采矿外文翻译---在煤矿主井通风设备中与安全有关的控制系统的用途.docx

英文原文THE USE OF SAFETY RELATED CONTROL SYSTEMS IN PRIMARY MINE VENTILATION RECIRCULATIONSYNOPSISThis paper describes a ventilation problem at a large underground coal mine.The Proposals were made to provide additional limitation of conventional solutions is ventilation quantity to the inbye workings discussed,along with the proposed solution by recirculating part of the return air using an underground recirculation fan in back into the intake at a point some 6km the primary mine ventilation system.from the shafts.This was to be achieved Foreseeable potential hazards associated by a recirculation fan of sufficient rating to overcome the pressure difference between with the proposals are identified.The paper describes the need for emergency shutdown of the recirculation fan and the use of a programmable electronic system (PES) to monitor and automatically initiate a shutdown in the event of predetermined criteria being exceeded.The system had to be designed to ensure the stoppage of the fan on early detection of adverse conditions, but unnecessary interruption of the ventilation system when conditions were satisfactory had to be minimised.The selection and assessment of the programmable electronics (PE) and the selection and location of suitable transducers to continuously monitor various parameters is outlined.The use of a transducer voting system controlled by the PE to take account of reliability and replacement of transducers is also described.VENTILATION PROBLEMLarge quantities of air have to be circulated through the underground workings of coal mines to dilute mine gases, prevent accumulations of mine gases, dilute dust concentrations, and provide reasonable working environments in terms of temperature and humidity.The resistance to ventilation in mine airways increases as the working places advance away from the TO maintain or increase the shafts.ventilation quantity may involve increasing the surface fan capacity, installing or uprating main underground fans (booster fans), minimising leakage paths between intake and return airways, providing additional airway capacity, or sinking extra shafts or boreholes.LIMITATION OF COVENTI0NAL SOLUTIONS At one coal mine where the undersea workings had extended over lokm from the shafts,large surface and underground booster fans had already been installed, and leakage paths minimised.The provision of additional airway capacity would take many years to complete and by itself would be unlikely to provide a satisfactory solution.The feasibility of sinking a shaft offshore was considered,but was not pursued due to cost, technical problems, and security.PROPOSED SOLUTION AND IDENTIFICATION OF ASSOCIATED HAZARDSProposals were made to provide additional ventilation quantity to the inbye workings by recirculating part of the return air back into the intake at a point some 6km from the shafts.This was to be achieved by a recirculation fan of sufficient rating to overcome the pressure difference between UK the return and intake airways.Present Mining Regulations prohibit recirculation in mine ventilation systems.However, selective exemptions have been granted by the Health and Safety Executive (HSE) to allow the successful use of recirculation techniques in the ventilation of drivages 15 years.When any exemption is for over considered the health, and safety of those employed at the mine should not be compromised in any way.HSE will Only grant an exemption subject to clearly or defined conditions designed to maintain improve the level of health and safety of the workers.Partial recirculation of air does not result in a build up of contaminant gases.The concentration of a contaminant gas in any ventilated region of a mine is given by the rate at which the contaminant gas enters the region divided by the flow of fresh air into the region.It does not depend on any recirculation that may be taking place Leach and Slack.19691.The most serious foreseeable hazards identified were the possible recirculation into the intake air of smoke and products of combustion or high concentrations of flammable gas (methane) Mitche11,19891.The products of combustion resulting from an outbreak of fire, if recirculated,would prevent escape from the workings through uncontaminated air.Protection against these hazards was to be based on early detection of adverse trends, stopping the recirculation fan and reverting to conventional ventilation.Stopping the recirculation fan would also have to be initiated in the event of excessive recirculation factor, fan vibration, and operation of the fire control apparatus at the fan site.Additionally, overcurrent, earth leakage, and pilot circuit electrical fault protection would need to be incorporated.Stopping the recirculation fan would result in a ventilation short circuit leakage path being opened between intake and return.Means to ensure this path was closed off had to be provided.THE NEED FOR AUTOMATIC SHUTDOWNThe need to stop the recirculation fan automatically in response to adverse considered necessary due to indications was the quantity and complexity of the environmental and associated data involved.This decision was taken prior to the design stage.It was clear that automatic control would need to be provided by a microprocessor based system capable of handling and processing data from numerous transducers.Dependence on lengthy data transmission lines to the surface control room was to be avoided and this ruled out the use of the surface computer to effect automatic control.The PE were to be installed in an underground substation near the fan.The automatic system would not provide for any discretion being exercised by the surface control room operator,and would not be liable to operator error.DEVELOPMENT OF VOTING SYSTEM TO INITIATE AUTOMATIC SHUTDOWN Methane and carbon monoxide levels in the return air would need to be continuously monitored.The recirculation of return air into the intake would need to be prevented by automatically stopping the fan at predetermined levels.The intake of the recirculation circuit would additionally need to be monitored for carbon monoxide, and the fan automatically stopped at a predetermined level see Fig 1Single environmental monitors were not satisfactory since a failure or erroneous indication might lead to interruption of ventilation when conditions were satisfactory,or in the event of an erroneous indication,permit continued operation in adverse conditions.A single monitor would also require the fan to be stopped for monitor replacement.In a system using twin environmental monitors,although maintained in a healthy state,the failure of a single monitor would result in the fan then being controlled from the remaining monitor.The use of three control environmental monitors was considered in which a failure or adverse indication from any two would initiate a stop.Conversely,for the fan to continue running would require a healthy indication from at least two monitors.This voting system was considered to be the most appropriate control.A single monitor failure would not stop the fan and the system would permit replacement of a monitor without interrupting ventilation.The three sets of three monitors (two sets for carbon monoxide, and one for methane) would continuously supply data to the PE.The data would also be continuously transmitted to the surface environmental computer for information and display on thecontrol room VDU.The PE would process data from the sets of environmental monitors and from other sensors.It would be programmed to interrupt the pilot circuit of the recirculation fan and initiate a trip in response to predetermined criteria.An EPROM chip programmed in a non volatile memory contained the logic for the safety related and automatic shutdown of the fan.The instructions in the EPROM could be changed only by the manufacturer thus overcoming the need for security of access by non competent people.SYSTW DESCRIPTION1. FIREDAMP The Sieger BM3 methane monitor was selected as the control monitor to supply data to the programmable electronics on methane levels.This instrument operates over a range of 0 - 3% with an accuracy of +/- 0.1% (from zero to 1.25%).It is powered from a d.c.supply with a built in rechargeable battery permitting up to 30 hours operation independent of the external power supply.A set of three BM3s were installed to monitor the methane content in the return air of the recirculation circuit.The methane content in the main return airways was typically 0.5% with occasional peaks up to 0.7%.An automatic stop level of 0.8% was set initially, this being considered operationally practical, and took account of transient increases which might be experienced on stopping the recirculation fan.(b) CARBON MONOXIDE Monitoring of carbon monoxide was considered the most reliable means of detecting the products of combustion from an outbreak of fire.The Sieger BCOl carbon monoxide monitor was selected to supply data continuously to the PE.This instrument has three operating ranges up to 1000ppm,the appropriate range for this duty being 0 - 5Oppm.The BCOl has a similar battery back up to the BM3.The automatic stop levels were selected with due regard to operational carbon monoxide production from diesel exhausts and shotfiring fumes.A level of 5Oppm was established for the set of three control monitors in the main return airway and a level of 25ppm in the intake of the recirculation circuit.(C) RECIRCULATION FACTOR The recirculation exemption specified a maximum of 37% of the return air to be recirculated back into the intake, this proportion being known as the recirculation factor.While loss of control of the quantity recirculated in certain circumstances could lead to increased methane or carbon monoxide levels,protection was provided the arrangements previously described.$owever systems have been designed and installed to stop the recirculation fan in the event of loss of recirculation factor control.One system used air pressure transducers to monitor the pressure difference across the recirculation fan and associated booster fan and initiate a stoppage of the recirculation fan through the programmable electronics on either fan exceeding + or - 15% of the preset normal operating pressure.A second system was installed using Sieger BAS velocity monitors to compute the air quantity in the main return and the air quantity recirculated.The programmable electronics continuously compare the data and initiate a trip in the event of excess recirculation factor.4. VENTILATION SHORT CIRCUIT PROTECTION Stopping the recirculation fan would result in a ventilation short circuit leakage path being opened between the main intake and return airway.Since the safety features of the recirculation system were based on automatic shutdown, the closing of anti- reversal doors to prevent short circuiting also had to be designed for automatic operation.Hinged flaps were provided at the outlet side of the fan casing.These were opened by the pressure generated at the recirculation fan and closed by pressure difference when the fan stopped.Secondary, centre or side hinged steel doors were installed as back-up anti- reversal doors to the inlet or outlet side.The closure was assisted by counterweights.The positions of both sets of anti-reversal doors were monitored at the surface control room and the operation checked as part of the routine testing procedure.(e)OTHER PROTECTION A fire control water curtain was installed at the outlet side of the recirculation fan.This was activated by a fusible link in a tensioned wire.Breaking the wire causes the gravity operated supply valve to open.Operation of the valve also opens an electrical contact resulting in an automatic stop of the fan.Vibration monitorinq ecruiDment is Drovided - fin to seise and at the recirculation indicate any developing mechanical fault.A lower vibration level gives alarm indication.The fan is automatically stopped on reaching the higher vibration level.(f)OTHER CONTINUOUS lloNITORING Comprehensive continuous environmental monitoring was provided throughout the mine in addition to those sensors dedicated to the control of the recirculation fan.This was provided by various strategically placed monitors supplying.data to underground outstations, which in turn relayed information to the surface HINOS (Mine Operating System) computer via a data highway to provide records, and a display in the control room.Parameters monitored include firedamp levels, carbon monoxide levels and air quantities at face workings and auxiliary ventilated places.The recirculation fan monitoring data was transmitted to the surface via the same data highway.A totally separate carbon monoxide monitoring system was installed in the main conveyor roadways with transducers at lkm intervals.This system, known as the J Jones PDT 300 Envirosystem, had a separate data transmission highway operating on a constant current basis.This was connected to the surface control room where it received its power supply and displayed information on a VDU.Other equipment was also installed to continuously monitor the operation of the mine firedamp drainage system.THE PROGRAMMABLE ELECTRONIC SYSTEMThe complexity of the recirculating fan monitoring and control system necessitated the use of PE which when connected to the input/output transducers and linked by a data highway to the surface of the mine, forms a PES.It was decided that the PE would need to comprise two parts.The first would be a microprocessor located at the fan site some6km from the mine shaft and the second would be the existing surface MINOS computer with its twin DEC PDP 11/73 mini-computers.The former would be a Transmittion Ltd General Purpose Monitoring and Control Unit (GPMC) type AA.It would be configured as an intelligent station with various input and output devices and would operate essentially in a Control mode.The latter would display information in the surface control room and operate essentially in a Monitoring mode.This arrangement has the advantage that the safety related control functions are dealt with locally, are independent of the surface computer and the information transmitted via the data highway is kept to a minimum.The underground PE would in addition to any other safety assessments, need to be of a type Certified by HSE(M) as suitable for use in a potentially explosive atmosphere.CERTIFICATION OF PROGRAMMABLE ELECTRONICS As with other electrical equipment used at the underground fan site the PE needed to be certified as suitable for use in a potentially explosive atmosphere.This requirement is well known to manufacturers and users of Group I Certified Electrical Equipment (ie that used in mines susceptible to firedamp).The HSE(M) certification is in two parts, a pit worthiness assessment and the issue of a certificate of compliance with the appropriate standard HSE Electrical Equipment Certification Guide 1982.Historically, this involvement by the Mines Inspectorate in the electrical certification process has ensured that before equipment arrives for installation at the workplace all three of the following requirements are met: i) compliance with appropriate statutory requirements.(eg It has the necessary electrical protection and guarding required by mining law): ii) compliance with the relevant British or Harmonised European Standards relating to protection against ignition of flammable gas: iii) compatibility with accepted UK mining industry practice.where the intended equipment purchaser is British Coal HSE liaises with British Coals HQ electrical engineering staff who simultaneously carry out assessment under their Electrical Acceptance Scheme.This avoids misunderstandings and helps manufacturers to design equipment to suit the requirements of both the industry and the legislation.In the case of the recirculating fan PES, the Mines Inspectorate performed the pit worthiness assessment, British Coal performed the acceptance assessment and HSE(M) Buxton certified the apparatus as complying with BS 1259:1958 as an Intrinsically Safe System comprising intrinsically safe apparatus.The non IS (power) circuits were contained within flameproof enclosures certified to BS 4683:1971 with an interface from the PES to the power circuit via a hardwired pilot circuit.The analogue signals from the measuring instruments,such as the methanometers,were designed to comply with BS 5754:1980 and the overall quality control of the manufactured products was checked by British Coal to be in accordance with BS 5750:1987.Having dealt with the flammable gas ignition risk,the legal requirements and some of the safety related aspects of the hardware,there remained a need to assess the system as a whole.ASSESSMENT OF TEE PES i) The surface minos computerThe British Coal HINOS computer has operated in over 160 separate installations throughout the world.The DEC PDP hardware is used in millions of other computers.AS British Coal write and have control over their own MINOS software, there is vast experience with both the hardware and the software.This experience, coupled with the fact that the data transmission system would also be constructed to BS 6556:1985 system,indicated that detailed safety assessment of this part of the PES would be unnecessary.ii) 输入输出设备The input and output devicesThe main problem which arose in the assessment of the input/output transducers,was that of attempting to reduce the risk of failures to the unsafe mode by Common Cause Failure (CCF).For example, while several types of methane monitor were available on the market all but a few operated using a hot pellistor in a Wheatstone bridge.These are susceptible to head poisoning and calibration drift when used continuously in methane concentrations of about 1% in air.In this si