Treatment of emissions by chemical methods
Methods of cleaning exhaust gases are diverse, vary in equipment structure as well as in cleaning technology. Waste cleaning method is selected according to the volume and composition of waste. In addition, it was selected on the basis of comparing economic – technical analysis. To achieve high emissions treatment efficiency, it is necessary to use a combination of different methods and filters simultaneously. To protect the environment one of the ways Waste Gas Treatment quite effective and thorough contribution to environmental protection it is Waste Gas Treatment chemical method. Principles of treatment of emissions by chemical methods
Perform chemical interactions to convert toxic gases into less toxic products with special catalysts. Made in the reaction device.
The role of chemical method in Waste Gas Treatment
Helps increase chemical reactions in exhaust treatment.
Specifically, this treatment has two problems: Converting C, CO, COV to non-toxic CO2 by oxidation reaction, which means burning in the presence of O2. Switch NOx to O2 and N2, is the reducing reaction opposite to the above reaction. These two processes must be performed simultaneously. Therefore, it is necessary to find a permissible “range” to adjust the oxygen concentration so that both processes can work together, and find the appropriate catalyst. Both jobs require a lot of time and lots of specialized modern equipment. Therefore, in Vietnam it is very difficult to do, this field is almost left open.
In ferrous metallurgy, aluminum production by electrolytic fusion melting usually contains CO, people often use catalysts containing 0.3% Pt bearing on aluminum oxide. Organic compounds are the main components in the exhaust of plastics, antibiotics, phatalic aldehydes, paint lines, etc. The catalysts commonly used here are Pt, Pd and Rh. Pt and Pd are usually carried on Al2O3 to oxidize the alkanes. The Pd-based catalysts are highly active in CO oxidation, which is lower than Pt. Pt has the highest activity for oxidation of propane at 5000C, while Pd is the better catalyst for oxidation of ethane, methane and olefins. Rh has the lowest activity in the propane oxidation reaction, but when combined with Pt will form the best catalyst material for oxidation and reduction of NOx.
The chemical method is the process by which the gases are adsorbed due to the chemical reaction with the adsorbent, the molecular binding force in this case is stronger than in the physical adsorption. So the amount of heat is bigger, and the energy needs more.
Besides, also use chemicals such as: Water, Base solutions: KOH, NaOH, Na2CO3 , K2CO3 , Ca(OH)2 , CaCO3… to absorb gases with liquids (chemicals) and is the process of transferring the gas molecules to be processed into the liquid phase by dissolving chemicals when they come in contact with each other.
These processes create a process to treat emissions by chemical methods.
The method of treating emissions by chemical methods
Thus, the treatment of emissions by chemical methods is essentially a treatment method applying chemical absorption and chemical adsorption methods to the treatment equipment.
Exhaust gas treatment by absorption method
Absorbing emissions by chemical methods is the method of using liquid and solid materials to absorb toxic gases from the manufacturing process of the factory. This is the process of transferring toxic gases to be processed into the liquid phase. Thanks to the dissolution process, they are made in contact with each other. There is a chemical reaction during absorption.
Absorption treatment by absorption process is also widely used to dehumidify air, toxic gases and smell in exhaust gas. It helps recover vapors, clean gases mixed with air or exhaust.
Image of exhaust treatment mechanism by absorption tower
The mechanism of adsorption treatment technique consists of 3 steps
- Step 1: Diffusion of gaseous pollutant molecules in the exhaust gas mass to the surface of the absorbing solution
- Step 2: Penetration and dissolution of gases into the surface of the absorbing solution.
- Step 3: Diffusion of dissolved gases on the separating surface deep into the absorption liquid
During absorption, the pollutant particles in the exhaust gas are trapped on the surface of solid and clean materials. The toxic gases that are trapped are called absorbed.
The activities of dehumidifying in air, eliminating harmful gases and odors in exhaust gas, recovering valuable gases and gases are called absorption process.
The most commonly used absorbers
- Water (H2O)
- Base solutions: KOH, NaOH, Na2CO3, K2CO3, Ca(OH)2, CaCO3,…
- Monoetanolamin (OHCH2CH2NH2), Dietanolamin( R2– NH), tritanolamin (R3– NH).
Application of the exhaust gas treatment method by chemical absorption method to:
- Handling pollution emissions.
- The adsorption method treats emissions with large emissions.
- The absorption method is commonly used to treat SOx, HCl, H2S, HF, Cl2, NOx, acetone, …
- Recovering circulating matter or transferring to other production stages.
Waste Gas Treatment by adsorption method
Adsorption is the phenomenon of gas, liquid and ionic molecules retained on the phase interface. Very diverse phase separators can be gas-liquid, gas-solid and liquid-solid layers. Exhaust gas treatment by adsorption method is a process based on the dissociation of gases by the affinity of some solids with certain gases present in the gas mixture, in the process of which the gas molecules contamination in flue gas is retained on solid material. The application of adsorption method to treat gas source with small gas and air impurities content, to clean and dry the air, separate the gas or steam mixture to form each molecule, conduct the process of influence. surface anomalies.
The solid material used in this process is called adsorbent.
The gas that is trapped in adsorbents is called adsorbate.
Chemical adsorption of gases is the method where gases are adsorbed due to chemical reactions with adsorbents, the molecular binding force in this case is stronger than in physical adsorption. Therefore, the amount of heat generated is greater, and requires more energy.
Image of exhaust treatment mechanism by adsorption tower
The mechanism of the adsorption treatment process consists of 3 steps
When conducting adsorption in tower 1: Emissions are put into the bottom of the tower (open valve 6 and close valve 5). The gas passing through the adsorbent layer is heated to increase the adsorption capacity, where the treated gas is trapped in the material layer. Clean air exits through the valve pipeline (valve 2 open, valve 1 closed).
While tower 1 performs the adsorption process, tower 2 proceeds to return the material: Steam is put into tower 2 in a top-down direction (valve 3 open, valve 1 closed). The steam that passes through the material will carry the pollutant out to the condensate, separate the water from the pollutant, and the polluted gas will continue to be treated.
When the materials in tower 1 are no longer adsorbed, proceed with the material recovery and conduct adsorption in tower 2.
Desorption: The desorption is an important stage of the adsorption cycle, confirming the economics of the exhaust gas cleaning process. This process aims to restore the inherent activity of the adsorbent and is the reverse adsorption process.
The application of the exhaust gas treatment method by chemical adsorption method used to treat polluted gas has the following characteristics:
- Unburnt or difficult to burn
- Valuable and in need of withdrawal.
- There is low concentration in the exhaust gas that other processes cannot apply.
- Used to adsorb NH3, SO2, Cl2, mercury vapor, …
Advantages of treating emissions by chemical methods.
- This method helps totreat polluting emissions
- Helping to handle emissions with large emissions
- This method helps to treat SOx, HCl, H2S, HF, Cl2, NOx, acetone, etc.
- Waste Gas Treatmenthigh efficiency
The application of chemical waste gas treatment is an effective and advanced method, giving people as well as the earth a fresh air, avoiding harmful agents. With information about chemical methods in Waste Gas Treatment Hope to get useful references for how Waste Gas Treatment before discharging into the environment.