Table of Contents
Disc stack centrifuge performance depends on operational parameters that the use of optional equipment can enhance. The following is a detailed list of disc stack centrifuge options and the benefits of each option. We also indicate alternatives that centrifuge customers can provide on their side to extract the same benefits.
It is necessary to describe the scope of supply of a base centrifuge system to differentiate the options from the standard accessories included with our disc stack centrifuge systems.
We describe the scope of supply of a typical base centrifuge system designed and manufactured by Dolphin Centrifuge.
Each centrifuge system features a new or remanufactured Alfa Laval disc stack centrifuge. The centrifuge could be a ‘self-cleaning’ or ‘manual cleaning’ type depending on the sludge or solid content in the process fluid.
We install a new electric motor on the centrifuge, suitable for the centrifuge and application environment.
For example, a centrifuge designed for explosion-proof locations will have a suitable Class 1 Div 1 or Div 2 motor. We replace the standard friction clutch with a direct-drive coupling with a corresponding VFD or inverter accommodated in the local or remote control panel.
Other centrifuge upgrades could include special elastomers for specific applications, upgraded material for wetted parts (stainless steel), inert gas purging for centrifuge casing, unique bowl adaptation, etc.
The centrifuge system is mounted on a welded steel base structure (carbon steel). This platform includes lifting eyes or elevation feet for moving or transportation. The centrifuge, interconnecting piping, valves, electrical cables, control panel, water harness, etc., are electrically and mechanically integrated into this base structure.
The sludge discharge mechanism of self-cleaning disc stack centrifuges requires a water harness. Manual clean centrifuges do not require water harnesses.
Again, the solenoids are suitable for the operating environment, such as explosion-proof or hazardous areas depending on the application.
This standard feature includes the flow control valves, pressure-reducing valves, and reinforced clean vinyl hoses connecting the solenoids to the centrifuge operating water device.
The base system includes the electrical and mechanical integration of the water harness into the centrifuge module.
A local control panel (LCP) is part of the base centrifuge skid supplied by Dolphin Centrifuge. A NEMA 4 enclosure affixed to the skid-mounted mounting structure houses the LCP. All power and instrument cables are part of the supply scope.
Unless otherwise specified, conduits and glands suitable for NEMA 4 rating are standard supply. Of course, explosion-proof or hazardous area systems feature suitable enclosures and inert gas purging systems, cables, glands, and conduits.
All base disc-stack centrifuge systems come with a breakover or liquid seal alarm. This alarm system includes a pressure sensor that monitors the pressure in the outgoing fluid pipe and triggers the alarm if the pressure falls below a predetermined level.
Self-cleaning disc stack centrifuges also have fail-to-shoot and fail-to-close alarms. These alarms monitor the sludge discharge function of the self-cleaning bowl and trigger an alarm if either function fails.
Each option below explains the additional alarms specific to the option.
Each centrifuge system supplied by Dolphin Centrifuge is fully assembled and integrated mechanically and electrically.
Mechanical integration includes interconnecting pipes of suitable material (often carbon steel or stainless steel), flow control valves, directional valves, vibration isolators, vibration dampeners, sample port valves, pressure and temperature indicating gauges, etc.
Pneumatic pressure or gravity fill tests are standard leak testing methods for tanks and welded steel pipes.
System assembly, including centrifuge mounts and pipe flanges, use graded fasteners specified by the manufacturer.
Electrical integration of the system includes the interconnection of power, control, and instrumentation cables using UL specifications. Cable conduits and glands between the local control panel and each electrical component are suitable for the specific application and type of component.
All centrifuge systems undergo a rigorous testing process to ensure that the mechanical and electrical functions of the system are fully functional per the design specifications. We use hydraulic oil to test systems that process oil-based fluids and water for wastewater and other water-based applications.
Dolphin Centrifuge has an in-house test procedure that documents all system parameters that must meet set criteria during the test process.
As mentioned above, in addition to the standard centrifuge system with its scope of supply described in the previous section, additional disc stack centrifuge options enhance the centrifuge performance.
Some optional accessories help reduce the preparatory work that a customer may otherwise need to perform.
The following is a list of optional accessories we recommend based on customer-specific applications.
Description: A dedicated feed pump installed on the centrifuge skid sucks the process fluid from the customer's supply tank and feeds it to the centrifuge. Typically a VFD controls the feed pump speed, which allows the operator to control the flow rate during operation. This sub-system has a pressure sensor to detect pump flow to prevent dry running and overpressure in the feed line.
This is the most commonly requested of all disc stack centrifuge options.
Benefit: The PLC operating the centrifuge also controls the feed pump. This feature allows the PLC to shut off the feed in case of an alarm or system shutdown.
Also, using the bypass line that is a part of the pump system allows the user to recirculate the process fluid back to the supply tank, which helps agitate the process fluid.
Alternative: The centrifuge user may choose to supply their pump or use an existing pump. However, letting the centrifuge PLC control the user's pump is essential.
Also, centrifuges do not work well with air diaphragm pumps due to the pulsation generated by such pumps. A positive displacement pump with feed control is ideal for use with centrifuges.
Description: Special heaters with a gentle heating design avoid the charring of oils passing through the heaters. In addition, the multi-bank design of heaters allows gradual heating and controls the electrical load created by the heater.
The thermostat controller monitors the fluid temperature and controls the various banks of the heater. It also shuts off the heater to prevent overheating.
Centrifuge systems installed pre-heaters have flow monitoring devices to prevent the heater from turning on without process fluid. Pressure relief valves and standard drains prevent over-pressurization of the heater vessel.
The electric pre-heater is the most cost-intensive of all the disc stack centrifuge options.
Benefit: Disc stack centrifuge efficiency is highly dependent on the viscosity of the process fluid. A pre-heater installed on the centrifuge allows heating of the process fluid to reduce viscosity and thereby increase separation efficiency.
Alternative: The customer may install heat exchangers or have existing heated tanks that can supply hot process fluid to the centrifuge. Even in such scenarios, an electric pre-heater may help bring the process fluid to the optimum temperature for optimum separation.
Description: The centrifuge base platform integrates a welded steel tank beneath. The sludge discharge of the self-cleaning centrifuge falls into this tank. A level switch activates a sludge pump automatically to evacuate the accumulated sludge. This complete sub-system enables sludge handling.
Benefit: The integrated sludge tank and pump allow the centrifuge system to be modular, i.e., self-contained and moveable.
Alternative: The user may choose to build an elevated platform for the base centrifuge skid. This elevation allows the user to place a sludge receptacle under the centrifuge sludge discharge chute.
Such platforms serve the purpose but are also anchored to the floor, thus fixing the centrifuge location.
Description: A collection tank on the centrifuge skid acts as a receptacle for the clean (separated) fluid exiting the centrifuge. This local tank has a level sensing device and suitable pump to transfer the clean fluid to the user’s collection tanks.
Benefit: An elevated or extended clean fluid return pipe to the user’s tanks generates back pressure on the centrifuge. Varying back pressure has a detrimental effect on the centrifuge performance.
The availability of a local collection tank prevents the creation of back pressure on the centrifuge outlet. This option automatically allows the user to return the separated fluid to remote collection tanks.
Alternative: A locally available tank to collect the separated fluid that eliminates the back pressure mentioned above serves the same purpose as this option. Using centrifuge-generated pressure to transfer the separated fluid over long distances or tall tanks is not recommended due to the back pressure created by such piping setups.
Description: A pair of basket-style filter housings on the centrifuge inlet are pre-strainers for the incoming process fluid. The housing has differential pressure sensors to detect the filter back pressure. A 3-way valve manifold allows quick switching between the strainers when one gets full without the need to stop the fluid flow.
Benefit: The pre-strainer prevents particles bigger than the inter-disc space from entering the centrifuge and potentially plugging up the disc stack.
Alternative: The user may pre-treat or filter the supply tank to a certain level to eliminate such large particles from the supply fluid. A decanter centrifuge upstream of the disc stack centrifuge works well to de-sludge the process fluid for bulk solids.
Description: Certain applications require absolute filtration, meaning that particles above a specific size are not allowable. In such cases, the cleaned or separated fluid passes through a filter to catch stray particles that may escape the centrifuge.
Again, a duplex filter allows easy switching between the filters on the fly.
Benefit: A post-processing or polishing filter ensures the processed fluid meets the customer’s required filtration level.
Alternative: The user may not require absolute filtration or can supply their filters for polishing the fluid separated by the centrifuge.
Detailed Description: Some applications require chemicals to augment the separation process. For example, a demulsifying chemical may help break the emulsion in emulsified oils. A chemical injection port followed by an inline static mixer works well for introducing chemicals.
Benefit: A skid-integrated chemical injection system eliminates the need for a separate chemical injection module. This setup saves space and cost for the user.
Alternative: The user may introduce the chemicals upstream of the centrifuge or in the supply tank if the chemical reaction requires a set period.
For other options such as Viton Gaskets, Stainless Steel Piping, Explosion Proof or Hazardous Area applications, Heat Exchangers, Steam Heat Loops, etc. - please contact Dolphin Centrifuge or call our sales engineer at (248) 819-1732.
by Sanjay Prabhu MSME
Engineering Manager, Dolphin Centrifuge