43; 2) Within the test range, a set of parameters of the best separating effect were found: furnace air velocity of 0.393 m/s, selective air velocity of 2.245 m/s (ωs= 5.71), and the height difference of 150~200mm;⑥The bench structure design was reasonable, and the materials'fluidization was in good condition, and the separating effect of coarse/fine particles was obvious within the test range. Thus proved the selective slag discharge device invented was feasible and popularized further into the industry.