As markets remain tight, many mills look for ways to reduce costs. Rising costs for energy – mainly natural gas, electricity, and fuels – can have a significant impact on the profit margin of lumber manufacturers, which typically is about 3%-4%.
According to the U.S. Department of Energy, the price of natural gas for industrial use has more than doubled from 1997 to 2007, and electric energy prices have risen 40% during the same period. Both energy sources account for about a quarter of total energy consumption by the sawmill industry. Moreover, stumpage prices (cost of hardwood logs) historically have increased at a faster pace than lumber prices (Figure 1).
The forest products sector uses 12% of the total energy input for the U.S. manufacturing industry, according to the Department of Energy. This includes 5% that is consumed by the lumber manufacturing industry (hardwood and softwood sawmills). Sawmills consumed 127 trillion BTU in 2002. However, 63%-80% of the BTU was generated from wood residues, which is one of the great contributions of the industry to the overall energy needs in our country. In 2001, the industry spent $368 million for electricity and $128 million for fuels.
Factors Impacting Mill Energy Use
The amount of energy required by each process varies widely, but in a typical sawmill energy usage is distributed as shown in Figure 2. For a sawmill with kiln-drying operations, thermal energy is by far the largest part of the energy consumption.
The single most important component of energy in a sawmill that kiln-dries lumber is thermal energy. According to researchers, energy consumption of kiln-drying is usually 6 to 9 times more than that of a sawmill. And 43% of sawmills have drying operations, according to a national survey of hardwood lumber manufacturing operations.
One way to dramatically reduce energy in drying is to practice air-drying. For example, drying 1-inch-thick red oak from an initial moisture content of 80% (drying down to 7%) requires more than twice the energy input compared to an initial moisture content of 30%. (Figure 3). It is estimated that 55% of hardwood sawmills currently practice air-drying.
Figure 3 also illustrates the importance that sawing accuracy can have on energy usage during the drying process. For example, drying red oak lumber that is only 3/32-inch thicker than the target will require an additional 200,000 BTU per thousand board feet from 80% to 7% moisture content; thicker lumber requires more energy to dry. Implementing a thickness variation reduction program not only will increase lumber recovery but will reduce energy usage during drying.
The largest potential for energy savings is found in the operation, maintenance, and technology of dry kilns. A kiln with damaged insulation and-or a poorly maintained heat generation and transfer system may not reach set points easily; therefore, it will need more steam and take longer to complete the drying process.
Research has shown that variable speed fans can save up to 50% in energy use with a 20% percent reduction in fan speed once lumber drops below 30% moisture content. Heat recovery technologies present good opportunities for reducing energy, too. Two common options for heat recovery are conventional recuperation, where exit air heats incoming air in kilns, with savings of about 0.2 million BTU per thousand board feet; and flue gas condensation, where heat is recovered from the boiler flue gases, with savings of approximately 0.5 million BTU per thousand board feet.
In the sawmill an automated bin or sling sorter, for example, needs significantly more energy per output unit than manual sorting. A band head rig produces lumber with less sawing variation than a circular head rig, thus effectively reducing energy during drying. Pneumatic conveyors use more than 10 times the energy of electrical conveyors.
A substantial part of federal energy policy is the improvement of energy efficiency in manufacturing. Energy efficiency is the quantity of product that can be manufactured with a given amount of energy. Increased energy efficiency means savings in energy costs and compliance with energy and environmental regulations.
Table 1 lists some initiatives of the U.S. Department of Energy to improve energy efficiency in manufacturing facilities. The degree of adoption by the sawmill industry is also shown as percentage of surveyed facilities.
Free Energy Audits
Since 1978, the Department of Energy, through its Office of Energy Efficiency and Renewable Energy, has conducted free energy assessments to small and medium-sized qualified industries. To be eligible for an energy assessment, a manufacturing plant needs to meet certain criteria, such as less than $100 million in sales and 500 employees, and annual energy bills higher than $100,000 but lower than $2 million.
The objective of these assessments is to identify opportunities for energy savings. The office claims that implementing the recommendations from energy assessments can result in energy savings of 10% to 15%. During the assessments, experts spend three days in the plant, and there are follow-ups on the implementation (or not) of the recommendations. Participating plants implement an average of 53% of proposed improvements, and usually shorter payback periods and lower costs are favored.
Information gathered during energy assessments since 1980 (the program started in 1976) is contained in a database available at the program’s Web site. There are 13,822 assessments listed to date with more than 102,000 recommendations issued. Table 2 lists the top nine recommendations issued to sawmills, by frequency.
To determine your eligibility and-or get more information on the Save Energy Now Program, contact the Department of Energy or visit the Web site at: www1.eere.energy.gov/industry/saveenergynow/index.html.
Many utilities, state agencies and consulting firms also offer energy audits. Services can range from a simple walk-through to an investment-grade audit and may involve the hiring of consulting services. Check with your state government or state manufacturing extension program.
While all the energy saving ideas proposed in this article may not be suitable for all companies, I encourage you to look into ways to reduce energy. Many of the potential savings, such as those identified through energy audits, do not require capital to implement, and those that do often pay back in less than one year.
(Editor’s Note: Omar Espinoza is a graduate research assistant in the Virginia Tech Department of Wood Science and Forest Products.)
