Pulsation Control in Hi-Temp Coffee Extraction Towers
Problem: The Coffee Manufacturer operates interconnected vertical extraction towers where hot water is circulated at extreme temperatures to produce coffee extract. During operation, the customer observed:
- Rapid water evaporation above 175°C resulting in air pockets inside pipelines
- Slow-reacting temperature instruments, allowing entrained air to persist
- Centrifugal pumps forced to move both air and liquid, leading to:
• Severe water hammer
• Excessive piping vibration
• Damage to plate evaporators and instrumentation
• Partially filled distribution lines on startup, requiring air displacement before flow could stabilize—intensifying water hammer
These issues disrupted extraction quality, compromised equipment life, and increased maintenance cost.
A review of the extraction tower circulation system revealed two primary contributors to the instability:
1. Air Entrapment Due to High-Temperature Evaporation
At 175°C, water rapidly vaporizes. Air and vapor bubbles accumulated in the recirculation lines and plate evaporators. Because the system’s temperature instrumentation responded slowly, air remained trapped far longer than expected—allowing pumps to ingest and compress air repeatedly.
2. Pumping System Not Designed to Handle Vapor Pockets
The 1½” centrifugal pumps recirculating extract between stages were forced to push air through evaporators and distribution lines. This caused major hydraulic consequences:
- Violent pressure spikes (water hammer)
- Resonant vibration in vertical and horizontal piping sections
- Structural stress on evaporators and associated equipment
- This unstable flow environment also threatened extract consistency and overall process quality.