I have stressed the importance of temperature to cleaning processes many times in previous blogs. This blog will discuss the heat source options for achieving and maintaining the temperatures required for effective cleaning.
Electric heat is, without a doubt, the most prevalent heat alternative used for cleaning applications. This is because electric heaters are relatively inexpensive, relatively small, easy to control, and because electricity is a utility readily available in most facilities. Electric heaters are appropriate for applying heat to both liquids and gasses making them useful in heating liquids for cleaning and rinsing as well as air for drying. The two basic types of heaters used to heat liquids are surface mount heaters (often called “strip” heaters) and immersion heaters. Surface mount heaters have a flat profile which allows them to be affixed to the exterior of tanks using clamps, weld studs with bolts and other means.
In the case of irregularly shaped tanks, the heaters can be formed to match the profile of the tank. It is important that heaters of this type be firmly and permanently attached to assure efficient heat transfer from the heater through the tank wall and into the liquid. In some cases, a heat conductive paste is used between the face of the heater and the tank wall to maximize heat transfer. The surface of the heater not facing the tank wall can be covered with insulation to minimize heat radiation to the ambient and is especially important in enclosed spaces.
Immersion heaters are placed directly in the liquid to be heated with electrical leads either looped over the top edge of the tank or exiting the tank through an appropriate fitting mounted on the tank wall. In the case of immersion heaters, the efficiency is nearly 100% since the only path for heat is into the liquid.
In cases where air (or another gas) is to be heated, electric heaters may be provided as an open coil or with an enclosed element (similar to a strip heater) with fins to improve conduction and radiation.
The use of steam circulated through a heat exchanger immersed in a liquid is another means of heating liquids for cleaning and rinsing. In most cases, steam is selected when the facility already has an existing source of steam making it economical. The control of steam is usually accomplished using valves electrically actuated by a temperature control or by mechanical means using a capillary bulb or bi-metallic actuator. Steam is an excellent choice in systems using flammable materials as, with steam, there is a greatly reduced chance of electrical discharge which might otherwise initiate combustion of flammable liquids or vapors.
Gas heat utilizes a burner head attached to a combustion tube immersed in the liquid to be heated. The application of gas heat is used primarily in very large tank systems because of the inherent size and configuration restrictions that apply to the combustion tubes which are several inches to a foot or more in diameter and must be of sufficient length to assure complete combustion. The products of combustion of gas, of course, also need to be vented to the outside of the facility which is not always easy. In general, tanks with a volume less than 800 to 1,000 gallons are not practical candidates for being heated by gas.
– FJF –