The alcohol industry has so far not benefited to the fullest extent from advanced control solutions. This is typical of small units or processes where MPC (model-predictive control) or Neural Network technologies are rather costly to implement. This situation fits in well with our proprietary DCS-based advanced control schemes which are geared towards processes that lack significant multivariable interactions. Of course when the need calls for true MPC technology, we offer MPC also, as needed.
We are presently developing packaged solutions for alcohol plants as we have done for Polyethylene and polypropylene plants.
Application of PiControl technology to Ethanol plants will improve plant-wide key performance indicators and accrue the following benefits:
- Increase ethanol production rate by automatically identifying and pushing against the active constraint, continuously in real-time. Constraints include process, equipment, economic or market constraints at any given time. The overall approach constantly moves the process in the most profitable direction.
- Minimize fermentation batch cycle time using Expert System based adaptive sequence technology. This increases the overall ethanol throughput because of increase in fermenter capacity.
Maximize fermentation yields to ethanol by optimizing fermentation process conditions using both the Expert System and an online real-time optimizer.
- Minimize alcohol losses in the three distillation column product streams by improved control of distillation variables and product specifications using various advanced process control schemes. The control schemes minimize alcohol losses from stillage, fusel oil and water.
- Increase alcohol content of the beer and reduce overall energy consumption by optimizing fermentation temperature.
- Minimize water addition to ferment beer mash with higher levels of solids. This reduces the cost of handling and treating the water later. In addition, higher solids result in higher “beer” yields in the same or less time.
- Increase overall process automation thus reducing the level of manual intervention needed from control room operators, thereby allowing them focus on more important, potentially money-saving tasks.
- Improve plant-wide process control quality by reducing deviation of product specifications and other critical controlled variables from their setpoints.
PiControl technology performs closed-loop dynamics identification followed by controller parameter optimization to provide optimal control of all variables. PiControl engineers will custom-analyze every single existing controller in the plant and look for control improvements through re-configuration, new algorithms or optimized tuning.
For the Ethanol Process, we provide PID tuning, advanced control and optimization for the following areas:
The milled grain is mixed with process water, the pH is adjusted to about 5.8, and an alpha-amylase enzyme is added. The slurry is heated to 180-190°F for 30-45 minutes to reduce viscosity.
The slurry is then pumped through a pressurized jet cooker at 221°F and held for 5 minutes. The mixture is then cooled by an atmospheric or vacuum flash condenser.
After the flash condensation cooling, the mixture is held for 1-2 hours at 180-190°F to give the alpha-amylase enzyme time to break down the starch into short chain dextrins. After pH and temperature adjustment, a second enzyme, glucoamylase, is added as the mixture is pumped into the fermentation tanks.
SIMULTANEOUS SACCHARIFICATION FERMENTATION
Once inside the fermentation tanks, the mixture is referred to as mash. The glucoamylase enzyme breaks down the dextrins to form simple sugars. Yeast is added to convert the sugar to ethanol and carbon dioxide. The mash is then allowed to ferment for 50-60 hours, resulting in a mixture that contains about 15% ethanol as well as the solids from the grain and added yeast.
The fermented mash is pumped into a multi-column distillation system where additional heat is added. The columns utilize the differences in the boiling points of ethanol and water to boil off and separate the ethanol. By the time the product stream is ready to leave the distillation columns, it contains about 95% ethanol by volume (190-proof). The residue from this process, called stillage, contains non-fermentable solids and water and is pumped out from the bottom of the columns into the centrifuges.
The 190-proof ethanol still contains about 5% water. It is passed through a molecular sieve to physically separate the remaining water from the ethanol based on the different sizes of the molecules. This step produces 200-proof anhydrous (waterless) ethanol.
During the ethanol production process, two valuable co-products are created: carbon dioxide and distillers grains.
As yeast ferment the sugar, they release large amounts of carbon dioxide gas. It can be released into the atmosphere, but it is commonly captured and purified with a scrubber so it can be marketed to the food processing industry for use in carbonated beverages and flash-freezing applications.
The stillage from the bottom of the distillation tanks contains solids from the grain and added yeast as well as liquid from the water added during the process. It is sent to centrifuges for separation into thin stillage (a liquid with 5-10% solids) and wet distillers grain. Some of the thin stillage is routed back to the cook/slurry tanks as makeup water, reducing the amount of fresh water required by the cook process. The rest is sent through a multiple-effect evaporation system where it is concentrated into syrup containing 25-50% solids. This syrup, which is high in protein and fat content, is then mixed back in with the wet distillers grain (WDG).
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