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TL-159

Figure 1. Cutaway of a Vanton sump pump

with all immersed components of solid

homogeneous PVDF thermoplastic that is

inert to the corrosive bromine.

Pump Material Selection

Guide: Bromine

INDUSTRY:

ENTITY:

SOLUTION(S) PUMPED:

PUMP TYPE(S):

Chemical

Various

Bromine, Sodium thiosulphate

SUMP-GARD Thermoplastic Vertical Pump

 

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Reprinted from World Pumps

 

Guide to the selection of materials for pumping the

halogen bromine

 

In this second of a series of articles on materials selection for pumping

corrosive, abrasive and hazardous chemicals, George Black considers

the problems presented by bromine. Dense, toxic and highly

aggressive, its handling demands specialized pumping solutions, as

illustrated by a look at some actual field installations.

 

Bromine

 

Bromine is a very dark, reddish brown, extremely heavy (specific gravity

3.11), corrosive and hazardous fluid derived from seawater and natural

brines by oxidation of bromide salts with chlorine. It is used in the

manufacture of ethylene bromide, a component of anti-knock mixtures,

as well as for water treatment, as an intermediate for fumigants, a fire

extinguisher fluid, and as bromide salts in pharmaceuticals,

photography, catalysis, and precious metal extraction. Other

applications include poison gas and shrink proofing wool. Its fumes are

toxic and irritating and it indiscriminately destroys most metals

including the stainless steels and exotic alloys, as well as most plastics.

Best results have been secured with the fluoropolymers.

 

Case history applications

 

Nickel components failed

 

Experienced process engineers were surprised when the nickel pumps

they specified for handling bromine provided an average of only two

months service before they had to be repaired. According to the

corrosion charts they used as guides, nickel is resistant to bromine as

long as it remains free of moisture. The problem was uninhibited nickel

corrosion caused by the bromine becoming wet by virtue of its

deliquescent properties, which caused it to absorb atmospheric water.

The short life of nickel pumps might have been acceptable if not for two

problems. One was the long and unreliable delivery time for the nickel

components. The other was the hazards involved with dismantling the

pumps. Pump designs involved many voids and cavities in which

residual bromine might be trapped and released during dismantling.

 

This danger, in combination with exposure to escaping fumes,

demanded an alternative solution. Initial attempts to substitute FRP

pumps proved disastrous. Service life was reduced to hours. The

answer has been found with the standardization on specially designed

vertical sump pumps with all fluid contact components made of solid

virgin grade polyvinylidene fluoride (Kynar PVDF) (Figure 1). To

minimize the danger from escaping fumes, a unique shaft sealing

arrangement was developed. It consists of a solid PVDF stuffing box

packed with woven Teflon (PTFE) fitted to the shaft where it emerges

above the mounting plate. Since the use of water for cooling this

stuffing box was out of the question, the use of nitrogen gas was

required. The necessary cooling along with inhibiting vaporization of

the bromine was accomplished with controlled leakage of highly

compressed nitrogen gas into the bromine tank.

 

Solving the heavy weight bromine problem

 

The 3.11 specific gravity of bromine presents a major mechanical

problem when large sump pumps are required. An application involved

a vertical Kynar PVDF pump with a 12-foot stainless steel shaft

completely isolated from the bromine by a thick PVDF sheath.

Conditions of service included delivery of 20 gpm at 100 feet TDH,

operating at 1750 rpm. This translates into operating against 135 psi,

and more than 1200 pounds of force over the cover plate, the clamping

flanges and the bolts. PVDF was out of the question for these

components because tensile strength would not be sufficient to

withstand the pressure. Here's how this problem was solved.

 

The cover plate was supplied in high strength chlorinated polyvinyl

chloride (CPVC), but the underside, the surface in contact with the

bromine, was provided with a thick liner of PVDF. Steel bolts were used

to anchor the cover plate to the top flange of the pump, but they were

sealed off from the fluid by special caps made of PVDF (Figure 2).

 

The clamping plates were furnished in structural steel, and the bolts in

cast iron. Both the plates and the bolts were isolated from the fluid by a

50-mil coating of ethylene chlorotrifluoroethylene (Halar ECTFE). This

fluoropolymer, like PVDF, resists the corrosive bromine and is an

excellent coating material. The exposed threads of the

PVDF-encapsulated cast iron bolts could not be satisfactorily coated, so

they were isolated from the fluids with PVDF sealing nuts (Figure 3).

 

Long service life with peristaltic pump design

 

The facilities at a chemical company were designed for toll and contract

bromination of organic chemicals. This required a self-priming pump

that could safely transfer liquid bromine with minimal maintenance. A

leakproof pump design was essential to protect plant personnel from

fumes or direct contact with this corrosive fluid. In this application the

bromine was pumped from drums of the nickel/copper INCO alloy

(Monel) to a glass-lined steel reactor through a Kynar® (PVDF) piping

system with a glass elbow in the line to observe the flow. The drum is

scale-mounted to monitor flow rate and the amount of bromine added

to the reactor. Air entering the drum during the pumping action passes

through a drying column to remove moisture that could react with the

bromine and form destructive hydrobromic acid.

 

The decision was made to use a flexible liner, rotary pump design,

which transfers fluid by means of a gentle peristaltic action with minimal

turbulence. The pump selected has only two components in contact

with the fluid — a thick-sectioned Teflon® pump body and a readily

replaceable Viton Fluoroelastomer flexible liner (Figure 4). Pumping

action is by an eccentrically mounted rotor pressing against the inner

surface of the liner and progressively moving the fluid trapped in the

channel between the outer surface of the liner and the pump body. This

unique sealless pump design eliminates leakage, toxic emissions and

similar problems associated with shaft seals, check valves, gaskets or

stuffing boxes (Figure 5).

 

The pump was furnished with a rotary vane air motor to control the

speed and regulate the flow of the bromine. In this application the

motor is operated at 300 rpm providing a controlled pumping rate of

0.25 gpm or 5 lb/min of bromine. At the time of this report, the pump

had been in service for five years, operating an average of 4.5 hours per

day. At the end of each day's run, the pump is flushed with sodium

thiosulphate. The low cost flexible liners are changed quarterly since

over time changes in their resiliency affect the accuracy of the metering.

Average maintenance time for liner change is reported to be

approximately 30 minutes, and is done without the use of special tools.

Figure 2. Close-up of PVDF caps that

seal the metal threads of bolts joining

the CPVC cover plate, which is isolated

from the bromine by a protective layer

of PVDF material.

Figure 3. Steel clamping plates and cast

iron bolts are completely isolated from

the bromine by a 50 mil coating of

ECTFE. The threads are then protected

from the fluid by PVDF sealing nuts.

Figure 4. Installation of a seamless

flexible liner rotary pump with

speed-controlling air motor. This unit

has provided many years of trouble-free

service. Only two components are in

contact with the bromine: the

heavy-sectioned pump body of PTFE and

the Viton fluoroelastomer flexible liner.

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