- Material to be Heated
- Environment in Which Heating Occurs
- Heatup Times Required
- Desired Level of Energy Efficiency
- Material-Handling Considerations
- Calculate Costs
Throughout the process industries, manufacturers traditionally have utilized a range of methods to heat their drums and totes, including band heaters, immersion heaters, steam jackets and homemade in-plant hot rooms. Over the years, operators in the chemical, food and pharmaceutical industries have turned to drum-warming ovens as a safe, cost-effective way to heat 55-gal drums.
But, before a manufacturer commits to one specific technology, it is important to understand the considerations that should go into selecting the proper heating technology for their specific needs. Six important factors must be considered prior to selecting a heating method, starting with the material that is being heated.
When heating drums and totes, it is critical to fully understand all of the characteristics of the material to be heated. Operators should consider the following questions:
- Is the material flammable?
- Is the material caustic or corrosive?
- What happens when the material is heated?
- Does the material have an autoignition temperature?
- Will excessive heat burn or degrade the material?
- Will heating the material produce a dangerous or foul fume or vapor?
Flammable Materials. If the material is flammable, specific equipment must be used. For instance, in an oven built to National Fire Protection Association standards (called an NFPA Class A oven), a hazardous-duty band heater or water bath may be necessary.
Caustic and Corrosive Materials. Likewise, caustic or corrosive materials may require special coatings or stainless steel construction.
Materials Expand When Heated. If the materials expand when heated, spill containment may be needed, or the bungs on the drum may need to be adjustable so operators can loosen the bungs to relieve pressure caused by heating.
Materials with an Autoignition Temperature. The autoignition temperature of a material is the lowest temperature at which it can spontaneously ignite in a normal atmosphere without an external source of ignition such as a flame or spark. The temperature at which a chemical will ignite decreases as the pressure or oxygen concentration increases. It is critical that operators take the proper steps to ensure the material being heated never reaches the autoignition temperature.
Materials that Can Burn, Degrade or Create Fumes and Vapors. Precise temperature control and temperature uniformity are critical requirements for ensuring excessive heat does not burn or degrade the material to be heated. Some fragile materials such as honey will burn when subjected to excessive heat. Band heaters, which concentrate intense heat on a small section of the drum, should not be used. Likewise, if heating the material will create a dangerous fume or vapor, operators must take steps to ensure the proper exhaust.
Environment encompasses the area where the drum heating will take place. When considering environment, all hazards and classifications in the area must be known. If it is an explosionproof area, the heater must be designed properly for the hazard classification. This may require the use of steam heat, hazardous-duty-rated heaters and NEMA 7/9 controls.
Within the established environment, operators must consider whether or not the heat created by the heating of drums will impact the ambient temperature. To avoid negatively affecting the ambient conditions, the process heating equipment can be designed to prevent heat from escaping during the heating process. For instance, insulated ovens with door switches can be used to prevent heat from being blown out of the oven when the doors open, or even exhausting the oven prior to the doors being opened. Special construction and controls are necessary for use in wet areas such as outdoor applications and washdown areas.
A third factor to consider when heating a drum is the heatup time. How quickly a drum must melt or reach a certain temperature will dictate the heating method to be used. Certain methods produce faster heatup times than others. For example, a prefabricated drum oven generally will melt a drum faster than a band heater.
Factors to consider when predicting heatup times include the material’s starting temperature, its melting point, specific heat, heat of fusion and the maximum temperature to which the material can be exposed. A reputable supplier of drum heating equipment will be able to estimate heatup times and may even warranty its equipment to ensure that it meets the specified heatup times.
As stricter legislation has dictated the implementation of more environmentally friendly equipment worldwide, energy efficiency must be a top consideration for operators. Certain methods of drum heating are more energy efficient than others. One example would be a compact, fully insulated drum oven, which is much more energy efficient than a large homemade, in-plant hot room. Drum ovens are compact and only heat the space directly around the drum.
By comparison, some processing plants build dedicated hot rooms to heat drums. Sizes can vary greatly, but traditionally, these rooms are large enough for a forklift to maneuver in and out of with ease. Some hot rooms can hold as many as 100 pallets in them. While capable of heating a large number of drums, hot rooms typically are inefficient from an energy perspective due to their tall ceilings and large surface areas. The entire room must remain heated even if the space is partially full. In addition, many in-plant hot rooms are poorly insulated. Temperatures fluctuate greatly due to their size and lack of adequate airflow. Doors in these hot rooms may be left open for long periods as forklifts drive in and out, pushing heat out of the hot room and onto the plant floor.
The heating medium used also will dictate energy use, and the heating medium used will depend on what is available at the plant. If an abundance of steam is available, it can be utilized as an efficient method of heating. Electricity also is convenient and efficient if the oven or hot room is properly sized, insulated, temperature controlled and provides adequate air circulation.
Drum handling is an important factor to consider when deciding upon a heating method. The entire drum heating process must be thought out to ensure the least amount of drum handling as possible. Hot drums are inconvenient and unsafe to handle and may even leak or spill when transported far distances.
One way to eliminate transportation concerns would be to have the drums heated near the process in which they are going to be used. Whether the drum is simply dumped into a tank or requires a more controlled removal method such as pumping or metering, it is convenient and practical to have the drum heater near the process. The advantage of having a drum next to its destination is that there is less handling required and less time for it to cool down. If pumping is required, it is critical to keep the drum warm because this process can take a long time. If operators choose this option, drum ovens, band heaters, drum wraps and immersion heaters are ideal. They can be located near the drum filling line, tanks or pumping station for convenience.
Other considerations in the material-handling process should be convenience and flexibility. Drum ovens and smaller heating methods such as band heaters provide greater flexibility as they can be turned off when not in use. It also is easier to heat the drums or totes to various temperatures when not utilizing a large hot room.
For example, if 16 drums need to be heated quickly to 200°F (93°C), a 16-drum oven can be set to the desired temperature. This is not an option in a large, central hot room environment where varying materials are stored. Some may not be able to take the heat. If large numbers of drums must be heated, band heaters and other single-drum heaters will be time consuming and labor intensive to use. A properly sized drum oven or in-plant hot room makes more sense.
While cost should not be a top concern, operators must consider equipment that will perform the jobs at an economically acceptable level. Initial purchase price as well as lifetime running costs must be weighed. Plants can use band heaters, which represent the least expensive heating option, or they can invest in homemade, in-plant hot rooms, which represent a substantial cost to the company. It is expensive and time-consuming to build a hot room: labor is required to design it, procure the materials and build it.
While cost should not be a top concern, operators must consider equipment that will perform the jobs at an economically acceptable level.
Other costs to consider beyond the initial purchase price include the cost involved with downtime. Some heating options are not as reliable as others and require frequent maintenance. Durability and dependability also tie into maintenance costs.
In conclusion, when manufacturers consider methods for safely heating their valuable products, they must consider the material characteristics, heatup times, energy use, material handling and costs. While band heaters, homemade hot rooms and immersion heaters can meet many heating needs, each technology has disadvantages that make them an inefficient option in some applications.
For many applications, drum warming ovens offer the energy efficiency and safety that other heating methods cannot. They can protect employees and the environment from dangerous, ignitable vapors while providing cost-effective heating in less time.