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Annals of the University of Petroşani, Mechanical Engineering, 20 (2018), 105-110 105
ANALYSIS OF QUALITY INDICATORS FROM
SLURRY DECANTERS
FLORIN FLAVIUS ȘOICA1, ANGELA EGRI2,
ALEXANDRA STANIMIRESCU3
Abstract: In the coal preparation plant situated in Vulcan, a part of raw coal extracted
from the mining units in the ”ValeaJiului” is being processed. The small grit coal from
circulating waters is concentrated with cyclone batteries and recovered and drained with the
help of special screens. The fine tailings from residual water aredirected into the slurry
decanters and the water is purged using reagents. For appropriate dosing of the reagents, weekly
samples of water containing tailings are collected form the slurry decanters. In the following we
will analyze and interpret the indicators obtained from the processing of these samples.
Key words: press filters, separation plant, water treatment plant ash, residual material,
sampling, statistical analysis.
1. INTRODUCTION
The Petroșani Depression is the largest depression in the country, has a
tectonic origin and expandsto east-west direction 43-45 km and widens 3-9 km on the
courses of the two main affluentsof ”Jiu” river.
The sedimentary complex of the basin belongs to the Upper Cretaceous, the
Upper Oligocene and the Miocene and is transgressively and discordantly disposed
over the palaeo-mesozoic crystalline formations.
In the productive formation, of oligocene age, at the beginning there were
identified about 20 layers of coal. The useful substance in the deposit is made up of
coal with compact and relatively homogeneous composition. The coal of the Jiu
Valley, which is superior to most of other coal found in our country, is a hard type
coal.
1Ph D. student, University of Petrosani
2Associate Professor, Ph.D.Eng, University of Petrosani
3Ph D. student, University of Petrosani
Șoica, F.F., Egri,A., Stanimirescu, A.
106
The shift to the systematic exploitation of coal in this basin, on an industrial
scale, was only made at the end of the 19th century.
Coroești coal preparation plant is the third coal preparation plant built in the
Jiu Valley, located in the eastern part of Vulcan, on the right bank of the West Jiu, in
the Coroeşti settlement area - from where its name comes [1].
Coroeşti coal preparation plant was founded on June 1, 1963, and in 1969-
1971 it was modernized, the changes being claimed by the necessity of producing
increased quality energetic coal.
Later, between 1978-1981, the following were added:
- a wagon rollover machinery for unloading the train wagons full of coal
- a raw coal sorting line
- a siloingstation for the washed coal by building two silos of 8,000 tons each,
one for special coal, called coke and one for energy mixes
- waste water treatment plant(press filters) with the purpose of retaining and
evacuating or commercializing the tailings from waste water and cleaning the water for
recirculation in the washing section [2].
The coal processing plant was initially designed for a capacity of 4 million
tons per year approved by Decree 176 / 13.05.1978. The plant operated with two
washing lines and a spare one with a capacity of 330 tons per hour on a line (with an
effective work time of 18 hours).
In 2003, the upgrade, refurbishment and modernization plan was implemented
with the help of the integrated ITOCHU-KOPEX project, resulting a new separation
plant(the commissioning held on 31.03.2003) and a new washing plant (the
commissioning held on 30.05.2003). The refurbishment of the water treatment plant
was done in two stages, two sets of filters were put into operation with the separation
plant and the other two with the washing plant.
Due to the poor state of the existing machinery and the modernization of the C
the refurbishment of waste water treatment plant was absolutely necessary.
The waste water treatment plant was equipped with new automatic
displacement filters (4 sets), new slurry water pumps, new clean water pumps, high
pressure pumps(to tighten the filter plate) and an automated preparation and dosing
station for reagents [3].
2. METHODOLOGY AND RESULTS
During the course of this study, for the observation of the technological
parameters of the residual water treatment phase, several water samples were collected
from the plant feed pipeand the solid phase concentrations (g / l) and ash content were
determined. Also laboratory tests were conducted in order to check reagent
consumptions and performance [4].
The old recipe for polyacrylamide (PAA) and calcium chloride purification
reagents has been replaced, the new recipe that includes two of the most effective types
Analysis of quality indicators from slurry decanters
107
of clarifying reagents currently used worldwide, namely ZETAG 7195 coagulant and
MAGNAFLOC 919 as a flocculant [5].
Fig.1 Graphical representation of the obtained results
In the laboratory tests, the same reagent consumption was used as at industrial
scale, respectively 0,25 ml / l Zetag concentration 5% and 0,615 ml / l Magnafloc
concentration 0,2% corresponding to specific consumption of 10 g Zetag / m3 clean
water and 1.23 g Magnafloc / m3 of clean water.
The effectiveness of the cleansing tests has been established by determining
two basic parameters, respectively the rinsing speed and the turbidity.
Between January 2011 and December 2016, 266 samples of water from the
slurry decanters were collected and sent to the Coal Quality Laboratory.
Following specific tests, the residual material and ash content were determined
(Figure 1).
In the figure above, the X-axis of the graph represents the ash content (A)
expressed as a percentage, and the Y axis represents the concentration of the residual
material (C) in the water sample expressed in g / l.
In the studied period, the ash content ranged from 48.9% to 77.4% with an
average of 61.5% (Figure 2), while the concentration of residual material in the
decanter ranged from 129 g / l to a maximum of 487 g / l, with an average of 257.72 g /
l (Figure 3).
Șoica, F.F., Egri,A., Stanimirescu, A.
108
Fig. 2 Variation of ash content (%)
Fig. 3 Concentration variation (g / l)
Next, we calculated some benchmarks in order to perform aobjective statistical
research,as shown in Table 1 and Table 2.
Table 1 Ash and concentration deviation
Min
Max
Medium value
Mean linear deviation
(absolute)
Ash (A)
48,9
77,4
61,84
3,9145
Concentration (C)
129
487
257,72
45,9914
Analysis of quality indicators from slurry decanters
109
Table 2 Ash and concentration dispersion
Dispersion
Coefficient of variation
Ash (A)
25,0013
8,0844
Concentration (C)
3893,859
24,2118
The charts above where made using Microsoft Excel, based on the collected
data. Also in order to obtain an eligible variation law we used the trendline function of
MS Excel, which implements mathematical regression (linear, exponential,
polynomial, etc.) [6].
After interpreting these datawe can conclude the following results:
- the series of values describing the variation of ash is very homogeneous with
a small standard deviation
- the series of values describing the concentration variation is homogeneous
(coefficient of variation <35%)
We then searched for a variation law that best describes the relation between
the two indicators using the regression functions and we obtained the following results:
2
2,825x 83,002 ; R 0, 0512
y=+=
(1)
0,0095 2
139,26 ; R 0,0471
x
ye=⋅=
(2)
()
2
170,19 ln 443,7 ; R 0,0472yx= ⋅− =
(3)
22
0, 2866 x 33,433x 1222,2 ; R 0, 0766y= ⋅− + =
(4)
3. CONCLUSIONS
As a result of the calculations, the dosing of the reagent for the sedimentation
of the tailing, respectively the cleansing of the water in the decanter was optimally
achieved, obtaining a series of homogeneous values (in the case of variation of the
residual material concentration) and very homogeneous (in case of ash variation), but
there were cases when water suspensions exceeded 300 g / l reaching almost 500 g / l.
To avoid these situations, it is necessary to increase the frequency of sampling,
constant monitoring and supplementation of the operating hours of recirculation
pumps, screens and cyclones in order to recover more slurry from decanters.
After the mathematical analysis of the interdependence between ash content
and tailing concentration, using mathematical regression, it was not possible to define a
reliable variation law. The highest degree of confidence was obtained for the
polynomial regression function, with a value of 0.0766. This value represents a low
degree of confidence, which is why we can say that the variation of the ash tailing is
not dependent on the tailing concentration in the decanter, or reverse.
Șoica, F.F., Egri,A., Stanimirescu, A.
110
REFERENCES
[1]. Handra A. D., Popescu F. G., Creșterea eficienţei energetice în mineritul de suprafață,
Editura Universitas, Petroşani, 2011, pag. 116, ISBN 978-973-741-170-9.
[2]. Sârbu R., Prelucrarea datelor experimentale şi optimizarea proceselor (Processing of
experimental data and process optimization), University course, University of Petroşani.
[3]. Sârbu R., Bădulescu C., Tehnici şi tehnologii de procesare a resurselor minerale
(Techniques and technologies for processing mineral resources), University course,
University of Petroşani.