INTRODUCTION
In connection with the constantly growing necessity of industry in a high-grade fuel and raw material for the production of coke the amount of the enriched coal grows continuously. During the last period there is a steady tendency was set to multiply maintenance of shallow classes and their ash-content in coals heading on enrichment.
In ordinary coals amount of shallow classes less than 0,5 mm makes is about 30%.
Imperfection of dewatering apparatus leads to the slurry accumulation in the system of circulating waters.
Efficiency of enrichment of coarse-grained slurry by gravitation methods and flotation methods is very low.
The problem of dewatering arises when coarse-grained slurry dehydrating. In the examined chart the slurry of a the first stage of condensing goes to dewatering in a conical of screen together with the shallow concentrate of dense medium machines.
In this connection the problem of this work is development of a rational flowsheet of slurry processing of the first stage of condensing, providing the decline of circulation of streams and increase of efficiency of enrichment.
ANALYSIS OF KNOT OF COARSE-GRAINED SLURRY PROCESSING. BASIC DISADVANTAGES
According to the examined flowsheet the shallow concentrate of control dense medium machine and dense medium machine of shallow coal goes to the primary dewatering in conical screen, and then in to the centrifuges. Subsieves waters of conical screens head for condensing in pyramidal deckers. The condensed product of pyramidal deckers and centrifuges is fed with a shallow concentrate on conical screen, circulating in the system "conical crash - pyramidal deckers".
Pyramidal deckers do not provide satisfactory classification on the size of material acting on condensing. Acording to the sieve analysis a condensed product contains 76,2% class 0-0,5 mm, which constantly circulates in the system. Coarse-grained slurry is hatched with water-free shallow coal, wears down and goes back into pyramidal deckers, creating the additional loading on flotation.
The hydroclassifying and thickening of slurry is realized with the specific loading on pulp15,3 m3/(m2*h) and on hard 2,0 t/(m2*h).
Value of the circulatory loading C is expressed:
for screens CS it makes:
on hard
C=(72,5+21,6)/363,5*100=26%
on water
C=(250+124,4)/1420,5*100=26,4%
The dewatered product of screens goes to the centrifuges with moisture (to 50%), and makes worse the process of dewatering in centrifuges.
That is why it is necessary to carry out the work of pyramidal deckers in the open cycle with the leadingout of coarse-grained slurry to the independent cycle of dewatering.
PROCESSING OF SLURRY IN PYRAMIDAL DECKER
The hydroclassifying and thickening of slurry waters is carried out in pyramidal deckers with general area 108 m2.
The fed pulp in them is considerably dilute (130 g/l), that provides the good settling of grainy material.
Work of pyramidal deckers is estimated by the index of efficiency of lighting up:
nl=(Bf-Bp)/Bf*100,
nl is efficiency of lighting up, %;
Bf is maintenance hard in the feed, g/l;
Bp is maintenance hard in a plum, g/l.
The index of efficiency of lighting up makes:
nl=(130-100)/130*100=23%.
The work of pyramidal decker is presented on a figer as animation:
Figer 1. - Pyramidal decker
1 - sluice;
2 - engine.
CONCLUSION
The analysis of work of knot of slurry thickening testifies to imperfection of technology of their treatment.
The detailed research of reasons of unsatisfactory work of the system of processing of coarse-grained slurry processing is allowed to develop measures on their removal.
The followings conclusions flow out on the basis of the executed researches:
1.Circulation of coarse-grained slurry in the system "pyramidal deckers - conical screens CS" leads to the overloading on hard and on water of centrifuge and pyramidal decker. As a result of it humidity of shallow concentrate rises and the process of classification of slurry going to condensing is worse.
2.The realization of flowsheet providing the conclusion of coarse-grained slurry from circulation in the knot of the independent processing is grounded.
3. Dependences of maintenance of division hard in products are found on the change of size of extraction of dewatering of coarse-grained slurry hard by a knot.
4. High efficiency of dehydration of coarse-grained slurry is set in pyramidal deckers.