Acid Corrosion Phenomenon Research On Wfgd In Power Plant

The Wet Flue Gas Desulfurization(WFGD) environmental technology of thermal power plant, because of its high desulfurization rate, broad application of coal quality, mature technology, stable operation of long cycle, small impact when load changes, large gas processing capacity and other characteristics, has been widely used in large and medium-sized thermal power plants, and become the dominant flue gas desulphurization technology of domestic and foreign power plant. Gas-Gas Heat exchanger (GGH) is one of the most important equipment in the system of wet desulfurization equipments, and its importance is lower than absorption tower. Its effect is cooling the original flue gas and reheating the net one. When the flue gas through GGH and the flue gas temperature is lower than its dew point temperature, the sulfuric acid vapor formed by SO3 and water vapor was condensed on the pipe wall, and the low-temperature corrosion is caused. It directly affects the construction costs, equipment life and maintenance. So, it is necessary to calculate the flue gas acid dew temperature and predict the corrosion environment. Reasonable prevented corrosion measures will be used during designing, and it is important to control the influence of acid corrosion during operation. It has great significance to ensure that the equipmentThis paper first reviews the main acid dew point calculation formulas at present. Based on the flue gas parameters (100% load and 40% load), the acid dew point for some typical equipments, using different formula, are computed. According to the results and the designed, different acid dew point formula are compared and evaluated. The formula of acid dew point calculation is obtained under this design situation.Then, Based on the two-dimensional model of heat exchanger length and width direction, this paper simulates the temperature field, and flow field, and sulfuric acid vapor condensation and the deposition rate of sulfuric acid vapor are calculated. The result shows that along the direction of gas flow, gas temperature decreases, and both the gas velocity and the concentration of sulfuric acid are also reduced. The condensation deposition rate of sulfuric acid on the pipe wall does not show a consistent trend but the change is gradually reduced totally. The places that near the heat exchanger exit and the pipe wall are easy to suffer corrosion.The gas inlet velocity, pipe spacing and the way of pipe arrangement have a significant effect on the distribution of all fields. With the flue gas velocity of heat exchanger entrance increases, the outlet temperature of flue gas increase, and the flow field in the heat exchanger also increases. As a result, it reduces the internal corrosion and the number of pipe corrosion. With the pipe spacing of heat exchanger entrance increases, the outlet temperature and velocity of flue gas increase. It reduces the internal corrosion and the number of pipe corrosion, but the heat is reduced. Along the flue gas flow, when the pipes are crossed, the internal temperature and velocity of GGH heat exchanger reduces quicker than the situation of pipes arranged neatly. In this case, the pipes are easy to corrosion. The number of corrosion pipes increase, and the corrosion degree is deeper.By analyzing the Distribution of sulfuric acid vapor condensation and the deposition rate of sulfuric acid vapor. The result show that with the H2O content in flue gas increase, the condensation deposition rate of GGH heat exchanger on the pipe wall increase clearly, especially in the entrance and the posterior part. With the SO3 content in flue gas increase, the condensation deposition rate of GGH heat exchanger on the pipe wall increase clearly. The deposition rate of sulfuric acid increases with the flue gas SO3 content in proportion except individual pipes.Lastly, three-dimensional model is used to simulate the temperature field. The result shows that when flue gas flow through the heat exchanger, the elbow part of pipe is easier to suffer low temperature corrosion than the straight part.