To maximize throughput and yield, start with liquefaction

By Laurie Duval | August 28, 2014

Increasing throughput and yields at the same time has proven difficult to accomplish for many of even the most experienced ethanol operations teams. Recently, however, new enzyme technology has become available that makes it possible to reduce the conventional tradeoffs. The enzymes allow plants to reframe their goals of maximizing plant output and profitability by combining increased throughput and yield at the same time.

During full-scale trials over the past two years, Novozymes has gained experience in the strengths and special requirements of this different approach using its new enzyme technology, trademarked Avantec. Novozymes’ data, collected from 84 trials completed since January 2012, show that 80 percent of all Avantec trials demonstrate at least a 1 percent increase in ethanol yield when the plant was able to follow the protocol. Furthermore, 70 percent of Avantec trials have shown at least 1.5 percent increase in yield, and 54 percent have seen a 2 percent or more ethanol yield gain (see accompanying chart).

In addition to yield, a number of trials have demonstrated the ability to run higher grind rates with Avantec. Improved viscosity reduction and starch conversion at high mash solids has allowed plants to remove or minimize bottlenecks in the cook process. As the enzyme alters  physical characteristics in the corn mash, a ripple effect of small changes occurs throughout the plant. The changes must be identified and the process refined in order to control them. Only then can the full benefits of throughput and yield be realized.  

During early trials with Avantec, Novozymes ran into a challenge with backend fouling, and in the process, learned some useful lessons for further helping their customers maximize plant outputs. This journey is described below.

Data-driven Approach

In 2012, Novozymes concluded 13 full-scale trials with its new, low-pH cook, liquefaction enzyme before the formal product launch of Avantec in October. An additional five trials were in progress at the time of launch. Two of the 18 plants trialing the enzyme reported backend fouling. The evaporator tubes at these two plants fouled and clogged at a higher rate than normal, evaporator pressure rose and, in the worst case, the plant had to shut down temporarily to hydroblast the tubes clean.

The first time it happened, Novozymes did not know whether the problem was related to the new enzyme or to the process changes related to running a low-pH cook (pH 5.0-5.3). When the problem reoccurred, Novozymes created an internal 10-person task force with specialists from R&D and Technical Service to solve the issue as quickly as possible. Members of this task force consulted with industry experts, including ICM Inc. Plant samples were collected throughout the process and rigorously analyzed. Every step in the trial process was examined.

“Novozymes’ pursuit of a solution was quick and aggressive, otherwise ICM would not have been called in as soon as we were,” said Dr. Scott Kohl, ICM Technical Director for Product Development. “The issues were observed at only two plants, where others were happy with the performance of Avantec. Novozymes took a proactive stance in working with those two customers to try to identify the problem.”

At one of the plants experiencing the issue, Novozymes compared all available process data with data from a similar plant not running the enzyme. ”At first, we didn’t know what we were looking for. Usually we look at fermentation data. But we asked for more data on the whole process, and gradually we began to piece it together,” said Patrick Mandulak, senior scientist for Novozymes Technical Service.

By comparing the data from the two plants, the Novozymes team noticed the differences when Avantec was introduced. The lower-cook pH required several process changes:

  • -Ammonia added to slurry was reduced or even discontinued, resulting in less ammonia nitrogen in fermentation.
  • -Urea addition increased to compensate for the reduced ammonia nitrogen.
  • -The lower-pH slurry resulted in reduced or discontinuing sulfuric acid addition post liquefaction.
  • -These process changes led to a higher pH profile in fermentation.
  • -An increase in sulfuric acid after the beerwell was necessary to maintain baseline pH in the beer feeding distillation and ultimately evaporation. Monitoring of resulting sulfuric levels in DDGS was an important aspect to this process change, but the impact was minimal with no instances of approaching the DDGS sulfur specification observed.

 

”One of the things we noticed was a pH increase in the distillation area. We asked the plant manager to increase acid to get the pH back to the baseline level,” Mandulak explained. “And when that was done, the problem with fouling disappeared.” At that point, Novozymes changed the trial protocols to include the following steps:

  • -Cook pH adjustment to target between 5.0 and 5.3. Many Avantec users discontinue ammonia use entirely, but others opt to keep some ammonia in slurry as a cost-effective nitrogen source.
  • -Nitrogen replacement via urea, ammonia to fermentation, or protease.
  • -Fermentation glucose profile optimization through changes in glucoamylase dosing.
  • -Beerwell or backend pH control to maintain similar pH as found in baseline conditions.
  • -Phytase addition as needed.
  • -Solids set-point control in evaporation to maintain solids as in baseline conditions.

 

With the lessons learned over the past two years, implementation of Avantec has become a routine operation. “We have developed a holistic process approach to ensure successful trials,” Mandulak said.

“Avantec allows a plant to run higher solids prefermentation at the same or lower viscosity, allowing for the plant to optimize around this new ability. While plant managers may feel uncomfortable at first taking these recommendations, time will prove the benefits. Avantec is new, and the process may not look the same as it once did,” said ICM’s Kohl.

Kevin Cox, biofuel technical service director with Novozymes, agreed. “Our learning with Avantec was not completely unexpected since, as plants push throughput to obtain higher production, the potential for backend fouling increases. Lower mash viscosity created by Avantec allows ethanol plants to push harder, which if not accounted for, could contribute to fouling in the backend of the plant. Best practice cleaning and maintenance routines, as well as controlling solids and pH in the backend, will prevent an increase in the rate of fouling.”

Five additional tips to optimize liquefaction with Avantec to achieve higher throughput and yields include:

1. Ensure proper cook temperatures to strike the best balance between maximum starch gelatinization and enzyme activity.

2. It may seem counter-intuitive, but acid use is not lowered by removing ammonia from cook. Make sure there is an acid line installed after the beer well for flexibility in controlling pH to distillation.

3. Do not overdose urea when moving from a normal pH process to low pH cook. Add just enough total nitrogen to allow fermentations to consistently finish to completion.

4. Adjust glucoamylase dosing to prevent high glucose levels in the yeast prop and in early fermentation.

5. To achieve the operationally and economically ideal viscosity and starch solubilization, use a modern, liquefaction-quality measurement assay, such as Novozymes’ InDex tool, to optimize enzyme dosing levels and the split between slurry and liquefaction.

Customer Experience  

Red Trail Energy LLC is a 50 MMgy plant in North Dakota that was looking to increase both ethanol yield and throughput. Red Trail had already demonstrated a good production recipe, and the approach suggested by Novozymes to try Avantec created some apprehension. But after starting a trial in June 2013, the plant saw a significant gain in yield. Throughput also increased, even with worn pumps in slurry. “Some of the best yields that Red Trail has seen were on Avantec,” reported Bill “Buck” Schimetz, operations supervisor. “This experience has taught us that if you don’t talk to a stranger, you might never meet a friend. We’ll be less shy in the future to try new products.” 

The situation was different at the Green Plains plant in Atkinson, Nebraska, a 50 MMgy DeltaT plant. “I really wanted to use Avantec to get the viscosity thinner, to basically debottleneck my front end,” explained Brian Constable, plant manager. Constable had used the enzyme at another facility, where he had seen a significant yield increase, “I knew what it was capable of, and I knew I would get the viscosity.” The plant started with Avantec in October 2013. Obviously, the cost is higher with Avantec than other products, but we had our math penciled out, and it’s a better product that pays for itself. We got what we wanted with the yield and throughput increases. It looked like to me that I could get 5,000 gallons more alcohol throughput per day,” he concluded.

Author: Laurie Duval
Regional Marketing Manager, Novozymes, BioFuel NA
919-494-3000
http://bioenergy.novozymes.com