Research For 300MW Circulating Fluidized Bed Boiler Firing Gangue

As we know, gangue is a solid waste discharged at the process of coal mining and coal washing, the characteristics of which are high ash content, high sulfur content and low heat value. A great quantity of gangues stockpiling not only occupy ground but also pollute environment. According to the coal industry development plan of China, it will strive to develop circular economy and make great effort to govern and utilize gangue, mine water and pulverized coal ash based on the principle of reducing, recycle and reuse. China has been given aid to gangue power generation from revenue, electric dispatch etc and circulating fluidized boiler (CFB) power plant is the optimal choice for gangue power. As well as, the large capacity 300MW CFB has more advantages in technology, economy and environmental protection.Through compares with and analyzes the designed data of the 300MW CFB firing lignite, this paper summarizes the design characteristic of 300MW CFB firing gange which based on stationary state design and material balance principle, and this paper analyses the main parameters selected:according to the characteristic of gangue, the particle size of the coal is controlled under 4mm in fine limit and 10mm in coarse limit, and rolling ash cooler is designed; the bed temperature selected is at 870℃on the basis of NOX and SO2 emission requirement; the primary air rate selected is 37.4%, and the heat exchanges in rear pass absorb 10% or above more heat than lignite CFB; the boiler designs external bed and pouring wear-resistant castable in all locations where abraded easily; the boiler adopts island arrangement, all steel structure, insulated solid-air cyclone and double air distributors arrangement.Boiler cold test indicates:the air distributor resistant is 4.5KPa when the air flow at the single side of furnace is 180000m3/h in cold condition and the critical fluidized air flow of single side is 90000Nm3/h in hot condition. Also, the air distributing of the air distributor is uniform and the bed material fluidized well.This paper researches various bed temperatures, bed pressure and excess air coefficient affecting boiler operation through combustion adjustment. It indicate:properly increase bed temperature can strengthen combustion and heat exchange, reduce the unburned carbon content in fly ash and bottom ash, improve combustion efficiency, but it limited by the coal deformation temperature, decrease the desulfur efficiency and increase the pollutant, such as SO2, NOx, emission at the same time; properly increase bed pressure can increase circulating material quantity, be advantage to heat exchange, reduce the unburned carbon content in fly ash and bottom ash, improve combustion efficiency, decrease the SO2 emission, meanwhile effectively decrease bed temperature, inlet temperature cyclone and return material temperature of siphon and make the bed temperature more uniform, but it increase power consumption, so various factors should be taken into consider overall in practice; increase excess air coefficient can reduce unburned carbon loss in total, reduce unburned carbon content in fly ash but increase that of in bottom ash, and reduce post-combustion temperature after cyclone seperator, but too large excess air coefficient will lead to the increase of q2 loss more than the decrease of q4 loss, so it should be overall consider the loss of q2 and q4 to determine the excess air coefficient; increase the secondary air proportion can reduce the unburned carbon content in fly ash but increase that of in bottom ash, so it should be overall consider the two factors to determine the proportion of primary air and secondary air; turn up the lower secondary air opening can strengthen combustion and make the bed temperature tend to uniform, and same opening of the lower and the upper secondary air will be advantage to fuel burnout, both in fly ash and bottom ash, which bring relatively lower unburned carbon content, and the upper differential pressure will decrease following the increase of upper secondary air opening.Finally, the paper confirms the boiler total performance combined with boiler performance appraisal test:all the main performance evaluations reach or exceed guaranteed values, and the external bed and spray water can fit the requirement of steam temperature adjustment, all auxiliary machinery, thermodynamic system and automatic control equipment can be normal operation during the test and match the requirement of BMCR, the boiler can reach rated output and all the tubes metal temperatures of heating surface do not exceed limits.