Experiences from First Start-up of an Ash Leaching System, 2002 Fall Technical Conference

An ash leaching system, supplied by Kvaerner Pulping, has been installed at Aracruz Celulose SA.

The main factors prompting the development of an ash leaching system are future environmental restrictions on dumping recovery boiler ash, and economic issues.

The purpose of the ash leaching system is to offer an alternative to dumping recovery boiler ash, as a means of controlling the chemical balance of chlorides and potassium in the liquor cycle. In the ash leaching plant, potassium and chlorides are bled from the electrical precipitator filter ash in a leaching step prior to recycling the ash to the liquor cycle. The amounts of chlorides and potassium in the recovery cycle are thus decreased, while most of the sodium sulfate in the recovery boiler ash is recovered.

The expected removal efficiency for chlorides and potassium is 68-69%, the recovery efficiency for sodium is 80% and for sulfate 85%.

The leaching plant has been in operation 55% of the time since start up. Over the past month (24/4-24/5) the corresponding figure is 67%.

The conclusion is that savings from reduced amounts of make-up chemicals will be approximately USD 1 000 000 per year.