Energy use in manufacturing

Industrial processes consume roughly 46 percent of world energy each year. In the United States, about 80 percent of that energy goes to the basic production industries of iron, steel, aluminum, paper, chemicals, and nonmetallic minerals (cement, brick, glass, and ceramics).

Background

The sophistication of a society’s technology can be judged by what it can make and how efficiently it can make those items. In ancient civilizations, and wood yielded to metal, fired pottery, and glass. Bronze and brass weapons swept aside stone. Then iron and steel replaced the softer metals.

Muscle power was sporadically aided by water power in antiquity, but the intensive use of water power began in Europe in the Middle Ages. Besides grinding flour, water mills supplied power for large-scale weaving, for sawmills, and for blowing air onto hot metal and hammering the finished metals. The gearing required to modify the motion and move it throughout a workshop also applied to wind power, and Dutch mills led manufacturing in the late Middle Ages.

A series of inventions led to James Watt’s improved steam engine in 1782. The immediate goal was pumping water out of coal mines, but steam engines also allowed factory power to be located anywhere. Steam-powered locomotives allowed materials to be more easily moved to those locations.

At the beginning of the twentieth century, small electric motors allowed a further decentralization of industry. A small shop required only a power cable, the necessary equipment, and a flick of a switch rather than a large engine and the inconvenient (often dangerous) belts used to transfer power to various pieces of equipment.

Energy efficiency and materials efficiency grow as technology evolves. Often, increased efficiency is simply a by-product of increased production or quality. Each doubling of cumulative production tends to drop production costs, including energy costs, by 20 percent. These improvements are connected to control of heat, control of motion, and the development of entirely new processes.

Heat

Heat is the greatest component of manufacturing energy use. Heat (or the removal of heat) involves the same issues that space conditioning of a home does. One can add more fuel or reduce losses through increased efficiency. Efficiency can be increased by having more insulation in the walls, a furnace that burns more completely, a furnace that uses exhaust gases to preheat air coming into it, a stove with a lighter rather than a pilot light, and controls that shut off heat to unused areas.

Manufacturing has the additional option of selling excess heat or buying low-grade heat for cogeneration. Often a manufacturing plant only needs low-grade heat of several hundred degrees for drying or curing materials. This heat production does not fully use the energy of the fuel. An electrical power plant running at 600° Celsius can generate electricity and then send its “waste heat” on to the industrial process.

A manufacturing plant also applies energy to materials, and in these processes there are many choices. Heat may be applied in an oven (large or small). Some energy may also be applied directly. For instance, oven curing of paint on car parts has been replaced by infrared (“heat lamp”) radiation for quicker production. Some high-performance aerospace alloys are heated by microwave radiation in vacuum chambers.

There are a variety of other energy-saving approaches. Automated process controls are a major energy saver. In chemical industries, separating materials by their different boiling points with distillation columns requires much less steam than other methods. Also, the continuous safety flames at refineries are being replaced by automated lighters.

Another energy-efficient technique is to combine processes. For instance, steelmaking often comprises three separate heating steps: refining into blocks of pig iron, refining that into steel, and then forming the steel into products, such as I beams or wire. An integrated steel mill heats the materials only once to make the finished product. A steel “minimill” tends to be smaller, uses expensive electricity, and goes only a short distance in the production process—from iron scrap to steel. On the other hand, the minimill is recycling a resource, thereby saving both energy and materials. The recycling of paper, plastics, and some metals typically requires one-half the energy needed to produce virgin materials. The fraction for aluminum is about one-fourth.

Motion

Cutting, grinding, pumping, moving, polishing, compressing, and many other processes control the motion of materials and of heat. They use less energy than heating, but they often represent the high-grade energy in electricity.

Eighty percent of the electricity used by industry is used for motors. Motors can be made efficient in many ways, including controllers that match power use to the actual load, metal cores that drop and take electric charges more easily, and windings with more turns of wire. Easing the tasks of industrial motors requires many disciplines. For example, fixing nitrogen into ammonia (NH₃) is typically done with streams of nitrogen and hydrogen passing over a catalyst. An improved catalyst pattern increases the reaction rate and thus decreases the hydrogen and nitrogen pumping. Automated controls again can control pumping, using it only where and when it is needed.

Reducing Energy Use

Several processes can reduce energy use. For example, a lower-pressure process for making polyethylene plastic uses one-fourth of the energy used in the previous process. Plastics have replaced energy-intensive metals in many commercial products. Silica in fiber-optic cables is replacing copper for communications. Composites, made with plastics and glass, metal, or other plastic fibers, not only require less energy to fabricate than all-metal materials but also have greater capabilities. Composites in railroad cars and airplanes reduce weight and thus energy costs of operation.

Vacuum deposition of metals, ceramics, and even diamond provide cheaply attained materials that multiply savings throughout industry. Diamond-edged machine tools operate significantly faster or longer before replacement. Rubidium-coated heat exchangers withstand sulfuric acid formed when the exhaust from the burning of high-sulfur coal drops below the boiling point, which allows both harnessing that lower heat and recovering the sulfur.

Other new processes have been contingent on developments in entirely new, even radical, fields. In Engines of Creation (1986), K. Eric Drexler discussed the concept of “nanotechnology,” proposing microscopic robots small enough to build or repair objects one molecule at a time. The “nanobytes” could manufacture items with unprecedented strength and lightness. Today, society already sees the benefits of the miniaturization of nanotechnology in areas such as the electronics industry. The continuing improvement in data storage and processing speed made possible by smaller parts is just one example. Genetic engineering reduces energy costs in the chemical industry. Parasitic bacteria on legumes (such as peanuts and soybeans) fix atmospheric nitrogen into chemicals the plants can use. Breeding similar bacteria for other crops can largely eliminate the need for ammonia fertilizer (and thereby decrease nitrate runoff).

Economics and Efficiency

Costs are the biggest factor affecting energy efficiency in manufacturing. When the price of was fixed by law at a low rate, for example, steam lines in some chemical plants had no insulation—it simply was not cost-effective to insulate.

Even after prices rise, there is often a long time lag. For example, the use of bigger pipes in a chemical plant means lower pumping costs, but the cost of installing big pipes is not justified when energy costs are low. When energy costs rise, new plants being built might use the larger pipes, but old plants might well run for many years before replacement or a major refit.

Similarly, highly efficient electrical motors are only about 15 to 25 percent more costly than conventional motors and are able to return the extra cost and start generating profit within three years. However, rebuilt conventional motors are available for one-third of the price of new motors. Thus, the investment in efficient new motors might not pay for itself for several additional years.

Finally, social and political factors affect the adoption of energy-efficient technologies. Government policies have often discouraged recycling by granting tax subsidies to raw materials production and establishing requirements for their use rather than recycled materials. Tax policies have not allowed enough depreciation to encourage long-term investments in energy efficiency.

Government policies and programs can lead the way to decreased energy use in manufacturing. In 2024, the Biden-Harris Administration announced that it would be working with the U.S. Department of Energy to provide roughly $430 million to accelerate the development of domestic clean-energy manufacturing in former coal communities. This funding was intended to address energy supply chain vulnerabilities while reducing the nation's carbon output.

Bibliography

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