Thin stillage evaporation concentrates a process stream consisting of water and dissolved solids. The process is most common in the ethanol industry, with the dissolved solids coming from the corn used to make ethanol. Undissolved solids typically have already been removed using a centrifuge. A stream that consists of both dissolved and undissolved solids is commonly known as whole stillage, a stream with just dissolved solids is thin stillage, while the concentrated thin stillage is referred to as syrup.
A typical feed concentration to the evaporation system would be at 5% to 7%, while a typical final concentration from the evaporation system (the syrup) would have a concentration of 30% to 35%.
Where Is It Found?
The most common application for thin stillage evaporation is in ethanol plants, utilizing corn as a feedstock and producing fuel grade ethanol. The thin stillage evaporators allow the ethanol plant to concentrate up the dissolved solids, to either go to a dryer or sold as syrup. The dissolved solids come upstream from the fermentation process and consist of solids not digested in the ethanol fermenters. The dried solids (DDGS, Dried Distillers Grains with Solubles) can be sold to cattle farmers as feed, and has a long shelf life. Alternately, the syrup (CCDS, Corn Condensed Distillers Solubles) can be fed to cattle, however it has a much shorter life span.
How Is the Thin Stillage Concentrated?
The thin stillage is concentrated by evaporating off the water, leaving a more concentrated stream. The process often requires multiple stages of evaporation and multiple effects to reduce the amount of heating media (steam) required.
Each time the process fluid is concentrated through evaporation, it’s considered one stage of evaporation. In a three stage evaporation system, for example, the thin stillage could be concentrated from 7% to 14%, then 14% to 30%, then finally 30% to 35%.
A multiple-effect evaporation system is a means by which we reduce utility steam consumption by utilizing the steam we generate in evaporation to evaporate the process stream in the next effect. We do this by reducing the pressure at which the evaporation takes place. As an example, the first stage evaporation may take place at 5.15 psia generating steam at 163.4F. The second effect would operate at 3.83 psia, where boiling would take place at 151.3F. The steam generated at 163.4F (produced using low-pressure steam available at the plant) would be utilized to generate the steam at 151.3 in the second effect. We could have a third effect as well, at a lower operating pressure and temperature.
Evaporation equipment utilized for this service typically consists of shell and tube heat exchangers, most often configured as falling film evaporators. Large diameter tubes are preferred as the thin stillage is fouling. As an alternate, plate and frame exchangers can also be utilized as suppressed boiling exchangers. Suppressed boiling occurs when the process steam has sufficient heat input into it in the liquid phase, as sensible heat under pressure, such that after exiting the exchanger it can be flashed. Suppressed boiling is utilized for plate and frame exchangers to reduce the potential for fouling of the plate and frame exchanger.
The Thermal Kinetics Advantage
Thermal Kinetics has extensive experience designing complete thin stillage evaporation systems. Our goal is to provide a system with the best payback period, balancing the cost of the utility steam versus the cost for a multiple-effect evaporation system. Thermal Kinetics also provides systems utilizing mechanical vapor recompression to further reduce utility steam consumption.
Our systems are typically run under vacuum where the operating temperature is low, reducing fouling rates and thereby increasing run times. Thermal Kinetics can supply the control valves, pumps, and all ancillary equipment (skidded system). Further, we recommend to our customers that they utilize a CIP system (clean in place) designed by Thermal Kinetics to clean the equipment with very minimal downtime.
As the name suggests, evaporators are devices that cause a material to evaporate, or enter its gaseous state. Because of their broad range of practical uses, they can be found in a variety of applications, ranging from agriculture to waste management. To illustrate the versatility of these essential devices, we’ll briefly walk you through some of their most common uses and applications below.
Common Uses for Evaporators
Evaporators are widely employed in most industries that depend on a constant supply of fluids or chemicals. HVAC systems, for example, use evaporator coils to vaporize compressed cooling chemicals, removing heat in the process. These systems also use condenser coils to exhaust the heat outside, making the entire process much more effective.
Heat recovery evaporators are used to convert seawater into clean water in desalination plants. Utility companies tend to prefer these evaporators over alternative solutions because of their simplicity and minimal energy requirements. The end result is lower operational costs.
Evaporators are also used in oil fields to separate water and various other compounds from crude oil. Though more difficult to use than other types of evaporators, these are nevertheless popular among energy companies because they can reduce operating costs while meeting government-mandated standards. Because they are relatively compact, they can also be easily transported to other locations.
The food industry employs evaporators to achieve product consistency. Coffee is a case in point. Evaporation is also used to concentrate liquid foods such as noodles and make condensed milk, the product of a process that removes water from milk. Similarly, pharmaceutical companies use evaporators to remove excess moisture from drugs, thus improving product stability.
Common Applications for Evaporators
Because of their efficiency, evaporators are well-suited to an array of industrial applications. They are particularly common in processing industries. Food and dairy products such as tomato purees, milk, herbal extracts, gelatin, coconut water, and whey and milk proteins are all processed with the help of evaporators. The same is true for chemicals such as dyes, ammonium nitrate, glycerin, sodium nitrate, paints, and pigments.
Evaporators are also ideal for very low temperature applications in the food and pharmaceutical industries. These include the production of plasma, fermented products, coffee extracts, fruit juices, bulk drugs, glycerin, sweet water, yeast extract, and protein hydrolysate. Whey, gelatin, malt extracts, glucose, fructose, dextrose, sorbitol, and maltodextrin are all produced with evaporators, as well.
Another field in which evaporators are widely used is waste management. Waste management providers rely on them to treat effluents, or wastewater, from various plants, including distilleries, grain mills, abattoirs, textile plants, chemical reactors, and storage tanks.
Designed to serve a variety of practical uses, evaporators are a versatile solution to many common industrial challenges. At Thermal Kinetics, we use our experience and expertise to manufacture evaporators that thrive in any application.
Regardless of your needs, Thermal Kinetics can supply you with an industrial grade evaporator that minimizes operating costs without undermining productivity. Contact us to learn more about how we can help you find the perfect evaporator for your company.
A truly versatile device, evaporators are used in a wide range of industrial settings. Beverage manufacturers use evaporators to concentrate product and to optimize product consistency; pharmaceutical companies use them to eliminate potentially damaging moisture from medicines; and a number of industrial chemical sectors, such as the chloralkali industry, use them to concentrate chemical solutions.
Evaporators vary greatly in their design and capabilities. To optimize performance, ensure product quality, and help reduce waste and operational costs, it’s important to select the right type of equipment for your unique application. Several factors should be kept in mind when choosing an evaporator.
First, consider the materials of construction of the evaporation system; materials can greatly impact system functionality, lifespan, and maintenance requirements.
Since evaporation generally takes place at elevated temperatures in the presence of corrosive chemicals, your evaporation equipment should be manufactured from a durable, strong material that can withstand severe process environments.
On the other hand, in industries where strict hygiene must be maintained, such as the food, beverage, and pharmaceutical sectors, it’s more important to select materials that are easy-to-clean and that can withstand the rigors of the chemicals used to Clean-in-Place (CIP) the process wetted surfaces.
Second, various operational characteristics should also be taken into consideration. For example, if the product you are evaporating is heat sensitive, a low-pressure or short time duration-evaporator will be ideal. A product’s propensity for fouling, fluctuating solid concentrations, reactivity, and viscosity should all be carefully considered. If you’re using the wrong evaporator, these properties can lead to process shutdowns, increased downtime for cleaning, and higher maintenance costs.
Energy efficiency is frequently achieved through process integration and TKE’s DDE design is no exception. But highly integrated process are sometimes hard to troubleshoot. In every instance in which Calgren has been baffled by DDE process issues and found it necessary to reach out to TKE for assistance, they have responded with sage and knowledgeable advice.
– Lyle J. Schlyer, President of Calgren Renewable Fuels