Updated: July 2002

1. Outline of the facility

NKK has long studied on the issue of dioxins emission from municipal waste incineration plants, focusing on the analytical method of dioxins and on the technology to remove and suppress the generation of dioxins. As a part of the activities, NKK has introduced the WKV Dioxins Removal System from WKV GmbH (Germany). The System removes dioxins from flue gas along with heavy metals such as mercury.
The system adopts activated carbon base adsorbent packed in a specially designed adsorber to remove dioxins and heavy metals from flue gas. Owing to the efficient contact of flue gas with the adsorbent, the removal efficiency is high. Furthermore, a part of the adsorbent is regularly drawn out from the adsorber to assure stable operation of the system for a long period.

2. Features

(1) Sustainability of high removal efficiency for long period
Flue gas is passed through the adsorbent packed bed via a special shape gas distribution plate, which attains good contact between the gas and the adsorbent, and assures high removal efficiency. The used adsorbent is successively drawn out from the adsorber, and fresh adsorbent is supplied, which ensures high removal efficiency for a long period.
(2) Stable operation with less variation in pressure loss
The flue gas at the exit of the dust collector contains a very small amount of dust. Even if the dust accumulates in the gas contact section of the adsorbent packed bed, the accumulated dust is drawn out with used adsorbent at specified time intervals. As a result, the pressure loss is kept within a certain range and therefore this system assures long period of stable operation.
(3) Separation of adsorbent from fly ash
Since the system is positioned after the dust collector, the adsorbent can be treated separately from the collected ash. In addition, since the used adsorbent is incinerated with waste in a furnace, the adsorbed dioxins are thermally decomposed. Consequently, the used adsorbent does not cause environmental pollution.

3. The process principle

The flow diagram of the WKV Dioxin Removal Facility is given below.
(1) Flue gas is introduced from the bottom of the adsorber.
(2) Toxic substances such as dioxins in flue gas are removed by the adsorbent packed in the adsorber, and the cleaned flue gas is vented from the top of the adsorber.
(3) The adsorbent degraded by adsorption of toxic substances is drawn out from the bottom of the adsorber, along with the small amount of accumulated dust. Fresh adsorbent with the same quantity to the drawn out adsorbent is supplied from the top of the adsorber.
(4) Since the quantity of used adsorbent is relatively small, the used adsorbent will be incinerated in a furnace, and dioxins will be decomposed.

4. Application and treatable materials

Since the system uses activated carbon based adsorbent, the process performance and cost mainly depend on the adsorbent quality and performance. NKK has already carried out pilot plant tests and has confirmed the applicability of activated carbon in crushed form, or in granulated shape.