Mixer stands up to chemical waste requirements

Congleton, UK - Since November 2008, the treatment of chemical wastes prior to landfill has to be carried out under much more tightly controlled conditions. In particular, the mixing of waste with binding agents must be carried out in a closed vessel inside a building to minimise the risk of contamination to both the environment and workers.

With the legislation pending, hazardous waste management company Augean PLC decided to make a substantial investment to provide the company with what is claimed to be the most advanced treatment unit for chemical waste in the UK.

At the heart of the £1.2-million project is the mixing unit, which combines the shredded waste with cement and PFA (pulverised fly ash) to form a cake which can then be safely consigned to designated hazardous landfill sites.

The plant can accept a wide variety of waste containers ranging from large IBCs through to 200-litre steel drums and 50-litre plastic drums. The operator loads combinations of these containers onto a large infeed conveyor which delivers them to the heavy duty shredder reducing everything to 25 mm or less.

Waste is then fed into the mixer with a measured amount of cement and PFA, the mixer then combines and encapsulates the waste particles with a cementicious coating. The finished product is then discharged into a skip for transport to landfill. After loading the containers the process is remotely controlled from the computerised operator panel keeping human intervention to a minimum.

The mixing is a pretty brutal process and the mixing machine needs to be up to the job. So Augean turned to J R Boone of Congleton, to provide the machine they were looking for.

A series of tests were carried out in a pilot plant on a full range of wastes that showed the proposed design could meet the brief. This was scaled up into the full size unit, which comprise a six-tonne horizontal paddle blade mixer, driven by a 132Kw motor.

The mixer features a semi-omega shaped mixing chamber with outboard bearings carrying a contra flow paddle blade agitator. Adjustable packed glands seal the agitator as it passes through the ends. The mixing chamber, ends and agitator are made from carbon steel with agitator blades in wear resistant ‘Abro’ steel. The discharge is via a specifically designed heavy duty flush fitting valve.

Making the unit dust-tight was another key requirement and there is also an extraction and treatment system for volatile components.

On a typical 16-hour day, the installation can process up to 360 tonnes of finished solidified/stabilised material for hazardous landfill. The types of waste handled are broad and include ceramics, adhesives and resins, and centrifugal sludge from waste oil.