Updated: July 2002

1. Purpose

Kobe Steel has developed and commercialized circulating fluidized bed (CFB) sewage sludge incinerator in cooperation with Foster Wheeler K. K., which has built many CFB boilers. Outline of the incinerator is as follows.
- Incinerator is comprised of a furnace, a hot cyclone, and a loop seal.
- Due to the high superficial velocity, particles become entrained in the flue gas and are carried out of the bed. The coarser entrained particles are separated in a hot cyclone. The hot particles from the cyclone are fed back to the furnace via loop seal.
- Dewatered sludge is fed into the outlet of the loop seal. In case of co-combustion with screenings and/or grit from water treatment plant, it is mixed with dewatered sludge before being fed into the furnace.
- The sludge is dried and mixed with the combustion air and circulating materials in the furnace. The combustion takes place in this suspension and it is completed in the furnace.

2. Features

(1) High combustion efficiency
The sludge is mixed with hot sand particles after the loop seal and this mixture is flowing into the dense bed area in the bottom of the furnace. Due to turbulent mixing and long residence time in the circulating bed, high combustion efficiency is achieved.
(2) Can burn wide range of sludge
Due to the large heat capacity and mixing of the bed, CFB incinerator is able to accept wide range of sludge properties. Even temperature distribution between the bed and top of the furnace is achieved. Therefore, it is suitable for co-combustion with screenings and/or grit from water treatment plant.
(3) Low emission
CO, NH3, and HCN are decomposed since complete combustion takes place at high temperature. NOx generation is reduced due to the two-stage combustion.
(4) Low power consumption
Primary air pressure is low compared to bubbling fluidized bed. Therefore, power consumption of the air fan is decreased by 20-40%.
(5) Small installation space
Due to the high superficial velocity, furnace diameter is small compared to bubbling fluidized bed. Therefore, small installation space is required.

3. Application

Sewage sludge incinerator in Japan
It is suitable for co-combustion with screenings and/or grit from water treatment plant.