Dry Steam Cleaning is a sanitizing method favored by many food, beverage, and pharmaceutical producers as a high temperature, relatively dry, chemical-free process for cleaning production equipment in accordance with various codes and standards. The steam is hot enough to sanitize but because it is superheated, the steam has a low water content, effectively leaving behind dry surfaces. The process was developed in Europe where concerns about high water use, chemical sensitivities, waste management, and stepped up hygienic standards led away from more traditional sanitizing procedures. This article briefly describes the process and equipment, some popular applications, and some other cleaning alternatives.
A typical dry steam cleaning setup includes a tank for storing water, a boiler, a delivery hose, and various nozzles and valves. Most of the larger industrial machines rely on three-phase power to the boiler although smaller capacity units are produced which operate on single-phase power. These boilers should comply with ASME codes or Euro standards. Larger units will incorporate multiple boilers for greater steam volume. Systems are generally designed for portability, requiring only power hook up. Systems are often mounted on casters. Hoses are usually fixed lengths, with 12 and 20 ft. being common sizes. Larger machines sometimes offer dual hoses to permit two workers to work from the same machine.
Machines may have a single, refillable boiler or a two-tank system where feed water is kept in a separate non-pressurized tank and fed to the boiler as needed. Single tank systems must be depressurized before refilling while two-tank systems can be refilled on the fly, thereby eliminating the downtime associated with the cooldown, refill, and reheating of the unit. Some machines permit optional hookup of a supply line. Others permit the delivery of sanitizing chemicals along with the steam.
Typically, a brush is used in conjunction with the nozzle with special configurations available for cleaning floors, around pipes, and so forth. Special systems are available for permanent attachment to conveyors. Often, the dry steam process is followed by a wipe with a microfiber cloth to pick up any remaining residue.
Although the portability of these machines is a major advantage, some larger processing operations have installed centralized steam generators that are capable of operating continuously. Often these are used to provide continuous sanitizing of transport belting, etc.
Steam is delivered to the nozzle over a range of pressures and temperatures; steam at 260°F will kill any microbe on earth with direct contact. Many pathogens lie beneath a biofilm, however, which protects them from the killing power of steam. The steam, instead, strips away the biofilm and along with it any microbes it may be harboring. For a similar reason, chemical sanitizing agents must be allowed to dwell on surfaces to give them sufficient time to break through the biofilm. Steam also avoids the possibility of bacteria developing resistance to chemicals. The steam, under pressure, can work its way into cracks and crevasses but does not blast grime everywhere the way hosing or pressure washing can. Water use is minimized as is the volume of cleaning residue. Sometimes a machine may be “tented” and immersed in a cloud of dry steam in a manner similar to the way in which houses are tented to eliminate infestations.
The sanitizing requirements of the food, beverage, and pharmaceutical industries make facility sterilization by dry steam a good fit. Dry steam is used safely around control panels, conveyors, directly on walls, within ducts, etc. – all places where grease and residue can accumulate and harbor bacteria. Heat exchanges coils, filters, etc. are routinely cleaned using dry steam. Any facility that packages fresh fish, poultry, meats, cut produce, and similar items must be especially vigilant in its sanitation regime. The use of dry steam allows surfaces that contact food to be sanitized without chemical residue. Production machinery and equipment can be sanitized during worker breaks without shutting down production. Beverage makers use dry steam to clean bottling machines, conveyors, wooden barrels, etc. Refrigerated storage facilities may be cleaned without removing food products. Motors, wiring, and other electrical equipment may be degreased and sanitized without fear of harming the equipment.
Beyond those industries, others are finding applications for dry steam cleaning. Hotels, spas, and gyms are starting to use the process to kill bedbugs and other insects in carpets and bedding and to sanitize surfaces that come in frequent contact with their guests. Airlines and passenger trains and buses are increasingly using dry steam for the sanitation of their passenger compartments. Auto detailers are using the technology to clean and sanitize automotive interiors. Medical labs and dental offices are beginning to find the technology useful as well. Even homeowners are using consumer-based versions of dry steam machines to rid their houses of fleas and other pests without resorting to chemical treatments.
Although the dry steam is hot enough to kill microbes on contact, because of its low moisture content, the steam does not pose a burning hazard to operators. In many instances, no special protective gear such as gloves is required when operating the equipment.
Dry steam cleaning is not as fast as wet steam cleaning and for facilities with floor drains and washdown rated equipment wet steam may still be a preferred method. Wet steam has much higher water content and with that comes an increased flushing action. Likewise, heavy-duty removal of dirt and grease from agricultural machinery and the like is still best tackled by the application of wet steam, pressure washing, or a similar process –assuming it takes place outdoors or in a semi-enclosed environment. Dry ice blasting is another alternative for cleaning of bakery equipment, molds, etc.