Chlorine dioxide technologies - Best available techniques (BAT) for ClO2 production

SVP-LITE®
Our large-scale, single-vessel processes (SVP) generate chlorine dioxide in a vacuum environment and produce a solidsalt cake by-product. SVP-Lite systems use methanol as a reducing agent.

Reaction chemistry
Our SVP-LITE process generates chlorine dioxide (ClO2) by reducing sodium chlorate (NaClO3) using methanol (CH3OHor MeOH) in a sulfuric acid (H2SO4) solution, according to the following reaction:
12 NaCIO3 + 3 CH3OH + 8 H2SO412 ClO2 + 4 Na3H(SO4)2 + 3 HCOOH + 9 H2O

The by-product of this reaction is an acidic salt cake, sodium sesquisulfate Na3H(SO4)2 that is approximately 18 - 25 wt.%
sulfuric acid. By recovering the sulfuric acid from the sodium sesquisulfate salt, acid feed requirements and salt cakevolume can be reduced by approximately 17% and 25%, respectively. Recovering this acid is the function of the salt-cakewash (SCW).
Overview of the SVP-LITE process

Benefits of SVP-LITE
The SVP-LITE process is an ideal choice for pulp mills thatwant to:••••Eliminate chlorine in the chlorine dioxide water inorder to produce real ECF pulp
Have low salt cake make-up requirements
Economically expand the capacity of existing SVP(R3) plants
Eliminate chlorine water or sodium hypochlorite use

It is possible to convert any SVP process to another with
only minor equipment changes.

The key feature of the SVP-LITE process is the circulation of
the main reactor vessel, which is kept under vacuum:
1.

Reactants (chlorate, methanol and sulfuric acid) are fed to the reactor
system where they react to form chlorine dioxide and a salt cake byproduct precipitates

2.

Steam is added to the reboiler to evaporate water from the generator
solution3.

Gas leaving the generator is a mixture of chlorine dioxide and watervapor, which is absorbed into water in the absorption tower

4.

The absorption tower tail gas is further scrubbed to avoid emissions

5.

A side stream of the reactor solution is fed to the filter, which removes
the salt cake by-product6.

The reactor solution is returned to the reactor

7.

Chlorine dioxide water from the absorption tower is transferred tostorage tanks

8.

An emergency stop interlock system is in place that will shutdown
the process should pressure, temperature or flow parameters
operate out of range

Chlorine dioxide technologies - Best available techniques (BAT) for ClO2 production

SVP-SCWThe SVP-SCW (salk cake wash) process is an add-on option to the SVP-LITE process.

Reaction chemistry
Our SVP-SCW process generates chlorine dioxide (ClO2) by reducing sodium chlorate (NaClO3) using methanol (CH3OHor MeOH) in a sulfuric acid (H2SO4) solution, according to the following reaction:
12 NaCIO3 + 3 CH3OH + 8 H2SO412 ClO2 + 4 Na3H(SO4)2 + 3 HCOOH + 9 H2O

The byproduct of this reaction is an acidic salt cake, sodium sesquisulfate Na3H(SO4)2, that is approximately 18 - 25 wt.%
sulfuric acid. By recovering the sulfuric acid from the sodium sesquisulfate salt, acid feed requirements and salt cakevolume can be reduced by approximately 17% and 25%, respectively. Recovering this acid is the function of the salt cakewash (SCW).
SCW – sulfuric acid recovery

Benefits of SVP-SCW
The SVP-SCW process is an ideal choice for pulp millsthat want to:• Reduce their salt cake by-product (approximately 25%)
• Lower their acid consumption (approximately 17%)
In addition to acid recovery, SVP-SCW features all thesame benefits as SVP-LITE. It is possible to convert any
SVP process to another with appropriate equipmentchanges.

To recover the sulfuric acid from the sodium sesquisulfate
salt, it is filtered from the generator solution by the first salt
cake filter. Then it is transferred to a metathesis tank where
it is dissolved in hot water.
The sesquisulfate is converted to sodium sulfate and a weaksulfuric acid solution, according to the following equation:
2 Na3H(SO4)2

H2SO4 + 3 Na2SO4

The slurry from the metathesis tank is pumped to a second
salt cake filter where the sodium sulfate is recrystallized andsent to the mill’s recovery system or other applications.

Chlorine dioxide technologies - Best available techniques (BAT) for ClO2 production

HP-A®
Our HP-A system features several advantages over earlier atmospheric chlorine dioxide processes, removing the needfor historical reducing agents (such as sulfur dioxide, methanol and sodium chloride) and improving the sodium chlorate
yield. Thanks to equipment similarities, HP-A is frequently used to upgrade older atmospheric installations.
Reaction chemistry
Our HP-A process produces chlorine dioxide (ClO2) by reducing sodium chlorate (NaClO3) with hydrogen peroxide(H2O2) in a sulfuric acid (H2SO4) solution, according to the following equation:
2 NaCIO3 + H2O2 + 2 H2SO4

2 ClO2 + + 2 NaHSO4 + 2 H2O + O2

Byproducts of this reaction are oxygen (O2) and spent acid containing sodium sulfate (NaHSO4): oxygen is released tothe atmosphere and the acidic sodium sulfate is reused in other plant processes. Using hydrogen peroxide as a reducing
agent brings a number of advantages, including higher capacity for existing generators, a more user friendly reducing
which produces the purest chlorine dioxide available.
HP-A process overview

Benefits of HP-A
The HP-A process is an ideal choice for pulp mills thatwant to:
••
•
•

1.

In the HP-A process, reactants (sodium chlorate, hydrogen peroxideand sulfuric acid) are fed to a reactor system, consisting of theprimary and secondary generators, and a stripper unit:

2.

Heat used to balance the reaction derives from the dilution of thesulfuric acid3.

Large quantities of air are introduced into the generator for mixing
and keeping the ClO2 concentration (in the gas phase) within the safe
operating range

4.

Liquor from the second generator overflows to a stripper andremaining ClO2 is removed before the spent acid solution isdischarged from the system

5.

Liquor from the primary generator overflows into the secondary
generator where the ClO2 reduction process continues6.

Gas is transferred from the reactors and strippers to the absorption
tower where chlorine dioxide gas is absorbed, then transferred tostorage tanks

7.

Tail gas exiting the absorption tower is further scrubbed to avoidemissions

8.

An emergency stop interlock system is in place that will shutdown
the process should pressure, temperature or flow parameters
operate out of range

Upgrade existing atmospheric installations
Increase sodium chlorate yield
Minimize chlorine by-product production
Reduce operating complexity

Chlorine dioxide technologies - Best available techniques (BAT) for ClO2 production

SVP-HP
The SVP-HP process is based exclusively on use of hydrogen peroxide (H2O2) for the reduction of sodium chlorate(NaClO3 ).

Process chemistry
Our SVP-HP process generates chlorine dioxide (ClO2) by reducing sodium chlorate (NaClO3) with hydrogen peroxide(H2O2) in a sulfuric acid (H2SO4) solution, according to the following equation:			2 NaCIO3 + H2O2 + H2SO4 		

2 ClO2 + Na2SO4 + O2 + 2 H2ODepending on the acidity of the process solution, the byproduct salt is either sodium sulfate (as in the formula) or sodium
sesquisulfate. The byproduct oxygen is released to the atmosphere or applied elsewhere in the bleaching process oreffluent treatment process.
The reaction chemistry can be much faster when using hydrogen peroxide and dependent on the chosen chemistry;
low acidity or high acidity. Talk to a Nouryon expert to find out the best solution for your plant

SVP-HP Benefits
The SVP-HP process is an ideal choice for pulp mills that want to:• Reduce their salt cake by-product (approximately 30%)
• Produce a sodium bi-sulfate cake by-product• Lower their acid feed requirements (approximately 25%)
• Eliminate dangerous and US PSM regulated methanol from the site
• Reduce organic loading to effluent treatment system• An emergency stop interlock system is in place that will shutdown
ccthe process should pressure, temperature or flow parameters
ccoperate out of range
In addition to these improvements, SVP-HP delivers the same
benefits as SVP-LITE: The first SVP-HP plants were started up in 1993.
It is possible to convert any SVP process to another with only minor
equipment changes.

Typical chemical consumption for Eka® ClO2 generators

Process

SVP-LITE

SVP-SCW

SVP-HPHP-A

ClO2

1.0

1.0

1.0

1.0

ClO2 water

100

100100100NaClO3

1.65

1.65

1.65

1.65

H2SO4

1.0

0.80.82.1

H2O2 (red. agent)--

0,310,29

MeOH

0.18

0.18-

-

Steam

4.2

5.5

5.5-

Spent acid-

-

-

3.5

Na3H(SO4)2 (aq)

5.4-

3.8-

Na2SO4 (aq)

-

4.6-

-

O2-

-

0.27

0.26

Component
ProductRaw material

ResidualUnits media produced/consumed per unit ClO2 produced
Get in touch!
For more information about our technologies,
please contact our engineering experts:bleaching_experts@nouryon.com

May-2021