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Waste Gas Treatment by Absorption Tower

Emissions are gases emitted from industrial production, trade, services or activities. Emissions often contain pollutants such as dust, SO2 gas, NOx, VOC,.. if discharged directly into the environment will cause air pollution, acid rain, greenhouse effect,… threaten human health and the ecosystem.

What is absorption tower?

Absorption tower is a device designed to remove pollutants in flue gas by physical or chemical adsorption method. It is an effective flue gas treatment solution for many industries such as metallurgy, chemical, cement, petroleum, power generation, etc…
Definition and operating principle of absorption tower: Absorption tower is a tower containing adsorbent material, the exhaust gas is brought in from the bottom of the tower and flows upward, the pollutants in the exhaust gas will be absorbed to the surface of the material. After filtering through the material layer, the clean exhaust gas will escape at the top of the tower.
Structure and main components of the absorption tower: Absorption tower is usually cylindrical, the height can be up to several tens of meters. The main components include:
  • Tower body: contains adsorbent material stacked in the form of layers or bulk piles
  • Gas distribution system, which distributes exhaust evenly throughout the material
  • Liquid collection system: collecting water from the absorption process to the bottom of the tower for further treatment
  • Auxiliary devices: fans, pumps, control systems,…

The steps of waste gas treatment by absorption tower include:

  1. The exhaust is fed in from the door in the tower body, through a heat exchanger if necessary to lower the temperature to a level suitable for the adsorption process.
  2. The gas passes through the of the adsorbent material and flows upward through the cavities of the material layer.
  3. The pollutants in the flue gas will be absorbed onto the surface of the material particle. After passing through the thick material layer, the flue gas is cleaned.
  4. Clean exhaust gases escape from the top of the tower through the exhaust pipe. This gas must be tested to ensure the standard before being released to the environment.
  5. The liquid condensed during the adsorption process is collected and sent to the bottom of the tower by the drainage system for further treatment.

흡수탑에 의한 폐가스 처리 Tháp Hấp Thụ Xử Lý Khí Thải Absorption Tower Waste Gas Treatment

How absorption towers remove pollutants from exhaust gases

In the absorption tower, the adsorption material particles have a very large surface area, which is suitable for the pollutants in the flue gas to cling to the surface. When the flue gas passes through the material layers, the pollutants tend to stop on the surface of the material due to the interaction between the molecules of the pollutant and the material molecules. This process is called physical adsorption. Besides, some materials also catalyze the chemical reaction between the pollutants together to form less toxic products.

Absorption tower gas treatment application in the following industries:

  • Metallurgy: gas treatment SO2, HF, HCl
  • Chemical: remove VOC, NH3, H2S
  • Pharmaceutical: recovery of evaporated organic solvent
  • Food: handling odors and VOCs
  • Cement, ceramics: dust treatment and gases NH3, HF, HCl
  • Waste incineration: H2S, NH3, Hg treatment
  • Power generation: handle SO2, NOx, dust
Describe some specific examples of the use of absorption towers in practice
  • In Vietnam, absorption tower is widely used in thermal power plants, cement, chemical, paper and pulp, etc…
  • At Pha Lai thermal power plant, the absorption tower is used to treat SO2 emissions.
  • At Hoang Mai cement plant, the absorption tower is used to treat dust and SO2 emissions.
  • At Dinh Vu chemical plant, the absorption tower is used to treat HCl and HF exhaust gases.
  • At Bai Bang pulp and paper plant, the absorption tower is used to treat SO2 and CO emissions.

Benefits of using absorption tower:

  • Environmental benefits: Effective technology, which can reduce the content of pollutants in exhaust gases to very low levels, reaching acceptable standards before being released into the environment.
  • Economic benefits: Investment and operating costs are suitable for a wide range of industries. At the same time allow waste reuse, recovery of valuable products (e.g. H2S, SO2).

Some limitations of the application of absorption tower:

  • Limited absorption capacity, can only be applied when the pollution content is low.
  • High operating costs due to constant replacement of the absorbed material.
  • Small scale, only applicable to small exhaust flow.
  • Difficulty in selecting, designing and operating the appropriate system. A specific evaluation is required before applying this solution.


Absorption tower is one of Natural Star Vina s widely used waste gas treatment technologies in many industries and provides high performance. It allows for efficient removal of gaseous pollutants at a moderate cost. However, certain limitations should be noted to assess feasibility when applied. This technology is expected to grow strongly in the future thanks to the increasing demand for industrial pollution treatment.

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