Feeling the Heat
July 1, 2004
Feeling the Heat
Plate heat exchangers help dairy processors keep their cool when it comes to effective and reliable heat-transfer functions.
by Lynn Petrak
If it seems as if dairy processors have a lot on their plates at times, it may not be a bad thing.
Plate heat exchangers, used since the early part of the 20th century to indirectly heat and cool liquids, are a venerable but still crucial part of many daily dairy operations. After all, without proper heating and cooling functions, an otherwise smooth dairy process can turn disastrous — and costly.
Sanitary plate heat exchangers come in a variety of sizes and patterns, used for many types of dairy products that are, or were at one point in the process, a fluid base.
The premise is simple and remains effective today: Liquids are run down a channel (also called a porthole) on either side of a series of thin corrugated metal plates fitted with a gasket to direct the fluids into alternative channels, in order to effectively transfer heat or cool down products with minimal fouling and sedimentary buildup.
The versatility of such a basic structure is impressive, considering it is used in various points in processing and for an array of products and associated temperatures. Plate heat exchangers can be installed in areas ranging from raw milk receiving to pasteurization areas, run in extremely high temperatures or at cooler degrees, and constructed with as many as 1,000 or as few as 100 plates, among other application features. Products run on sanitary plate heat exchangers include fluid milk as well as cheese milk, whipping cream, whey, sour cream and yogurt smoothies that do not have a high level of particulates.
While other types of heat exchangers are available and used by manufacturers — such as tubular, scraped-surface and spiral — various forms of the plate heat exchangers have proven to be a dairy standard. In general, plate heat exchangers take up less space than other types of heat-transfer systems like tubular exchangers and can be more easily alternated in plate number, location or flow depending on process requirements.
Although the basic design and premise of plate heat exchangers has not varied much over the years, refinements and innovations have improved the heating and cooling process. The reasons behind improvements or redesigns in plate heat exchangers are similar to upgrades made in other types of processing components.
“From a quality standpoint, dairy customers want longer run times, so plate heat exchangers have to have a design that runs longer,” says Carl Lemke, business development manager for heat exchangers for the Pleasant Prairie, Wis.-based sanitary segment division of Alfa Laval Inc., which markets a broad range of heat exchangers as well as separators, decanter, pumps, valves and fittings. “Also, whenever you are putting a plate heat exchanger in a food or dairy application you are not just worried about heat transfer, you have to design it to be cleanable.”
Don Bohner, manager of heat exchangers for Vernon Hills, Ill.-based Tetra Pak Inc. (which both develops its own and markets various Alfa Laval heat exchangers under its own brand name), agrees that increased efficiency and cleanability are significant factors in plate heat exchanger innovation. “Processors are looking for longer run times, and they have tended to go to more aseptic and extended shelf life processing,” Bohner says. “In conjunction with that, with so much of the process of formulations changing and new products being developed, it is important that plate heat exchangers be sized properly for these new products.”
John C. Bohn, co-founder and director of engineering for AGC Engineering, Bristow, Va., also underscores the wide-ranging but equally important demands of today’s dairy operating environments and the respective competitive challenges. “Typically people want reliability and quality construction,” he says. “If they have purchased something that is somewhat cheap, they learn their lesson and don’t ever go back to it.”
Responding to Pressure
Although plate heat exchangers can be among the most durable of dairy processing equipment — with maintenance, some last upwards of 20 years — suppliers regularly research and develop new designs geared to increased robustness. One case in point is Tetra Pak, which offers a full line of plate, tubular and scraped-surface heat exchangers and often introduces new features and accessories.
On the plate heat exchanger side of its business, Tetra Pak’s latest product is its Tetra Plex® C, which features corrugated plates in a chevron pattern for maximum strength and glue-free, clip-on gaskets for ease of use. “That is our Cadillac, if you will — a plate heat exchanger that is very hygienic and designed primarily for liquid food processing,” says Bohner, noting that since the inception of the Tetra Plex line two years ago, the company has made some refinements. “The upgrade was going to a higher pressure frame, to 300 psi, through heavier materials and frame plates. The frame itself is heavier duty.”
The changes in durability, says Bohner, have had positive results. “It takes care of the hiccups in their systems,” he says. “Also, plate heat exchangers have a tendency to leak or blow gaskets, so a heavier pressure frame gives customers more reliability and longer run times.”
Emerging and changing dairy product lines and their accompanying processes have also impacted the design of plate heat exchangers, including the Tetra Plex C, says Bohner. “Gasket materials are important in higher temperature processing. The way gaskets are put on have changed over time and we no longer glue gaskets in. The glueless gasket makes it easier for customers to change gaskets,” he says, pointing out that the temperature rating of gaskets also has improved. “When processing at temperatures above 212 degrees F, the pressure tends to get higher as well, and that is where the 300 psi frame comes in.”
Beyond higher-temperature processing, other product changes have affected plate function and design at Tetra Pak. Reduced-carbohydrate products, including low-carb ice cream bases, tend to be more viscous and are best run on plate heat exchangers with a higher-pressure frame and wider gap between the thin corrugated plates. In such instances, exactness becomes even more critical. “There are good ways and not so good ways when it comes to measuring viscosity of products and implementing them into plate heat exchanger design. It is about understanding the rhealogy of the liquid in the plate heat exchanger,” says Bohner. To that end, in addition to providing a line of plate heat exchangers, Tetra Pak offers viscosity testing to its dairy customers.
Another factor driving refinements in plate heat exchanger design is customers’ interest in lowering energy costs. “Some people are specifically looking for that. They may be at 90 percent regeneration and want to go up to 94 percent,” says AGC’s Bohn, adding that energy rates have gone up across the board but are more of an issue in some regions than others.
To address such concerns about energy savings, AGC has updated some of its previous plate heat exchangers and introduced new variations. The company’s Pro5 model, which has replaced many outmoded and less efficient plates in recent years, is the plate heat exchanger of choice for most of the company’s dairy and food customers, according to Bohn, and was recently improved.
Over the past year, AGC also has complemented that heat transfer system with a new Pro5 Plus™ line, developed with energy efficiency in mind. “That provides customers the ability to expand existing units by over 25 percent or increase regeneration without piping changes or major over-hauls,” he says, noting results have been positive and measurable. “Energy savings using the Pro5 Plus plate range in the area of $20,000 to $35,000 per year using current energy costs.”
By installing new Pro5 Plus, Bohn adds, an existing pasteurizer operating at 90 percent can increase to 92.5 percent without any piping changes.
One reason the latest Pro5 models are so energy effective is based on the structure of the plates themselves. “With the gap on the plate, you can put 130 Pro5 Plus plates into the same space as 100 of the old style plates,” Bohn says. “Therefore, you get a greater heat transfer area and more energy savings.”
Another focus of R&D work on plate heat exchangers at AGC has been on sanitation. The inlet design of the plate heat exchanger, for example, has been expanded to allow higher clean in place (CIP) flow rates. Also, like other suppliers of heat-transfer systems, AGC has found that today’s dairies are looking for more flexibility for processing a greater variety of products. “The expanded inlet design also allows our plates to process the heavy viscous products at higher production flow rates without the damaging affects of high pressure,” Bohn says. “Several customers have upgraded their units and commented the pressure drop has decreased — over 25 percent — and they are not hindered by product viscosity.”
Tetra Pak and AGC are not the only suppliers upgrading sanitary plate heat exchangers to reduce cost and boost efficiency. Thermaline Inc., which produces sanitary plate heat exchangers for large suppliers like Waukesha Cherry-Burrell/SPX, has introduced five new heat exchangers during the past several months: the THX, TR2, TR3, TR35 and TR5 models. The reason for the change, says company president Jerry Sanders, stemmed in part from the firm’s move to accommodate the varying needs of manufacturers and to focus on custom solutions.
“In sizing an application for dairy processors, the new additions allow Thermaline to select a plate heat exchanger that will have outstanding performance and value,” Sanders says. “As dairies become larger, this creates a demand to increase the size of their plate heat exchangers, and Thermaline’s models T28, T45 and TR5 with 4-inch sanitary connections are used to fill this demand.”
Other improvements in plate heat exchangers are geared toward a different type of fluid heating and cooldown. “In addition to plate heat exchangers used for processing dairy products, we also have plate heat exchangers to treat the utility liquids in dairy plants, like hot water, CIP and coolants,” Bohn says.
Likewise, Alfa Laval recently launched a new type of plate heat exchanger called the TS-6 for steamed water transfer. “That is used on the utility side of hot water sets, for pasteurizers and for CIP solutions,” Lemke says.
Innovations in plate heat exchangers are not just relegated to the function of heat transfer. Spindle hydraulic closure frames, now offered by most of the major plate heat exchanger suppliers, represent one type of advancement.
“We’ve also added in the last year what we call a spindle type of closure frame to make it easier for customers to open and close, which we accomplished by using two air wrenches,” Bohner says. Alfa Laval and AGC also offer variations on spindle hydraulic closure frames.
Tonawanda, N.Y.-based APV Products, one of the first companies to successfully develop a commercial plate heat exchanger in the 1920s, also has recently improved its frame technology. “Established plate heat exchangers typically do their heat transfer job efficiently but when it's time to open the machine for cleaning or inspection, a number of difficulties still exist. Reducing this non-productive downtime can provide a significant competitive advantage for the end user,” says APV’s U.S. marketing coordinator Donna J. Crumley.
Powered closing systems have been an improvement, Crumley says, but operators must still manually measure and adjust for what’s known as plate pack pitch. After opening a plate heat exchanger, she explains, it is necessary to close it to a fixed dimension called the pitch, which is determined by the number and thickness of plates, gaskets and grids and varies from unit to unit.
As a solution, APV has developed a new Quad-Drive®, which incorporates an intelligent hydraulic closing unit that is factory set to close to the proper pitch, resulting in various benefits to the user. “Any changes in the field can be reprogrammed into the PLC by the end user with a security-protected code. This two-speed closure allows the user, when finished with his or her inspection, to simply press a button and walk away,” Crumley says. “The four tie-bars assure a positive alignment every time and are strategically placed so as not to interfere with the removal and replacement of plates and gaskets.”
The new closing system, she says, is especially effective on high flow rate applications like milk and whey pasteurizers and whey starter units.
Lynn Petrak is a freelance journalist based in the Chicago area.$OMN_arttitle="Feeling the Heat";?>