Process Optimization for New and Existing Dryers
Here is an overview of key issues associated with maximizing dryer performance and energy efficiency
While our industry has been fortunate to have low energy prices over the last couple of years, the importance of effective and efficient drying of linens has never been more important for the following reasons:
- Full drying of classifications is making up a larger share of the healthcare (80%) hospitability (55%) and F&B (40%) market segments. This trend looks to continue as synthetics enter the marketplace, allowing one to have a less wrinkled finish when handled properly in the drying process.
- Synthetics are making up a larger share of the marketplace. These products normally carry less water after extraction, lowering energy costs and speeding dry times. They also usually carry very specific tolerances to heat that will greatly reduce the linen life cycle, if not followed specifically to the manufacturer’s recommendations.
- Low-energy costs are no reason to avoid process optimization. Every dollar contributes to the bottom line and insulates end users from eventual energy market inflation.
KEY MECHANICAL FEATURES
Let’s consider a couple of general items outside of the dryer that laundry operators must consider— whether one’s looking at a new or existing dryer.
Proper ductwork for both exhaust and intake. This probably remains the No. 1 reason for inhibited dryer performance, and increased energy usage. When the ductwork is improperly sized or installed, it can lead to linen damage and unsafe operating conditions. For about $30, one can purchase a manometer, make a sample port in their exhaust ductwork and measure backpressure. If it is .5 inches of water column or less, all is good in the world. If it is over 1.5 inches, the dryer should be shut off as you are wasting time, money and linen.
While a separate article can be written on proper ductwork, one can seek out a host of resources from the manufacturer of the dryer, as well as local ductwork contractors to fi gure out the weaknesses with one’s exhaust and intake system. For those of you questioning the benefi ts of fresh air intakes, just take note how your doors close automatically as the facility starts to keep garage doors closed in the fall. Outside air is typically less humid (assuming your operating space is not conditioned), which results in less moisture being introduced into the dryers. Proper air volume, movement and quality directly impact the performance. (See figure 1 on page 48.)
IT’S ALL ABOUT THE AIR!
Proper gas sizing. While most dryers built today won’t operate once gas pressure falls below a certain point, older dryers may continue to operate given the crude nature of their design, resulting in poorer performance. Dryers have an optimum gas pressure... Achieve it! If your owner’s manual doesn’t have this information, the plate on the dryer may give the output capability of the equipment. From there, the manufacturer of the dryer and your local contractors should be able to assist you in ensuring you have or can get proper gas volume to the dryers.
Leaving aside these general items, most of the practices necessary to keep a dryer operating efficiently can be found in one’s OEM manual. Let’s look at some major culprits.
Remember it’s all about the air!
For an existing dryer with some years of operation on it, the major culprits are:
- INFUSION OF PLANT/AMBIENT AIR INTO THE DRYER BASKET: Whether due to a poor door design, leaks elsewhere, or just substandard tolerances in manufacturing, all adversely impact dry times and energy consumption. Air that enters the drying chamber without going through the burner only hinders the process.
With today’s dryers, one should see very small tolerances between the basket and outer cylinder, almost airtight door designs, and a seal scientifically placed to ensure all air going through the goods has gone through the combustion chamber.
- AIRFLOW BY ART NOT SCIENCE: Dryers built 15 years ago or so had airflow designs that an engineer or maybe a welder on the floor thought would work. This hypothesis was anything but scientific or proven. Today’s use of modern diagnostics and computer- aided modeling tools (like computational fluid dynamics) allow for airflow designs to be scientific and extremely effective. (Figure 2).
- COMBUSTION BLOWERS/FILTERS: These features will be found on most dryers 10 years and older. A dirty filter will lead to a poor air/gas mixture, poor flame quality, and may even damage the burner or lead to a dryer fire (if clogged completely). Many of the burners on dryers built in recent years do not require this filter, thus removing the PM obligation. (Figure 3).
- SEALS: All dryers have some form or type of wearable seal/s in them. Due to improved manufacturing tolerances, more recent designs will have seals that are smaller, easier to replace and more durable. (Figure 4).
- BLOWER WHEELS: The blower wheels move the air, which dries the linens. When the dryer was delivered to the plant, this wheel was clean and precisely balanced; and if the wheel is belt driven, the belts were brand new and properly tightened on the wheel to allow the motor to spin it at maximum rpm. As nuts, bolts, lint, and dirt hit and coat these wheels, they become unbalanced. As the belts become old and loose, the rpm slows down. So blower wheels need to be kept clean, and belts tightened or replaced. If excessive vibration occurs even after the blower wheel is cleaned, it may be damaged. Replacement will then need to be considered as this vibration can damage other components. This problem has been improved over the years through the use of swing out blowers, which allow for easy maintenance access, or through the use of lint shedding wheels that do not accumulate debris by the nature of their design. (Figure 5).
- DRYER PANELS: They are perforated as it’s all about the air. Techniques for keeping dryer cylinders clean continue to evolve. From Teflon to ceramics, there are a host of coatings that are effective in keeping cylinders clean. Unfortunately, they’re all coatings that wear over time. So the more particulates, zippers, snaps, and such one has on the items they’re drying, the faster these coatings will wear out. Cleaning the cylinders has evolved as well. With the same warning, never use excessive heat on the cylinder or scrape/ brush it with a material harder than the cylinder metal that may scratch or damage the cylinder. The most recent removal system utilizes dry particles instead of sand for blasting the material off the cylinders. While costly, it’s fast and effective. (Figure 6).
- AIR FILTERING/LINT COLLECTION: In the past, this was mostly a post-equipment item, mainly concerned with the quality and cleanliness of air being sent out to one’s neighborhood. However, they need to be checked regularly, ensuring they work properly so as to not inhibit airflow. Today, one will find such systems built into the dryer as an integral and critical part of the effective operation and performance of that dryer. These systems not only help to keep the blower wheel clean and free from damage, but today these internal lint systems are part and parcel of the critical airflow design of a dryer, playing a major part in the performance of such.
WHEN BLUE IS THE RIGHT COLOR
Eight items out of nine that we’ve just covered have something to do with how the air is handled in one’s dryers... so what’s left? Burners, control technology and operating practices.
- BURNERS: From boiler burners to linear burners, all have the same basic guideline: a flame color of blue is good, and a flame color of yellow is bad. Whether a burner is clogged with lint, or needs tuning or repair, flame color should be checked daily. For efficiency and production, an up-to-date modulating burner, teamed with a proper control technology and operating practices will lead one down the road of dryer efficiency.
- CONTROLS: The critical item of a dryer’s performance is how it controls the burner in relation to the specifi c formula and classifi cations of goods to be dried. Today’s dryers allow goods to have the least amount of heat placed on them when they are at their driest. This minimizes linen damage and shrinkage. Dryer formulas can be set up to the exact parameters called for by the manufacturer of a specifi c product. This represents an improvement over the “too little or too much heat” operation of past low- and high-fi re-only dryer technology. (Figures 7 and 8).
Lastly, the simple operating practice of loading a dryer to its stated capacity will affect e fficiency and production (See Graph below) With the changes of linen makeup and the densities of certain fabrics compared to others and related issues, this involves working with one’s dryer somewhat to see what load weight for specific classifications is most effective. (Figure 9).
The drying process is more dynamic and scientific than this condensed article is able to cover. We recommend that end users work closely with the original equipment manufacturer to learn as much as they can about the science behind drying, as they evaluate solutions that must not only maximize, but also provide reliable and durable service. Staying on top of these items will lead to effective and efficient dryer operation.