On-site Sodium Hypochlorite Generation
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The ClorTec™ skid-mounted, pre-assembled
units can be fully operational in less than a day. |
Transporting bulk chlorine on crowded highways and into residential
areas has become a major safety concern. Federal and local authorities
have recognized this problem and are dictating better solutions. More stringent
regulation of toxic gases and accidental releases of chlorine have required
industry professionals to seek alternative methods of disinfection.
Pressurized chlorine gas, the industry standard for decades, has become
regulated to the point where many utilities have evaluated the alternatives
and found on-site generation of sodium hypochlorite to be their best available
technology for disinfection.
Water and Wastewater Solutions spoke with Earl Ahrens, new business development
manager for Severn Trent Services’ ClorTec™ product
line, about on-site generation.
How long has on-site generation of sodium hypochlorite been available as
an alternative to pressurized chlorine gas?
On-site generation of sodium hypochlorite has been a key process in water
treatment for municipal and industrial applications for more than 30 years.
ClorTec™ systems
have been designed, manufactured, installed and operated since 1988.
What are the benefits of on-site generation?
On-site hypochlorite is a dilute form of disinfectant compared to chlorine
gas or concentrated commercial hypochlorite. As a result, handling, transportation
and containment are easier and safer. The benefits of the process over
chlorine gas and bulk hypochlorite include:
• Eliminating
the bulk storage of chemicals
• Reducing risk to plant personnel because of drastically reduced hazardous
material storage and handling requirements
• Eliminating transportation liabilities
• Reducing the threat to public safety
• Reducing disinfection byproducts
• Creating a consistent solution concentration and increasing water quality
• Reducing overall disinfection costs.
On-site generation also eliminates
OSHA process safety management training, risk management planning and purchasing
and transportation of HazMat
chemicals that are required when dealing with pressurized chlorine gas.
How does on-site generation work?
The operation of the ClorTec system is very straightforward:
• Salt (NaCl) is dissolved in a tank to form
a concentrated (30%) brine solution.
• The brine solution is reduced in concentration with demineralized water
to 3%.
• The diluted brine solution is pumped through an electrolytic cell. The
cell consists of numerous titanium plates packed into an equal
number of plates acting as anodes and cathodes. DC power is applied to the cell
from
a rectifier. Chemically, chlorine is evolved at the anode surface,
while hydrogen is evolved at the cathode surface. The secondary reaction of
chlorine,
sodium and the hydroxyl ion results in sodium hypochlorite at a
0.8% solution.
• The 0.8% hypochlorite solution flows into a storage tank.
• A metering pump delivers the disinfectant to an ejection point in the
well water treatment system.
How safe is the system?
The ClorTec system is designed from the ground up to provide safe generation
of sodium hypochlorite. As a comparison, household bleach typically
is delivered in a 3-6% concentration. By generating a much weaker 0.8%
hypochlorite
solution, there is greatly reduced risk to the operator through accidental
exposure.
The system also is designed with a four-tier safety interlock, preventing
the system from operating unless all system components are positively
shown to be operating properly. And ClorTec’s unique design addresses
the problem of hydrogen formation by diluting the gas through the addition
of forced air before venting to the atmosphere. This design maintains
hydrogen
concentrations at less than 25% of the 4% LEL (Lower Explosive Limit).
How do the costs of on-site hypochlorite generation compare to purchasing
commercial hypochlorite?
The only costs for on-site generation are electricity, salt and water.
Savings vary depending on energy costs, but the typical user of a ClorTec
system realizes savings of 40-75% in operating costs compared to commercially
purchased sodium hypochlorite.
What are the maintenance requirements for the
ClorTec system?
Maintaining ClorTec on-site generators is simple and inexpensive. A regular
check of the system is necessary to insure proper performance and operating
conditions (i.e., cell condition, voltage, amperage and hour meter
reading). Cell descaling is necessary on a periodic basis dependent upon
the water
hardness.
Inspection and adjustment of the metering pump and water testing may
also be required. All systems can be provided in a SCADA-compatible
configuration enabling integration and adjustment with existing process
control.
Electrode replacement is the only major repair cost. During the selection
process, consideration should be given to determine the potential cost
and frequency of replacement cells. D.S.A. (dimensionally stable) titanium
electrodes are coated with a proprietary blend of rare earth oxides.
With proper care, these electrodes typically last eight to 12 years.
For more information on sodium hypochlorite generation, contact Severn
Trent Services at info@severntrentservices.com.