Daily Question, July 20, 2016 (EIA Discussion): 3 Wealth points as a reward for replying, plus 5 Wealth points for correct answers (multiple-choice question)

Thread Content

This post was last edited by Zhang Xiaopeng on 2016-7-21 at 09:17. In the organic waste gas produced by a certain enterprise, the volume fraction of volatile organic compounds is approximately 0.6%. The suitable methods for treating such organic waste gas are ( ). A. Adsorption method B. Biological method C. Condensation method D. Membrane separation method. Answer: CD. Refer to page 377 of the technical methods textbook. Internationally, there are mainly two categories of basic treatment techniques for volatile organic compounds: one is the recovery-based methods, which include adsorption, absorption, condensation, and membrane separation; the other is the destruction-based methods, which include combustion, biological treatment, low-temperature plasma treatment, and catalytic oxidation. Based on the requirements for compliant emissions, a single method or a combined method should be selected to treat volatile organic compound waste gases. (1) Adsorption method. It is effective for the separation and removal of low-concentration volatile organic compound emissions, and it is currently the most widely used method for VOC recovery. This method has been extensively applied in the shoe-making, painting, printing, and electronics industries. Granular activated carbon and activated carbon fibers are the most widely used in industry. Due to the limited adsorption capacity per unit, it is advisable to use it in combination with other methods. (2) Absorption method. It is suitable for the treatment of volatile organic compound waste gases with high flow rates, high concentrations, low temperatures, and high pressures. The process flow is simple, and it can be used in industries such as painting, insulating materials, bonding, metal cleaning, and the chemical industry. However, for most organic waste gases, their water solubility is poor, so their use is not widespread. Currently, the absorption method is primarily used to treat benzene-based organic waste gases. (3) Condensation method. It is suitable for the recovery and treatment of waste gases containing high concentrations of volatile organic compounds; it represents an efficient treatment process that can be used as a pretreatment method to reduce the organic load in waste gases. It can be combined with other methods such as adsorption and combustion to recover valuable products. When the volume fraction of volatile organic compound waste gas is above 0.5%, the condensation method should be preferred for treatment. (4) Membrane separation method. It is suitable for the separation and recovery of exhaust gases containing high concentrations of volatile organic compounds, and represents an efficient treatment process. When the volume fraction of volatile organic compound waste gas is above 0.1%, membrane separation should be preferred for treatment, and measures should be taken to prevent membrane clogging. (5) Combustion method. Suitable for treating exhaust gases containing flammable, thermally decomposable volatile organic compounds that cannot be recovered under current technical conditions, the combustion method should recover the heat from the combustion reaction to improve economic efficiency. When using combustion methods to treat volatile organic compound waste gases, it is essential to avoid secondary pollution. If the exhaust gas contains components such as sulfur, nitrogen, and halogens, the combustion products must be treated and disposed of in accordance with relevant standards, for example by using catalysts after catalytic combustion. (6) Biological method. It is suitable for various volatile organic compound waste gases at normal temperatures, with low concentrations and good biodegradability. For waste gases containing sulfur, nitrogen, phenol, cyanide, etc., which are difficult to treat using other methods, a biological approach involving the oxidative decomposition by specific microorganisms can be employed. When the volume fraction of volatile organic compound waste gas is below 0.1%, biological treatment is preferred; however, volatile organic compound waste gases with high chlorine content should not be subjected to biodegradation. When using biological treatment, other processes should be employed subsequently to remove those malodorous substances that are difficult to oxidize, in order to avoid secondary pollution. a) Biological filtration: Suitable for treating volatile organic compound waste gases with high flow rates, low concentrations, and large concentration fluctuations; it enables the simultaneous removal of various types of volatile organic compounds and is widely used in industrial applications ； _ b) Biological washing method: Suitable for treating volatile organic compound waste gases with low gas flow rates, high concentrations, good water solubility, and low biological metabolic rates ； c) Biological trickling filter: Suitable for treating volatile organic compound waste gases with high flow rates and low concentrations that produce acid during degradation; it is not suitable for treating waste gases with high inlet concentrations or large fluctuations in flow rate. (7) Processes such as low-temperature plasma method, catalytic oxidation method, and pressure swing adsorption method are suitable for the treatment of various volatile organic compound waste gases with high gas flow rates and low concentrations.