tailieunhanh - AIR POLLUTION CONTROL TECHNOLOGY HANDBOOK - CHAPTER 11

Sự hấp thu cho HAP và VOC kiểm soát Hấp thụ một khối lượng chuyển diffusional hoạt động mà theo đó một thành phần hòa tan khí được lấy ra từ một dòng khí bằng cách giải thể trong một dung môi động lực cho chuyển khối lượng là sự khác biệt nồng độ chất tan giữa các giai đoạn khí và chất lỏng. Trong trường hợp hấp thụ lực này có thể được hiểu là sự khác biệt giữa áp suất riêng phần của khí hòa tan trong hỗn hợp khí và áp suất hơi của khí hòa tan. | i i Absorption for HAP and VOC Control INTRODUCTION Absorption is a diffusional mass-transfer operation by which a soluble gaseous component is removed from a gas stream by dissolution in a solvent The driving force for mass transfer is the concentration difference of the solute between the gaseous and liquid phases. In the case of absorption this driving force can be interpreted as the difference between the partial pressure of the soluble gas in the gas mixture and the vapor pressure of the solute gas in the liquid film in contact with the gas. If the driving force is not positive no absorption will occur. If it is negative desorption or stripping will occur and the concentration of the pollutant in the gas being treated will increase. Absorption systems can be divided into those that use water as the primary absorbing liquid and those that use a low volatility organic liquid. The system can be simple absorption in which the absorbing liquid is used in a single pass and then disposed of while containing the absorbed pollutant. Alternatively the pollutant can be separated from the absorbing liquid and recovered in a pure concentrated form by distillation or stripping desorption . The absorbing liquid is then used in a closed circuit and is continuously regenerated and recycled. Examples of regeneration alternatives to distillation or stripping are pollutant removal through precipitation and settling chemical destruction through neutralization oxidation or reduction hydrolysis solvent extraction and pollutant liquid adsorption. AQUEOUS SYSTEMS Absorption is one of the most frequently used methods for removal of water-soluble gases. Acidic gases such as HCI HF and SiF4 can be absorbed in water efficiently and readily especially if the last contact is made with water that has been made alkaline. Less soluble acidic gases such as SO2 C12 and H2S can be absorbed more readily in a dilute caustic solution. The scrubbing liquid may be made alkaline .