Updated: July 2002Rotary Kiln Furnace
1. Outline of system
The rotary kiln furnace incinerates combustible industrial wastes, especially wastes containing a high percentage of plastic wastes, on a stable basis, reducing the volume of wastes and rendering them harmless.
As shown in Fig.1 and Fig.2, solid wastes are fed into the inclined rotary kiln by means of the dumping crane and feeder, and while solid wastes pass through the kiln with rotary motions (kiln action), they are thermally decomposed by heat radiation from the re-combustion chamber, and then, residues are burned at the rear end of the kiln and by the after-burning stoker. Also, decomposition gas is completely burned with secondary air fed to the re-combustion chamber. For information, liquid wastes are sprayed into the re-combustion chamber, where they are burned or evaporated, whereas highly viscous wastes which cannot be sprayed are fed from the kiln inlet and incinerated. Combustion waste gas is subjected to heat recovery in the boiler, and then, it is led to the exhaust gas treatment equipment.
(1) It is possible to thermally decompose (gasify) and burn plastic wastes, and perform low-NOx operation.
(2) Because the rotary kiln furnace is used, pre-treatment is very simple and easy.
(3) The main body of the furnace is a cylindrical and horizontal type and has a fireproofing wall structure. It can perform operation with no trouble even if materials to be treated which have high calories, and burn while they melt, such as plastics, are fed.
(4) One furnace can treat materials extensively, ranging from solid matter and liquid matter to gaseous matter.
(5) Because the residence time in the furnace is relatively long, about 30 to 60 minutes, load variations on the feed side are absorbed, and thus, stable combustion is possible.
Combustion temperature 850-1,000ºC
NOx in exhaust gas 15-150ppm (O2=12%)
CO in exhaust gas 100ppm or less
4. Applicable fields and materials to be treated
The rotary kiln furnace is optimum for the treatment of waste plastics, wood chippings, paper cuttings, sludge, waste oil, waste liquid, etc.
A part of the exhaust gas with an O2 concentration of about 10% and a temperature of about 300ºC is fed into the kiln inlet, and together with heat radiation, a temperature region necessary for thermal decomposition of waste plastics is formed in the kiln. Waste plastics and similar materials gasify in the kiln and contact a sufficient amount of air in the re-combustion chamber, thereby burning completely. Therefore, black smoke due to incomplete combustion is not generated. Gasification followed by combustion in this way is a method indispensable to materials to be treated which burn at high speed and require a large amount of air at a time, such as waste plastics and similar materials.
Fig.1 Flow for the compound incinerator with the rotary kiln as the core
Fig.2 Explanatory diagram of retarded combustion (Our company's own technology)