In last month's column, I began to look at ways to reduce energy costs by minimizing the system losses. Suggested methods include optimizing process performance, using a heat recuperation system or employing a direct heating approach, among others.
These same concepts hold true for other processes - to the dryer's benefit. For example, if one has an oven that generates combustible gases, using the oven gas as the dryer's heat source, be it direct or indirect, would offer an economic advantage. Or, by recovering the stack losses from other heat-generating equipment such as high temperature calciners, smelters or reactors, this energy could be used directly or through recuperating systems.
The more prevalent heat losses associated with dryers are not those that occur by definition (stack losses, for example) but those that occur due to poor design or lack of maintenance. Hot spots, missing insulation (or worse yet, no insulation), process leaks (ingressive and egressive) and poor system setup and maintenance account for the more severe efficiency losses. For example, burner setups, damper positions, feed rates, feed moistures, etc., frequently are altered over time. As one is modified due to the effect of another, the problem compounds. Remediating these types of losses can easily increase operational efficiencies with a relatively low investment.
Designing the system to optimize the energy requirements (reducing the safety margins) and sizing the associated equipment (fans, mixers, etc.) appropriately also will reduce operating costs. In many instances in my international experience, crucial decisions about how to proceed on a project were made based on the expected full-load condition. Using a 250 hp motor instead of a 400 hp motor clearly reduced the startup cost and full load energy draw. One should carefully consider the ramifications of oversizing devices and utilities "just in case."
Operating Labor CostsOne of the most beneficial projects I have managed replaced a series of rotating tray dryers with flash dryers for mineral concentrates. The new system reduced the labor requirements from around 70 per shift to two per shift, yielding obvious labor savings. For this project, technology played a significant role in labor reduction, but automation can reduce labor intensity and improve control just as astoundingly.
Training and implementation of operating procedures also will provide a disparate improvement when compared against the effort. Education, operator quality and operating environment will affect plant operation and potentially reduce labor requirements. These savings are borne out of the fact that operators will spend more time operating and improving and less time waiting, maintaining and cleaning up. Productivity will be enhanced significantly.
MaintenanceIt has been proven the world over that regular preventative maintenance and system tuning increases reliability, reduces downtime and improves productivity. Components that wear or are central to operations should be checked and maintained routinely. The cost of production downtime, together with the labor costs for maintenance to work on emergency repairs and wait for parts, is a significant operating cost.
Systems should be inspected regularly, and loss areas should be repaired or improved. In addition, the system should be audited routinely to compare current parameters with the initial setup parameters. Improvements should be logged and implemented.
Reducing the maintenance costs and investing in a training program will increase your yield and enhance the profitability of the operation. After the capital outlay has long been forgotten, running costs will continue to endure. Careful and honest evaluation will reduce these, potentially resulting in huge savings over the life of a machine.