A method of concentrating sludges wherein liquor is heated under pressure indirectly with flue gases from the combustion of previously concentrated sludge, after which the sludge is caused to expand or subjected to reduced pressure which results in evaporation of water and concentration of the sludge...http://www.google.com.au/patents/US4909899?utm_source=gb-gplus-sharePatent US4909899 - Method of concentrating sludges
