KIcking the coal habit

By Tom Powell and Budyong Hill

It is encouraging to see Marlborough businesses and government facilities converting their space and process heating from coal to renewable energy sources.  They are to be commended. 

The Wairau hospital and Woodbourne Air Base are considering alternatives to their boilers currently fired by coal and diesel.  Talley’s has just received a $1m Government Investment in Decarbonising Industry (GIDI) grant to replace its coal and diesel boilers with one that burns wood pellets.  Nelson Forests at the Kaituna Mill recently received a Cawthron award for halving its greenhouse gas emissions, largely by replacing waste oil with wood chip and sawdust for drying timber.  The Kinzetts glass house farm, outside Blenheim, led the field, converting from coal to wood chip back in 2009.

This follows a trend observed by DETA Consulting of Christchurch, which recently conducted a survey of South Island businesses burning coal for process heat.  Most were planning to convert from coal by 2030, ahead of the government’s deadline in 2037.  And most of those were planning to convert from burning coal to burning biomass, such as wood chip and dried wood pellets.

The road to net zero carbon will be bumpy, however, and with a few wrong turns.  One of those wrong turns may be too much reliance on biomass for process heat.

At the moment, biomass products designed for combustion are largely sourced from forest residue and mill waste.  Wood chip is made from low grade wood and mill waste, which can be further dried and pressed to wood pellets.  Forestry residue in slash piles can be ground up on site to make ‘hog’, the lowest grade biomass product due to its impurities, but still suitable for many furnaces.

While Marlborough appears to have plenty of biomass sources, many regions of the country do not.  The DETA survey also found that, at least in a few regions, anticipated biomass demand will easily outstrip local supply.  Some businesses in these regions are even contracting suppliers that would plant new biomass ‘farms’ to supply them.

So, here is the problem: Do we want to see farms converted to growing biomass, either production forest or some other biomass crop?  Right now New Zealand’s forests supply wood for construction and paper products and for export, with a limited supply of forest and mill ‘waste’ available for making biomass fuel.  If much of that forest estate instead goes to making just biomass fuel, we either need to plant more production forest or start chipping up logs that would otherwise go to making timber and paper or to export.  How much of New Zealand do we want to see covered by production forest?

To add to the mix, the government’s proposed biofuels mandate is expected to increase uptake of biofuels for heavy freight, including for trucks, trains and ships, which would put more demand on agricultural land.  How much farm land are we prepared to convert from food production to biofuel and biomass feed crops?

The other problem is that biomass isn’t exactly clean and renewable.  Wood burning creates smoke which is harmful to our health and creates black carbon, which is a powerful greenhouse emission.  From health and emissions perspectives, electrical power generated by wind, solar and hydro are much preferable.

The carbon-neutral status of biomass is also questionable.  Under current IPCC guidelines, the burning of biomass is considered ‘zero carbon’ because the carbon dioxide released to the air when woody material is burned has only recently been sequestered back from the air to grow the wood.   No new carbon is added to the environment, in difference to the burning of fossil carbon (i.e., coal, oil & gas), which releases carbon which has been locked away underground for millions of years. 

The steps needed to get biomass fuel to the furnace, however, result in a net increase in carbon emissions.  Harvesting, grinding, drying and transporting biomass, as of now, are largely reliant on fossil fuels.  These emissions can best be minimised by using heat from that same biomass to dry the product (as is now done at the Kaituna mill) and by keeping transport distance to a minimum but it will be a while before biomass burning is truly carbon neutral.  

In conclusion, NZ needs to plan the whole biomass supply and demand process very carefully, otherwise we could easily find ourselves having expectations of biomass that can't be met or result in undesirable consequences.  The ‘net zero’ future we are all hoping for should not be one where food production competes for farm land with fuel production.
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Biomass should be thought of as a transitional fuel, where there is enough local forestry residue to supply it.  Long term, renewable sources of electrical power are a better solution for process heat.