TL-128

 

Flow diagram of heavy duty scrubbing

system

Big Scrubber, Big Pump,

Big Emergency

INDUSTRY:

ENTITY:

SOLUTION(S) PUMPED:

PUMP TYPE(S):

Pollution control

 

Hydrochloric acid, Zinc ammonia, Zinc chloride solution

CHEM-GARD Horizontal Centrifugal Pump

 

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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

chemistry.

 

Our check of the existing installation had revealed that the pumps

selected were

 

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

servicing.

6. The pumps were to have direct water flush to cool the seal and extend

service life.

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

equipment.

 

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

America!

 

Copyright 2016 - Vanton Pumps (Europe) Ltd - All rights reserved

About Us

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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mail@vantonpump.com

(+44) 01260 277040

Vanton Pumps (Europe) Ltd.

Unit 4, Royle Park

Royle Street

Congleton CW12 1JJ

UNITED KINGDOM

www.vantonpump.com