Mitsui Mining is the first company in the world to successfully develop a dry-process, simultaneous desulfurization and denitrification technology for commercial use on an industrial scale. This process is applicable for SOx, NOx, Dust and Toxic trace elements removal from boiler, furnace and chemical plant flue gases.
The activated coke instrumental to this process is also a Mitsui Mining development, which we produce commercially.
1. PROCESS DESCRIPTION
The Mitsui-BF System is a three-part process: adsorption, desorption, and optional by-product recovery. The system is capable of simultaneous desulfurization and denitrification. Alternatively, it can perform either DeSOx or optionally DeNOx functions.
<Adsorption>
Flue gas passes through a bed of activated coke moving downwards in the two-stage adsorber at a constant flow rate. The activated coke consists of carbon, and has a large, porous inner surface area.
In the first stage, sulfur oxides are largely removed from the gas by a process of adsorption into the activated coke, where oxidation occurs, yielding H2SO4 (sulfuric acid) maintained on the inner surfaces at a temperature of 100 to 200 deg.C.
After desulfurization in the first stage, the flue gas passes through the activated coke bed in the second stage. Here, it works as a catalyst in the decomposition of NOx to nitrogen (N2) and water (H2O) by the injection of ammonia gas(NH3) into the activated coke bed. This chemical reaction occurs at a temperature of 100 to 200 deg.C.
The adsorber, with its moving activated coke bed, also functions as a particulate remover. Following the adsorption process, the particulate emissions will not exceed 30mg/Nm3 when inlet particulate concentrations are kept within 500 mg/Nm3.
<Desorption>
As the activated coke becomes loaded with sulfur oxides(SOx), its adsorption capacity deteriorates. The SOx-saturated activated coke is then conveyed by bucket elevators to the desorber, and regenerated at a temperature of 400 to 500 deg. C. Simultaneously, ammonium sulfate((NH4)2SO4) in the activated coke is decomposed to nitrogen(N2), sulfur dioxide(SO2) and water(H2O).
After cooling, the regenerated activated coke passes over a vibrating screen to eliminate mechanically and/or chemically degraded material, and is then recycled back to the adsorber. This ensures that only activated coke meeting design-size parameters will be reused in the adsorber.
Activated coke fines can be returned to the boiler as fuel.
This desorption sequence optionally incorporates statistical process control, to optimize the adsorption capability for site-specific applications, as the adsorption capacity of the activated coke deteriorates in the process.
2. BY-PRODUCT RECOVERY
In the process of regenerating the activated coke in the desorption unit, SO2-rich gas is released. This SO2-rich gas(20 to 25% volume in SO2 concentration) can be treated to form elemental sulfur(S) or sulfuric acid(H2SO4) by standard methods.
<Production of Elemental Sulfur>
SO2-rich gas is reduced to H2S in a reduction column by using a carbonaceous reduction agent. The reduced gas is partially oxidized to SO2 by air injected at the upper portion of the reduction column and a mole ratio of H2S/SO2 is maintained at 2.0. Finally, the mixture of H2S and SO2 is converted to elemental sulfur in a Claus unit. The carbonyl sulfide (COS) which is generated secondarily in the reduction column is hydrolyzed in the Claus unit, and elemental sulfur is obtained.
<Production of Sulfuric Acid>
After dust and impurities are removed from the SO2-rich gas, the gas is oxidized in a converter to form SO3. The SO3 is then absorbed in an absorber to form 98% sulfuric acid.
3. ACTIVATED COKE
Mitsui Mining produces high-quality activated coke, and is deeply committed to research and development in the field of advanced coal refining technology. This work, conducted at our research institute, maximizes the efficiency of the Mitsui-BF process
Activated coke is a carbonaceous, porous adsorbent/catalyzer produced by thermal treatment of coal, yielding carbonization and activation. This product is able to adsorb the sulfur oxides(SOx) contained in waste gases from boilers and from various chemical plant operations. It can decompose nitrogen oxides (NOx) catalytically into nitrogen (N2) and water (H2O) in the presence of injected ammonia (NH3). Activated coke is also able to remove Toxic trace materials and heavy metals.
4. PROCESS FLOW

5. FEATURES
- Dry process
- SOx removal efficiency higher than 98%, NOx removal efficiency higher than 80%
- Flexibility Simultaneous DeSOx/DeNOx, or DeSOx-only, DeNOx-only operation
- Low power consumption - Minimum installation space required
- No waste water generated - Gas reheating not required - High quality by-product
- Ease of operation - Low maintenance requirements
6. APPLICATIONS
- Coal-fired power station - Industrial boilers - Chemical plants
- Petroleum refineries (such as FCC) - Smelting works - Sintering furnaces
- Incinerators used for trash, refuse, waste oil and sludge
- Glass furnaces - Sulfuric acid plant tailgas

7. COMMERCIAL INSTALLATIONS WITH PERFORMANCE