CO-FIRING COAL WITH BLACK PELLETS

China added 78GW of coal-fired power to its energy mix in 2025, and coal storage yards like this one in Ningbo City are becoming more commonplace across the country. But coal can be co-fired with steam explosion black pellets to help nations meet their climate targets. 

Conventional biomass pellets must be transported and stored in specialized, climate-controlled silos because exposure to moisture causes them to swell. The infiltration of any water causes white pellets to lose their structural integrity, and ultimately revert back to being sawdust.

This disintegration of white wood pellets results in significant fuel loss. In large volumes, it triggers a biological fermentation process that leads to spontaneous combustion. It also causes conveyor systems to clog.

Steam explosion exposes and redistributes hydrophobic lignin, making black pellets highly water-resistant. They can be stored in open-air stockyards and exposed to rain and humidity alongside coal, without degradation. This physical durability minimizes dust generation during handling, removing explosion risks in facilities. 

Standard white pellet biomass is fibrous and elastic, and notoriously difficult to process in traditional coal mills. It causes spikes in mill power consumption, severe mechanical wear and leads to uneven particle size distribution. Expensive plant modifications are needed to process white wood pellets.

Steam exploded biomass is reinforced by the redistribution of lignin. It has much higher mechanical strength than white biomass, with a Hardgrove Grindability Index (HGI) approaching that of coal.

Power generating stations can feed black pellets directly into existing coal pulverizers.  When processed with ball mills and vertical spindles in existing coal infrastructure, steam-treated black pellets fracture cleanly into a fine powder, rather than tearing into strings, with no motor overloads or loss of throughput.

Advanced black biofuel pellets possess all of the positive qualities of coal – high energy density, compatible grindability, total water-resistance – but burning them creates just six percent of coal’s carbon footprint, making them an ideal fuel for carving out an energy transition pathway. 

Dropping black pellets into a coal furnace for co-firing with the fossil fuel improves supports stable combustion thermodynamics.

Standard white wood pellets contains large volumes of volatile matter, in the form of fast-burning chemicals and moisture. They cause hot pockets of fire that destabilize furnace burns which become difficult to control. This heat-shock can also crack and rupture furnace boiler pipes.

Steam explosion cooks off those fast-burning chemicals before the pellet reaches the power plant, allowing both fuels to be consumed in synchronization. 

Advanced black pellets release their flammable gases at the same speed as coal, and reach and complete their char burn-out phase at the same time as coal. This optimal temperature control eliminates any need for burner re-configuration or modification.

Low-grade white wood biomass pellets contain elevated concentrations of alkali metals combined with chlorine. 

During combustion in facility furnaces their potassium and sodium mineral deposits quickly become volatile at low temperature, and form molten eutectic salts that splash onto furnace walls. These salts form rock-hard slag that corrodes furnace walls, impedes heat transfer and reduces boiler efficiency.

The condensate draining phase of Valmet’s high-pressure steam explosion leaches away most of these water-soluble alkali minerals and chlorides. 

Ash produced by advanced black pellets doesn’t melt and splash onto furnace boiler tubes, to leave slagging and fouling. Instead, it resists intense heat to form a dry powdery dust that drops into ash collectors without damage to furnace walls and reducing critical convective heat transfer.

Black pellets manufactured using steam explosion offer much better co-firing characteristics than preceding white wood pellets. Their net calorific value, low volatility, high bulk density, hydrophobicity and Hardgrove Grindability Index make them the perfect match for coal.