| 摘要 |
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.
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