Cane Diffuser

Overview

The cane diffuser is a moving-bed extraction vessel that recovers residual sugar from bagasse (exhausted cane fiber) after primary crushing. Rather than mechanical squeezing, diffusion uses hot water or recycled juice to dissolve and leach remaining sucrose from cellular cavities. A slow chain-conveyor with perforated buckets advances bagasse from top to bottom while hot juice flows countercurrent upward, maximizing contact time and extraction efficiency. Modern diffusers achieve 80–90% recovery of sugar remaining in bagasse, increasing overall mill efficiency by 3–5 percentage points.

How it Works

Mill bagasse from the Sugar Mill Roller discharge enters the diffuser hopper and drops into the moving-bed conveyor. The chain moves continuously (0.5–1 m/min) carrying bagasse downward in a cascade through the vessel. Simultaneously, hot juice is pumped from the extraction sump and sprayed onto the top of the bed via Distribution Header. As juice percolates downward through the bagasse, it dissolves residual sugar. The countercurrent motion maximizes time for diffusion, bagasse spends 30–60 minutes inside the vessel.

Direct Steam Sparger bubbles steam through the lower bagasse zone, raising local temperature to 70–80 °C. This accelerates dissolution (sugar solubility increases exponentially with temperature). An immersion Heating Coil pre-heats returning juice from the Recirculation Pump.

Extracted juice overflows the Overflow Weir and passes through a Drain Screen to remove fiber fines, then accumulates in the Extraction Sump for dispatch to clarification and Vacuum Pan. Exhausted bagasse exits the bottom and is conveyed to the boiler for fuel (bagasse is 45–50% moisture but has sufficient calorific value to generate steam for the sugar plant).

Design Considerations

Moving-bed diffusers are preferred over static vessels because continuous advancement prevents compaction and dead zones where juice stagnates. Countercurrent flow (juice down, bagasse up) maximizes the concentration gradient driving diffusion, juice at the top is strongest (already extracted), weakest juice meets fresh bagasse at the bottom.

Temperature control is critical: below 60 °C extraction is slow; above 85 °C bagasse begins to degrade and juice color worsens. Most plants maintain 72–76 °C as a compromise.

Juice circulation rate balances extraction (faster = better) against bagasse erosion and energy cost. Typical design is 200–250 L/min for a 60-tonne/hour mill.

The Drainage System is essential: any trapped dead-leg juice will sour (ferment) and degrade downstream products. Continuous weir overflow and positive drainage prevent accumulation.

Operational Issues

Over-extraction (high temperature, high residence time) darkens juice and reduces final sugar quality; low-temperature under-extraction leaves sugar in bagasse. Real-time Control Instrumentation monitor extraction temperature with feedback loops to trim steam flow.

Bagasse bridging (arching in the conveyor) is a common mechanical failure. Modern designs use vibrators or shock-release mechanisms to break bridges and maintain even bed advancement.

Process Chain

Bagasse from Sugar Mill Roller → Cane Diffuser → bagasse to fuel; extracted juice → clarification → Vacuum Pan → Sugar Centrifugal → packaging.