Updated: July 2002

1. Introduction

Treatment of exhaust gas from municipal waste incinerator is indispensable for pollution control, and its needs tend to increase in its scope and grade. A highly advanced Treatment capable of inhibiting not only hydrogen chloride (HCl) and sulphur oxides (SOx) but also recently dioxins and heavy metals are called for NKK-LIMAR BAG SYSTEM is a highly efficient system designed to remove toxic gases that can meet these needs.

2. Outline

The combustion exhaust gas that is emitted from the incinerator is, with its temperature reduced in boiler or gas cooler, fed into LIMAR BAG SYSTEM, where an alkali agent is blown into the combustion exhaust gas. In Japan slaked lime is mostly used as an alkali agent, and it is the Dry system that sprays the powder of slaked lime. On the other hand, the Semi-dry system employs a method of spraying lime slurry consisting of a mixture of slaked lime and water. The Semi-dry system LIMAR designed to atomize the slurry by NKK Atomizer and making the resultant fine particles contact acidic gas uniformly is favourably accepted by our uses.
The slaked lime that is atomized into the combustion exhaust gas performs gas-liquid contact or solid-gas contact with the acidic gas. As a result, neutralization takes place, and acidic gas is removed to some extent (primary reaction).
As the next step, the combustion exhaust gas containing slaked lime, reacted products and incineration dust is led to baghouse, and the acidic gas is further removed by the unreacted alkali contained in this dust layer (secondary reaction). Besides, having high performance of dust collection, this dust layer itself can remove the particles of dioxins or heavy metals at high efficiency.

An example of the chart of gas analyzer

Reaction formula
2Ca(OH)2+2HCl -> CaCl2Ca(OH)2H2O+H2O

3. Features

1) Highly efficient removal of acidic gas
The secondary reaction with the alkali substances remaining in the dust layer accumulating on the filter cloth of baghouse removes the acidic gas (HCl, SOx, etc.) with the efficiency equal to that of wet system.
2) Highly efficient removal of soot and dust and heavy metals
Since the dust layer accumulating on the filter cloth of baghouse has high performance in removing fine particles, the soot and dust as well as the particles of heavy metals and similars can be removed with the effectiveness of 99%.
3) Capability of removing mercury and dioxins
It can remove mercury and dioxins by reducing the treatment gas temperature.
4) Easy handling of reacted products
The dust discharged from baghouse is well-dried so that disposal is easy.
5) The system can dispense with wastewater treatment facility
Since the water used in this system is completely evaporated in the gas cooler or semi-cry scrubber (LIMAR) completely, no waste water comes out.