Updated: July 2002

1. Outline of system

Air bubble type fluidized incinerators have been adopted as sewage sludge incinerators in the past. However, it is now necessary to meet various needs including the changes in the nature of sludge in recent years, further purification of exhaust gas, compacted system scale, etc.
In response thereto, we have put to practical use the Mitsubishi circulating fluidized incinerators enabling safety operation with excellent exhaust gas nature and cost performance by adopting the system that can disperse sand throughout the whole area of the incinerator.

2. Characteristics

(1) Stabilized operation:

- It is possible to equalize the temperature inside the incinerator and secure stabilized operation because the circulating sand absorbs the temperature differences in each portion of the incinerator.
- During plant residue mixed combustion, it is also possible to enhance stabilized incineration and improve the rate of mixed combustion.

(2) Acceptable nature of exhaust gas:

- Perfect incineration is promoted in equally heated spots.
- 2-step incineration reduces the generation of NOx gas.

(3) Highly efficient desulfurization in the incinerator:

- High contact efficiency between desulfurizers and furnace gas brings high desulfurization efficiency.
- Without using Caustic Soda.

(4) Reduced degree of greenhouse effect:

- Stabilized furnace temperature facilitates high-temperature incineration, substantially decreasing the amount of dinitrogen monoxide.
- The amount of dinitrogen monoxide is also reduced by the desulfurizers acting as a catalyst inside the incinerator.

(5) Energy saving:

- It is possible to decrease the amount of auxiliary fuels because the operation is possible at a low air ratio.
- The majority of the combustion air is fed as the secondary air.
Consequently, the fluidizing blowers require small power.

3. Performance

Table 1 shows the nature of the exhaust gas discharged from circulating fluidized incinerators for example. It is possible to reduce simultaneously CO, NOx, DXNs and SOx under the following conditions.
* Air ratio: 1.3
* Combustion temperature: approx. 900ºC

Table 1 Nature of exhaust gas at the outlet of incinerators for example
(oxygen dioxide converted at a rate of 12%)

4. Applicability and objectives

(1) Applicability: waste incinerators
(2) Objectives: sewage sludge, screenings and RDF

Figure 1 Mitsubishi circulating fluidized bed incinerator

Figure 2 Plant flow