Can a Wear-Reducing Bend Increase Pressure Loss in a Fly Ash Line?

Can a Wear-Reducing Bend Increase Pressure Loss in a Fly Ash Line?

A fly ash conveying elbow needs replacing, and a ceramic-lined elbow with a different bend geometry is proposed to reduce wear. Can the replacement be approved by comparing ceramic grade and lining thickness alone?

Review the conveying duty as well as the wear protection. A change that improves one part of the problem still needs to fit the pressure and capacity requirements of the line.

Wear reduction and pressure loss are separate checks

A numerical comparison of three pneumatic-conveying bend geometries found that lower predicted erosion often came with higher pressure loss. The relationship changed with operating conditions. [1]

That study used quartz particles and a specified wall model. It was not a field trial of ceramic-lined fly ash elbows, so its results cannot supply a pressure penalty or service-life improvement for a proposed replacement.

The practical implication is to request a duty-specific comparison, rather than assume that every wear-reducing shape has the same effect.

Compare both options at the same duty

Give the existing and proposed bends a common assessment basis:

• Required solids throughput and the relevant feed range.
• Conveyed ash properties and particle-size information.
• Air mass flow, pressure, temperature, and the reference conditions used for reported air volumes.
• Finished internal bore, bend geometry, and adjacent pipe arrangement.

A stated air volume is difficult to interpret without its pressure and temperature basis. A comparison can also become misleading if one option is assessed at a different solids feed rate.

Ask the conveying-system designer to identify which inputs are measured, specified or assumed.

Include the downstream recovery zone

Particles can lose speed through a bend and regain speed in the following straight pipe. That downstream region is often called the reacceleration zone.

Experiments involving fly ash and cement treated bend-curvature losses and downstream reacceleration losses separately. [2] This supports checking where the pressure measurements or calculation boundaries begin and end.

For a replacement assessment, ask whether the comparison includes the relevant downstream region. Pressure taps placed only close to the fitting may describe a different boundary from a model that includes particle recovery farther along the line.

There is no universal pressure-tap spacing offered here. The designer should select a suitable arrangement for the actual system and measurement purpose.

Check the ceramic lining and finished bore

When specifying an alumina ceramic-lined elbow, review the finished bore after the lining is installed. Confirm the transition to adjoining ceramic-lined pipe fittings or steel spools, the actual lining layout, and any change in bend geometry.

Retain the requirements for backing, attachment, seals, and the steel body. A ceramic material temperature rating cannot establish the operating limit of the complete assembly.

The ceramic supplier should define the lining details; the conveying-system designer should confirm their compatibility with the required duty.

Agree on the commissioning comparison

Before ordering, define what will count as a successful change. Useful records include solids throughput, air consumption, pressure behaviour, blockage events and later wear observations under comparable conditions.

If extra air is proposed, review its effect on the full operating point and energy demand. Increasing air supply should not become an automatic response to an unreviewed geometry change.

For an initial discussion about a ceramic-lined elbow replacement, send ELACERA a line sketch, the existing bend drawing or photographs, and a brief description of the wear problem. Available operating records can follow; a complete data package is not needed to start the conversation.

Technical References

[1] E. Drescher; S. Mohseni-Mofidi; C. Bierwisch; H. Kruggel-Emden. A numerical assessment of different geometries for reducing elbow erosion during pneumatic conveying. Powder Technology 449, 120357. 2025; first published online 10 October 2024. DOI: 10.1016/j.powtec.2024.120357.

[2] A. Sharma; R. Poddar; G. Saluja; S. S. Mallick. Modeling pressure drop in curvature and reacceleration zones in bends during pneumatic conveying of fine powders. Particulate Science and Technology 42(3), 377–392. 2024; first published online 11 September 2023. DOI: 10.1080/02726351.2023.2255865.

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