As a chemical engineering graduate from the University of Oklahoma, John Robinson worked in several different forestry, paper and chemical companies in his long career: International Paper Co. and Dow Chemical Co. to name a few majors. Decades spent working with forest products, timber and plywood provided Robinson with a vast amount of knowledge and experience, which he ironically used to develop a simple moisture control system from first principles. These first principles are irreducible, elemental and fundamental to a field, whether its engineering, physics or chemistry—and sometimes can be overlooked. In the late 1970s, using the age-old engineering term Delta T, where T stands for temperature and Delta connotes a difference, Robinson derived a control model that relates moisture to temperature drop. "It's so simple that when we tell people about it, many say, 'You can't do that,'" Robinson says.

The idea was patented in the mid-80s and a couple of years later Robinson formed his own company, Drying Technology Inc., based on these first principles and Robinson's application of them. "The system was first applied in making plywood, which uses a veneer—the thin wood that goes into plywood," he tells EPM. Once Robinson realized that his system worked on the conveyer dryer, he applied the model to other dryers and found out that it was universally applicable. Five dryers work particularly well with what Robinson calls the Delta T Moisture Control System: conveyer, spray, flash, fluidized bed and, most common in the ethanol industry for distillers grains drying, rotary and ring. "I applied it in the plywood industry and we actually became the industry standard," he says, thanks in large part to Georgia-Pacific, which bought 30 of his systems in one shot. "That kind of gave us a good start." A good start was all Robinson needed.


Delta T Moisture Control System

After saturating the plywood industry with his company's moisture controls, he proceeded to apply them to batch systems for drying lumber and then in the carpet and textile industries. "Then we got into the food industry servicing big-name companies like Kraft—Maxwell House instant coffee, which uses spray dryers," Robinson says. "Then, after that, we turned to the panel board industry for applications drying fiber for medium density fiberboard, which is used in furniture and uses flash dryers for drying the pulp. And then we got into pet food." It appears it was only a matter of time before Robinson set his sights on the ethanol industry. In fact, he's already servicing big names in an industry that's closely related to the ethanol industry: corn wet milling. About 1½ years ago, Robinson sold his dryer control system to a company called Roquette, for use in a ring dryer for gluten. The French-owned company now has plans to incorporate four more of Robinson's moisture control systems. Another well-known wet-miller in the ethanol industry has recently purchased a Delta T to utilize the simple, highly effective moisture control method to gain tighter control, increase profits, reduce energy consumption and produce a more consistently dried product. Robinson requested that the name of the company remain confidential until the deal is finalized.

The System
Robinson's Delta T system measures moisture with two temperature sensors and a mathematical model. Because it's based on fundamental principals it's universally applicable. "I put some stuff together—a couple of differential equations—and solved them, and the mathematical analysis produced this simple model that relates moisture to the Delta T, the temperature drop, minus a term for production rate," Robinson says. "It has constants and exponents in it, and what I immediately saw was a convenient, variable temperature drop that could be easily obtained using ordinary temperature sensors. Most importantly, it enabled a moisture sensor for the first time to be installed inside the harsh environment of a dryer." Surely if he could do it others could too—right? Not according to Robinson.

Even though the patents have expired and now reside in the public domain, there's proprietary information at play in the Delta T system. "There are a lot of theoretical things that have to be helped along," he says. "We've got more than 20 years experience with it. Most people are building moisture sensors and must install them on the end of the dryer—that's too far away."

He details at least three major deficiencies with current moisture control systems utilized in the U.S. ethanol industry: The use of exhaust temperature as a substitute for the moisture content of the exiting product; the lack of moisture sensors inside the dryer to effectively reduce dead time (the time required to detect a "disturbance" with inbound feed) and the lack of a general moisture control model based on first principles.

A majority of distillers dried grains dryers use plain exhaust temperature. There is an evident correlation between exhaust temperature and moisture if there are no disturbances—changes in the water rate or the evaporative load—but "we live in the real world and that never happens," Robinson says. "There are always changes in either the percent moisture of the feed coming in or maybe changes in production rate. The overall water load that has to be evaporated varies and that distorts the correlation." Once the correlation is distorted, another set point is needed to maintain target moisture.

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