6 replies to this topic

[Ali Malik]

Dear All,

I would to take advice from an expert to please guide me complete design of a condensers for Ethanol vapors and re-cooling water. The objective is to condense the ethanol vapors (78 C) to 50 C and then to 23 C in two steps using re-cooling water of 27 C as a coolant.
The Vapors are in shell side and water in tube side.
Material used must be copper and condensers must be VERTICAL in position.
The mass flow rate of condensate is roughly 700 lit/hr (overall for both condensers).
Mass flow rate of re-cooling water is unknown.

I would be extremely thankful for kind help on urgent basis.

If any could at least give me a same kind of solved problem?

OR

If one could guide me step by step procedure of condenser design.

[katmar]

If you have access to Volume 6 of the Chemical Engineering series by Coulson and Richardson you will find this is well handled there.

You should note that you cannot cool to 23 C using water at 27 C.

Why are you constrained to use a vertical condenser? Consider vertical and horizontal and select the optimum. It is expensive to use copper tubes and in modern ethanol plants you will find tubes are almost exclusively stainless steel.

[Andrei]

Katmar,

You are right if you are talking about fuel grade ethanol, but if you talk about human consumption ethanol, copper is the right material.

[katmar]

You are right if you are talking about fuel grade ethanol, but if you talk about human consumption ethanol, copper is the right material.

It is true that having some copper in contact with potable alcohol does make for a better, more neutral taste and smell. My experience is that the condenser tubes are not the best place to put this copper, but it could be done that way.

Certainly in the past (1950's) it was common practice to use copper tubes, and although I know of instances where they are still working I have never seen a copper tubed condenser installed during my career. As the old ones develop leaks they are gradually replaced by stainless units.

The problem is, we design and do economic evaluations based on a 10 or 20 year lifespan for equipment, and then we run it for 100 years!

[Art Montemayor]

Although my comments may not be related directly to a condenser process design, the note by Katmar is one familiar to me and my experience concurs 100% with his recommendations and comments. I’m offering my experience on this theme because I think it could conceivably be of interest and useful background to a soon-to-graduate student in Chemical Engineering.

When I entered Chemical Engineering I inherited existing plant and process equipment that was designed and built prior to World War II. Early in my career I was assigned to make modifications and improvements to the original Furfural plant in the world – located in Cedar Rapids, Iowa. This plant was essentially 80 to 90% built of copper and brass – piping included. Katmar will probably smile when he recalls our prior communications on my experience in replacing the original steam injection system on the copper Furfural stripper with a stainless steel, thermosyphon reboiler. This was in 1970. Prior to this, I had operated and modified air separation columns – all of which were fabricated of copper and brass materials.

I vividly recall my visits to Air Products in Allentown, Pennsylvania where I saw 75 + year-old men soldering air separation columns and equipment. They were recruited out of retirement in order to continue exploiting their hard-earned skills and artisan crafts. In other words, it was increasingly difficult – if not impossible – at that time to find young soldering coppersmiths capable of dominating the craft at that time. The only solution to working with copper was to continue to rely on the expert and time-proven abilities of the retired old-timers. In Cedar Rapids I found the same hardship – except at a worse level due to the lack of a local industrial base that cultivated this special craft. I grew up working in a shipyard and learned to weld electric arc and also do my own soldering. I have installed various copper piping systems (all silver-soldered) in the past houses I have built or modified. So I know a little of what it takes to make a good “joint”. However, even I don’t qualify for working on copper-based equipment like air separation columns. Expert craftsmanship and experience is required to do this type of industrial soldering and I seriously doubt if you are going to find it available in today’s industrial world. This is an area of very specialized craftsmanship and it is going to be rare and expensive to find capable, qualified solders today. Believe me, Katmar is correctly pointing out an important point in equipment fabrication. Unless you are forced to use copper, the smartest thing to do is to employ stainless steel. It will be much less expensive (and reliable) fabricated out of stainless.

This interesting subject goes to the heart of field practical engineering: process containment within reliable and maintainable industrial equipment. A hands-on knowledge of how equipment is formed, cut, and joined together to produce leak-proof, pressure vessels is not only a requirement – but is an essential tool to have when making strategic decisions on materials of construction. It is one thing to simply state that you require a certain metal to combat the negative properties of a fluid; but how does one ensure that the existing fabrication techniques can furnish the required strength, integrity, and durability needed? If you look at how you can make a copper joint you will soon discover that you basically have only two means: rivets and solder. And in most cases you require both – with additional mechanical bracing and reinforcing.

I still recall my unit in Cedar Rapids with nostalgia and the romance of working with simple materials, lap-joint flanges for copper piping and solving process problems regarding an inability to make butt welds and insert fittings wherever one pleased. Gone is the romance involved and the challenges. But Stainless is much stronger, flexible, workable, and efficient.

[katmar]

Art, your post did indeed bring a smile to my face! I was reluctant to bring up the problem of unavailability of qualified craftsmen because I feared it might be a local South African phenomenon. The last time I needed serious work done on copper (about 15 years ago) we had to fly an artisan up from the Cape Province (about 1000 miles away) where there is a thriving wine and brandy industry, and there were still a few coppersmiths available. If Ali is in California he may be in luck!

This discussion brings up a very real problem that students face. When set an impractical task by a supervisor, do they point out the impracticality or do they simply accept it and submit the answer they know the lecturer wants? If they go against the lecturer's instructions they risk failure, even if their work is actually sound. I suppose the best would be to discuss it with the lecturer before submission, and if it is clear that there is no flexibility they simply have to swallow their pride and submit the "expected" answer.

[Art Montemayor]

Harvey:

I'm afraid that if Ali were located in California, he would be out of luck! All the wineries that I've visited there have - guess what? - stainless steel equipment! There are no coppersmiths to be found in our 50 states, I'm afraid. We are forced to import them from South Africa.

I agree with you on how a student should approach the problem posed by an inexperienced or impractical engineering professor. In my time we also had the same type of dilemma posed from time-to-time. Then we called the solution: "Cooperate and Graduate". It should still work today.

Regards.