Temperatures are the key to heat load efficiency

By Tim Albrecht | June 11, 2018

Process heat began the Efficient Ethanol Production Seminar and it brought it to a close Monday afternoon. The panel titled “Towards the More Efficient Delivery of Common Process Heat Loads at Ethanol Plants” featured speakers Jim Fraser, senior industry sales manager for Hydro-Thermal Corp.; Hank Brittain, director of optimization and advanced control for OpX Control Inc.; and John Kwik, president of Fluid Quip Process Technologies LLC.

Brittain got things rolling by discussing fermentation temperature control and how to do that via model-based proportional-integral-derivative (PID) tuning.

You have to learn about the process and then educate the PID controller. Most people tend to tune by trial and error. It takes longer, it’s disruptive to the process and almost never achieves optimal results.

A good example of proper tuning is to put the loop in manual and step the output to the valve. If I increase the output to the valve and get more cooling water the temperature is going to go down. If decrease the signal to the valve and there will be less cooling, so the temperature will go up. That’s a cause and effect. First rule in process control is there must be a cause and effect. If there is a reproducible cause and effect, then it can be tuned.

The way I learned my control strategies is by observing good operators. I was able to develop strategies that did the same things they did via manual operation.

Fraser continued along the lines of Brittain’s temperature emphasis. “It’s all about temperature,” for Fraser. Everything Hydro-Thermal does is about delivering a processed fluid at a precise temperature. Temperature control creates the optimal temperatures for your product, he said.

The benefits of temperature control include precise temperature control, improved efficiency in distillation, we can reduce the amount of steam you use in the process, Fraser said. “The efficiency of the steam savings would pay for this project within a year.”

Temperature control also creates the ability to run longer on the beer mash exchangers before needing to CIP, that results in a reduction in chemical usage and the elimination of fouling, Fraser said.

Kwik switched gears to dryers, focusing on the fundamental understanding of what the dryer is supposed to be doing so “you can quickly identify problems and identify solutions,” he said.

When your product goes into the dryer its heated via some form of electricity, natural gas or some other form of energy. You’re increasing the dry bulb temperature and maintaining the wet bulb temperature. As you heat the dry air you actually create water in the combustion. The heat “flashes” the water off the surface of your product. The air is now humid and the dry air temperature is higher, while the wet bulb stayed the same, Kwik said.

Wet bulb controls relative humidity. It’s a ratio between the water in the air and the dry air. Depending on how much you’re drying the relative humidity is critical, Kwik said.

One problem area for dryers is air leakage, which can affect the relative humidity and final product moisture. You have to heat that leaked air to the operating temperature of the dryer. You may find that you can’t put enough Btus into your dryer to meet that operating temperature because you have so many air leaks, Kwik said. “Air leaks in a rotary dryer is the number one reason you have lack of production.”

Leaking air anywhere in the process, including the exit of the dryer, the cyclone or the flue gas recycle, does nothing for you and can leave problems such as clumping or balling, Kwik said.

The Efficient Ethanol Production Seminar is one of two June 10 preconference seminars at this year’s Fuel Ethanol Workshop and Expo. The other is the traditional Ethanol 101. The 2018 FEW is being held June 11 to 13 at the CenturyLink Center in Omaha.