Disertation

Russian Ukrainian

Investigation of insteady condition

of slime-water schemes work on concentrating mills.
Supervisor: D.S. Nazimko Y.I.

The accumulation of coal slime in circulating water is negatively telling on work of main coal cleaning processes - it makes worse the results of coal cleaning.

It is necessary to use following principles of slime-water schemes construction to improve slime-water schemes:

guarantee of classifying by size with high efficiency in operations of slime removal from run-of-mine coal and in operations of cola cleaning products dewatering with the purpose of preventing coarce slime penetration in slime-water lines and tanks;
it is necessary to use flotation to regenerate circulating water, especially time of cleaning coal and coal cleaning products with water with the purpose of reducing sludge particle formation as a rock maceration result;
prevention of fine particles accumulation in circulating water be means of thickening-clarificational apparatuses that direct their overflow back to the gravity separation department. It is impossible to improve the work of this apparatuses, they should be expelled from slime-water scheme;
it is necessary to rise slime extraction into dewatered products of regeneration department by means of more effective apparatuses;
cutting down water use on technological processes in gravity separation department by choicing and arranging corresponding apparatuses;
it is necessary to use closed slime-water schemes without outward slime ponds.

The accumulation of slime in slime-water schemes of concentrating mills evaluates in terms of slime circulation factor K.

where:

F and G - quantities of slime, accordingly with size smaller and bigger than interface size of slime in slime water when equilibrium is established in system, t/h;

f and g - quantities of slime, accordingly with size smaller and bigger than interface size of slime in slime water after first cycle, t/h.

There was worked out mathematical model of closed one-flow slime-water scheme by Treskov Y.G. and it is possible prediction of equilibrium slime concentrations, estimation of slime accumulation kinetics and slid phase content regulation using it.

According to this model, slime mass balance equation have the following form:

(1)

where:

W - volume of water in slime water system, m³;

V - rate of slime water flow in system, m³/h;

K - solid phase content in slime water, t/m³;

K_v - solid phase content in process water, t/m³;

Р - the mass of cleaned in gravity separation department coal, t;

c - relative summary mass of slime (which is coming with run-of-mine coal and getting as a result of breakage of coal), relative units;

dt - infinitesimal time interval;

r - average slime density, t/m³;

l - constant, which is characterize relative slime amount in volume unit of liquid phase, which is removing out of system with products of coal cleaning, submultiple units.

After separation of variables in equation (1) and integration it under initial conditions К=К₀ and t =0 there was got an equation of slime accumulation kinetics:

(2)

where:

K Ґ - slime concentration when t -> Ґ .

(3)

According to the equation (2):

process of equilibrium slime concentration in system K Ґ achievement goes under the exponential law;

slime concentration increase goes when К₀< К Ґ , decrease goes when К₀> К Ґ .

According to the equation (3) equilibrium slime concentration quantity is independent of initial slime concentration К₀ and, what is particulary important, it is dependent of volume of water W in system. It is determined by the slime concentration in water that come in system V, by slime quantity, that come in system with cleaning coal and get as a breakage of coal result.

It is taken in practice slime concentration deviation from equilibrium slime concentration, that is determined by formula:

Then, subject to equations (2) and (3), the time, when slime concentration in system will be equal to K(T_a) will be calculated by formula:

(4)

According to the equation (4) the characteristic time of reaching equilibrium slime concentration increases proportionally with value of equilibrium slime concentration and with volume of water W in system and decreases directly proportional to the sum K_vV+ c P, that is with increasing of quantity of slime, coming with water and coal and forming in cleaning processes. Also, the time T_a depends on K₀/KҐ and a, but to a lesser extent (T_a increases with K₀/KҐ and a decreasing).

There was elaborated on mineral resources dressing sub-faculty of DSTU a procedure of design low-operational circulating water regeneration systems. Slime circulation, that depends on closed system construction is controlled factor. Slime water schemes are represented as generalized technological block-units.

My master work investigates unsteady condition of slime-water schemes work, that is the condition, when quantity of slime in flows not equal to equilibrium slime concentration. Transportation lag of flows T exerts a considerable influence on slime accumulation in this period of time and it consists of transportation lags of flows in pipe-lines T_тр and lags of slime in different apparatuses of scheme T_a.

T=T_тр+T_a

Transportation lag of flows in pipe-lines T_тр depends on pipe-line diameter, pipe-line length, pump capacity or quantity of pulp that goes in pipe-line by gravity, sumps volume.

The lag of slime in apparatuses depends on details of construction and technologic features of apparatuses. For example gravity thickener is high lag apparatus, the lag of slime in it makes up average 15 minutes, but hydrocyclone works quickly - slime stays in it for few seconds.

Computer analysis of systems work in unsteady condition allows to find optimal combination of technologic apparatuses, that provides more fast system reaching the work in steady condition.

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