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I would like to ask about required H2/HC ratio and coker naphtha processing in a naphtha hydrotreater.
We have a unit processing a mix of straight run and coker light naptha. Unit consists of two reactors, one for diolefin saturation and one for HDS and olefin saturation, both use regenerated NiMo catalyst. Colleagues intend to raise coker naphtha ratio, which is currently maximized in 12%. I made some calculations which resulted, that coker naphtha has around 90 Nm3/m3 chemical H2 consumption, and the units H2/HC ratio is around 60-100 Nm3/m3 depending on throughput. 12% naphtha results in ~16 Nm3/m3 chemical H2 consumption. If I remember well, the H2/HC ratio should be at least 5 times the chemical consumption, in this case 5*16=80. Am I right, or can this value safely be reduced? Does anything else restrict the max ratio of coker naptha processing? Temperature raise is about 25-28 °C on HDS reactor with an inlet temperature of 290 °C.
24/04/2015 A: Prabhakar Reddy Seerapu, SATORP, redi_nfcl@yahoo.co.in
I am presently working in a similar Naphtha hydrotreater which is fed with mix of Coker Naphtha and straight Naphtha from Crude unit.we have 3 reactors.One for di-olefins conversion operating in liquid phase and at low temperature to ensure conversion.second for olefins hydrogenation and third for hydrogenation and nirogenation. well our designer AXENS has specified as maximum coker can be 19 Wt% of the total feed rate.recently we had to process double the quantity of coker Naphtha as second train of NHT was down for catalyst replacement.In this case we had processed coker Naphtha up to 35 Wt% even. Axens has specified that this situation cannot be for more period of time as silicon trap has not been designed for such higher silica content in second reactor.regarding operation point of view we don't have gas to oil ratio indications in DCS in Naphtha unit as compared to Diesel/Kerosene Hydrotreaters. But u can calculate this easily considering the Recycle gas purity.try to maintain Gas/Oil ratio unless it there is a limitation.Specially look for your reactor DP which is the main parameter to observe for. temperature rise was more than 55 Deg.c in our second reactor,so we had to reduce our second reactor inlet temperature even 10 deg.c below SOR to sustain.all the above time unit was on-spec and no other issues encountered
24/04/2015 A: Kumar Kurapaty, KNPC, kumar83che@gmail.com
You can consider the usage of Liquid Nitrogen for leak test in case if you want to avoid Hydrogen.
As the process will be having Fired Heaters, you can inject Liquid Nitrogen once into the system and then heat up till the required System Pressure is achieved.
23/04/2015 A: rvidner chib, RIl, rschib@rediff.com
Being a Coker Naphtha HT and NIMO catalyst H2/HC ratio you can be safer at more than 65 .For COMO catalyst you can go upto 50.
23/04/2015 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
Other things to consider are the Si content of the coker naphtha and the impact that will have on runlength. Since your unit is already designed to process coker naphtha, it may not be a problem but needs to be considered. The coker naphtha impact depends on lot on quality. If the naphtha is high end point, it can have higher than expected negative impact on hydrotreater operation. That can also carry over into catalytic reformer operation through higher end point gasoline and/or increased coke make.