(June 14th, 2021)

Control and prevent BS&W accumulation with high velocity, bottom-scouring circulation. Choose a Philadelphia Side Entry Mixer.

THE PROBLEM: Crude oil held in storage tank farms, refineries, pipelines, and terminals usually contains varying amounts of sediment and water sometimes laden with paraffin, heavy ends, sand, and silt. Left unchecked, these materials can accumulate and cause corrosion of the tank floor and lower shell plates. The accumulation can also seriously limit operational flexibility, damage the floating roof when the tank is being pumped down, damage transfer pumps and meters, and disrupt refinery process units if sediments break free.

THE SOLUTION: To control or prevent this basic bottom sediment and water (BS&W) accumulation, the tank needs high velocity circulation that will completely scour the tank bottom and keep sediment, water, and solids in suspension. A Philadelphia Mixing Solutions’ side-entry tank mixer with 60 degrees rotation is ideal for handling this problem. The mixer can be equipped with an electric motor with long-life sleeve mounted bearings, one-piece cast iron drive housing, steel mounting flange with integrated swivel angle assembly, mixer drive shaft with pre-lubricated, sealed-for-life shaft bearings, rugged transmission and special impeller to minimize maintenance and operating problems. A tank shut-off device and hydraulic ball seal in the swivel-angle assembly can provide zero leakage to meet the stringent environmental requirements of the petrochemical industry. The mechanical shutoff device is engineered to ensure ‘no-oil-on-the-ground’ environmental control. It includes a stainless steel taper to-taper shut-off that ensures secure locking during bearing and mechanical seal change-out. Maintenance can be done under full tank conditions.

APPLYING THE SOLUTION: Since the rate of BS&W accumulation in an oil storage tank varies with the quality of the crude oil, one to six mixers per tank may be recommended for effective control. In large storage tanks, a savings of one mixer is possible. Installation of swiveling side-entry mixers in the recommended quantity and orientation to deal with the rate of bottom accumulation can provide highly effective control. In addition to limiting corrosion and other damage to equipment, control of BS&W also helps ensure that tanks are available for maximum storage capacity, allows quicker and less costly tank inspection, repair, alteration or reconstruction and limits personnel exposure to hazardous manual tank cleaning come API 653 or EEMUA 159 tank inspections. Controlling the accumulation of BS&W especially in crude oil storage tanks, demands high velocity circulation in order to completely scour the bottom of the tank. To achieve the desired process results, the mixers should be located so that maximum flow can be induced across the tank bottom to keep it free of BS&W and maintain a clear suction line. The swivel angle tank mixers should be placed opposite the outlet to allow the free range of movement across the full 60-degree swivel. Where more than one mixer is installed on a crude tank to control BS&W, locate the mixers between 15 degrees and 30 degrees apart, but generally within a quadrant of 90 degrees.

The use of computational fluid dynamics (CFD) facilitates the mixing partner with the ability to give proof of successful operations. In a refining application, the crude oil feed to the crude distillation unit from a day tank is also of equal gravity; thus, allowing the unit operators to maintain peak performance without having to worry about feed stock quality swings. When used in a pipeline application where the need to is blend, [enhance, optimize, upgrade] to a certain recipe then the same equipment can be used except for the position of the propeller should point 10-degree to the left. This is the prime angle to generate a flow pattern in the storage tank for mixing bottom to top to bottom. Sized correctly there is minimal diluent used and gravity equalization [measurement] to the fourth [0.0000] decimal point; viscosity is also equalized.

CONCLUSION: Operating the equipment in accordance with the manufacturers’ operational program through the various angles will ensure oil movements continue unhindered. It is critical to select a trustworthy mixing partner, make the right equipment selection for the given application(s), operate it per the equipment manufacturer’s guidelines, make sure the propeller will provide the necessary mixing and not just localized zonal agitation.