TECHNICAL PAPER- Optimizing Pneumatic Conveying for Abrasive Reclaim Materials

Subject: Date: October 2023

Author: Delta Ducon, LLC

Abstract

Handling high-density reclaim materials (pebble, dust, and regrind) presents unique challenges for industrial processing facilities. These materials are often characterized by high bulk densities (approx. 90 PCF) and abrasive properties that cause rapid wear on standard pneumatic components. Furthermore, the handling of fine reclaim dust creates significant housekeeping and environmental compliance issues. This paper outlines the engineering advantages of utilizing Vacuum Conveying technologies combined with Severe Duty rotary valves and integral wear-back piping to mitigate equipment failure and fugitive dust emissions.

1.0 Introduction

In many industrial applications, the "reclaim" circuit is often an afterthought compared to the primary process line. However, reclaim circuits often handle the most difficult materials—mixtures of variable size, sharp edges, and high density.

Standard "Heavy Duty" components often fail prematurely in these applications because they rely on surface hardening treatments which wear away, exposing softer base metals. To ensure system longevity and operational efficiency, three critical design factors must be addressed:

1. Motive Air Configuration: Preventing fugitive dust.

2. Metering Technology: Maintaining airlocks in abrasive environments.

3. Conveying Line Integrity: Managing impact wear at directional changes.

   
   

2.0 Motive Air Strategy: The Case for Vacuum Conveying

While positive pressure systems are common for long-distance conveying, Vacuum Conveying is the superior engineering choice for reclaim applications involving multiple pickup points and fine dust.

2.1 Fugitive Dust Containment

The primary advantage of a vacuum system is the pressure differential relative to the ambient environment. In a positive pressure system, a worn gasket or pipe leak forces dust out into the plant. In a vacuum system, leaks pull ambient air in. This inherent physical characteristic eliminates fugitive dust emissions from the conveying line, significantly improving plant safety and reducing housekeeping labor.

2.2 Filtration and Separation

Effective vacuum systems utilize Pulse Jet Filter Receivers to separate the product from the airstream.

• Target Box Entry: High-velocity material should not impact the filter bags directly. A properly designed receiver utilizes a target box inlet where material impinges upon itself or a wear plate, slowing velocity before entering the expansion chamber.

• Surge Capacity: The collector hopper must provide adequate surge volume (e.g., 7 CF for smaller lines) to prevent material re-entrainment into the filter media.

  
  

3.0 Metering Component Selection: "Heavy Duty" vs. "Severe Duty"

The rotary valve (airlock) is the critical interface between the storage hopper and the conveying line. In abrasive applications, standard cast iron or stainless steel valves suffer from "blow-by" as the rotor tips wear, causing a loss of conveying capacity.

3.1 Material Hardness: The P-33 Advantage

For abrasive service, surface hardening (such as chrome plating or tungsten coating) is insufficient. Once the coating is breached, the valve fails catastrophically.

Delta Ducon utilizes PERMA/flo XT / XL valves constructed from P-33 Alloy, a proprietary Chrome-Iron alloy.

• Hardness: 500–600 Brinell Hardness Number (BHN).

• Structure: Solid alloy casting (not a surface treatment).

• Longevity: Maintains hardness throughout the entire depth of the wear component.

  
  

3.2 Geometric Design Optimizations

To handle difficult reclaim materials, the valve geometry must be optimized for pocket fill efficiency:

• Pocket Count: Increasing rotor pockets (e.g., from 9 to 10) allows for a wider inlet shoe.

• Inlet Throat: A wider shoe exposes a two-pocket width to the material stream, increasing the inlet area by up to 82% compared to standard designs. This minimizes bridging of interlocking reclaim pebbles.

• Adjustability: Unlike fixed-tolerance valves, the rotor-to-shoe clearance should be field-adjustable to maintain a tight seal throughout the valve's lifecycle.

  
  

4.0 Conveying Line Integrity

The most common point of failure in a pneumatic conveying line is the elbow, where material changes direction and impact forces are highest.

4.1 Integral Wear Backs (IWB)

Standard Schedule 80 carbon steel piping is insufficient for directional changes in abrasive service. The engineering solution is the use of Integral Wear Back (IWB) fittings.

• Hardness: Cast from alloy with ~450 BHN hardness (vs. ~140 BHN for 316SS or ~180 BHN for Cast Iron).

• Design: Material is reinforced on the outer radius where particle impingement occurs.

  
  

4.2 Installation and Maintenance

To facilitate maintenance, IWB elbows should be installed using compression-style pipe couplings rather than welded flanges. This allows for:

• Thermal Expansion: Accommodating temperature fluctuations.

• Alignment Tolerance: Providing up to 4 degrees of deflection to correct minor misalignment in field piping.

  
  

5.0 Conclusion

The total cost of ownership for a reclaim system is not defined by the initial capital expenditure, but by the frequency of maintenance intervals and the labor cost of housekeeping.

By selecting Vacuum Conveying for containment, P-33 Solid Alloy Rotary Valves for metering, and 450 BHN Wear Back Fittings for the transport line, facilities can transform a high-maintenance reclaim process into a reliable, closed-loop system.

About Delta Ducon Since 1921, Delta Ducon has provided equipment and full systems for the material handling industry. We specialize in severe duty applications where standard equipment fails.

Ready to Optimize Your Reclaim System?

Don't let abrasive wear and fugitive dust compromise your plant's efficiency. Contact Delta Ducon today to discuss your specific material handling challenges. Our engineering team is ready to conduct a system audit and recommend a Severe Duty solution tailored to your facility.

Contact Us:

Phone: 610.695-9700

Email: sales@deltaducon.com

Website: www.deltaducon.com