Selecting and Buying Process Equipment

The first step in buying new or used process equipment is to truly understand what it must do. Usually this requires that a process line—or the specific piece of equipment—be designed, a classic engineering task. What this means is that all of the pieces of equipment in a line must be identified, including those pieces, such as conveyors, that connect various operations. Sometimes a line is similar to others in the company, but often the line is a new arrangement intended to make an unfamiliar product. This situation calls for creativity in assembling the unit operations, choosing from among alternative approaches, and understanding how the performance of each step is characterized.

The preparation of material and energy balances is a critical step in the course of designing a line. These are fairly simple, but essential, calculations that account accurately for all material and energy entering and leaving each step or unit operation. For example, an evaporator might have a feed rate of 10,000 lb/hr of fruit juice and a product rate of 2,500 lb/hr. The difference between those two rates—7,500 lb/hr—is the water-removal rate, which often characterizes an evaporator, along with the pressure at which it operates and the configuration of its heat-transfer surface. Roughly 7.5 million Btu/hr must be provided and removed in this example. In the case of evaporators, there are many possible choices, involving trade-offs between capital and operating costs, which we will not deal with here. An engineer—either a company staff member, a consultant, or an equipment vendor—makes some detailed calculations and determines the desired heat-transfer area, material of construction, and mode of operation.

For other types of equipment, there are appropriate parameters. For instance, a pump is described by its mode of operation—centrifugal or positive displacement; the size of its drive motor; and its performance curve, which shows flow rate against various pressures. It is an oversimplification to think of a pump only in terms of its nominal capacity—30 gal/min, for example. Heat exchangers are described by their heat-transfer area and the details of their construction—plate, shell and tube, triple tube, swept surface—and dimensions, such as plate clearance. Tanks and vessels are described by their capacity, material of construction, dimensions, and other features, such as jackets, agitators, and number of nozzles for adding and removing streams.

Equipment with more specialized functions and designs is often described by its nominal capacity (so many lb/hr) or, in the case of packaging equipment, so many packages/min. Mass flow rates (lb or kg/hr) should be converted to volumetric rates (cubic ft/min, cubic meters/sec, or gal/min), as well, because equipment sizes and capability often are more dependent on volume than on mass. This obviously requires knowledge of the bulk density of various streams. Many fluid streams found in food plants are mostly water and so may be approximated with the properties of water. Solids, such as powders and grains, however, are not only more variable in density, but their density may change in the process due to aeration, attrition (particle breakage), and moisture pick-up or loss.

The material of construction for much food equipment is stainless steel, but this is not dictated by law. Rather, the requirement of good manufacturing practices is that food-contact surfaces be non-corrodible, easy to clean, and easy to inspect. Stainless steel satisfies the requirement, but so, also, do high-quality epoxy coatings, approved polymers, and even carbon steel in certain services, such as for holding oils and syrups.

Buying New Equipment
Vendors of new food processing equipment can be categorized as multi-line suppliers or as more specialized suppliers. Through consolidation, many formerly specialized suppliers have become part of larger organizations that offer diverse catalogs of equipment. Much food equipment is manufactured by international firms, and even U.S.-based firms may fabricate many of their offerings overseas. This may be a factor in a purchasing decision because international designs may be in metric dimensions, and, with international sources, the supply of parts and service may be challenging. Most foreign firms have substantial representation in the United States because it is such a large market. A multi-line firm may be able to provide most, if not all, of a line, which can be convenient, but not necessarily the most-economical or highest-quality approach. It is rare that every offering in a large catalog is the best-in-class.

In an effort to simplify maintenance, training, and parts inventory, many companies establish lists of preferred vendors, especially for such common units as controls, pumps, and valves. If a buyer is responsible for purchasing a piece of equipment in one of these categories, the choices may be limited to those on the list. However, in other cases, it may be necessary to find qualified suppliers. The Internet is a great help, of course, as are equipment directories or buyer’s guides, which are published by a number of companies.

Having identified potential sources, how does a buyer make a choice? The more completely described or specified a need is, the more likely it will be filled satisfactorily. That is, the more information that can be provided, the better job a supplier will likely do. There needs to be a balance, however, between defining specific needs and allowing some flexibility in response. Some types of equipment are custom-fabricated exactly to order, while others are standardized, although the range of options can be very broad. It is important know which parameters are critical and which are less so.

Cost, of course, is always important, but it should not be the only determining factor. Competition is healthy and is expected; almost every type of equipment can be obtained from more than one source. Specifications and requests for quotations may be sent to three or four possible suppliers with a deadline for reply. More bids are rarely necessary and only add to the effort of evaluation. Soliciting fewer requests introduces the risk of not having much choice because some candidates may decline to reply. The quality of communication, timeliness, and amount of detail provided in a bid should influence the evaluation of a bidder. If a buyer does not have direct experience with a supplier, he or she should seek references and directly inspect samples of the supplier’s work. Both reliability and total costs over the life of a piece of equipment (including purchase, operating, maintenance, and salvage costs) should be estimated and compared.

When Used Makes Sense
A major advantage of used equipment, in addition to generally good prices, is quick delivery compared with that of new equipment, which may have a delivery time that approaches 9 months to a year.

The used equipment business has changed significantly over the past decade. There has been a flight to quality, according to Patrick Paden, Sales Associate at Aaron Equipment Co., Bensenville, Ill., (phone 630-350-2200), one of the world’s largest used equipment dealers, which maintains an in-house inventory of equipment.

Aaron focuses on process equipment for the food, pharmaceutical, chemical, plastics, and related industries. The company obtains its inventory by purchasing complete plants, lines, and individual items worldwide.

Historically, buying used equipment has had its risks. Used equipment was purchased at auction or through dealers who sold only on an “as is, where is” basis. Paden says his company has reduced or eliminated most of these issues by purchasing only high-quality equipment for resale, including many items that are “new in the box” or have never been used. The company also has its own repair and reconditioning facility that enables it to test run the equipment prior to shipping. Under certain circumstances, Aaron can provide a return option, allowing customers to return or exchange equipment.

The key today is being flexible. A customer may have to deviate from the ideal specification. For example, a tank may be larger or a filler may be slightly faster than is needed. In addition, Paden says, equipment that is of good quality sells quickly. Customers need to be prepared to purchase as soon as they know that the equipment will meet their needs. Finally, understanding which parts are prone to wear and which types of equipment are likely to hold up well is critical to inspecting and evaluating used equipment.

by J. Peter Clark,
Contributing Editor, Consultant to the Process Industries, Oak Park, Ill. 
[email protected]