The design and installation of efficient temperature control within plant systems has been subject to relatively little innovation for decades. (Some plant managers and installers may even have felt they suffered from a lack of choice.) Ammonia has been used as a primary refrigerant in industrial applications for more than 150 years. It is the go-to refrigerant in many applications, including food processing and storage, process cooling and building services.
Although environmentally sound, ammonia unquestionably requires the safe design and operation of the refrigeration system to avoid the risks associated ammonia’s hazards and acute toxicity. “Refrigerated release incidents” involving ammonia can happen and, while many events cause lower-level injuries, a number have proved fatal.
It is much the same when it comes to secondary refrigerant systems. For decades, plant managers have had to choose a between fluid that is nontoxic but gives poor performance, or one that offers enhanced performance but is toxic.
It could be argued that industrial temperature control is overdue a step change and that process engineers deserve better.
Among others, chemists who study the flow of liquids have been working to improve process cooling media options. Some have set their sights on secondary refrigerants with good results. As a result, recent developments may help end the toxicity vs. efficiency tradeoff for some process cooling applications. They also may lead to new options and cost savings for industry.
The current status quo offers four choices of heat transfer fluids for secondary refrigeration:
- Ethylene glycol (EG)
- Propylene glycol (PG).
- Salt brines.
Ethylene glycol-based heat transfer fluids are used in many cooling systems. They offer good physical properties, but they are toxic. They pose a risk to human health if there is incidental contact with items intended for human consumption.
Propylene glycol-based fluids — the preferred alternative by many — have a safer profile than ethylene glycol-based fluids. The tradeoff is they are less efficient at transferring heat energy, particularly at low circulation temperatures. Plant managers must find the balance between managing or removing risk and cooling performance.
Among others, chemists who study the flow of liquids have been working to improve process cooling media options.
Ethanol is another alternative, but it brings with it a high flame risk. When used with pressurized ammonia, the results of a leak or incident could represent an explosive combination.
Salt brines perform well but have proven to be corrosive to pipework and systems.
One company with a history developing in anti- and de-icing fluids sought to apply that experience to heat transfer fluids for process cooling. The fluid development objectives include creating a fluid that was nontoxic and as efficient as — or more efficient than — current fluids.
While working in the laboratory, the company focused on developing a heat transfer fluid that could help reduce the incidence of pressure drops across the system. Another goal was to help reduce pumping costs and increase hydraulic efficiency. The resulting fluid is formulated with organic, approved inhibitors and viscosity modifiers. The fluid has an operational temperature to -40°F (-40°C), and it has been approved by the NSF as safe for incidental food and beverage contact.
Case in Point
The fluid manufacturer worked with Canadian energy management consultants I.B. Storey to evaluate the fluid. The consultant had been asked by a chocolate manufacturer in Ontario to review its plant’s energy efficiency.
According to the consultants, after a trialing with the new heat transfer fluid, the company identified potential electricity savings of more than $14,000 per year — primarily through a savings of 39 percent of pump operating costs. Because heat transfer fluid viscosity was 15 percent less than the current fluid the chocolatier was using, capital costs also were reduced. The companies estimated construction cost savings of more than $17,500.
These results are in line with the fluid specifications, according to the fluid manufacturer. Company testing has shown it to be 66 percent less viscous than polypropylene, which can help companies accomplish energy savings as high as 35 percent.
Further savings related to the use of the heat transfer fluid have been identified through the reduction of piping from 10” to 8”. By shrinking the size of pipes on new installations, manufacturers could see piping installation savings.
Taking these potential benefits into account, there is a case to be made for incorporating the low viscosity heat transfer fluid into the initial design phase of the manufacturing plant. This would facilitate the inclusion of smaller pipes and allow a facility to realize the installation savings.
While working in the laboratory, the company focused on developing a heat transfer fluid that could help reduce the incidence of pressure drops across the system.
Data from external tests on the performance of the low viscosity fluids is being submitted to OEM simulators. The fluids manufacturer expects the tests to demonstrate the efficiency and performance benefits as well as evaluate the use of smaller hardware. Moreover, once results are returned, the fluid manufacturer expects that, due to the efficiency of the low viscosity heat transfer fluid, there may be an opportunity to review primary refrigeration system setups.
Market prohibitions on CFCs and increasingly HFCs have meant industry has been encouraged to turn back to ammonia for primary refrigerant. The low viscosity heat transfer fluids under testing could show benefits for the primary refrigerant setup in terms of efficiency and equipment installations. With the fluid on the secondary side of the cooling loop, making things more efficient, there may be opportunity in some applications to reduce the ammonia charge — or potentially remove it completely in some applications. PC