Reactive ashes: Italy's largest energy supplier uses AVA mixers

December 2021

The reference at a glance


Conditioning of reactive ashes for an Italian energy supplier


BHS horizontal mixer AVA HTK in heavy-duty design

Operating site

Sardinia, Italy




Processing of reactive fly ash


Two BHS AVA HTK mixers for conditioning reactive ashes for an Italian energy supplier

Fly ash, which is produced during incineration for energy generation, contains highly reactive substances such as free lime (CaO). For this reason, it must not go to landfill untreated, but must first be conditioned in a multi-stage process. In order to carry out this demanding process safely and efficiently, one of Italy's largest electricity suppliers equipped its power plant with AVA mixers from BHS-Sonthofen.

Power plant operators are increasingly confronted with changing and in some cases declining coal quality, which is becoming increasingly difficult to burn. As a result, increasingly complex waste gas purification processes are required, for which energy suppliers are upgrading the incinerators of their power plants with modern and effective waste gas purification systems. At the end of these complex processes, fly ash with an increased free lime content is also produced.

In order to be able to dispose of this reactive fly ash safely and sustainably, operators must first convert it into a dust-free, landfillable end product. For this process, an Italian power plant operator relies on the continuously operated BHS AVA HTK horizontal mixers in the particularly robust heavy-duty version. In the mixer, the addition of water causes a precisely calculated over-wetting, which triggers an exothermic reaction, neutralizing the CaO. The crucial point in this process step is the exact metering of the water: Exactly as much water must remain in the ash after the reaction as is needed to obtain a non-dusting end product, but not unnecessarily much, as the additional weight would drive up the disposal costs of the ash.

The heat of the exothermic reaction also causes some of the water to evaporate. The resulting water vapor contains many fine dust particles and cannot simply be released into the environment for emission control reasons. It is therefore precipitated via a so-called vapor scrubbing system and the resulting suspension is then fed back into the mixing process to minimize the amount of water used - an extremely environmentally friendly and resource-saving system.

In the second process step, another HTK mixer cools the resulting hot granules of the reacted ash by convection down to a temperature below 60 degrees. The now dust-free end product can then be easily loaded into open trucks and safely deposited. Thanks to the fully automatic process control system from BHS, the Italian power plant operator is able to easily monitor the loading of the end product onto more than 50 trucks per day.

The energy supplier also benefits from the reliability of the BHS horizontal mixers: due to their robust design, even a highly reactive and abrasive product such as ash cannot harm the mixing technology. Thanks to special mixing units, the BHS continuous mixers also achieve very high throughput rates with a small size.