Dilute ethanol-water wash liquor from the centrifuge (first-wash and subsequent wash stages) is not discharged — it is routed to this distillation system, which separates and concentrates the ethanol for reuse as fresh wash solvent and reaction diluent in the kneader reactors. This closed-loop solvent recovery is one of the largest cost-saving elements in CMC and PAC production economics.
This alcohol recovery system separates ethanol from the water-ethanol wash liquor generated during CMC and PAC washing, allowing the recovered solvent to be reused in the kneader reactors and centrifuge wash cycle rather than purchased fresh and discharged as waste. The system comprises eight pieces of equipment working in series: a preheater, a packed distillation column, a reboil heating train (distillation still, reboiler, and heater), and a three-stage condensing train.
Wetted equipment in direct contact with the concentrated ethanol vapour and liquid — the preheater, column, still, reboiler, and heater — is constructed in titanium for corrosion resistance and long service life. The downstream condensing train, handling cooler, more dilute streams, uses 304 stainless steel.
| Equipment | Qty | Type | Medium | Size / Area | Dimensions (mm) | Material | Weight (kg) |
|---|---|---|---|---|---|---|---|
| Waste Alcohol Preheater | 1 | Vertical | Ethanol, water | 20 m² (Ti tube / Ti shell) | 3000 × 600 × 800 | Titanium | 400 |
| Distillation Column (packed) | 1 | Vertical | Ethanol, water | Ø800 × 14,000 · 7-layer packing | 2 × shell sections 7000×1000×800; packing modules 1000×1000×2100 ×7 | Titanium | 3,400 (shell) + 8,500 (packing) |
| Distillation Still | 1 | Vertical | Ethanol, water | 2.5 m³ | 1600 × 1800 × 2500 | Titanium | 2,000 |
| Reboiler | 1 | Vertical | Ethanol, water | 40 m² (Ti tube / 304 shell) | 4000 × 800 × 1000 | Titanium / 304 | 700 |
| Heater | 1 | Vertical | Ethanol, water | 10 m² (Ti tube / Ti shell) | 2500 × 600 × 800 | Titanium | 300 |
| 1st-Stage Condenser | 1 | Horizontal | Ethanol, water | 50 m² (304 tube / 304 shell) | 4000 × 900 × 1550 | 304 stainless steel | 800 |
| 2nd-Stage Condenser | 1 | Horizontal | Ethanol, water | 30 m² (304 tube / 304 shell) | 3000 × 800 × 1450 | 304 stainless steel | 500 |
| 3rd-Stage Plate Heat Exchanger | 1 | Vertical | Ethanol, water | 15 m² (304) | 800 × 800 × 600 | 304 stainless steel | 300 |
Operating and design temperature/pressure conditions for each unit are confirmed at project design stage based on wash liquor concentration and target ethanol recovery purity — contact ZHAOYUAN for the full process design basis.
- Titanium construction on all ethanol-wetted heat-transfer equipment: the preheater, column, distillation still, reboiler, and heater are all titanium (or titanium tube with steel shell), providing excellent corrosion resistance to the ethanol-water-chloride environment typical of CMC/PAC wash liquor recovery, and long service life under continuous reboil duty.
- Packed column design for efficient separation: the distillation column uses structured/random packing across 7 layers rather than trays, providing high separation efficiency with lower pressure drop — well suited to the ethanol-water system encountered in cellulose ether solvent recovery.
- Dedicated preheater improves energy efficiency: the waste alcohol preheater raises the temperature of the incoming dilute wash liquor before it enters the column, recovering heat and reducing the reboil duty required from the reboiler and heater — lowering overall steam consumption.
- Three-stage condensing train for high recovery efficiency: overhead ethanol vapour is condensed progressively across the 1st-stage condenser (50 m²), 2nd-stage condenser (30 m²), and 3rd-stage plate heat exchanger (15 m²) — maximising ethanol recovery while allowing staged cooling water temperature control for energy efficiency.
- Full 8-unit package engineered as one system: ZHAOYUAN supplies the complete recovery train as a matched set, sized together to the same throughput and concentration targets, avoiding the bottlenecks that arise from mixing individually-sourced components.
| CMC / PAC Wash Solvent Recovery | Recovers ethanol from the first and subsequent wash centrifuge liquor for reuse as wash solvent and kneader reaction diluent, reducing fresh solvent purchase and wastewater treatment load. |
| HPMC / HEC Production | Applicable to solvent recovery in hydroxypropyl methylcellulose and hydroxyethyl cellulose lines using similar ethanol or isopropanol wash systems. |
| General Ethanol-Water Separation | The column and condensing train design is applicable to other ethanol-water distillation duties outside cellulose ether production where a titanium-rated system is required. |