A sawmill is looking to solve a waste problem and cut costs by branching out into the export, energy and biochar markets.

For most business owners the energy revolution involves a bit of risk and arithmetic. Should we invest in rooftop solar or think about a power purchase agreement? Are we big enough to take part in the demand response market? Have we explored every possible route to using less energy?

Every business is different, so the menu of solutions can be very, very long.

But what if you produce epic amounts of a byproduct that can be turned into energy so long as some new kit is installed? That’s the quandary a NSW sawmill pondered as it watched the sawdust pile up alongside its energy bills. The solution involved the decision to buy a $2.8 million pyrolysis reactor, a machine that turns residual waste from milling – and other sources – into valuable syngas and biochar.

Only 40% of what goes into a sawmill comes out as finished planks and beams. At Sweetman sawmill the residual matter – sawdust, bark, twigs and branches – used to be sold to Japan to be used to make paper. After an export company the mill used went broke the problem of finding use for the residue became acute. “It’s like the old analogy with the butcher shop,” says Sweetman Renewables chairman John Halkett. “If you only sell the T-bone steaks and not the rest of it the business is looking a little shaky.”

Chop chop

As much residue as the mill produces, which is about 50 tonnes a day, Sweetman Renewables is securing more. It has approached sawmills in northern NSW and negotiated commitments for supply of residue at a better price than the $15/tonne the stuff is sold for to use in landscaping backyards. The same stuff on a boat to Japan is worth about $US110/tonne, where it is being used in thermal plants as the country slowly turns away from coal. “It’s quite valuable,” Halkett tells EcoGeneration. “As opposed to wind and solar, biomass provides predictable, renewable dispatchable power.”

Sweetman is working with Australian companies Midway and Boral towards exporting this biomass through the Newcastle port. “If we can afford to pay the sawmills a lot more than they’re getting now then we can send it to Japan and get a decent price for it.”

The company also has a contract to supply a half-million tonnes of biomass to Verdant Earth Technologies, owner of the 151MW Redbank Power Station near Singleton in the Hunter Valley. The plant is being converted from low-grade coal to biomass, although it’s not quite certain yet when it will begin testing the new fuel. Export is being weighed as an option until Redbank can take the biomass. It will go through the same Newcastle Qube Logistics facility that processed woodchip shipments to Japan for Boral.

When Redbank has been converted it will be Australia’s third-largest dispatchable renewable power station after Snowy Hydro and Hydro Tasmania, Halkett says. “It’s not insignificant.”

With the grain

For Sweetman Renewables, the priorities are to export, supply the Redbank plant and get the pyrolysis plant at the sawmill up and running. To prepare itself as a supplier of raw materials for export and large-scale and small-scale power plants it is looking beyond sawmills to secure supply from forestry waste and industrial waste, scooping up the heads of trees, branches, rotten stumps and low-grade unharvested plants loggers leave behind. Industrial waste comes in the form of old pallets, for example, and the 20% of residential landfill that is wooden.

“If we can pull all that out and put it through a grinder we can use it as biomass,” Halkett says. “We don’t have any problem getting biomass: it comes from residues from existing sawmills with contractual government contracts, forest waste and industrial and residential waste.

“If you put a log through a sawmill and you’re doing really well 40% of it ends up as boards and beams,” he says. “You don’t chip a good log and put it into biomass when you can get $3,000 a cubic metre for spotted gum or blackbutt or turpentine or tallowwood.”

Power up

A Patriot pyrolysis reactor. Image: Patriot Hydrogen.

An arrangement with Patriot Hydrogen will see a pyrolysis plant hungry for 24 tonnes of woodchip a day to turn into syngas and biochar. Syngas can be used to make hydrogen but the reactor will be coupled with a Siemens genset. “That will generate twice as much electricity as we need,” Halkett says. “We’ll run the sawmill off our own electricity and sell the rest as green energy.”

If all goes well the plant will produce 2 tonnes of syngas a day, which is 40% hydrogen, 15% methane and the remainder carbon compounds. The syngas will be stored in bottles and fed into a V12 biogas fuel engine designed to burn high-temperature hydrogen compounds. “If you pump normal hydrogen into a normal reciprocating engine it burns so hot it will burn the pistons out,” says Sweetman Renewables director Garry Miller. “These pistons have been tungsten- and carbide-treated, so they can operate at very high temperatures.”

Of the 750kWh produced by the genset, just under half will be used onsite and the rest exported to the NSW TransGrid network, negotiations pending.

“We want to use our biomass, which we generate every day – we have to find a use for it – and we couldn’t think of a better way to do it than turn it into a hydrogen-rich gas and produce electricity,” Miller says. “One of the number one expenses we have, apart from log supply, is electricity. All the saws and planers are heavy stop-start electric.”

Bag it for later

Inside the reactor the woodchip is heated to 500°C in an oxygen-free environment, which cracks the chemicals in the cellulose to produce the gases. What’s left is biochar, a carbon-rich byproduct that can be bagged and sold to the agriculture sector. When ploughed into topsoil biochar can help retain moisture and sequester carbon. It can also be added to feedstock to reduce cattle’s methane emissions.

If the pyrolysis unit at the sawmill works out then others can be deployed at the mill or other locations near sources of biomass, Halkett says. Residue can pile up at so fast at sawmills it has to be removed every second day in some cases. “If a sawmill can’t deal with the biomass, they drown.”