Vapour degreasers in industrial cleaning

A related issue pertains to drying the parts after cleaning. The latent heat of vapourization measures the energy required to shift a chemical from liquid to gas phase. Aqueous cleaning systems will use more energy both to heat the cleaning agent above the boiling point of water and to dry water from cleaned parts than a system that uses a solvent with a lower latent heat of vapourization, lower specific heat and a lower boiling point. Again, modifications such as air knives are available for aqueous systems, but these increase energy consumption.

By the Numbers

Given that water has to work harder than solvents to accomplish the same cleaning task, it’s informative to compare the energy consumption of the two types of systems. But before we do, there is one important caveat: Cleaning systems come in myriad sizes, configurations and capabilities. Different soils and part geometries can dramatically affect the cleaning efficiency of a given system. As they say in the automotive ads, your mileage may vary.

In general, most solvent cleaning processes tend to be vertical, moving parts up and down in the cleaning system. Entirely self-contained, vapour degreasers usually are single-box machines about the size of a large desk or kitchen table. For example, a typical medium-sized vapour degreaser has outer dimensions of about 60×30 inches, with two cleaning tanks that are 10 inches wide, 12 inches long and 10-12 inches deep. Such a machine typically will use 3-5kw of electricity per hour of operation.

In contrast, aqueous processes tend to be horizontal, moving the parts through a series of dip tanks. Aqueous cleaning systems have typically a 50-60% larger footprint than vapour degreasers of the same capacity, simply because of the need for more tanks, larger pumps, blowers, filters and so on. These machines typically use 8-10kw of electricity per hour of operation.

Many aqueous systems enhance cleaning with ultrasonics, adding a further 200-500W of power consumption per tank. But whereas most vapour degreasers have only one tank fitted with ultrasonics, aqueous cleaning systems generally have three or more. So, ultrasonics adds roughly another 1-2kw of energy consumption to aqueous systems.

Auxiliary Equipment

Aqueous systems are not single-box designs. Auxiliary equipment required in addition to the basic three- to five-tank washing and rinsing system includes a deionized (DI) water system, some type of dryer and a wastewater treatment system. Each auxiliary process has its own energy requirement.

A typical aqueous batch system has one wash tank and two or three rinse tanks that require 2-5gpm of DI water. The DI system also needs to heat the water to operating temperature; typical aqueous systems cannot tolerate large influxes of cold water. Assuming a cleaning temperature of 140°F, the deionizer will need at least 2-3kw of power simply for purification and heating and more for the pumps and support equipment.

At the other end of the system, parts need to be dried. Infrared heaters, blowers, turbo-blowers and air knives are used. On a typical aqueous cleaning system, any of these drying approaches can easily use 5kwh. That number could double on a bigger machine simply because of the larger motors, fans and compressors required.

Wastewater treatment is a very complex issue because of the wide variety of processes and options available. In addition, some plants have suitable facilities already in place, so the extra energy consumption of waste treatment for a cleaning process may not be significant.

However, if the primary use of the water treatment system is to support the aqueous cleaner, then the energy costs and footprint of the waste treatment system are opportunities for savings. Assuming the system needs to process 5gpm of wastewater, even the most frugal waste treatment system is going to use 3-5kw of power. In general, aqueous cleaning systems always add cost and burden to plant treatment facilities.

Each of these auxiliary systems also adds heat to its surrounding environment, increasing the load on plant HVAC systems. The differences here are striking: the vapour degreaser mentioned above will add about 82,000 Btu/hr of heat to the room in which it is operating, while the aqueous system will add nearly 300,000 Btu/hr. The aqueous system also will add approximately 15lb (roughly 2 gal) of water into the plant air of the plant every hour, which will need to be removed by the HVAC system.

One last consideration is stand-by power draw – that is, use of electricity to keep the machine ready for operations. In order to minimise solvent losses, vapour degreaser refrigeration units should be kept operational at all times. This generally requires 0.5-1kw/hr of electricity. But at many companies, the heaters on aqueous cleaning systems are never shut down because of the long delay in reheating the water. This means the system uses 2-5kw of electricity, hour after hour, day after day, even when not in use.