Metalworking fluid recycling process with pasteurization by direct steam injection

Claim 1

A process for recycling water-based metal working fluids, said process employing the following equipment: a used fluid storage tank to store and allow for gravity settling of solid contaminants in a collected, used, water-based fluid to be recycled; filtration means to further remove solid contaminants from said collected fluid to be recycled; a mixing tank for receipt of said fluid to be recycled after it has passed through said used fluid storage tank and said filtration means, said mixing tank containing steam injection means for the introduction of low pressure steam beneath the surface of said fluid to be recycled contained within said mixing tank, said mixing tank additionally containing tramp oil removal means for the removal of tramp oil lifted to the top of said fluid to be recycled; heat exchanger means for cooling said fluid to be recycled to ambient temperature after steam has been injected and tramp oil has been removed from said fluid, said fluid to be recycled and a cooling fluid passing each other on opposite sides of a heat-conducting barrier, thereby transferring heat from said fluid to be recycled to said cooling fluid while preventing intermixing thereof; a recycled fluid storage tank for receipt and storage of said fluid to be recycled after it has been cooled by said heat exchanger means; and fluid transfer means for transferring said fluid to be recycled from one process step to the next; said recycling process comprising the following steps: collecting used water-based metalworking fluid in said used fluid storage tank; then removing solid contaminants from said used metalworking fluid by gravity settling in said fluid storage tank; then removing solid contaminants from said used metalworking fluid by passage through said filtration means; then passing said used fluid into said mixing tank; then injecting low pressure steam beneath the surface of said used fluid in order to raise said fluid to pasteurization temperature, to provide gentle mixing to said fluid to keep unstable emulsions and inversely soluble additives from separating, to strip volatile and malodorous impurities from said fluid, to lower the concentration of dissolved solids in said fluid, and to provide lifting action to lift tramp oil to the top of said fluid; then removing said tramp oil from said fluid using said tramp oil removal means; then passing said fluid through said heat exchanger means to cool said fluid to ambient temperature; and finally transferring the resulting fluid into said recycled fluid storage tank, thereby obtaining recycled water-based metalworking fluid.