Running a mine with a mouse — modern mine monitoring
From pit ponies to mice, coal miners have travelled a long way in terms of productivity and safety. Mining is still a hard job and conditions underground are testing, yet modern machinery and process control has changed the face of underground coal mining.
Increased sophistication of both machines and software has allowed total control of the process through supervisory control and data acquisition (SCADA) and other integrated systems. The former is not new to UK Coal, which owns the Daw Mill Colliery near Coventry, UK.
Previously, collieries used the mine operating system (MINOS), which was developed over a number of years and had proved reliable. However, it became increasingly obsolete, difficult to maintain, costly to support and unable to provide the process control required today. A better solution is to use an off-the-shelf, flexible system that can be tailored to the mining needs of the 21st century. The system, chosen after extensive study and evaluation of existing SCADA systems, is Wonderware’s Factory Suite.
Keeping in touch
The main benefit of this version of SCADA is the graphical interface that shows the coal mining and transport systems employed. Through a terminal server, total reporting and control of all operations is achieved.
The hierarchical system has a number of components. The applications machines have In Touch software installed to control the plant. Terminal servers have In Touch and Factory Suite Gateway installed, allowing local and remote access to the machines hosting that software.
These machines are the colliery control room and have 100% standby redundancy. They act as a link to the underground programmable logic controls (PLC), which have the ability to run the process should the external link to servers be lost. All the servers and software are linked to the control centre at the mine site, with access available from anywhere else in the world.
Linking all these components is a multimode fibre optic cable, transmitting on Ethernet carrying Ethernet IP. The Ethernet switches and media converters are all intrinsically certified safe and the type of fibre cable employed is an eight-core silica with a 62.5ºm inner and 125ºm outer. It is robust enough for mining applications. Daw Mill is currently transmitting data at 10Mb/s and looking to go to 100Mb/s. This compares well to MINOS on copper cable communications that transmits at 600 bits a second.
The modern coal face
At Daw Mill, the coal seam is mined using an automated coal shearer that tracks along the face. The roof above the mined coal is supported by hydraulically powered supports, and the coal is moved from the face by an armoured face conveyor (AFC) and beam stage loader.
Belt conveyors move the coal through the mine to the surface and onto the coal preparation plant. The major challenge is to ensure that all these components work seamlessly and actual or forecast events do not disrupt production.
The situation is complicated at Daw Mill by the disparate capacities of the components. The Eickhoff coal shearer under optimum conditions has the capacity to mine 4,000t/hr. Similarly, the armoured face conveyor underneath the coal shearer is rated at a maximum of 3,250t/hr. However, the conveyor belt system that moves coal from the coal face district through the mine and up the surface drift (the inclined roadway to the surface) has only a maximum load rate of 2,000t/hr.
Given all the other factors that can affect production, such as geology or machine breakdown, a computer-controlled system must be capable of alerting operators and determining the operating speeds of the equipment.
The powered roof support data is among some of the most used information at Daw Mill. Since being implemented, it has prevented many roof falls onto the AFC that can result in lengthy delays – in some instances up to five days.
It is possible to view the machine location with the chock and ram positions exhibiting leg pressures. Daw Mill has weak ground at the coalgate end of the face, up to around chock position 60. Many of the pressures in this area are as low as 1,600psi. From 60 chock to the tailgate, the roof is sound with the chocks set at around 4,800psi. This information is used in the daily management of the face.
The Eickhoff coal cutting shearer has an internal speed control that limits the maximum speed of the cut. It also controls the flit speed of up to 23m/min when not in full cut. The problem at Daw Mill, however, is the coal that spalls and falls onto the AFC. With a five-metre seam, this can be in large amounts.
Slowing the shearer can ameliorate spalling, and its speed can be controlled by the computer system in relation to the gate roadway belt conveyor capacity of 2,000t/hr. The system employed to limit the speed under these circumstances continually averages the current of the four Breuer variable speed electric motors that drive the gate conveyor. This value is sent by fibre cable from the conveyor PLC to the face PLC on the shearer, slowing the machine cut speed down proportionately and maintaining a constant capacity of 2,000t/hr. Indeed the biggest challenge faced today at Daw Mill is finding and using the optimum cutting speed for the coal face. The new system allows fine tuning of cutter speed.
The system control of the Breuer motors incorporates a frequency inverter that gives speed control from zero to maximum at full torque. This advantage translates into lower belt tensions, minimal belt stretch on start-up, control of the start-up torque, modular drive units that are easy to dismantle and transport, potential for matching gate belt speed to face performance, and slow speed facility available for belt change and joint examination. By comparison, a single head drive would need 560kN of tension requiring a Type 18 belt – as thick as a man’s arm. The logistics of handling this style of belt in these quantities is prohibitive.
The final part of the computer-controlled operation is the coal preparation plant supplied by the drift gateway conveyors. This plant has a maximum capacity of 1,000t/hr with the remaining feed going to stockpiles via a by-pass conveyor. Feed to the coal preparation plant (CPP) is via the drift conveyors and from the reclaim if there is insufficient coal from the drifts.
Providing the feeds are two Westerland units connected to the CPP via Ethernet. Once the rate is fed into the CCP controller the rest is automatically handled, providing coal from the drifts and the reclaim as necessary. The last feature of the system is a link to the Breuer motors on the drift conveyors that reduces to half speed when the by-pass conveyors are unable to cope with the 1,200t/hr potential. Once the bypass conveyor is up to speed, full power is restored to the drift gateway conveyors.
The installed system also allows a number of other measurements to be recorded throughout the mine, including methane levels, speeds, temperatures and currents of the electric motors of the shearer and conveyors, hydraulic pressures, water pump capacities and many other functions of the operating machinery. The nature of data transmission allows interrogation from the surface of all the underground machinery. It also allows remote access offsite.
Routinely the operating parameters at Daw Mill are interrogated via the UK Coal central server at Haworth HQ, which monitors the coal face some 150km from Daw Mill, 11km from the pit bottom and 700m below surface. Such is the flexibility and accuracy of data transmission that the Eickhoff machinery in action at Daw Mill can be viewed at the manufacturer’s facility in Germany, allowing others to undertake in the development of current and future machines.
This article is an edited version of the 2007 paper that won the Noel E Webster medal of the Midland Institute of Mining Engineers. It was presented at the National Coal Mining Museum for England, Caphouse Colliery, Wakefield, UK, with a live video link to Daw Mill and Eickhoff in Bochum, Germany.
To view detailed images, graphs and diagrams referred to in this feature, please download the PDF of the original article using the link below.