PART ONE

1. Introduction
2. Assumptions
3. Description of Some Forest Industry Mills

1. Introduction

Much attention has been paid recently to the wood wastes of the mechanical forest industry as a potential source of fuel. The rising oil price and the growing risk of disturbances in oil supply are calling for an increased utilization of wood wastes in energy production. At the present price level of fuel oil, wood based power and heat generation seems to be economically justified even in small scale forest industries.

Compared to oil, wood combustion is not an altogether easy thing. Fuel handling is more extensive, the boiler construction is more complicated and to generate the same amount of heat from wood fuel, a bigger boiler is needed than with oil.

As a result, a wood fired power or heat plant is generally more expensive than an oil fired one, and although the relative cheapness of the fuel may lead to considerable savings in operation costs, wood based energy generation is not always the most economical solution.

This study will investigate the feasibility of wood waste utilization in the power and heat generation at small scale forest industry mills in developing countries. The aim is to find out the rate of self-sufficiency to be attained in the energy supply of a mill utilizing the processing wastes of its own.

The subject is limited to concern various hot water and steam applications in generation of industrial heat and power. The energy content of wood wastes could be used in many other ways as well, for instance in flue gas heating or drying, in hot oil boilers and in running prime movers with belt drives instead of electric generators.

These alternative methods have, however, a rather narrow range of application possibilities when compared to water and steam based systems. Therefore, they are not included in this study.

The methodology of the study will be the following:

First, eleven different small scale mills - four sawmills, four panel plants and three integrated plants - are examined. In selecting them the aim has been to cover as wide a range as possible both of output capacities and of different solutions in technical design.

To satisfy the need of thermal and (or) electrical energy of these mills, in a way that makes use of the fuel of their own - i.e. their processing residues - four different basic types of wood fired power and heat plants are presented.

The mills and the plants are all non-existent.

Each of the eleven forest industry mills are equipped with one of the power and heat plants, the size and output of which is adjusted to correspond to the energy demand of the mill. The different combinations will be evaluated both from the technical as well as the economical point of view.

To evaluate the economics of the energy generation based on wood wastes, the generating costs are finally compared with a fuel oil alternative.

All mills and all power and heat plants are designed to conform with the main principle of the Portfolio, i.e. labour intensive solutions and proven technology with a low degree of automation are applied.

The study is divided into three parts as follows:

Part one, chapters 1...3, lists the basic assumption used in calculations and presents the eleven mechanical forest industry mills briefly.

Part two, consisting of chapters 4 to 11, deals with wood combustion equipment. The thermal properties of different types of wood wastes are listed. Wood fired boilers are examined as well as wood gasification equipment and various types of prime movers. Such subjects as water treatment, fuel handling etc. are briefly presented.

The last chapters of the study, making its third part, investigate the technical properties of the power and heat plants. Further the economics of energy generation are calculated case by case for the different forest industry mills.

Calculation prices refer to a specific Far East country. Although the numerical results may not necessarily be valid for other locations, it is, however, felt that the advantage of wood waste combustion within the mechanical forest industry is of the same magnitude in most developing countries.

2. Assumptions

The preparation of this study is based on the following assumptions.

2.1 Location

The plants are non-existing but referred to as if they were located in the Philippines in South-East Asia.

2.2 Infrastructure

It is presumed that the development of the surrounding region has reached such a level, that a small scale forest industry mill can be erected and taken into operation without infrastructural investments.

2.3 Water and Electrical Energy

Fresh water and electrical energy is supplied in required amounts by the public distribution system. If power is generated at the mill and generation exceeds demand the surplus is sold to the public grid. The case of mill operation without connection to the public grid is examined as well.

2.4 Transports

The transport system allows regular transportation of raw material, fuel and manufactured products at reasonable costs.

2.5 Labour

Labour is available in abundance, but there is a lack of people with technical education.

2.6 Production

The industry mills operate 300 days per year. Production efficiency is 90 %, which means that a sawmill with a rated capacity of 30 000 m³ per year actually produces 27 000 m³ per year.

The sawmills operate in one shift, the plywood plant in two shifts and the other panel plants in three shifts.

2.7 Energy Demand

The load factor of the industry plants varies between 0.5 and 0.7. This means that average demand for electrical energy is 50...70 % of the maximum power consumption.

The maximum demand for thermal energy exceeds average demand by 20 %.

2.8 Power and Heat Plant Design

The aim has been a simple plant design based on proven technology but with a low degree of automatization. In this way investment costs have been reduced and the demand for highly educated maintenance personnel lessened.

2.9 Fuel

Power and heat plant fuel is primarily wood waste from the mills. It is assumed that there is no alternative use for these wastes and that they are available at no cost.

Some mills have a waste yield, which is not sufficient to cover its fuel demand. In these cases cheap fuel wood, such as logging residues and small-size roundwood, is purchased to fill the demand gap. The fuel wood is hogged before combusting.

Neither the wood used as raw material nor the fuel wood is debarked.

In plant start-ups and shutdowns as well as in cases of high moisture of the fuel wood, light oil is used as an additional fuel. The light oil consumption is estimated at 5 % of total fuel consumption.

2.10 Other Assumptions

Price of
- fuel wood	USD/t (green)	8, 5
- light oil	USD/t	300
- heavy fuel oil	USD/t	165
- electricity (purchased)	USD/MWh	48
- electricity (sold)	USD/MWh	34
Labor costs	USD/person, a	490
Building costs	USD/m3	50
Interest rate	%	10
Taxes and import duties		-
Price level	Fourth quarter of 1979

3. Description of Some Forest Industry Mills

As mentioned in the introduction, eleven different mechanical forest industry mills are examined in this study. The mills have all some features in common. First, their production capacity is low in comparison with modern mills in industrialized countries. Further, they are designed according to labour-intensive technology, as developing countries generally are scarce in capital but possess large reserves of labour.

When this type of technology is applied it does not only reduce plant investment costs, but has also a lessening influence upon energy consumption per unit. Taking also into account the plant location in the tropical region - reducing the need of heating - energy consumption values are lower than those of, for instance, European mechanical forest industry mills.

In the following pages the forest mills are briefly presented.

3.1 Sawmill, Natural Drying

The two first plants are sawmills. The smaller one has an output capacity of 50 m³ sawnwood per day and the bigger one is twice that large.

After sawing and trimming, the sawnwood is piled in the open air for drying. For this reason no generation of steam or hot water is needed.

In the following these two plants are referred to as Sawmills No. 1 and 2.

Technical data:		Sawmill No. 1	Sawmill No. 2
- production	m3/d	50	100
- installed power	kW	180	360
- consumption of electrical energy	kWh/m3	20	20
- consumption of thermal energy	GJ/m3	-	-

Raw material balance:
sawnwood	50 %
chips and sawdust for fuel	43 %
various losses	7 %
log input	100 %

with reprocessing (chips and sawdust used as raw material in panel manufacturing)

sawnwood	50 %
fuel chips and sawdust for	8 %
reprocessing	35 %
losses	7 %
log input	100 %

3.2 Sawmill, Kiln Drying

The next two sawmills, referred to as Sawmills No. 3 and 4, are identical to Sawmills 1 and 2 with the exception that the sawnwood is dried in chamber-like kilns. The kilns are heated with hot water entering the kiln at a temperature of 110...120 °C. The kiln air is circulated by fans. Due to the fans the consumption of electrical energy is significantly higher than at sawmills 1 and 2.

Technical data:	Sawmill No. 3		Sawmill No. 4
- production	m3/d	50	100
- installed power	kW	240	480
- consumption of electrical energy	kWh/m3	40	40
- consumption of thermal energy	GJ/m3	1.5	1.5

The raw material balance of Sawmills 3 and 4 are indentical to those of Sawmills 1 and 2.

3.3 Plywood Plant

Of the four panel plants to be investigated in this study the first one, a plywood plant, is presented here. It is called Panel Plant No. 1.

In general, the panel plants consume more energy than the sawmills and the plywood plant is no exception to this rule. Its most important heat consumers are the veneer dryer, the hot press (requiring a water or steam temperature of 160...200 °C) and the steaming pits.

Technical data:
- production	m3/d	30
- installed power	kW	665
- consumption of electrical energy	kWh/m3	240
- consumption of thermal energy	GJ/m3	4.6

Raw material balance:
plywood	47 %
fuel	46 %
losses	1 %
log input	100 %
or
plywood	47 %
fuel	10 %
chips for further processing	36 %
losses	7 %
log input	100 %

(Source: FAO-Portfolio, Plywood Plant, Doffine-Consult GmbH.)

3.4 Fibreboard Plant

The fibreboard plant. Panel Plant No. 2 has considerable energy costs per output unit. Medium-pressure steam at a temperature of about 200 °C is used in three major phases of the manufacturing process. First the raw material is defibrated by steam treatment in a digester. At a further stage the wet mat is dried and pressed in the hot press, which is heated by steam. Finally the board is given heat treatment in a board dryer, the drying energy of which also is supplied by steam.

Technical data:
- production	t/d	20
- installed power	kW	850
- consumption of electrical energy	kWh/t	600
- consumption of thermal energy	GJ/t	10.1

The fuel yield is 0.16 m³ sanding dust per every ton of produced fibreboard.

3.5 Particle Board Plant

Panel Plants No. 3 and 4 are producing 25 respectively 50 m³ of particle board per day. As raw material the process uses sawmill and plywood manufacturing residues or low grade logs or both.

Main heat consumers are the dryer and the hot press, using steam at a temperature between 140 and 200 °C.

Technical data:		Panel Plant No. 3	Panel Plant No. 4
- production	m3/d	25	50
- installed power	kW	670	1150
- consumption of electrical energy	kWh/m3	420	250
- consumption of thermal energy	GJ/m	3.6	3.6

For every m³ of particle board produced 0.06 m³ of sawdust is obtained, which can be used as fuel.

Panel Plant No. 3 is designed to be expandable at a later stage to twice its initial capacity. This leads to a rather high power consumption per output unit in the first stage.

(Source: FAO Portfolio, Particle Board Plant, Fahrni Institut AG.)

3.6 Sawmill Integrated with Plywood and Particle Board Plant

As mentioned in the previous section a particle board plant can operate on the wood waste from a sawmill or a plywood plant. The following mill to be presented is an integrated unit, consisting of a sawmill, a plywood plant and a particle board plant. It is called Integrated Plant No. 1.

The technical data is simply obtained by summing the figures of the units of which the integrated plant consists (cf. sections 3.2, 3.3 and 3.5).

Technical data:
- production of sawnwood	m3/d	100
- production of plywood	m3/d	30
- production of particle board	m3/d	50
- installed power	kW	2295
- consumption of electrical energy	MWh/a	6400
- consumption of thermal energy	TJ/a	116

Raw material balance:
sawnwood	38 %
plywood	11 %
particleboard	19 %
fuel	24 %
losses etc.	8 %
log input	100 %

3.7 Sawmill, Plywood Plant and Particle Board Plant Integrated with Housing Components and Door Manufacture

The next plant. Integrated Plant No. 2, is an extension of the previous one. 20 % of the sawnwood output and some 50 % of the particle board is processed further in a housing components and door manufacturing unit. This department increases the demand of hot water (about 115 °C) by 700 kW and the consumption of electrical energy by 170 kW compared with Integrated Plant No. 1.

Technical data:
- production	cf. section 3.6
- installed power	kW	2570
- consumption of electrical power	MWh/a	7135
- consumption of thermal energy	TJ/a	136

Taking into consideration the further processing of part of the sawnwood and the particle board, the raw material balance is otherwise the same as in section 3.6.

3.8 Plywood and Veneer Plant integrated with a Particle Board Plant

The last mechanical forest industry mill in this chapter is a plywood and veneer plant combined with particle board manufacturing. The plants are identical to those presented in the Portfolio studies on Plywood Plants and Fibreboard Plants (by Doffine-Consult GmbH and Fahrni Institut AG) and are referred to as Integrated Plant No. 3.

The veneer process differs from the plywood process by its shorter manufacturing line: the veneer is extracted immediately after the dryer, while there is a greater number of phases in the plywood process.

Technical data:
- production of plywood	m3/d	30
- production of veneer	m3/d	30
- production of particle board	m3/d	25
- installed power	kW	1670
- consumption of electrical energy	kWh/a	6035
- consumption of thermal energy	TJ/a	27 450

The raw material balance of the plant is as follows:

plywood	26 %
veneer	26 %
particle board	21 %
fuel	18 %
losses etc.	9 %
log input	100 %

3.9 Summary on the Mechanical Forest Industry Plants

To conclude this chapter the forest industry mills are listed in table 3.1, where their technical characteristics are compared.

The kW-columns under the headings consumption of electrical/thermal energy indicate the average consumption of electricity and heat of the industrial process.

Table 3.2 shows the ways in which the industry mills will be combined with the various power and heat plants. The energy generation costs are calculated for these combinations.

Note that at the present stage of technology wood based power generation at Sawmills No. 1 and 2 is not possible in an economically acceptable way. For these mills the energy costs are calculated only for the case, where the power is supplied by the public grid.

The following abbreviations are used to indicate the different power and heat plants:

Heat Plant A	Warm water (120 °C) boiler plant
Heat Plant B	Boiler plant generating saturated steam (15 bar)
Power Plant C	Boiler generating superheated steam plus 250 kW steam engine set
Power Plant D	Boiler generating superheated steam plus 1 MW steam turbine set.

Table 3.1. Technical Characteristics of the Industry Mills

	Production		Installed power	Load factor	Consumption of electrical energy			Consumption of thermal energy					Number of shifts
	m3/d	m3/a	kW		kWh/m3	kW	MWh/a	GJ/m3	(kWh/m3)	kW	TJ/a	(MWh/a)
Sawmill No. 1	50	13 500	180	0.7	20	125	270						1
Sawmill No. 2	100	27 000	360	0.7	20	250	540						1
Sawmill No. 3	50	13 500	240	0.7	40	170	540	1.5	420	870	20.3	5 625	1
Sawmill No. 4	100	27 000	480	0.7	40	330	1 080	1.5	420	1 740	40.5	11 250	1
Panel Plant No. 1	30	8 100	665	0.7	240	450	1 940	4.6	1 280	2 400	37.3	10 350	2
Panel Plant No. 21)	20	5 400	850	0.6	600	500	3 240	10.1	2 810	2 340	54.5	15 150	3
Panel Plant No. 3	25	6 750	670	0.7	420	440	2 835	3.6	1 000	1 040	24.3	6 750	3
Panel Plant No. 4	50	13 500	1 150	0.5	250	520	3 375	3.6	1 000	2 080	48.6	13 500	3
Integrated Plant No. 1			2 295	0.6		1 300	6 395			6 220	127	35 100	1...3
Integrated Plant No. 2			2 570	0.6		1 540	7 135			6 920	146	40 645	1...3
Integrated Plant No. 3			1 695	0.6		1 080	5 495			5 800	98.8	27 450	2...3

¹⁾ Output given in tonnes

Table 3.2 Examined Energy Generation Alternatives

	Heat Plant A	Heat Plant B	Power Plant C	Power Plant D	Fuel Oil + Grid
Sawmill No. 1					x 1)
Sawmill No. 2					x 1)
Sawmill No. 3	x		x		x
Sawmill No. 4	x		x		x
Panel Plant No. 1		x			x
Panel Plant No. 2		x			x
Panel Plant No. 3		x			x
Panel Plant No. 4		x			x
Integrated Plant No. 1		x		x	x
Integrated Plant No. 2		x		x	x
Integrated Plant No. 3		x		x	x

¹⁾ no boiler