Which is the minimum gas velocity required in natural gas exchangers (gas-gas/chiller) to provide adequate glycol distribution and good hydrate inhibition?
Is it velocity the correct parameter or others may be used
(e.g. ro.v2)?

Pardon me why is glycol injection required?/filter

Normally, natural gas is dehydrated at the production site (offshore or onshore) using TEG dehydration prior to sending it to downstream equipments for further processing.

Methanol injection is done to protect the piping from the gas well to the gas processing facilities. Glycol is seldom used or heard of for this function.

Perhaps, you may want to consider building a gas dehydration facility to remove most of the water prior to sending it for further processing.

There are 2 sides of a coin
One is to give, one is to take
Give until it hurts with a smile.

Glycol injection is done onto the face of chillers that are taking the gas below hydrate temperature in order to recover heavy hydrocarbons.  Downstream of the chiller, a three phase separator is used to separate the gas, HC liquid and glycol.  In this service, ethylene glycol is commonly used.

Adequate glycol injection is usually accomplished by ensuring you have proper dP across the glycol spray nozzles and the design of the spray nozzles themselves to distribute the glycol across the face of the exchanger inlet tubesheet.  Gas velocity is not usually intended to redistribute poor glycol distribution.

The gas flow and the temperature drop across the exchanger will give you how much water will condense.  Simulators or the Hammerschmidt formula will give you the required 'rich' glycol concentration coming out of the exchanger.  A mass balance around the exchanger on the glycol side will give you the required flow rate based on the lean glycol concentration your regeneration system will give you (typically about 80% for this type of a system I believe).  A significant safety factor is commonly applied to make sure you have enough glycol to prevent hydrates.

And here's a few rules of thumb...

(1) Try to put about 80% of the glycol that you inject at the front end of the exchanger train. If there is a front end split, divide the amount injected evenly between each exchanger.

(2) When you select a nozzle try to get a very finely atomized pattern. Spend some time and calculate the distance the nozzle needs to be from the tube sheet so that the tube sheet is fully covered by the spray pattern. Try for about 100 psid (the nozzle mfg shuld be able to give you cone angle and should want to know what the nozzle delta P will be). Don't overlook downstream pressure drop in the delta P calc. By that I mean exchanger pressure drop. If you have exchangers in series the downstream exchanger will operate at some pressure that is lower than the upstream exchanger. Simple yes but easily overlooked.

(3) When you install the nozzle try to install it in such a way that it is easily removed. Nozzles wear out. Also, install a block valve before the nozzle piping enters the vessel and then a vent valve downstream of the block. If the nozzle plugs up you can sometimes shut it in and open the vent valve to allow gas to flow backward and unplug the nozzle. Sometimes that works and sometimes it doesn't.

(4) Pay attention the the rich return stream composition. Specifically it's freeze point. Try optimize the lean injection rate to result in a return stream that is at the very lowest point of the curve.

(5) Don't over circulate!

(6) Pay attention to the residence time of the 3-phase separator boot. I like to have no less than 45 minutes. Doing so will minimize the amount of hydrocarbon entrained in the return steam. This will cut down on reboiler load and stack emissions to some degree.

(7) Don't over Cicrculate!

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