If this newsletter is not displaying correctly, view an alternate version here.
PBE News
PBE on the Web
Home
Article Index
Bookstore
Subscribe
Webinar
Sponsors
Agglomeration
Equipment

Franklin Miller
Hosokawa Micron Powder Systems

Airlocks, Blowers & Related Equipment
FLSmidth
K-Tron
Nol-Tec
Smoot
Vortex Valves

Bagging Equipment
Chantland
K-Tron
Taylor Products

Bin Activators, Vibrators & Material Flow Aids
Acrison
Eriez
K-Tron
Monitor Technologies LLC
Nol-Tec
Smoot
Vac-U-Max

Bin Level Indicators
K-Tron
Monitor Technologies LLC
Vac-U-Max

Bulk Bag Fillers & Dischargers
Acrison
APEC
Chantland
Flexicon
K-Tron
Nol-Tec
Schenck AccuRate
Taylor Products
Tecweigh
Vac-U-Max

Bulk Bags
Chantland
Taylor Products
Tecweigh

Custom Services
Chantland
Flexicon
Jenike & Johanson
K-Tron
Nerak Systems
Nol-Tec
Tecweigh
Vac-U-Max
Vortex Valves

Dryers
Hosokawa Micron Powder Systems
K-Tron
Marion Mixers

Dust Collector Media
Camfil Farr APC
Nol-Tec
Smoot

Dust Collectors & Related Equipment
Camfil Farr APC
K-Tron
Monitor Technologies LLC
Nol-Tec
Smoot
Vortex Valves

Feeders
Acrison
Chantland
Eriez
FLSmidth
Hosokawa Micron Powder Systems
Jenike & Johanson
K-Tron
Nol-Tec
Schenck AccuRate
Smoot
Taylor Products
Tecweigh
Vac-U-Max

Flow Meters
Acrison
APEC
K-Tron
Monitor Technologies LLC
Schenck AccuRate

Linings (Abrasion Resistant)
Hosokawa Micron Powder Systems
Vortex Valves

Material Handling
Acrison
Chantland
FLSmidth
Flexicon
Hosokawa Micron Powder Systems
Jenike & Johanson
K-Tron
Lorenz Conveying Products
Nerak Systems
Nol-Tec
Schenck AccuRate
Smoot
Taylor Products
Tecweigh
Vac-U-Max
Vortex Valves

Mechanical Conveyors
Acrison
Cablevey Conveyors
Chantland
Eriez
Flexicon
K-Tron
KWS Manufacturing Co Ltd
Nerak Systems
Taylor Products
Tecweigh
Vac-U-Max

Metal Detectors & Separators
Eriez

Mixers & Blenders
Acrison
APEC
FLSmidth
Franklin Miller
Hosokawa Micron Powder Systems
K-Tron
Marion Mixers
Nol-Tec

Particle Analyzers
Hosokawa Micron Powder Systems

Pneumatic Conveying Equipment
FLSmidth
Flexicon
HammerTek Corporation
K-Tron
Lorenz Conveying Products
Meridian Manufacturing
Nol-Tec
Smoot
Vac-U-Max
Vortex Valves

Product Reclaim Equipment
Hosokawa Micron Powder Systems

Samplers
Sentry Equipment
Tecweigh

Sifters, Screeners & Classifiers
Eriez
Hosokawa Micron Powder Systems
Progressive Industries

Silo Cleaning Equipment & Service
Vac-U-Max

Size Reduction Equipment
Franklin Miller
Hosokawa Micron Powder Systems
Jet Pulverizer Co
Progressive Industries

Sizing Tools
Hosokawa Micron Powder Systems

Storage
FLSmidth
Jenike & Johanson
K-Tron
Meridian Manufacturing

Vacuum Cleaning Equipment
Camfil Farr APC
Vac-U-Max

Valves
FLSmidth
K-Tron
Lorenz Conveying Products
Nol-Tec
Smoot
Vortex Valves

Weighing Equipment
Acrison
APEC
Chantland
Flexicon
K-Tron
Meridian Manufacturing
Nol-Tec
Schenck AccuRate
Smoot
Taylor Products
Tecweigh
Vac-U-Max

Other
Acrison
APEC
Chantland
Flexicon
Franklin Miller
Jenike & Johanson
K-Tron
Meridian Manufacturing
Tecweigh
Vortex Valves


Bulk-Online


Bulk-Online

» Skip to Continue point

Ask an Expert

Reducing elbow wear in pneumatic conveying

Q: My pneumatic conveying system, which transports an abrasive mineral, suffers from extreme bend wear problems. We're never done welding up the elbows—some fail every week or two—and the worst always seem to be the ones at line's end and the silo's top, which present a safety hazard to access. Would it help us to change to a longer bend radius?

Mike Bradley, of The Wolfson Centre for Bulk Solids Handling Technology, says: Anywhere that you have hard, angular particles, there's potential for them to cause bend wear due to the particles' impact on the bend’s inner radius. It's tempting to think that a longer bend radius will allow the particles to follow the flow more easily and will reduce collisions with the wall. However, this is a fallacy—even in a very long radius bend, the particles still travel in virtually a straight line from the inlet to the impact point. A longer radius bend will give some extension to wear life because the impact zone is longer in respect to the arc’s length. Tests in our laboratory have shown roughly a doubling in bend life when the ratio of radius to diameter increases from 6 to 12. However, if you have a serious wear problem, you need much more than a doubling of bend life!

A key to one of the most important matters lies in your observation that the bends at the line's end wear out much faster. People think it's Murphy's Law that the most difficult bends to replace—those on top of the silo—wear out most often, but actually it's not Murphy's—it's Boyle's law! Boyle's law states that when a gas's pressure falls, it expands. System pressure drops along a pneumatic pipeline, which causes the gas to expand and therefore the gas velocity to increase toward the pipe's end. As gas velocity increases, so does the particle velocity, and research has shown that erosion rises dramatically with velocity:

       Erosion= k • velocityn

       where 2.2 < n < 2.7 depending on the material.

This has a drastic effect; doubling air velocity means erosion goes up between 5 and 7 times. This is why the bends at the system's end wear through much more often! In a system working at 15 psi, the air velocity at the line's end is double that at the inlet. The higher the system pressure, the stronger this effect.

Conversely, small reductions in air velocity give a big reduction in wear: A 25 percent reduction in air velocity will give a doubling of wear life, and a 50 percent reduction would return a wear life 5 to 7 times longer.

There are several ways to reduce air velocity. One is to make sure that the airflow is only just above the minimum value required for successful conveying, avoiding excess air flow. Another is to increase the pipeline's bore along its length to stop the air velocity from becoming excessive. If it's a blow tank system, avoid the "blowdown" along the pipeline at the conveying cycle's end by venting the tank, because this is when most of the wear will occur.

Reducing air velocity will have other benefits—reduced energy consumption, greater transport capacity, less particle damage, and less dust generation—so it's a no brainer. However, it has to be done with care, keeping in mind the material’s minimum conveying air velocity, to avoid blockages. Off-line material characterization in a test center helps in this regard.

Wear-resistant linings can also be very useful to extend bend life, and in many instances can deliver great economic benefit. The key is to understand different linings' wear life extension so that a sensible economic choice can be made. This potential can be measured with an erosion tester.

Certain bend geometries such as blind tees and specialty elbows such as the Vortice-Ell are also more wear-resistant and can be a useful choice, but most of these increase pressure drop and energy consumption and can seriously compromise the transport rate. Thus, they should be applied with care, especially if you have more than two bends in the pipeline. Before choosing these, conduct a quick test on an industrial-scale test system to know the effects in advance.

Mike Bradley is the director of The Wolfson Centre for Bulk Solids Handling Technology at the University of Greenwich.

Think you’ve got what it takes to be the Expert?
We’re looking for guest contributors for the Ask the Expert section—email awiebe@cscpub.com for more info.

back to top ↑


Copyright 2011, CSC Publishing Inc. All rights reserved.
PBE-News provides information updates about the dry bulk materials processing and handling industry twice a month. The opt-out link below will allow you to opt out of future PBE-News. This will in no way affect our contact methods regarding your subscription or communication. Thank you.


PBE-News Editor                                                       PBE-News Designer
awiebe@cscpub.com
                                           kweyandt@cscpub.com