Carbon dioxide (CO2) is used as a refrigerant in many food processing applications. It has a number of advantages over the alternatives, including environmental acceptability, nontoxicity and nonflammability. Historically, CO2also has been inexpensive and widely available. However, when sourced as a byproduct of refineries, the supply of CO 2is highly dependent on the productivity level of these refineries. If a refinery stops production, whether planned or unplanned, CO2production also stops. When this occurs, food processing companies that purchase CO2from industrial gas companies may fall victim to force majeure, sometimes having to pay double the cost with a curtailment of supply.
This was the scenario facing one U.S. food processing company in 2007. The plant had relied exclusively on CO2for low-temperature cooling in its production processes for approximately 10 years. However, nearby refineries were shutting down. With sometimes only half of its typical CO2supply, the food processing company was forced to decrease its production to prevent product loss. Unfortunately, maintaining lower production levels came at a relatively high operations cost.
After experiencing supply issues with CO2for more than two years, the plant managers decided that they had had enough. There had to be a more dependable cooling medium that would be equally effective in their operation. The risk of product loss and budgetary limitations was far too great to continue working with CO2exclusively. But how could they test new cooling mediums without incurring high costs, sacrificing production levels or damaging products?
A Promising AlternativeUsing a propylene glycol solution to replace CO2seemed like a possible solution. The company decided to test this modification on a slip stream of the existing process.
The plant wanted to design a test system for low-temperature cooling using a heat exchanger. Using temporary utility equipment would allow the plant to determine whether a capital investment was necessary. However, process engineering expertise would be needed to tie into the existing system effectively.
After receiving a referral from another plant, the food processing company contacted Houston-based Aggreko North America, a company that specializes in providing rental utility solutions that can be applied to daily maintenance as well as process-related needs. Aggreko involved technical specialists as well as engineers from its process services division, Aggreko Process Services, to assist with the system design and performance.
The team worked closely with the food processing company’s engineers and plant managers to determine the best combination of temporary equipment and services to meet the processing objectives.
“The food processing company had three objectives going into this project,” says Rick Mello, project manager at Aggreko. “First, they wanted to be able to test new cooling mediums without lowering the productivity of the plant. Next, with the high cost of CO2, saving money on a new product was very important. Lastly, the project needed to be completed without damaging any of the currently stored product stock at the facilities. If this test proved successful, a full-scale transition from CO2to glycol would result in substantial cost savings.”
Right-Sizing the SystemDesign conditions required that the propylene glycol solution enter the heat exchanger at 5°F (3°C). For a safety factor, the system needed to be able to produce a leaving brine temperature as low as -10°F (-6°C). Aggreko supplied a 30-ton low-temperature process chiller capable of reaching temperatures of -15°F (-8°C) with a water tank, pump and accessories. An Aggreko technician facilitated the startup of the chiller and adjusted the valves to obtain the proper flow throughout the temporary and fixed parts of the system.
The equipment provided the plant with the flexibility to tie into its current system and test using a propylene glycol solution to cool the facility’s inventory.
“When dealing with a food product, there are regulations to be cognizant of, and this project presented some unique challenges and risks,” says Colum Clarke, sales consultant at Aggreko. “The product must be kept within a specific cool temperature range to avoid spoiling. We were able to tie into their existing system, including the heat exchangers, and keep production up and running during the entire process.”
In addition to providing the rental equipment and accessories, the Aggreko team also provided the food production facility with valuable insights about the operation. “Over a two-month period, Aggreko was able to provide extended on-site time with planning, execution and troubleshooting,” Clarke says. “Our engineering capabilities allow us to change and adjust systems very quickly to optimize the outcome.”
Increased FlexibilityThe slip stream test resulted in 100 percent replacement of CO2. Based on the test results, the plant determined that it would be able to replace 80 percent of the CO2used as a cooling medium in the entire manufacturing process, which would provide an estimated $600,000 to $800,000 savings annually. Regular production at the plant was not interrupted during the test, so there was no loss of production. And importantly, the food products at the facility were cooled effectively, without freezing or sacrificing the product quality.
“Using a temporary process system, Aggreko and the food processing company were able to successfully test the new cooling system by replacing CO2,” Clarke says. “With the volatility of CO2in the market, the company is no longer tied to this one option for cooling its products.”