w&p Zement GmbH, an Austrian cement producer, operates a clinker kiln in the province of Carinthia, Austria. The plant design capacity is 2200 t/d of clinker, due to market demand present-day production is 1600 t/d. The raw material comes from a nearby quarry; the fuels are coal and selected wastes, which come by rail and truck. The flue gas flow is about 174 000 m³/h (STP). The main parts of the plant are: A rotating kiln, a preheat tower with 5 cyclone levels, a calciner with a combustion chamber, a rotating pan mill with flue gas passage, a (new) bag house filter and a Regenerative Thermal Oxidation (RTO). The plant for abatement of mercury ("Exmercury") is operated in a side stream of the preheat tower. The RTO and the "Exmercury"-plant are the subject of this paper.

The author, as a chartered engineer had the honor to accompany the implementation of both processes as consultant to the government of the province of Carinthia.

The plant is located in the valley of the river Görtschitz. The character of the valley is mainly agricultural and there is some tourism. Unfortunately ventilation is poor.  The firing of wastes, even if they are selected and pretreated, is accompanied by the emission of mercury and organic carbon (TOC). With the aim to reduce the burden of these pollutants on the valley, the company decided to take action for reduction of the emission of both these substances to a level far below the legal requirement.

For the reduction of mercury in the flue gas of waste incinerators or of power plants, there are several processes available in the market. These, however, are not suitable for the clinker process, since, after the addition of bromine salts to the fuel, the mercury would end up in the cement, which is not wanted. Activated char coal as an adsorbent is - considering the large flue gas flow - economically not viable.

The newly developed "Exmercury" process relies on the fact, that the dust, which is separated in the bag house filter is very fine and thus has a very big specific surface area, on which the mercury and its compounds adsorb. This dust is fed to a stripper, together with a hot flue gas side stream taken from the preheat tower in order to reach a temperature which is high enough to desorb the mercury from the dust. Then flue gas and dust are separated in a hot gas filter with ceramic filter candles. The dust goes back to the clinker process, while the flue gas is quenched and afterwards contacted with doped charcoal, on which the mercury adsorbs. In another filter the flue gas side stream is separated from the char coal and returned to the clinker process. The laden char coal is filled into drums for shipping. Finally both the dust and the flue gas side stream are returned to the clinker process. Only the mercury remains in a relatively high concentration on the charcoal. This may be a base material for recovery of mercury or is dumped in underground storage, which is practiced at present. Removal ratios of 90 % and more are achieved. Before installation of the "Exmercury" plant the mercury concentration in the flue gas was often up to the emission limit of 50 µg/m³ (STP, 10%O₂), on 7. October 2017, 1 pm we measured                 1,5 µg/m³ (STP, 10%O₂).

Regenerative Thermal Oxidation (RTO) is a common process for cleaning ventilation air in many industries, which use organic solvents. Using RTO for oxidation of organic carbon in the flue gas of clinker kilns is rather new, since the flue gas flows may be as large as 300 000 m³/h (STP). At present there are three clinker kilns equipped with RTO in Austria. The reason is to remove TOC and odors from the flue gas. The RTO plant in consideration has just started operation on 1. October 2017. The results up to now are overwhelming. Before installation of the RTO the TOC emission with the flue gas was up to emission limit of 100 mg/m³ (STP, 10% O₂), on 7. October 2017, 1 pm it was 0,78 mg/m³ (STP, 10 % O₂).

Through installation of RTO and "Exmercury" the clinker plant of w&p became a pacemaker in environmentally benign clinker production.