In the absence of a steam trap maintenance program, it is common to find up to 15% to 20% of steam traps malfunctioning in a steam distribution system . Energy savings for a regular system of steam trap checks and follow-up maintenance is conservatively estimated at 10% . One industrial case study indicates a payback period of less than four months . Although this measure offers a quick payback period, it is often not implemented because maintenance and energy costs are generally separately budgeted. In addition to energy and cost savings, proper functioning of steam traps will reduce the risk of corrosion in the steam distribution system. At a Land O’Lakes dairy facility in Tulare, California, a U.S. DOE sponsored energy assessment estimated that implementing a steam trap maintenance program would save nearly 20,000 MBtu of natural gas per year and lead to annual energy savings of around $278,000 .Steam trap monitoring. Attaching automated monitors to steam traps in conjunction with a maintenance program can save even more energy without significant added cost.
This measure is an improvement over steam trap maintenance alone, large round plant pots because it gives quicker notice of steam trap failure and can detect when a steam trap is not performing at peak efficiency. Employing steam trap monitoring has been estimated to provide an additional 5% in energy savings compared to steam trap maintenance alone, at a payback period of around one year . Systems that are able to implement steam trap maintenance are also likely to be able to implement automatic monitoring. Leak repair. As with steam traps, steam distribution piping networks often have leaks that can go undetected without a program of regular inspection and maintenance. The U.S. DOE estimates that repairing leaks in an industrial steam distribution system will lead to energy savings of around 5% to 10% . At a Land O’Lakes dairy facility in Tulare, California, the U.S. DOE estimated that natural gas savings of $18,000 per year could be realized by implementing a steam leak maintenance program . Additionally, regular inspection and leak repair can reduce the likelihood of major system leaks, which can be very costly to repair. Flash steam recovery. When a steam trap purges condensate from a pressurized steam distribution system to ambient pressure, flash steam is produced.
As with flash steam produced by boiler blow down, steam trap flash steam can be recovered and used for low grade facility applications, such as space heating or feed water preheating . The potential for this measure is site dependent, as its cost effectiveness depends on whether or not areas where low-grade heat is useful are located close to steam traps. Where feasible, this measure can be easy to implement and can save considerable energy. For example, an analysis of a U.S. based food processing facility predicted that the installation of a flash steam recovery system used for feed water preheating would save the plant around $29,000 in fuel costs annually at a payback period of less than 1.8 years . Based on the reduction in boiler fuel use, it was further estimated that the plant’s carbon emissions would be reduced by 173 tons per year.Process integration. Process integration refers to the exploitation of potential synergies that might exist in systems that consist of multiple components working simultaneously. In facilities that have multiple heating and cooling demands, like those in the fruit and vegetable processing industry, the use of process integration techniques may significantly improve facility energy efficiency by linking hot and cold process streams in a thermodynamically optimal manner. For example, the heat rejected in a facility’s cooling process can be recovered and used in process heating applications . Developed in the early1970s, process integration is now an established methodology for improving the energy efficiency of continuous industrial processes . At Elite Salads and Snacks, a Dutch producer of pre-cooked foods for the catering industry, continuous demand for both heating and cooling provided an attractive opportunity to integrate both functions into one common system.
The company used rejected heat from its cooling system in combination with recovered heat from its flue gas condenser to pre-heat process water. The rejected heat from the cooling system was also raised to a higher temperature via the addition of a heat pump. The process integration initiative led to natural gas savings of approximately 120,000 cubic meters per year with a payback period of around 2.5 years . McCain Foods, a major producer of frozen French fried potatoes, installed an integrated heat recovery system in its Scarborough, England, facility in 1995. Heat was recovered from fatladen fryer exhaust gases via a vapor condenser and from boiler flue gases via economizers. The recovered heat was used to pre-heat air for potato chip dryers, to provide hot water for potato blanching, and to provide hot water for miscellaneous processes around the facility. The project led to annual energy savings of £176,000 and a simple payback period of 3.6 years . Pinch analysis. Pinch analysis takes a systematic approach to identifying and correcting the performance limiting constraint in any manufacturing process system. It was developed originally in response to the “energy crisis” and the need to reduce steam and fuel consumption in oil refineries and chemical plants by optimizing the design of heat exchanger networks. Since then, the pinch analysis approach has been extended to resource conservation in general, whether the resource is capital, time, labor, electrical power, water, or a specific chemical species such as hydrogen. The critical innovation in applying pinch analysis was the development of “composite curves” for heating and cooling, which represent the overall thermal energy demand and availability profiles for the process as a whole. When these two curves are drawn on a temperature-enthalpy graph, they reveal the location of the process pinch , and the minimum thermodynamic heating and cooling requirements. These are called the energy targets. The pinch analysis methodology involves first identifying the targets and then following a systematic procedure for designing heat exchanger networks to achieve these targets. The optimum approach temperature at the pinch is determined by balancing capital and energy tradeoffs to achieve the desired payback. The procedure applies equally well to new designs and retrofits of existing plants. Energy savings potential using pinch analysis far exceeds that from well-known conventional techniques such as heat recovery from boiler flue gas, insulation, and steam trap management. At the Nestle Svenska food processing facility in Bjuv, Sweden, a pinch analysis study was performed in 1993 to optimize facility-level energy consumption. The pinch analysis identified improvements to the facility’s steam system—specifically, plant pots round heat recovery opportunities in the facilities soup, baby foods, and vegetable departments—that would reduce the facility’s annual energy consumption by 10% with an expected payback period of around three years . The expected annual savings in energy costs were estimated at around 300,000 Swedish Kronor .Motors are used throughout a typical fruit and vegetable processing facility to drive process equipment , conveyors, ventilation fans, compressors, and pumps. According to the U.S. DOE, the typical industrial plant in the United States can reduce its electricity use by around 5% to 15% by improving the efficiency of its motor-driven systems . Pumps are particularly important pieces of motor-driven equipment in many fruit and vegetable processing plants. Pumps are used extensively to pressurize and transport water in cleaning, water fluming, and wastewater handling operations, for transporting liquid food streams between processes, and for circulating liquid foods streams within the processes themselves . Studies have shown that as much as 20% of the energy consumed by pumping systems could be saved through changes to pumping equipment and/or pump control systems . This chapter presents some of the most significant energy efficiency measures available for motors and pumps in industrial applications.When considering energy efficiency improvements to a facility’s motor systems, it is important to take a “systems approach.” A systems approach strives to optimize the energy efficiency of entire motor systems , not just the energy efficiency of motors as individual components.
A systems approach analyzes both the energy supply and energy demand sides of motor systems as well as how these sides interact to optimize total system performance, which includes not only energy use but also system uptime and productivity. A systems approach typically involves the following steps. First, all applications of motors in a facility should be located and identified. Second, the conditions and specifications of each motor should be documented to provide a current systems inventory. Third, the needs and the actual use of the motor systems should be assessed to determine whether or not motors are properly sized and also how well each motor meets the needs of its driven equipment. Fourth, information on potential repairs and upgrades to the motor systems should be collected, including the economic costs and benefits of implementing repairs and upgrades to enable the energy efficiency improvement decision-making process. Finally, if upgrades are pursued, the performance of the upgraded motor systems should be monitored to determine the actual costs savings .Strategic motor selection. Several factors are important when selecting a motor, including motor speed, horsepower, enclosure type, temperature rating, efficiency level, and quality of power supply. When selecting and purchasing a motor, it is also critical to consider the life cycle costs of that motor rather than just its initial purchase and installation costs. Up to 95% of a motor’s costs can be attributed to the energy it consumes over its lifetime, while only around 5% of a motor’s costs are typically attributed to its purchase, installation, and maintenance . Life cycle costing is an accounting framework that allows one to calculate the total costs of ownership for different investment options, which leads to a more sound evaluation of competing options in motor purchasing and repair or replacement decisions. A specific LCC guide has been developed for pump systems , which also provides an introduction to LCC for motor systems. The selection of energy-efficient motors can be an important strategy for reducing motor system life-cycle costs. Energy-efficient motors reduce energy losses through improved design, better materials, tighter tolerances, and improved manufacturing techniques. With proper installation, energy-efficient motors can also run cooler and have higher service factors, longer bearing life, longer insulation life, and less vibration.The choice of installing a premium efficiency motor strongly depends on motor operating conditions and the life cycle costs associated with the investment. In general, premium efficiency motors are most economically attractive when replacing motors with annual operation exceeding 2,000 hours/year. However, software tools such as MotorMaster+ can help identify attractive applications of premium efficiency motors based on the specific conditions at a given plant. Sometimes, even replacing an operating motor with a premium efficiency model may have a low payback period. According to data from the Copper Development Association, the upgrade to high-efficiency motors, as compared to motors that achieve the minimum efficiency as specified by EPACT, can have paybacks of less than 15 months for 50 hp motors . Payback times will vary based on size, load factor, running time, local energy costs, and available rebates and/or incentives . Given the quick payback time, it usually makes sense to by the most efficient motor available .NEMA and other organizations have created the Motor Decisions MatterSM campaign to help industrial and commercial customers evaluate their motor repair and replacement options, promote cost-effective applications of NEMA Premium® motors and “best practice” repair, and support the development of motor management plans before motors fail. At the Odwalla Juice Company’s facility in Dinuva, California, an IAC energy assessment found that the installation of more energy efficient motors would lead to $6,300 in annual cost savings with a simple payback period of only eight months . Similarly, in energy audits of seven fresh fruit and vegetable processing facilities in California, the installation of premium efficiency motors as motors wear out was expected to yield simple payback periods ranging from 0.7 to 1.6 years . Stahlbush Island Farms, a grower, canner, and freezer of fruits and vegetables in Corvalis, Oregon, also replaced targeted motors with higher efficiency models as motors wore out. The expected average payback period was estimated at 2.7 years . When all targeted motors are replaced over a 12-year period, the company expects to save 50,000 kWh of electricity per year and to cut their electricity bill by around $2,300 per year. In some cases, it may be cost-effective to rewind an existing energy efficient motor, instead of purchasing a new motor.