Overcoming Design Challenges Using Unconventional Methods
It was a great opportunity for me to participate in IIChE (Indian Institute of Chemical Engineers, NRC) Lecture Series titled “Learning with the Leaders” as a Guest Speaker. It was a great experience participating in such a learned and distinguished gathering. I thank all at IIChE (Indian Institute of Chemical Engineers, NRC) for giving me this wonderful opportunity.
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I have discussed the most critical shell & tube heat exchangers that pertain to service which is high pressure/ high temperature, corrosive and dirty. These stringent requirements are in both the Fertilisers as well as Oil and Gas sector which compel us to have large size openings for ease of maintenance. These have to be pressure tight and hence we have to provide gasketed joints. The bolts to tighten these joints may go to 6″ and more in diameter. How do you open this in service? The shutdown periods are very limited because we want the plant to quickly startup again.
We have addressed these problems more than a decade ago and as such the Screw Plugs have now become a viable option.
We’ll first talk about the bypass from shell to the channel or vice versa depending on the pressure gradient.
This leakage which is not visible (internal) is responsible for the inefficiency in heat transfer, but in some processes it causes a much bigger problem where the two fluids should not mix, like in de-sulfurization and similar such cases. So this is where we’ve come up with a gasket which will not allow that. Having said that let me explain what happens to the normal gasket.
With the joint like this where fluids are at high pressure & high temperature, refining you know is not only dirty but also corrosive and so the internals are made of stainless steel that has high coefficient of expansion. The channel barrel is made of stainless steel lined low alloy steel material that has lower coefficient of expansion. The reason for not using stainless steel as a base metal is firstly because stainless steel is expensive in comparison and the wall thickness required would be much higher, as the allowable stresses go down drastically with increase in temperature in this case. We therefore are left with different metallurgies as regards the internals (non-pressure part). The pressure part is the channel barrel.
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