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Heating HCl in a push pull pickling line

I am working in a company which Has PP Pickling line.. in which we are using HCl acid line, to heat the acid we are using hot water boiler what type of heat exchanger is best ? we are using graphite but heat transfer rate is slow, and how to increase the line speed ?

How to run the pickling line without stoppage, continuous feeding( thickness varies from 1.6 to 8 mm)

Senthil Kumar
Tube manufacturing - India
2005

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2005

I WOULD SUGGEST THAT YOU USE A PTFE TUBE AND PLATE HEAT EXCHANGER ALTERNATIVELY YOU CAN ALSO GO FOR A HEAT EXCHANGER PLATE TYPE IN WHICH THE PLATES ARE PLATED WITH PTFE COATING.

THESE COATINGS ARE EXTENSIVELY DONE IN MUMBAI AREA AND THE LIFE OF SUCH COATING IS VERY GOOD. COST WISE THEY WOULD BE EITHER SAME OR A BIT LESS EXPENSIVE THAN GRAPHITE HEAT EXCHANGERS.

BEST OF LUCK,

VIDU GOYAL
- INDIA

Hot water heaters are not effective because you are limited to something less than 100 °C water temperature. Your differential temperature (delta T) is small so heating is slow. Find a reference book and look at the temperature of steam at say 5 psi. It is much higher! Also, it has the heat of vaporization that it can give up as it condenses back to water which is a huge amount of heat. In the USA, most people will limit a steam boiler to a max of 15 psi as it is defined as low pressure steam and is not as strictly regulated, as well as it is more than adequate to heat large tanks with the same size heat exchanger in the tank. The boiler and water do require treatment and tender loving care a lot more than a hot water heater.

James Watts
- Navarre, Florida
2005

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There is a new, innovative system for heating acid solutions which utilizes submerged combustion as the means of heat transfer. Submerged combustion is the practice of heating liquids by bubbling a burner's hot combustion products through them, creating excellent heat transfer. Research shows that this process will give efficiencies of over 90% in process tanks heated up to 160 °F.

The system uses graphite & plastic in its construction, both of which are inert to hydrochloric acid. The system is called the Thermaflow Heating System. I would highly recommend looking into this system for heating most acids.

David Jaye
Houston, Texas
2005

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2005

Hi Senthil,

That reply of James Watt was very erudite and I certainly could not have come up with that thinking ! Well done!

But I'm not in favour of a Teflon heat exchanger ... too much loot (i.e., $$$) ... but would definitely go to a PVDF
one which is OK for 140 °C ,,, BUT all plastic heat exchangers are not as efficient as metal ones. That's the nature of the beast. Maybe the answer is to use an OVERSIZED heat exchanger to compensate.

P.S. I hope you are using a scrubber for that HCl line ...
a good 12 micron eliminator will work very satisfactorily.

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

Good heat transfer is obtained from condensing steam. Transfer coefficient from liquid to liquid is poor. Use of graphite heater by using saturated steam is a standard practice. Depending on design of available HE you can consider steam pressure of 3.5 kscg and improvement in heat exchange may be 10 times. Other method is Teflon tube bundle immersed in the bath but this may require major changes. regards

Sabyasachi Bose
- Kolkata, W Bengal, India
April 15, 2008

Hi, all. The practicality of hot water heating depends on the temperature of the tanks. Although the great majority of heating systems for metal finishing tanks over the years have been steam, I've been involved in a number of successful installations where hot water was used.

If you are only trying to reach about 140 deg F in most of the tanks, and the coils can be metal, hot water can be very simple and overall less expensive. Even though the coils are larger than steam coils, they are not huge, and the piping is dirt simple. But as required tank temperatures move towards 180 °F and up, or the coils must be plastic, the coils become too big and impracticably expensive.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 21, 2008

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Q. Dear Sirs

We use HF+HNO3 mix in PP tanks for pickling SS Coils, Tubes, etc. We are looking for a cost effective and safe system for heating the pickling solution to a temperature of 50 to 55 °C. Would appreciate for advice on the issue

Regards

Srinath Mayur
foils and tubes- Chennai, Tamilnadu, India
July 20, 2012