7 replies to this topic

[rahulavyas]

Although the theory says that there is no theoretical limitation to Reforming reactor pressure, and it is only govern by the pressure drop in the system, My question is that what is the minimum pressure at which Reformers are operated and is the catalyst stability only criteria due to which the reformers are operated at higher pressure say over 8-10 barg?

 

What will happen if the pressure is lowered?

 

[golden_gate]

Hi, which type of Reforming are you referring to?

 

If the reaction produces more gas molecues in the forward reaction, then ideally operating at a lower pressure would favour the equilibrium in producing more of the products. However, operating at lower pressure means that the mass throughput for a given reactor volume is less, i.e. for the same size of reactor volume, less mass of reactants would be going through at a reduced pressure.

[rahulavyas]

It is a gasoline reformer, After I reffered the literature it stated that with lower pressure operations the conversion are more but this affects the catalyst life in negative way, mailny due to more acclerated coke formation

[Himanshu Sharma]

hey !

 

The type of pressure range you are talking applies to Fixed Bed reformers wherein you have to optimize coke laydown to meet cycle lengths.in a continuous reformer pressure level are much lower 45.5~3.5 Kg/cm2 g because you regenerate catalyst  in situ for any coke deposition.

 

and of course lower pressure favors  reforming reactions !

 

Regards

Himanshu

[Mainak Sarkar]

There are 2 prominent reasons for operating reformer at high pressure (28 - 30 barg)

 

1. At higher operating pressure you can process reasonable amount gas with in a reasonable size of reactor. But if you want to operate at lower pressure, to process same amount of gas the reactor size will be enormous.

 

2. In a hydrogen generation Plant (HGU) after reformer reactor there are two more reactors (i) High Temperature shift reactor and (ii)  Low temperature shift reactor and finally PSA system for purification of hydrogen. Therefore there are reasonable pressure drop across the system. Moreover the PSA system require at least 20 barg to operated properly. So if Reformer is operated at low pressure to take the thermodynamic advantage of equilibrium then after reformer reactor the reactor effluent need to be further pressurize by compressor, which involves cost. So a HGU is a highly pressure balance system.

 

To make you  understand the  process I must say you that there is no gasoline reformer unit. You must be referring about Naphtha reforming unit. You should understand the difference between Naphtha & Gasoline. Although Gasoline is prepared from naphtha range cut but Naphtha & Gasoline are not the same thing. Gasoline is finished product, have high aromatic olefins and isomers to have high octane number. The naphtha used for HGU is generally straight run and have poor octane value.

 

The second thing, you mentioned about coke formation. But I must say you that in reformer, pressure has little effect on coke formation. The main coke formation is due to poor Steam to hydrocarbon ratio. If you maintain proper Steam to hydrocarbon ratio the coke will suppress. So in a reformer Steam to hydrocarbon ratio is about 5 to 7. The effect of pressure on coke formation is found in hydro processing or hydrocracking type of process.   

 

Another important thing is Pre-reformer. Any commercial reformer unit operating with naphtha as feed should always have a pre-reformer prior to reformer unit.

[Himanshu Sharma]

Utter chaos and confusion in the thread !

 

Seems like we have mixed two type of reforming unit commonly present in Refinery Complex

 

1.Steam Reforming of HC/Natural gas to produce Hydrogen.

2.Heavy Naphtha Reforming to form reformate which is an important blend component of gasoline pool owing to its high octane number.

 

As per my understanding the query relates to Heavy Naphtha reforming (though it should have been more specific) as it talks about keywords like Low pressure reforming,pressure drop in the reactor and operating pressure range close to Fixed Bed reforming.I request you to  relate my reply above to Heavy Naphtha reforming.

 

Just for the records (for anyone reading this thread at a later date) I believe that 'Mainak' above is talking about Steam reforming to  Hydrogen and thus most of the comments are specific to it and they don't  hold good for Heavy Naphtha reforming.

 

Thanks and regards

Himanshu

[Mainak Sarkar]

Himanshu,

 

There is no confusion at all. In refinery two types of feed are being used for hydrogen generation, (i) Naphtha (Light or heavy) (ii) Natural gas (NG). Now since natural gas are available in India so some reformers are being changed to NG feed from LN/HN feed. But whatever may be the feed for HGU the reformer reactor operating pressure is 30 to 28 barg only. This is because irrespective of feed (NG or LN) the actual feed for Reformer reactor is CH4 i.e. methane only. Suppose LN is used as feed then prior to Reformer reactor one Pre-reformer reactor is present which converts LN to Methane and CO. The methane and CO is then fed to the reformer reactor. The pre-reformer operates at 32-30 barg pressure. The catalyst is Ni, same as that of reformer reactor. Direct LN is not fed to the reformer reactor generally. Since that may cause coke formation. Some licensor (M/s Linde) also feed LN directly to the reformer reactor but then the catalyst sequence is different. But even then the reactor pressure is maintained between 28 and 25 barg. Pressure is must because at 600 degree C (inlet temp of Reformer reactor) the naphtha is also in gaseous state.  So the sequence for hydrogen generation unit is :

 

Pre-reformer --> Reformer --> High Temperature Shift reactor (HTS)--> Low temperature Shift reactor (LTS) --> Pressure swing Adsorption unit (PSU)

[Himanshu Sharma]

I salute your love and expertise for Hydrogen production and apologies if you felt offended by my clarification above !

 

but please note the clarification provided by thread originator

 

"It is a gasoline reformer, After I reffered the literature it stated that with lower pressure operations the conversion are more but this affects the catalyst life in negative way, mailny due to more acclerated coke formation"

 

I don't want to run into some other discussion off the topic but i felt the topic needed clarification.