3 replies to this topic

[asade abiodun]

Hi all,

Please I need information on sump pit/ tank design.

The concept i have at hand is to design a vessel that will aid in separation of waste water from the waste petroleum product at the tank farm. this will aid effecient disposal of water to meet the environmental regulation.

Also, Kindly help me with liquid- Liquid settler design informations.

I would appreciate your assistance.

all 4 one, One 4 all

[Zauberberg]

Separating water from petroleum products usually requires high residence time, and chemicals supporting the process of de-mixing (demulsifier agents supplied by Betz, Nalco, Chimec etc.). Since you have mentioned the environmental way of wastewater disposal, gravity settling in my opinion would not be sufficient. Also, if there are H2S, mercaptans, NH3 and other contaminants in the product or water, you'd probably need downstream water tretment as well.

The most frequent criteria for efficient liquid-liquid separation (as far as hydrocarbon-water mixtures are concerned) is by maintaining overall liquid phase axial velocity below 15mm/s. In any case, you should follow your company's standards for designing the suitable separation vessel or tank.

[Andree]

Indeed, Shell DEP suggests velocity of 15mm/s through coalescence media (e.g. mats), however my knowledge and experience tells that this is probably too low. Shell recomendation in an official document is very "safe" from the point of view of process guarantee, but it will probably result in oversized design. Velocity through coalescing internals is proprietary value as it depends on specific element design. And it also depends on process conditions (viscosity, IFT, water cut etc). Velocity in separation section can be different than through mat (e.g. if we deal with cartridge elements) and is set so that hydrodynamics must assure stability of coalesced droplets (rule for sizing diameter as well as sufficient space to fit in the internals). Length is calculated by comparing time of settling for design droplet size (based on Stokes law; design size - confidential information used by design companies) and time of flow in horizontal direction.

When dispersed phase concentration is approx. below 10% then control of interface level is not on the vessel main body, but in additional sump (boot). This element is sized based on required (quoted) control time.

I recently uploaded a design manual for L/L coalescers and separators, please search forum.

[asade abiodun]

Thanks guys,

i will look into the information you have given me, and i will update you as the design commences.

I appreciate...