Bob Baker and Trey Ragsdale, Atlas Copco Compressors Compressed air is a critical component in many manufacturing processes. It is often referred to as the fourth utility, beside electricity, gas and water, because it is used to power applications throughout the manufacturing process. In food manufacturing, compressed air is used in processes such as ingredient mixing, pneumatic conveyance and packaging, among others. In the industry, this is referred to as ‘active’ air; because it touches the final product in many food manufacturing applications, the air must be clean and free of any potential contaminants.

Air compressors have come a long way to ensure that the air used in food manufacturing processes is as absolutely pure as possible. Consider the modern lubricated screw compressor; technological advances have ensured that the oil content in the air is very limited and can be further reduced by using a multi-stage filter solution. However, it is difficult to control the amount of oil present in the air after filtration due to factors such as temperature, which has a significant impact on the separation process. The process of filtration is never really fail safe; failure of any component in the filter chain could lead to large amounts of oil contaminating the process and the compressed air distribution system.

An oil-free screw compressor virtually eliminates the need for in-line oil filtration and in most cases will eliminate the risk of oil contamination completely. The need for costly filter replacements, large sump tank oil changes and ongoing maintenance due to oil residue is eliminated and can result in substantial compounded savings over the life of the compressor. The result is life cycle savings that are much greater than the initial cost of choosing oil-free over oil-injected compressors.

For these reasons, most food manufacturers choose oil-free compressors that meet the ISO 8573-1 Class 0 2010 edition standards that define air quality levels and methods for determining contaminants in the air system. Class 0 is the industry standard in food manufacturing compressed air processes, as well as other industries that require 100 percent pure, oil-free air, such as the pharmaceutical, medical and critical electronics industries.

Oil-free air is one of the top priorities in the successful operation of a food manufacturing plant. If contamination were to occur, the operation would have to be slowed or stopped altogether, resulting in downtime, product waste, loss of productivity and a damaged reputation if product recalls become necessary. Food manufacturers largely have realized the benefit of eliminating the risk of oil contamination and many now operate Class 0 air compressors.

But switching to an oil-free compressor does not guarantee that one food manufacturing plant will operate more efficiently than another. Other advancements in design and packaging help make today’s air compressors more efficient than ever before. Additionally, improved maintenance procedures, state-of-the-art monitoring equipment and increased attention to air usage have all contributed to loweroperating costs while increasing productivity.

For a food manufacturer to remain competitive, energy efficiency and energy savings must be a top priority. Considering that the cost of electricity to power compressors can be as high as 40 percent of a plant’s electricity bill, reducing energy consumption is a simple way to contribute to the bottom line with positive results.

An innovative way to reduce energy consumption is to capitalize on the heat by-product of air compression to defray the costs of other necessary food manufacturing processes. By using energy recovered from heat, manufacturers can save typically 95 percent (with potential savings up to 100 percent) of the original electrical input energy used to power the air compressor.

How does energy recovery work?

The law of thermodynamics states that energy can neither be created nor destroyed; rather it changes from one form to another. When air is compressed, the energy transforms from electrical energy to potential energy in the form of compressed air and to thermal energy, or heat. After compression, air is often at a temperature of 325-400 degrees Fahrenheit.

Before the compressed air is distributed into the piping system and delivered to the end-process, the heat has to be extracted from the air. If the heat is not recovered, it becomes waste. Most oil-free compressors are a two-stage design and come standard with an intercooler between the first and second stage and an after-cooler, which is located after the second stage. The intercooler and after-cooler can either be air- or water-cooled.

Air-cooled systems are more common for small- to medium-sized compressors and heat recovery is often limited to the cool seasons, when heated air is more likely to be required. The discharged cooling air can be routed to nearby buildings for supplemental heating, offsetting the energy originally required to perform the same function.

Water-cooled systems can recover a higher amount of energy than air-cooled systems and are based on one of three main principles: open systems without circulating water, open systems with circulating water and closed systems with circulating water. In the closed system with circulating water, the same water continually circulates between the compressor and some form of external heat exchanger that transfers the heat to the process. In a closed system, the water is treated and there is little to no mineral deposit buildup in the cooling media components, as with an open water system. If correctly implemented, a closed water system requires little supervision and has low maintenance costs. Energy recovered by means of a closed cooling system enhances the compressor operating conditions, reliability and service life due to an equalized temperature level and high cooling water quality.

Once the compressed air has passed through a water-cooled system, the water contains (in the form of heat) approximately 95 percent of the energy used to compress the air. The heated water can then be used throughout an operating facility to preheat tap or process water or heat the building via shunt circuits. In food manufacturing, the hot water can be used for sterilization, scalding or melting applications or simply to pre-heat a boiler. The energy that would normally be used in these processes is offset by the recovered energy, resulting in energy savings.

With rising energy costs and growing demands for environmentally sustainable processes, food manufacturers should consider energy recovery, along with 100 percent pure, oil-free air, as a top priority. With these practices, food manufacturers can impact the environment and the ever-important bottom line with positive results.