| The photo-thermal conversion efficiency of tower photo-thermal power station is closely related to the dust-accumulation-degree of heliostat mirror,and the existing cleaning strategies are generally based on regular cleaning.When the dust accumulation is too much,and is not cleaned in time,the photo-thermal conversion efficiency of heliostat mirror field will be reduced,and the cleaning time and mirror damage will be increased;when the dust accumulation is less,and is cleaned in advance,and this will waste the scarce water resources in the plateau desert area.In order to realize an automatic matching and cleaning strategy requirements of heliostat according to dust-accumulation-degree,this paper has proposed a method of making standard plate for dust-accumulation-degree of heliostat,and has developed a special dust spraying device,and has given a calibrating and grading method of dust-accumulation-degree.The main research works and results are as follows:(1)Through the finding and reading of domestic and foreign literature,it is confirmed that the reflection ability decrease of heliostat mirror is positively correlated with the level of mirror dust accumulation,and it is confirmed that the replacement of the commonly used concept of mirror "cleanliness" with the concept of mirror "dust-accumulation-degree" is the scientific rationality,and thus the production and calibration for the standard plate of dust accumulation level are carried out.For the judgment requirements of actual site mirror cleaning,the dust-accumulation-degree of the mirror is classified,the standard plate of dust-accumulation-degree is made,and the measurement and calibration are carried out in order to give the method of site quantitative test of dust-accumulation-degree.(2)Through the study of the mirror characteristics and dust accumulation process characteristics of heliostat,a standard plate making method and device for the quantitative spraying of dust and liquid mixture by the spray pen has been proposed,The device can adjust the distance between the spray pen and the mirror arbitrarily according to the size of the mirror,and so as to control the spraying range.The experimental studies are conducted by using 38μm,180μm grain size and a quartz powder of the two mixture,the results show that the device can be applied to dust particles of various particle sizes,with the better dust spraying uniformity and adhesion stability,and it has the transportability for the specific dust accumulation in photo-thermal power station.(3)In order to calibrate the accumulated dust amount on the standard plate of dust-accumulation-degree,the accumulated dust amount of per unit area for the mirror is weighed and calibrated.Taking the standard plate for dust-accumulation-degree of mirror made of 115 microns particle size quartz powder as an example,the model of the dust spraying times and the dust accumulation mass for per unit area of the mirror has been established,the maximum dust mass that can be attached per unit area of the mirror is 1.86 g/m2.According to this,the level of dust accumulation in the mirror can be divided into five levels,and the corresponding level of the standard plate of mirror dust-accumulation-degree can be made.The measurement of reflectivity measuring instrument has showed that the dust accumulation amount of the made standard plate of dust-accumulation-degree is negatively correlated with the reflectivity.The measurement by the CCD camera shows that its dust accumulation amount is positively correlated with the dust level value measured by the CCD camera.Therefore,the standard plate of dust-accumulation-degree and the calibration method will effectively promote the field detection of the heliostat dust-accumulation-degree,and realize the cleaning strategy as required. |
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