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26/03/2011
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J Rout, B. Tech, routjhr@gmail.com
Catalytic reforming N+2A, N+3.5A, and N+A are called feed index. Higher the value, better the feed for reforming and requires low severity. The objective of reforming is to convert the feed to aromatics for RON improvement. Conversion of Naphthalene to Aromatic is the easiest reaction in Reforming, so if N is higher conversion will be easy. The Aromatic component in feed does not require conversion. So if N+2A is high Reforming will be possible at lower severity and we can expect better RON for reformate.
Further, some licensors also recommend for A+0.85N as feed index. These indices are used for estimation of estimation of Normalized Reactor Inlet temperature, i.e. the optimum temperature for Reformer operation. Normalized RIT deviation from actual RIT indicates the catalyst deactivation.
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28/09/2009
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Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
As you would expect, the higher the N+2A, the higher the IRR of a potential project to install a reforming unit. Because so many studies have been made based on various field condensates as feed, a process licensor can look at the N+2A and immediately say whether such a project would be viable.
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22/09/2009
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Alan Goelzer, Jacobs Consultancy, alan.goelzer@jacobs.com
I concur with previous answer. Just some additional comments follow. Parameters cited have been employed as a means of correlating the responsiveness of various hydrotreated heavy naphtha feeds to catalytic reforming. Personally, I prefer "N+A" since this also provides an indication of how much of the cat feed is paraffins. As noted, greater degree of processing severity is required to convert substantial percentages of C7 to C11/C12 normal paraffins and isoparaffins into alkyl benzenes and hydrogen against a given RONC objective for the C5+ reformate.
Quite obviously, if the objective is to make higher octane alkyl benzenes with just limited "hydrocracking" into C3 to C6 paraffins, the aromatics in a HT heavy naphtha are already there and providing substantial octane contributions. However, aromatics in the cat reformer feed do not contribute significantly to co-product hydrogen production. Naphthenes [including cyclohexane and methyl cyclopentane] convert into aromatics + hydrogen quite easily, while C7 to C11/C12 paraffins are more challenging and require more processing severity against a given RONC in C5+ reformate.
Note that isohexanes and n-hexane are relatively resistant ["refractory"] to becoming benzene while the cyclic C6 [MCP + CH + Bz] are prime precursors for benzene.
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21/09/2009
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Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
In CRU, the quality of feed dictates operating parameters for desired product qualities and consequently product spectrum with yields. Very good process correlations have been developed by IIP-EIL, UOP, IFP, IOCL etc using N+2A, N+3.5A or N+A or likewise for the predictions of yields at specified ON, temperatures , aromatics contents, temperature drops, heater and inter heater duties, cycle length, coke deposition etc. Lower the N+2A higher the temperature of the reactors and lower the reformate yield, higher the coke deposition at specified ON. We have observed the N+2A as low as 35 to 40 vol % and as high as more than 100 depending on feed source. Process licensors may specify these criteria to meet guarantee for a plant for a certain duty be it a CCR or SR plant. CCR perform better than SR due to obvious reasons which is not in the scope. For details, you may refer to book on Catalytic Reforming by D. M. Little, Pennwell Publishers
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21/09/2009
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Kamaljit Medhi, Indian Oil Corporation Ltd, medhik@indianoil.in
Please read as catalytic Reformer (both SR & CCR) and not only as CCR as mentioned in the first line of my previous answer where Naphthenes & Paraffins get converted to Aromatics.
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21/09/2009
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Kamaljit Medhi, Indian Oil Corporation Ltd, medhik@indianoil.in
The objective of any CCR is to convert the Naphthenes and Paraffins to Aromatics. Also some isomerization reaction take place. Naphthene gets converted to Aromatics very easily while conversion of Paraffin to Aromatics by dehydrocyclisation reaction requires severe process parameters. So most of the naphthenes get converted to aromatic in the first and second reactor while Paraffin to aromatic conversion take place in the last reactor.
So more the N+2A value means the feed is rich in Naphthene and Aromatic which is good for catalytic reforming. Higher this value, we will require less severe process parameters in the Reformer to achieve required RONC improvement which will result in higher catalyst life. In Assam Crude, the N+2A is very high and of about 75 which is an excellent feed for Reformer but not good for Isomerization catalyst.
With low N+2A, you will require higher severity and the choice of reformer type will be CCR.
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