An Investigation For Slag Water Evaporation In Water-cooled Deslagging System Of Coal-fired Boiler

Evaporation phenomenon has been studied zealously for many years because of its extensive and significant in various fields of engineering and technology. However, we still have difficulty in precise predicting the evaporation rate which takes place in the water-cooled deslagging system of coal-fired boiler, until now. When high-temperature slag fell into submerged slag conveyor, it happened with cooling water strongly interacting, and then produced the slag water. Slag water evaporation has an important impact on calculating the balance temperature and the supplementary water capacity of deslagging system, and also it’s the theoretical basis of the system optimization design. Therefore, it’s necessary and meaningful to research the evaporation law of water-cooled deslagging system.There are three forms of evaporation in water-cooled slag handing system, burst evaporation, slag water surface evaporation and conditional evaporation. Experiments were conducted to research the effect of the amount of slag, the slag temperature and the cooling water temperature on the burst evaporation. By the experiment, a kind of impact factors function model was established, and the cooling water temperature and the slag temperature function were represented as the exponential form, and the slag amount function was represented as a linear form. Finally, an experimental correlation was found by the nonlinear multiple regression which could accurately predict the evaporation when cooling water temperature between35℃and65℃, and slag temperature was in the range of500～1000℃,and the correlation coefficient was0.92. It has been conducted another set of experiments to study the effect of the surface water temperature and the relative humidity (RH) on the slag water surface evaporation rate under the condition without wind. Under the windless condition, another experimental correlation was obtained to forecast the slag water evaporation rate in the water-cooled slag handing system(surface evaporation25～75℃, RH=40～90%), the correlation coefficient was0.96.A set of comparative experiments showed that there were some different between slag water and pure water surface evaporation, by analyzing the impact of ion concentration in slag water on evaporation we sought out the reason. From the thermodynamic point of view, ions change the surface free energy of slag water and influence the evaporation finally. Based on the mass balance and energy balance of the system, a relationship of the water surface evaporation rate of the furnace bottom per unit area and the slag water surface evaporation rate outside the Shutoff Gate per unit area was found. By theoretical derivation and field measurement of deslagging system, a new way was explored to predict the evaporation rate of the furnace bottom (conditional evaporation).