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I wa surprised by couple of assertions you made. I'm not saying you're wrong. I can't say that because I'm not directly involved with refinery work any more. But I'm surprised.
The first surprising assertion was that gasoline is typically not controlled using feedback from on-line analyzers.
I haven't done a gasoline blending controller for 15 years. But at that time we designed a control system that used on-line analyzers for octane,RVP, and if I remember correctly, 50% boiling point. There was a capability to use several others, actually, but the RVP and octane were the main ones people worried about. I think the others were generally well within spec with the mix of belnding components available at that particular refinery.
We designed a system that took into account the characteristics of the tank heel and calculated a recipe that would end up with the tank at the spec for the desired product when the tank was full. We then used on-line analyzers to correct the properties by feedback. The tanks were circulated and sampled to the lab when the blend was completed.
The lab was the final control of the properties of the products, but there was definitely closed-loop control along the way.
The control systems we used at that time were solved by a linear program, so there was an implicit assumption that the properties of the final product were a linear combination of the individual component properties. That assumption is known to be only approximately correct, and besides, there were no on-line analyzers of the blend components, just periodic lab data. On-line analyzer feedback was therefore required.
At that time, people were beginning to talk about blending straight into the pipeline. I don't know if they've gotten to that point yet, or not. Your comment seems to indicate that they haven't.
The other assertion I found surprising was that some refiners don't spec their gasoline tightly enough by ASTM D4814 so that major refiners would use their products. As I recall, ASTM D4814 is the test for octane. The product specs I am aware of had only a minimum spec on the octane, not a maximum. You were on-spec for 87 Regular if you were 87.1 or 90.4.
I do agree with you that some refiners put some nasty stuff in their gasoline. Way back when I was involved in this kind of work, I heard of one East-coast refinery (whch will remain unnamed, but which had at least one "X" in the name) that put Coker naphtha in their gasoline without hydrotreating it. That would give you a distinct "rotten egg" smell. I suspect that the unsaturates would also cause some deposits in the combustion chamber.
It's been fun remembering the early days of my career, but I'm afraid we may be boring everyone else. If you have any more comments, though, why don't you email me?
Oh, and as for the Chevron discount... I don't think the credit limit on our Chevron account could stand everyone from TSN using it. But if you're in Houston, I'll buy you a tank of Chevron's finest.
Best regards,
Dave
posted by 24.238.190...
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