Monte Carlo Simulation Of The Passive Nuclear Level Gauge Used On Hopper

Material position detection is a very important branch in the field of automatic control,how to monitor the material and powder level has become urgent problem to the power plant.Without the use of radiation source,only through receiving the gamama particles flow and signal processing to get the material information is an obviously advantage on the material level measurement in the ash and dust removal system of the power plant.Not only avoiding the easy hanging,easy loss and the disadvantages of other methods,but also have the charicterristic of complete non-contact meseasurement,stable opertation,low maintenance cost,accurate measurement,easy installment and so on.Passive nuclear ash hopper material level meter exist the following problems:(1)the material level meter calibration process need artificial determination of material level height,which is cumbersome and needed to repeat calibration many times.The artificial calibration workload is big and low accuracy,and can't calibrate automatically.(2)Ignore the important effects brought by the changes of radioactive activity in the coal ash,the changing in the coal ash radioactive activity would cause material level measuring error and even misinformation and accident.(3)when the radioactive activity in the coal ash is weak,the material level measuring accuracy is low.To absolve the above problems,use the monte carlo method to simulate the changing rules of the radioactive accumulation/reduce along with the change of material level in the electrostatic precipitator ash hopper,improve the design of the passive nuclear ash hopper material level meter and the accuracy of measurement and realize the automatic calibration.The main research results about the article are as follows:(1)Put forward the "quadruple combination detection" automatic calibration method,which solved the previous passive nuclear ash hopper material level meter calibration problem.(a)Using quadruple combination detection and "contour multistage measurement model",fitting the ratio of absorbed dose rate detected by adjacent cascade probe with corresponding actual material level,then using the fitting parameters to calibrate automatically which don't need ash hopper stop working,And this can effectively save the calibration time and cost.(b)effectively eliminate the material level measuring error brought by the changes of radioactive activity in the coal ash,which improve the measuring precision and material level positioning accuracy.There are many factors affecting the radioactive activity of coal ash which vary in Different feeding period,or after refueling.And this may cause measurement error and misinformation.Using quadruple combination detection and contour multistage measurement model,when the radioactive activity in the coal ash changes,the passive nuclear meter level gauge can be revised according to the calibration curve or calibrated automatically.Which eliminated the effects brought by the changing of coal ash radioactive activity,saved onerous repeatedly calibration procedure,also improve the accuracy of the calibration,avoid misjudgment,and can improve the accuracy of measurement.The conclusion shows that when the radioactive of the material doubles,the "quadruple combination detection"method results reduce the error to the range of 1.1 percent and 5.4percent,apparently better than the traditional methods(12percent to 57percent).when the radioactive of the material reduce by half,the "quadruple combination detection"method results reduce the error to the range of-1.7percent and-7.6percent,apparently better than the traditional methods-25percent to-43percent).(2)The essay is about the Monte Carlo simulation of the passive nuclear level gauge used on the electrostatic precipitator's hopper.finding the best detection angle by changing the detection angle of the passive nuclear level gauge,when the angle increase to 30 degree,the interface integral flow increase and reachs to the maximum at the 30degree,then when the angle turns to 40 degree to 90 degree,the interface integral flow decrease and finally to the minimum.so we can conclude that when the angle between the probe and level line reachs 30 degree,this is the best detection angle.(3)with the combination of the Monte Carlo method and the research on passive nuclear gauge,we establish the complete electrical precipitator hopper and passive nuclear gauge model,and gain the absorbed dose rate curve on different ash height level.We get the absorbed dose rate curve in different ash height level of the low level passive nuclear level gauge and high level passive nuclear level gauge under the 30 degree detection angle,then we can not only know the trendency of the ash increase or decrease,but also find the switching point through the two order derivative method.We finally conclude that when the low level passive nuclear level gauge is installed at the height of 90 centimeter,the change rate of the absorbed dose rate reachs to the maximun when the ash height reachs to the 100 centimeter,when the high level passive nuclear level gauge is installed at the height of 270 centimeter,the change rate of the absorbed dose rate reachs to the maximun when the ash height reachs to the 300 centimeter.(4)We get the relationship between the coal ash level and corresponding absorption douse rate through the gamma space field theory formulas and algorithms.it is concluded that the relative standard deviation between the simulation results and derivation results was within ten percent,which proves that using the monte carlo method to simulate the running of the passive nuclear level gauge on the four squaretable hopper is reliable and correct.(5)we found that the relative standard deviation between the actual measurement result and monte carlo simulation result was within ten percent,and the trendency of the material level change curve was almost the same between the actual measurement and monte carlo simulation.We can conclude that the monte carlo method is reliable and correct.(6)design and programme a passive nuclear level gauge monitoring system,which has simple operation and friendly man-machine interface and relatively perfect monitoring function.it can monitor the trend of grey level in the ash hopper,and has perfect alarm mechanism?data query system,efficient data acquisition module and real-time visualization of data graphs.The article achieve the goal that complete the research on the key technology theory and monte carlo simulation of the passive nuclear level gauge used on the power electric device ash hopper.due to the time limit,there was not an in-depth research on the environment background correction problem,which remained to be done in the further research in the future.