RESULT 343
IEA
OECD
energy efficiency
CA 98.502/2C.C02
Converting dryers to
use waste hydrogen
Waste hydrogen in dryers
at chemical plant
Summary
Eka Chimie Canada Inc.
in Québec, manufacturers
of sodium chlorate used
in the pulp and paper
industry, have succeeded
in reducing their plant’s
energy costs. The most
recent energy efficiency
project adopted by the
company concerns using
waste hydrogen from the
manufacturing process as
an energy source for
drying the sodium
chlorate. The company
expects to reduce its
annual electricity bill by
CAD 225,000 through
this project.
Highlights
• Recovers around
250 metric tonnes of
hydrogen per year
• Reduces electricity
consumption by
6,400 MWh per year
• Payback period
of 1.3 years
Eka Chimie Canada plant, Magog, Québec.
Centre for the Analysis and Dissemination of Demonstrated Energy Technologies
Aim of the Project
As part of their focus on energy
efficiency, major projects have
been carried out in recent
years, including the conversion
of process waste to energy. For
example, the heat released by
the process is now recovered
and used to purify sodium
chlorate (NaCIO3) using a technique patented by Eka Chimie
Canada Inc. The company was
also interested in recovering
hydrogen (H2) resulting from
electrolysis processes. This is
why in 1996 the decision was
made to use hydrogen to fuel
the plant’s dryers.
The Principle
Sodium chlorate is used by the
pulp and paper industry as a
pulp bleaching agent. Because
of its environmental benefits, it
is an excellent substitute for
the chlorine traditionally used
to bleach pulp. The company is
environmentally conscious, so
most of the chemicals involved
in the manufacturing process
are recycled internally or sold
to paper mills.
Producing sodium chlorate
requires a substantial amount
of electricity. As part of this
process, a large amount of
hydrogen gas is formed during
electrolysis of the brine
(NaCl-H2O or salt water) used
as the basic material. Around
8,500 metric tonnes of
hydrogen are produced in this
way annually. Of this total,
65% is recovered and piped to
a liquefaction plant owned by
BOC Gaz. The surplus
hydrogen was simply
exhausted into the atmosphere,
as the internal thermal energy
needs had mostly been met.
However, a technical
feasibility analysis revealed
that the plant’s two sodium
chlorate dryers were ideal for
burning hydrogen. These
fluidised bed dryers, each
equipped with an 800 kW
electric heater, require a
substantial amount of energy
to dry the product.
Recovering part of the waste
hydrogen, around 250 metric
tonnes per year (or about 3%),
amply provides the energy
required by the dryers. The
expected electricity reduction
is 6,400 MWh/yr.
The Situation
To convert the dryers to burn
hydrogen, each dryer was
fitted with a direct-fired
Maxtherm burner, also called
an airflow burner. Although
the flame temperature is very
high, the length of the flame is
quite small because of the
considerable flow of air in the
duct (10,000 m3 per hour) for
about 1 MW of energy. Only a
small amount of NOX is
produced. This type of burner,
compact and simple in design,
provides excellent
performance, since combustion
occurs within the stream of air
to be heated. Therefore there
are no energy losses related to
heat exchange. For this project,
the burners were installed
directly into the drying air
ducts, upstream from the
electric heaters, which were
kept as a backup system.
The hydrogen released by the
electrolytic process is
recovered and purified by a
wet scrubber to remove the
chlorine. It is then pressurised
to 100 kPa by booster
compressors and led to an
activated carbon filter to
eliminate residual organic
contaminants. From there, the
hydrogen is fed to the dryers,
where it is regulated and
injected into each burner for
combustion. On contact with
the flame, the process air is
heated to the desired setpoint
(130°C) and mixed with the
water vapour resulting from
hydrogen combustion.
However, the amount of water
vapour in the air is not enough
to affect the performance of
the dryers. As it leaves the
burner, the pressurised hot air
is directed to the fluidisation
area of the dryer to dry the
sodium chlorate. The moisture
content of the chlorate is
reduced from 2.5% to 0.02%
during the drying process.
The exhaust air leaving the
dryer is then treated by an air
purification system consisting
of a cyclone separator and
wet-type air washer. Figure 1
illustrates the process for
manufacturing sodium
chlorate.
When operating these systems,
a number of steps must be
taken to make the use of
hydrogen as safe as possible.
Hydrogen, like sodium
chlorate, requires certain
precautions, and plant
employees are made aware of
these safety aspects through a
continuous training
programme.
1
2
3
- Atmosphere
- Plant
- Client
NaCl
Sodium chloride
Settling
tank
Separator
Chiller
H2
Hydrogen
Water
Untreated
brine
Chemical
products
Electrolysis
Settling
tank
+
DC current
Heat
exchanger
Filter
NaClO3
Sodium chlorate
Dryer
Silo
Liquid
chlorate
tank
Clients
Clients
Purified
salt
Water
Figure 1: Process for manufacturing sodium chlorate.
The Company
Economics
Eka Chimie Canada Inc. in
Magog, Québec, Canada, is a
division of the multinational
Akzo Nobel Corporation.
Since 1979, the plant has used
an electrolytic process to
produce sodium chlorate. The
Magog plant, which has
80 employees, produces
150,000 metric tonnes of
chlorate per year in accordance
with the IS0 9002 standard and
strict health and safety
standards.
Eka Chimie Canada Inc. has
invested CAD 300,000 to
convert its dryers. In return,
the expected annual energy
savings are around
CAD 225,000. The investment
payback period is therefore
approximately 1.3 years.
Host Organisation
Eka Chimie Canada Inc.
1990, Saint-Patrice East
Street
Magog, Québec
J1X 4X6, Canada
Tel.: +1-819-8438772
ext. 21o1
Fax: +1-819-8433269
Contact: Mr M. Tardif
E-mail:
[email protected]
Internet: http://
www.ekachem.com or
www.ekachemistry.se
Engineering
Organisation
Government
Agency
CIMA+
3385, King west street
Sherbrooke, Québec
J1L 1P8, Canada
Tel.: +1-819-5653386 ext.
4114
Fax: +1-819-8214283
Contact: Mr J-Y Cloutier
E-mail:
[email protected]
Internet: http://
www.cima.qc.ca
Natural Resources Canada
580, Booth Street, 13th floor
Ottawa, Ontario
K1A 0E4, Canada
Tel.: +1-613-9473812
Fax: +1-613-9471016
Contact: M. Lamanque
E-mail:
[email protected]
Internet: http://
www.rncan.gc.ca
Please write to the address below if you require more information.
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Co-operation and Development
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March 1999