Available reports state that thermal dehydration, or drying, accounts for as much as 6% of the world consumption of energy. In the United States, we are literally spoilt with the relatively low cost of energy. Even the oil crisis of the early '70s did little to dampen the rampant and frequently inefficient use of energy for dehydrating systems.
It is my experience that in the United States, little evaluation of the operating or running costs is performed or accounted for in drying system evaluations. This trend has produced an era of inefficient, expensive-to-run dryers. Shockingly, this mindset of inefficient design to reduce capital expenditure is still prevalent.
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. But, 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, to just operate the 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% 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 preventative maintenance and stock strategic spares. This discussion holds true for both new and existing installations.
Energy CostsIn 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.