Flue gas discharged from municipal incineration plants contains harmful components such as fly ash, HCl, SOx, NOx, dioxins and heavy metals including mercury, there has been a strong demand for a flue gas treatment system to control emission of harmful gas strictly for environmental protection.
Recently, the flue gas treatment system needs bigger size and more space, as not only treatment methods have diversified but also higher efficiency of the treatment has been required.
Accordingly the system needs smaller size and higher efficiency at the same time. With such standpoint, integrated flue gas treatment system, which removes several harmful substances simultaneously, has been put to practical use and now mostly used for a flue gas treatment system.

2. System Flow

Process flow of this system is shown in Figure 1. First, flue gas is induced into quenching chamber where its temperature is kept 150 deg.C to 230 deg.C by water injection. Next, slaked lime and special dose are fed through powder injector and contact with acids such as HCl and SOx. Furthermore, the flue gas containing the injected agent is induced to filtering reactor, where secondary neutralization occurs during dust removal process, and HCl and SOx are removed with high efficiency through the filter media.
In the meantime, NOx is reduced into harmless water and nitrogen with ammonia sprayed into gas at catalytic NOx removal unit installed after filtering reactor.

Fig. 1 System Flow

3. Removal Mechanism of Filtering Reactor

A removal mechanism of HCl, SOx and fly ash in the surface of filter media is shown in Figure 2. Slaked lime sprayed into flue gas is piled on the surface of the filter media along with fly ash and constitutes powder layers.
When flue gas passes through these layers, unreacted slaked lime in the layers and acid gas in the flue gas are neutralized.
Dioxins are considered to be comprised in or adhere to submicroscopic particle when temperature is 150deg.C to 230deg.C and are removed by this filtering process.
Mercury also adheres to the powder layers and is removed out of flue gas.

Fig.2 Concept figure of de-HCl, de-SOx. dust collect

4. Performance

An example of removal efficiency of fly ash, HCl, SOx, and NOx is shown in Table 1.

Table 1. Actual Performance Data

The actual removal performance of dioxins is less than 0.5 ng/m³N(TEQ) when the temperature is 200 deg.C and less 0.1 ng/m³N(TEQ) when the temperature is 150 deg.C at inlet of filtering reactor.
The removal efficiency of mercury can be expected approx. 70% when the temperature is 200 deg.C and more than 90% when 150deg.C.
Furthermore, if the temperature at the filtering reactor inlet is 150 deg.C, the removal efficiency of harmful components will be greatly improved. However, gas at the inlet of catalytic NOx removal unit need to be reheated to more than 200 deg.C to maintain the NOx removal efficiency.

5. Denitration Bag Filter

Denitration Bag Filter is the newly developed equipment to make the integrated flue gas treatment system smaller size. This equipment, in which the filter media is coated with denitration catalyst with special technology, enables all those components such as fly ash, HCl, SOx and NOx to be removed with only one equipment.

6. Supply Record

Integrated flue gas treatment system:  3 plants/under operation 
                                             5 plants/under construction 

Denitration Bag Filter:                  1 plant/under operation 
                                             1 plant/under construction