9 replies to this topic

[dinesh]

Dear all,

I am arvind, working in design consultant plz help me out for the safe ventillation of the hydrogen from the reactor.

Basically in the 200 m3 reactor the Hcl conc. is ~ 5% and is getting reacted with the Fe to form the FeCl2 and the biproduct H2 at the rate of ~ 24 kg/ hr ( 332 M3/ hr) along with water vapor @100 Kg/Hr for the safe venting of produced H2 what should be the venting arrangment suggested



help me

[Nirav]

hello arvind,

I would ask some more things before giving any suggestion.

What is the pressure of reactor?
Does reactor outlet consist of two phase flow?
Do you have a basic flow scheme of your process?

[dinesh]

dear Nirav,

thanks for replying me.
as per your request i m sending the information.

The pressure in the reactor is about 1 atm.
There is only one phase but their are two immescible componants that are 1) Hydrogen 2) Water Vapour
There is just a single reactor of 200 m3 .

Thanks ,
Arvind

[Nirav]

Hello,

Is it a batch reaction or continuous? can you provide a flow scheme for your process? Where does reaction product go from reactor? How are you maintaining reaction pressure at atmosphric condition?

If your system is closed, hydrogen in product mix. will increase pressure of the system. In such a case, you must have a simple pressure control loop in your system which will keep venting hydrogen from system and maintain the pressure of closed system.

I work in hydrocarbon processing field. Therefore, i never came across such 'inorganic' process. But i'm interested to know about it.

warm regards,

[Technocrat]

dear dinesh,

i am a chemical engineer from mumbai having experience in methanol plant.

what is the composition of the gas mixture? you should vent the gas mixture to a flare because H2 is a flammable gas. or you may bottle the H2 gas after purification.

regards.

[GKKannan]

As Dinesh said, H2 should be vented to Flare header only. Or if Flare header is not there, you should provide a small flare stack specially for venting hydrogen. Before venting it should be burnt with a pilot gas at the flare tip. You can not observe any colored flame for H2 burning. However you can observe in the night time (pale to very pale yellow flame).

GK Kannan.

[Milutin]

In our refinery we have diesel HDS unit designed 20 years ago. Designer routed all streams which contain hydrogen in separate "hydrogen flare", actually simple pipe, 20 meters high above ground, without pilot burner, "flare" is situated in the middle of unit. Hydrogen stream from high pressure separator contain: hydrogen, H2S and light hydrocarbons.
I do not understand reason for this, because refinery flare header pass only few meters from plant, and other "non hydrogen" streams from same unit are connected to flare.

We considered this dangerous and decided to connect hydrogen streams to refinery flare

[Technocrat]

dear milutin,

you should call the 'hydrogen flare without pilot' as 'hydrogen stack' and not a flare.

regards.

[dinesh]

Dear all

I am Dinesh ,
For the same topic of Hydrogen disposal in the atmosphere i would like to tell u that the process is carried out in the batch process initially the reactor is fill with Leach liquor 200 m3 of density 1320 kg/m3 at temp. 45°C containing ( 5% HCl & 4% ferric chloride FeCl3 ) and iron scrap @ 11000 Kg is dumping in the reaction mass total reaction timing is @ 30 Hrs from that it @ 20 Hrs for the complete dissolution (reaction ) for the scrap if we calculate then @ 12 kg/hr of H2 is getting generated during reaction with water vapor @ 100 kg/hr. during reaction the temp. is goes up to the 70°c

Plz guide me about the disposal of the H2 as it LEL is 4% UEL is 74% with air (v/v)


regards
Dinesh

[Nirav]

Dear all

I am Dinesh ,
For the same topic of Hydrogen disposal in the atmosphere i would like to tell u that the process is carried out in the batch process initially the reactor is fill with Leach liquor 200 m3 of density 1320 kg/m3 at temp. 45°C containing ( 5% HCl & 4% ferric chloride FeCl3 ) and iron scrap @ 11000 Kg is dumping in the reaction mass total reaction timing is @ 30 Hrs from that it @ 20 Hrs for the complete dissolution (reaction ) for the scrap if we calculate then @ 12 kg/hr of H2 is getting generated during reaction with water vapor @ 100 kg/hr. during reaction the temp. is goes up to the 70°c

Plz guide me about the disposal of the H2 as it LEL is 4% UEL is 74% with air (v/v)


regards
Dinesh

Dinesh,

I think yours is different process than what other people are explaining for normal refinery hydrogen disposal. I was also confused with it first.

First of all, you must have a "closed" reactor in order to effectively handle hydrogen and other vapors being produced during reaction.
Is it agitated reactor?
Earlier also, I asked you for simple flow scheme to understand the "process flow" better. What I understand from you is that you have a "batch reactor" for your process. You also said that it works at 1 atm pressure.

Now, unless and until you have closed system, you will not be able to dispose "hydrogen" safely. Even though, the basic principle is simple, actual design requires proper analysis and understanding of various design aspects for safety.

In principle, you can have following scheme. I would suggest you to go to "reputed consultant" to study the feasibility of scheme in detail and then design it based on your requirement. What I'm writing is one example.

[1] "Closed" reactor or system
[2] Nitrogen blanketing of reactor which will help to maintain reaction mass out of contact with air. You can use superheated steam also if you don't have nitrogen easily available.
[3] Pressure gauge &/or transmitter which will indicate pressure rise in reactor.
[4] A vent line from reactor leading to safe height in atmosphere.

In a continuous process plant, this kind of operation would be performed by 'control valves' mounted on both the nitrogen and vent line. This will maintain pressure inside reactor. Depending on quantity and frequency, a vent line will also not be open to atmosphere. But it will go to dedicated hydrogen stack or flare.

However, in your case, it's a very very small quantity (12 kg/hr) of H2. So, in my opinion, you can have manual operation with the scheme I explained above.

The brief procedure could be as follows.
[1] Evacuate all air from your reaction system with the help of nitrogen or steam and then charge the reactor with reaction mass. You must ensure there is no air inside it by laboratory analysis.
[2] As reaction progress, it will rise the pressure of the system since there will be hydrogen and water vapor in product. You must monitor the rise in pressure through pressure gauge mounted on reactor.
[3] Once reaction is stopped, you can vent all hydrogen from the vent line. During venting, you must keep the nitrogen or steam blanketing line open so that it will keep replacing hydrogen being vented and there will not be any air ingress in the system. If any time, air comes in contact with hydrogen which is inside reactor, it will form a DANGEROUS explosive mixture. So, you must be careful. Hydrogen can be vented at safe height into atmosphere. This will not form any dangerous mixture due to the fact that there will be water vapor also along with hydrogen and once it is open to atmosphere, it will further dilute very quickly.

Now, you must consult some reputed design firm, so that you don't miss any safety, design & regulatory standards to make your process work safely. What I was trying to explain is just one example or direction.

I hope it helps.
Warm regards,