THE ADVANCE OF STEAM TREATED PELLETS

Wood pellets have been considered an alternative to fossil fuel for almost half a century.

The energy industry first used compressed sawdust as a fuel source in the early 1970s, when oil’s market price quadrupled and it was rationed.

Ten years later, new factory machinery turned wood into a type of industrial charcoal through a process known as torrefaction.

Unfortunately, the extreme dry heat used in torrefaction created a brittle end product – making its handling, transport and storage highly challenging at utility scale.

But the advent of steam explosion technology in biofuel has brought a new advanced black pellet to the fore, as a viable and timely alternative to burning fossil fuel.

Steam-treated black pellets manufactured from a hydrothermal process, rather than from simple heat degradation, are a true direct ‘drop in’ replacement for coal.

Steam explosion preserves and redistributes lignin in cellulosic materials – rather than degrades it – so granular woody mass can be bound together naturally, tightly and securely under industrial compression.

This reallocation of lignin – responsible for waterproofing plant cell walls – creates a hugely resilient, hard, energy-dense pellet capable of withstanding all weathers, knocks and abrasions.

In multiple ways, advanced steam-treated black pellets exist and behave just like coal. Only, when burned, they emit just six percent of the carbon dioxide released by coal and no harmful local particulates.

The density and durability of advanced steam-treated pellets are qualities that were first seized upon in 2015, by Thunder Bay Generating Station in Ontario.

The power plant became the first facility worldwide to fully convert from burning coal to using steam-exploded pellets.

But only now, as nations and regions approach stringent deadlines for their phasing out of coal, are steam-exploded advanced pellets receiving the full attention and credit that they deserve.

Here are the five key reasons why energy companies and power stations around the world are turning to advanced steam treated pellets as the only obvious low-emission direct ‘drop in’ replacement for coal:

1. Mechanical Strength

Steam explosion alters the biomass structure of cellulosic materials. The high pressure and temperature involved in the process causes lignin to soften and disperse, acting as a natural binder during the pelletization of advanced black pellets. This gives steam-treated black pellets a much higher mechanical strength than torrefied and white wood pellets – so they retain their bulk density and experience less fragmentation during handling.

2. Energy Consumption

Steam explosion requires a maximum temperature of 260°C to produce advanced black pellets while torrefaction needs roasting temperatures of 300°C and above. When produced on industrial scale for large energy utilities, this difference in treatment temperature represents significantly higher energy use. Steam-treated black pellets can be mass produced for a much lower cost than torrefied wood pellets, and with less harm to the environment.

3. Bulk Density

Steam explosion creates hard, ultra-dense pellets with a tighter bind of granular organic mass. This maximizes their energy payload per each unit of volume. Steam-treated pellets offer 14-18 GJ of energy per cubic meter. Lighter, more brittle torrefied ones muster just 12-16 GJ of energy per cubic meter. This allows utilities to reduce shipping volumes significantly, and to stockpile more energy in each storage silo, reducing their operational expenses.

4. Water Resistance

Steam treatment gives advanced black pellets a surface coating of lignin which makes them completely hydrophobic. They remain entirely intact when submerged in water, where the pellet structure of torrefied wood pellets often disintegrates – as torrefaction offers only partial water resistance. This allows steam-treated pellets to be stored outdoors, and exposed to rain and snow without coverings, reducing capital expenditure costs.

5. Pellet Grindability

Both steam treated and torrefied biofuel pellets offer excellent grindability for co-firing with pulverized coal and other materials. But while steam treated pellets require slightly more energy to pulverize, they grind more like coal – becoming granular again. When ground by industrial pulverizers, torrefied wood pellets become powdery and create a safety profile that needs specific measures to prevent dust, off-gassing and combustion.

To learn more about PowerWood Canada Corp’s advanced steam-treated black pellets, or its steam explosion manufacturing process, please use the contact details available on this website.