May/June 2013
Issue 3 • Volume 4
Shifting focus
The largest natural gas fuelling
chain in the US is investing
heavily in renewables
Compare and contract
Raw material scarcity is still
impacting the pellet market in
Scandinavia
This degression will
not stand
A change to the RHI is needed
to avoid the risk of unnecessary
tariff degression
Regional focus: Scandinavia
contents Bioenergy
Contents
Issue 3 • Volume 4
May/June 2013
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2 Comment
3 Biomass news
8 Biopower news
9 Biogas news
14 Biopellet news
17 Technology news
25 Incident report
26 Green page
29 US House farm bill removes funding certainty
A small round-up as the US moves towards sealing its
farm bills which will affect energy sectors
30 IBTC: Setting the standards for torrefied biomass
32 Plant update – Scandinavia
34 Power to neutrality
Ena Energi CEO explains why he is not satisfied with
simply being a ‘provider’ of renewable energy
35 Looking long-term
Could diversification be on the cards at Norwegian
pellet company Pemco Trepellets
36 Compare and contract
In a region dense with forestry it’s surprising to learn that raw material scarcity
is still one factor impacting the pellet market in certain parts of Scandinavia
39 Danish power in the Far East
An abundance of feedstock and change of attitude toward renewable
energy has made China the destination of choice for PlanEnergi
40 Denmark’s hot topic
41 This degression will not stand
A small but important change to the Renewable Heat Incentive is
needed to avoid the risk of unnecessary tariff degression
43 Hammering coal
Biomass is finding a niche as more and more power
plants look for alternatives to coal
45 Retrofitting for the future
47 Hybrid theory
A Germany-based paper mill needed a biomass system that seemingly
did not exist – so how did it get to where it wanted to go?
49 Achieving renewable compliance
Follow us on Twitter: @BioenergyInfo
50 Shifting focus
No part of this publication may
be reproduced or stored
in any form by any mechanical,
electronic, photocopying, recording
or other means without the prior
written consent of the publisher.
Whilst the information and articles
in Bioenergy Insight are published
in good faith and every effort is
made to check accuracy, readers
should verify facts and statements
direct with official sources before
acting on them as the publisher
can accept no responsibility in this
respect. Any opinions expressed
in this magazine should not be
construed as those of the publisher.
ISSN 2046-2476
Bioenergy Insight
The nation’s largest natural gas fuelling chain is investing heavily in renewables,
and wants to provide biogas producers access to an untapped market
52 New additives address biomass boiler operational issues
Fouling, corrosion and agglomeration issues related to
biomass combustion can be mitigated using additives
54 The grass can be greener
55 Success is tough times
57 Cleaning up
A US gasification plant chose to use a wet syngas-cleaning
system as opposed to a solely dry technology
MAY/JUNE 2013
Issue 3 • Volume 4
Shifting focus
The largest natural gas fuelling
chain in the US is investing
heavily in renewables
59 Food waste digestion becomes reality in Somerset
Compare and contract
62 The coal copycat
The start-up of two torrefaction plants could prove industry game-changers
Raw material scarcity is still
impacting the pellet market in
Scandinavia
This degression will
not stand
64 Digesting the possibilities
A change to the RHI is needed
to avoid the risk of unnecessary
tariff degression
65 Attention to detail
66 An Insight into ADBA
76 Event listing
Ad index
Regional focus: Scandinavia
FC_Bioenergy_May/June_2013.indd 1
04/06/2013 17:09
Front cover image courtesy of ADBA
May/June 2013 • 1
• Value-adding solutions for boiler performance •
Aurora™ Solutions eliminate
slagging, fouling & corrosion
Aurora™ Solutions broaden
your fuel portfolio
Aurora™ Solutions treat
the entire fireside system
www.imerys-aurora.com
Bioenergy Insight
May/June 2013 • 27
Bioenergy biomass boilers
Fouling, corrosion and agglomeration issues related to biomass combustion can be
mitigated using additives
New additives address
biomass boiler
operational issues
W
hile
approximately
11% of the
world’s
total energy
is provided by biomass
combustion1, operational
problems in biomass boilers
can arise from ash-forming
elements in fuels. These
include silicon (Si), calcium
(Ca) and alkali metals, of
which potassium (K) is the
most prevalent in biomass.
Alkali metals are released
during combustion as vapour
phase alkali chlorides,
hydroxides and sulphates.
These cause fouling and
corrosion, necessitating
periodic tube cleaning
or even replacement.
Additionally, alkali
compounds also react with
silica and form low melting
silicates which enhance
slagging and the formation
of sticky, agglomerated ash.
This ash is problematic for
bottom ash handling due to
the creation of large clinkers
which require additional
work time for removal.
Feedstock
Biomass feedstocks are
sourced primarily from
wood yet a variety of agrowaste can also be used
for combustion. Residual
materials and byproducts
including bark, sawmill
residuals such as sawdust and
wood shavings, and energy
crops grown specifically to
create biomass feedstocks
such as willow and
switchgrass, can all be viable
materials. Pelletised wood
Typical tube fouling after six weeks in operation
Source: Imerys
Increasing tendency to form deposits utilising selected biomass feedstocks
52 • May/June 2013
and agricultural residues are
easy to handle making them
a popular option, but they
also contain the ash-forming
elements that contribute
to deposits and corrosion.
These non-wood feedstocks
can pose increased challenges
related to deposits. And the
more ‘exotic’ fuel options
show increasing tendencies
to contribute to deposits
such as slag, fouling,
agglomerations and clinkers.
One option for avoiding
these increased depositrelated issues could be
to simply avoid materials
containing significant
amounts of alkali including
short rotation crops such a
straw or fast growing forest
residues such as leaves and
twigs. This would, however,
limit biomass flexibility and
lessen the opportunity to
utilise feedstocks that are
economical by virtue of
their proximity to the heat/
power generating facility.
A more preferable
countermeasure for dealing
with these deposit-related
issues is mitigation through
dosage of additives.
Case study
Norbord is a global
manufacturer of woodbased panels used in the
construction, furniture and
DIY sectors, headquartered
in Toronto, Canada. At its
UK-based medium density
fiberboard (MDF) plant in
Bioenergy Insight
biomass boilers Bioenergy
Top (left) and bottom (right) of thermal oil heat exchanger following the 54 day trial period
Cowie, Scotland Norbord
was experiencing fouling
issues in a 15MWth travelling
grate boiler used to heat
thermal oil consumed in
the ~280˚C MDF mat hot
pressing process prior to
final trimming and packaging
of finished MDF sheets.
Fuel for the boiler, a
mixture of wet wood fibres
and dry wood fibre, is fed
directly into the grate via
dual feed screw conveyors.
The fuel analysis indicated
high alkali metal and
chlorine content which was
believed to be contributing
to heat exchanger tube
fouling and corrosion, ash
accumulation, large bottom
ash clinkers and high solids
levels in the fly ash.
The boiler required
shutdown every four to six
weeks to address thermal oil
heat exchanger tube fouling.
Also, large and coarse
bottom ash clinkers caused
plugging of the grate and, at
times, blocked the bottom
ash conveyor. Plant operators
commonly had to open the
boiler in difficult conditions
during operation to break
down the larger clinkers into
Bioenergy Insight
more manageable pieces.
In addition, the high
level of suspended and
dissolved solids in the boiler
flue gas required a wet
electrostatic precipitator
(WESP) for removal. The
volume of high solids in
the fly ash contributed to
unplanned outages and
high maintenance costs for
the WESP sludge pumps.
In October last year, a
54-day trial was conducted
at the Cowie plant for the
purpose of evaluating the
effects of dosing Aurora, an
additive manufactured by
solution provider Imerys,
headquartered in France,
into the boiler with the fuel.
Aurora is a proprietary fuel
additive which prevents the
formation of slag, fouling and
corrosion by reacting with
the alkalis in the fuel. Once
delivered into the boiler,
Aurora is heat processed from
a hydrous to a dehydrated
form which in turn reacts
with the vapour phase alkalis.
The alkalis are
preferentially captured by
the heat-processed Aurora,
controlling the deposit
mechanism by forming
compounds with melting
points above the operating
temperature of the boiler.
This process prevents the
formation of sticky alkalisilicate layers which bind
deposits together. The
resulting agglomerates are
thus smaller and friable,
allowing easy removal
with the boiler ash.
During the trial period,
Aurora was added onto the
main fuel feed conveyors
using an injection skid.
Boiler availability,
efficiency, heat output,
fuel injection set point
(feeding screw frequency)
and WESP behaviour were
monitored during the
trial period and compared
to a 76 day reference
period just prior to the
commencement of the trial.
Findings
Several improvements
were observed, notably:
• There were no boiler
shutdowns due to fouling,
slagging or bottom ash
agglomeration during the
54 day trial period. Boiler
tubes remained clean
and backpass fouling was
dramatically decreased.
• Boiler efficiency improved;
the study compared the
average heat output of the
boiler and feeding conveyor
screw frequency before and
during the trial and found
the average heat output
of the boiler increased
by 11% and the feeding
conveyor screw frequency
decreased by 10%.
• A reduction of suspended
and dissolved solids in
the WESP was observed.
Aurora, by reacting with
volatile alkali compounds
released in the boiler, forms
stable phases that become
trapped in the bottom
ash thus accounting for
the reduction of solids.
• Finally, there was no
blockage of the stoker grate
or bottom ash conveyor.
Examination of the bottom
ash clinkers showed they
were smaller and more
friable. In addition to
reducing maintenance
costs for the bottom ash
conveyor, this positively
impacts health and
safety as operators can
avoid frequent opening
of the boiler to break
down large clinkers.
Norbord today also utilises
Aurora to control fouling in
biomass boilers at two of its
oriented strand board plants
in North America. Andrew
Taylor, process and technology
manager for Norbord Europe,
says: ‘We continue to utilise
Aurora to realise these
benefits and evaluate added
efficiency improvements.’ l
References:
1
Overand, R., Direct Combustion
of Biomass, National Renewable
Energy Laboratory, Golden, Colorado,
USA Encyclopedia of Like Support
Systems http://www.eolss.net/
Eolss-sampleAllChapter.aspx
For more information:
This article was written by
Olivier Haerlingen, technical
sales manager Europe, Power and
Energy (olivier.haerlingen@imerys.
com), and David Osby, global
product manager, for Aurora,
Imerys (dave.osby@imerys.com)
May/June 2013 • 53