Decanter Centrifuge

Decanter Centrifuge Alfa Laval NX 418

Table of Contents

Decanter Centrifuge

A decanter centrifuge is an industrial liquid-solid separating machine. It separates solids from one or two liquids using the high centrifugal force generated by the rotating bowl. Solid particles need to have a higher density than the liquid for a decanter centrifuge to work.

Alfa Laval decanter centrifuges – detailed information.

Decanter Centrifuge Operation

A decanter centrifuge separates fluids from solids. Continuous process industrial centrifuges can process a large volume of fluids with sludge. Centrifugal force (upwards of 3,000 g) causes differential settling and separates the fluid from small sediment (50µ).

The rotating bowl has a concentric scroll which rotates at a differential speed to that of the decanter bowl. This speed differential allows the scroll to transfer the separated sludge.

The slurry is fed into the machine through an axial feed tube, which injects it into the conveyor. The injected slurry strikes against an accelerator in the conveyor feed zone. This action accelerates the flow outward, through the feed ports into the bowl, forming a ‘pond.’

The solids, being of higher density, displace the liquid and settle to the wall of the bowl. The solids are continuously scrolled by the conveyor, up the angled conical part (beach). The solids exit the bowl through 360° solids discharge ports located at the rear end.

The clarified liquid rises to the surface of the pond and flows over the dams located in the front bowl hub. At this point, the liquid discharges from the bowl.

Decanter Differential Rotation
Decanter Centrifuge Bowl and Scroll Differential Rotation

Types of Decanter Centrifuges

Decanter centrifuges are available in 2 configurations, namely 2-phase and 3-phase. In other words, solid-liquid separation and solid, liquid, liquid separation.

2 Phase Decanter

The two phase-type is a solid-liquid separator. In other words, it separates the fed slurry into a solid phase and one liquid phase.

Most de-sludging duties use a two-phase design. These include industrial sludge thickening, municipal wastewater, hemp biomass separation, etc.

3 Phase Decanter aka Tricanter

A 3 phase type separates solids from 2 immiscible liquids. In other words, a 3-phase decanter centrifuge produces a solid phase and two separate liquid phases.

For example, a 3-phase configuration separates crude oil from tank bottom sludge and water. Olive oil separation from water and biomass is another example.

Specifications

The following table lists some of the essential technical specifications of Alfa Laval decanter centrifuges. Of course, each manufacturer has a slightly differentiated specification. In general, high quality, decanter centrifuges have similar properties.

Material of Construction (MOC) 316L Stainless Steel (established, high-quality brands)
Max. Bowl RPM 2,000 ~ 6,500
Bowl Diameter 6″ to 60″+
G-Force (Centrifugal Force) 4500 G’s Max.
Particle Size Separation Range 50 µm to 1/2″
Processing Capacity 5 GPM to over 1,500 GPM
Drive Power 5 HP to Over 150 HP
Size (Footprint) 2′ x 4′ to 8′ x 15′
Differential Speed 1 ~ 25 RPM
Gearbox Type Planetary Gearbox; 1 kN-M to 3.5 kN-M Torque

Decanter Centrifuge Manufacturers, Sizing and Cost

Prospective buyers should consider some crucial aspects listed below before the selection and purchase of a decanter.

Manufacturers

There are many decanter centrifuge manufacturers worldwide. Yet, it is essential to consider the origin and legacy of the manufacturer—especially given the initial cost and sophistication of these machines.
 
Long term durability and field experience have proven the reliability and longevity of a few brands.
 
Alfa Laval is the top quality manufacturer in centrifuges for over 100 years! Alfa Laval is a ‘name brand’ among centrifuge manufacturers. It is not uncommon to see Alfa Laval centrifuges last 50+ years.
 

Sizing

A decanter centrifuge comes in different designs and sizes. For optimum process efficiency, the sizing is a critical parameter in decanter selection. A decanter rated at 100 gallons/minute on wastewater will likely process 20 gallons/minute on thick waste oil. Therefore, the user should carefully consider the process-fluid properties and decanter design features to size a proper decanter for each process.
 
Other design features such as auger pitch, beach cone angle, gearbox ratio, bowl speed, and auger speed all significantly affect decanter sizing. Consulting an experienced centrifuge company with extensive decanter application history is highly desirable and recommended.
 

Price Range

Decanter centrifuges are considered capital equipment based on their expected operating life and durability. Their price depends on the manufacturer and size/capacity.

A new machine (from a quality, established manufacturer) starts from around $50K for a small capacity unit to over $1M  for a large capacity machine. Accessories such as explosion-proof upgrades, control systems, pumps, etc. are optional and add to cost.

Remanufactured models range from 40% to 60% compared to new models of similar capacity. 

Operating Costs

Decanter centrifuge operating costs can be categorized as follows.

Power Consumption

The only power-consuming component of these centrifuges is the motors. Consider the following example:
 
Your cost per kWh: 25 ¢
Capacity:  5 GPM
Volume processed per hour: 300 Gallons
Cost per gallon processed: 25 ¢ / 300 = 0.08 ¢
 

Spare Parts

The availability of spare parts is an important consideration for the longer-term operating costs.
 
For ‘no-name’ decanters, the buyer is wholly dependent on the single source manufacturer overseas. Stock, availability & part cost are essential considerations for critical equipment.
 
On the other hand, generic spare parts are readily available for established, brand name manufacturers. The manufacturers themselves have parts stock worldwide, for quick delivery.
 

Labor

Decanter centrifuges are continuous processing, self-contained machines, which means there are no operating labor costs involved. Only service and maintenance require labor.
 

Chemical Use

Specific processes need chemicals to aid separation, which is an extra cost that the buyer should consider.
 

Maintenance & Service

Decanters from high-quality manufacturers are generally very reliable. As long as the user maintains them per the manufacturer’s recommendation, they provide reliable service.
 
Ongoing maintenance involves periodic gear-box oil change and bearing lubrication. The primary service involving bearing replacement is every few years, depending on the severity of use.
 
Processes involving abrasive solids such as drilling mud will need scroll or screw rebuild based on wear rate.
 

New versus Remanufactured

New machines from branded manufacturers like Alfa Laval is the first choice. However, given the cost of new models, buyers often seek remanufactured decanters from trusted and established companies.
 

Important considerations before buying a remanufactured decanter centrifuge

  • Manufacturer of the original centrifuge.
  • Credentials & experience of the re-manufacturer.
  • Previous use.
  • Wear status of the bowl and conveyor.
  • Parts used in the rebuild – especially bearings.
  • Balancing of major rotating components.
  • Vibration check and complete testing of the centrifuge assembly per OEM specifications.

We have condensed 35 years of our centrifuge specialty into a 9 Step Guide to Selecting Your Perfect Industrial Centrifuge.

Industrial Applications

Decanter centrifuges are perfect for the separation of liquids from high amounts of solids. In real terms, they can separate over 50% (v/v) solids from liquids continuously. Decanter centrifuges can produce up to 4000 g’s of centrifugal force, which is sufficient to separate particles down to 50µ.

The following are some of the industries using our remanufactured machines.

Alfa Laval NX416 Decanter Centrifuge
Decanter Centrifuge - Alfa Laval NX416 - 60 GPM
Alfa-Laval-NX418-Oilfield-Centrifuge

Remanufactured Decanter Centrifuge from Dolphin

Dolphin Centrifuge has been remanufacturing Alfa Laval decanter centrifuges for over 30 years. We have a similar experience with Sharples decanter centrifuges.

Our remanufacturing process follows OEM guidelines. We strictly adhere to all the remanufactured decanter considerations listed above.

We have a stock of over 50 Decanters at our factory in Warren, MI. Our stock decanters are carefully selected based on their previous use. We stock gently used decanters from olive oil or other similar benign last use.
We avoid decanters from drilling mud or other abrasive applications.

Contact Dolphin Centrifuge for price & technical details for our remanufactured and new decanter centrifuges in stock.