In 2008, our firm published the results of a survey collecting data on sustainability goals across the industries we serve. The results indicate that overall, 45 percent of companies surveyed have formalized sustainability goals, and that those goals are reducing energy consumption; recycling; achieving sustainable facility design; and using energy-efficient products and equipment. Sustainable design, whether it relates to a facility or process, has become such a universal goal that instead of asking, "Should we.?" companies are asking, "How should we.?"
Food manufacturers and processors have discovered opportunities to execute a wide range of "green" initiatives, from "5,000 feet up" strategies such as energy and sustainability master planning and LEED certification to improving immediate results by managing utilities. Water and natural gas, in particular, are typically used in abundance in older plants. Yet there are effective strategies for sustainable management of these resources.
Cooling Water Usage
Thermal food processing plants can benefit from reuse of water and waste heat from their processes. Energy audits of frozen food plants, for example, often find a pattern of high water usage, both in processes and for cleanup operations.
Here is a case in point. In a ready-to-eat soup plant located in the Midwest, the once-through process they were using for immersion cooling of filled, sealed soup cans used approximately 2 million gallons of water per day. Engineers enabled the plant to reuse that water through design and implementation of a recirculation system. Specifically, the process cooling loop system recovers process cooling water after use and pipes it to plate-and-frame heat exchangers, where it is indirectly cooled by a cooling tower; if necessary, the water can be further cooled using chillers. Cooled water is then returned to the process. The capital cost of the system was approximately $4 million, and the project met the 2.5-year payback/40 percent return on investment (ROI) benchmark.
Another source of significant water usage and, even more important, change-over time is the use of low-pressure wash systems to clean food processing equipment. In many cases, engineers have replaced low-pressure wash systems with high-pressure wash systems, achieving a significant reduction - as much as 75 percent - in change-over time.
Returning Heat to the Process
As in the case of the soup plant, a Midwest condiment manufacturing plant cooled its batch product using a heat exchange system with once-through city water as the heat exchange medium; however, the resulting hot water went right down the drain. The utility cost of the water was $2.30 per thousand gallons; the sewer cost added another $2.35 per thousand gallons. In this case, use of a recirculation cooling loop saved $4.60 per thousand gallons of water. In this plant, the cooling-process improvement afforded an added benefit: the cooling water, which comes off the final step of the cooling process at 160 degrees F, is now piped to another heat exchanger to preheat the ingredients at the front end of the process, saving on the cost of natural gas. This $1.25 million project saves approximately $500,000 a year, achieving a 40 percent ROI.
In another food plant, in this case, a soup plant in the South, a heat exchange system was designed to take residual heat off the top of boiler stacks, using condensing stack economizers to recapture the latent heat in water vapor and use it in the manufacturing process. This system saved the owner $800,000 in the first year of operation.
More recently, engineers have identified an opportunity to redesign a vacuum cooling operation that utilizes steam educators and steam pumps as the vacuum generator, to vacuum pumps and low temperature chillers, the end result being a significant reduction in natural gas usage.
Part of the challenge of these types of projects in existing plants is to control the negative impact on plant production, particularly during installation. Smart project planning results in lower total cost and reduced downtime for the owner. In all of these cases, the engineering team successfully avoided operational interruptions during installation and production startup.
Benchmarking Utility Meters
One potential source of savings that is often is overlooked is the utility meters themselves. At relatively low cost, an owner can install independent meters to validate the actual usage of utilities such as steam, natural gas, and water against the meters that are used for billing.
In one case, a cereal manufacturer that purchased process steam from an adjacent sister plant installed an independent steam-flow meter at the entrance to the plant to verify the billings. They learned that they were being billed for up to twice as much as the volume of steam that was actually delivered.
Moreover, installation of benchmark meters shows how much it costs to run individual production lines, facilities, and operations as a whole - and in real time. For example, independent metering of two lines running side by side can reveal information about equipment reliability and the need for maintenance. Benchmark metering can also be used to identify the utility costs associated with operations at particular times of the day - and possible opportunities to reduce costs through demand-side management and off-peak usage - or in various geographic locations, both domestic and international.
Also, where it makes sense, cogeneration may be a good option for the owner. In areas of the country in which electric rates cost 4.5 to 5 cents per kilowatt hour, it is difficult to cost-justify a cogeneration system. However, in other areas of the country, notably the West, where electric rates are 15 to 20 cents per kilowatt hour, one can more readily cost justify the capital cost of cogeneration. If an owner is going to replace its power plant, it makes sense to analyze the base loads and consider whether cogeneration offers any benefits.
Start at the End
The best outcomes - and greatest savings - can be achieved when an engineering team takes an integrated approach to renewable energy, resource management, and sustainable plant design and operation, and implements best practices from the industry.
That's why it is important to start at the end; that is, to understand the owner's performance criteria and determine how to achieve them. Owners need not accept the performance that the existing systems and equipment delivers; they need the systems and equipment that deliver the performance they require. But the best-designed system won't get in the door if it doesn't deliver a realistic ROI. In the food industry, a utility savings project typically must meet or exceed the financial benchmark of a 2.5-year payback, which translates to a simple ROI of 40 percent. An analysis of an operation's processes and utility usage history often reveals opportunities to implement projects that meet this benchmark.
At a 40 percent ROI, it should be noted, a food manufacturer may be able to interest an independent performance-based contractor in funding, building, and operating a utility savings system on a shared-savings contract. Nevertheless, prudent owners still engage a consulting engineer with experience in food production to provide objective, third-party due diligence. The consultants can review the system design to ensure that it is properly designed for the application and operationally reliable.
In today's economy, more than ever, the food industry is looking for smart strategies and best practices to assure sustainable food production. Effective management of water and natural gas resources is a good place to start.