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Flare Location Rules 2

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StoneCold

Chemical
Mar 11, 2003
992
I am working on installing a small ground flare for an intermittent reactor off gas. The off gas is a mixture of butane and ethane at about 10 scfm. Turns out to be about one million BTU/hr. My problem is this. I have not been able to find any locating information on flares. There is an API guideline but I am not sure it is really applicable. My insurance company is quoting the API guidline. It states my flare must be 100 ft from any building. (My reactor is in a large concrete building). That is not a huge problem. But the second statement is the flare must be 300ft from the nearest open flame. Since this flare is on a small plot of land I can not meet that criteria. Fire codes etc seem to be silent on industrial gas flares.
I talked to the flare people about switching to a thermal oxidizer because my insurace company seems to look at them as harmless, they can go right next to the building if you want. They thought I was nuts for suggesting the switch.

Does anyone with experience with small ground flares have a reference that I can use in locating my flare?
Can I get around the 300ft by having flame out interlocks? (I am planning on having them anyway)

Thanks

StoneCold
 
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Is the 300 ft requirement from the base of the flare stack or the tip?

Also, where do you have an open flame in your lease?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
 
Ashereng.
I think the 300ft is from the base. The flare we are thinking about getting is about 9ft high so it does not really matter. The other open flames I have are my boiler and some indirect fired heaters on the roof of the building.
I presume that they constitute "open flames". I could be totally wrong on that.

Thanks for your questions they really make me think about some of my assumptions.

Regards
StoneCold
 
Stone:

I'm on my way out to the airport on a field trip to West Texas and just read your post. You're right; there is cause for concern. The main concern is the radiation heat given off by the flare's flame and impacting on personnel and fixed property in the surroundings. There is a way to calculate the expected temperatures and thereby predict, with some degree of accuracy, the resulting heat up in the surroundings. This could be tough with a rather low height on your proposed flare.

You're right, the thermal oxidizer is far easier to predict, site, and control as far as environmental impacts are concerned. If possible, this in my opinion, would be your best solution - at least to give you the least troubles and potential future problems.

If I can find any thing else in my files when I get back, I'll let you know. Sorry I can't give you more info for now, but I'll keep my eye on this thread. Good Luck!

Art
 
9 feet seems a bit short, but I am sure your flare vendor has the calculations for heat radius and such. We typically use a 30' flare stack, and taller. Then again, you are only flaring 10 scfm, plus constant purge I guess.

I haven't heard about the 300' radius open flame requirement. If I find out more, I will let you know.



"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
 
Part of our problem is the small size of the flare. We are not a refinery we just want to intermittantly burn some ethane and butane to prevent the need to vent the gas. Simple as that sounds it has not turned out to be that easy.

Montemayor. I have made a simplified model of the radiant heating and determined a safe minimum distance to stay away from the operating flare. Turns out the radiation drops to 1 kw/m2 at around 15ft in my model. This is an open flame model so the enclosed flare should be much better but I have not got a confirmation on that from the flare vender.
 
StoneCold: whose ground flare are you using? I'm looking for a small enclosed flare for a job I'm working on right now, with similar conditions: low duty and intermittent operation.

As to the thermal oxidizer, I'd be afraid that the transient performance won't be nearly as pleasant as you might expect from your little ground flare. If your stream is intermittent and of short duration, wouldn't you burn a whole lot more pilot gas idling a thermal oxidizer than you would to run a flare pilot?
 
moltenmetal Some of the companies we are looking at are, Flaregas, John Zink, and Zeeco.

Whether it is a ground flare or a thermal oxidizer I have no intention of running the pilot gas or purge gas all the time. We are a batch company so I can light the pilot on the flare then run the process and shut it down afterwards with minimal engineering and administrative controls. The thermal oxidizers are scaring me off because of the cost.

Regards
StoneCold
 
any possibility of burning the off-gas in other equipment? for example, use an ejector (burn motive gas + off-gas) for a fuel source? brainstorming thought . . .

if cost was not an issue, what would be your choice (flare or oxidizer)? but since cost is a factor, think about the future risks involved with a ground flare. your location and surroundings certainly are a worthy consideration in terms of any future impacts.

as far as flare suppliers, the first two mentioned are reputable. furthermore, if you provide them the off-gas composition + flow rate conditions (norm, min, max), they will provide you the radiant heat profile diagrams from the flame at the conditions stated. using this information will be helpful in determining distance. i certainly would question the source of the 300-ft criteria as well. from what i remember, the distance requirements are dependent upon the radiant heat output of flare flame + solar flux. once the flare output data is known, the flare height & ground distance requirements can be determined.

good luck!
-pmover
 
Stonecold,

At current Henry Hub prices you will be flaring or wasting about $240 of fuel per day. Of course that is for 24/7 operations.

Here is a suggestion. I'll provide you a PlasmaWhirl at NO COST for a one year demonstration. You decide what to do with the hydrogen. Buy a fuel cell and generate electricity.

You can bank the tax credits as well as credits for not emitting NOx and CO2.

Todd
 
Thermal oxidizers can be run on a batch basis such as for loading terminals. Trucks pull in, the TO is automatically started and when it's up to temperature, the truck loading permissive is given. The delay can be a factor since the trucks don't like to be kept waiting but on the other hand, as you point out, the fuel consumption can be significant.

However, on a capital cost basis they are higher. They can be a good choice if you need to avoid noise, light or heat radiation issues.

John Zink or any other flare company can do the heat radiation calculations for you but there are a lot of factors and some subjective assumptions have to be made.
 
StoneCold

Sorry that I'm jumping into this a little late.

It seems to me that there are some issues of terminology which need resolving by you and your insurance people.
That's not really surprising because the Flare Industry doesn't really have a handle on what to call what in the area of Ground Flares.

A Ground Flare is essentially a small flare at or close to ground level.
If you are in an Oil field application (in Kuwait for example) that might mean a line of small pipes sticking out of the sand, with open flames. It could equally be a field full of the same type of pipes arranged in a matrix and put behind a metal, brick or concrete wall to keep people out.
More frequently in the USA and Europe, it means an enclosed device like a furnace, with insulated walls which directly contain the flame and direct the flue gases up out of the open top, which is basically the chimney, but may be the same size as the firebox itself.
One vendor calls this a Thermal Oxidizer.

A real Thermal Oxidizer would also have some controls included to manage the internal temperature and assure destruction (on the basis that the intent is to really get rid of a nasty material rather than just burn something). The more sophisticated these controls become, the closer the device comes to being called an Incinerator, which the regulatory authorities love because they have rules about incinerators and want you to apply every one of them (!!!) regardless of your application.
Also, Incinerator can easily migrate into Catalytic Incinerator and then it's really big time stuff.

With all these descriptions, it's not surprising that you can find it difficult to resolve some rules.

It is my suspicion that you are really looking for an enclosed Ground Flare. This would have an uncontrolled air inflow based simply on the height and natural draft through the furnace and a height determined by the internal capacity and the discharge elevation needed to avoid all that hot flue gas drifting across sensitive equipment or personnel areas. Normally once the equipment is running all flow is inward and upward (natural draft) and you don't have to worry about radiation because the walls are insulated, so there's no outward heat flow to speak of. The device would have a local protective barrier of some sort to prevent personnel access when the firebox is active.
However, your basic gas feed may present a HAZOP concern which needs to be considered. If the main flame goes out, what back up do you have. Does the gas flow stop, go somewhere else or just pour out all over the floor ? Constant flame presence is something which needs to be addressed. If your gas is cold Butane and you lose the flame, the insurance company have a right to be concerned.

I'm not sure this solves your problem but it may help to keep others who chance on this diatribe out of trouble.

Good luck

David
 
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