Moistening incinerator bottom ash with the BHS pug mill

October 2020

The reference at a glance


Five ash humidifiers for processing incinerator bottom ash as a secondary building material


AVA pug mills HTK 350 and AVA pug mills HTK 150

Operating site





Fly ash from waste incineration


Five single-shaft pug mills in continuous operation

Waste is turning into an increasingly important source of raw materials. Even incinerator bottom ash still contains a large number of materials that can potentially be recycled. Metals such as iron, copper, and aluminum make up about ten percent of the ash. But what happens to the non-recyclable fraction? It must be deposited in landfills in a safe manner for as long as possible. However, operators of waste incineration plants face the challenge that incinerator bottom ash emits a considerable amount of dust. A North American waste incineration plant operator therefore decided to humidify the ash using a total of five BHS pug mills. The mixers of type AVA HTK now reliably convert the ashes into a dust-free, transportable product at three sites.

In addition to useful raw materials, incinerator bottom ash consists of fine-grained combustion residues that generate a lot of dust. In order to be able to safely dispose of the residual ash after all recyclable components have been recovered, it must therefore be moistened and solidified. In addition, the product destined for the landfill must not exceed specific eluate levels.

This places considerable demands on the mixing technology. For this reason, a North American operator of waste incineration plants decided to replace its legacy mixers with a total of five ash humidifiers from BHS-Sonthofen. The single-shaft pug mills are used in 24-hour continuous operation and process up to 7.5 tons of ash per hour. The mixers are ideally suited for processing incinerator bottom ash as they ensure reliable operation and deliver high product quality. Moreover, they are efficient and allow for easy cleaning and maintenance. The self-cleaning design includes a special BHS agitator and a dead space-optimized mixing drum, which significantly increases plant availability. Thanks to their highly compact design, they also require little space.

Another advantage is their heavy-duty construction, which provides reliable protection against wear. The mixing tools of the pug mills have a special carbide hardfacing that protects them against the highly abrasive ash, thus ensuring a long service life and high availability. Being able to withstand the acid additives mixed in with the ashes, the five mixers in use at the waste incineration plants in North America are made of robust stainless steel. The design of these pug mills complies with U.S. power plant safety standards.