Stronghold Digital wants to burn tires for fuel, environmental groups strike back

Stronghold Digital Mining is a Pennsylvania-based miner that repurposes waste coal for bitcoin mining

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In a move that’s sparked outrage from environmental groups, Stronghold Digital Mining is looking to continue burning tires to fuel its bitcoin mining data center in Nesquehoning, Pennsylvania.

StateImpact Pennsylvania, a reporting project of NPR member stations, reported on Stronghold Digital’s plans last Friday, which led to the Clean Air Council issuing a public rebuke on X, formerly Twitter.

“We are calling on state regulators and [the Pennsylvania Department of Environmental Protection] with [Earthjustice] and [PennFuture] to deny a permitting request from Stronghold Digital Mining to burn tires as fuel for its bitcoin mining operations,” the non-profit wrote on Monday.

Stronghold Digital told Blockworks that Pennsylvania-based environmental groups like PennFuture and Earthjustice “paint a really inaccurate picture.”

The Pennsylvania-based miner added that it already had a temporary permit from the state’s Department of Environmental Protection (DEP) to use tire-derived fuel, in other words, energy that is produced by burning tire scraps.

“The current application process with DEP is to obtain a permanent permit…to continue to burn the [tire-derived fuel] in the same manner and [in] limited quantity, given [that] several years of testing have proven no adverse effects,” a company spokesperson told Blockworks in an email.

Blockworks reached out to the DEP, PennFuture and Earthjustice for comment, but didn’t receive any responses before publication.

But how bad would burning tires for fuel be? To answer that question, let’s take a closer look at what happens when tires are melted down.

According to the US Environmental Protection Agency (EPA), in uncontrolled tire fires, tires will break down into hazardous materials including “gases, heavy metals and oil.”

That’s not the end of it though, because when burned, tires also produce emissions that contain “polycyclic aromatic hydrocarbons (PAHs), benzene, styrene, phenols and butadiene.” Earthjustice also pointed this out in an Aug. 21 press release.

Many of these chemicals have the propensity to cause cancer in humans. Benzene, in particular, has been definitively classified as a carcinogen.

Stronghold Digital told Blockworks that random tire fires do not reflect its operations.

At the Nesquehoning location, dubbed the Panther Creek site, the company uses two circulating fluidized bed combustors (CFBs) — a type of boiler — to burn waste coal, a byproduct of coal mining, and tire scraps.

According to Science.gov, CFBs have been known to completely vaporize ventilation air methane from the act of burning coal.

Stronghold Digital collects waste coal from polluted areas in the state with the help of the DEP, a spokesperson told Blockworks. That waste coal is then converted into energy that, in part, is used to mine bitcoin. Some of it is also transferred back to the grid.

Stronghold Digital wants to continue limited use of tire-derived fuel, which it says accounts for less than 7% of the burned material at its 80 megawatt power plant in Nesquehoning.

Additionally, the EPA does in fact support tire-derived fuel as an alternative to fossil fuels. That’s because tires often end up in landfills, and if they catch fire, that could lead to even more disastrous consequences than if a third party had burned them in a controlled manner.

“Disposal of scrap tires in tire piles is not an acceptable management practice because of the risks posed by tire fires,” the EPA wrote in a 2005 memo.

In a 2016 article, the EPA added that “it is better to recover the energy from a tire rather than landfill it.”

And in the DEP’s copy of a general permit for the disposal of tires, it lays out exactly how tires ought to be used for energy production.

“The permitted beneficial use of whole waste tires, tire chips, baled tires, tire shreds, and crumb rubber is limited to use in recapping, as fuel in boilers or other combustion units,” the permit stated.

Updated Aug. 30, 2023 at 3:24 pm ET: Additional context provided by Stronghold Digital regarding operations at its Panther Creek site

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