Look to wood biomass for electricity in dry years

Look to wood biomass for electricity in dry years
     Story: Jim Childerstone Forest Services

Recent government announcements on electricity supply during power shortages briefly mentioned “logs” to generate that extra power.

This was apparently part of the “battery” options, particularly during dry periods for hydro.

It was to also achieve up to 100 percent locally-sourced renewable energy generation for this country.

It's known as torrefaction of woody biomass energy.

The technology behind this latest innovation has the potential to add a significant bulk product to our forestry industries.

So how does this work?

In fact it is a major breakthrough, using our forestry resources to boost a low-cost energy source to replace fossil fuel.

That is for both domestic and industrial space heating and electricity production.

The product, known as torrefied pellets, is the next step up from biomass wood chip currently replacing coal fired boilers throughout New Zealand. 

Thanks to the latest trials by Genesis Energy at its Huntly Power Station, up to 600,000 tons of imported coal can be replaced through little modification to at least two of its 240 megawatt (mgw) boilers.

And Genesis Energy is dead keen to go ahead with a permanent supply.

In the trial at Huntly 1000 tonnes of torrefied pellets were imported from Canada, but in future this could be processed by large-scale plants locally.

The project basically also backs up Government’s proposal for added electricity supply during droughts and extreme weather events. Read climate change.

Cutting greenhouse gases

There has been little mention of the Lake Onslow hydro scheme lately, although alternative solar and wind energy still appear in the mainstream media.

Replacing coal for electricity cuts a massive tonnage of greenhouse gases being emitted into the atmosphere, not counting carbon miles.

Wood biomass equates to less than 10% of CO2 emissions compared with coal. And rotational production forests continue to sequester carbon.

Much of this work is to do with research on torrefaction of wood residues into high-heat-producing pellets equal to coal in calorific value per gigajoule.

Genesis reports that two of its 240 mgw boilers would provide the extra power needed in an average dry year.

Eight of its early coal boilers have slowly been decommissioned and pensioned off.

Wood chip supply for boiler conversions has steadily increased here, but so far there has been little development for torrefied black pellets.

This could make a huge difference to New Zealand’s energy supply based on the sustainable renewable exotic forestry industry, also providing a boost in jobs.

However, it is recognised by stakeholders that this would mean using more low-grade logs instead of exporting them to China.

Currently mostly pulp log, reject timber and slash is used for space heating, now known as white wood biomass.

But there is competition with demand by MDF plants and manufacturers of particle board. Also, domestic firewood merchants.

Development of torrefaction plants could be established with little delay, with a low carbon footprint compared to other products.

Looking at speculative figures, it is possible to establish a torrefaction plant capable of producing around 50,000 tonnes of pellets annually...

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