Author: Bernard ZANELLI

How is water separated from jet fuel? The principle of coalescence

Coalescence is a process for separating a mixture of two phases in emulsion. Fixed bed coalescence consists in passing the emulsion to be resolved through a granular or fibrous medium in order to cause the coagulation of the droplets of the dispersed phase. Separation is based on different interactions between the coalescing packing and the two phases of the emulsion. The packing should preferably be wetted by the dispersed phase and not wetted by the continuous phase of the emulsion.

Operation :

Step 1: interception of micro-droplets of the dispersed phase by the coalescing solid.

Step 2: Attach the micro-droplets of the dispersed phase to the packing and flow the two phases separately through the coalescing bed. The adhesion of the dispersed phase on the packing is conditioned by the physico-chemical nature of the coalescing solid. The coalescing solid should preferably be wetted by the emulsion microdrops. The hydrophilic character is suitable for the resolution of inverse emulsions (water in oil), the packing with hydrophobic character is suitable for the resolution of direct emulsions (oil in water).

Step 3: release of the two phases out of the coalescer. The last stage results in the formation of large drops of coalesced phase. This stage depends on the last layer of the coalescer bed. Unlike the first layers of the bed, this area must be wetted by the continuous phase. Otherwise a foam is formed at the outlet of the coalescer which is detrimental to separation. Other factors conditioning this release stage are: the ratio of the two liquid phases to be separated, the interfacial tension, the density difference and the speed of passage of the treated emulsion.

 

How to simply analyze a diesel fuel?

This gasoil from a storage tank in an oil depot was subjected to a microbiological analysis on a Petri dish using the SAFRAN method and a SAFRAN AQPS 490 Special Process Qualification Certificate.

The results are as follows:

Bacteria: 4600 germs/ml

Yeast: 0 germ/ml

Mushrooms: 8500 sprouts/ml

These results are illustrated by photos of the Petri dishes.

Water in the tank damages your engine! How do you know if there is?

Water in jet fuels comes in two forms: dissolved and suspended.

• Dissolved water is invisible to the naked eye. Its proportion depends mainly on:

1. the nature and temperature of the fuel;
2. the temperature and hydrometry of the ambient air.

Dissolved water increases with temperature from about 35 ppm (0.0025%) at 0°C to 140 ppm (0.008%) at 40°C.

• Jet fuel can contain a certain amount of free water ranging from a few ppm to 30 ppm.

This water is visible to the naked eye, except for a small fraction consisting of very fine droplets.

It can have several origins

1. imperfect dehydration from the refineries;
2. phenomena of "breathing" of oil reservoirs leading to moisture condensation;
3. temperature reductions with release of some of the water in solution.

This water, regardless of its form, can be determined by the method Karl Fisher (ASTM D 6304): on a test jet fuel containing dissolved and suspended water, the suspended water is allowed to settle for 48 hours. The suspended water settles on the walls of the container as well as on the bottom. The jet fuel is collected without the decanted water on which the dissolved water is determined by the Karl Fisher method (ASTM D 6304). The amount of dissolved water is determined by this initial determination.

Shake the container vigorously for 5 minutes and dose the water using the same Karl Fisher method as before. This second dosage determines the total amount of dissolved and suspended water. The quantity of water in suspension is obtained by the difference between the total quantity of water and the quantity of dissolved water. 

This table summarises the methods of analysis of middle distillates for contamination by micro-organisms, water and sediment and the limit values not to be exceeded.

These types of contamination are most common during long-term fuel storage.

1			GAZOLE	FOD	JET A1
2	Moisture content	Standard	Standard NF EN 12937 Dosing of water Karl Fisher titration method by coulometry	Standard NF EN 12937 Dosing of water Karl Fisher titration method by coulometry	Standard NF EN 12937 Dosing of water Karl Fisher titration method by coulometry
3		Value	less than 200 mg/kg	less than 200 mg/kg	value maintained between 1 and 15 ppm thanks to coalescing filters
4	Particulate contamination	Standard	NF EN 12662 Determination of total contamination of middle distillates, gas oils and methyl esters of fatty acids	NF ISO 3734 Determination of water and sediment content in residual fuel oils. Centrifugation method	ASTM D5452 Particulate Contamination in Aviation Fuels by Laboratory Filtration
5		Value	Less than 24 mg/kg	Less than 0.10% (m/m)	Maximum: 1,0 mg/l
6	Microbiological analysis	Standard	IP 385 / 99 Enumeration of living micro-organisms in fuels with a boiling point below 390°C. Filtration and culture method	IP 385 / 99 Enumeration of living micro-organisms in fuels with a boiling point below 390°C. Filtration and culture method	IP 385 / 99 Enumeration of living micro-organisms in fuels with a boiling point below 390°C. Filtration and culture method
7		Value	No limit value defined	No limit value defined	No limit value defined