Overview

A dry-process cement facility was experiencing recurring wet dust buildup at the bottom of its gas cooling tower (GCT). The buildup contributed to unstable preheater gas temperatures, process upsets, raw mill interruptions, and elevated baghouse maintenance. Lechler worked with the plant to optimize the existing gas cooling system by improving atomization, tightening temperature control, and significantly reducing compressed air demand.

Following installation and commissioning in August 2025, the site reduced compressed air usage for the gas cooling system from about 700 SCFM to approximately 205 SCFM, while stabilizing GCT outlet temperature control near a 320°F (150°C) target.

At a Glance

Industry: Cement manufacturing
Application: Gas cooling tower on preheater exit gas (upstream of raw mill and dust collection)
Primary challenge: Wet dust buildup, temperature instability, and high compressed air consumption
Target conditions: Inlet gas typically ~820 to 840°F, outlet temperature target 320°F (150°C)
Lechler solution:VarioCool® nozzle-lances with protection tubes, upgraded measurement, and optimized control strategy
Commissioning: Completed within 48 hours after installation (during a planned shutdown)
Payback: Less than 10 months (as reported by the project team)

The Challenge

Operations and maintenance teams were dealing with:

• Wet dust accumulation in the GCT and on spray components
• Unstable outlet temperature control, requiring frequent operator intervention
• High compressed air consumption, measured around 700 SCFM
• Buildup-driven disruptions contributing to mill stops and maintenance burden

A Lechler engineering review found that instability was driven by a combination of:

• Poor droplet size distribution during transients
• Delayed temperature feedback to the control loop
• Over-spray leading to wall wetting and dust agglomeration

Engineering approach

Lechler completed an assessment that included a heat balance and a review of spray performance, nozzle placement, and control response.

Key design inputs used for sizing and verification:

• Gas flow rate: 98,574 Nm³/hr
• Inlet temperature: up to 840°F
• Target outlet temperature: 320°F
• Calculated water requirement: 64 gpm

The team also identified opportunities to reduce compressed air consumption through improved atomization efficiency and by adding instrumentation to verify air and water delivery across operating conditions.

The Solution

The retrofit focused on three areas: spray performance, measurement, and controls.

Spray system upgrades

• Replaced existing spray lances with Lechler VarioCool® nozzle-lances and protection tubes
• Improved atomization to reduce wall wetting and prevent wet dust formation
• Configured the system for lower compressed air demand while maintaining cooling capacity

Instrumentation and controls

• Added compressed air flow measurement and alarms
• Relocated outlet temperature measurement closer to the gas exit to reduce measurement lag
• Updated DCS logic and alarm limits to support tighter temperature control and reduce manual intervention

Execution and validation

• Installed during a planned shutdown with no major structural changes
• Cold and hot commissioning included loop step-response checks and a 72-hour continuous run
• Acceptance criteria included no visible condensation or wet dust buildup

Results

Performance summary:
 

Financial Impact

• Projected savings (estimate): Using $150 per SCFM per year and a reduction from 700 SCFM to 208 SCFM, the projected savings were approximately $73,800 per year.
• Documented savings: The plant reported $114,400 in savings over three months (Aug to Nov 2025). Annualized, this equates to approximately $457,600 per year.

Challenges and Lessons Learned

• Early skepticism focused on whether compressed air reduction could still maintain sufficient atomization. Commissioning data and stable operation helped resolve concerns.
• Atomizing air supply pressure fluctuations were addressed by validating supply stability and setting appropriate alarms and operating guidance.

Key takeaway: Nozzle selection, atomization quality, and control response work as a system. Improving droplet distribution reduced wall wetting, which reduced buildup and stabilized operation while cutting operating cost.

Replicability

This retrofit approach is well-suited for cement plants facing:

• GCT buildup and plugging issues
• Temperature instability upstream of raw mill and baghouse
• High compressed air consumption in dual-fluid atomization systems
• Frequent operator intervention during load swings