Process and apparatus for dehydrating waste solids concentrates

Claim 1

In a process for dehydrating initially water-containing waste solids concentrates chosen from the group consisting of secondary sewage sludge, digested sewage sludge, mixtures of primary and secondary sewage sludges, those having relatively high quantities of iron-fatty acid soaps, those derived from packing industry wastes, and those containing animal manure, said concentrates having a non-fat solids concentration in the range 10% to 35% by weight on an oil-free basis, that process comprising the steps of (1) admixing such a waste solids concentrate with a relatively non-volatile oil to obtain a mixture which will remain fluid and pumpable after the removal of its water content by heat evaporation; (2) dehydrating the resultant oil-containing mixture by heat evaporation in a multi-stage evaporator in a sequence of steps so ordered that the vapors evolved from each such step except the first are used as a heating medium in the preceding step, and (3) withdrawing a substantially anhydrous waste solids and oil slurry from a late stage of said evaporator, the improvement which comprises recycling at least a portion of the slurry so withdrawn and admixing it with the waste solids concentrate and oil in step (1) to form a mixture constituting a steady state feed material to said multi-stage evaporator having a non-fat solids content of from 25% to 60% on an oil-free basis.

Claim 11

An apparatus for dehydrating an initially water-containing waste solids concentrate, that apparatus comprising (1) a tank having means for receiving a stream of waste solids concentrate, means for receiving a stream of fluidizing oil and means for effecting mixing of those streams and having an outlet whereat a mixture so formed may be withdrawn from it; (2) a multi-stage evaporator having means for heating and dehydrating continuously a mixture of waste solids concentrate and oil formed in said tank and means for discharging water driven off therefrom as vapor, said evaporator having an inlet in its first stage whereat it may be supplied with material to be heated and dehydrated and an outlet in a late stage whereat substantially dehydrated material may be withdrawn from it; (3) conduit means extending from said outlet of said tank to said inlet of said evaporator wherethrough a mixture of waste solids concentrate and fluidizing oil may be supplied from said tank to said evaporator as feed material therefor; (4) means extending from said outlet of said evaporator for withdrawing a substantially anhydrous waste solids and oil slurry therefrom, and (5) means connected to said slurry withdrawing means and extending to said tank for recycling at least a portion of the slurry so withdrawn to said tank for mixing therein with said initially water-containing waste solids concentrate and said fluidizing oil.

Claim 12

An apparatus for dehydrating an initially water-containing waste solids concentrate, that apparatus comprising (1) a tank having means for receiving a stream of waste solids concentrate, means for receiving a stream of fluidizing oil and means for effecting mixing of those streams and having an outlet whereat a mixture so formed may be withdrawn from it; (2) a multi-stage evaporator having means for heating and dehydrating continuously a mixture of waste solids concentrate and oil formed in said tank and means for discharging water driven off therefrom as vapor, said evaporator having an inlet in its first stage whereat it may be supplied with material to be heated and dehydrated and an outlet in a late stage whereat substantially dehydrated material may be withdrawn from it; (3) conduit means extending from said outlet of said tank to said inlet of said evaporator wherethrough a mixture of waste solids concentrate and fluidizing oil may be supplied from said tank to said evaporator as feed material therefor; (4) means extending from said outlet of said evaporator for withdrawing a substantially anhydrous waste solids and oil slurry therefrom, and (5) means connected to said slurry withdrawing means and extending to said tank for recycling at least a portion of the slurry so withdrawn to said tank for mixing therein with said initially water-containing waste solids concentrate and said fluidizing oil.