Study On Pulverized Coal Volume Concentration And Distribution Measurement In The Pneumatic Conveyor

In power boiler, whether direct firing pulverizing system, intermediate storage tanks type hot blast feeding system or gas sends powder system, the working substance in the conveyance air pipeline as the pneumatic pipeline is the mixture of hot air and pulverized coal. The flow of the mixture belongs to the typical gas-solid two-phase flow. The measurement of the parameters of the hot air-pulverized coal two phase flow in the primary air pipeline directly relates to the safety of the power boiler combustion, operational economical efficiency and reliability. Gas-solid two-phase flow is recognized as a complex nonlinear dynamic system, interfacial effect and speed exist between phases, which make the measurement of the as-solid two-phase flow parameters difficult.Based on widely studies the existing technology, the paper divides the hot air-pulverized coal two phase flow research to three levels:the first level is the need of the boiler combustion safety, the second is the need of operational economical efficiency, and the third is the need of gas-solid two-phase flow theory research level.The aim of the paper is to make up effective method which can be applied to actual engineering hot air-pulverized coal two phase measurement, using current technology, to meet the need of the first level and part of the second level.Therefore the paper respectively provides a hard field sensing absolute measurement method based on y-ray absorption law. The real-time measurement of pulverized coal concentration and phase distribution is possible in engineering. In the process of realizing the above aim the main statistical innovation is below:1.The method of pulverized coal volume concentration and distribution measuring in the pneumatic conveyor. The y point source was used and fixed at the cross-section centre of the sensor conduct; the collimation exit portal was vertical to the axis line of the conduct, in which the outgoing beam of they rays was assumed at the plane 360°; The profile of the ionization chamber was designed ring cross section in dependent multi-cavity. By which the equivalent thickness of the pulverized coal could be determined from the axis to the pipe wall of the sensor all around the 360°circle, the ratio between the equivalent thickness and the radius of the pipe could be take as volume concentration in the subspace in the sensor while serving as the distribution of the pulverized coal in the corresponding radius. The method present in this dissertation belongs to a hard-field sensing, absolute measurement. The measured value of the concentration as well as distribution of the pulverized coal in a pneumatic conveyor could not be influenced by the changes of humidity, fineness temperature, flow pattern, velocity of the continuous phase. The effected by the alteration of effect alterations caused by categories of the coal could be eliminated setting different linear absorption coefficient according the coal.The measurement method of the value concentration and distribution presented in the dissertation as the technology nucleus has been applied for a China patent. Date:2008.12.17;No.200810240327.O2. Combined Kovar alloy and Al2O3 Ceramics as the material of the sensor conduct was suggested with regard to industrialγray source, the lower radio activity level, the easier radioactivity protection was accomplished, Al2O3 Ceramics and Kovar alloy composited sensor conduct was adopted for the purpose of reduction inγray source radioactivity. On the premise of the resolution ratio, accuracy requirement, that was an innovation solution presented in this dissertation the linear absorption coefficient of the alloy and ceramic double compound material toγray was less than steel besides its high-temperature resistance, the radioactivity of the measurement demanded to theγray source could be reduced obviously and the radiation protection could be easier to reach the standard of the nation.3. A discrimination theory of sedimentary condition, identification method about the optimum ratio between blow and pulverized coal in a phpnoumatic conveyor were advanced in the dissertation.The flow of pulverized coal in the pheumatic conveyor belongs to thin gas-solid two phase flow the sedimentary condition was caused by the force of gravity when the velocity of the continuous phase was underspeed,in the regular service conditions,the difference of the concentration and the distribution different are a effect in area affects of the cross section was not obvious,the pulverized coal deposition first emerged at the lowest point in the sensor conduct when the sedimentary condition occurred, so the sedimentary condition could be identified when the measured value of the pulverized coal concentration in the directly below measurement space was thicker than adjacent space over a threshold value, and the superior limit to the lower limit of the threshold value could be defined as optimum ratio between below to and pulverized coal and the threshold value could be used as feedback signal to control the velocity of the primary air.