4 replies to this topic

[sealittle]

Hello CHEResources Members!

I am relatviely green (5 months into my career) and have been assigned the task of generating a Fuel Gas Scrubber Equipment Scope of Supply.

The fuel gas scrubber package will take clean gas from our sales gas line and use it in the plant to maintain plant operations. The plant is approx 8MMSCFD (fairly small) and is processing SWEET gas.

I need help in determining the capacity of my scrubber and storage.

I understand that typically one ensures 100% backup gas is available.

I am wondering if anyone has any rules of thumb for determining required fuel gas for various instrumentation and start-up gas requirements.

Any insight you may have will be helpful!

Thanks,

Sealittle

[Art Montemayor]

Sealittle:

You are indeed a young and green engineer. You still lack the ability to communicate with the correct information and ask the key questions. Allow me to give you some comments to your query in order to get your query correct and properly understood:

The plant is approx 8 MMSCFD (fairly small) and is processing SWEET gas.
Are you trying to say that your natural gas (you fail to tell us WHAT kind of gas, so I have to guess) plant processes 8 MM Scfd of natural gas and now is going to consume a portion (you fail to define the portion of gas you are to feed back into the plant) as fuel.

I need help in determining the capacity of my scrubber and storage.
YOU have to determine how much gas your plant is supposed to consume. We can’t possibly help you determine that. Use the plant’s operating manual to find out the various consumption points and the expected gas consumption. Check out the actual consumption of gas from the fuel gas meters that must be measuring the consumed fuel gas at present. And if those two sources of gas consumption are non-existant, then take the measurement of feed gas into the plant and subtract the quantity of Sales gas produced and the amount of sour products removed from the Sales gas. Your processing plant HAS TO HAVE an inlet gas meter for the sour gas and another gas meter on the Sales gas – that is a prerequisite for any natural gas processing plant. If you don’t have those two meters you can’t know what you are doing. They must exist.

I understand that typically one ensures 100% backup gas is available.
That is a decision that your plant’s management establishes. If I were the plant manager, that’s certainly what I would ask be included in the Scope of Work for the proposed “scrubber and storage”.

You don’t explain why, if your plant is putting out good and proper sales gas, you have to use a “scrubber”. What, exactly, are you “scrubbing”??? I think what you intend to say is that you are installing a solids separator. I don’t believe it would be possible to have any liquids in Sales gas. Even the possibility of solids in the Sales gas seems remote. I suspect you are using a fuel gas storage system for startup of the plant. Am I correct?

Fuel gas is not used for instrumentation. Please explain accurately what you mean. We really need a complete, detailed Scope of Work if we are to give meaningful recommendations. For example, exactly what kind of gas storage are you proposing? We can’t comment until you reveal the total fuel gas consumption rate and the time required for startup – both are items that originate in your plant’s records or log of operations.

Await your reply.

[sealittle]

Art,

Thank you for your prompt comments regarding my query.

Yes, the plant is natural gas. I assumed referencing SWEET and placing it in the "Refining, Hydrocarbons, Oil and Gas" Forum would have been enough to for members to conclude the Plant is a Sweet Natural Gas Processing Plant.
My apologies for not being specific- as my professor use to say, give me specificity or give me death.

But yes, the plant will be processing 8MMSCFD of Sweet NATURAL Gas.

This is a grass roots facility and I am currently trying to determine how much of our sales gas is required to maintain plant operations.

I was simply posing the question to see if anyone has any experience, or helpful tips, in determining the quantity required.

A scrubber is necessary as a means of backup. I agree, during typical operation this scrubber should be removing very little from the clean sales gas. However, we must include this scrubber to ensure (given unforseen cirsmstances) dirty gas does not foul process equipment.

In conclusion, I am looking to determine my fuel gas consumption rate and would like some tips on how I should begin looking at it and any other experience based tips from the great members of CHEResources.

[ankur2061]

I am wondering if anyone has any rules of thumb for determining required fuel gas for various instrumentation and start-up gas requirements.

Sealittle

Sealittle,

In upstream oil and gas installations where gas is abundantly available and can be treated to produce clean sales gas with very low dew points it is a common practice to use this gas instead of instrument air to operate pneumatically operated instruments. The economics of using clean dry natural gas are much more favorable in such cases compared to instrument air.

However, if clean dry gas has to be used for instruments, the instruments should be specified to use gas instead of instrument air during the engineering and design phase of the plant. Otherwise you will need to go back to the supplier of the pneumatic instrument to check for suitability of the pneumatic cylinder or actuator if it was previously being used with instrument air. This is because the torque or specific impulse generated by the gas maybe different than for instrument air at the same pressue level and / or flow rate to operate the pneumatic cylinder or actuator.

Hope this helps.

Regards,
Ankur.

[sealittle]

Thank you for the response Ankur!