One of the sources of carbon dioxide is a flue gas. Flue gas is generated from the machinery that produces heat energy from the organic fuels. In most countries, the technology of carbon dioxide/ CO2 capture from flue gas was not adopted into the chemical and manufacturing sectors. Industrial growth in developing countries worries the environmentalist about the mass of flue gas generation and release into the atmosphere without any treatment. In this situation, there is demand for an improvement in the technology that meets the low-cost operation requirements of the companies (who do not want to spend much money on the treatment process).
Engineers and researcher worked out on the concept of using solid materials which have the equivalent absorption capacity that of liquid materials. Because when compared to liquids sorbents, solids can be handled and treated with less operation cost if the packed bed or fluidised bed unit operation techniques are applied in the design.
One of the best method for CO2 capture
Liquid absorbent like potassium chromate (K2CrO4) is used for removing the carbon dioxide by absorption operation and at room temperature, it exists in the solid state. The idea of using the solid form of potassium chromate as a packed bed can give out some advantages over a liquid operation like:
- Avoiding the loss and leak of liquid sorbent in case of a liquid operation which required a separator for recovery from carrying over
- Eliminating the regeneration pumps and column from the process.
- Avoiding the large liquid storage tanks.
The K2CrO4 can be obtained in stable solid form by mixing with organic binders and dispersants. With help of the spray driers, the liquid form of the prepared slurry can be solidified giving out the perfectly spherical shaped solids. By calcination (the process of heating in the presence of air) of these solids, the required porosity and hardness can be achieved.
By using fluidized bed technique, the flue gas (CO2, H2O, CO and N2) stream can directly pass into the fluidized bed column containing solid sorbents of K2CrO4 to remove the carbon dioxide by carbonation. This operation can be conducted around 200 to 250 oC temperature conditions. This adsorption technique provides the facility of regeneration of spent K2CrO4 also. For small-scale industries, the technique of solid utilization to remove carbon dioxide from flue gas would provide a lot of contribution in preventing the atmosphere pollution by greenhouse gas.
Other materials useful as solid adsorbents:
- Activated carbon
- Potassium carbonate
Regeneration techniques for activating the solid adsorbents:
- Pressure swing adsorption (PSA)
- Temperature swing adsorption (TSA)
Flue gas produced in chemical process plants contains CO2 in excess. We have absorption systems that absorb carbon dioxide but to the recovery of CO2, more than 95% and final output CO2 product with 99.99% the process should be well optimised with absorbent and equipments arrangement. With respect to absorbent, to achieve the above target the absorbent solvent should have a long life with stable chemical structure, good heat transfer properties, viscosity and density be consistent with the wide range of temperature and pressure operations.
In this prospective Korea Institute of energy research facility have developed an absorbent and process named KIERSOL claiming that it is the best-updated process for carbon capture from flue gas. They developed an absorbent using water, K2CO3 and mixture of agents. This process if designed to use solid adsorbents than it could even be used to CO2 capture from automobile exhaust.