ABSTRACT

of the Master's Qualification Work
"Automation of coal preparation process using vibration-pneumatic separator"

Introduction

Urgency. As a coal preparation technology for the last few years a vibration-pneumatic method has been used. This technology's features [7,8,9] which are embodied in modern separators, allow engineers to clean run-of-mine coal efficiently and in wide range of sizes. Insufficient knowledge of the separator as a control object and very low automation level of a preparation system based on it, bring operator to exercise control generally manually, basing on his own experience. This enhances the risk of irregular control and therefore loss of separator's work. Development of control laws for separator will allow to improve its economic performance and reliability. Particularly interesting to describe a motion of particles forming the separator's bed in conditions of mechanical shaking and under the influence of air upflow. Development of adequate model and then defining control laws for separator, will give the opportunity for creation of effective control system and advance of separator's performance.

The object of the research. Gravitational enrichment of coal using vibration-pneumatic separator.

The purpose of the research. Increase of coal preparation efficiency using vibration-pneumatic separator development of a control system.

The idea. To apply the physical and mathematical apparatus to the description of the processes occurring at gravitational enrichment of coal using a vibration-pneumatic separator.

Methods. mathematical simulation, mathematical statistics and probability theory, experiment planning method.

Problems. Problems to be solved in order to achieve assigned purpose:

1. Study and analysis of vibration-pneumatic coal preparation technology. Search of known methods for increasing the separator's performance
2. Development of mathematical model with the purpose of examining the motion of separator’s bed particles. Analysis of received simulation results
3. Method substantiation and development of an algorithm of separator management
4. Control system simulation and check of its effectiveness
5. Development of technology (hardware)

The process of separation of raw coal using vibration-pneumatic separator is shown on fig.1 (refresh this page if animation isn't going).

Figure 1. Raw coal separation using separator
(Gif-animation: file size - 65 КB; resolution - 640x480; frames count - 12; delay between frames - 200 мс; number of cycles - 10; while creating this animation next programs were used: 3dsmax 6.0 and Macromedia Fireworks MX 2004)

(watch quality and more informative video)

The technology of vibration-pneumatic coal preparation

Currently, there are several different principles of separation of the rock mass in order to separate out and further use of the most valuable part – coal. Each method corresponds to the particular machine design. In this case all methods of separation and corresponding machines have certain advantages and disadvantages that affect the choice of technology and equipment for the enterprise.

The main criteria of choice:

• accuracy of coal extraction
• performance;
• the influence of humidity on the efficiency of the rock mass separation;
• vibration load on the structure of the building where the machine is situated;
• use of water in the process of separation;
• pollution of the environment;
• equipment cost.

Recently, widespread and continues to develop the technology of vibration-pneumatic coal enrichment. This area is developing successfully in Australia, Russia, Kazakhstan, the USA, Japan and China. For the implementation of this technology enrichment plants with vibration-pneumatic separators are used. Examples of foreign plants are FGX-6 (China) and Allair (Germany). In Ukraine, Lugansk Machine-Building Plant ltd named after A. Parkhomenko (Луганский машиностроительный завод им.Пархоменко) produces SVP-5,5x1 (СВП-5,5х1) separator, which is designed to enrich in the air flow coal ore and other bulk materials with a surface moisture of up to 8%, with fineness up to 75 mm. It is used for the enrichment of bituminous coal and anthracite in the regions with low water supply, and for re-cleaning of mine dumps [1].

Among the machines of its class SVP-5, 5x1 leads on quality indicators for the concentrate extraction, while remaining more affordable. When comparing the separator SVP-5, 5x1 with similar machines for dry coal processing like FGX-5 (China), and SEPAIR (СЕПАИР, Russia), it was found that the Ukrainian separator has a higher performance and efficiency of separation with a lower cost of the final product.

However, the separator's disadvantage is a low level of automation of a technological process. Currently, regulation of the lifting mechanism 4 and the angles of deck 5 is carried out manually by the operator, there are no sensors to check the level of separator's bed fluidization, air flow, vibration parameters (fig.2). The development of automated control system for the separator and controls for the main technological parameters of dry processing would eliminate the human factor on the final result and the associated non-productive downtime of mechanical equipment. It also wiil enhance the quality indicators of the product obtained.

Vibration-pneumatic separator

At vibration-pneumatic coal enrichment under the influence of an air stream and simultaneous mechanical shaking occurs a separation of the mountain mass which is situated on the perforated surface of the machine [3]. Depending on size and density of grains of a material occurs its fluidization and stratification. Division of a material into products is carried out by moving of formed layers of bed on a working surface of the machine in several directions.

In vibration-pneumatic separators (fig. 2) the separation of formed layers occurs gradually on all area of a working surface that provides various concentration of a material on different sites depending on density and size of grains. Unloading is made from peripheral sites of a deck.

Fig 2. The scheme of the SVP-5,5x1 separator:
1 – the technological fan; 2 – air line; 3 – support; 4 – the elevating mechanism; 5 – deck;
6 – bed; 7 – shaker's drive; 8 – exhaust hood

The most important technological parameters and their influence on enrichment process are shown in tab.1.

Table 1 – Key parameters

The primary goal of automatic control of vibration-pneumatic separators consists in operating mode choice at which the best branch of extraneous impurity from coal is provided at its minimum losses in a waste. Tab. 1 analysis shows that management of enrichment process on a separator consists of regulation of following key parameters [2]:

• Air flow rate Q_air, m³/h;
• Box shaking frequency ω, sec^–1;
• Box shaking amplitude Δ, mm;

Structure scheme of control of vibration-pneumatic separator is shown on fig.3:

Figure 3. Structure scheme of control of separator

Changing granule structure of coal and its density is revolting influence f (t). Operating influence u (t) is presented by change of the air flow rate Q_air, frequency ω and amplitude Δ of box shaking. The supervision vector y (t) is presented by target signals of measuring converters about concentrate ash content А^c, middle product A^mid and waste А^w, and also about the degree of bed looseness.

Thus, management of a separator consists in operative change of values of parameters of operating influence depending on revolting factors for the purpose of reception of a quality product.

Measuring instrument

For normal course of enrichment process it is necessary to loosen rock mass and to lead it to condition of fluidization. Nowadays there are no the devices that allow to estimate degree of loosening of vibration-pneumatic separator's bed of a material. Thus, rate of loosening is the most important indicator on which depends the efficiency of separating ROM coal using vibration-pneumatic separator.

Now there are the devices intended for loosening measurement of bed of jigging machines. One of such devices – the device for automatic loosening measurement of bed of jigging machines, contains a float with lever system, the inductive gauge of loosening and the scheme for formation of a signal of measurement [4].

The device including immersed in bed probes, executed in the form of the cores strengthened in directing bearings [5] is known also. There is a device including a measuring element, established on an electric motor shaft. At immersing a measuring element in bed of a material and inclusion of the electric motor at the expense of braking of a shaft of the motor by bed grains there is a twisting moment which is transformed to deformation of an elastic measuring beam. Beam deformation is registered by strain gages [6].

However, the devices mentioned above are designed for application in conditions of jigging machines unlike which at vibration-pneumatic enrichment there is the vibrating field (created by shaking separator’s bed) that influences the accuracy of measurement.

I have developed a device of the automatic control of loosening rate for separator’s bed. The scheme of device is shown on fig.4. The device consists of the measuring element 1 strengthened on a shaft 2 of motor of direct current with independent excitation 3 which case is fixed motionlessly. The voltage drop on the constant resistor 4 (which is included in an electric motor chain) is sensed by analogue-digital converter (ADC) of the microcontroller unit (MCU) 5.

Figure 4. The device for measuring a loosening rate of vibrating-pneumatic separator

After applying the supply voltage U on a winding of an anchor of the motor, motor starts rotating, experiencing the moment of resistance M_C depending on geometrical parameters of a measuring element 1 and loosening rate of bed of the investigated material ρ. The less loosened the bed of the material, the more is the resistance moment applied on a shaft 2 of electric motor 3. With growth of the moment of resistance on a shaft reduces a speed of rotation of the motor and therefore reduces the current I_a consumed by the motor. As loosening increases current of electric motor decreases. According to a current voltage drop on the resistor changes. This sag is transformed by ADC of the microcontroller. Then MCU forms a corresponding signal of management of a separator.

In the established operating mode pressure U_a (enclosed to an motor anchor) is counterbalanced by electromotive power (EMF) Е, induced in an anchor, and a potential drop in an anchor chain:

where

c – constructional coefficient of the motor;

Φ – magnetic flow created by a winding of excitation of the motor or constant magnets;

ω_m – angular speed of rotation of a motor's shaft;

I_a – current in an anchor chain of the motor;

R_a – resistance of the motor's anchor chain;

R – resistor's resistance.

Change of angular speed ω of a shaft under the influence of the resistance created by bed of a material (loosened to certain degree) leads to change of EMF E and, therefore current I_a.

Thus, it is possible to estimate loosening rate of separator's bed by measuring the current consumed by the electric motor of the device. Application of the developed device will allow to form operating influence for maintenance of high efficiency of a separator and an exit of a qualitative product of enrichment.

Control system

As I have shown earlier coal preparation plant based on vibration-pneumatic technology is effective. But efficiency can be raised. It is possible by elimination of its main lack – a hand control. The main machine of a plant (vibration-pneumatic separator) is subject to a considerable idle time. The reason - absence of executive mechanisms for change of technological parameters. Also there is no sensor for measuring bed's loosening and a control system of enrichment process. It leads to considerable influence of the human factor on efficiency of separation.

СThe control system can be constructed as a set of blocks. Each of blocks is responsible for measurement and change of certain parameters of a separator. All blocks co-operate with the central device. This device (according to algorithm) operates process of separation and creates inquiries and information reports to the operator.

On fig.5 the scheme of separator plant with the blocks located in it is shown. Following blocks are used for control:

• DLB – dust collection block;
• DSB – deck shaking block ;
• LIB – longitudinal inclination block;
• CIB – cross inclination block;
• ASB – air supply block;
• MSB – material (ROM coal) supply block;
• BCB – bed’s condition block.

Task of DLB is giving operator the information about dust collection system (serviceability of the fan, pressure in the pipeline and so forth). DSB measures and changes a mode separator's decks shaking. LIB and CIB measure and change accordingly longitudinal and cross-section angles of deck's inclination. ASB measures and changes parameters of an air supply mode (the air flow rate and air pulsations). MSB operates a feeder. BCB informs about a condition of bed of a material (measures the loosening).

Figure 5. Scheme of the separating plant[1]:
1 – the technological fan; 2 – air line; 3 – support; 4 – the elevating mechanism; 5 – deck;
6 – bed; 7 – shaker's drive; 8 – exhaust hood; 9 – storage bunker; 10 – feeder; 11 – lifting mechanism; 12 – air cleaning

The central unit (CU) interacts with each block by means of the two-wire communication line. It allows raising reliability of ht system (compared with more economic topology «the common bus»). CU interacts with the computer by RS-232 interface (fig.6). Also operator should have a possibility of a hand control through CU.

Figure 6. Structural schematic of control system

Use of computer will allow using a difficult model for efficient control of the process. Also gathering and an archiving of the data about separator functioning and visualization of a current state of the process is possible.

Creation of such system will results as follows:

• Process visualization
• Fast failure search
• Faster control of the separator
• Computer model based control
• Human factor minimization

References 

1. Каталог товаров ЗАО «Луганский машиностроительный завод имени А.Я.Пархоменко»
2. Б.Д.Бесов Аппаратчик пневматического обогащения углей. Справочное пособие для рабочих. М.: Недра, 1988, 77 с.
3. Справочник по обогащению углей. Под ред. И.С.Благова, А.М.Коткина, Л.С.Зарубина. 2-е изд., перераб. и доп. М.: Недра, 1984, 614 с.
4. Авторское свидетельство СССЗ №989790, кл. В03В 13/00, 1980
5. Авторское свидетельство СССР №155763, кл. В03В 13/00, 1962
6. Авторское свидетельство СССР №219479, кл. В03В 13/00, 1966
7. Gravity_separation, en.wikipedia.org
8. Кузбасс внедряет «сухой» способ обогащения угля
9. «Сухое» обогащение – реальная замена устаревшим технологиям (эта статья есть в библиотеке)
10. Рубинштейн Ю.Б, Волков Л.А. Математические методы в обогащении полезных ископаемых. – М.: Недра, 1987. – 296 с.
11. Гравітаційна сепарація корисних копалин: Навч. посібник /П.І.Пілов.– Дніпропетровськ: Національний гірничий університет, 2003.– 123 с.
12. Автоматизированные системы управления технологическими процессами обогащения руд / Хорольский В.П., Хоцкина В.Б., Бабец Е.К. // Збагачення кописних копалин: Наук.–техн. зб. – 2004. – Вип. 21(62). – С. 105–114