5 replies to this topic

[empire]

Hi,
In my Naphtha hydrotreating Unit, due to fouling in CFE, the furnace inlet temperature drops down.
Our furnace was designed for only gas flow into tubes. So, we have to keep inlet temperature above dew point of mixture of naphtha and hydrogen.
Based on your experience/any document, how many degree above dew point is enough?
Thanks in advance.
Empire

[iyer]

Well, I think your heater should be able to handle liquid also. The NHT units I have seen often see the phase change in the heater. Moreover during initial sulfiding and start up, the flow through the heater changes phase. Now things to look at will be, if the heater has two passes or more, you would need to balance the passes, to adjust both the tube skin temperature and the flow rate through each pass (this may arise due to liquid being more in one pass). Another thing is the reactor downstream. Now the inlet distributor should be able to handle both liquid and gas, but if you have more than a bed, the the second bed may not have a vapor-liquid mixing chamber. Plus a two phase mixture creates a possibility of channeling.
As such I dont think the heater should be a big issue, but as always try maintain a temperature higher than dew point.



Hi,
In my Naphtha hydrotreating Unit, due to fouling in CFE, the furnace inlet temperature drops down.
Our furnace was designed for only gas flow into tubes. So, we have to keep inlet temperature above dew point of mixture of naphtha and hydrogen.
Based on your experience/any document, how many degree above dew point is enough?
Thanks in advance.
Empire
[/quote]

[empire]

Thanks,
Based on Vendor databook, this heater was designed with vapor phase inlet. It has 4 passes but nothing to adjust the flow for each pass.
That why we have to consider of making coke inside coils. We have only skin temperature to monitor the flow.
We should keep above dew point but inlet temperature will drop down eventually.

[iyer]

So how do you control flows through each pass, If you dont have any flow control? i suppose you also have TI's on the outlet of each pass, are the readings close to each other or are they hugely apart. What is your inlet temperature right now and the unit pressure?

[empire]

We cannot control flow for each pass. At the moment, the outlet temperature difference between each pass is still small (max=3C), Inlet temp=252C, Pressure@Separator= 21kg/cm2(g).
But in the future, as I mentioned in the first post, furnace inlet temperature will drop eventually.
So,I want to know the limit.
Thanks

[iyer]

Well, since you are asking for a number, I guess 236-240 degrees should be when you start to see liquid. Although, I still believe that your limit will be the heater. You may reach a point when you are over firing your heater as your inlet temperature falls. Again keep an eye on tube skins and differential pass temperatures. Any idea what caused the fouling. Are you having coker naphatha feed, in that case what is the diolefin number?
Please keep us updated on your progress