Screw Conveyor Power Calculation / Screw Conveyor Capacity calculation
The weight or volume per hour is known as the capacity of a bulk material which can be transported safely and easily using a screw conveyor through that screw conveyor power calculation is made.
What is Screw Conveyor?
Screw conveyors are one of the most common transportation and delivery systems for bulk solids. Screw conveyors are commonly used to transport bulk materials, depending on the material characteristics of the particular bulk material, at 15, 30 or 45 % trough loading. In general, 45 % trough loading may be used for bulk materials that are lightweight, free flow or non-abrasive. For denser, lenient and abrasive bulk materials, trough loadings of 15 and 30% are usually used.
Screw conveyors are one of the most reliable and cost-effective methods for conveying bulk materials. Due to their versatility, screw conveyors can convey a wide variety of bulk materials ranging from dry, free-flowing portland cement to wet, sluggish dewatered biosolids.
Screw conveyors can be designed to operate in almost any position, from horizontal to vertical. Inclined screw conveyors are used to convey and elevate bulk materials from one level to another. Depending upon the bulk material and the objective, proper design and construction of an inclined screw conveyor will provide many years of uninterrupted service and productivity. The purpose of this article is to help the reader understand the basics of inclined screw conveyor design for various applications.
History of Screw Conveyors
Archimedes designed the screw conveyor in the third century B.C. The first screw was used for removing water from ships and for irrigating farmland. The original device consisted of spiral flights fixed to the inner wall of a hollow cylinder driven by a center shaft. As the assembly rotated, water was conveyed and lifted from one location to another. The spiral design is based on the theory of the inclined plane. The screw conveyor has evolved in modern times and is now used in almost every major industry.
Power requirement of Screw Conveyors or Screw Conveyor Power Calculation
It must be noted that those formula aim at giving an idea of the size of the screw conveyor (which means its diameter) and the speed at which it will operate, based on some assumptions and some design decisions (choice of screw pitch, inclination). The formula can also be used to roughly check the capacity of an existing screw conveyor power calculation.
The driving power of the loaded screw conveyor is given by:
P = PH + PN + Pst
PH = Power necessary for the progress of the material
PN = Driving power of the screw conveyor at no load
Pst = Power requirement for the inclination of the conveyor
Power necessary for the progress of the material PH: / Screw Conveyor power calculation
For a length L of the screw conveyor (feeder), the power PH in kilo watts is the product of the mass flow rate of the material by the length L and an artificial friction coefficient λ, also called the progress resistance coefficient.
PH = Im.L. λ.g / 3600 (kilowatt)
= Im.L. λ / 367 (kilowatt)
Im = Mass flow rate in t/hr
λ = Progress resistance coefficient
Each material has its own coefficient λ. It is generally of the order of 2 to 4. For materials like rock salt etc, the mean value of λ is 2.5. For gypsum, lumpy or dry fine clay, foundry sand, cement, ash, lime, large grain ordinary sand, the mean value of λ is 4.0.
In this connection it should be noted that the sliding of the material particles against each other gives rise to internal friction. Other resistance due to grading or shape of the output discharge pattern contributes to the resistance factor. That is why the parameter λ is always higher than that due to pure friction.
Drive power of the screw conveyor at no load, PN: / Screw Conveyor Power calculation
This power requirement is very low and is proportional to the nominal diameter and length of the screw.
PN = D.L / 20 (Kilowatt)
D = Nominal diameter of screw in meter
L = Length of screw conveyor in meter
Power due to inclination: Pst
This power requirement will be the product of the mass flow rate by the height H and the acceleration due to gravity g.
Pst = Im.H.g / 3600
= Im.H / 367
H should be taken positive for ascending screws and will be negative for descending screws.
Total power calculation requirement of screw conveyor
The total power requirement of screw conveyor power calculation is the sum total of the above items
P = (Im (λ.L + H) / 367) + (D.L /20) (Kilowatt)