• Seawater FGD
• High Concentrated SO₂ Gas Treatment Plant

Flue Gas Desulfurization systems can be divided into a dry system, a semi-dry system, and a wet system. Tsukishima Kikai has technologies, such as the pre-coated bag system for dry desulfurization, the alkali mist system for semi-dry desulfurization, and the gypsum recovery system, MgSo₄ purge system, Na₂SO₃ recovery system, Na₂SO₄ recovery system, and seawater system for wet desulfurization.

Gypsum recovery system

By adding HCOOH, absorption will be made by HCOOH, which has high solubility in comparison with straight CaCO₃. This brings the following advantages over the conventional system.

1. Since a high desulfurization rate can be maintained even at low pH levels (4-5pH), the following characteristics can be seen
   1. Areas with low pH levels have no cause for build-up of CaSO₃, so the scaling that occurs on the inner walls of the absorption tower is very limited
   2. As CaCO₃ is utilized highly as absorbing agent, the purity of CaSO₄ ⁄ 2H₂O as co-product is also high (it is possible to keep the excess rate of CaCO₃ low)
   3. Absorption is based on a solution, so stable operation is possible even when the SO₂ load varies
2. Since a spray tower is used for absorption, the internal structure is simple, and there is minimal pressure loss in the absorption tower (40-100 mmAq)
3. If impurities such as Cl- do not exist, there is essentially no waste water.
4. Since oxidation occurs inside the absorption tower, there is no need for an external oxidization tower.

Gypsum recovery system for Desulfurization
Condition of the inside of the absorption tower one year after starting the operation.
There is no scaling, and the original lining surface can be seen.

Photo: Gypsum recovery system for desulfurization

MgSo₄ purge system,
Na₂SO₃ recovery system,
Na₂SO₄ recovery system (Recovery / Discharging)

1. For the absorption tower, two plate type spray towers are adopted. The pH of the absorption liquid is changed between plate No. 1 and plate No. 2. Plate No. 1 is low alkali and plate No. 2 is high alkali.
   As a result, the following advantages can be obtained
   
   1. The absorption rate of SO₂ is high
   2. Stable operation is possible even when the SO₂ load varies
   3. It is possible to minimize the use of chemicals
2. Since a spray tower of cylindrical shape and 2 plate type is used for absorption, the internal structure is simple, and pressure loss at the absorption tower is low as 70 mmAq or less.
3. In the case of the MgSO₄ purge system, since Mg(OH)2 is used as the absorbing agent, it is cheaper than NaOH, which used for the Na₂SO₃ recovery system.
4. In the case of crystallization of the Na₂SO₄ recovery system, an MVR (Self-vapor recompression) system is used, resulting in high energy savings.

Photo: Na₂SO₃ recovery system for desulfurization

Seawater FGD

1. The absorbing agent is seawater only, and alkaline chemicals are not required
2. Since the facility consists of only an absorbing tower, a seawater supply pump, and aerator, the composition is simple. So there are few problems, making operation and maintenance easy
3. The cost of the system is low, as operation and maintenance are easy as mentioned above, especially in case that there is a power generating facility, and large amounts of seawater are readily available
4. No by-products being formed; the absorbing liquid can be released to the sea after adjusting the pH, COD, and DO.
   

   more detail information

Semi-Dry system

1. This system is cheaper than the wet system
2. Since all of the water supplied to the absorption tower evaporates, there is no waste water
3. Since the gas at the absorption tower outlet is not saturated with moisture, there is no emission of white smoke.

Photo: Semi-dry system for desulfurization

We have treated many kinds of characteristic gases such as oil/coal burning boiler flue gas, glass melting furnace flue gas, kiln waste gas, tail gas of sulfuric acid plant, smelting furnace flue gas etc.
Especialy, SO₂ of kiln waste gas and smelting furnace flue gas is percent order and a load fluctuation of these gases is very big, so it is very difficult to treat with these gases. In case that the above mentioned gases are treated at desulfurization facilities, generally speaking, the gases are attenuated with air to several thousand ppm, and then is treated in the absorption tower. However in these cases, the size of the absorption tower has to be extremely large.
We, based on its experience and knowledge, enabled to treat from SO₂ gas of several percent concentration (at the inlet of the absorption tower) up to SO₂ gas with a maximum concentration of 10vol%. As a result, it has become possible to minimize the absorption tower and the incidental equipment.