Pandemic Impacts Longwall Production

Despite COVID-19 related curtailments and soft market conditions, the U.S. adds another face to its fleet

by steve fiscor, editor-in-chief

In a year that saw total U.S. coal production drop from 708 million tons in 2019 to 540 million tons, it would be foolish to believe U.S. longwall production would be immune to COVID-19. On a percentage basis, the 2020 decline in U.S. longwall production, which dropped 26.2% to 120 million tons from 162.7 million tons in 2019, followed closely with the overall decline in U.S.  coal production. Total U.S. coal production fell by 24% in 2020. This is clearly a coal sales problem, not a capacity problem, and the softness in seaborne coal markets last year might explain the two point difference in production figures.

There is, however, some good news to report. The total number of faces grew from 39 to 40 and the total number of longwall mines grew from 34 to 35. Those figures include two trona mines in Wyoming and five mines that operated two longwall faces. One longwall face was added in West Virginia, Arch Coal’s Leer South mine, which is expected to begin production during 2021. Foresight Energy began producing from its Deer Run longwall mine in Illinois, which was idled in 2016.

According to the latest statistics from the U.S. Mine Safety and Health Administration, none of the major longwall complexes achieved more than 10 million tons per year (tpy) during 2020. That has not occurred in at least 10 years. The annual production figures for the top three longwall mines, all of which operate two faces, ranged from nearly 8.9 million tons to nearly 7.2 million tons. Only seven longwall mines produced more than 5 million tpy in 2020. In 2019, 13 long-wall installations produced at a capacity of 5 million tpy or greater (See Table 2).

Several new names appear in this year’s longwall census. Murray Energy emerged from bankruptcy as American Consolidated Natural Resources (ACNR). Murray Metallurgical, which operates the Oak Grove mine in Alabama, is now Hatfield Metallurgical. Arch Coal changed its name to Arch Resources. Iron Senergy purchased the Cumberland mine in Pennsylvania from Contura Energy.

This year was a difficult year for coal operators. Many were forced to idle operations at different times due to the COVID-19 pandemic. The export market for metallurgical coal also softened. Coronado briefly suspended production at the Buchanan mine. Peabody was forced to suspend production at its Shoal Creek mine in Alabama during the third quarter of 2020 and it remains idle. That market is now recovering. (See Coking Coals, p. 30)

“After an extremely challenging second quarter of 2020, we saw steady improvement in the demand for our coal throughout the third quarter of 2020,” CONSOL Energy President and CEO Jimmy Brock said. “Our sales volumes at the Pennsylvania Mining Complex were nearly double those of the second quarter.” Brock expected to see further improvements for the fourth quarter and into 2021.

When fully operational, Leer South is expected to produce up to 4 million tpy of High-Vol A coking coal. It will operate in tandem with Arch’s flagship Leer mine for the next 20 years or more. “The Arch team continues to maintain great momentum at its world-class Leer South growth project, where development remains on time and on budget,” Arch COO John
T. Drexler said.

As of the third quarter of 2020, Arch had invested $256 million in the $390 million project. “Leer South is expected to enhance our already high-performing coking coal portfolio across every major metric — boosting our volumes, lowering our average unit cost, enhancing our overall product quality and expanding our profit margins across a wide range of market conditions,” Drexler said. “Moreover, with a gradually improving market outlook heading into 2021, we believe our decision to drive forward with the buildout during the recent market trough could prove highly advantageous as well.”

Industry Demographics

Longwall ownership in the U.S. remained relatively unchanged. ACNR and the companies it controls (Foresight Energy and Hatfield Metallurgical) operate 13 longwall faces spread across Alabama (1), Illinois (4), Ohio (1), Utah (1) and West Virginia (6). CONSOL Energy operates three mines with five longwall faces in Pennsylvania. Alliance Resource Partners, Arch Resources and Warrior Met Coal own three longwall faces.

With 11 faces, West Virginia remains the longwall leader, followed by Pennsylvania (6), Illinois (5) and Alabama (5).

Looking at the numbers, the average U.S. longwall mine operating in coal produced 3.75 million tons in 2020 compared to 5.21 million tons in 2019. On average, it has a cutting height of 95.6 in., a panel width (or face length) of 1,210.1 ft, and a panel length of 12,341.3 ft. Last year, those numbers were 96.4 in., a panel width (or face length) of 1,216 ft, and a panel length of 12,308.2 ft, respectively. A total of eight longwall faces have face lengths of 1,500 ft or greater. A total of 14 longwalls operate in the Pittsburgh No. 8 seam. The maximum overburden on average reaches 1,045 ft. Except for a few mines in Utah, most are developed with three entry gates. Using an 1,853.1-hp double-drum, ranging-arm shearer, they take a 40.2-in. cut. The average yield setting on the shields is 1,053.3 tons. All of the faces except for three operate at 4,160 volts. CONSOL Energy’s Crabapple face at the Bailey mine in Pennsylvania is the longest: 1,576 ft. Coronado’s Buchanan mine is the deepest at 2,000 ft. At 22,500 ft, Signal Peak Energy’s Bull Mountains mine in Montana has the longest panel.

Integrating Automated Systems

From a technology standpoint, more U.S. longwall mines are moving toward more automation or what Joy Mining Machinery calls “remote management,” explained Shawn Franklin, shearer product manager for Joy. “Long ago, longwalls established themselves as  the least manually intensive underground mining method and we’re now letting the equipment rely more on the sensors,” Franklin said.

Today, more shearers in the U.S. are running with Joy’s Advanced Shearer Automation (ASA) and these longwall operators are starting to see the benefits with consistent extraction heights and floor profiles. “The immediate, primary goal with remote management is to keep the operators out of harm’s way,” Franklin said. “Ultimately, the goal would be to let the equipment run from remote locations even on the surface. Different mines are at different points along that automation journey.”

The transition from describing remote operations as remote management reflects the role of the longwall operators, explained Allan Black, roof support product manager for Joy. “Remote operations would imply autonomous operations and that’s not really the case,” Black said. “These are highly automated longwall mining systems, not autonomous longwalls. The step change we are seeing is leap-frogging from remote management underground, where a remote management center located outby the stageloader
or even 300 m outby the maingate [or headgate], to a surface installation. The underground installation has to meet MSHA’s regulations regarding intrinsic safety, which limited the technology that could be used.”

With the surface installation, the operator still fulfills the same role. He starts the shearer, primes the roof supports and starts the armored face conveyor (AFC). He can monitor the performance of the dynamic chain control. He can monitor the cut, ASA and pitch steering. All the information is available to him. He can initiate a production start and monitor its progress.

“After a lot of discussion internally around remote operations, we felt we were almost setting expectations too high  compared to where the technology was,” Black said. “An automated system generates repeatable and predictable cuts from the shearer and predictable roof support cycles, but it doesn’t learn from its mistakes. So, you still currently need a certain level of human interaction.”

Someone needs to input the parameters. Take the lower, advance and set cycle (LAS) of a powered roof support as an example, the operators will set the parameters to achieve the optimum speed for the LAS. They know how far the roof support needs to be lowered. They know where they need to activate the base lift within the advance part of the LAS and how long it takes to set the support. These are currently user definable parameters so the system cannot learn and make changes itself.

“Levels of autonomy will come, but that’s the next generation,” Black said. “Some of the technologies with seam and band recognition are starting to get close.”

When it comes to automated cutting, many people wrongly assume that cutting the tailgate is the most difficult part of the mining sequence. “It’s no secret that the tailgate T junction is the unloved part of the longwall face,” Black said. “If conditions are suitable, no over break with little or no debris in the supports, automating the cutting sequence for the tailgate can be quite simple. It’s actually the easier end to automate provided the conditions are suitable. Automating the cutting sequence for the main gate can have major consequences dealing with the matilda, BSL alignment and the AF head frame itself when it goes wrong. This process, however, has also been successfully automated.”

New Technology for AFCs and Roof Supports

This spring, Joy will introduce OptiDrive for the AFC. “A constant speed AFC is limited as far as its ability to interact with face automation systems,” said Daniel Sharpe, AFC product manager for Joy Mining Machinery. “The next step for us is the speed control on the AFC, which will allow controlled production. The technology was introduced first in Australia and now at Alliance’s Tunnel Ridge mine in the U.S. This will be a huge achievement for the AFC team.”

The AFC OptiDrive system controls speed and torque via variable frequency drives. This is a step change from other variable frequency drives in the industry through the application of medium-voltage electrical systems (4,160 volts).

“With speed control, we have the ability to reduce chain travel that in turn reduces chain wear and wear to other associated products.”

“As panels get longer and wider and extended equipment life becomes more critical, fatigue, alongside wear, becomes a major factor,” Sharpe said. “Alongside speed control we are looking at destressing the chain system.”

Sharpe said AFC chain diameters will continue to increase with longer panels and wider faces. “Alongside reduction in chain travel, an effective way to increase chain life is to utilize Joy Broadband chain, which increases the diameter, contact points and therefore decreases the stress in the chain,” Sharpe said. “With Joy’s Broadband AFC chain, we can place a larger chain in existing AFCs.” He thinks that 60 to 64 Joy Broadband will soon be a reality and supersede the growing number of 56 Joy Broadband systems.

The new major improvement with roof supports will be made with the controls. “We are currently looking at high-speed data backbones for the in-support controls,” Black said. “That supports the new technology we’re introducing, such as optical cameras, which require additional lighting and a power source. The data backbone would also transmit data from the transducers such as inclinometers mounted on the roof support’s three main structural components (canopy, caving shield and rear links). With real-time data on the geometry of the support, we can determine where the support is and the potential collision hazards. We can also see convergence during long periods of downtime.”

The anti-collision information comes from the inclinometers or tilt transducers and the double-acting rams. “We know the shearer position and size and we can map it in relationship to the roof supports from the previous AFC advance to determine the potential for a collision,” Black said. “Proximity detection will also be an important part of these automated operations. With less people on the face, you need a system to watch over the humans. It goes hand-in-hand with automation.”

Black marvels at the fact that customers anywhere in the world can speak directly with Joy’s design engineers for roof supports in Manchester, England. “We have had several recent contracts for faces in the U.S. and Russia,” Black said. “Video conferencing tools were used for factory acceptance testing while COVID-19 lockdowns prevented travel. Customers were able to sign off on systems remotely.”

Looking toward the future, Franklin said he enjoys helping customers solve problems. Sharpe agreed saying that Joy has a global team looking after more than 100 longwalls worldwide that vary from sophisticated systems in mature markets to new systems in emerging markets.