Q & A > Question Details
In a semi regen. fixed bed platforming unit for HOBC production, what is the impact of operating the unit at an increased Hydrogen to hydrocarbon mole ratio or increased H2 partial pressure than recommended? I have noticed that whenever the mole ratio is increased by virtue of increase in recycle gas flow, sum of delta Ts across reactors drop, especially across Rx 1.
I want to know is there any positive or negative impact of this practice on reformate RONC, RVP and yield?
02/07/2010 A: RENE AGA, SECOT, renelaga@telefonica.net
You have to maintain a H2/HC ratio to avoid catalyst deactivation, but platforming is a dehydrogenation process. Dehydrogenation is an equilibrium reaction favoured by low H2 partial pressure. Thus it is recommendable not to increase H2 ratio higher than necessary for catalyst protection.
13/03/2010 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
Enhanced amount of circulating recycle gas gains additional enthalpy in heaters and interheaters in reaction circuit. You may consider it as inert without taking part in reactions. Thus the enhanced enthalpy will add heat to the medium in the reactors. So delta T across the reactors will drop though the conversion reactions are not affected. You may make simple energy balances. This will show the resulting change in delta T. If you are interested, I will forward the published detailed method for such estimation. There are no remarkable benefit of more than optimum recycle rate. The negative aspects are higher circulating cost in compressor, higher heating cost in heaters and interheaters and higher cooling costs in air and water coolers without any benefit to the process.
12/03/2010 A: Hubert Mueller, Bayernoil, guhumueller@web.de
The benefit of a higher H2/HC ratio is a longer cycle length because of a reduced coke laydown.
But your energy consumption both for compressing and heating the additional recycle gas will go up.
So it turns out to be an economical trade off. The direct influences on yields are minimal.
Your remark regarding the delta t`s is correct and is a result of the "dilution" of the dehydrogenation reaction by the additional recyclegas
11/03/2010 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Your process licensor should have correlations available for your use, if you know who it is and the unit is not too old for such a contact. At no change in reactor inlet temperature and fresh feed rate, even though the LHSV by definition is unchanged, the oil "sees" the catalyst for a shorter period of time, resulting in reduced conversion, RONC and yield. If the temperature is not increased to compensate, theoretically, the run length would increase. RVP is most affected by the fractionation.
11/03/2010 A: keith bowers, B and B Consulting, kebowers47@gmail.com
One must remember that hydrogen has a very high heat capacity (in fact is used for coolant in the quench zones.) One must 'adjust' the per bed temperature rise to account for the additional hydrogen and its heat capacity. I would not expect to observe any significant change in reactor product distributions and properties if the 'design' values were sufficient.
One 'might' see a slightly slower rate of decay in catalyst activity. It is seldom economically attractive to operate at more than minimum required hydrogen partial pressure as determined by the catalyst, feedstock, and desired product qualities. Circulating additional hydrogen consumes significant additional recycle compressor power and reactor feed heater fuel.