Effect of environmental humidity on the water absorption characteristics of pulverized coal

Pulverized coal is widely used in boiler combustion.The high moisture content will affect the safety of pulverized storage coal and boiler production.Coal adsorbs the moisture in the environment.In order to study the influence of environmental humidity on water absorption of pulverized coal,the three kinds of raw coal with different metamorphic degree were selected to prepare pulverized coal.The samples were divided into two groups,the group Ⅰ was the basic pulverized coal,and the group Ⅱ was dry coal,and a total of six samples were collected.The water absorption characteristics of pulverized coal were studied under the conditions of 45% and 70% ambient humidity.At 45%and 70% ambient humidity,the water content curve of group Ⅰ shows a downward inflection point after continuous increase,then rises slightly until it is basically stable.The trend of water content curve in group Ⅱ is different under two humidity.At 45% ambient humidity,the moisture content of pulverized coal in group Ⅱ rises until it is stable.At 70% ambient humidity,the trend of change is to first increase,then declines inflection point,and then rises until it is basically stable.At 45% ambient humidity,the water content of three kinds of pulverized coal at inflection point is 4%-5% lower than that at 70% ambient humidity,mainly due to the different reasons of inflection point.The first inflection point at 45% ambient humidity is the desorption effect of pulverized coal on water due to hydrogen bond breakage.The second inflection point at 70% ambient humidity is due to the wetting heat generated by the combined action of coal and oxygen after coal powder adsorbing water.The amount of evaporation from the sample itself exceeds the amount of adsorption.Under two humidity conditions,the moisture content of pulverized coal in group Ⅱ is lower than that of pulverized coal in group Ⅰ after the adsorption reaches saturation.The reason is that when the dry coal sample is dried,a certain degree of upgrading and modification has taken place.At the same time,the pore structure will collapse a little,and the hydrophobicity of the coal will increase,resulting in that the moisture content of the dry base is lower than that of the received base when the adsorption equilibrium is reached.The absolute water absorption and water absorption rate of group Ⅱ are higher than those of group Ⅰ,because the difference of capillary pressure between ambient water vapor and drying coal is greater than that of group Ⅰ.When the amount of water adsorbed and the rate of adsorption at 70% humidity are higher than those at 45% humidity,the other experimental conditions are basically the same,because when the humidity is high,the partial pressure of water vapor is high,the water vapor is more easily absorbed by pulverized coal,and it is easier to actively enter the internal structure of pulverized coal,indicating that environmental humidity is an important factor affecting the amount and speed of water adsorbed by pulverized coal. At last,the water adsorption of pulverized coal with different metamorphic degree is compared.Because the surface electrostatic potential and active functional groups of low rank coal are more than those of high rank coal,the water absorption performance of low rank coal is stronger than that of high rank coal.When the ambient humidity is 45%,the ambient vapor pressure is not different from the capillary pressure of three kinds of pulverized coal,so the adsorption capacity is small and there is little difference At 70% environmental humidity,the law is more obvious.