The overarching goal of any manufacturer is to keep its plant running smoothly while making as much profit as possible. As a dryer manufacturer, Bühler is often asked to help customers improve their dryers and help them improve their operations. Dryer optimization can include adjustments to process conditions such as retention time and fan speeds, production parameters such as feed rate and product bottom depth, or mechanical adjustments to dampers or internal plates. These changes focus on improving product quality and reducing dryer energy consumption. However, in many cases, shortly after the Bühler technician leaves, the equipment reverts to its previous operating conditions and is poorly used again. In order to maintain optimal dryer performance in the long run, managers need to ensure that their employees have the appropriate knowledge, resources, and motivation to improve and maintain their drying equipment.
The importance of improvement
Dryers are typically the most energy-intensive equipment in a process line, and relatively small increases in efficiency can result in large payoffs. To reinforce the importance of dryer optimization, consider the following example of pet food dehydrators. Dryer power usage and configurations vary widely across industries, but pet food dryers provide a good basic example. The example below shows how quickly an unoptimized dryer can accumulate additional costs. This calculation was made for a hypothetical pet food company with the following basic criteria which are typical of what is to be seen in the industry. Additional specifications for this example can be found in Appendix A.
* Feed production rate 12500 kg/hr
* Drying target with moisture from 24% to 9% dry weight
As explained above, energy inefficiencies in dryers can build up quickly and lead to significant operating expenses throughout the year. Energy evaluations of two-track pet food dehydrators with production rates greater than 12,000 lb/hr (about 5,800 kg/hr) over the past several years have shown annual savings potential of more than $50,000. These savings come from a combination of mechanical improvements and process changes that are directly related to the use of gas or steam in the dryer. Losses in operating efficiency – up to 25% – are common in older drying equipment. These losses are compounded by the loss of additional revenue from operating a dryer below the maximum production rate. Capacity reductions can easily run into hundreds of thousands of dollars over the course of a year. If there is so much potential savings, why are unrefined dryers so popular?
Key criteria for sustainability improvement
Practical Knowledge Advocacy
The first major component of maintaining an improved dryer is having the knowledge to make changes to the process when needed. Production lines are seldom in a completely stationary state, and changes must be made frequently to take into account changes in the rate of production or the quality of the incoming product. In some cases, significantly different products may be processed on the same device and settings need to be changed to adjust for differences. The dryer is usually set to the lowest common denominator (whichever setting will successfully operate each product or mod without further changes). Often this is because operators or individuals do not feel comfortable enough with the equipment to risk making changes. Training in dryer basics and operation can help operators better understand equipment and allow them to feel more comfortable making more frequent changes to help improve efficiency. Dryer basics include things like understanding the properties of the air, discussing how moisture evaporates from a product, and reviewing interior dryer layouts. To maintain consistency between operators or shifts, many factories find it useful to create recipes or specification sheets for optimal settings for different recipes or rates. Almost any manufacturer will already have recipes for process conditions such as temperature or retention times, but very few also include changes to calculate production rates, damper modes, or product dispenser settings.
Ensure that employees have access to resources
The second most important criteria for maintaining a dryer improvement is ensuring that employees have the resources to implement the changes, such as time and money. Factory personnel are usually familiar with the equipment. They operate it every day and are familiar with most of its aspects, especially the mechanical ones. They know which components are annoying and most likely to break or malfunction. In many facilities, operators are aware of the issues that reduce dryer effectiveness, but they do not have the resources to properly maintain equipment. The most common is a lack of time to devote to performing repairs, inspections or preventative maintenance tasks. Many plants try to reduce downtime, which means that process lines only stop long enough for a quick clean-up between production runs. Equipment inspections for missing interior panels, broken hinges, or damaged base plates are unlikely unless specified by management.
Reward process efficiency and results
This leads to the last point, which is that employees need motivation to improve the dryer. Plant operators are generally tasked with monitoring and operating several pieces of equipment in a processing line. However, there are rarely incentives for employees to take the initiative to constantly ensure that the dryer is operating as efficiently as possible. The ‘success’ of a transformation is often measured on the basis of the productivity of the salable product, and efficiency is seldom considered. Factories are commonly seen using natural gas stoves with no way to measure a dryer’s gas consumption at all. If employees are rated on the basis of efficiency (or are also rewarded for high enough efficiency scores), they are more likely to go the extra mile to adjust and check equipment to ensure it is operating as efficiently as possible. This will allow the dryer to produce a more consistent product, use less energy, and reduce downtime due to unexpected or long-term issues.
Operating production lines is expensive, and a dryer is usually the most expensive equipment to run. Even small improvements in efficiency can lead to big savings. In order to realize the savings potential, managers must ensure that operators and plant personnel have the knowledge to feel comfortable making process changes, the resources to properly repair damaged equipment, and the incentive to take the time to check and inspect the equipment to keep it operating as efficiently as possible in the long run. . A single individual with in-depth knowledge of the drying process can be effective in achieving improved and sustainable performance of the dryer. However, support from the rest of the organization is required for the facility to operate at its maximum potential.
Al Worthington is a Process Engineer, Buhler Group. It can be accessed at [email protected]
The pet food example shows how quickly an unoptimized dryer can accrue additional costs. The calculations for an example of a pet food company were made by the following criteria:
* Feed rate 12500 kg/h
* Target end product moisture is 9% dry weight
*Estimated energy cost 0.0171 USD/kWh
* Production time 24 hours / 345 days
dryer 1 (optimal)
* 12500kg/h feed production rate at 24% moisture
* Uniform moisture discharge of +/- 1% body weight
* The supply air for thermal areas is exhaust air from the coolant at 60°C
* Exhaust air humidity 0.1 kg water / kg dry air
* Retention time on family 1 and 2 of 8 and 12 minutes, respectively, at 150 °C
Desiccant 2 (not improved):
*12500kg/h feed yield at 27% dry weight (3% higher than dryer 1, could be caused by extruder issues)
* Regular discharge humidity of +/- 3% body weight, resulting in a target discharge humidity of ~7% (usually caused by poor airflow uniformity or incorrect bed depth settings)
*Feed air is ambient air at 20°C
* Exhaust air moisture 0.76 kg water / kg dry air (35% excess, likely due to incorrect damper settings)
*Holding time in Beds 1 and 2 of 6 and 9 minutes respectively at 220°C (note that this temperature is useless to run on a real pet food dehydrator; this temperature is due to the energy usage that would be required to dry by default this amount of The product is within the above parameters.In a real system, the production rate must be reduced to compensate.)