Improving production technologies to optimize production cycles, increase machinery efficiency, reduce ingredient waste and intermediate products, and increase the shelf life of the final product without compromising quality remain key objectives of the food and beverage industry. In many food processing plants, however, accomplishing such goals requires the support of reliable and efficient auxiliary process lines such as secondary cooling (glycol, brine and water).
Traditionally, metal piping systems have been used for secondary cooling. The weight of the metal pipes must be factored into the load calculations of a building’s structure because most loops run on the roof or hang from the ceiling. Also, metal piping requires routine maintenance and is subject to corrosion, scaling and condensation, and mold.
Corrosion. Whether internal or external, metal pipes can corrode. If they do, they must be replaced to maintain system integrity.
Internal corrosion can be minimized with the use of corrosion inhibitors. However, if the fluid is not maintained properly (i.e., if an inadequate quality of water is added, the concentration of inhibitors is decreased, or different types/brands of inhibitors are mixed), corrosion will appear sooner or later, along with scaling.
Scaling. Unless there is a need to intervene in the line, scaling is not easily detected. Scaling gradually affects system efficiency. Inner-wall roughness in metal pipes contributes to fixation of corroded particles, causing a reduction of the pipe’s inner bore. This reduction will decrease the flow allowed through the pipeline, making it more difficult to reach the desired temperature. The problem usually can be mitigated by regulating the pumps or decreasing the fluid temperature, which translates into a higher temperature delta at the chiller and higher energy consumption.
Condensation and Mold. Conveying a fluid at a temperature below the ambient without condensation or mold requires adequate thickness of the proper type of insulation and a good, intact vapor barrier. The challenge is keeping the integrity of the insulation, vapor sealing and external jacket during the lifespan of the system. Problems range from pipe supports compressing the insulation and creating a thermal bridge to workers stepping on the jackets and insulation. There are many ways insulation can be damaged in a plant, thereby compromising the vapor barrier.
Corrosion and condensation can work hand in hand to destroy metal piping. Condensation will accelerate corrosion on the external surface of a metal piping system. Condensation also contributes to mold development on the insulation. This in turn promotes propagation of bacteria and potential contamination of the facility.
Corrosion in metal pipes can lead to increased maintenance costs because pipes need to be cut and replaced, which necessitates shutting down the line.
Efficiency is Key
An alternative to metal piping in secondary cooling applications is plastic piping. Some systems can be supplied pre-insulated to minimize installation time.
For instance, a pressure-rated acrylonitrile butadiene styrene (ABS) piping system can be pre-insulated with closed-cell polyurethane insulation and protected by a UV-resistant high density polyethylene (HDPE) outer jacket. Besides being corrosion free, the plastic piping offers an inner-wall smoothness that helps prohibit the buildup of deposits from the fluid. This helps processors avoid flow reductions in the piping.
FIGURE 1. In a new build for a sauce manufacturing facility where the cooling loop was to be mainly outdoors on the roof, ABS pre-insulated piping was chosen for its UV resistance and its reduced weight when compared to metal. This allowed the equipment to be installed on the roof without the need for structural reinforcement. Relocating the piping to the roof also allowed the sauce manufacturer to gain more production and storage floor space.
ABS has a pipe roughness factor of 2.33 10-5 ft compared to steel’s 3.10-4 ft, which is about 12 times smoother. This characteristic improves system efficiency in terms of reduced pressure loss. By using a material that eliminates the risk of corrosion or scaling, the need to intervene into the piping system is limited only to potential additions or changes to the layout.
With some pre-insulated ABS piping systems, the high density and closed-cell insulation is manufactured directly on the pipes and fittings. This means there is no room for thermal bridges. Such a manufacturing technique helps provide temperature stability along the line and prevent condensation in extreme temperatures and humidity conditions. A stable temperature with lower heat loss along the pipeline allows for a higher cooling temperature that decreases the temperature delta at the chiller and reduces energy consumption. This stability results in an optimization of production cycles, for example, in fermentation processes.
Also, in some pre-insulated ABS piping systems, the insulation is bonded to an HDPE hard jacket by the manufacturers. The water- and vapor-tight jacket can incorporate UV resistance, making it suitable for rooftop installations. The hard jacket helps ensure the insulation integrity, easing the manipulation of parts during installation.
During installation, ABS pre-insulated piping is joined quickly with solvent cement using an inner-nipple connector without removal of any polyurethane insulation. An integrated pipe stop creates a gap for visual inspection during pressure testing. The gap is sealed afterward to ensure the connection is water- and vapor-tight.
Damaged jackets and insulation are part of the daily challenges in cooling installations. Repairs and replacements need to be scheduled quickly before further damage occurs.
As noted earlier, in new build projects and in retrofits, the pipeline weight is of great concern because it has tremendous impact on structural considerations. When considering a pipeline for rooftop installation, a weight savings of approximately 40 percent may allow for a lighter structure, or it can free space on the production or storage floor by moving equipment overhead.
For instance, on a new-build project for a sauce manufacturer (figure 1), the stainless steel pipe alone — without insulation — weighed 72, 872 lb. A comparable system manufactured with pre-insulated ABS piping weighed 59,217 lb. When looking at a retrofit, very often the roof needs to be repaired or reinforced before replacing the pipes. This level of weight savings prevents extra expense of time and budget.
The application of plastics in process lines as critical as secondary cooling is decreasing the downtime for repairs and, therefore, maintenance costs. The use of ABS piping also can help improve the efficiency of the overall production process. PC