The whole area surrounding the sleepy village of Arigna, in County Roscommon, near the Leitrim border, was once one of Ireland’s lively mining and ironworks hotspot. Thousands of miners, generation after generation, extracted ore from the heart of the nearby rugged mountains. The dirty business of mining and smelting went on for four centuries – although with some hiatuses, as in 1690, when local charcoal production used to fuel the smelting process was disrupted when the once lush native forests of Connaught were all clear-felled! But I digress… 

[Arigna miners. Image courtesy of arignaminingexperience.ie (c)]

The ore provided a steadfast source of livelihoods for the many families settled in this harsh, penurious and ungenerous land. After the iron times, coal was discovered in the area in the final decades of XVIII, which carried the industry to the modern era. Until 1990, the year when the last remaining mine was shut down. The legacy of that past can be relived in Arigna Mining Experience interpretive centre. 

Nowadays, a relatively young enterprise inherited part of that legacy: Arigna Fuels. We in Good Energies Alliance Ireland paid them a visit, intrigued by their sustainable biofuel production line. Dr. Robert Johnson was our Virgil in the journey to this burning hell – a metaphor, but mind you, the reactor’s temperature can top 450 degrees Celsius. What follows is the story of our trip to a (quite literal) hotspot in Ireland bioeconomy landscape

Still coal, but cleaner than most 

Let’s rip the band-aid first. Yes, Arigna Fuels does produce smokeless coal ovoids for domestic use. Coal is, in general, the dirtiest and most carbon dioxide emitting of the commercial fossil fuels lot. But not all coal is created equal. The raw coal imported from the mainland Europe and processed in Arigna facilities is thoroughly tested in the local lab, and is more than compliant to the strictest European environmental standards in terms of pollutants content – under 2% sulphur during manufacture and well under 5 grams of particulate per hour emitted during combustion, a market primacy. It is characterised by a long slumbering rate, which translates to a slow and consistent burning, while delivering constant high heat output. It’s also more efficient than the average, smokeless, and with low ash and unburnt material content left behind.  

[pictures of Arigna Fuels lab testing equipment] 

All coal must be phased out of the energy market in a fast and orderly fashion, granting a just transition for workers in the industry. In the meantime, if there are no other options, you can choose to burn a certified cleaner coal.  

Now, let’s move on. 

A flame from the harvest 

Arigna Fuels recently gave birth to its green spin-off, Arigna Biofuels. Biofuels are fuels that result from the high temperature processing of organic material, mostly plant biomass, which keeps growing. Hence, they are renewable energy sources. In fact, they are the most ancient form of renewable energy, and of energy all together. A prime example of biofuel, or bioenergy, is firewood. 

Arigna Biofuels has launched its first product with the catchy name of Harvest Flame, and is marketing it as an excellent substitute for coal, wood and peat. It’s smokeless, carbon tax free and carbon neutral. Some of us are trying it already in our stoves, and are pleasantly surprised by it. Judging by its external looks, you wouldn’t distinguish it from a conventional coal briquette. But it’s the content that differs. 

[Harvest Flame briquettes burning. Image courtesy of Arigna Biofuels]

Journey of an olive stone 

The Harvest Flame’s raw material is olive stones. A decade ago, these had little or no use, nor economic value, and were categorized as agricultural waste. Recently, with the stimulus offered by the bio and circular economy, a market is developing around agricultural (and industry) residues, that is assigning a value to biomass products, re-injecting them in the supply chain. Olive stones employed for Harvest Flame come from olive farmlands in Spain and North Africa. Currently they are the best choice for Arigna’s process, in terms of energy density (energy content per unit of weight) and logistics. Woodchips don’t deliver the same heat content per kg, are bulkier and have higher moisture content, not the optimal feed for the reactor. 

[picture of Olive Stones used by Arigna Fuels] 

The secret behind the metamorphosis from olive stones to carbon neutral fuel is in a process called pyrolysis. My ancient Greek comes in handy here, as I can tell you that it means “separation by fire”, or something like that. The first step is torrefaction, which, to a smaller scale, is the same technique that Italians use to prepare their coffee at home, using mokas. Technically, it’s the roasting, or slow cooking, of biomass in the absence of oxygen – an anoxic reaction – at a temperature that goes from 250 to 280 degrees for about 30 minutes. 

[step #1 of the olive stone journey. Image courtesy of Arigna Biofuels] 

Natural gas is used only to kickstart the reaction. Once the torrefaction process is up and running (i.e. working temperature is reached) the reaction is self-sustained, or autothermic. Why? Because the pyrolysis of the plant structure releases gas, up to 15% of the original mass. This gas is sent to a burner, and the heat output is rerouted in the reactor, in a circular, zero-waste fashion. 

[step #2 of the olive stone journey. Image courtesy of Arigna Biofuels] 

The torrefied material is then cooled, crushed, bound back with resin and moulded into briquettes. The torrefaction process designed at Arigna Biofuels returns an energy dense final product, carbon-rich, and purified of low heating value residues such as tars and volatile substances. Carbon makes up for about 60% of the final product, and the net gain in energy content is 17% (from 19MJ/kg to 23MJ/kg). Production capacity is in the region of 1.5 tons per hour. 

[step #3 of the olive stone journey. Image courtesy of Arigna Biofuels] 

The product is currently in the launching phase, sold locally at a price that makes it highly competitive with other conventional solid fuels. And since it’s exempted from the carbon tax, which is programmed to increase up to €80 (per ton of CO2 emitted) in Ireland by 2030, it is set to vanquish its fossil competitors. Right now, the product is distributed within a small local circuit to collect early consumers’ feedback. In the near future, Arigna intends to explore the feasibility of using native alternatives instead of imported olive stones, like wood pellets from local forestry, thus lowering the life-cycle emissions. 

In theory, every family in the North-West currently using dirty solid fuels could switch to biofuel. For Leitrim, the switching decision would result in above 10,000 tons of avoided CO2 emissions in ten years, and improved indoor air quality for thousands of households.  

The plant. Reactor’s “tunnel” is visible in the lower left part of the structure. Image courtesy of Arigna Biofuels

Still with us? This is where the fun begins. 

Black Earth 

Ancient Amazonian tribes were (are) environmental-friendly societies. Like pretty much every pre-industrial indigenous human community, they exerted low pressure on natural funds, produced virtually no waste, and thoroughly applied the three Rs – Reduce, Reuse, Recycle. The Amazonian tribes, living on very acidic tropical forestland, made large use of what the Portuguese conquistadores named terra preta, black earth. They were the first to experiment with its amazing properties as a soil amendment product. What the Amazonians did was bury their organic waste in the soil, slowly heat it up with a gentle fire, and profit from the transformed pitch black, earth-like porous material that was high in carbon. Did I just describe pyrolysis again? Yes! 

Terra preta, Amazonian amazing soil.

Biochar, the next big thing 

Nowadays we rebranded that old black earth biochar, crisis of biological charcoal. Biochar qualifies as a super-material. It has many virtues, well summed up here. Biochar was also featured in Project Drawdown’s list of solutions to reverse global heating. Biochar is, in fact, carbon negative. It means that during its life cycle, from production to use, it takes a net amount of carbon out of the carbon cycle, by storing it in its very structure. 

Arigna Biofuels recently started a pilot biochar production, probably one of Ireland best kept secrets. Its production process shares similarities with Harvest Flame, as it is based on olive stones, but the pyrolysis reaction times and temperatures are increased. As of now, it happens to be more labour-intensive (6 man-hours per tonne of product, in comparison with 3 man-hours employed in Harvest Flame). The final product loses about half of the volume of the input material on a dry basis, but is converted to a substance that is 80% pure carbon and has a moisture content under 5%. Which is why it makes for a good fuel, too. However, quoting Dr. Robert Johnson directly: “It’s just too good to be burned”. Processing it further, it transforms into activated carbon, another multi-purpose high-value material employed, for example, in water filtration and treatment. 

Torrified material. Image courtesy of Arigna BioFuels.

Biochar eco-nomics 

In Europe, biochar is still a niche market, but burgeoning fast. The industry is suffering of dwarfism and lack of unified standards, as there are many small producers scattered around, each one doing their own thing. To reach economies of scale, lowering average costs, the industry needs financial stimulus and technical guidelines, while producers would benefit from gathering in co-ops to share best practices and expand outreach. The average European price of biochar, €1750 per ton, is still too high to be competitive and accessible. At Arigna BioFuels, current production rate is between 500-700 kg/hour, and they estimate a potential production of 3,500 tons/year.  

Arigna’s biochar’s end market at the moment is horticulture, via Probio Carbon, that refines and sells it as soil substrate and co-fertiliser media. But it is in farming where Dr. Robert Johnson – and us – see the next frontier of application. If every farmer in Leitrim (and Ireland) would add biochar to their farm system, either directly on pastures or mixed with slurry prior to spreading, they will benefit from: 

  • increased growing rate of grass;
  • reduced need of conventional nitrogen fertilisers;
  • increased water and nutrients retention capability of soil, and  
  • (when added as additive in animal feed) better livestock health.

Whilst contributing to agriculture emissions mitigation, sequestering thousands of tonnes of CO2, and contributing to nitrates control. 

Fostering a bioeconomy revolution 

There are numerous studies that prove that biochar added to the soil also mitigates methane and nitrous oxide emissions, but figures vary substantially depending on type of soil, moisture, temperature and other factors. We agreed that a joint project for the near future could be the exploration of biochar application on soils in the North-West, involving local farmers and the already established Sustainable Energy Communities. 

Another application that Dr. Robert Johnson mentioned is biochar addition to anaerobic digestion lines. Early experiments indicate that a high proportion of biochar added to dairy sludge increases biogas yield by 17% on a w/w basis. And biochar enriches the digestate by-product, making it even more effective as soil amendment. The company is now reducing the ratio of biochar addition to 3-5% to see what happens to the yield, searching for an efficient sweet spot. 

Digestate. Looks like compost, but it’s better.

All in all, biochar and the whole bioeconomy sector promise climate-resilient opportunities for generations ahead, and as such are welcomed in our Cróga initiative. The bioeconomy ecosystem encompasses anything from home compost to biobatteries to anaerobic digesters. It connects farmers, industry and households. We in GEAI would be happy to support the creation of a bioeconomy community hub in the North-West, acknowledging the economic and environmental value of forestry and agri-residues, that are plentiful in the area. 

The Arigna valleys boast a centuries-long heritage in energy production, that is gradually shifting to cleaner sources. There are stark symbols of the ongoing transition to a net-zero community in the dozens of white giant windmills that tower above the mountains’ plateau. Maybe less grandiose, but closer to our households, Arigna bioindustry is also part of that transition. 

This article was written by Nicoló G. Tria, GEAI Researcher in AFOLU 

The author and GEAI would like to thank Dr. Robert Johnson for his time and dedication