US 4,301,000 A · Method and apparatus for fractionation and recovery of limestone grits in kraft pulping process

Abstract

The limestone grits, formerly considered a waste product of the lime slaking process, become economically salvageable after successful fractionation to separate them into three parts: (1) caustic chemicals useful in the kraft pulping process; (2) under-, and over-calcined small limestone particles having an impurity level virtually identical to that of raw limestone; (3) caustic-free large particles containing the majority of residual impurities such as silicon, iron, magnesium, and chromium. The fractionation of limestone grits is economically carried out by a refluxive hydraulic washing system in which the untreated limestone grits from the slaker and first introduced into the open mouth of a vortex washer where they undergo an initial separation in which most of the smaller particles and caustic chemicals are recovered. The larger particles pass from the vortex washer into a second separation stage in the form of a rotating screen drum having fine screens of 20 mesh grade, irrigated by an internal water spray. In this rotating drum, any remaining caustic chemicals and small limestone particles are washed and separated from the large, impure particles by passing through the mesh screening of the drum. The limestone particles and caustic-laden wash water are returned via a pumped line to a liquid inlet in the side of the vortex washer. Passing tangentially into the vortex washer, they constitute a rotating counter-current which achieves the above-mentioned initial separation of the incoming untreated limestone grits. The smaller limestone particles congregate near the top of the vortex washer from which they and the recovered caustic chemicals are pumped to re-enter the kraft pulping process.

Claims21

Dependent claims

A refluxive washing apparatus for the fractionation of a wet sludge mixture of particles of varying sizes and liquid soluble chemicals for the purpose of rejecting from said mixture all said particles larger than a certain preselected size, comprising:

a vortex washer having, a hollow body member into which said wet sludge mixture is introduced, said body member including a substantially cylindrical wall portion oriented with its major axis generally vertical;
a liquid inlet conduit intersecting said cylindrical wall portion in a direction selected to inject a flow of liquid from said liquid inlet generally tangentially of said cylindrical wall portion to produce a sheet of liquid rotating around the interior of said cylindrical wall portion;
an accept outlet tube intersecting said cylindrical wall portion generally above said liquid inlet tube;
and
a reject outlet located generally below said liquid inlet conduit and positioned generally axially of said cylindrical wall portion;
and
a screen washer having an inlet connected in fluid flow communication with said reject outlet to receive the flow of rejected matter from said vortex washer, said screen washer having a mesh screening of a mesh size selected to pass only those of said particles smaller than said preselected size;
a liquid inlet for communicating with an external source of washing liquid;
a sprayer positioned to direct a spray of said washing liquid generally in a direction to wash said smaller particles through said mesh screening;
a screen washer accept line positioned and arranged to receive all liquid and particles passing through said mesh screening, said screen wash accept line being connected in fluid flow communication with said liquid inlet conduit of said vortex washer by means of a vortex washer pump, whereby said particles and liquid passed by said mesh screening are used as a source of liquid in said vortex washer.

7 more elements

Apparatus for fractionating a mixture of constituents, comprising:

a vortex constituent separator having a body member defining a cavity extending along a principal axis, a mixture inlet intersecting said body member for introducing said mixture into said cavity, a separatory medium inlet intersecting said body member for introducing a separatory medium flow that circulates in said cavity about and travels in a direction along said principal axis and fractionates said mixture, a plurality of first outlets intersecting said body member to be in flow communication with said separatory medium flow in said cavity, said plurality of first outlets is arrayed along the body member mutually spaced apart in the direction of said separatory medium flow along said principal axis of said cavity for receiving and discharging different first fractions of said mixture, and a second outlet intersecting said body member at a position for receiving and discharging a second fraction of said mixture from said cavity;
and
a secondary constituent separator for fractionating mixtures having a charge inlet and a fraction accept outlet, said charge inlet coupled to an outlet of said vortex constituent separator for receiving the fraction discharged therefrom, and said fraction accept outlet coupled to receive and discharge a selected fraction of said fraction received from said outlet of said vortex constituent separator, said fraction accept outlet coupled to the separatory medium inlet of said vortex constituent separator for delivering said selected fraction to said separatory medium inlet and forming the separatory medium.

Apparatus for fractionating a mixture containing particles of various sizes, comprising:

a vortex constituent separator having a body member defining a cavity extending along a principal axis, a mixture inlet intersecting said body member for introducing said mixture into said cavity, a separatory medium inlet intersecting said body member for introducing a separatory medium into said cavity in a manner productive of a separatory medium flow that circulates in said cavity about and travels in a direction along said principal axis and fractionates said mixture, a first outlet intersecting said body member to be flow communication with said separatory medium flow in said cavity at a position spaced from said separatory medium inlet in the direction of said separatory medium flow along said principal axis for receiving and discharging a first fraction of said mixture comprised of particles principally of a size smaller than a selected size, and a second outlet intersecting said body member at a position for receiving and discharging from said cavity a second fraction of said mixture comprised of particles principally of a size larger than said selected size;
and
a secondary constituent separator for fractionating mixtures having a charge inlet and a fraction accept outlet, said charge inlet coupled to the second outlet of said vortex constituent separator for receiving the second fraction discharged therefrom, said secondary constituent separator fractionating said second fraction to separate therefrom particles principally of a size smaller than said selected size and form a selected fraction, and said fraction accept outlet coupled to receive and discharge the selected fraction, said fraction accept outlet coupled to the separatory medium inlet of said vortex constituent separator for delivering said selected fraction to said separatory medium inlet and forming the separatory medium.

Apparatus for fractionating a wet sludge mixture of particles and liquid soluble chemicals, comprising:

a vortex constituent separator having a body member defining a cavity extending along a principal axis, a mixture inlet intersecting said body member for introducing said mixture into said cavity, a separatory medium inlet intersecting said body member for introducing a separatory medium into said cavity in a manner productive of a separatory medium flow that circulates in said cavity about and travels in a direction along said principal axis and fractionates said mixture, a first outlet intersecting said body member to be in flow communication with said separatory medium flow in said cavity at a position spaced from said separatory medium inlet in the direction of said separatory medium flow along said principal axis for receiving and discharging a first fraction of said mixture including particles within a selected size range and said liquid soluble chemicals, and a second outlet intersecting said body member at a position for receiving and discharging from said cavity a second fraction of said mixture including particles of a size outside said selected size range;
and
a secondary constituent separator including a liquid washer and particle size separator for fractionating mixtures, said secondary constituent separator having a charge outlet and a fraction accept outlet, said charge inlet is coupled to the second outlet of said vortex constituent separator for receiving the second fraction discharge therefrom, said fraction accept outlet is located for receiving and discharging a selected fraction of said second fraction, said liquid washer is in fluid flow communication with the second fraction received at said charge inlet for subjecting said second fraction to a wash by a liquid that removes said liquid soluble chemicals from particles included in said second fraction, said particle size separator separates particles of a size within said selected size range from other particles included in said second fraction, and said fraction accept outlet is coupled to receive said separated liquid soluble chemicals and separated particles of a size within the selected size range and discharge them to the separatory medium inlet of the vortex constituent separator as the selected fraction.

Dependencies are inferred from the claim text.

Method and apparatus for fractionation and recovery of limestone grits in kraft pulping process

Life of this patent

Method and apparatus for fractionation and recovery of limestone grits in kraft pulping process

Life of this patent

Abstract

Claims21