Drying technology is one of the largest consumers of production-line energy for any industry, including food, feed, fibers and polymers. An industrial dryer reduces moisture content using thermal energy to produce specific product attributes. It can be a major investment for any company; however, the major cost is not necessarily from the initial investment, which includes design and assembly. Instead, it usually is found in the long-term, daily operation of the dryer. This is where the ability to control the drying process is important to consistently optimize energy usage and achieve the desired quality needed every time. Even over a short period of time, the value of savings realized by energy efficiency, increased throughput and higher quality product can easily outweigh the investment cost for the dryer itself.
Manual control is the most common way to adjust production and power during the drying process, but the operator selections can be limited. Also, the choices made often are based on expertise developed through years of experience and local knowledge. With changing product characteristics and multiple variables, being able to adjust the drying conditions is not always straightforward.
By contrast, using advanced controls, an operator has many opportunities to enhance a dryer’s performance with smart systems that are algorithm based for repeatability and high quality. Following are 10 reasons to add an advanced control system for your drying process.
1. Monitor Evaporation
Evaporation control is a temperature-control method that uses the weighted mean temperature to reduce the variability of the final product-moisture level. In the evaporation-control mode, dryer controls automatically adjust the drying-air temperature to compensate for changing product conditions entering the dryer. The result is a reduction in time-based variation in the discharge product-moisture content level.
For example, a fiber dryer responds to differences in the performance of dewatering compression rolls upstream of the dryer. If the application is food or feed, the dryer can react to differences in inlet moisture caused by changes in raw feed. In addition, vegetable dryers have to adapt to short-term upsets as materials are supplied from different growers. There is a more gradual change in product-moisture levels as vegetables are removed from storage during the process season.
2. Control Moisture Levels
Moisture control is the automatic adjustment of each zone’s temperature setpoint to achieve a specific discharge product-moisture setpoint, based upon actual discharge-moisture readings. The reference moisture reading may be the result of a quality control sample or a reading from a product-moisture sensor. This control affects both product color and quality. For example, moisture feedback lets you precisely control the final drying temperatures, reducing them to prevent overdrying and discoloration.
3. Maintain Setpoints for Humidity
A humidity-control system is designed to maintain process air at the desired humidity level. Simple humidity can be directly measured in the drying environment. The control function is programmed within the PLC, and positioning motors are used to modulate the exhaust dampers to control humidity and maintain the required setpoint. Therefore, a dryer can react to changes in incoming humidity load and adjust to internal changes in dryer feed (higher or lower moisture). It also can adjust to external factors such as ambient humidity, where moisture-critical products require adjustments for even the daily changes in ambient conditions.
4. Achieve Yield Improvements
A yield improvement can be estimated by collecting moisture data and calculating the average and standard deviation of the data. An advanced control system under normal conditions can reduce the standard deviation by as much as 50 percent compared to manual control. This allows the calculation of a new target moisture level closer to the maximum moisture constraint while still producing product under the specification.
For pet-food applications, yield improvements can be realized for applications involving bags. In these cases, the reduced moisture deviations will allow tighter specifications for bag overfilling and thereby an increase in the number of bags filled (yield) for a given amount of finished product.
5. Increase Capacity
Control of the drying process can boost capacity by reducing the evaporation load at the current production rate, reducing process upsets and increasing product yield. The benefits of increasing capacity can be derived in two ways:
• The dryer loading can be increased to raise the production rate.
• Plant capacity will increase while using the existing equipment.
Typical capacity increases using process controls are 5 to 10 percent.
6. Monitor Energy Use
Energy performance is a combination of actual and calculated data that shows the operating efficiency of the dryer. An energy-monitoring screen allows operators to verify that the dryer is operating at its peak efficiency. A warning alarm will notify operators when the efficiency goes outside of the target ranges.
7. Efficiently Consume Raw Materials
Where materials are being processed before the drying phase, the increased amount of product that meets specification means more raw materials are converted into finished product. Product that does not meet specifications may be subject to penalties, reworked or scrapped.
8. Track Product
An advanced control system can track the presence of your product and its location in the dryer. It also can react to changing process conditions, sensing and adapting to changes in throughput because of upstream disturbances.
9. Determine Depth
The tracking works in conjunction with a product-depth sensor located at the feed end of the dryer, between the feeder and the inlet to the initial drying zone. The product-depth reading is displayed on the operator-interface screen to help the operator measure, for instance, a typical pressure drop in product or recovered starch by reacting to changes in upstream extruders or filter settings. Having a visual display of the product in the dryer also allows for faster product changeover.
10. Efficient Troubleshooting
Enhanced data analysis helps quality-assurance personnel, engineers and operations managers evaluate process production and performance more easily. This can result in a benefit that could be realized at 10 percent of personnel cost. Combined with the fact that returned product is costly to the producer and normally cannot be reprocessed, there also is a reduced risk of lost sales caused by off-specification product.
In conclusion, an advanced control system gives a processor more options to efficiently manage production. It also can help the operator troubleshoot the drying process with reduced downtime. Consider the value of an advanced control system. Partner with a manufacturing company that can help you realize long-term savings and efficiency.