Summary of the final work
Content
- Introduction
- 1. Technological process as an object of automation. Design Objective and Requirements for an Automation Device Being Developed
- 2. A critical overview of existing solutions and the choice of basic automation equipment
- 3. Circuit solution of automation system
- Conclusions
- Reference List
Introduction
Analysis of fires in mines on belt conveyors shows that the ignition of conveyor belts is possible from two groups of ignition sources:
- external sources formed during the ignition of a wooden shaft mount, coal or other combustible objects, when there is a conveyor in the burning zone.
- internal sources that are formed during the operation of the conveyors themselves, mainly from the friction of the belt on the conveyor drums, faulty rollers, etc.
All these problems can only be solved if fundamentally new technical tools and solutions are used in automation equipment circuits — microprocessors, mathematical software. In recent years, a number of works have been carried out to improve serial products, transfer them to a new elemental base and increase efficiency of use. Such serial products include: AUK.2M complex [6], KS.1M device, DM-3 sensor, VKA switches, UKTL devices. But despite the introduction of the latest developments in the mines, there are constantly recorded cases of fires on belt conveyors, especially related to the ignition of conveyor belts due to slipping in places of communication with the drive drum. Therefore, the actual task is the operational control of the temperature of the drive drums of belt conveyors of the mine. At the same time, it is necessary to create such a device that would be a hub of information about the thermal mode of operation of belt conveyors, such as places that are dangerous in the event of a fire source.
1. Technological process as an object of automation. Design Objective and Requirements for Developed Automation Device
The object of the study is a main conveyor line consisting of two or more conveyors.
For the transportation of rock mass through the major (main) horizontal and inclined workings, bremsberg and inclined shaft shafts, stationary belt conveyors with belt widths of 1000 and 1200 mm, produced in accordance with the size range, are produced.
These are high-capacity conveyors, the drive power of which can be from 500 to 1000 kW, the belt width is 1000 and 1200 mm. Structurally, they differ from precinct conveyors in that the belt clamp in them is located at the end of the conveyor. In conveyor drives, asynchronous motors are used, both with a short-circuited and with a phase rotor. Conveyors are intended for operation in the workings of coal and slate mines with an installation angle of -3 °; up to + 18 °, i.e. can be installed in horizontal and inclined workings. It is on these conveyors that a large number of fires are registered [7].
Consider the design and equipment installed on an inclined belt conveyor 2ЛУ120 [5].
The conveyor capacity is 1200 t / h, the drive power is 500 kW. The drive station is five-drum, with both drive drums covered by the clean (non-working) side of the tape.
Figure 1 - The appearance of the inclined conveyor belt 2ЛУ120
Becoming conveyor cable construction with suspended articulated rollers. The drive drums of the conveyor rotate by two drive blocks, each of which consists of two short-circuited engines of 250 kW each with hydraulic couplings GLP500, which provide the necessary smooth start-up of the conveyor, gearbox TsDN710 and shoe brake TKTG500 driven by an electromagnet. The first along the tape, the drum is equipped with a ratchet stop, which keeps the loaded part of the tape from reversing when the conveyor is stopped in emergency cases when for some reason the shoe brakes do not work. The external (discharge) drum is mounted on a cantilever frame, which allows it to be installed on a separate foundation at a considerable distance from the conveyor drive station. The stand of the conveyor consists of two parallel ropes, stretched along the route of the conveyor, transitional, linear and tension racks, upper roller supports and lower rollers. The tension section is the tail section of the conveyor. The tension drum is mounted on a frame, it has four rollers on which it moves along guide rails. The belt is tensioned by an electric winch, which is connected by a rope through a system of blocks to the frame of the tension drum. Conveyors are designed for workings with a tilt angle of 100 or more, equipped with belt catchers for the upper and lower branches. Unified complete groups (Figure 1) of the conveyor: 1 - remote head, 2 - drive station, 3 - middle part (becoming), 4 - tape, 5 - loading device, 6 - tension head, electrical equipment for automated control of high-voltage electric conveyor of KUP 2LU . The smoothness of the launch of these conveyors is ensured by the inclusion of starting resistances in the rotor electric circuit using the explosion-proof station SUV2LU120 for a rated voltage of 660V. The control station consists of five sections: four are designed to control the electric motor of the conveyor, the fifth to control the brake system and accessories of the conveyor.
The electrical equipment of the conveyor (Figure 2) includes the control unit - the AUK-1M equipment control unit, the PU - the AUK control panel; DZ - gauge sticking; 1УСТ, 2УСТ - signaling and telephone communication devices; UKPS - a device for monitoring slippage and belt speed; USI - a control and information device containing a relay block BR, a display unit BI, linear modules 1ЛМ-16ЛМ; UKPL-1 - the device of preventive control of the strength of the conveyor belt; AT-3 - irrigation automation equipment at overloads, which includes a control valve
Figure 2 - The layout of electrical equipment on a conveyor belt
WU, sensor DNM material availability on the tape; 1PVI, 2PVI, 5PVI - conveyor starters; 3PVI - brake actuator; 4PVI - belt tension winch starter; 1D - conveyor drive motor; 3D - engine winch tension; 1ПЭТ.2 - electromagnetic drive of the conveyor brakes; 1VPV - ground control switch triggering catchers; KP - push-button control of the tensioning winch in the local mode; 1СВ.1-11СВ.1 - sound signaling devices; 1KKA - 11KKA - emergency switches of an emergency stop of the conveyor; 1ВКА-01 - 12ВКА-01 - emergency tap control switches; BKV - sensor of contactless rotation control; Boots-control unit and alarm; DN - tension sensor; DM - sensor control the frequency of rotation of the drive drum.
In this case, the automation device and sensors noted above are well known and described in [5], [6]. Unknown remains the temperature control device of the drive drums. The fact is that for the ignition of the ribbon in its aggregate state from external sources, a long-lasting impact of a powerful source with a temperature of hundreds of degrees is necessary. The ignition of the tape from sources that are formed during the operation of the conveyor (slipping of the tape) occurs at relatively low power and lower temperatures. This is explained by the fact that in the second case, there is a primary fire not on the whole tape in its aggregative state, but on fine particles that are formed when the tape surface is erased [8].
The slippage of the tape can occur due to the production of the lining of the driving drums and with insufficient tension of the tape when its “slack” is formed. When slip occurs, the mechanical connection between the tape and the drum is lost, the tape can be stopped, while the drum continues to rotate, intensively erasing the surface of the tape with the formation of fine fractions. These fractions and dust settle to the bottom of the drum, which is heated by friction. The fine particles are heated, which causes smoldering in the initial stage, and then fire at a temperature of 100-150 ° C. Thus, the required controlled range for measuring the temperature of the drive drum should be in the range of 20-90 ° C.
Determine the metrological requirements for a temperature control device:
- measurement accuracy ± 5 ° С;
- sensitivity when measuring the temperature of the drive drum is a constant value;
- due to the fact that a fire at 100% slip occurs after 10-15 minutes, the response time within 3 minutes is enough to prevent the occurrence of the fire.
A special feature of measuring the temperature of the drive drum is that the object is constantly in motion and remote control is necessary to determine the temperature, since the use of another type of measurement will be associated with technical difficulties in implementation.
2. A critical overview of existing solutions and the choice of basic automation equipment
To control and monitor the work of stationary and semi-stationary unbranched conveyor lines, with the number of conveyors in a line up to ten, there is a control system for conveyors AUK.1M, which can also be used to control branched lines with a number of branches to three [6].
A block diagram of the AUC.1M complex is shown in Figure 3.
Figure 3 - AUC.1M hardware block diagram
AUC.1M hardware consists of the following elements:
- PU control panel;
- no more than ten control units of the CU, the number of which corresponds to the number of conveyors in the line;
- push button control KU;
- a remote instrument showing the runway;
- PST alarm and telephone devices;
- unit of the BPA starting equipment, which consists of actuators of conveyor drives;
- DB sensor block. The structure of which includes sensors of speed DKS, derailment of tape KSL, DZhtyptyovka and cable cable switches KTV-2.
AUC.1M hardware performs the functions:
a) for management:
- Automatic switching on the conveyor line in the opposite direction of the traffic flow;
- Manage conveyors in repair and commissioning mode;
- Disable the pipeline from any point along its length;
- Termination of the launch of the conveyor line from any control unit;
b) by blocking:
- Prohibition of starting the conveyor in case of faulty sound alarm control circuits;
- Start of each subsequent conveyor only after the speed of the previous conveyor is set at the nominal level;
- Prevent automated start and work in an automated mode of the conveyor, transferred to the repair and debug mode, as well as all the conveyors behind it;
c) for protection:
- shutting down the conveyor when the belt is out, reducing its speed, when the conveyor is being sewn;
- Disable the conveyor line when short-circuit. or broken line;
- zero protection;
- Sound an audible warning signal before starting the line and when the conveyor is stopped;
d) by indication:
- the number of pipelines operating in automated mode;
- disabling the pipeline with protection or KTV-2,
- the presence of voltage on the control unit;
d) two-way duplex telephone communication.
To start the conveyor line, you must click the Start button on the remote control PU. In this case, a start signal is sent to block BU1, which, after the end of the audible alarm, issues a command to turn on the tape at nominal speed, issues a start signal to block BU2, and so on. After turning on the last conveyor in the line, the end-of-relay BKR block stops the start of the conveyors and translates them into an automated mode of operation. At the same time, the speed of the conveyors, the absence of seals and ladders and the absence of signals from the KTV-2 switches are controlled. The number of working conveyors is displayed on the runway.
Disconnection of the conveyor line occurs when the above-mentioned sensors are triggered, a break or a short circuit. communication lines, as well as when you click the " Stop " on PU or KP.
BU blocks are usually located near the electric drive of the conveyor. The remote control PU is placed in the location of the operator of the conveyor line, the unit БУ1. In the same place place and WFP, and KP, and PST. The belt speed sensors are mounted on an empty conveyor branch, immediately behind the drive head. The sensors of the DZhtaybovka stacking are installed in the places of the overflow from one conveyor to another. Sensors KSL and KTV-2 are installed along the entire length of the conveyor. Starting from the bypass drum at a distance of no more than 75 m from each other. The VUK-1M equipment is accepted as a basic. The device being developed must work together with it
To date, the only temperature control equipment for the driving drums AKTL - 1 [6], [5] has been developed. The equipment is designed to control the shell of the non-lined drive drum of a belt conveyor in order to protect the belt from fire when it slips. The control is carried out both in the process of rotation and when the drum is stationary.
The equipment of AKTL-1 consists of a stabilized power source, a high-frequency signal generator, a thermal sensor, a node for receiving and transmitting signals, and an alarm unit. Diagram of the external connections of the equipment is shown in Fig. 4.Figure 4 - Circuit of external connections of AKTL-1 equipment
The temperature sensor TD-1 is an empty steel stud, inside of which there is a temperature-sensitive element, made in the form of an inductance coil with a ferrite core. Thermal sensor is sealed with epoxy compound and embedded in the shell of the drum. The principle of the sensor is based on the effect of a sharp decrease in magnetic permeability when it is heated to a certain temperature. The node receiving - transmitting signals of the ferrite core is a transformer consisting of two fixed and one moving coil. Stationary coils are placed in blocks TN - 1, mounted on the frame of the conveyor. The movable coil is located in the TP-1 ring unit, mounted on the drum shaft and rotating with it. The coil inductance of the TD-1 sensor is included in the moving coil circuit.
Apparently, the hardware has several disadvantages:
- The complexity of the design and principle of operation;
- The inability to quickly transfer to another object of control;
- Inability to coordinate with automation equipment of conveyor lines;
- The inability to control the belt tensioning station;
- The inability to collect information on thermal conditions from several conveyors in a line;
- Morally obsolete element base of the device.
Thus, AKTL-1 does not meet the requirements of the equipment being developed and cannot be used as a base. We take the complete equipment for automation of conveyor lines - AUK-1M as basic equipment.
Let's analyze the existing methods and means of contactless temperature control. To determine the type of pyrometric transducer, consider a number of common types and choose one of them. Further, based on the characteristics of the selected temperature-sensitive element, a mathematical model of the automation device will be built.
Radiation thermoelements (RTE)
The currently developed RTEs are designed to work at constant and variable irradiation. Mainly bimetallic thermoelements work on constant irradiation, although most of them work on a modulated flow with a frequency of about 5 Hz.
Thermocouples made of semiconductor materials have a higher thermal emf. Metallic and semiconductor RTEs can be wire, pin, tape and film. As a rule, all RTEs are manufactured with compensating junctions to increase the stability of work.
The radiation thermoelement consists of the receiving part (collector) and SE. The exceptions are anisotropic and some high-speed film PTE. As a receiving part of high-speed RTE (30-100 ms), use thin gold or silver foil coated with golden niello. In DC-DC, a cone with a copper foil, as well as a wedge or sphere can serve as a receiving part.
To increase the sensitivity of the RTE, its PE is placed in a vacuum case. However, vacuum RTEs eventually lose their sensitivity due to the ingress of air into the case. RTE is made single and multi-element. Thermolabs and thermopiles may consist of a large number of thermocouples connected in series (in order to increase the conversion rate and simplify coordination with the measuring circuit).
For many years, RTE has been used as an SE for optical devices in the ultraviolet, visible, and infrared spectral regions. Due to the simplicity of design, reliability in operation, stability of parameters and cost effectiveness of RTE, they have not lost their relevance even now. They are widely used in radiation pyrometry, spectrometry, radiometry, including actinometry, technology and dosimetry of ionizing radiation. When measuring temperatures close to room temperature, a thermostabilizing device is needed, which complicates the design and reduces the measurement accuracy.
Bolometers. The bolometer effect is based on a change in its resistance when absorbing the incident radiation flux, which leads to modulation of the voltage (current) in the measuring circuit in which the bolometer is turned on.
To determine the characteristics of the bolometer and their interconnection, it can be represented as a system with lumped parameters.
The effect of electrothermal coupling in a bolometer is caused by the flow of current through the sensitive element. Its essence lies in the fact that when the resistance of the bolometer changes under irradiation, heat is additionally dissipated in it, which affects the output signal.
Currently developed metal, semiconductor and dielectric bolometers. Due to the use of cryogenic effects, superconducting isothermal and non-isothermal bolometers are created.
Bolometers are used in IR radiometry, spectrometry and pyrometry, infrared and laser technology and in other areas of optical instrumentation [8]. In near and middle IR spectrometry (1-25 microns), bolometers are used as radiation detectors. However, with a slow scanning of the spectrum at low modulation frequencies (5–9 Hz), it is preferable to use vacuum radiation thermoelements that have the same sensitivity but allow for simplifying the electronic circuit. When working at higher modulation frequencies (9-250 Hz), bolometers are more preferable than RTE, since they have better response speed and higher sensitivity.
Pyroelectric radiation detectors. Having a sensitivity comparable to that of other TPIs at room temperature, pyroelectric radiation detectors (PPIs) are fast-acting [31]. Their sensitive element, having a capacitive character, can be made in the form of figures of complex shape with large dimensions of the receiving area. Unlike bolometers, these receivers do not require additional power sources during operation. PPIs have versatility, consisting in the fact that by changing the value of the load resistance you can change the time constant of the receiver by many orders of magnitude.
Thanks to the combination of its unique properties, PIP in the past decade have been widely developed. This was especially promoted by the rapid development of laser technology, which led to an expansion of the range of measured radiation fluxes by more than 15 orders of magnitude.
Common to all single-element PITs is the presence of a pyroactive crystal, two electrodes, and an absorbing coating deposited on one of them. The electrode, which is irradiated, can be made without an absorbing coating, if it is made translucent. This is especially important when developing high-speed PPIs.
PPI with sensitive elements on thin, pre-metallized organic films possess high vibration resistance.
The differential coordinate PIs include two-site, quadrant, cruciform, and diagonal receivers. Photoelectric and thermal differential radiation detectors have long been known. The principle of their operation is based on the occurrence of a difference signal when the beam is displaced relative to the center of two receivers.
Fields of application of PPI are expanding rapidly. PPIs were used for energy and power of intensive flows in a continuous mode with a power of 1 &10 W / m 2 , a peak power of 10 2 & 10 4 W / m 2 pulses of nanosecond and second duration, image conversion with sensitivity 10 -8 - 10 -10 W / m 2 associated with the use of bioactive elements.
Pyrometers with PPI produced by a number of foreign firms. An infrared pyrometer with a pyroelectric detector for the region of 8–14 µm is designed to measure temperatures in the range of 0–400 ° C when the ambient temperature changes from 0 to 60 ° C.
Pyroelectric detectors are superior in their detection capacity to better heat sinks.
Thus, having considered the currently existing methods and methods for contactless temperature measurement, the most appropriate option for solving the problem is to use a pyroelectric temperature sensor based on the following principles:
a) pyroelectric radiation detectors are thermoelectric, current generators unlike thermocouples and bolometers;
b) PPIs have versatility, which is that by changing the value of the load resistance you can change the time constant of the receiver by many orders of magnitude;
c) high sensitivity;
d) inexpensive technology;
e) high-speed and not sensitive to constant thermal effects;
g) Pyroelectric detectors are superior in their detection capacity to heat receivers.
To build a pyrometric temperature control sensor, we take a coordinate-sensitive differential square pyrometric sensitive element because it is the ideal solution for constructing an automation device being developed based on the above patterns.
3. Circuit solution of automation system
For full automation of the belt conveyor and the tension station, it is necessary to develop a system that allows you to implement an algorithm for controlling the conveyor according to information about the temperature of the drive drum.
The control equipment being developed must work together with complete automation equipment for belt conveyors of the type AUK 1M or AUK 2M. The control unit and the control panel of the automatic temperature control system must have an audible alarm, the function of which is to alert personnel to accidents on the conveyor line (the control unit is responsible for generating an alarm signal on the length of the conveyor on which the thermal sensor triggered; the control unit controls the alarm signal on central control point of the conveyor line). The equipment should have a hub of information on the thermal mode of operation of the conveyors in the line, which should be located in the SACT unit. It should also be noted that the information hub (console) must have access to a personal computer in order to make changes in the operation of the console and to obtain information about the operation of the conveyor line.
To prevent accidents and ensure safe operation of the conveyor, the designed device should provide continuous control of the temperature of the drive drum, depending on the tension of the conveyor belt. The need to quickly assess the situation and make management decisions when the conveyor is operating in conditions of significant separation of tension drive stations and the conveyor requires that the automation device provide extensive information capabilities. The following indication should be provided:
- Indication of the operation of conveyor drives and tensioning station;
- Ribbon tension indication;
- Indication of the cause of the shutdown that occurred;
- Indication of the integrity of the temperature sensor circuits.
It is also necessary to fulfill the requirements for the explosion protection of devices and the intrinsic safety of output and input circuits.
Based on the measurement tool developed above, it becomes possible to develop an automatic temperature control system. Its structural diagram is presented in Figure 5 and includes: PDT – pyroelectric temperature sensor; DZA – air pollution sensor; SNM &; scheme of setting the sensor on the object; ATP – signal amplification circuit; SID, SIPU – diagrams of interfaces of the sensor, control unit and control panel; MK DT, MK BU, MK PU – microcontrollers of temperature sensor, control unit and control panel; SI PD – intrinsic safety circuit of the output signals of the pyroelectric sensor; SISD – intrinsic safety scheme of input signals of the control unit; MC – signal multiplexer; SKVS1, SKVS2 – switching circuits of the output signals of the unit and the control panel; KU1, KU2 – control buttons of the unit and control panel; MI1, MI2 – module of indication of the block and the control panel; BR1, BR2 – register blocks.
Figure 5 – Block diagram of the automatic temperature control system
Conclusions
In the process of implementation of the graduation project proved the need to control the temperature of the drive drum, as a dangerous place for the occurrence of the fire. When considering the conveyor as an automation object, the main technical requirements for the developed control equipment are formulated. On the basis of a critical analysis of the existing temperature control devices, the need to use pyrometric temperature control sensors has been established, since they are the ones who carry out non-contact temperature control and also allow to take into account the dustiness of the working space.
Thus, it can be concluded that the developed equipment meets the requirements and allows for the on-line automatic control of the temperature of the driving drums of belt conveyors.
Reference List
- Правила технической эксплуатации электроустановок потребителей и Правила техники безопасности при эксплуатации электроустановок потребителей / Глав. Упр. Гос. Энергетического надзора Минэнерго СССР.- четвёртого изд.- М .: Енергоатомиздат, 1989.- 432с.
- Правила устройства электроустановок / Минэнерго СССР. - Шестой изд. пере. и доп. - М: Энергоатомиздат, 1985. - 640 с.
- Правила безопасности в угольных шахтах.- К .: Основа, 1996.- 421 с.
- Автоматизация производства на угольных шахтах / Г.И. Бедняк, В.А., Ульшин, В.П. Довженко и др. - М .: Техника, 1989. - 272 с.
- Батицкий В.А., Куроедов В.И., Рыжков А.А., Автоматизация производственных процессов и АСУ ТП в горной промышленности: Учеб. Для техникумов. - Второй изд., Перераб. и доп. - М .: Недра, 1991.
- Справочник по автоматизации шахтного конвейерного транспорта / Стадник Н.И. и др. М .: Техника, 1992. - 438с.
- Борьба с пожарами на ленточных конвейерах в шахтах. – М.: Углетехихдат, 1959
- Ленточные конвейеры в горной промышленности. В.А. Дьяконов и др. – М.: Недра, 1982 г
- Взрывопожаробезопасность горного оборудования/ С.П. Ткачу, В.П. к – К.: 2000
- Руководство по ревизии, наладке и испытанию ленточных конвейеров и конвейерных линий угольных и сланцевых шахт. М.С. Глухов и др. – М.: Недра, 1983
- Гордов А.И., Жагулло О.М. Основы температурных измерений. – М.: Энергоатомиздат, 1992