Absolute Energy Tackles Evaporator Fouling

Proper treatment resolves multiple bottlenecks caused by mineral deposits.
By Jerry Tegels and Kevin Mundell | May 14, 2013

In northern Iowa, Absolute Energy LLC was experiencing heavy mineral fouling issues at its 115 MMgy ethanol plant. Fouling in the evaporators resulted in elevated steam pressures that inhibited the plant from increasing production rates. Sulfuric acid was being utilized to lower the pH in an attempt to alleviate the fouling. Chemical and maintenance costs, along with employee exposure to dangerous chemicals, were increased, while frequent cleaning in place (CIP) and hydro-blasting were required to keep the plant operating at less-than-desired production rates. 

Many industrial processes are prone to mineral fouling, the severity of which depends on water pH and process temperatures. Fouling creates insulating deposits on hot metal surfaces that reduce heat transfer efficiency. In ethanol plants, the sources of the problematic minerals, calcium and magnesium, are primarily incoming corn and water. Ethanol plants and distilleries around the world have always dealt with calcium oxalate deposits (commonly referred to as beerstone) given the nature of the processes they employ. 

Buckman Laboratories International Inc. was asked to analyze the mineral deposits at Absolute Energy and come up with a solution that would reduce or eliminate the need for sulfuric acid. Buckman performed qualitative and quantitative analyses on the deposits, ultimately determining that calcium oxalate was the main cause of the fouling, even though there were other minerals present, as well as organics.

As a chemical solutions company working on process and water treatment needs in multiple industries, Buckman has developed Bulab 8301, a special blend of polymers that reduces calcium oxalate deposition in process operations where high temperatures exist in conjunction with relatively higher pH ranges. At Absolute Energy, Bulab 8301 was fed into the thin stillage stream with the use of a programmable metering pump. The amount used needs to meet allowances set by the U.S. Food and Drug Adminstration that are intended to maintain the safety of animal feed and thus ultimately, the human food supply. Buckman uses an outside consultant to evaluate the suitability of ethanol process treatments for safe use. Based on this analysis and the FDA allowances, Bulab 8301 is used as an evaporator deposit control additive up to 20 parts per million, based on thin stillage flow to the evaporators.

Using the treatment, the plant was able to reduce sulfuric acid usage by 45 percent (0.75 truckloads per week), decrease CIP frequency, increase process pH, increase syrup solids, improve water balance, significantly decrease hydro-blasting down to none in the past 30 months, operate the beer column more consistently, thus reducing steam usage and base losses, decrease employee exposure to acid handling, reduce maintenance costs associated with acid pumps and piping and maintain lower sulfur levels in the distillers grains.

Buckman and Absolute Energy personnel have collaborated for more than four years in an effort to maximize the benefits to the process from the treatment. Over time, it has been discovered that starting with extremely clean metal surfaces gives the best results. Minimizing mineral fouling also reduces the amount of organic fouling as the organics need something to bind to in order to build up—an important key to reducing the need for hydroblasting. Absolute Energy also believes the corn oil centrifuges stay cleaner with the treatment system, although it doesn’t have a baseline to measure against since oil extraction was implemented after the antifouling measures were taken. With other plants making the same observation, Buckman is now seeking verification. Bulab 8301 has the potential to help with beerstone deposits in other areas of the process, such as the beer column top trays and beer mash exchangers. Data is currently being collected to verify the application economics.

The recent addition of phytase-based products to the ethanol process has somewhat masked beerstone concerns, as high phytase dosages have resulted in elevated levels of magnesium phosphate, which precipitates onto hot metal surfaces. This fouling is more significant than typical beerstone levels as it builds deposits quickly, resulting in increased evaporator pressures that many times require ethanol operators to reduce operating rates and increase hydroblasting and CIP frequency. The challenge for the ethanol plant manager is to minimize overall mineral deposits as much as possible by reducing phytase addition and then treating areas of deposition with the correct chemical application. Understanding which mineral deposition is occuring is crucial. Bulab 8301 targets beerstone deposition, so plants that are challenged with both calcium oxalate and magnesium phosphate fouling benefit from combination products.

Mineral depositions create many challenges within the ethanol plant and producers should choose their chemical applications carefully to ensure they are giving their process the best chance to produce every gallon as economically as possible.
Authors: Jerry Tegels
District Manager, Buckman

Kevin Mundell
Ethanol Manager, Buckman


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Evaporated Pressure Graphs

These graphs give a historical snapshot from the distributed control system of the Absolute Energy plant. In each, the top line represents the incoming steam pressure to the first effect evaporator that fluctuates with the steam demand for distillation and is directly related to production levels. The bottom line represents the steam pressure to the second effect, which increases if fouling occurs in the evaporator tubes. If the differential pressure between the effects (the delta-P) is maintained or decreased when incoming pressures increase, it's a good indication that fouling is not occurring. If the delta-P increases, causing the bottom line to move farther from the top line, it’s an indication that fouling is occurring. The reduced heat exchange efficiency will cost the ethanol producer more in fuel costs as more steam is required. Both graphs show that a delta-P was maintained, with a few exceptions caused by events such as a power outage or a sensor freeze-up during cold weather.