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[Art Montemayor]

Guest:

You request help in analyzing this problem, and I offer the following analytical comments – all directed to you as a Chemical Engineering student, not as a fellow professional engineer:

1. This problem is based on a very established and well-known Unit Process called the Shift Reaction, as you have noted. However, I would advise you to communicate better in the future. Never assume that other people, especially engineers, will immediately understand what you mean by an acronym such as “FBCR”. This is the same as any foreign language. I presume you mean “Fixed Bed Catalyst Reactor” and if that is what you mean, then spell it out and qualify it with its assigned acronym and use that later on. That is the proper way to communicate what you mean.

2. You have typed a rather long description of a text book problem involving the design of a FBCR. The only comment I could have on this is that you did a good typing job. I hope that you don’t expect other fellow students or engineers to jump in and immediately resolve your problem for you in detail so that you can reap the answers and submit them for credit. I would not hold my breath while waiting for that to happen. As a Chem Eng student I give you credit for having more common sense and ingenuity than that. This problem is a typical Kinetics course problem and should be readily attacked and resolved by you.

3. A shift reactor is commonly used in Hydrogen reformer plants to maximize the H2 production while converting (“shifting”) the CO impurity to CO2 (which is subsequently removed –typically, with an amine process). You should easily be able to drop the exit CO content below the 0.6 mol % value. Two types of catalysts (High temperature & Low temperature) are used for shift conversion, depending on the temperature at which the reaction is carried out. I have used High Temperature shift followed by Low Temperature shift – in a two-stage/two vessels – process. The high temperature catalyst is chromium-promoted iron oxide which is active within the temperature range of 650 to 1,100 oF. Low temperature catalysts (copper-zinc) are effective over a temperature range of 350 to 700 oF and are used advantageously when very low carbon monoxide contents are required. Almost complete conversion of carbon monoxide – on the order of 99% - is possible with low temperature catalysts, even in a single stage operation.

4. I consider the shift reaction to be one of the most important and basic reactions in industry and one that should be not only well-understood and appreciated by all chemical engineers, but totally dominated in its operation as well. It is a pivotal reaction that leads to the world-wide production of Ammonia and – as such – represents the successful ability of a nation to fertilize its crops and feed its peoples. Since CO is a notorious poison for Ammonia converter catalyst, the reaction is the basis for the successful operation of an Ammonia plant.

5. This Unit Operation is a classical example of a Gas Phase through a Fixed Catalyst Bed and offers the opportunity to apply the equally classical Ergun equation in order to determine (or employ) the associated pressure drop across the bed.

6. You should obtain and thoroughly read background material on this operation. I strongly recommend you obtain a copy of “Gas Purification” by Kohl & Riesenfeld. This book is a great source for this type of operation. For background on the practical application of Shift Converters I recommend you read “Technology and Manufacture of Ammonia” by Samuel Strelzoff; John Wiley & Sons; NY (1981)

I hope this analysis helps you out – although perhaps not in the manner you had hoped for. It is up to you and you alone to do your own work – both mental and physical. Otherwise, you will fail as a Chemical Engineer.

Art Montemayor