Figure 1. Overview of compact
odour-scrubbing installation showing the
six Vanton ANSI end-suction
polypropylene pumps handling acid and
alkaline solutions over the pH range
from 3 to 12 at 650 gpm against a 38'
Figure 2. Two Vanton polypropylene sump
pumps handling caustic soda and chlorine
Pump Material Selection
Guide: NaOH Sodium
Chemical, Metal Finishing, Wastewater Industrial
Caustic soda, Chlorine, Hydrochloric acid, Hydrogen
CHEM-GARD Horizontal Centrifugal Pump, FLEX-I-LINER
Sealless Self-Priming Peristaltic Pumps, Nonmetallic Tank
Pump Systems, SUMP-GARD Thermoplastic Vertical Pump
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Reprinted from World Pumps
Guide to the selection of materials for pumping
NaOH and NaOCl
This third article in an on-going series on the selection of materials for
pumping corrosive, abrasive and hazardous chemicals considers the
challenges presented by the caustic alkali sodium hydroxide and its
close relative sodium hypochlorite. George Black looks at the problems
and some practical solutions.
Sodium hydroxide and sodium hypochlorite
Sodium hydroxide (NaOH) is a corrosive alkali, commonly called caustic
soda or soda ash. It must be handled with care because it destroys
organic tissue and requires protection of the skin and eyes. It is derived
by electrolysis of sodium chloride, or by treating a solution of soda ash
with a solution of lime. It is widely used in the manufacture of other
chemicals, in the manufacture of detergents, pulp and paper, soap and
textiles, for regeneration of spent process solutions and for
neutralization of acidic wastewater.
Its sister chemical, sodium hypochlorite (NaOCl), is a salt generally
derived from electrolysis of a cold dilute solution of seawater. It is
unstable in air unless mixed with sodium hydroxide. NaOCl is usually
stored in what is known as Labarraque's solution, and is readily
recognized by its disagreeable, sweetish odour and pale green colour.
It is widely used for the bleaching of paper, pulp and textiles, for water
purification, for medicines and in conjunction with sodium hydroxide for
treating and neutralizing wastewater. Although both of these chemicals
area readily handled by polypropylene, temperature variations and
wear-related service conditions often suggest the use of vinyls and
fluoropolymers for pump construction.
Scrubbing systems minimize obnoxious odours
The process design engineers at CH2M Hill were charged with the
responsibility of providing this Miami, FL, facility with a multi-stage air
scrubbing system that would achieve 99.9% H•S and odour removal. In
addition, it would have to assure H•S discharge less than 0.1 ppm. In
conjunction with this mandate, the new system was to be designed to cut
maintenance and conform to the latest projected environmental regulations
for plant emissions.
Pump selection and material specification were critical to dependable
operation of the scrubbing towers and related equipment because in all stages of the system, both chlorine and caustic additions were required. The
chlorine feed was provided by sodium hypochlorite and the system
incorporated the flexibility to adjust and control the 50% truck concentration
down to 25% as needed.
The six recirculation scrubber pumps (Figure 1) were specified as ANSI
horizontal centrifugals suitable for delivering 650 gpm against a 38' TDH
over a temperature range from 55-110°F. To ensure that no metal
would be in contact with the corrosive NaOH, NaOCl and H•S fluids required
to handle the broad range of pH values from 3 to 12, all fluid contact
pump components were to be furnished in homogeneous, chemically
inert polypropylene or one of the fluoropolymers. The stainless steel
shafts were to be isolated from the fluid by a thick sleeve of Kynar®, the
PVDF fluoropolymer, and the mechanical seal was to be reverse
mounted so that the metal component would be out of the fluid area.
These pumps are driven by 25 HP, 1800 rpm, TEFC motors.
An additional ANSI PP horizontal centrifugal pump with the PVDF shaft
sleeve was specified to recycle the NaOH caustic. This 4x3x10 pump
was required to deliver 500 gpm against a 16' TDH. It is driven by a 15
HP, 1750 rpm, TEFC motor. The same requirement for no metal in fluid
contact set for the other centrifugals applies to this pump.
The pumps required to transfer the 50% NaOH caustic soda and 12.5%
NaOCl chlorine solutions from their 1500 gallon fibreglass (FRP) storage
tanks are vertical centrifugal units designed to deliver 200 gpm against a
13' TDH at a temperature range from 50-90°F (Figure 2). These pumps
are driven by 5 HP, 1800 rpm, TEFC motors. The basic pumps have
all-wetted components in the pump head furnished in PP and the shaft
sleeve in PVDF, but the vertical pump columns are also specified in
PVDF. The wetted bearings are nonmetallic, consisting of Vanite and
Since installation of the new scrubber system, the facility has been achieving
99.99% reduction in sulphide levels and 99.5% reduction in odour measured
by inlet and outlet H•S and odour values (ED50).
Packed tower scrubber neutralizes sulphuric acid
Field reports on the use of sophisticated Gaylord Foundry scrubbers in
conjunction with resin bonded core mould operations indicated
unusually high maintenance problems traced to pump failure under the
severe corrosive and abrasive nature of the caustic and acidic fluids
they had to handle. Not only did the wetted parts of the pumps have to
be inert to varying concentrations of the sulphuric acid and the sodium
hydroxide needed for neutralization, but they had to withstand impact
and abrasion from sand particles as well.
In a typical operation, the SO• gas coming from the core machine flows
upwards through a deep bed of polypropylene rings continuously wetted by a
5% by weight NaOH solution supplied from a fibreglass tank. In the original
design, an externally-mounted centrifugal plastic pump was used for the
continuous circulation. Repeated failure of the seals, and the messy cleanup
required, led to a design change. When an in-tank polypropylene sump pump
with an integral pump/motor shaft was designed into the system, the seal and cleanup problems were solved.
Here's how the revised Gaylord Foundry Equipment scrubbing system
works. Two very different nonmetallic pumps are used to assure
dependable delivery of the neutralizing caustic. Controlled feeding of
50% NaOH is provided by a flexible liner peristaltic type rotary pump,
instrumented to respond on demand from the pH probe in the tank.
The two components of this sealless pump in contact with the fluid are
the Teflon® pump body and the Hypalon® flexible liner. Continuous
circulation of the caustic solution in the tank is maintained by the
polypropylene sump pump, which has no seals or sleeve bearings in
contact with the fluid (Figure 3).
Automatic regeneration of the neutralizing solution so that the pH stays
at 8.5 is maintained in this manner. A portion of the spent solution is
discharged, energizing the caustic transfer pump to meter a controlled
quantity of NaOH. Make-up water is then added to maintain the sump
at its preset level. A similar Gaylord scrubber design for the foundry
industry uses a sulphuric acid-based scrubbing solution. Since the
pump materials are inert to both the acid and caustic, the same pumps
provide satisfactory service.
Maintenance problems solved with CPVC/PVDF pump
The Burbank Drum & Barrel Company of Glena Park, TX, reconditions
half-a-million 55-gallon steel drums per year. The process involves
immersing the drums in a stripping solution of sodium hydroxide,
steam flushing them with the same solution, and power rinsing them
with 20% sulphuric acid. In addition to the required resistance to the
chemicals, the pumps at the reconditioning station faced a number of
wear factors that resulted in costly downtime for repairs.
Service factors included: chemical heat generated by the addition of
acid and water makeup, frequent start/stop operation, and abrasion
from oxide and scale. Here's how the problems were solved. The
existing pump was replaced with a vertical centrifugal design that had
the high wear components, the casing and impeller, made of
precision-moulded polyvinylidene fluoride (PVDF, Kynar). The column
and its welded vertical support gussets were provided in chlorinated
polyvinyl chloride (CPVC).
This combination of cantilever design and high tensile strength
engineered thermoplastics with superior abrasion resistance where
needed did the trick. Pump downtime for repair has been completely
Advantages of converting from hydrated lime to liquid caustic
Ever since the Harpeth Valley Water Treatment facility in West Nashville,
TN, switched their manual granular hydrated lime neutralizing system to
an automated system based on the use of 25% sodium hydroxide,
production has been up and costs have gone down. A critical factor in
the success of the new system is the selection of magnetically driven,
sealless ANSI centrifugal pumps with no metal in contact with the
corrosive fluid (Figure 4).
Figure 3. This compact packed tower
scrubbing system relies on two very
different thermoplastic pumps: a
flexible liner peristaltic type rotary
pump to meter 50% NaOH on demand to the
vertical in-tank circulating pump, which
provides a continuous flow of 5% NaOH
scrubbing fluid to the tower.
Figure 4. Close-up of one of the two
magnetically-driven centrifugal pumps
automatically delivering the required
volume of 25% NaOH on demand.
Figure 5. Polypropylene plastic tank and
pump station with pneumatically-operated
plastic valves, used in processing
In the 1950, Vanton developed a revolutionary all-plastic pump for use in conjunction with the first heart-lung device. The design limited fluid contact to only two non-metallic parts: a plastic body block and a flexible liner. This was the birth of our Flex-I-Liner rotary pump. Its self-priming sealless design made it an industry standard for the handling of corrosive, abrasive and viscous fluids as well as those that must be transferred without contaminating the product. Vanton now offers the most comprehensive line of thermoplastic pumps in the industry.
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(+44) 01260 277040
Vanton Pumps (Europe) Ltd.
Unit 4, Royle Park
Congleton CW12 1JJ