Research On Structures And Properties Of Submerged Combustion Evaporator

Submerged combustion evaporation (SCE) is a new technology to evaporate liquid quickly by blowing the high temperature gas into the liquid directly, which is characterized by high efficiency, low energy consumption, low pollution and low emissions. As Oilfield wastewater has complicated species, high salinity, and is difficult to get handled, submerged combustion evaporation technology was adopted to conduct the desalination of oilfield wastewater. To improve the burner performance and evaporator thermal efficiency, structures and properties of submerged combustion evaporator were studied. The characteristics of exhaust emissions, combustion efficiency and evaporation efficiency under different excess air coefficients were investigated; heat and mass transfer performance of different evaporator structures were studied.The main research and results are as following:(1) The emissions of SCE were monitored; emission characteristics of air pollutant gas HC, CO and NOx under different excess air coefficient were analyzed. It was found that with the increasing of excess air coefficient, the concentrations of exhaust HC and CO decreased at first and then remained unchanged. Throughout the testing process, the concentration of NOx emission did not exceed15ppm, much lower than the atmospheric emission standards200ppm. Therefore, submerged combustion is a low NOx emission and environmentally friendly combustion technology.(2) The results of combustion characteristics experiments showed that the combustion efficiency was the highest when excess air coefficient was between1.2and1.5. The combustion efficiency was low when excess air coefficient was too small; but when excess air coefficient was greater than1.6, the flue combustion would be instable, vibration and noise increased.(3) The relationship between the evaporation efficiency and excess air coefficient were studied. It was found that the increasing of excess air coefficient could increase the evaporation efficiency as well as decrease it. Considering the evaporation efficiency, combustion efficiency and emissions characteristics, it was identified that the optimum excess air ratio ranged from1.2to1.4. (4) Designed three different evaporator structure:the straight tube style, the distribution disk style and the circulation baffle style. Experiment studies were carried out to compare the gas-liquid two-phase flow, efficiency and resistance. The results showed that, under the same experimental conditions, the baffle style evaporator had the highest heating and evaporation efficiency then followed the distribution style and the strait tube style was the lowest. This indicates that the heat and mass transfer between the gas and liquid phases can be strengthened by adding baffle or distribution disk to the evaporator.(5) As the baffle style evaporator could significantly improve the heating and evaporation efficiency, therefore, further study was carried out to find how the baffle structure to improve heat and mass transfer. Through the steady-state evaporation experiments under different immersion depths, gas load and damper position, the following conclusions could be obtained:â‘ The strengthen effect of baffle increase with both the immersion depth and the gas load;â‘¡Overflow could be got by setting the baffle some distance above the liquid level, foam district could be formed which was in favor for the heat and mass transfer. The optimum overflow height of the apparatus was10mm.