Re: DMC on Alky Spent Acid

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Posted by Brian Burgio on June 02, 1999 at 12:18:09:

In Reply to: DMC on Alky Spent Acid posted by Jim Gunderman on May 28, 1999 at 19:33:16:

Jim,

Here are some questions I would have based on my understanding of alkylation units.

1) How well does your inferential perform. This type of inferential is very susceptible to the operation of the acid settler. The inferential will suffer if there is significant and inconsistent hydrocarbon carryunder.

2) Do you measure all the significant variables that effect acid consumption and thus acid strength. Acid consumption is a function of many different variables. Some are fixed, such as equipment design. Others vary. Some are measured, others are not. Some variables that acid consumption is a function of are: olefin feed type, contaminants in system, unit feed rate and/or olefin space velocity and temperature.

Other comments:

The volume of acid in the contactors and settlers is very large relative to the fresh and spent acid rates, so any changes that are made will take a long time to observe.

Typically, the flow rates of spent acid from each acid settler are adjusted to hold a constant inventory of acid in that settler as shown in its overall gauge glass – this is something you will not have a measurement of.

Maintaining sufficient acid strength to avoid an “acid runaway” is very important.

These are just a few thoughts I had. Hopefully someone with first-hand experience will also be able to provide some insight into you question.

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: Jim,

: Here are some questions I would have based on my understanding of alkylation units.

: 1) How well does your inferential perform.  This type of inferential is very susceptible to the operation of the acid settler.  The inferential will suffer if there is significant and inconsistent hydrocarbon carryunder.

: 2) Do you measure all the significant variables that effect acid consumption and thus acid strength.  Acid consumption is a function of many different variables.  Some are fixed, such as equipment design.  Others vary.  Some are measured, others are not.  Some variables that acid consumption is a function of are:  olefin feed type, contaminants in system, unit feed rate and/or olefin space velocity and temperature.

: Other comments:

: The volume of acid in the contactors and settlers is very large relative to the fresh and spent acid rates, so any changes that are made will take a long time to observe.

: Typically, the flow rates of spent acid from each acid settler are adjusted to hold a constant inventory of acid in that settler as shown in its overall gauge glass – this is something you will not have a measurement of.

: Maintaining sufficient acid strength to avoid an “acid runaway” is very important.

: These are just a few thoughts I had.  Hopefully someone with first-hand experience will also be able to provide some insight into you question.



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