Disc Centrifuge Accessories: Heaters, Filters & Skids

Dolphin Centrifuge's Electric Pre-Heater

A disc centrifuge is often used as an oil centrifuge to separate water and solid contaminants from the oil. One of the process liquid properties that influences the centrifuge separation efficiency is the oil's viscosity.

As shown in the graph below, the viscosity of an oil is inversely proportional to its temperature. So it is essential to process hot oil through a centrifuge for best results.

It is easy to integrate an oil preheating system into a disc centrifuge module. Apart from the benefit of centrifuging hot oil, a centrifuge oil heating system is much more efficient than heating the oil in the storage tank. Heated oil storage tanks lose most of the heat to the environment and are therefore not energy-efficient or environmentally responsible.

The following are some of the options for preheating the process fluid before centrifugation.

Electric Heating

The most straightforward and convenient oil preheater is of the electrical type. A circulation-type electric heater heats the process fluid before it enters the centrifuge. The primary benefit of this design is that it heats only the fluid in circulation and not the entire storage tank volume. Therefore, this type of preheating system is highly efficient.

Electric oil heating systems have digital temperature monitoring systems, overheat shutoff, automatic or manual bypass valve manifolds, etc.

Steam Heating

Although steam heating systems are pretty inefficient, they are popular due to their simplicity and the availability of steam at existing plants. A simple, off-the-shelf heat exchanger uses steam to heat the fluid before the centrifuge.

The heat exchanger is susceptible to clogging or blockage from the process fluid if the fluid has significant sludge content. The sludge tends to settle out within the heat exchanger over time and reduces the efficiency and flow rate of the system.

Special Non-Clogging Heat Exchanger

Fluid Heating System for Disc Centrifuge

Dolphin Centrifuge has developed a proprietary pipe-in-pipe heat loop system for efficient heating of process fluids before centrifugation. The design of these heat loops centers around ease of cleaning and the ability to use steam or heat transfer fluid as the heating medium.

These heat loops are perfect for preheating process fluids with a large proportion of sludge.

Depending on the application, filters play an essential role in centrifugal separator performance and optimization. Filters upstream and downstream of the centrifuge serve different purposes. The industry refers to the upstream filters as pre-filters, and the downstream filters are known as post or polishing filters.

Dolphin Centrifuge's Pre-Strainer System with Electric Heater

Pre-Filters

A disc stack centrifuge has an inherent limitation on the maximum particle size the centrifuge can accept. This limitation is due to the inter disc spacing of the disc stack. Typically, the discs have a clearance of 1 mm between them.

Large particles can get wedged between the discs and block the fluid passing through the discs. Therefore, it is essential to pre-strain the process fluid before entering the centrifuge to keep the large particles out of the centrifuge. A pre-filter or inline strainer prevents such large particles from entering the centrifuge.

Disc Centrifuge Pre-Filters

Post Filters (Polishing Filters)

Post or polishing filters provide absolute filtration after the centrifuge. In other words, disc centrifuges are mechanical separating machines that separate the particles by the magnified force of gravity. Though these centrifuges are powerful enough to separate particles as small as 1 micron, some large particles can pass through the centrifuge for various reasons, such as high flow rate or centrifuge malfunction.

A post or polishing filter catches any stray particles that escape the centrifuge and thus ensures the centrate meets the specified purity level.

The separated sludge from a disc stack centrifuge falls out under gravity from the centrifuge frame sludge chute. Most disc centrifuges have the sludge discharge chute oriented downward.

The two main options for installing a self-cleaning disc stack centrifuge are installing the centrifuge on an elevated platform to place a sludge receptacle below the centrifuge, or integrating a sludge collection and transfer sub-system as part of the centrifuge module.

The second option offers the benefit of the centrifuge module being moveable and not anchored to the floor. This option also eliminates the requirement of constructing an elevated platform on site.

Sludge Tank

The optimum design for a system-integrated sludge tank is to install a centrifuge on top of a structural tank that receives the falling sludge ejection from the centrifuge.

The sludge tank is a welded steel box structure with a sloping bottom. The sludge slurry accumulates in the tank towards the sloped end.

Sludge Transfer Pump

The disc centrifuge ejects the separated sludge as a thick slurry. An air-operated double-diaphragm (AODD) pump is best suited for pumping this slurry.

The sludge handling system integrates an AODD pump automatically activated by a level sensor or a level switch inside the sludge tank.

Tank Heater

The separated sludge from crude oil, bunker fuel, and other similar thick fluids is very viscous. Once it accumulates in the sludge tank, this sludge often solidifies and is no longer pumpable.

A sludge tank heater keeps the separated sludge at a higher temperature, keeping it in a pumpable state. Sludge tank heaters are electric heating elements inside the tank that remain submerged in the sludge. These heating elements are temperature-controlled and automatically activated based on the sludge level in the tank.

Centrifuge Flow Meter

A flow meter or totalizer is an inline flow measuring device that monitors the fluid flow into the centrifuge. The actual flow rate is a crucial parameter in the operation of a self-cleaning disc stack centrifuge.

The sludge discharge cycle period depends on the percentage of solids and the flow rate of the fluid. An accurate discharge cycle period is essential for the centrifuge to operate in high-efficiency mode.

When integrated into the centrifuge control system, the totalizer records the total batch volume processed by the centrifuge.

Mechanical, turbine-type flow indicators let the centrifuge operator know the actual flow rate of the process fluid and, therefore, calculate the appropriate sludge cycle time.

Disc Centrifuge With Clean Fluid Tank

The disc centrifuge discharges the clean centrate under pressure. However, the operator should not use this pressure to transfer the fluid over long distances or to exert excessive backpressure on the centrifuge. A local clean fluid collection tank is an excellent solution to alleviate this problem.

A local, skid-mounted, clean fluid tank with a transfer pump is a popular optional accessory for a disc stack centrifuge system. The clean fluid transfers to this tank with the centrifuge-generated pressure with negligible backpressure.

The level sensor on the clean fluid tank activates the transfer pump, which transfers the fluid to remote storage tanks.

Some applications such as emulsified oil or crude oil require chemical or flocculants to assist in the separation of the fluid phases. A chemical injection port on the inlet side piping of the centrifuge system facilitates introducing the chemical to the flow stream.

The operator can dial in a chemical metering pump to supply the correct amount of additive into the process stream.

A high-shear, inline, static mixer vigorously mixes the chemical into the process fluid before the fluid enters the centrifuge. This system eliminates the need to add chemicals to the supply tank and avoids related wastage of chemicals.

Disc Centrifuge Accessories — Heat Recovery Skid

Large volume applications such as crude oil dewatering require large amounts of energy to heat the crude oil before centrifugation. The separated water and oil phases exiting the centrifuge have thermic energy that the users typically waste in the storage tanks.

A heat recovery system is essentially a plate and frame heat exchanger that uses the heat from the clean fluid leaving the centrifuge to heat the incoming, unprocessed fluid. Such an accessory can lead to considerable energy savings.