Tank Cleaning with Rotary Impingement Technology

By J.W. Resenhoeft | September 19, 2013

Rotary impingement technology is the dominant method of tank cleaning within the ethanol industry, and there are numerous reasons why it’s considered the best. Simply put, cleaner tanks mean reduced bacteria levels, beer stone and higher yields. Of course higher yields and less downtime equal more profit for ethanol companies. To understand the technology, it’s important to first explain what rotary impingement is, and how it reduces tank downtime and eliminates contamination, as well as help companies realize sustainability goals via significant water savings.

Four Factors of Cleaning

To optimize a cleaning process, one must first understand the basics of cleaning. Herbert Sinner, a former chemical engineer for Henkel, first summarized the basic principles of cleaning in 1959. His summary, now referred to as the Sinner’s Circle, describes the four factors that can be manipulated in any cleaning scenario: temperature, chemical action, time and mechanical force.

When the effectiveness of any factor is reduced, it must be compensated with the increase of one or multiple other factors. Washing dishes is an effective example of how the four factors interact. Hot water (temperature) is going to remove stuck-on food better than cold. Adding soap (chemical action) makes the process even easier, and you can either soak a dish overnight (time) or scrub the dish clean (mechanical force).

When cleaning tanks, it is imperative to examine not only the effectiveness of the cleaning process but the efficiency as well, especially in such a competitive marketplace. Sinner’s Circle can be easily applied to tank cleaning as a way to compare the efficiency of processes. The most common tank cleaning processes are: boiling out, manual cleaning, wetting (static spray balls), rotary wetting (rotary spray balls) and rotary impingement cleaning.

Boiling out offers similar cleaning action at an even slower rate, with even more effluent and temperature, and no mechanical action. Boiling out is when a vessel is filled wash fluid and chemicals and the internal agitators of a tank are run. Often, the vessel is heated externally via steam jackets to maintain a given temperature.

Manual cleaning, on the other hand, offers a reasonable amount of mechanical force with minimal effluent but can result ineffective cleaning, based on who is doing the job at any given time. The main issue with manual cleaning is that it is time-consuming to scrub down a huge tank. Also with safety in mind, lower temperatures must be utilized to clean the tanks, increasing the time it takes to complete the job. There are numerous reasons why manual cleaning, particularly confined space entry, is considered unsafe.

Spray balls, also known as rotary wetting or wetting machines, are more easily understood as a “cascading method.” By applying massive amounts of cleaning solution to the tank interior, the residue eventually erodes off with the aid of chemicals, which requires significant amount of time and effluent consumption and a minimal reliance on temperature and mechanical force (the average force from a spray ball, rotary or static, is less than 0.25 pounds).  

As the second most common form of tank cleaning within the ethanol industry, spray balls are considered a less effective form of tank cleaning by many in this industry compared to rotary impingement. Because spray balls effectively wet a tank, but provide little to no impact, cleaning times are much longer and therefore much more water is used. An Iowa ethanol plant conducted a side by side comparison between a standard spray ball and a Gamajet E-Z8 rotary impingement cleaner. The spray balls were much more prone to clogging and required maintenance typically every 80 to100 hours of use. The rotary impingement machine resisted clogging and required preventative maintenance every 800 59 1000 hour of use, 90 percent less than the spray ball. The plant also reported significant water savings and overall faster cleaning times.

Understanding Rotary Impingement

Originally developed for the brewing industry, the crossover to ethanol has been an easy transition due to the similar nature of the tanks. Rotary impingement tank cleaning machines combine pressure and flow to create high impact cleaning jets.  Cleaning occurs at the point at which the concentrated stream impacts the surface. It is this impact and the resulting tangential force that radiates from that point and blasts contaminants from the surface, scouring the tank interior. In conjunction with this impact, these machines are engineered to rotate in a precise, repeatable and reliable, 360-degree pattern. This full-coverage, indexing pattern ensures the entire tank interior is cleaned, every time. This combination of impact in a controlled indexing manner results in an economic homerun, because impact is a one-time investment; chemicals, temperature and time are continual, never-ending expenditures.

Many ethanol plants run on a strict 24/7 schedule and tanks must stay in production, with the exception of scheduled cleanings. During those scheduled cleanings, work must be accomplished as quickly and effectively as possible, eliminating all sources of contamination while maintaining a production schedule. Tanks must be drained, effectively cleaned, and then begin creating the next batch of ethanol. Rotary impingement machines are perfect for this type of demanding schedule. They deliver the impact necessary for a tough job, and they do it quickly. Typically, customers who switched from using spray balls to rotary impingement machines report a 75 to 85 percent decrease in time spent cleaning. Additionally, they report a 70 to 80 percent decrease in chemical and water usage.

Fermentation and propagation tanks by nature are not only dirty, but have multiple obstructions, also known as shadow areas, that can easily hinder the cleaning process such as coils, agitators and baffles. A 50-foot tall, 20-foot wide fermentation tank would require two strategically located rotary impingement machines to ensure all areas are cleaned, including shadow areas. Typically the machines are run at 80 to 140 gallons a minute for a 12 to 18 minute cycle time.

When the demand for fuel ethanol began to grow in the 1990’s and the surge of plant construction occurred in the 2000’s, little thought was given to the type of machines used to clean tanks.  If you were to ask any plant manager during this time about their “tank nozzles”, you probably would have received a grumble and a few choice words.  With everything they had to deal with on a daily basis, the last thing they needed to worry about was continuous headaches and downtime because of tank nozzles. 

Choosing the Right Tool

As with most situations, using the right tool for job is the only way to work.  Unfortunately for many plants, off-the-shelf, commodity purchases of tank cleaning machines were specified at construction.  In fact, most of the tank nozzles specified into plants are 40-year-old technology designed for other applications.  The result was frustration caused by clogged tank cleaners, high levels of repair and cost, leading to downtime and inefficient production. When considering a purchase, plants should ask suppliers why their particular tank nozzle offering is best for the plant.  It sounds obvious, but the question is important.  There are machines available that were engineered specifically for the fermentation process.  These machines were designed to eliminate clogging from the inherently dirty CIP water, allowing large amounts of solids to pass through.  As such, these machines come equipped with sealed, protected gear trains that allow the wash solution pass around the gear (not through them), which also increases the lifetime of the machine.  

Any piece of machinery that gets heavy usage, quality construction is a top priority. Quality construction will help minimize maintenance costs and repairs; however, regular maintenance on the machines is necessary. For example, preventive maintenance after every 1000 hours of use is recommended for the Gamajet E-Z8.  When purchasing a rotary impingement machine, ask the supplier about service programs.  If you have to wait more than a week for parts or repairs, there are better options for you, such as 24-hour turnaround for parts and service. 

Next, consider the practical issues involved with tank cleaning.  Ask anyone who has climbed the icy steps to the top of 50-foot fermenter will tell you what it’s like to carry two 32 lb. tank cleaners along with them.  Large tank cleaners can be heavy and burdensome for workers to carry. There are rotary impingement machines for cleaning large tanks that are half the weight of standard models, yet pack the same impact.

Finally, the more impact you are able to deliver, the cleaner your tanks will be.  Even better, more impact will reduce the amount of time it requires to clean, thus reducing the amount of chemicals and water used and resulting in less bacteria and higher yields, which is what all ethanol plants are working towards.  Ask suppliers to provide exact impact data to prove how much impact they are able to deliver based on your pressure and flow conditions.  Compare these to other offerings and you will be surprised at the difference.

Both four-nozzle and two-nozzle options are available for rotary impingement machines. When deciding, just remember that two-nozzle machines deliver more impact and less leakage than their four nozzle brothers, and this is just because of the nature of the machine designs.

While these factors may seem obvious, the savings add up. Reducing the cleaning time per batch from 1.5 hours to 0.75 hours, increases throughput by 22 batches over a year’s time. Add that to an improvement in yield due to better hygiene, and it can add impressive gallons. And, eliminate the costs associated with infections. One plant estimates the cost in yields as much as $40,000 per infection.  

While proper tank cleaning and rotary impingement technology are not ordinarily considered “water cooler” topics, done properly, they can yield some pretty exciting results. Simply put, cleaner tanks produce higher yields and thus more ethanol. Higher yields and less downtime equals more profit and therefore happier ethanol companies. The right rotary impingement machine can enable significant results, directly impacting the bottom line.

Author: JW Resenhoeft
Senior Vice President of Sales
Gamajet, Alfa Laval Group