Ethanol is reaching new heights in popularity as an alternative energy source. Gasoline in most states contains 10% ethanol, and an increasing number of “dual fuel” vehicles have engines that can accommodate 85% ethanol, which is known as E85. E85 is not yet widely distributed but there are a growing number of fueling stations that carry it, especially in the Midwest. The ethanol industry started in the Midwest becauseit’s a corn-based product. However, it’s now being made throughout the country, with other feedstocks being used in its manufacture.
As the interest in ethanol has grown, more than 100 new plants have been built to increase its production. Many of these plants use a dry milling process to produce between 40 million and 100 million gallons of ethanol per year. These plants have been built on fast timelines, and the design engineers haven't always optimized the control systems. As a result, new ethanol plants can improve production reliability, output and quality by reviewing and improving their controls.
In one example, a 50 million gallon-per-year plant in western Nebraska was using a tank and pump system to mix and transfer water and urea. The original system used an off/on switch and a reset button located near the tank and pump. This required the operator to shut off the pump when the mixture was transferred out of the tank. The pump would occasionally be allowed to cavitate and run dry, which resulted in seal failures.
The problem was solved by adding a PumpSmart controller from ITT Goulds Pumps (www.pumpsmart.com). The operator starts the process by filling a 350-gallon tank with water and starting the pump, which simply recirculates the water in the tank. The PumpSmart unit incorporates a flow controller that maintains a 100 gpm flow rate. Because the pump takes suction from the bottom of the tank and returns the flow to the top of the tank, a small change in speed would result in a substantial flow change, so by slowing the PID loop, the unit locks into a stable flow rate.
At this point, the operator dumps bags of urea into the tank and lets it mix until it dissolves. The operator then opens the valve to transfer the mixture to a process tank. The controller speeds up the pump to maintain the 100 gpm flow rate as the head increases.
The operator is now able to pump the tank down without running dry because the controller includes torque-based dry-run protection. Instead of running it dry, the controller shuts off the pump when the water and urea mixture has been transferred.
The controller unit is located in a control room. Because it requires a manual reset after shutting down on a dry run alarm, the plant wired a remote reset button at the pump and tank location so the operator can simply hit the button and restart the pump for the next batch.