FAMAC KWM system concept
Under methane hazard conditions, one of the main factors limiting extraction are cuts in the electricity supply in the longwall face area caused by exceedances of the permissible methane concentrations detected by automatic methane measurement systems. Resuming production is only possible after a decrease in methane concentration to a safe level, confirmed by the staff, and the start of the whole process of deposition. Due to the lack of electricity (including lighting), the use of downtime for other activities is limited.
The main task of the FAMAC KWM Methane Emissions Control System is to reduce downtime caused by power cuts by mine safety systems, while maximizing the longwall shearer's production capacity by making the shearer's speed limit dependent on its position in the wall and on the current dynamics of methane release along the longwall excavation, to prevent dangerous concentration.
The core of the system (Fig. 1) is the underground computer to which aerological data from the area (distribution of methane concentration along the wall, absolute pressure, air flow velocity in the bottom gallery) and data from the longwall shearer on the mining process (location, speed, load of the drives) flow. Additionally, important information about events affecting methane hazard in the area, as well as about work performed by the staff, which cannot be registered by the sensors available in the system, is input manually. Effective analysis and archiving of diverse data required designing an integrated environment based on modern non-relative databases: designed for time series for sensor data and for storing data in the form of documents for event information.
Fig. 1. Visual diagram of the FAMAC KWM system
The system operates by tracking the dynamics of methane release in connection with the course of the mining process and changes in ventilation parameters in the area, and on this basis determining the optimal (maximum) speed of the mining machine under given conditions, which is continuously sent to the control system of the longwall shearer.
Due to the unique nature of the data aggregated by the system, it was necessary to develop a special visual analysis tool (web application connected to a time series database), which clearly presents the change in the distribution of methane concentration along the wall in correlation with the mining process data (e.g. the machine's position) and allows to analyse the influence of process parameters on methane hazard. Ultimately, it is planned to integrate this tool with the FAMAC KWM system application.
FAMAC KWM system construction
The FAMAC KWM system includes (Fig. 2) built-in on selected sections (e.g. every 10÷20 sections) autonomous methane detection heads (1) connected via junction boxes (6) to the bus system running along the wall face. Each head equipped with an electrical connection is built in a steel sheath/sling to increase resistance to mechanical exposure and ensure convenient calibration or replacement (Fig. 3).
Fig. 2. FAMAC KWM system devices
An absolute pressure sensor (4) is installed at the entrance to the wall (from the side of the subwall gallery) and at its end. A wing anemometer (5) is connected to the voltage input of the sensor. Like the methane detection heads, the pressure sensors are connected to the bus via junction boxes (6 and 8).
The junction boxes are connected with 4-pin connectors, 20‑m long, bus cables (3). Two wires are used as a 12V power line and the others as a communication bus in RS 485 standard.
All sensors are 12-volt intrinsically safe power supply (7) powered, built in the subwall gallery.
Data from the longwall face measurement system are sent to an apparatus-mining computer (9).
An optical-acoustic signalling device (10) is installed in the vicinity of the computer, informing about possible damage to the FAMAC KWM system.
The underground computer runs the FAMAC KWM system application responsible for data acquisition and archiving, analysis of the dynamics of methane generation and determination of recommended mining parameters in order to reduce the probability of the central methanometric system turning off the power. The condition for the system to be operational was to equip the longwall shearer with a two-way communication link and a system for identifying the position of the shearer in the wall, as well as to modify the shearer software accordingly.
Fig. 3. Methane detection heads in the sheath
FAMAC KWM system application
The operation of the FAMAC KWM system is controlled from the EH-O computer installed in the longwall of the mine, on which a web-based visualization application works, as well as control and communication applications in the form of micro services.
The software has built-in mechanisms for automatic generation of backups, control of communication with the environment and monitoring of computer status (use of operational memory, disk occupancy, load on processor cores, time from turning on the computer).
On the main application screen (Fig. 4), the location of all sensors of the FAMAC KWM system in the wall area is shown. For each device, its status, the value shown and the trend indicator are visible. A separate window presents basic current operating parameters of the shearer - location, speed and load of the drives, as well as the maximum allowable mining speed determined by the system. On the application screen you will also find communication lights with the aerological parameters measurement subsystem, shearer and surface.
Wykres [W] – Figure [W]
Komunikacja [E] – Communication [E]
Konfiguracja [Y] – Configuration [Y]
Chodnik nr – Subwall gallery No
Fig. 4. FAMAC KWM application main screen
From the main screen, one can use the drop-down menu to access the screens that allow to track the time waveforms from the selected sensors (Fig. 5), configuration of the sensor network (Fig. 6), parameterization of the methane hazard analysis algorithm and speed control of the shearer, communication control and data archiving management.
Wykres [W] – Figure [W]
Komunikacja [E] – Communication [E]
Konfiguracja [Y] – Configuration [Y]
Fig. 5. Time signals of selected sensors during integration with test heads
The application was divided into four independent modules:
- Communication with the measuring system and calculations.
- Visualization by means of panels in a web browser.
- Time series registration.
- Registration of data in the form of documents.
Wykres [W] – Figure [W]
Komunikacja [E] – Communication [E]
Konfiguracja [Y] – Configuration [Y]
Odczytaj kolejność – Read the sequence
Zapisz – save
Wyświetl pliki lokalne – show local files
Wyświetl pliki na pamięci przenośnej - show files on portable memory
Kopiuj - copy
Fig. 6. FAMAC KWM system configuration screen
Visualisation panels are available locally as the main screen on the underground computer and can be viewed remotely from computers connected to the same network.
The modern technologies used (Node.JS + NodeRED and Docker) allow for the full system portability. It can be run independently of the hardware platform and operating system (either directly or after minor modification). It is also possible to disperse the system to many devices and redundant functionality on other programmable devices. Some modules can be transferred directly to the shearer controller, to the surface or, if necessary, to the servers in the organization's infrastructure or to the cloud.
FAMAC KWM system tests
Preliminary tests of the FAMAC KWM system were carried out between 26 January and 20 March 2019 for the configuration shown in Figure 2. During the tests, the resistance of the measuring heads to the conditions prevailing in the longwall excavation was confirmed and no significant discrepancies were found between the indications of the FAMAC KWM system and the methane concentrations recorded by the central methanometry system in the wall area. Despite the fact that the sensors were not calibrated, the time signals recorded by most of the heads comply with the theoretical character and correspond to the mining process and are in accordance with the indications of independent instruments.
During the tests, no excessive destruction of the system's devices was found, however, a significant problem in its operation was the maintenance of the bus cables conducted along the wall.
A significant difficulty in conducting the tests was the fact that the computer installed in the longwall, built directly above the conveyor belt, was not connected to the mine's Ethernet network, as a result of which it was practically unavailable during work shifts.
Due to a significantly lower than anticipated methane concentration in the area of wall, it was not possible to verify the possibility of limiting the number of energy cuts by temporarily limiting the speed of a longwall shearer mining.
Analysis of FAMAC KWM system test data
Special visual analysis tools developed in the framework of the project were used to analyse the collected data, allowing for efficient graphical analysis from various data sources. Written in JavaScript language, the web application cooperates directly with the time series database, using its capabilities of dynamic data aggregation, which allows for a very fast generation of methane distribution maps, on which the position of the shearer correlates with the load on its drives (Fig. 7).
Położenie kombajnu – shearer’s location
Fig. 7. Correlation between the position of the shearer in the wall and methane concentration - homogeneous colour scale
The distribution of methane concentration along the longwall face generated on the basis of measurement data is fully consistent with the theory - a significant increase in concentration in the upper part of the wall (Fig. 8).
Fig. 8. Distribution of methane concentration along the wall
Due to the large variation in methane concentration levels along the length of the wall, the impact of the shearer can only be observed for the last 20 sections. In order to highlight small changes in methane concentration in the lower part of the wall, the option of colour scale normalization was introduced, consisting in individual scaling of the colour scale for each sensor separately (normalization of sensor indication in the observed time range). The diagrams generated in this way clearly show a temporary increase in methane concentration in the vicinity of the cutting machine (Fig. 9).
Położenie kombajnu – shearer’s location
Fig. 9. The correlation between the position of the shearer in the wall and the methane concentration - colour scale standardised individually for each sensor
Summary of FAMAC KWM system tests
During the FAMAC KWM system's underground tests, the technical possibility of automatic adjustment of the longwall shearer's cutting speed in order to reduce the methane release in the longwall face was confirmed. The autonomous methane detection heads installed along the entire length of the wall provide information on the dynamics of methane release, which makes it possible to anticipate that the permitted methane concentration in the area can be exceeded and on this basis it is possible to determine the maximum permitted cutting speed. Such solution should allow increasing the availability of the mining machine by significantly reducing the frequency of power cuts in the complex by the central methane detection system. A confirmation of the effectiveness of the FAMAC KWM system will, however, be possible after further tests under conditions of a greater methane hazard.
Łukasz Herb
