Optimization and Renovation of Calcination Furnace Gas Tee Equipment in Soda Ash Production

Literature Overview

This paper by Liu Huan, Li Ruifeng, Zhou Chuanfeng, and Li Qiming, published in the Soda Ash Industry journal (2019, No. 4, pp. 19-21), documents a process and equipment improvement project at Tangshan Sanyou Chemical Co., Ltd. The study focuses on the optimization of the tee (three-way fitting) configuration in the calcination furnace gas system of a light soda ash production line, addressing persistent problems of high gas velocity, dust carryover, scaling blockage, and frequent maintenance requirements.

Technical Background and Problem Analysis

In the soda ash production process, the calcination furnace converts sodium bicarbonate to sodium carbonate through thermal decomposition. The furnace gas system collects and recycles off-gas containing CO2, water vapor, and entrained solid particulates. The tee fitting connecting the furnace gas ducts to the recovery system serves as a critical flow junction where gas direction changes and flow rates converge.

The original design employed U-shaped bend pipe configurations with the following deficiencies:

• High gas velocity at bends: The U-shaped geometry creates abrupt flow direction changes, accelerating gas to velocities exceeding design limits at the bend apex.
• Dust accumulation and scaling: Entrained calcination dust deposits on the inner surfaces of bends, progressively reducing effective flow area and increasing system resistance.
• Frequent blockage: Scale buildup eventually causes partial or complete blockage, requiring shutdown for manual cleaning.
• Production constraint: The gas system resistance directly limits the maximum achievable calcination furnace throughput.

Optimization Approach and Engineering Solutions

The improvement project addresses the problem through a multi-faceted approach combining process optimization and equipment modification:

Flow Path Redesign

The U-shaped bend configuration is replaced with a modified tee geometry incorporating:

• Diverter channels: Internal baffles that guide gas flow gradually, reducing turbulent eddies and particle impaction.
• Increased cross-sectional area: The tee body is enlarged to reduce gas velocity below the erosion threshold for the specific particulate-laden gas stream.
• Smooth internal transitions: Welded internal inserts eliminate sharp corners where particles preferentially accumulate.

Material and Surface Treatment

Process Integration

The improved tee is integrated with:

• Dissolution tank optimization: Enhanced gas-liquid separation downstream reduces particulate loading.
• Flow monitoring instrumentation: Pressure transducers at tee inlet and outlet enable real-time resistance monitoring and early blockage detection.
• Scheduled maintenance protocol: Based on measured scale accumulation rates, cleaning intervals are optimized to minimize unplanned shutdowns.

Performance Evaluation

The optimization results demonstrate significant improvements in operational performance:

• System pressure drop: Reduced by approximately 30-40% compared to the original configuration.
• Cleaning frequency: Increased from every 15-20 days to every 45-60 days, reducing maintenance labor by more than 60%.
• Production capacity: The calcination furnace throughput increased as the gas system resistance limitation was alleviated.
• Equipment life: Internal surface deterioration rate significantly reduced due to lower gas velocity and improved material selection.

Engineering Practice Considerations

This case study illustrates several important principles for piping system design in particulate-laden service:

1. Flow velocity management: In gas systems carrying solid particles, the critical parameter is not merely pressure drop but particle impaction velocity. The erosion threshold for carbon steel in dust-laden gas is approximately 15-20 m/s; exceeding this value accelerates wear exponentially.
2. Geometric optimization: The bend radius to diameter ratio (R/D) directly affects pressure drop and erosion rate. For particulate service, R/D ≥ 1.5 is recommended, and 2.0 is preferred for severe conditions.
3. Maintenance accessibility: Tee fittings in gas collection systems should be designed with inspection ports and cleaning access, as complete blockage removal from inaccessible locations requires cutting and replacement.
4. System-level thinking: The tee fitting is not an isolated component but part of a system where upstream dust generation, downstream separation, and intermediate transport must be balanced. Optimizing a single fitting without considering system interaction yields suboptimal results.

Study Insights and Implications

The paper demonstrates the value of systematic process-equipment integration in solving operational problems. The original U-shaped tee design likely met initial design specifications but failed to account for the actual operating conditions—specifically, the particulate loading and gas composition that developed over time. This highlights the importance of commissioning feedback loops where actual operating data informs design revisions.

For engineers involved in chemical plant piping design, the key takeaway is that fittings in particulate service require special consideration beyond standard pressure drop calculations. The economic cost of frequent maintenance shutdowns often far exceeds the incremental capital cost of a properly designed fitting. A life-cycle cost analysis should always be performed for critical gas handling components, incorporating maintenance labor, production loss during shutdowns, and material replacement costs.