Temperature of wood and straw pellets at carbon burning out

Keywords: solid biofuels, pellets, carbon, burning out, particle overheating

Abstract

Main technological problems at solid biofuels burning are
ash sintering and submicron solid particles emission, especially
at straw and straw pellets combustion.
A significant content of potassium compounds in the cereal
straw causes low temperatures of ash sintering and melting. At
straw burning in ash residue at temperatures above 800oC reactions
with the formation of secondary oxides and silicates occurs,
which can form a fusible compound blocking movement and
burning out of fuel.
Low melting salts of solid biofuels ash at temperatures over
900oC start to rapidly evaporate and condense with lowering of
the flue gases temperature, which causes a significant content of
submicronic solid particles, creating environmental problems of
biofuels usage.
According to literary data at solid biofuels burning it was
observed the overheating of blazing particles above muffle temperature.
Overheating of blazing fractions of wood and straw
pellets and its dependence on process conditions are not covered
in literature. Obviously, the overheating of blazing particles can
lead to the intensification of the mentioned negative processes even
at furnace temperatures lower than that for ash sintering and its
atomization.
In this paper experimentally investigated a change in temperature
of individual parts of the wood, wood and straw pellets
during their thermolysis with volatile burning and subsequent
oxidation of formed cokeash residue with free air access in a
muffle furnace discovered the impact of high ash content on a
particles overheat. Research conducted by the method of an individual
particle burning in a muffle furnace preheated to
400...800oC, at that the temperature inside of cylindrical particles
of wood, straw and wood pellets were measured by means of thin
thermocouples.
The maximum temperature of cokeash particle is achieved on
it's axis just before completion of carbon burnout. Dependence of
the maximum temperature of cokeash particle from furnace temperature
has a complex saddle character with a local minimum at the furnace
temperature 500...550oC.
It has been found that with an increase in fuel ash content the
overheating of burning particle increases: for willow particle
with ash content 0.9% it was up to 450oC; for willow pellets with
ash content 1.4% it was up to 530oC; for pine pellets with ash
content 0.4% it was up 350 оС, and for straw pellets with ash
content 9% it was up to 470оС.
For investigated muffle temperature range the maximal
overheating for the cokeash residue of straw pellets were higher
by 130… 60 degrees in comparison to that for wood pellets.

Author Biography

M. Zhovmir, Institute of Renewable Energy, NAS of Ukraine

zhovmir_mm1.jpg

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Published
2017-09-11
How to Cite
Zhovmir, M. (2017). Temperature of wood and straw pellets at carbon burning out. Vidnovluvana Energetika, (3 (50), 93-100. Retrieved from https://ve.org.ua/index.php/journal/article/view/46