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Monitoring and control systems to minimise the influence of mining plants on environment
Copyright ® IFAC Future Trends in Automation in Mineral and Metal Processing, Finland, 2000
MONITORING AND CONTROL SYSTEMS TO MINIMISE THE INFLUENCE OF MINING PLANTS ON ENVIRONMENT
Wladyslaw Mironowicz, PhD Stanislaw Wasilewski, PhD Research & Development Centre for Electrical Engineering and Automation in Mining EMAG Katowice, Poland
Abstract: Mining carries a great number of noxiousnesses for the environment. In the deep coal mines, there are many hazards in underground workings and on the surface around mining plants. The mine ventilation systems emit to the atmosphere large quantities of air including mine air constituents from which methane, CO or CO2 have an effect on air pollution around the surface ventilation stations. The noxiousnesses of ventilation stations are equally vital owing to considerable consumption of electric energy and noise making. One of the possible minimisation forms is complex monitoring of ventilation stations within the range of upcast air parameterS, reduction in electric energy consumption by the control systems of the fan motors. The scattered monitoring system of ground deformations and damages to industrial objects, apartment buildings and housing estates can be used for observation of mining activity on the surface. Coal preparation plants are the essential sources of environment pollution. It is considered to monitor and control coal quality parameters underground. Copyright @2000 IFAC Keywords: measuring, monitoring, control applications, computer systems, cascade, environmental engineering
1. INTRODUCTION
reduce fire hazard. Pressure below atmospheric produced by main fans, has an important influence on these hazards. Continuous regulation of the fan output makes it possible not only to minimise hazards but also to reduce electric power consumption and ventilation costs. This especially concerns the modernised mines and those being under liquidation where it is necessary to limit excess air flowing through mine workings. Operational tests have shown that a decrease in the fan rotational speed for the purpose of their efficiency reduction results not only in economic benefits, owing to reduction of electric energy consumption, but also in reduction of gas emission to atmosphere through upcast shafts and of noise around the fan station.
Natural resources mining are bound together with a series of the natural environment disturbances. In the case of deep hard coal mines an unfavourable effect concerns both the underground workings as well as on the surface in the surroundings of mining plants. Harder and harder mining conditions connected with exploitation depth, gas emission from beds and thermal hazards, compose a high level of natural dangers underground in mines. To protect environment and workplaces of miners at underground workings the hazard monitoring and ventilation control systems are used. The purpose of these systems is to provide such conditions that at any moment a fire or methane explosion risk would not arise and thermal conditions (climatic) have to fulfil mining standards. The idea of ventilation monitoring and control is based on continuous measurement of air parameters and emergency signalling, and also on automatic de-energising in methane explosive conditions.
Tests related to monitoring of mine influence on environment have shown that upcast shafts make the emission source of both the gases producing greenhouse effects (C~, CO2) and toxic ones (CO, S02, NoJ. As it results from that all actions tending towards the reduction of gases emission have an effect on the decrease in the mining plants arduousness for environment.
Resulting from mmmg the voids make gases containers of remarkable capacities-therefore the action of ventilation services aims at such ventilation control to not permit the dangers caused by gas release. Equally the control of mine ventilation has to
Exploitation of coal beds especially at Upper Silesia collieries and heavily-urbanised and denselypopulated areas carries the hazards related to ground vibration due to tremors. The new monitoring and
323
measuring seismic apparatus placed around the mines provides to record ground vibration and warn of dangers and in the critical situation it can stop mine operation. Coal preparation plants, on mine site, using various technologies improve qualitative parameters of dressed coal, producing at the same time remarkable quantity of dust on heaps of refuses. One of the methods to limit these pollutants is modernisation and automation of coal preparation plants. But this method reduces only the results and has no effect on the causes. It seems that the underground coal quality monitoring system makes a more effective and perspective way. Fig.l.The SMP methane and fire hazard monitoring and ventilation control system.
2. COMPUTER-BASED MONITORING SYSTEM FOR MINE VENTILATION
The system uses the microprocessor-based underground outstation type CCD, which participates in the exchange of data between underground sensors and the surface station and also ensures remote power supply to the sensors. The outstation enables continuous measurement of mine air parameters (8 analogue inputs), monitoring of binary signals (16 binary inputs) and also 4 control outputs.
The idea of the ventilation monitoring system (Balicki, et aI., 1997) is based on the continuous measurement of mine air parameters. The underground sensors (methane, carbon monoxide, smoke, velocity, temperature and pressure of air) deliver current information making a basis for monitoring the methane hazards and early detection of fires. This modem computerised dispatching system provides remote and continuous measurement of signals and signalling of abnormal condition and also automatic electric energy switching-off.
The surface central station provides a supply of underground systems and data transmission. It consists of a data transmission system, a power supply system and a master IBM PC computer.
Its hierarchic and modular structure allows its adaptation to the needs of large and small mines. The system includes analogue and binary sensors, local underground outstations and central station on the surface. The system structure is shown in Fig. 1.
The SMP dispatching system, put into practice with a success at hard coal mines (Balicki, et aI., 1997), provides among others: - continuous monitoring and control of methane and fire hazard and other ventilation parameters - central supply of all underground equipment (outstation and sensors) from the surface, - automatic switching-off of electrical energy during alarm and abnormal situations, - early fire detection, - monitoring of air parameters, even during a fire, due to remote supply, - supporting a dispatcher during rescue operation after a fire alarm and mine staff in fire fighting, - monitoring of ventilation parameters and ventilation units operation to prevent hazard state, - monitoring of air distribution in a network to limit air leakage, - monitoring and control of the main fan parameters and energy consumption.
At present a series of air parameters sensors is used in the system, among them: - MM-2 microprocessor-based methane monitor, with 0+ 100 %CH4 continuous measurement range, - CMN-l methane sensor, with 0+5%CH4 continuous measurement and high concentration signalling, - ACO-4 carbon monoxide analyser, based on electrochemical cell, with measurement range of up to 0.02 % of CO volume, - ACD-I analogue ionisation smoke detector, - CT-2 air temperature sensor; range: 0+50oC, - CTG-2 rock and coal mass temperature sensor; range: 0+50oC, -AS-2 ultrasonic anemometer, range: 0+±15 mls, - TS-2 oxygen sensor, based on electrochemical cell with measurement range of 0+ 25% of 02, - CRC pressure difference detector based on pneumomechanical measuring converter within ranges: 0+±500 Pa for doors and: 0+6hPa for main fans depression.
3. VENTILATION MONITORING AND CONTROL SYSTEM The control of the main fan causes disturbances in the network, therefore the continuous monitoring of the
324
In practice, a way of adapting the fan parameters to a network are (Fig. 3): a change in setting of steering instrument or blade angle, use of air bleeds or its throttling on dampers in channels of main fans. Throttling of flows by stopping in network is also very popular and used now by about 65% mines in Polish coal mines (Wasilewski 1995b). All of these ways are uneconomical and they generate remarkable losses of energy. Throttling is also unfavourable from the ventilation point of view, because it causes an increase in fan pressure as well as fire hazard in ventilation system.
ventilation process is required in order not to let, at any time, break the safe work of the miners. Such monitoring can be realised by a dispatching system of continuous recording of the ventilation parameters (Balicki, et al., 1997), with current signalling of state at the mine dispatcher's e.g. the SMP monitoring system of methane-fire hazards and ventilation.
3.1. Monitoring offan operation.
Monitoring of the operation of the main fans at the shaft is performed in accordance with the regulations being in force in Polish mining, at the same time all parameters of the main fan operations are recorded and documented. Besides, the operation state of the equipment and all shut-downs are signalled at the dispatcher's room. The ventilation monitoring system records the following parameters: - fan output, - static pressures in fan channel (in front of and over a damper), - static pressure in the shaft, - gas concentration in output air, - active power of drive (electric energy consumption by fan), - temperature of bearings.
p ""
I - - --
0.8
+-----__+.
~-__+-=-~___I
0.6
0.21----
o
0 .2
--+--
-
-A- - - - - i - --
0 .6
--
..
---0""
Fig. 3 Comparison of changes in fan power Pw for various ways of changing its performance Q: a - throttling, b - adjustment of stator blades, c - rotational speed control.
In 1995, the first system of this kind was applied at the MIECHOWICE mine (Trutwin et aI., I 995a) where additional devices enabling on-line measurement, recording and monitoring of fan operation parameters were installed. At present a few mines use this solution.
As it results from Fig. 3, the same efficiency can be achieved at different power consumption. Method "c", i.e. change in the fan drives rotational speed features the highest effectiveness and an additional advantage of this method is the simplicity of control equipment. In this case the energy saving can be quite easily estimated from the known relationship (Roszczynialski et ai., 1992):
3.2. Adjusting the main fan parameters to simplification ofthe ventilation network.
:' ~ (:,r
Modernisation of the ventilation system and liquidations of some parts of the network cause changes in resistance of the ventilation system, and usually the operating point (Fig. 2) has a tendency to go to the right (fan output increase). This causes an increase in fan pressure as well as a high fire hazard in the ventilation system as well as gas emission from goaf (gas bunkers).
where P, P' are values of power consumption before and after speed change, n, n' are corresponding values of the fan rotational speed. This is favourable from the economical point of view, and owing to the dependence of driving power in the third power on rotational speed it can bring up to 80% savings of electric energy at full range of regulation.
4. OPERATIONAL TESTS ON FAN CONTROL SYSTEM The control by change in the rotational speed of the main fan drives is the most profitable method to readjust the fan operation parameters to the needs of a mine. Exactly such a control of the main fan output at the ,,Bangow" shaft by changing rotational speed
Fig. 2. Changes in the operating point on main fan characteristic. 325
using subsynchronous cascade was used at SJEMIANOWICE mine under liquidation (Wasilewski and Wikiera 1997). This is profitable not only from the ventilation viewpoint but also from the economical one. First of all, the real range of the WPK-3,9 fan output regulation at ,,Bangow" shaft with a cascade was determined. It was the range within 1,0-0,68 nominal rotations.
~
4.2. Hazard produced by unstable operation during main fan control. Changes of the network parameters as a result of the control process, cause ventilation transient states, which under some conditions may lead to emergency states. A dangerous transient state in the fan network arrangement (Trutwin et aI., 1997) was recorded during the experiment on working point control of a main fan of axial type which operates with network on the left part of the ''with-saddle'' fan characteristic. The change of working point was obtained by change of the network characteristic inclination by alternating degree of damper opening. Under some conditions the transient states occurred with abrupt changes of air output and pressure of high amplitude. The changes were of underable character (so called ''pumping of the fan") and similar to unstable flow i.e. such in which, owing to small disturbances, the large out-of-control changes of air pressure and output in ventilating channel followed and which then propagated along mine ventilation system. These transient states of the fan - network system operation are dangerous and can result in mechanical damage of the fan.
operating point
Fig. 4. The WPK-3.9 fan characteristics for different drive speeds The characteristic of the WPK-3 .9 fan was determined for various rotational speeds (Fig. 4) and the different motor revolutions (ni' = 93%, n2' = 80% and n3' = 68%). The tests have proved a wide range of fan parameters regulation and the parallel curves for rotational speed change confirm the usefulness of this kind of regulation.
Approaching the fan control one should remember that every change in operation parameters of fan disturbs the condition of mine ventilation system. That means that control must be conducted with the observation of specific rigours so, as at any moment emergency for men working underground does not arise. The parameters of fan operation (in main fan channel) and the state of the air parameters should be currently monitored that the out-of-control hazardous states do not come into existence at a given time.
4.1. Estimation of active power consumed by fan drive To estimate active power absorbed by the WPK-3.9 fan drive with a cascade the total power consumption for various rotational speeds has been determined. The tests have shown that in case of the cascadecontrolled drive the total power consumption is equal to the difference between input power of the motor and output power to network by a cascade transformer. The first operational effects have proved (Wasilewski and Wikiera 1997) that together with rotational decrease not only the power consumed by the motor diminishes but additionally the power developed by cascade transformer increases (Fig. 5), that means improvement in the system efficiency. P 600
5. THE INFLUENCE OF MINING PLANTS ON THESURFACEENVmONMENT
5.1. The ARP 2000 measuring system ofdispersed structure to record vibration acceleration of the earth face, produced by mining tremors. Recently much attention has been drawn to the effects of mining tremors on the face of the earth. Mining processes disturb geomechanical equilibrium of rock mass. These produces ground cracking going together with violent liberation of energy. A part of released energy, in a form of elastic vibration, produces mining tremors which, producing an effect on the surface, create a danger for building objects causing their damages. The last seismic events at Upper Silesia, owing to the buildings vibration at the "Paderewski" housing estate resulting from not-deep tremors, have led to stoppage of mining at the
j ...___• ....;Acti:·ve power consumed by motor
500 400 300 200
Total active ~r
100 -100 -200
Active power d8\leloped by transformer
Fig. 5. Total active power consumed by fan drive for different drive speeds.
326
"Katowice" hard coal mine. This fact has confirmed the need to record ~e mining tremor effects. An effect of tremors on the surface is relative to many factors, among them the tremors energy, their hipocentral distances and also the mechanisms of tremors forming, the way of elastic energy radiation, geomechanical parameters of rock medium, geological structure, tectonic net and local structure of surface measures. An effect of tremors on surface has random structure with defined entropy level. Therefore the estimation of tremors effect must be made by means of hypothetical methods. The statistic methods require the proper excess information (suitable redundancy), so a network of a great number of measuring points should conduct the effects on the surface.
of coal quality is essential for overall on-line control in coal preparation plants. The basic parameters to be measured on-line are ash and moisture content in coal. Measurement methods use radiometric ash and microwave moisture metering. Recently the sulphur content has also become an important parameter to be monitored. The coal preparation plants produce many pollutants, which are stored on the surface. The ash pollution from dump can be danger for environment of mining plants. Recently at Polish hard coal mines the use of the underground coal quality monitoring and control system for raw coal from different areas has been considered. Such system was implemented in two collieries. To avoid radiometric devices in underground, the special methods for measuring natural coal radioactivity are used.
The ARP 2000 measuring system has been developed (Cianciara and Isakow 1997) and put into practice by EMAG Centre. The system has dispersed structure and modem transmission of the recording results of the ground vibration acceleration produced by mining tremors. It enables remote acquisition and central processing of measuring data. The system provides: - ternary recording in the tens of local measuring concentrators, placed in areas being in the distance of some or a dozen or so kilometres from coal mine drawing shaft or copper ore output shaft, - precise synchronisation of time base in local measuring concentrators and in recording devices at adjacent mines, - recording of seismic events on the surface with the most possible dynamics for signal changes. (dynamics of90 dB), - ternary recording of ground vibration by the accelerator sensor or optionally electrodynamical velocity ones within the frequency range of 0,5 to 500Hz, -local processing of signals in probes and their digital transmission to local concentrator, - detection of important events in local measuring concentrator, buffering of recording in internal store (SRAM) with battery support and preliminary processing of recorded data, - reliable, two direction wire or wire-less digital transmission by means of data transmission in the Plus GSM system between local measuring concentrators and a data concentrator in the processing part, - buffered power supply of concentrators.
The possibility of using the natural radioactivity of coals for continuous ash content measurements is the subject of research activities elsewhere in the world as well as in Poland (Mironowicz and Sikora 1998). As a result of this research a prototype of the ROOOS ash-meter, developed by the EMAG Centre, carried out industrial application tests in some coal mine. Test results obtained so far have shown that the accuracy of ash content determination achieved by the natural radioactivity method is comparable with other radiometric methods, being approximately 1.5 % for coarse coals and better for small. The moisture content or the chemical composition of coal does not essentially influence the accuracy.
5.3. Monitoring the gas pollutants emission from upcast shafts at hard coal mines
Intensification of the greenhouse effect following human activity and rapid growth of concentration of dangerous toxic gases in the air caused degradation of the ecological system. The upcast shafts at deep coal mines are the sources of gas emission to the atmosphere. Research projects have shown (Zgadzaj 1997), that gases disposed to the atmosphere through upcast shafts may be roughly divided into two groups: - The gases contributing into the expansion of the greenhouse effect (C0 2, CRt). Although they do not constitute an immediately hazard to the human health or life but have negative impact on the environment around mining plants. - The toxic gases, constituting a serious hazard to the human health (CO) and others, appear in the trace quantities (S02, NOx, H2S). The emission of gaseous pollutants appearing in the exhaust air of hard coal mines depends on fan output. Implementation to the deep coal mines of the system for monitoring and control of the main fan can be a tool to reduce this effect.
5.2. The coal quality continuous monitoring and control system in underground
The coal quality continuous monitoring systems (ash and moisture content, calorific value) for coals transported on belt conveyors have been developed (Mironowicz and Sikora 1998) for coal preparation products in coal preparation plants. The monitoring
327
Proceedings of the Conference: ,,Aerology '97", Mechanizacja i Automatyzacja Gornictwa 1111997. Wala A. Investigation ofDynamical Properties ofAir Flow Control in Mine Headings by Means of Modelling Methods (in Polish). Mining Problem Handbooks PAN Vol. 10/2 1972. Wasilewski S.: Monitoring and control of ventilation in underground mines for processes minimalization of energy consumption in fans stations. Reports of the Project No MPIBOM92-96 financed by Marie Curie-Sklodowska Polish-American Joint Found, Katowice 19931995. Wasilewski S.: Monitoring and control of main fans in underground mines (in Polish). Proceedings of the ICAMC'95 Conference, Gliwice Poland 1995. Wasilewski S. and Wikiera T.: Ventilation control in hard coal mines under liquidation. Operating (in Polish). Mechanizacja experiments i Automatyzacja Gornictwa 12/1997. Zgadzaj J. Contamination of air as a result of emission of gaseous pollutants from upcast shafts at hard coal mines. Proceedings of the Second World Mining Environment Congress Katowice Poland May 1997.
6. SUMMARY
The projects being under development in EMAG Centre aim at implementation of measuring, monitoring and control systems to minimise the arduous effects of mining plants on natural environment. Investigations show that an energysaving control of the rotational speed of the main fans makes the most effective way not only from the economic point of view but also to improve safety by reducing fire hazard in hard coal mines. . Savings obtained by using the modem and energy-saving control of fan output at SIEMlANOWICE mine have been estimated at 115 000 USD per year assuming the energy cost as 0.04 USD per 1kWh. The savings allow that the expenditure of money will soon be refunded. Mine operational tests have also shown that hazards may go together with the control of main fans. That is why monitoring of parameters in fan station is a very important not only from economical point of view but also reduction of the gas emission effects of upcast shaft. The way to minimise influence of mining plants on environment is to install the measuring equipment underground to monitor and control coal quality before coal is lifted on the surface. Monitoring of the ground vibration around the colliery, especially in heavy urbanised region, in critical situation can cause stopping of mine operation.
REFERENCES Balicki W, Mironowicz W, Mroz J, Wasilewski S: Monitoring and control of mine ventilation (in Polish). Proceedings of the Conference: ,,Aerology '97", Mechanizacja i Automatyzacja Gornictwa 1111997. Cianciara B., Isakow Z. The system of remote monitoring of the surface hazard with tremors produced by mining. Proceedings of the Conference "The New Application for Mining Electricity and Automation" Ustron 1997, Mechanizacja Automatyzacja Gornictwa 12/1997. Mironowicz W., Sikora T. Rapid quality analyzer for coals and coal preparation products (in Polish) Proceedings of the XIII International Coal Preparation Congress, Birsbane Australia October 1998. Roszczynialski W., Trutwin W., Waclawik J.: Mine ventilation measurements (in Polish) Publishing House "Slask", Katowice 1992. Trutwin W., Wasilewski S., Sielski J. Observation of Unstable Operation of the Fan (in Polish) 328
MONITORING AND CONTROL SYSTEMS TO MINIMISE THE INFLUENCE OF MINING PLANTS ON ENVIRONMENT
Wladyslaw Mironowicz, PhD Stanislaw Wasilewski, PhD Research & Development Centre for Electrical Engineering and Automation in Mining EMAG Katowice, Poland
Abstract: Mining carries a great number of noxiousnesses for the environment. In the deep coal mines, there are many hazards in underground workings and on the surface around mining plants. The mine ventilation systems emit to the atmosphere large quantities of air including mine air constituents from which methane, CO or CO2 have an effect on air pollution around the surface ventilation stations. The noxiousnesses of ventilation stations are equally vital owing to considerable consumption of electric energy and noise making. One of the possible minimisation forms is complex monitoring of ventilation stations within the range of upcast air parameterS, reduction in electric energy consumption by the control systems of the fan motors. The scattered monitoring system of ground deformations and damages to industrial objects, apartment buildings and housing estates can be used for observation of mining activity on the surface. Coal preparation plants are the essential sources of environment pollution. It is considered to monitor and control coal quality parameters underground. Copyright @2000 IFAC Keywords: measuring, monitoring, control applications, computer systems, cascade, environmental engineering
1. INTRODUCTION
reduce fire hazard. Pressure below atmospheric produced by main fans, has an important influence on these hazards. Continuous regulation of the fan output makes it possible not only to minimise hazards but also to reduce electric power consumption and ventilation costs. This especially concerns the modernised mines and those being under liquidation where it is necessary to limit excess air flowing through mine workings. Operational tests have shown that a decrease in the fan rotational speed for the purpose of their efficiency reduction results not only in economic benefits, owing to reduction of electric energy consumption, but also in reduction of gas emission to atmosphere through upcast shafts and of noise around the fan station.
Natural resources mining are bound together with a series of the natural environment disturbances. In the case of deep hard coal mines an unfavourable effect concerns both the underground workings as well as on the surface in the surroundings of mining plants. Harder and harder mining conditions connected with exploitation depth, gas emission from beds and thermal hazards, compose a high level of natural dangers underground in mines. To protect environment and workplaces of miners at underground workings the hazard monitoring and ventilation control systems are used. The purpose of these systems is to provide such conditions that at any moment a fire or methane explosion risk would not arise and thermal conditions (climatic) have to fulfil mining standards. The idea of ventilation monitoring and control is based on continuous measurement of air parameters and emergency signalling, and also on automatic de-energising in methane explosive conditions.
Tests related to monitoring of mine influence on environment have shown that upcast shafts make the emission source of both the gases producing greenhouse effects (C~, CO2) and toxic ones (CO, S02, NoJ. As it results from that all actions tending towards the reduction of gases emission have an effect on the decrease in the mining plants arduousness for environment.
Resulting from mmmg the voids make gases containers of remarkable capacities-therefore the action of ventilation services aims at such ventilation control to not permit the dangers caused by gas release. Equally the control of mine ventilation has to
Exploitation of coal beds especially at Upper Silesia collieries and heavily-urbanised and denselypopulated areas carries the hazards related to ground vibration due to tremors. The new monitoring and
323
measuring seismic apparatus placed around the mines provides to record ground vibration and warn of dangers and in the critical situation it can stop mine operation. Coal preparation plants, on mine site, using various technologies improve qualitative parameters of dressed coal, producing at the same time remarkable quantity of dust on heaps of refuses. One of the methods to limit these pollutants is modernisation and automation of coal preparation plants. But this method reduces only the results and has no effect on the causes. It seems that the underground coal quality monitoring system makes a more effective and perspective way. Fig.l.The SMP methane and fire hazard monitoring and ventilation control system.
2. COMPUTER-BASED MONITORING SYSTEM FOR MINE VENTILATION
The system uses the microprocessor-based underground outstation type CCD, which participates in the exchange of data between underground sensors and the surface station and also ensures remote power supply to the sensors. The outstation enables continuous measurement of mine air parameters (8 analogue inputs), monitoring of binary signals (16 binary inputs) and also 4 control outputs.
The idea of the ventilation monitoring system (Balicki, et aI., 1997) is based on the continuous measurement of mine air parameters. The underground sensors (methane, carbon monoxide, smoke, velocity, temperature and pressure of air) deliver current information making a basis for monitoring the methane hazards and early detection of fires. This modem computerised dispatching system provides remote and continuous measurement of signals and signalling of abnormal condition and also automatic electric energy switching-off.
The surface central station provides a supply of underground systems and data transmission. It consists of a data transmission system, a power supply system and a master IBM PC computer.
Its hierarchic and modular structure allows its adaptation to the needs of large and small mines. The system includes analogue and binary sensors, local underground outstations and central station on the surface. The system structure is shown in Fig. 1.
The SMP dispatching system, put into practice with a success at hard coal mines (Balicki, et aI., 1997), provides among others: - continuous monitoring and control of methane and fire hazard and other ventilation parameters - central supply of all underground equipment (outstation and sensors) from the surface, - automatic switching-off of electrical energy during alarm and abnormal situations, - early fire detection, - monitoring of air parameters, even during a fire, due to remote supply, - supporting a dispatcher during rescue operation after a fire alarm and mine staff in fire fighting, - monitoring of ventilation parameters and ventilation units operation to prevent hazard state, - monitoring of air distribution in a network to limit air leakage, - monitoring and control of the main fan parameters and energy consumption.
At present a series of air parameters sensors is used in the system, among them: - MM-2 microprocessor-based methane monitor, with 0+ 100 %CH4 continuous measurement range, - CMN-l methane sensor, with 0+5%CH4 continuous measurement and high concentration signalling, - ACO-4 carbon monoxide analyser, based on electrochemical cell, with measurement range of up to 0.02 % of CO volume, - ACD-I analogue ionisation smoke detector, - CT-2 air temperature sensor; range: 0+50oC, - CTG-2 rock and coal mass temperature sensor; range: 0+50oC, -AS-2 ultrasonic anemometer, range: 0+±15 mls, - TS-2 oxygen sensor, based on electrochemical cell with measurement range of 0+ 25% of 02, - CRC pressure difference detector based on pneumomechanical measuring converter within ranges: 0+±500 Pa for doors and: 0+6hPa for main fans depression.
3. VENTILATION MONITORING AND CONTROL SYSTEM The control of the main fan causes disturbances in the network, therefore the continuous monitoring of the
324
In practice, a way of adapting the fan parameters to a network are (Fig. 3): a change in setting of steering instrument or blade angle, use of air bleeds or its throttling on dampers in channels of main fans. Throttling of flows by stopping in network is also very popular and used now by about 65% mines in Polish coal mines (Wasilewski 1995b). All of these ways are uneconomical and they generate remarkable losses of energy. Throttling is also unfavourable from the ventilation point of view, because it causes an increase in fan pressure as well as fire hazard in ventilation system.
ventilation process is required in order not to let, at any time, break the safe work of the miners. Such monitoring can be realised by a dispatching system of continuous recording of the ventilation parameters (Balicki, et al., 1997), with current signalling of state at the mine dispatcher's e.g. the SMP monitoring system of methane-fire hazards and ventilation.
3.1. Monitoring offan operation.
Monitoring of the operation of the main fans at the shaft is performed in accordance with the regulations being in force in Polish mining, at the same time all parameters of the main fan operations are recorded and documented. Besides, the operation state of the equipment and all shut-downs are signalled at the dispatcher's room. The ventilation monitoring system records the following parameters: - fan output, - static pressures in fan channel (in front of and over a damper), - static pressure in the shaft, - gas concentration in output air, - active power of drive (electric energy consumption by fan), - temperature of bearings.
p ""
I - - --
0.8
+-----__+.
~-__+-=-~___I
0.6
0.21----
o
0 .2
--+--
-
-A- - - - - i - --
0 .6
--
..
---0""
Fig. 3 Comparison of changes in fan power Pw for various ways of changing its performance Q: a - throttling, b - adjustment of stator blades, c - rotational speed control.
In 1995, the first system of this kind was applied at the MIECHOWICE mine (Trutwin et aI., I 995a) where additional devices enabling on-line measurement, recording and monitoring of fan operation parameters were installed. At present a few mines use this solution.
As it results from Fig. 3, the same efficiency can be achieved at different power consumption. Method "c", i.e. change in the fan drives rotational speed features the highest effectiveness and an additional advantage of this method is the simplicity of control equipment. In this case the energy saving can be quite easily estimated from the known relationship (Roszczynialski et ai., 1992):
3.2. Adjusting the main fan parameters to simplification ofthe ventilation network.
:' ~ (:,r
Modernisation of the ventilation system and liquidations of some parts of the network cause changes in resistance of the ventilation system, and usually the operating point (Fig. 2) has a tendency to go to the right (fan output increase). This causes an increase in fan pressure as well as a high fire hazard in the ventilation system as well as gas emission from goaf (gas bunkers).
where P, P' are values of power consumption before and after speed change, n, n' are corresponding values of the fan rotational speed. This is favourable from the economical point of view, and owing to the dependence of driving power in the third power on rotational speed it can bring up to 80% savings of electric energy at full range of regulation.
4. OPERATIONAL TESTS ON FAN CONTROL SYSTEM The control by change in the rotational speed of the main fan drives is the most profitable method to readjust the fan operation parameters to the needs of a mine. Exactly such a control of the main fan output at the ,,Bangow" shaft by changing rotational speed
Fig. 2. Changes in the operating point on main fan characteristic. 325
using subsynchronous cascade was used at SJEMIANOWICE mine under liquidation (Wasilewski and Wikiera 1997). This is profitable not only from the ventilation viewpoint but also from the economical one. First of all, the real range of the WPK-3,9 fan output regulation at ,,Bangow" shaft with a cascade was determined. It was the range within 1,0-0,68 nominal rotations.
~
4.2. Hazard produced by unstable operation during main fan control. Changes of the network parameters as a result of the control process, cause ventilation transient states, which under some conditions may lead to emergency states. A dangerous transient state in the fan network arrangement (Trutwin et aI., 1997) was recorded during the experiment on working point control of a main fan of axial type which operates with network on the left part of the ''with-saddle'' fan characteristic. The change of working point was obtained by change of the network characteristic inclination by alternating degree of damper opening. Under some conditions the transient states occurred with abrupt changes of air output and pressure of high amplitude. The changes were of underable character (so called ''pumping of the fan") and similar to unstable flow i.e. such in which, owing to small disturbances, the large out-of-control changes of air pressure and output in ventilating channel followed and which then propagated along mine ventilation system. These transient states of the fan - network system operation are dangerous and can result in mechanical damage of the fan.
operating point
Fig. 4. The WPK-3.9 fan characteristics for different drive speeds The characteristic of the WPK-3 .9 fan was determined for various rotational speeds (Fig. 4) and the different motor revolutions (ni' = 93%, n2' = 80% and n3' = 68%). The tests have proved a wide range of fan parameters regulation and the parallel curves for rotational speed change confirm the usefulness of this kind of regulation.
Approaching the fan control one should remember that every change in operation parameters of fan disturbs the condition of mine ventilation system. That means that control must be conducted with the observation of specific rigours so, as at any moment emergency for men working underground does not arise. The parameters of fan operation (in main fan channel) and the state of the air parameters should be currently monitored that the out-of-control hazardous states do not come into existence at a given time.
4.1. Estimation of active power consumed by fan drive To estimate active power absorbed by the WPK-3.9 fan drive with a cascade the total power consumption for various rotational speeds has been determined. The tests have shown that in case of the cascadecontrolled drive the total power consumption is equal to the difference between input power of the motor and output power to network by a cascade transformer. The first operational effects have proved (Wasilewski and Wikiera 1997) that together with rotational decrease not only the power consumed by the motor diminishes but additionally the power developed by cascade transformer increases (Fig. 5), that means improvement in the system efficiency. P 600
5. THE INFLUENCE OF MINING PLANTS ON THESURFACEENVmONMENT
5.1. The ARP 2000 measuring system ofdispersed structure to record vibration acceleration of the earth face, produced by mining tremors. Recently much attention has been drawn to the effects of mining tremors on the face of the earth. Mining processes disturb geomechanical equilibrium of rock mass. These produces ground cracking going together with violent liberation of energy. A part of released energy, in a form of elastic vibration, produces mining tremors which, producing an effect on the surface, create a danger for building objects causing their damages. The last seismic events at Upper Silesia, owing to the buildings vibration at the "Paderewski" housing estate resulting from not-deep tremors, have led to stoppage of mining at the
j ...___• ....;Acti:·ve power consumed by motor
500 400 300 200
Total active ~r
100 -100 -200
Active power d8\leloped by transformer
Fig. 5. Total active power consumed by fan drive for different drive speeds.
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"Katowice" hard coal mine. This fact has confirmed the need to record ~e mining tremor effects. An effect of tremors on the surface is relative to many factors, among them the tremors energy, their hipocentral distances and also the mechanisms of tremors forming, the way of elastic energy radiation, geomechanical parameters of rock medium, geological structure, tectonic net and local structure of surface measures. An effect of tremors on surface has random structure with defined entropy level. Therefore the estimation of tremors effect must be made by means of hypothetical methods. The statistic methods require the proper excess information (suitable redundancy), so a network of a great number of measuring points should conduct the effects on the surface.
of coal quality is essential for overall on-line control in coal preparation plants. The basic parameters to be measured on-line are ash and moisture content in coal. Measurement methods use radiometric ash and microwave moisture metering. Recently the sulphur content has also become an important parameter to be monitored. The coal preparation plants produce many pollutants, which are stored on the surface. The ash pollution from dump can be danger for environment of mining plants. Recently at Polish hard coal mines the use of the underground coal quality monitoring and control system for raw coal from different areas has been considered. Such system was implemented in two collieries. To avoid radiometric devices in underground, the special methods for measuring natural coal radioactivity are used.
The ARP 2000 measuring system has been developed (Cianciara and Isakow 1997) and put into practice by EMAG Centre. The system has dispersed structure and modem transmission of the recording results of the ground vibration acceleration produced by mining tremors. It enables remote acquisition and central processing of measuring data. The system provides: - ternary recording in the tens of local measuring concentrators, placed in areas being in the distance of some or a dozen or so kilometres from coal mine drawing shaft or copper ore output shaft, - precise synchronisation of time base in local measuring concentrators and in recording devices at adjacent mines, - recording of seismic events on the surface with the most possible dynamics for signal changes. (dynamics of90 dB), - ternary recording of ground vibration by the accelerator sensor or optionally electrodynamical velocity ones within the frequency range of 0,5 to 500Hz, -local processing of signals in probes and their digital transmission to local concentrator, - detection of important events in local measuring concentrator, buffering of recording in internal store (SRAM) with battery support and preliminary processing of recorded data, - reliable, two direction wire or wire-less digital transmission by means of data transmission in the Plus GSM system between local measuring concentrators and a data concentrator in the processing part, - buffered power supply of concentrators.
The possibility of using the natural radioactivity of coals for continuous ash content measurements is the subject of research activities elsewhere in the world as well as in Poland (Mironowicz and Sikora 1998). As a result of this research a prototype of the ROOOS ash-meter, developed by the EMAG Centre, carried out industrial application tests in some coal mine. Test results obtained so far have shown that the accuracy of ash content determination achieved by the natural radioactivity method is comparable with other radiometric methods, being approximately 1.5 % for coarse coals and better for small. The moisture content or the chemical composition of coal does not essentially influence the accuracy.
5.3. Monitoring the gas pollutants emission from upcast shafts at hard coal mines
Intensification of the greenhouse effect following human activity and rapid growth of concentration of dangerous toxic gases in the air caused degradation of the ecological system. The upcast shafts at deep coal mines are the sources of gas emission to the atmosphere. Research projects have shown (Zgadzaj 1997), that gases disposed to the atmosphere through upcast shafts may be roughly divided into two groups: - The gases contributing into the expansion of the greenhouse effect (C0 2, CRt). Although they do not constitute an immediately hazard to the human health or life but have negative impact on the environment around mining plants. - The toxic gases, constituting a serious hazard to the human health (CO) and others, appear in the trace quantities (S02, NOx, H2S). The emission of gaseous pollutants appearing in the exhaust air of hard coal mines depends on fan output. Implementation to the deep coal mines of the system for monitoring and control of the main fan can be a tool to reduce this effect.
5.2. The coal quality continuous monitoring and control system in underground
The coal quality continuous monitoring systems (ash and moisture content, calorific value) for coals transported on belt conveyors have been developed (Mironowicz and Sikora 1998) for coal preparation products in coal preparation plants. The monitoring
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Proceedings of the Conference: ,,Aerology '97", Mechanizacja i Automatyzacja Gornictwa 1111997. Wala A. Investigation ofDynamical Properties ofAir Flow Control in Mine Headings by Means of Modelling Methods (in Polish). Mining Problem Handbooks PAN Vol. 10/2 1972. Wasilewski S.: Monitoring and control of ventilation in underground mines for processes minimalization of energy consumption in fans stations. Reports of the Project No MPIBOM92-96 financed by Marie Curie-Sklodowska Polish-American Joint Found, Katowice 19931995. Wasilewski S.: Monitoring and control of main fans in underground mines (in Polish). Proceedings of the ICAMC'95 Conference, Gliwice Poland 1995. Wasilewski S. and Wikiera T.: Ventilation control in hard coal mines under liquidation. Operating (in Polish). Mechanizacja experiments i Automatyzacja Gornictwa 12/1997. Zgadzaj J. Contamination of air as a result of emission of gaseous pollutants from upcast shafts at hard coal mines. Proceedings of the Second World Mining Environment Congress Katowice Poland May 1997.
6. SUMMARY
The projects being under development in EMAG Centre aim at implementation of measuring, monitoring and control systems to minimise the arduous effects of mining plants on natural environment. Investigations show that an energysaving control of the rotational speed of the main fans makes the most effective way not only from the economic point of view but also to improve safety by reducing fire hazard in hard coal mines. . Savings obtained by using the modem and energy-saving control of fan output at SIEMlANOWICE mine have been estimated at 115 000 USD per year assuming the energy cost as 0.04 USD per 1kWh. The savings allow that the expenditure of money will soon be refunded. Mine operational tests have also shown that hazards may go together with the control of main fans. That is why monitoring of parameters in fan station is a very important not only from economical point of view but also reduction of the gas emission effects of upcast shaft. The way to minimise influence of mining plants on environment is to install the measuring equipment underground to monitor and control coal quality before coal is lifted on the surface. Monitoring of the ground vibration around the colliery, especially in heavy urbanised region, in critical situation can cause stopping of mine operation.
REFERENCES Balicki W, Mironowicz W, Mroz J, Wasilewski S: Monitoring and control of mine ventilation (in Polish). Proceedings of the Conference: ,,Aerology '97", Mechanizacja i Automatyzacja Gornictwa 1111997. Cianciara B., Isakow Z. The system of remote monitoring of the surface hazard with tremors produced by mining. Proceedings of the Conference "The New Application for Mining Electricity and Automation" Ustron 1997, Mechanizacja Automatyzacja Gornictwa 12/1997. Mironowicz W., Sikora T. Rapid quality analyzer for coals and coal preparation products (in Polish) Proceedings of the XIII International Coal Preparation Congress, Birsbane Australia October 1998. Roszczynialski W., Trutwin W., Waclawik J.: Mine ventilation measurements (in Polish) Publishing House "Slask", Katowice 1992. Trutwin W., Wasilewski S., Sielski J. Observation of Unstable Operation of the Fan (in Polish) 328