When comparing bids, we all know (or need to stop fooling ourselves if we deny it) that initial capital cost is the primary consideration before placing a purchase order. Certainly, there are other factors, like brand loyalty. But, when comparing two systems that are identical in every aspect except that one has insulated exhaust ducting as well as recuperating systems for preheating the combustion air and recirculating a percentage of the air, how many of you would spend an extra $10,000 -- or even $10 -- if these additions have no effect on the quality of the final product? Most would not consider including this equipment a capital-saving decision.
Well, it is. The running costs may be an order of magnitude higher. It may cost you more than the total additional investment for the energy-efficient system in one year, or less, just to operate the less efficient system.
It is time that we start looking at operating costs seriously. Not only does energy cost, but so does operating labor, maintenance and downtime. These are real costs that reduce the profitability of any production. They impact the bottom line. Take a look at some of the basic issues that can improve efficiency and reduce running costs.
In some instances, improving existing system operating efficiencies can have a very short return on investment period. If you could save 50 percent of your annual operating costs on energy alone, how much would that total? Would it not make sense to invest that now and realize the savings for the next 10 or more years?
Operating costs can be grouped in three areas: energy, operation and maintenance. To reduce energy costs, one must minimize the system losses. To reduce operating costs, one must reduce the operation’s labor intensity. And, to reduce maintenance costs (including downtime costs), one must reduce the potential for downtime, perform regular preventive maintenance and stock strategic spares. This discussion holds true for both new and existing installations.
Energy CostsIn a drying system, the bulk of the energy is used in the form of heat. Other energy sources such as fan motors, drive motors and compressed air add to the overall running costs. During drying, heat is intentionally lost through the stack -- referred to as stack or exhaust losses. This is a necessary requirement for the process to work. These losses can be minimized by:
- Optimizing the process performance.
- Using this gas directly in a recirculation system.
- Using a heat-recuperating system to capture some of the residual energy to preheat or heat the process gas.
- Using the exhaust gases for some other less sensitive application.
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 included replacing 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. Productivity will be enhanced significantly.
MaintenanceIt has been proven the world over that regular preventive 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.
After the capital outlay has long been forgotten, running costs will continue to endure.