Patent GB-1374951-A (GB)
Title: Sludge separation systems
IPC: C02F11/13
Filed: 1973-02-21
Abstract: 1374951 Apparatus for freezing and thawing sludge CARRIER CORP 21 Feb 1973 [2 March 1972] 8412/73 Heading C1C [Also in Division F4] An apparatus for promoting the separation of the solid constituent of a sludge from the liquid constituent thereof comprises a first heat exchanger 10 having a plurality of vertical tubes 21 disposed within a shell 24, an upper header 19 comprising a liquid distributer 23 communicating with the upper ends of said tubes 21 and a lower header 20 communicating with the lower ends of said tubes 21; a second heat exchanger 11 having a plurality of vertical tubes 31 disposed within a shell 34, an upper header 29 comprises a liquid distributer 33 communicating with the upper ends of said tubes 31 and a lower header 30 communicating with the lower ends of said tubes 31; a reversible refrigeration system comprising a refrigerant compressor 12 for compressing a gaseous refrigerant and refrigerant passage means 40, 43, 45, 47, 49, 51 and 54 including refrigerant control means 42, 44, 48, 50 and 55 for selectively withdrawing refrigerant vapour from the shell side of either one of said heat exchangers 10 and 11, compressing the vapour in the compressor 12 and discharging the compressed refrigerant into the shell side of the other heat exchanger to condense the vapour, and for passing condensed refrigerant from said other heat exchanger to the shell side of said one heat exchanger for evaporation therein; sludge passage means 70, 73 and 76 or 70, 83 and 86 including sludge control means 71 and 74 or 72 and 84 for selectively passing raw sludge to the upper header of said one heat exchanger (in the embodiment of the Figure it is passed via the lower header), for distribution and passage downwardly through the interior of the heat exchange tubes therein, in heat transfer relation with refrigerant evaporating on the exterior thereof, whereby a portion of the sludge is cooled and frozen on the inner surface of said heat exchange tubes; recirculation passage means 76 and 86 including pumps 75 and 85 for recirculating liquid sludge from the lower header of said one heat exchanger to the upper header thereof to circulate liquid sludge downwardly through the interior of the tubes to freeze sludge therein, and for passing liquid from the lower header of said other heat exchanger and circulating it to the upper header thereof for passage downwardly through the tubes until substantially all of any previously frozen sludge therein is melted; and passage means 73, 78 and 90 or 83, 88 and 90 for passing melted sludge from said other heat exchanger to a location for settling of the sludge. The apparatus may also include passage means 92 or 94 for passing a liquid heat exchange medium or a separated liquid component of sludge into the upper header of said other heat exchanger to provide an additional cooling medium to condense the refrigerant vapour. The refrigerant control means may include means 57, 58 and 56 responsive to the level of refrigerant in said one heat exchanger for controlling the passage of refrigerant from said other heat exchanger to said one heat exchanger. The liquid distributers 23 and 33 are preferably annular. In practice sludge is passed downwardly through the tubes of one heat exchanger and frozen therein by evaporation of refrigerant vapour on the shell side thereof, the refrigerant vapour is compressed and passed to the shell side of the other heat exchanger where it condenses causing melting of previously frozen sludge in the heat exchange tubes. When all the pre-frozen sludge is melted it is drawn off from the lower header, fresh sludge is supplied and the refrigeration system is reversed, freezing the fresh sludge and melting the frozen sludge in the first heat exchanger. The sludge may be a sludge obtained from a water treatment plant wherein waste water is treated with aluminium salts and lime, sewage sludge or aluminium refinery effluent containing suspended iron oxide particles.