2. Energy consumption

2.1 Energy consumed by the industry
2.2 Energy supply
2.3 Pattern of energy input
2.4 Specific energy consumption
2.5 Proportional energy utilization in the manufacturing process

2.1 Energy consumed by the industry

Compared to other industries the wood and wood products industry is not considered energy intensive, and, as shown in Table 1, it consumed some 7.34 mtoe of energy in the OECD countries during the year 1983, accounting for approximately 0.3 percent of the OECD countries primary energy demand.

Table 1. Energy consumption in the OECD countries (1983)

		Electricity	Oil	Gas	Solid Fuels	Total	%
		(mtoe)	(mtoe)	(mtoe)	(mtoe)	(mtoe)
TOTAL CONSUMPTION		395	1 362	491	280	2 528	100
inclusive of
TOTAL INDUSTRY		166	246	202	208	822	33
including:
Iron and steel		20	9	20	92	141	6
Chemicals:		34	131	57	14	236	9
	Feedstocks	-	112	10	-	122	5
	Food & tobacco	10	15	16	6	47	2
	Pulp, paper & printing1/	18	15	14	12	59	2
	Wood & wood products1/	3	2	1	1	7	0.3

^1/ Does not include energy derived from process residues Source: (50)

However, on a national scale the proportion of energy consumed in the wood and wood products industry in relationship to industry as a whole, will vary according to the degree of its importance to the national economy, as indicated in Table 2. In the Nordic countries where the first industry, including pulp and paper, is regarded as one of the major manufacturers in their industrial sector, it accounts for 15 percent (101) of energy input to the manufacturing industry, and in the case of Finland their forest industry represents some 46 percent (101).

Table 2. Purchased energy consumption by the wood and wood products industry of selected OECD countries (1983)

Country	Purchased energy consumption
	Total industry	Wood & wood products industry
	(mtoe)	(mtoe)	(%)
Austria	5.98	0.12	2.0
Canada	50.58	0.66	1.3
Finland	9.16	0.47	5.1
France	46.10	0.32	0.7
Germany W.	67.14	0.60	0.9
Norway	7.01	0.22	3.1
Portugal	3.85	0.10	2.6
Spain	19.82	0.18	0.9
Sweden	11.90	0.67	5.6
USA	338.45	2.98	0.9
OECD Total	822	7.35

Source: (50)

2.2 Energy supply

2.2.1 Electric power
2.2.2 Heat
2.2.3 Heat applications
2.2.4 Secondary energy

In general, the energy supplied to the mechanical forest industries comprises electric power and heat.

2.2.1 Electric power

Electricity being mainly obtained from the following sources:

(a) purchased;
(b) on-site generation by:

- diesel or gasoline-driven generators;
- steam driven turbo-generators (in the case of co-generation plants);

and largely used for electric driven-motors and lighting.

2.2.2 Heat

Heat is derived from the combustion of such fuels as oil, coal, natural gas, wood residues, etc., which provide the thermal energy needed for process heating and drying as well as the conversion into secondary energy.

Steam, hot water and thermal oil serve as heating mediums and although saturated steam is considered the most efficient means to transmit heat in the production process in developing countries, hot water is generally used in small-scale mills. In recent years, the direct-firing of veneer drying kilns and particle dryers has become an acceptable option.

2.2.3 Heat applications

Apart from the generation of secondary energy, heat is used in the following production processes:

Sawmilling	- lumber drying
Plywood production	- log conditioning
	- glue preparation
	- veneer drying
	- hot pressing
Particleboard production	- particle drying
	- resin preparation
	- hot pressing

2.2.4 Secondary energy

Secondary energy may be produced with the aid of:

- steam driven turbo-generators;
- steam engines or turbine drives;
- diesel or gasoline driven direct mechanical drives.

2.3 Pattern of energy input

2.3.1 Input variations

On examining Table 3, it may be seen that electricity is the main source of energy in the mechanical wood processing industry, accounting for some 40-50 percent of the industry's energy needs. However, it should be noted that the predominant use of electricity reflects a proportionally larger use of mechanical processes (e.g. sawmilling, chipping, planing, peeling, transport) over those processes that require heat (e.g. drying, gluing, pressing) (101), in which fuel oil is the major source of thermal energy.

Although there has been a marked change in recent years in the industry's attitude towards the introduction of energy saving equipment and the adoption of conservation measures, the national trends for the industry over the past decade, in the selected countries examined, indicate an upward swing in consumption of between 20-40 percent per unit of product in most cases (101).

Such a rise may be generally attributed to the introduction of highly mechanized equipment and automated systems, with the object of increasing production and reducing manning levels. Also, more mills are kiln-drying their sawn wood and the drying of chips is now becoming widespread in the particleboard industry, combined with an overall increase in product finishing.

Table 3. Proportional fuel use in the mechanical wood processing industry of selected developed countries (1972)

Country	Proportion of total energy input
	Purchased electricity	Oil-based	Gas	Coal-based	Wood-based	Other
	(%)	(%)	(%)	(%)	(%)	(%)
Austria	40.9	45.8	7.9	1.0	4.4	-
Canada	48.8	18.7	14.9	-	17.6	-
Finland	27.8	16.7	-	0.1	15.4	40.01/
Germany W.	36.5	49.7	7.4	5.0	-	14.02/
Hungary	42.3	11.0	-	46.5	0.1	0.1
Norway	54.1	42.5	-	-	0.6	2.8
Spain	48.0	44.7	-	2.7	4.6	-
Sweden	54.3	42.9	-	-	2.8	-
U.S.A.	29.3	11.7	35.6	4.2	-	19.2
Yugoslavia	44.3	27.6	-	28.1	-	-

^1/ predominantly purchased steam
^2/ own-generated hydroelectricity
Sources: (101)(102)

Although there has been a marked change in recent years in the industry's attitude towards the introduction of energy saving equipment and the adoption of conservation measures, the national trends for the industry over the past decade, in the selected countries examined, indicate an upward swing in consumption of between 25-40 percent per unit of product in most cases (101).

Such a rise may be generally attributed to the introduction of highly mechanized equipment and automated systems, with the object of increasing production and reducing manning levels. Also more mills are kiln-drying their sawn wood and the drying of chips is now becoming widespread in the particleboard industry, combined with an overall increase in product finishing.

Yet, in spite of the high cost of fuel oil the use of coal is steadily declining, although the use of natural gas in the European countries and Canada has increased since the early seventies. In the USA and Scandinavia, purchased steam, from the combustion of wood residues and pulping liquors, is becoming an important energy source to the industry.

Regardless of the fact that wood residues are indigenous to the mechanical wood products industry they only account for some three percent of the total energy input (with the exception of USA, Canada and Finland and the sawmilling industry). However, there appears to be a general trend towards greater use of residues as a fuel source in modern installations.

Although the USA is the world's intensive user of energy in the sawmilling industry, it does obtain the major portion of its needs from its own resources and continually strives towards greater energy efficiency and use of residues as a fuel for kiln-drying. But the generation of electricity for sawmill use alone from waste is generally considered uneconomical (100), when compared to power drawn from the national grid, due to the capital costs involved and the low efficiencies of the relatively small generators deemed appropriate for sawmill use.

Table 4. Proportional fuel use in the sawmilling industry of selected developed countries (1981)

Country	Proportion of total energy input
	Purchased electricity	Oil-based	Gas	Coal-based	Wood-based
	(%)	(%)	(%)	(%)	(%)
Finland	16	____________841/___________
France	39	28	-	-	33
Germany W.	17	____________831/___________
Hungary	11	16	13	22	38
Poland	11	4	-	8	77
Portugal	25	64	-	1	8
Sweden	16	25	-	-	59
U.S.A.	14	3	3	-	80

^1/ Thermal energy
Source: (100)

2.3.1 Input variations

The variations in the proportional input of different forms of energy, as may be observed from Tables 3 and 4, are largely attributed to the overall energy supply situation in the country examined, the cost of power from the national grid, relative prices of fossil fuels, their ready availability, the national energy infrastructure and the make-up of the industry.

In the case of the sawmilling industry (Table 4), even greater variations exist, partly due to the above-mentioned reasons, but influenced mainly by the proportion of mills that kiln dry their lumber, differences in wood species, dimensions, etc., as well as the country's climatic conditions which play a major role in the drying process and the energy involved.

2.4 Specific energy consumption

2.4.1 Factors which influence energy consumption
2.4.2 Specific energy requirements

Unlike most other industries, there exist considerable variations between one like mechanical wood-processing plant and another, and the energy consumed in the production of lumber, plywood or particleboard are very much site specific.

International comparisons of energy consumed per unit of product, on a national average basis, are made difficult by the inconsistencies in data recording and reporting. Additionally, the extremely wide range of factors which may significantly influence both the specific energy consumption of individual mills and the national averages, as illustrated in Table 5, further complicates matters.

Table 5. Approximate national averages of specific energy consumption in the sawmilling sector of selected developed countries

Country	Electrical energy	Thermal energy	Total energy
	(kWh/m3)1/	(GJ/m3)	(GJ/m3)
Canada	50	0.80	0.98
Finland	61	1.16	1.38
Greece	34	-	-
Poland	64	2.61	2.84
Sweden	78	1.65	1.93
USSR	21	1.47	1.54

^1/ per m³ of finished product
Source: (100)

A study commissioned by the Canadian Forestry Service in 1982 highlighted such variations in the energy requirements of Canadian sawmills, the range being:

electrical energy	20 - 90 kWh/m3
thermal energy	0.3 - 1.6 GJ/m3

2.4.1 Factors which influence energy consumption

Such differences may largely be attributed to a multitude of factors, several of which are listed below:

- plant capacity;
- rate of plant utilization;
- age;
- equipment and the manufacturing process adopted;
- integrated or non-integrated operation;
- site layout;
- overall efficiency of operation;
- degree of mechanization of materials handling;
- extent of process automation;
- wood species, size and moisture content;
- product type and mix;
- degree of product finishing;
- proportion of air to kiln drying;
- climatic conditions;
- energy prices;
- load factor;
- steam and power balances;
- extent of energy conservation measures adopted;
- standard of housekeeping and maintenance.

2.4.2 Specific energy requirements

Obviously such dissimilarities between mills lead to an equally diverse range in the amount of energy required to produce each particular product.

Product	Range of process energy requirement
	(GJ/m3)
Sawntimber (air-dried)	0.06 - 0.20
Sawntimber (kiln-dried)	1.00 - 2.85
Plywood	4.00 - 7.50
Particleboard	2.00 - 4.50

However, the average specific energy requirements of typical plants which are well run and maintained, may be generally represented in Table 6.

2.5 Proportional energy utilization in the manufacturing process

Energy consumption in the mechanical wood-based industry may be broadly placed in three major categories, i.e.

- processing and materials handling;
- raw material and product drying;
- services, such as compressed air, space heating and lighting of premises.

Hence, for the purposes of comparative analysis the production processes of sawntimber, plywood and particleboard have been divided into various stages so as to provide an order of magnitude as to the proportion of total energy that each major process centre consumes during the products' manufacture.

The Sankey-type diagrams (Figures 5, 7 and 9) have been constructed in such a manner as to indicate the total energy input in the form of heat and electricity and the proportion of output at the various production stages.

Figure 4. Major energy consuming centres in the manufacture of sawntimber

Table 6. Energy requirements within the mechanical wood-based industry ^1/

	Electrical	Thermal	Motor fuel
	(kWh/m3)	(GJ/m3)	(l/m3)
SAWNTIMBER (air dried)
- hardwood	30	-	5
- softwood	20	-	4
SAWNTIMBER (kiln dried)
- hardwood	75	2.5	5
- softwood	45	1.5	4
PLYWOOD
- hardwood	230	6.0	4
- softwood	150	4.0	3
PARTICLEBOARD 2/
- hardwood	160	3.0	3
- softwood	120	2.0	3

^1/ Primary processing
^2/ Applicable for plant of 100-500 m3/day capacity
Source: (38)

Figure 5. Energy utilization in sawmilling

Figure 6. Major energy consuming centres in the manufacture of plywood

Figure 7. Energy utilization in plywood production

The bar charts (Figures 4, 6 and 8) help to illustrate the magnitude of each major energy consuming stage in the production process in relationship to the total electrical energy requirement, which in turn is compared to the overall thermal energy requirement. Additionally, the charts provide a rough guide as to the energy consumed as units of GJ/m³ of finished products. (For further details refer to Appendix IV, Tables 1, 2 and 3).

Figure 8. Major energy consuming centres in the manufacture of particleboard

Figure 9. Energy utilization in particleboard production

Although the diagrams are of an approximate nature they do serve to identify the relationship that each major energy consuming centre has with each other and also readily identifies the prime energy users to which particular attention should be paid in any conservation effort.

In all three product manufacturing processes heating is by far the largest user of energy, representing some 82-87 percent of the total energy requirement in the manufacture of sawntimber, plywood and particleboard, with drying accounting for approximately 87 percent, 61 percent and 62 percent respectively.

Log sawing, veneer peeling and particle reduction are the predominant users of power, representing approximately 27 percent, 23 percent and 30 percent of the manufacturing processes' total electrical requirements. In all three processes, materials handling features as a major consumer of electricity, accounting for some 1528 percent. Such services as lighting, space heating, hot water or steam systems, compressed air and workshops facilities have been grouped under the heading of miscellaneous, and although individually they do not represent a large power user, as a collective group their energy needs are quite significant.