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Energy consumption and efficiency of Appalachian hardwood sawmills.

Abstract

A study of energy consumption and efficiency for Appalachian

hardwood sawmills was conducted in the Appalachian region. Primary data

were collected through a mail survey on sawmills in the region in 2010,

while secondary data were obtained from site audits at 17 sawmills over

the last 10 years in West Virginia. The results from the mail survey

showed that hardwood lumber production volume ranged from 700 to 600,000

board feet (BF) per wk, and monthly electricity consumption per mill

averaged 220 kWh per thousand board feet (MBF) with an average electric

bill of $17.78/MBF/mo. The energy audit results indicated that hardwood

lumber production volume ranged from 4,250 to 400,000 MBF/y, and the

energy use and total cost per thousand board feet of lumber production

averaged 160.89 kWh/MBF and $10.04/MBF, respectively. The average

marginal cost for all energy audits was $17.87/MMBtu (6.10[cents]/kWh).

The annual carbon dioxide emission conserved was 587,045 pounds per

mill. On average, engineers on site visits proposed changes that could

save approximately 14.89 percent of the annual energy used. The results

presented in this article provide energy profiles for Appalachian

hardwood sawmills and reveal some potential techniques for reducing

energy consumption.

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The US hardwood sawmills at one time produced over 13 billion board

feet (BF) of lumber per year valued at $8 billion (Bowe et al. 2001).

Owing in part to the globalization of forest products market and the

slowing domestic housing market, sawmills are experiencing low demand

and falling profits. Hardwood lumber production in the United States has

fallen 25 percent since 2000 (Parhizkar et al. 2009). In the Appalachian

region, hardwood production has declined by more than 40 percent

(Luppold 2009, Wang et al. 2010). This is especially true during the US

financial and economic crisis of 2008 and 2009, which caused devastating

effects on the hardwood industry in the region.

To survive under the current difficult economic and market

conditions, hardwood sawmills must improve their sawmilling efficiency,

search for new markets, and reduce manufacturing costs. Lumber

production efficiency has always been a major concern to Appalachian

hardwood sawmills. Recently, cost-saving consideration through energy

conservation has gained much attention (Gopalakrishnan et al. 2003,

Mardikar 2007).

Hardwood production is very energy intensive. Energy use by the

lumber manufacturing industry accounts for 5 percent of the total energy

input in the US manufacturing industry (Bond 2008). In 2001, the lumber

manufacturing industry spent $368 million for electricity and $128

million for fuels (Bond 2008). A typical hardwood sawmill usually

consists of five main operations including log debarking, log sawing,

flitch edging and trimming, side-cuts chipping, and lumber drying. If a

sawmill produces only rough green lumber and has no kiln-drying

facility, electricity will be the primary energy consumed; otherwise

steam or combustion heat will be the most important component of energy

use. Kiln drying is the most energy intensive process in the production

of surfaced dry lumber, which uses six to nine times more energy than

the sawmilling operation itself (Wengert and Meyer 1992).

Energy costs can be a significant component of operating costs in a

lumber manufacturing industry (Gopalakrishnan et al. 2003). Energy costs

in a typical sawmill facility can vary between 1 and 10 percent of the

total operating costs (Mardikar 2007). In the past, energy cost did not

represent a large portion of total costs. However, today more attention

is being given to energy consumption as energy prices rise (Mate 2002).

Increasing energy costs have a significant impact on the profit margin

of lumber production, which is typically about 3 to 4 percent of the

total cost (Bond 2008). Both natural gas and electricity energy sources

occupied about 25 percent of total energy consumption by the sawmill

industry (Bond 2008). Energy waste in sawmills is becoming more and more

expensive, which is likely to increase operation costs.

The Appalachian region is one of the most important hardwood lumber

producing regions, supplying 68 percent of the eastern hardwood

sawtimber (Luppold 1995). Besides the challenge from globalization,

hardwood sawmills in the region have to deal with issues such as

increasing energy and fuel costs, log and logger availability, low-grade

timber, increased stumpage costs, and low demand from the domestic

housing market (Buehlmann et al. 2007). A better understanding of the

current energy consumption and efficiency will help the Appalachian

hardwood sawmills find effective ways of reducing energy consumption and

cost and thus increasing their competitiveness in the global forest

products market.

The objective of this study was to examine the energy consumption

and efficiency in Appalachian hardwood sawmills, particularly in the

state of West Virginia. Specifically, this study (1) assesses the energy

consumption of Appalachian hardwood sawmills, (2) provides

recommendations to sawmills regarding effective ways of reducing both

energy consumption and costs, and (3) determines energy conservation

opportunities by analyzing energy assessments.

Methods

Current profile of Appalachian sawmills

A formal mail survey of Appalachian hardwood sawmills was conducted

during the summer and fall of2010 to gather general energy consumption

and efficiency information. The survey design was based on

Dillman’s tailored design method (Dillman 2000). The mailing lists

of the Appalachian hardwood sawmills were obtained from the National

Hardwood Lumber Association (NHLA 2008), the Appalachian Regional

Commission (ARC 2009), and other state agencies. The 776 firms

identified as hardwood sawmills in the Appalachian region were selected

as the sample population. A total of 238 responses were received, of

which 58 surveys were usable. The responses included 21 from

Pennsylvania, 16 from West Virginia, 8 from Ohio, 6 from New York, and 7

from other states including Connecticut, Maryland, Missouri, and South

Carolina. The questions were designed to determine the monthly cost of

electric and gas bills, the efficiency of electric motors used along

with the percentage of total motors that were highly efficient, number

and type of air compressors, number of dry kilns, kiln capacity, type of

fuel used, and monthly electricity and natural gas consumption. The

survey also asked if any energy-efficient upgrades were going to be made

in the near future. Returned surveys were examined for completeness and

usability and were then entered into Excel spreadsheets and analyzed

using SAS.

Mill specific energy audits

In addition to the formal mail survey of sawmills in the central

Appalachian region, data were collected during intensive energy audits

at 17 hardwood sawmills in West Virginia by the Industrial Assessment

Center at West Virginia University. The intensive assessments included a

complete audit of all energy use at the participating mills. Information

such as electrical consumption, hours of operation, and load factor were

measured on major energy-consuming equipment at each mill. Recording

devices, including power analyzers, digital stroboscopes, and

temperature guns, were used in the data collection process. Motor Master

Software was used to analyze the energy data, especially for electrical

motors (Mate 2002, Gopalakrishnan et al. 2005). The audits helped to

define energy conservation practices that could be implemented over a

10-year period and the estimated cost savings that would occur given

these changes. Based on the audit data, energy conservation

opportunities and recommendations defined by these assessments were

summarized so that the results could be used to help sawmills better

understand their energy use.

Results and Discussion

Profile of Appalachian sawmills

Among the respondents, 74.1 percent reported being a single

facility, 25.9 percent had multiple facilities, and 89 percent used one

shift per week. The number of employees per mill averaged 30, with an

average weekly lumber production of 145,610 BF. In small sawmills

(200,000 BF/wk) were by far the most

efficient, with a per employee production of 5,145 BF/wk, which may be

attributed to the application of advanced automation technology and

better management at large sawmills. On average, the operation hours per

mill were 2,132 hours in 2010. Average residue production among the

respondents was 139.2 tons/wk for chips and 81.1 tons/wk for sawdust

(Table 1). When asked whether they have plans to upgrade their mills in

2011 to make them more energy efficient, 18.8 percent of the respondents

answered “Yes.”

Most respondents used electricity as the main energy resource; very

few used natural gas. Electricity consumption per month per mill

averaged 107,007 kWh, and the average electric bill was $9,278/mo;

therefore, the average electric cost rate was $0.0867/kWh. Based on

lumber production volume, the monthly electricity consumption per mill

ranged from 31 kWh per thousand board feet (MBF) to 588 kWh/MBF and

averaged 220 kWh/MBF. The monthly electric bill ranged from $2 to $41.67

per MBF with an average of $17.78/MBF.

Major energy systems

Motor systems.–Electric motors are frequently used by hardwood

sawmills in the Appalachian region and are the major

electricity-consuming units. The federal government, in conjunction with

energy utilities, has focused on increasing the use of highly efficient

motors (Dunning and Ward 1998). About 38, 45, and 17 percent of the

respondents ran electric motors at 80 to 90 percent, 91 to 94 percent,

and 95 percent or more efficiency, respectively. As evidenced by the

survey data, more attention needs to be paid to electric motor

efficiency. By increasing efficiency, the cost of the motor system is

reduced, leading to an overall increase in energy efficiency at

sawmills. Several methods can be used by hardwood sawmills to reduce the

cost of motor systems, such as switching motors off when they are idle,

keeping balance between maintenance and production, and selecting

suitable motor size. In addition, a motor management system can be used

to aid in improvement of energy consumption and efficiency by

documenting motor inventory and analyzing various energy conservation

opportunities.

Lighting systems.–Lighting systems are often overlooked as a way

to save energy. Different lighting systems may have different

efficiencies. As indicated by Wengert and Meyer (1992), the efficiency

of incandescent, fluorescent, mercury vapor, and sodium was 10, 20, 24,

33 percent, respectively. In these surveys, about 54 and 13 percent of

the respondents used the relatively less-efficient fluorescent lighting

and incandescent bulbs, respectively. Thirty-three percent of the

respondents used both lighting systems. Electric energy savings could be

achieved in sawmills through the use of more energy-efficient lighting

system, such as mercury vapor lamps or high-pressure sodium lamps.

Air compressor systems.–Compressed air plays important roles in

many automated processes in a typical hardwood sawmill. Wengert and

Meyer (1992) pointed out that the most inefficient use of electrical

energy is in compressing air at sawmills. About 40 and 50 percent of the

responding sawmills used conventional air compressors and

high-efficiency screw drive air compressors, respectively. An additional

10 percent of the respondents used both types of air compressors. Screw

drive air compressors can create a much larger volume of air while using

far less energy, thus making them substantially more energy efficient

(Elliot 2006). Respondents’ concern over effects of energy cost

indicates that air leakage was also a major problem. Identifying and

preventing air leaks can help reduce electricity consumption.

Kiln-drying systems.–Rough green lumber sawn from hardwood logs is

usually dried in conventional dry kilns using wood and fossil fuels as

heat sources (Denig et al. 2000). Kiln drying lumber is an energy

intensive process that can consume up to 60 to 70 percent of the total

energy needed to manufacture lumber (Breiner et al. 1987, Simpson 1991).

Respondents who used kilns owned five dry kilns on average. The average

capacity of all dry kilns was 4,521 MBF/y per mill. The electricity used

in kilns averaged 29,775 kWh/mo per mill, with an average monthly

electricity bill of $3,417. Based on the volume of lumber dried,

electricity consumption in kilns averaged 114 kWh/ MBF/mo per mill, with

an average monthly electricity bill of $16.08/MBF. It is noted that

sawmills produce a large amount of wood residues during the production

of lumber and other wood products from saw logs. Some large mills are

already burning their wood residues in boilers to produce heat for their

kiln dryers. For those responding sawmills that need to dry lumber, the

average monthly residue consumption was approximately 467 tons. Many

energy saving opportunities exist in kiln drying, such as predrying and

regular maintenance.

Energy conservation opportunities defined in energy audits

Mill manufacturers can implement a variety of energy management

activities to improve energy efficiency, especially by making an energy

audit. Energy audits can help a mill assess their energy use and

evaluate what measures could be used to improve energy efficiency

without negatively affecting production. Of the mills audited in this

study, the majority produced lumber, and the main energy source was

electricity. On average, mills that were audited operated for 2,951 h/y

and had 56 employees per mill. Annual lumber production averaged 55,444

MBF. Average energy use for each of the audited mills was 2,782,659 kWh.

Audit teams recommended procedures to conserve approximately 275,110

kWh/y per mill. Likewise, the conservation procedures recommended could

save the audited mills an average of 587,045 lb/y of carbon dioxide

emissions (Table 2). Results indicated that implementing the assessment

recommendations could significantly reduce the audited sawmill’s

energy consumption. The basic information, specific energy cost, and

conservation information for all the energy audits are shown in Tables 3

and 4.

Assessment recommendations.–Overall, 6 to 11 assessment

recommendations were made for each sawmill, with an average of 8 (Table

3). The most frequent recommendation was to implement a motor management

system, followed by replacing belts and working with air compressors

(Fig. 1). A motor management system such as MotorMaster+ software can

identify and analyze motor driven systems for various energy

conservation opportunities. Likewise, replacing belts can improve motor

efficiency. Standard V-belts have been shown to have an efficiency of

about 92 percent, while Cog Belts flex more easily and have the

potential to increase the efficiency of the drive system by 2 to 8

percent (Oregon Department of Energy 2007). Reducing compressor settings

and using outside air can also increase efficiency. The energy required

to compress and deliver air increases by 1 percent with every

2-1b/[in.sup.2] increase in pressure. Likewise, because it is generally

cooler outside a sawmill than inside, using outside air can also reduce

compressor energy requirements. Finally, repairing compressor air leaks

can increase the energy savings by reducing the amount of time the

compressor has to be operated to produce the air that is lost to

leakage. In lighting, recommendations included replacing existing T12

lighting ballasts and bulbs with T8 bulbs with electronic ballasts and

reflectors. This changeover can save up to 50 percent of the original

energy use. Also, replacing 400-W metal halide with 360-W metal halide

bulbs can reduce the amount of energy used for lighting (Oregon

Department of Energy 2007).

[FIGURE 1 OMITTED]

Implementation cost for assessment recommendations at sawmills

ranged from $0 to $100,000, with an average of $18,633 (Table 3). Some

assessment recommendations could be easily done at a low cost. Several

of the recommendations had no costs associated with them, for example,

turning off lighting when not in use. Others were costly, including

changing an existing natural gas fueled boiler to a sawdust fueled

boiler, with an investment approaching $100,000. Similarly, since the

implementation cost varied for each recommendation, the payback period

was also different. The payback period varied from immediately to 2.6

years. For example, the payback period for switching off equipment when

not in use was immediate, while it took 2.6 years to pay back an

installation of capacitor banks to reduce electrical spikes. Overall,

the average payback period was 8 months based on the average energy

savings and associated implementation costs.

Marginal cost per million British thermal units.–The marginal cost

of electricity per million British thermal units is calculated by

dividing the total cost of electricity for all months by the total

amount of electricity consumed in those months (Mate 2002). The average

marginal cost of a million British thermal units based on all energy

audits was $17.87/ MMBtu (6.1[cents]/kWh) ranging from $5.59/MMBtu

(2.0[cents]/ kWh) to $39.44/MMBtu (13.0[cents]/kWh; Table 4). It was

noted that the marginal cost per million British thermal units was quite

different among the visited mills. For example, the marginal cost per

million British thermal units was $5.59, $7.84, and $7.88 for Mills 5,

6, and 10, while the marginal cost increased to $39.44 for Mill 17. From

this we can see that Mills 5, 6, and 10 were more efficient than Mill

17. When we closely observed these mills, Mills 5, 6, and 10 had a large

demand cost, and energy consumed per year was much more than the other

mills. Mill 5 also produced rough lumber and other wood products such as

pallet, while Mills 6 and 10 conducted lumber drying along with rough

lumber production. Mill 17 was a small-scale plant that only produced

lumber; therefore, less energy was consumed, and its marginal cost was

higher compared with other sawmills.

Energy. use.–Energy use was analyzed by using energy use per

thousand board feet of production and energy use per employee (Fig. 2).

The energy use per thousand board feet of production is calculated by

dividing the total annual energy consumed in kilowatt hours by the

annual lumber production in thousand board feet. During all of the

energy audits, the energy use per thousand board feet of production

varied from 28.67 to 514.64 kWh/MBF, with an average of 160.89 kWh/MBF

(Fig. 2a). The energy use per thousand board feet of production was very

high for Mill 5 because of large energy demand in this mill as compared

with other mills, and the total operating hours per year was the

greatest in Mill 5. In addition, less volume of lumber was produced in

this mill. For Mills 6 and 10, energy use per thousand board feet of

production was low because of the large volume of lumber produced in

these two mills as compared with other mills. Energy use per employee

varied from 9,675 to 111,668 kWh per employee, with an average of 41,762

(Fig. 2b). Figure 2b also shows that energy use per employee in Mill 5

was very high compared with other mills. It was also found that energy

use was significantly different among all production levels (Fig. 3).

This can be explained by the wide variation in electricity rates and the

difference in demand rates. The energy use per thousand board feet of

production was very high for small production levels (

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