Flow diagram of heavy duty scrubbing
Big Scrubber, Big Pump,
Hydrochloric acid, Zinc ammonia, Zinc chloride solution
CHEM-GARD Horizontal Centrifugal Pump
Back to Articles
Reprinted from Pumps and Systems
By Thomas L. O'Connor
Our company has been designing, fabricating and installing air cleaning
and fume scrubbing systems since 1972. Every once in a great while,
we run into an emergency that demands beyond the call of duty activity
from other designers, construction crews and suppliers.
In October 1991, I received a call from an engineer who was in charge of
overseeing the start-up of a galvanizing process and its heavy-duty
scrubbing system. About 10 months before that, an air pollution "expert"
had designed and installed a ventilation system in this plant to ventilate
the hydrochloric acid tank and the flux tank with its zinc ammonia/zinc
chloride solution. The company had received a construction permit
from the state that was effective for one year — at which time they
were required to apply for an operation permit.
In evaluating the effectiveness of the ventilation system, the engineer
was dismayed to find that it didn't come close to meeting the 99.5%
removal efficiencies required to obtain the permit needed for the plant
to continue operating. He asked me to fly down and observe the
problems firsthand. Here's what I found:
• The ventilation on the tanks had been inadequately designed and was
now exposing the plant workers to toxic fumes.
• Equipment near the stacks was being severely damaged by the
improperly "scrubbed" airborne particles coming from the facility.
• The company had six weeks left on its temporary permit to design,
fabricate and install a system that would meet state standards... failure
would mean the plant would have to close down.
After a series of urgent phone calls to our component suppliers and a
review by our plant personnel, we agreed to accept the challenge. Our
company designed two systems — each requiring a 40,000 CFM
scrubber, and fabrication was begun almost immediately. The difficulty
in scrubbing hydrochloric acid in this application is that it requires
chemically inert thermoplastic centrifugal pumps, each able to pump
600 gpm to provide the liquid loading of eight gallons per square foot of
surface area needed for adequate entrainment of the hydrochloric
Our check of the existing installation had revealed that the pumps
recirculating only 120 gpm of the scrubbing solution. This was not
enough to achieve and maintain the heavy liquid loading on the packed
beds required to fully entrain the corrosive and noxious HC1 fumes. As
a result, a noticeable fog of acid was polluting the atmosphere and
corroding metal structures.
In addition to the systems design and installation, we had to guarantee
delivery and successful operation in six weeks. Since design and
fabrication of scrubbing systems is our business, we knew we could
handle that commitment. Our component manufacturers were tuned
into the emergency. The one problem we faced involved the pump.
When we discussed with various pump manufacturers the critical nature
of pumping as related to performance, chemical inertness and
unusually short delivery we got negative answers. But we persevered
and came up with a thermoplastic pump manufacturer that promised to
deliver the pumps we needed to withstand the chemistries, within the
limited lead time and at a competitive price. These pump specifications
were agreed upon:
1. The pump casing, suction cover and impeller were to be molded of
solid, homogeneous virgin polypropylene.
2. The wetted end of the large diameter stainless steel shafts was to be
sheathed in thick-sectioned PVDF, a fluoropolymer thermoplastic.
3. The mechanical seal was to be reverse mounted to avoid metal
contact with fluid.
4. The design was to incorporate a retractable front bearing on heavy
sliding bars to minimize shaft overhang.
5. Back pull-out and wide open seal area was required to facilitate
6. The pumps were to have direct water flush to cool the seal and extend
7. The rugged, heavy duty pumps were to be rated for flows to 1,000
gpm, discharge heads to 240 ft and temperatures to 275° F
8. Epoxy coated cast iron armor was required to protect the
thermoplastic casing against accidental damage from material handling
To assure system reliability, we incorporated dependable pH monitoring
instrumentation so that the recirculating scrubbing fluid would always
be neutral or slightly alkaline. The pH probe was set to energize a small
metering pump to deliver caustic solution automatically when the pH
rating dropped to 8.
Not only did our fabricated scrubbers and the related instrumentation
arrive on schedule, but the two heavy duty 6x4 polypropylene pumps
arrived on location the very day promised.
It was just what we needed to appease anxious plant engineers, who had become skeptical about the American work ethic and quoted promises. Extensive pump downtime, primarily due to seal failure, coupled with inadequate capacity had left their plant manager in a "show me" mood.
Both scrubbers were turned on, and to the amazement of the customer
the "fog" was gone, and the effluent was clear and neutral. The new
system operated on time and within regulations so that the company
received the required EPA Clean Air Act operating permits. One year
later, we double checked the ventilation system and found everything,
including the heavy-duty pumps, still operating perfectly.
Who says the "extra effort and quality emphasis" has gone out of
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.
Stay in touch
(+44) 01260 277040
Vanton Pumps (Europe) Ltd.
Unit 4, Royle Park
Congleton CW12 1JJ