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Best Practice Guide |
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Food and Beverage Growers and Processors |
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BoilersEnergy Use BasicsIn the food and beverage processing industry, steam and hot water account for more than half of all energy consumed. Steam is primarily used for process heat, and is important for sterilization, pasteurization, blanching, and evaporation. Most often, steam is generated onsite by a boiler system, which can also provide space heating and hot water for the building. If it is a high pressure steam boiler, adding a steam-powered extraction or backpressure turbine enables the boiler system to generate electricity, a process known as cogeneration or combined heat and power. Conversely, waste heat from on-site electricity generation via gas turbine or reciprocating engine can be captured and reused to heat or cool air or water, minimizing or eliminating entirely the need for boiler operations.
Boilers come in a wide variety of sizes, fuel sources, and designs. Once on site, each boiler system is uniquely configured to meet operational requirements and space capacity. Despite this variability in form, all boilers share a common function: to produce steam or hot water (thermal energy) by combusting fuel in an enclosed and pressurized tank. Boilers combust either fossil fuels or biomass fuels. Natural gas is the predominant fuel source, powering 78 percent of all industrial boilers and 56 percent of total U.S. industrial boiler capacity. Petroleum-based oil and coal are less common fossil fuel options. Biomass fuels are most common in facilities that have combustible by-products, such as wood and wood waste, industrial waste, fast-growing plant and tree materials, aquatic plants and algae, animal waste, organic municipal or agricultural crops and their residue. Choosing between boiler designs will often depend on which fuel source is most affordable and can be supplied reliably. A boiler is a major expense for any manufacturer. Typically, an industrial boiler system is installed for the life of the facility, even if plant operations or ownership change over time. Once in operation, utility costs quickly add up. As an illustration, let's suppose a food processor has an averaged-sized 20-MMBtu-per-hour natural gas-fired boiler that operates at full load 24-hours per day, 365 days per year (8760 hours). And let's say that the cost of natural gas is $10 per 1000 cubic feet (103ft3). 103ft3 is roughly the equivalent of 1 MMBtu, so a quick back-of-the-envelope calculation gives us an estimated annual energy cost: $10/103ft3 x 103ft3/1 MMBtu x 20 MMBtu/hour x 8760 hours/year = $1,752,000 per year. This is a very rough calculation that neglects several important variables, such as the energy content of natural gas, actual boiler loads, and hours of operation. The total cost of steam generated in a boiler system is more complex still, including variables such as the cost and temperature of boiler feedwater, water treatment, and fan power. For an in-depth look at the cost of steam generation, check out the DOE Technical Brief: How to Calculate the True Cost of Steam. Although it's not completely accurate, this simplified estimate is useful to illustrate how quickly energy costs add up. If this hypothetical owner improved boiler efficiency by even 5 percent, for example, more than $109,500 would be saved each year. To improve boiler efficiency and reduce operating costs, consider both proper maintenance and tuning, which extends the usable life of the system, and strategic equipment upgrades. In most cases, unless the boiler is very old, replacing a boiler is not a cost-effective option - boilers often last the life of the building. But if retiring an old boiler is an option, consider the many benefits of a combined heat and power system. Resources U.S. Department of Energy (DOE), Industrial Technologies Program. Improving Steam System Performance: A Sourcebook for Industry. This Sourcebook is designed to provide steam system users with a reference that describes the basic steam system components, outlines opportunities for energy and performance improvements, and discusses the benefits of a systems approach in identifying and implementing these improvement opportunities. Council of Industrial Boiler Owners (CIBO). CIBO Energy Efficiency Handbook. Burke, VA, 1998. The Energy Efficiency Handbook was pre-pared to help owner/operators get the best and most energy-efficient performance out of their boiler systems. This manual gives information and helpful operational tips on virtually every aspect of boiler operation, from Water Treatment, through Combustion and Heat Recovery, to Flue Gas Treatment and Cogeneration. Harrell, Greg, Ph.D., P.E. Steam System Survey Guide. Oak Ridge National Laboratory, May 2002. ORNL/TM-2001/262. This Steam System Survey Guide provides technical information for steam system operational personnel and plant energy managers on some of the major opportunities available to improve the energy efficiency and productivity of industrial steam systems. Northwest Food Processors Association Efficiency Practices and Emerging Technologies websites offer useful information and tips for the food processing industry. California Energy Commission websites on Food and Fiber Processing Technologies and Energy in Agriculture. Boiler System Guide. Pacific Gas and Electric webpage. Online, comprehensive information on purchasing, operating, and maintaining an efficient boiler. Steam System Assessment Tool. U.S. DOE, Industrial Technologies Program. Free, downloadable software that allows steam analysts to develop approximate models of real steam systems. Using these models, you can apply SSAT to quantify the magnitude-energy, cost, and emissions-savings-of key potential steam improvement opportunities. |