Overview of the U.S. Steam Industry

Benefits of Steam Uses U.S. Steam Market Energy-Intensive Industries Steam Generation Steam Distribution Steam End Use Condensate Recovery Steam Application Examples Hospital Market References cited in this document This document was last modified on 1/5/2006.

Benefits of Steam Uses

Steam has come a long way from its traditional associations with locomotives and the Industrial Revolution. Steam today is an integral and essential part of modern technology. Without it, our food, textile, chemical, medical, power, heating and transport industries could not exist nor perform as they do.

Steam provides a means of transporting controllable amounts of energy from a central, automated boiler house, where it can be efficiently and economically generated, to the point of use. Therefore as steam moves around a plant it can equally be considered to be the transport and provision of energy.

Steam has many performance advantages that make it an indispensable means of delivering energy. These advantages include low toxicity, ease of transportability, high efficiency, high heat capacity, and low cost with respect to the other alternatives. Steam holds a significant amount of energy on a unit mass basis (between 1,000 and 1,250 Btu/lb) that can be extracted as mechanical work through a turbine or as heat for process use. Since most of the heat content of steam is stored as latent heat, large quantities of heat can be transferred efficiently at a constant temperature, which is a useful attribute in many heating applications.

Steam offers several inherent advantages including:

• Water is readily available
• Water is inexpensive
• Steam is clean
• Steam is relatively safe
• Steam has a high heat content
• Steam gives up its heat at a constant temperature
• Steam is easy to control due relationship between temperature and pressure

Based on these advantages and the following factors below, steam is one of the most widely used commodities for conveying heat energy:

• Efficient and economic to generate
• Can distributed easily and cost effectively to the point of use
• Easy to control
• Easily transferred to the process
• The modern steam plant is easy to manage

Steam is efficient and economic to generate

Water is plentiful and inexpensive. It is non-hazardous to health and environmentally sound. In its gaseous form, it is a safe and efficient energy carrier. Steam can hold five or six times as much potential energy as an equivalent mass of water.

When water is heated in a boiler, it begins to absorb energy. Depending on the pressure in the boiler, the water will evaporate at a certain temperature to form steam. The steam contains a large quantity of stored energy that will eventually be transferred to the process or the space to be heated.

It can be generated at high pressures to achieve high steam temperatures—the higher the pressure, the higher the temperature. More heat energy is contained within high temperature steam so its potential to do work is greater.

• Modern shell boilers are compact and efficient in their design, using multiple passes and efficient burner technology to transfer a very high proportion of the energy contained in the fuel to the water, with minimum emissions.
• Boiler fuel may be chosen from a variety of options, including combustible waste, which makes the steam boiler an environmentally sound option among the choices available. A centralized boiler plant can take advantage of low interruptible gas tariffs, because any suitable standby fuel can be stored for use when the gas supply is interrupted.
• Highly effective heat recovery systems can virtually eliminate blow down costs, return valuable condensate to the boiler plant and add to the overall efficiency of the steam and condensate loop.

Steam can distributed easily and cost effectively to the point of use

Steam is one of the most widely used media to convey heat over distances. Because steam flows in response to the pressure drop along the line, expensive circulating pumps are not needed.

Due to the high heat content of steam, only relatively small-bore piping is required to distribute the steam at high pressure. The pressure is then reduced at the point of use, if necessary. This arrangement makes installation easier and less expensive than for some other heat transfer fluids.

Overall, the lower capital and running costs of steam generation, distribution and condensate return systems mean that many users choose to install new steam systems in preference to other energy media, such as gas fired, hot water, electric and thermal oil systems.

Steam is easy to control

Because of the direct relationship between the pressure and temperature of saturated steam, the amount of energy input to the process is easy to control, simply by controlling the saturated steam pressure. Modern steam controls are designed to respond very rapidly to process changes.

Energy is easily transferred to the process

Steam provides excellent heat transfer. When the steam reaches the plant, the condensation process efficiently transfers the heat to the product being heated.

Steam can surround or be injected into the product being heated. It can fill any space at a uniform temperature and will supply heat by condensing at a constant temperature; this eliminates temperature gradients which may be found along any heat transfer surface—a problem which is so often a feature of high temperature oils or hot water heating, and may result in quality problems, such as distortion of materials being dried.

Because the heat transfer properties of steam are so high, the required heat transfer area is relatively small. This enables the use of more compact plant, which is easier to install and takes up less space in the plant. A modern packaged unit for steam heated hot water, rated to 1200 kW and incorporating a steam plate heat exchanger and all the controls, requires only 0.7 m2 floor space. In comparison, a packaged unit incorporating a shell and tube heat exchanger would typically cover an area of two to three times that size.

The modern steam plant is easy to manage

Increasingly, industrial energy users are looking to maximize energy efficiency and minimize production costs and overheads. The Kyoto Agreement for climate protection is a major external influence driving the energy efficiency trend. In addition, the organization with the lowest costs can often achieve an important advantage over rivals. Production costs can mean the difference between survival and failure in the marketplace.

Ways of increasing energy efficiency include monitoring and charging energy consumption to relevant departments. This builds an awareness of costs and focuses management on meeting targets. Variable overhead costs can also be minimized by ensuring planned, systematic maintenance; this will maximize process efficiency, improve quality and cut downtime.

Most steam controls are able to interface with modern networked instrumentation and control systems to allow centralized control, such as a Building/Energy Management System.

With proper maintenance a steam plant will last for many years, and the condition of many aspects of the system is easy to monitor on an automatic basis. When compared with other systems, the planned management and monitoring of steam traps is easy to achieve with a trap monitoring system, where any leaks or blockages are automatically pinpointed and immediately brought to the attention of the engineer.

This can be contrasted with the costly equipment required for gas leak monitoring, or the time-consuming manual monitoring associated with oil or water systems.

In addition to this, when a steam system requires maintenance, the relevant part of the system is easy to isolate and can drain rapidly, meaning that repairs may be carried out quickly.

Studies have shown have shown that it is far less expensive to bring a long established steam plant up to date with sophisticated control and monitoring systems, than to replace it with an alternative method of energy provision, such as a decentralized gas system.

Todays state-of-the-art technology is a far cry from the traditional perception of steam as the stuff of steam engines and the Industrial Revolution. Indeed, steam is the preferred choice for industry today. Name any well known consumer brand, and in nine cases out of ten, steam will have played an important part in production.

Steam is flexible

Not only is steam an excellent carrier of heat, it is also sterile, and thus popular for process use in the food, pharmaceutical and health industries. It is also widely used in hospitals for sterilization purposes.

The industries that use steam range from huge oil and petrochemical plants to small local laundries. Further uses include the production of paper, textiles, brewing, food production, curing rubber, and heating and humidification of buildings.

Many users find it convenient to use steam as the same working fluid for both space heating and for process applications. For example, in the brewing industry, steam is used in a variety of ways during different stages of the process, from direct injection to coil heating.

Steam is also intrinsically safe—it cannot cause sparks and presents no fire risk. Many petrochemical plants utilize steam fire-extinguishing systems. It is therefore ideal for use in hazardous areas or explosive atmospheres.

Other methods of distributing energy

The alternatives to steam include water and thermal fluids such as high temperature oil. Each method has its advantages and disadvantages, and will be best suited to certain applications or temperature bands.

Compared to steam, water has a lower potential to carry heat, consequently large amounts of water must be pumped around the system to satisfy process or space heating requirements. However, water is popular for general space heating applications and for low temperature processes (up to 120°C) where some temperature variation can be tolerated.

Thermal fluids, such as mineral oils, may be used where high temperatures (up to 400°C) are required, but where steam cannot be used. An example would include the heating of certain chemicals in batch processes. However thermal fluids are expensive, and need replacing every few years—they are not suited to large systems. They are also very 'searching' and high quality connections and joints are essential to avoid leakage.

Broadly speaking, for commercial heating and ventilation, and industrial systems, steam remains the most practical and economic choice.

Go to top

U.S. Steam Market

The U.S. industry uses a lot of steam. In 1995, U.S. manufacturers consumed roughly 16.55 quadrillion Btu (quads) of energy for heat, power, and electricity generation [1]. According to the Council of Industrial Boiler Owners, approximately 66% of all the fuel burned by these companies is consumed to raise steam [2]. The U.S. manufacturing economy depends on over 54,000 large boilers to produce steam for process use. It is also a power source for equipment, as well as for building heat and electricity generation. But steam is not free. It costs approximately $21 billion (1995 dollars) annually to feed the boilers generating the steam [3]. Each year U.S. industry also releases approximately 196 million metric tons of carbon dioxide while producing steam [4]. These emissions represent over 40% of all U.S. industrial emissions of carbon dioxide.

Total demand for steam is projected to increase 20 percent in five major industries by 2015 (compared to 1990 levels), with demand in food processing and chemicals being even greater. Industrial requirements for steam are increasing most rapidly in the "other" category, which includes rubber, plastics, industrial machinery, and transportation equipment (See Figure 1).

Many manufacturing facilities can recapture energy through the installation of more efficient steam equipment and processes. A typical industrial facility can realize steam savings of 20% by improving their steam system. If steam system improvements were adopted industry-wide, the benefits would be $4.0 billion in fuel cost reductions and 32 million metric tons of emission reductions.

The whole steam system must be considered for improvements to best pursue reducing operating costs. Upstream inefficiencies will affect process heating and cost of producing steam; while downstream inefficiencies (leaks, bad traps, poor load control) can also affect process heating and have severe effects on the boiler and cost of producing steam. Example opportunities for savings are found in:

• Steam Generation through cogeneration applications, boiler controls, and water treatment;
• Steam Distribution through checking steam leaks, installing insulation and proper steam trap maintenance;
• Steam End Use through heat exchanger maintenance;
• Steam Recovery through condensate return.

Go to top

Energy-Intensive Industries

Aluminum, metal casting, glass, steel, petroleum, chemicals, and forest products are among the most energy and waste intensive industries in the U.S. The proportion of total energy used for steam was especially high in forest products, chemicals, petroleum refining, and steel (See Figure 2). These major energy-using sectors account for about 80% of U.S. manufacturing energy use.

Industries are characterized using data collected by the Bureau of the Census from establishments (plants) that are classified in a particular industry based on the value of the production of the plant and the industry that is identified as the origin of that product. This classification system, known as the Standard Industrial Classification (SIC), is being superseded by the North American Industry Classification System (NAICS). In addition to economic information collected by the Census, energy consumption is collected for the Energy Information Administration in the Manufacturing Energy Consumption Survey (MECS). According to the 1994 MECS, the most energy-intensive industries were, in descending order, Petroleum and Coal Products (NAICS 324); Paper and Allied Products (321); Chemicals and Allied Products (325); Primary Metals (331); and Stone, Clay and Glass Products (327). The range of intensity of these industries is from 44.3 to 13.3 thousand Btu per dollar of output (TBtu/$). A brief description of these most energy-intensive industries follows.

Petroleum and Coal Products. The major activity in this industry is converting crude petroleum into the petroleum products widely used in our economy—gasoline, diesel, fuel oil and lubricants. The process is a complex one of first separating the crude into different products, then recombining these components into the desired products. The separation is done through distillation and cracking that requires high temperatures and pressures, and is affected by the density of the original crude. Environmental considerations have greatly increased the complexity of this process, as reformulated and oxygenated fuels are increasingly needed to assure clean air quality. Another factor that has made for increased energy use in this industry is the declining availability of light crude and the greater processing requirements for heavy crude. Petroleum refining is the most energy-intensive industry with an intensity of 44.3 TBtu/$.

Paper and Allied Products. This industry converts fiber, usually from wood, into paper, pulp or paperboard, and then into a variety of products. The process begins with wood, which is first debarked and chipped, then either mechanically or chemically reduced to a slurry that is bleached, then formed into pulp, paper, or board. Though paper-making is a very energy-intensive process, much of the energy used is derived from the biomass that is the basic feed stock for the process. The Forest Products Vision process combines this industry with wood products manufacturing, which includes saw mills, plywood mills and engineered wood products. In 1994, energy intensity was 18.5 TBtu/$.

Chemical and Allied Products. The major segments of this industry are basic chemicals; resins, synthetic rubber and manmade fibers; pesticides, fertilizer and other agricultural chemicals; pharmaceuticals and medicines; paints, coatings, sealants and adhesives; soap, cleaning compounds and toilet preparations; and other chemical products. Basic chemical production includes petrochemicals, industrial gases, and other inorganic chemicals, and other organic chemical manufacture. Basic chemical production uses the bulk of the energy required by this industry and creates the largest volume of products. In all of chemical manufacturing, heat and pressure are used to separate and combine chemical building blocks into saleable products, either for final consumers or to other manufacturing. In 1994, energy intensity was 16.0 TBtu/$. When only basic chemicals are considered, the intensity is about twice as high.

Primary Metals. This industry includes the production of iron and steel (a Vision industry), aluminum (another Vision industry), and a variety of non-ferrous metals—lead, copper and zinc are the most important. The production of iron and steel falls into three sub-industries. Integrated producers transform iron ore into pig iron, then convert this to steel. The refined steel is cast or rolled into primary products such as sheet, bars, and billets. Specialty steel producers convert pig iron or steel into special products such as stainless and other alloy steels. Mini-mills produce primary steel products from scrap steel, usually in an electric arc furnace. Aluminum producers convert alumina (aluminum oxide) into aluminum metal using an electrolytic process. The major producers also convert ore, usually bauxite, into alumina, but that operation falls within the chemical industry classification. The intensity of this industry in 1994 was 15.3 TBtu/$.

Stone, Clay and Glass Products. "Nonmetallic Mineral Products," under NAICS, includes cement, glass (a Vision Industry), bricks, lime, and other stone and ceramic products. Pyro-processing, or the application of heat to assure a chemical reaction, is required in most of these subindustries, which is what makes them so energy-intensive. Cement and lime are formed at high temperatures in a kiln; glass is produced by melting silica sand; bricks, china and pottery are just clay until fired. The intensity of this industry is 13.3 TBtu/$.

Go to top

Steam Generation

Steam generation systems can generally be classified into two principal types: fired boiler systems and waste heat systems. The primary purpose of an effective steam generation system is to produce steam under the conditions—flow rates and pressures—required for the system end-use requirements. It is important to generate the steam at the highest possible generator efficiency. It is equally important that high-quality (dry) steam be produced; transmission of wet steam to the distribution system can lead to water hammer and also to inefficiencies in the end use of the steam produced.

Key components include the boiler itself, boiler system components including controls, valves piping and meters, water treatment equipment, economizers, and deaerators.

Key Inputs and Outputs

Key inputs include boiler feed water, hot condensate returned, water treatment chemicals and air/oxygen input. Key outputs include steam mass flow rate, steam pressure, steam quality, combustion gas conditions.

Opportunities for Improvements

• Determine the efficiency of your steam generation system (based on steam output/fuel input).
• Determine how much steam you use, and how much it costs to generate this steam. Steam generation needs to be measured with accurate, well maintained and calibrated flow measurement devices and reconciled by a rigorous steam balance. The steam balance should be done on a regular basis to confirm that the flow measurements are good.
• Optimize excess air in your boiler to increase steam generation efficiency. An often stated rule of thumb is that boiler efficiency can be increased by 1% for each 15% reduction in excess air or 40°F reduction in stack gas temperature. Good measurements of fuel flow and air flows are required to do this as well as good stack gas analysis.
• Maintain clean fire-side and water-side boiler heat transfer surfaces. A good deposit control program is necessary to do this.
• Optimize boiler blowdown to reduce Total Dissolved Solids (TDS) in the boiler system. Work closely with your boiler feed water additives vendor to do this.
• Optimize your boiler control system to optimize steam generation efficiency. Before you do this, make sure that the logic diagrams actually reflect what is wired into the system and that all the components of this system make sense and work.
• Ensure that an effective water treatment system is in place. Two approaches are available—mechanical treatment (i.e., deareation) or chemical treatment. Water treatment is an important aspect of boiler operation that can affect efficiency or result in plant damage if neglected. For instance, without proper water treatment, scale can form on boiler tubes, reducing heat transfer and causing a loss of boiler efficiency of as much as 10-12% [8]. Water treatment represents a substantial portion of overall boiler operating costs.

Go to top

Steam Distribution

The primary purpose of an effective steam distribution system is to link the output of the steam generation system to the steam end use equipment. The distribution system should supply high-quality steam to the end use equipment at the required rate and pressure, and with the minimum heat loss.

Key components include steam distribution piping, valves, and flanges, distribution system insulation, steam traps, air vents, drip legs, and strainers.

Key Inputs and Outputs

Key inputs include steam conditions (pressure and quality) from the generation system. Key outputs include steam distribution outlet mass flow and pressure, distribution outlet steam quality.

Opportunities for Improvements

• Properly select, size, and maintain your distribution system steam traps.
• Insulate all distribution system pipes, flanges, and valves.
• Ensure that steam mains are properly laid out, sized, adequately drained, and adequately air vented.
• Ensure that steam distribution system piping is correctly sized to produce the appropriate system pressure drops.
• Ensure that distribution system piping is adequately supported, guided, and anchored, and that appropriate allowances are made for pipe expansion at operating temperatures.

Go to top

Steam End Use

The primary purpose of the steam end use system is to maximize the effective use and heat content of the steam transmitted to the end use equipment.

Key components include a variety of end use equipment, including heat exchangers, unit heaters, and other process-specific steam use equipment. Other key components include steam trap systems to drain hot condensate from the end use equipment and piping to transmit steam through the end use equipment and hot condensate out of the end use equipment.

Key Inputs and Outputs

Key inputs include steam conditions (pressure and quality) from the distribution system and process inputs. Key outputs include product produced, steam and hot condensate resulting from specific end use applications.

Opportunities for Improvements

• Understand how much steam is used per unit of product produced. You can use this information to compare with other information—within your company and by your competition—to determine where there might be opportunities for improvement of your steam operations.
• Select, size, and maintain steam traps for specific end use applications.
• Blowdown of non-condensables from condensing equipment is critical. If non-condensables are not removed from condensing applications, the condensing equipment will quickly cease to function. The rule of thumb is that for every 1% of non-condensables there is in steam, the heat transfer coefficient decreases by 10%.

Go to top

Condensate Recovery

The primary purpose of an effective condensate recovery system is to make the most effective use of all remaining steam and hot condensate energy after process use.

Key components include hot condensate return piping, flash tanks, and condensate pumps.

Key Inputs and Outputs

Key inputs include hot condensate from the end use system. Key outputs include hot condensate returned to the generation system and low-pressure steam transmitted to applications that can use it.

The low pressure steam component will consist of flash from the condensate receiver (or steam trap) plus blow-through steam that accompanies the hot condensate.

Opportunities for Improvements

• Recovering hot condensate for reuse as boiler feed water is important way to improve efficiency of the steam system. The energy use used to heat cold makeup water is a major part of the heat delivered for use by the steam system, requiring an additional 15-18% of boiler energy for each pound of cold makeup water [7].
• Ensure that the condensate piping is adequately sized. Condensate piping has to accommodate two-phase flow B liquid and vapor. The vapor portion of the hot condensate stream is more voluminous than the liquid portion. In general, condensate piping must be sized to handle the flash and blow-through steam rather than just the liquid portion. Condensate piping that is sized for the liquid portion only will be grossly undersized.
• Ensure that your condensate return piping, flanges, and valves are properly insulated.
• Identify if it is possible to return hot condensate to a flash recovery system, so that you can use the flash steam to supplement low-pressure steam needs.

Go to top

Steam Application Examples

Industries and Processes

A common misperception today is "steam is going away and being replaced by hot water." While it is true that many steam heating applications are being replaced by hot water applications, steam is still widely used. The tables below summarize industries where steam is still being used.

In addition, steam use is especially significant in various industries designated as "Industries of the Future" by the U.S. Department of Energy that includes agriculture, aluminum, chemicals, forest products, glass, metal casting, mining, petroleum refining, and steel. For example, in 1994, the pulp and paper industry used approximately 2,197 trillion Btu of energy to generate steam, accounting for about 83 percent of the total energy used by this industry. The chemicals industry used approximately 1,855 trillion Btu of energy to generate steam, which represents about 57 percent of the total energy used in this industry. The petroleum refining industry used about 1,373 trillion Btus of energy to generate steam, which accounts for about 42 percent of this industrys total energy use.

Major Users of Steam:

• Food and Drinks
• Pharmaceuticals
• Oil Refining
• Chemicals
• Plastics
• Pulp and Paper
• Sugar Refining
• Textiles
• Metal Processing
• Rubber and Tires
• Shipbuilding
• Power Generation

Moderate Users of Steam:

• Heating
• Cooking
• Curing
• Chilling
• Fermenting
• Treating
• Cleaning
• Melting
• Baking
• Drying

Specific Examples

Below is a partial list of specific applications where steam is used today.

• Shrink-wrapping meat.
• Depressing the caps on food jars.
• Exploding corn to make cornflakes.
• Dyeing tennis balls.
• Keeping chocolate soft, so it can be pumped and molded.
• Making bottles look attractive but safe, for example tamper-proof, by heat shrinking a film wrapper.
• Drying glue (heating both glue and materials to dry on a roll).
• Making condoms.
• Making bubble wrap.
• Peeling potatoes (High-pressure steam is injected into a vessel full of potatoes then it is quickly depressurized, drawing the skins off).
• Heating swimming pools.
• Making instant coffee, milk or cocoa powder.
• Molding tires.
• Ironing clothes.
• Making carpets.
• Corrugating cardboard.
• Ensuring a high quality paint finish on cars.
• Washing milk bottles.
• Washing beer kegs.
• Drying paper.
• Ensuring medicines and medical equipment are sterile.
• Cooking potato chips.
• Sterilization.
• Cooking large vats of food by direct injection or jacket heating.

Go to top

Hospital Market

The following articles relate to modern steam application in today's hospitals. Articles are cited from newspapers or other sources and have been reproduced into an Adobe PDF document. Adobe Reader is required to view PDF documents.

• Hospital Building Booms in the ’Burbs
• Hospitals Go Where The Money Is
• Building Surge Results In Smarter Hospitals

Go to top

References

1. U.S. Department of Energy, Energy Information Administration. Manufacturing Energy Consumption Survey: 1991 and Monthly Energy Review: January 1997. Total input of energy for heat, power and electricity generation for U.S. manufacturing was 15.027 quads in 1991. Total industrial consumption of coal, natural gas, and oil was 19.277 quads in 1991. This ratio multiplied by 1995 total industrial consumption of coal, oil and natural gas for 1995 gives an estimate for total input of energy for heat power and electricity generation.
2. Council of Industrial Boiler Owners. 1993. CIBO NoxRACT Guidance Document, page 5 states, "...approximately two-thirds of all fuel burned by Unites Sates industry is consumed to raise steam." Multiplied 16.55 quads [1] by 67% to get steam energy consumption estimate of 9.34 quads.
3. U.S. Department of Energy, Energy Information Administration. Monthly Energy Review: 1997. Based on following fuel prices: $1.318/mbtu coal, $2.679/mbtu oil, and $1.984/mbtu natural gas. These fuel prices were multiplied by industrial steam use by fuel type for 1995.
4. U.S. Department of Energy, Energy Information Administration. 1993. Emissions of Greenhouse Gases in the United States 1985-1990. Table B-3. Subtracted 1991 CO2 total for electricity from CO2 total for all industry and multipled by steam energy ratio to arrive at steam CO2 emissions of 196 million metric tons in 1995.
5. Gas Research Institute. 1996. Sector Summary: Industrial Sector. Page 3.
6. G. Varga, U.S. DOE. 1997. Presentation to the Steam Power Partnership, January 16, 1997.
7. U.S. Department of Energy. Steam Digest: 2000. Steam Partnership: Improving Steam System Efficiency Through Marketplace Partnerships. Page 9.
8. U.S. Department of Energy. Steam Digest: 2000. Steam Partnership: Improving Steam System Efficiency Through Marketplace Partnerships. Pages 8-9.

Go to top

For more information, see the U.S. Department of Energy website.