Timber iQ February - March 2020 // Issue: 48 | Page 41

FEATURES
Replacing coal with
wood chips
Biomass chips is a viable alternative to
coal, especially in the poultry industry for
decentralised heating of broiler houses, and
outperforming coal in all environmental aspects.
By M.J. de Wet Pr. Eng. NRGen Advisors, Stellenbosch
In agri-industrial heating applications, replacing coal with wood chips as a
viable sustainable biofuel is a real solution.
C
limate change activists and environment-conscious
food consumers are putting huge pressure on
agri-industrial food and dairy processors, and
producers using coal for animal husbandry heating purposes,
to switch from fossil fuels (coal, gas, HFO) to renewable
biofuel. It’s now proven that wood chips produced from
unwanted biomass (waste wood, invasive alien trees, old
orchards) can successfully replace fossil fuels.
Resource surveys carried out in the Western Cape by Africa
Biomass Company [ABC] and NRGen Advisors (as audited by
the CSIR), confirm that sufficient biomass chips are available to
replace coal used by agri-industries in that province. The
surveys confirm that approximately 150 000 t.p.a of unwanted
invasive alien trees in the riparian zones of the Breede,
Zonderend and Berg rivers exist for harvesting for the next 20
years and beyond. By harvesting these trees, water runoff will
increase, the risk of bush fires is reduced and the original fynbos
and palmiet systems will return.
PREVIOUS ATTEMPTS TO REPLACE COAL
WITH WOOD FAILED
Several past attempts failed to lessen the negative effects of
coal. The most common consequence of these attempts are that
the moisture in the wood boiled (vaporised/condensed) and
mixed with the sulphur in the burning/smouldering coal to form
caustic acids which corroded the metallic components of
coal-fired heaters and the chain grates of boilers.
Pellets made from cleaned (debarked, and often washed)
SA-pine worked well as biofuel because of its dryness and easier
materials handling characteristics. White or soft wood pellets are
however too expensive to compete with lignite coal but can
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successfully compete with natural and methane rich gas.
The manufacturing of hardwood pellets is experiencing technical
(mainly wear) challenges. The hard woods of SA, especially from
the more arid areas, are hard and abrasive. Add to this the fact
that pellet making requires the milling down of the wood to a dry
(< 10% moisture) meal before compressing it into a pellet,
making the final product too expensive to compete with Heavy
Furnace Oil [HFO] and coal.
THE BREAKTHROUGH WITH WOOD CHIPS
FOR INDUSTRIAL HEATING APPLICATIONS
Africa Biomass Company [ABC], Worcester, and Calore
Sustainable Energy [CSE] of Paarden Eiland, Cape Town, have
pooled their technologies to establish a wood-chip-fired
heating solution, using dry wood chips. CSE have the
technology at hand to stop-and-start and modulate their
wood-fired burners as the heat load demands. The CSE
burners can automatically control the infeed of wood chips
onto a unique igniting system and can modulate the flame of
the burners to narrowly follow the temperature setpoint of, for
example, a broiler house to be heated.
ABC in turn can supply ‘dimensional’ chips to the required
specifications for the optimal operation of the CSE burners
including:
• Moisture content @ 15 ± 1%
• Particle size distribution to fit the infeed apparatus
• Net calorific value @ 15.5 ± 0.5 GJ/t
THE SULPHUR CONTENT OF INDUSTRIAL
FUELS
One of the major disadvantages of coal and heavy furnace oils
// FEBRUARY / MARCH 2020
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