In a conventional dry mill ethanol plant, the central processing area and one of the largest users of energy is the Distillation, Dehydration, and Evaporation (DD&E) system. Traditionally, ‘beer’, the source of the ethanol, is produced in a fermentation process using very large vessels.
From there it is pumped into a Beer Stripping Column where the ethanol is initially extracted using steam or vapor as the heat source. The dilute ethanol stream discharged from this column will be further refined, before being Dehydrated using Molecular Sieve technology in a Pressure Swing Adsorption (PSA) process.
The secondary column, or Ethanol Rectification Column (ERC), will generate a rich, 92% w/w ethanol overheads stream, which will then be fed to the PSA system. The molecular Sieves will dehydrate the incoming feed from the ERC to produce a 200 Proof ethanol product that is suitable for blending with gasoline.
Whole Stillage discharging from the bottom of the Beer Stripping Column is fed to a series of centrifuges (solid/liquid separation) whereby undissolved solids are removed. The liquid discharge from the centrifuges, which contains dissolved solids, is sent to an evaporator whereby the dissolved solids are concentrated to 30%-35% w/w. The solid rich effluent from the evaporation system is termed ‘Syrup’.
The undissolved solids from the centrifuge and the syrup are combined and used as either ‘Wet’ or ‘Dry’ cattle feed:
- ‘Wet’ Feed is used on an ‘As Is’ basis; it’s termed Wet Distillers Grain with Solids or WDGS in the industry. ‘Wet’ Feed has a short shelf life and must be used quickly to prevent biological activity.
- For a longer shelf life product, the combined streams are sent to a dryer to remove the majority of the water. The product from the dryer is termed Dried Distillers Grain with Solids or DDGS.
With over 35 years of experience designing state-of-the-art Ethanol DDE Facilities, Thermal Kinetics (TK) has developed and patented various process enhancements, to improve the functionality and energy efficiency of conventional plants that are currently in operation. These enhancements include:
- Lower ‘Backset’ or recycle to Fermentation; 57.3% Reduction in flow,
- Enhanced Removal of Fusel Oils,
- Lower Energy Usage;
- 21% lower usage based on current ethanol feed concentrations of (12%-13½% w/w),
- 31% lower usage when an enhanced 15% w/w ethanol feedstock is achieved,
- Improvements in Condensate Reuse; 56.5% gain in Condensate Recovery,
- Improvements in Processing Whole Stillage;
- Increased Solid Concentrations feeding the centrifuges
- 20% reduced load on the centrifuges,
- Enhanced Thin Stillage concentrations,
- Lower Operating Temperatures within the Evaporation System;
- Reduces Fouling, which leads to
- Longer production campaigns between maintenance shutdowns.
Based on these enhancements, TK has improved the overall efficiency of the DDE process as illustrated in the table below. The numbers illustrated are based on a 50MM gallon/annum ethanol production rate and a 13.1% ethanol concentration in the feedstock to the Beer Stripping Column.
|TK PATENTED PROCESS||CONVENTIONAL TECHNOLOGY|
|TOTAL STEAM REQ’D||56,210 LB/HR||71,525 LB/HR|
|EQUIVALENT HEAT||49.8 MM BTU/HR||63.37 MM BTU/HR|
|WHOLE STILLAGE FLOW||247,063 LB/HR||296,564 LB/HR|
|WHOLE STILLAGE CONC||16.22 WT%||13.51 WT%|
|CENTRIFUGE LOAD||430 GPM||529 GPM|
|EVAP FEED||243 GPM @ 8.65%||232 GPM @ 7.03%|
|RECYCLE TO FERMENTATION (BACKSET)||87.7 GPM||205.4 GPM|
|FUSEL OIL DECANTER||YES||NO|
|PROCESS CONDENSATE FOR RECYCLE RECOVERED||123,969 LB/HR
|1st EFFECT EVAP TEMP (F)||152°||199°|
|2nd EFFECT EVAP TEMP (F)||127°||185°|
|BEER COLUMN BOTTOM (F)||203°||185°|
Learn more by downloading our technical paper Simulation of Pressure Swing Adsorption (PSA) in Fuel Ethanol Production Process. Click here or below to download.
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Tags: dd&e, dehydration, distillation, evaporation