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How to Make and Operate The Iwate and The Yoshimura Black Charcoal Kiln

ARECOPAsia Regional Cookstove Program

The iwate How to Make and Operate Black Charcoal Kilns

The Iwate Black Charcoal Kiln

ARECOP - Asia Regional Cookstove Program 2

Acknowledgements

In the publication of this manual we are indebted to many individuals and organizations for their efforts to bring the contents of this manual together. We would like to acknowledge and thank Donatus Rantan and Rudijanta Utama of Yayasan Dian Tama, Indonesia, for their time and attention on the compilation of in-formation and technical editing, as well as Tsuyoshi Hirowaka of JANIC for checking the accuracy of the technical translation from Japanese to English

We are especially thankful to Professor Sadakichi Kishimoto and Mr. Akira Yamada of Sumiyaki No Kai (The Charcoal Association of Japan) for their generous untiring efforts to disseminate their valuable tech-nology to an international audience during the Training on High-Quality Charcoal Production (held in 1991 in Kalimantan, Indonesia) on which the kiln technology included in this manual is based.

ARECOP would also like to extend it’s appreciation to the organizers and supporters of the Training on High-Quality Charcoal Production in providing the opportunity for this technology to be introduced to a wider international community.

Asia Regional Cookstove ProgramYogyakarta, Indonesia1994



Table of Contents

I. Foreword 6

A. Charcoal and Charcoal Making: Background 6

B. Improving Traditional Charcoal Making 7

II. Preparing for Production 8

III. The Iwate Black Charcoal Kiln 10

Background: The Iwate Kiln: A Typical Black Charcoal Kiln of Japan 10

IV. Construction of the Iwate Kiln 14

A. Ground Preparation 15

B. Drainage Box Construction 18

C. Preparing and Making the Chimney 19

D. Marking and Shaping the Kiln Floor and Chimney Mouth 22

E. Kiln Wall Construction 22

E.1. Redrawing the dimensions following stamping and smoothing 26

E.2. Shaving and Shaping the walls 26

E.3. Drying the walls 27

F. Making the Ceiling 28

F.1. Loading the wood 29

F.2. Soil mixture preparation and testing for kiln ceiling 31

F.3. Stamping 34

G. Mouth of Kiln 35

H. Maintenance 35



V. Kiln Operation 36

A. Firing and Control 37

B. Opening the Kiln and Unloading the Charcoal 41

C. Yield Calculations 42

D. Reloading the Next Cycle 42



Foreword

The ideas and materials for this manual sprang "om a cooperative training effort held in Ponti-anak, West Kalimantan in 1991. It was the first time that an organized, hands-on training concen-trated on the construction of traditional Japanese black charcoal kilns of various shapes and sizes. The large Iwate kilns proved the most basic and popular, sparking the idea that a practical manual could further disseminate the knowledge gained by the participants. Much of the material appears here for the first time in English, courtesy of Dr. Kishimoto, head trainer and president of Sumiyaki No Kai (Japanese Charcoal Association).

A. Charcoal and Charcoal Making: BackgroundCharcoal is a major fuel in developing countries. Especially in urban areas, charcoal serves the needs of millions of people everyday for cooking, ironing clothes, blacksmithing, processing of dried food items, and everyday work. Its advantages include its light weight, high calorific con-tent, smokeless burning, ease of transport, and low cost. In addition, charcoal has often held a unique role as an art form and cannot easily be substituted with other energy sources.

Traditional charcoal making varies across countries, countries, and ecosystems. Some of the most basic methods use earth mound and pit kilns. These are low investments, small-scale methods that produce low quality charcoal mainly for local consumption. Charcoal is also pro-duced with the use of large brick, metal, or even cement kilns, with production capacities any-where from 1 to 100 tons per firing. These methods produce high quality charcoal for local, ex-port and industrial markets but at a high price and investment.



Yet another alternative is fired clay kilns. These kilns have developed out of the traditional earth mound kiln. Instead of loose soil, the kiln is constructed of tightly packed special clay which, when fired, becomes a strong and durable structure. The fired clay has all the advantages of a brick kiln without the high investment costs. The traditional Iwate black charcoal kiln is of this type.

B. Improving Traditional Charcoal MakingThe traditional process of charcoal making can often be very inefficient, requiring almost as much wood to fire the process as kiln converts into charcoal. Thus, the first challenge is to improve the charcoal production method by decreasing the amount of wood energy needed to produce char-coal. The second challenge is to increase the value of charcoal to improve the livelihood of char-coal producers. By improving the traditional charcoal making process, the quality of charcoal is increased and many local producers can tap higher markets for their products

The crux of the problem is developing a comprehensive program that takes into account the envi-ronmental shocks of improved charcoal making as well as the need to increase energy supplies and incomes. In general, local level charcoal makers can rarely take into account environmental impacts if they do not directly figure into their production costs. Few charcoal makers incorpo-rate tree planting or other components of sustainable forestry into their work simply because they see no immediate benefits; they have an abundance of raw materials (wood) and cannot afford such long term “investments.”

Consequently, any effort to improve charcoal products and methods of charcoal-making sit on a precarious development fence. On one side, planners look for better, more efficient means of charcoal production to increase incomes. Yet higher production of charcoal, if not managed properly, can damage the local environment and undermine other development efforts in the area.

Improving traditional charcoal making methods attempts to address both of these issues. More efficient production, when managed properly, can help to slow down deforestation. When char-coal producers are trained in simple, sustainable forestry management, they can employ tech-niques of selective cutting and replanting to ensure a long term supply of their production. At the same time, improved production and better yields can directly raise their incomes. With higher incomes, the charcoal producers can afford to consider long-term investments and further im-provement in their craft.

Sustainable charcoal making can also be locally controlled and managed. Providing forest com-munities with these skills puts control of local resources in their hands. If properly trained and given the assurance of ownership and responsibility, local producers can spearhead community-run forest conservation practices, which allow them to live off their own resources without ex-ploiting them.



Preparing for Production

Before beginning, one must first determine if an area is appropriate for charcoal production and if charcoal making wi( be profitable. A detailed business plan, area analysis, and an environmental impact study must be carried out in order to understand the local carrying capacity of the environ-ment. Consider carefu(y the cost of building, running, and maintaining a charcoal kiln. Consider also the impact of such a program on the local people and environment.

Field and site surveys should include studies on:

Wood and natural resource potential of an area. This must include types or species of wood, and the average age and population density of each species in the area.

Land and natural resource ownership patterns. Overlap in land ownership is com-mon in many places due to local systems of border determination. A forested area could be claimed as part of the community’s property and may cause problems in utilizing its resources.

Environmental impact assessment of potential production. The study must take into consideration the wood volume that can be cut within a certain time span, the time required for replanting and the growing rate of cut branches. The system ap-plied must be one of selective cutting and rotation among blocks allocated for cut-ting purposes.

Market research and analysis. In charcoal production, marketing must be taken into consideration before production begins. There are several types of charcoal



demanded by the market. To make sure the production level is sustainable a mar-ket study should be conducted beforehand.

Socio-economic profile of local charcoal producers. If local charcoal producers are already operating in the area, it is necessary to understand and pay attention to their existing system and regulations. Many areas have their own production and selling systems.

Socio-economic profile of the community at large. Existing social and economic factors should be taken in to consideration. People of a certain area may resist the adoption of new technology as introduced by a person foreign to the area.

Although this manual cannot provide details about these surveys, their importance cannot be un-derestimated. Improved charcoal production can lead to an efficient program of reduced environ-mental damage and other far-reaching benefits.




Iwate Kiln, Typical Black Charcoal Kiln of JapanBackgroundAs stated above, the Iwate kiln falls into the category of fired clay kilns. It can be constructed with local, low cost materials and produces exceptionally high quality charcoal. The original de-sign comes from Japan, from the city of Iwate. Japanese charcoal making dates back to the 9th century, and the Iwate is one of the most basic traditional kiln designs. It provides a permanent kiln structure and the advantages of protection and greater control over carbonization processes. There is a minimal level of investment and the kiln is able to produce high quality charcoal.

ShapeAs you can see from the illustration, the height of the ceiling is low and the length from the en-trance to the chimney is long. This is because the temperature at the top of the kiln is 300°C, and the temperature at the bottom is almost the same as the outside. If the ceiling is any higher, the difference in temperature will also be grater, which negatively affects the evenness and quality oAt the entrance, much of the wood burns away during firing, resulting in ash and low-quality charcoal. But in the middle and the back, good quality charcoal is produced. This is the reason for the long shape and larger back section (see illustration).

The kiln floor is level, except a slight declination at the rear and front of the kiln. This facilitates the heat to go down and exit, passing through the entire kiln. Gas circulation is absolutely nec-essary because it raises the temperature at the bottom of the kiln. If the floor has an inclination, then circulation is suppressed. Thus, a flat kiln bottom results in smooth gas circulation. Because water is prone to accumulate at the bottom of the kiln, it is important that water can be easily ab-sorbed into the ground. Kiln floors are traditionally made of wood and soil, but if constructed on soft and wet soil, it is necessary to use stones and brick for better drainage.



ChimneyThe Iwate kiln has only one chimney. If the kiln is round, such as the beehive kiln, then there can be more than one chimney. But for good quality charcoal, the carbonization process should be slow. More chimneys = faster carbonization = lower quality charcoal.

The shape of the chimney is one of the most important aspects of the kiln. Based on fluid dynamics, the shape greatly affects the quality of charcoal produced. The chimney is narrow at the top and wider at the bottom so that if air enters from outside, it circulates within the chimney and does not enter the kiln. If the chimney is too high or the chimney mouth too big, more drafts will be created and more smoke will be released. If too much smoke escapes, gas is lost and the pressure in the kiln becomes lower than the outside pressure, allow-ing air to enter from the outside. For gas can circulate, air pressure inside the kiln must be slightly higher than air pressure outside the kiln.

The stone at the bottom of the mouth of the chimney is the most im-portant part of the kiln. It is the heart of the kiln. This section must be made of firestone or firebrick and must be fire-safe up to 800°C.



10203015

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100

20

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Fig. 1. Technical drawing of Iwate Kiln

Fig. 2. General

drawing of chimney

mold

15 15

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6

Wood for Charcoal To produce high quality charcoal, freshly cut wood must be used. If dry wood is used, car-bonization is faster, but much the charcoal pro-duced will break or crack. With fresh wood, the process is longer but the quality of charcoal that results is better. For best results use only wood that is relatively fresh with a water content of 35%. If the water content is less than 35%, then carbonization will happen too fast and produce lower quality charcoal. But if wood moisture con-tent is too high, the process will require a larger quantity of wood and more time to process. Also, high-moisture wood is heavier and thus more dif-ficult to load into the kiln. In tropical conditions, wood should dry for 1-3 months (in Japan it only takes 3 weeks).

The carbonization process starts from the top of the kiln to the bottom. Wood is thus loaded with the larger end up so that pyrolysis will travel through the wood easier. There is a layer of wood at the bottom of the kiln to allow for complete carbonization of the main wood which is expected to produce the high quality charcoal.

Materials NeededMost tools and materials needed to make the Iwate kiln can be found locally. For instance, the traditional tools for stamping, shaping, and molding can all be fashioned from waste wood. To make an Iwate kiln, the following materials are needed:



Fig. 3. Wood for charcoal must be "eshly cutted

Construction Wood for Kiln

Bamboo stakes

Wood posts

Planks for walls

Construction Wood for Kiln

Bamboo stakes

Wood posts

Planks for walls

Materials for Kiln Construction

Clay soil: 48 m3

Portland cement: 3 bags

Sand: 8 m3

Bricks: 100 pieces

Materials for Kiln Construction

Clay soil: 48 m3

Portland cement: 3 bags

Sand: 8 m3

Bricks: 100 piecesFig. 4. Tools needed



Tools Needed

Stampler Hammer

Level Blade 3 mm plywood

Measuring tape Hack saw

String Trowels

Spade Nail (several sizes)

Axe Bamboo basket

Tools Needed

Stampler Hammer



String Trowels


Axe

Tools Needed

Stampler Hammer



String Trowels


Axe Bamboo basket

Fig. 5. General drawing of kiln, non technical

Construction of the Iwate KilnThe Iwate Black Charcoal Kiln


During construction, various activities can be conducted by several persons or temas at once to save time. Genera#y, the construction must fo#ow a logical building process:

During construction, various activities can be conducted by several

persons or temas at once to save time. Genera#y, the construction

must fo#ow a logical building process:

A. Ground Preparation

B. Drainage Box Construction

C. Marking and Shaping the Kiln Floor and Chimney Mouth

E. Wall Construction

E1. Redrawing the dimensions and shaping the mouth

E2. Shaving and Shaping the walls

E3. Drying the walls

F. Wall Construction

F1. Loading the wood

F2. Soil mixture for kiln ceiling and soil mixture testing

F3. Stamping

G. Making the Mouth of the Kiln

During construction, various activities can be conducted by several persons or temas at once to save time. Genera#y, the construction must fo#ow a logical building process:A. Ground Preparation


C. Marking and Shaping the Kiln Floor and Chimney MouthE. Wall Construction

E1. Redrawing the dimensions and shaping the mouthE2. Shaving and Shaping the wallsE3. Drying the walls

F1. Loading the woodF2. Soil mixture for kiln ceiling and soil mixture testingF3. Stamping

During construction, various activities can be conducted by several persons or teams at once to save time. Genera#y, the construction must fo#ow a logical building process:

A. Ground Preparation


C. Marking and Shaping the Kiln Floor and Chimney Mouth

E. Wall ConstructionE1. Redrawing the dimensions and shaping the mouth

E2. Shaving and Shaping the walls

E3. Drying the walls

F. Wall ConstructionF1. Loading the woodF2. Soil mixture for kiln ceiling and soil mixture testing

F3. Stamping

G. Making the Mouth of the Kiln

H. Maintanance

A. Ground PreparationOnce an appropriate site has been chosen (make sure the site is far enough above the local wa-ter table to avoid sudden water intrusion during rain), level the area around the kiln site. The ground preparation is important because water intrusion and poor drainage can cause several serious problems later.



Fig. 6. Ground foundation preparation

A. Dig 20 cm in depth and level the bottom in a space as large as the dimensions of the kiln

B. The kiln bottom consists of two layers and can be made as follows: Redrawing the dimensions and shaping the mouth This is to create a stable base for the kiln construction and prevent water intrusion from the ground

Second layer, 10 cm of well-stamped, firmly packed earth.The second layer should be stamped very well to make a water-tight layer

C. In case bricks and rocks are not available, wood can be used to substitute The first layer of wood (10 cm in diameter) is installed lengthwise and the second layer (10 cm in diameter) installed perpendicular across the first layer

D. Make a centerline using string and measure the inside diameter of the kiln to be con-structed

E. Draw a large circle over the diameter of the kiln (A) Use a string 100 cm long (radius of the main section), attached to the center pole Draw out circle A with a nail attached to the other end

F. Draw a smaller circle (B) with a radius of 63 cm. Its center is at the perimeter of circle A, on the center line at the front of the kiln

G.Draw out the mouth of the kiln Start at the perimeter of circle B, in front of the center line The mouth should measure 60 cm at the back, have a 60 cm length, and measure 48 cm at the front or mouth

H. Stake out the entire perimeter with stakes, equidistant around 25 cm, and around 30 cm high. Tie each of the stakes with a string for use in the next step (wall construction)



Fig. 7. Marking the ground



B. Drainage Box ConstructionTo allow water accumulation in the kiln to escape, a drainage box and water outlet is constructed at the back of the kiln, underneath the chimney. Water is produced because the kiln walls and wood are not completely dry. Without a good water outlet, the bottom of the chimney could break and slow down or stop the carbonization process.



A. Dig a hole and a channel at the back of the kiln to accommodate a drainage box and drain pipe. The drainage box can be made from bricks and cement.

B. Dig a hole and a channel at the back of the kiln to accommodate a drainage box and drain pipe. The drainage box can be made from bricks and cement.

C. Dig a channel from the back of the kiln to accommodate the drainage box and drain pipe. The channel should slope down so water can drain out and away from the kiln.

D. The drain pipe can be made of bamboo, or any type of pipe with some holes on the pipe’s wall. Alternatively, the drainage pipe can just be lined with small stones.

E. The drainage pipe should extend from the bottom of the drainage box. The entrance of the pipe, inside the drainage box, should be covered with medium sized rocks. Then, fill the entire box with small stones or gravel.

Fig. 8. Drainage box construction

C. Preparing and making the chimneyThe chimney is the most important part of the kiln. The outlet at the top is 15 X 15 cm2. It is shaped like a bottle so that wind that enters from the outside will circulate in the bottle and not enter the kiln itself. If air enters, then the temperature inside will drop and the change may cause the charcoal to crack.

The angle of the chimney is also crucial. If the chimney leans too much towards the front of the kiln, the smoke cannot escape easily and it is difficult for the wood to burn. But, if the chimney leans too far away from the kiln, the carbonization will go too fast and the wood will turn to ash. The angle of the chimney is always the same no matter what size the kiln.

The chimney mouth (inside the kiln) should be exactly level with the floor. The opening of the kiln is on a declination, lower than the floor (see figure 12).



A. MaterialsApply a little cement plaster to secure the chimney mold as a foundation. Chimneys usually crack because of high temperatures and are eroded by the high acid content of condensed smoke. Traditional kilns only use clay mixed with ash and small stones. To prevent crack-ing, it is better to construct the chimney using a mixture of clay and ash or some burned clay, with sufficient thickness (7-30 cm). If the chimney walls are too thin, they will certainly crack. A small amount of the cement mixture can be added as a hardening agent.

For the chimney mouth, firebricks are the best modern material available, but can be expensive. An alternative is red brick, if it is available. Make sure it is fire-proof and has a quality between firebrick and regular brick. This may be the best and lowest cost choice. Bricks should be joined using cement. Quartz stone can also be used. To test the stone, bake it at a high temperature and while it is hot, pour water over it. If it doesn’t break, it is good.

For the chimney walls instead of using plywood, you can use a brick mixture. When the kiln is test fired, the bricks will bake. This is a good traditional way to ensure a good surface of the inner chim-ney. If you are working on a hill, cut the chimney into dirt. There is no need to use a plywood form.

Fig. 9. Chimney molds



B. Chimney form Draw out forms according to the dimensions and construct a model out of 3 mm plywood (see figure 10 and 11). Cut out the shape using a blade. Use small pieces of wood, 2 X 2 X 3 cm, for the bottom and inside supports. Staple or nail them to the inside of the mold. Make sure to calculate the size of the firebrick (which may vary) so that with the firebrick in place, the chimney mouth is exactly 6 cm in height. The width can be 36 cm, or 12% of the inside length of the kiln.The angle of the back of the chimney is important. The top portion of the chimney back should be between a 90° and 96° angle with level ground. For the top section of the chimney, you can use a clay/earth pipe about 12-14 cm in di-ameter.

Fig. 10. Chimney molds, detail

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39

39

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17

9

6

57

39

39

15

17

9

6

57

39

39

15

17

9

6

57

39

42.5

15

36

57

39

42.5

15

36

57

39

42.5

15

36

Back

57

42.5

40

15

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57

42.5

40

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57

42.5

40

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Front



C. Insta(ing the chimney mold Line up the center of the chimney mold precisely with the center line and on top of the drainage box. The back, top portion of the chimney should be between a 90° – 96° angle to the ground. If necessary secure the mold by placing 2 strong posts at the back and a small support board between them. This will support the top, back part of the chimney. Secure the mold with string/rope. The mouth of the kiln should measure EXACTLY 6 cm from the ground to the firebrick, and 36 cm wide or 12% of the inside kiln length. The fire bricks, when in place, should be level with the base of the kiln (the back of the kiln slopes down a little to provide the 6 cm opening for the chimney mouth). Use firebricks to construct the mouth. Use a clay mixture to install an L profile iron rod to support the bricks and to secure between the bricks and on the face of the mouth (see il-lustration). The strongest and most level mouth would use a single, long fire brick to bridge the 36 cm gap for the mouth. Secure the base of the mold using regular bricks and secure them using a clay mixture.

ImportantWhen making the brick foundation at the back slope (inner surface of the chimney), make sure that you put a generous amount of cement between the mold and the bricks so that the inside wa( wi( be smooth. When the mold burns away, you must have a smooth surface to help the smoke escape easily (see i(us-tration).

Fig. 11. Chimney mold insta(ation

D. Marking and Shaping the Kiln Floor and Chimney Mouth

E. Kiln Wall Construction



The kiln walls are very important and much care must be taken in their construction. Good stamping is the key to solid walls. There are two types of wall construction; traditional and modern. The traditional method only uses wood forms for walls, while the more modern method uses plywood wall forms. Both methods can be used, but the traditional method is stronger, and so this manual will concentrate on the traditional form.

a. Materials for the walls

If possible, construct the walls with a mixture of fresh clay and burned clay. If you don’t have enough clay, just the inside section of the walls should be made from the mixture (30 cm thick). The inside wall will be exposed to the most heat and abuse, and therefore must be the strongest. The outside part of the wall is mainly for insulation and support. It can be made of soil 1 meter thick (see figure 14). If no good clay is available, you can use bricks to line the inner walls of the kiln. But you must use the same mixture as used for the chimney construction to join the bricks. Back the bricks with a wall made from normal soil, at least 70 cm thick. In mountainous areas, dig the walls into the side of a hill and line the inside with brick. Then construct a wall made of soil, properly stamped, at least 70 cm thick. It is important to prevent air intrusion in the kiln, which may cause difficulties in the cooling process. Make sure there is proper drainage to prevent rain water run-off from entering the kiln.

The walls should have a thickness of 100 cm and should be at least 5-10 cm higher than the length of the wood (normally wood is cut at a 100 cm length).

To install the chimney, first the kiln floor must be well prepared and the chimney mouth must be precisely in place.

Make sure the floor is level with the top level of the chimney mouth. From the center of the chimney mouth, draw a half circle (A) with a diameter of 36 cm. Draw another circle (B) with a diameter of 56 cm. From the perimeter of circle B, slope gradually up to the perimeter of circle A. The perimeter of circle B should be at floor level or level with the top of the chimney mouth. At the front of the kiln, the floor should slope down through and out of the door. The slope should be 60 cm in length, with a 10 cm drop in the slope. (see figure 13).

Fig. 12. Chimney mouth position to kiln floor



ImportantWe have to pay attention to the mixture of the material for the entire wa( construction. The mixture should be homogenous and have adequate moisture content. If the mixture is too wet, it may cause high shrinkage and cracks. If it is too dry, it may require more effort to solidify.

Fig. 13. Kiln wa(s



b. Preparation of wall construction

The perimeter of the walls should already be measured out with bamboo stakes when pre-paring the kiln floor. Tie a piece of string about 10 cm long at the base of each stake and lay it down facing inwards toward the kiln. This is done because later, when the clay walls are finished and the forms removed, we can scrape the walls smooth. The string will help us to find the bamboo stakes that mark the final perimeter.

Plant a wood post with a 6-10 cm diameter and 150 cm in length, equidistant and exactly 5 cm inside of the bamboo stakes (see figure 15). Plant them 50 cm into the ground so that 100 cm remains above the ground. Distance between posts should be 40 cm, and it is important that this distance be maintained. Stamp the ground around the posts. The posts are planted 5 cm inside of the bamboo stakes because later, the walls must be smoothed (see Shaving and Shaping the Walls). The 5 cm distance allows for errors and smoothing. After smoothing, the inside wall surfaces will be exactly at the bamboo stakes. To stake out the perimeter of the outside section, pound another set of posts (6-10 cm wide and 120 cm long) 110 cm back from the bamboo stakes. These posts should be around 40-45 cm apart. This distance should be well maintained. To maintain the wood post standing exactly 90° to the ground, support them with other posts (see figure 15).

c. Material preparation for wall forming

Between the posts (45 cm apart), stack rounded wood (branches) 6-8 cm in diameter and 45 cm long. If using plank wood, use 10 X 45 X 1-2 cm. Each section will require around 15-18 pieces (branches) or 10-12 pieces of plank wood. For the three posts on both sides of the kiln mouth, cut wood at 6 cm X 90 cm to fill be-hind the posts. This is for esthetics only. For the three posts on both sides of the kiln mouth, cut wood at 6 cm X 90 cm to fill be-hind the posts. This is for esthetics only. Cutting both ends diagonally will make the wood fit better with the adjoining wood. Leave the section designed for the mouth and chimney open

Fig. 14. Post insta(ation to construct kiln wa( in

traditional way

ImportantMake sure the required materials listed above have been prepared before continuing with the next step



d. Wall construction

Add 2 logs at a time, then add 5 cm of clay mixture (see a. Materials for wall) between the forms and stamp very well. This is a crucial point. Stamping must be slow; add only 5 cm of clay mixture at a time. Level the unstamped clay mixture. This must be done regularly and follow along the kiln pattern, so as to control the compactness of the wall. The quality and quantity of charcoal will be reduced if the walls aren’t constructed well and are not well stamped. If stamping is too difficult you can mix the clay with a little water. However, this will make the drying time longer and could cause cracking. IMPORTANT: The first 30 cm of the clay from the inside wall of the kiln (from the plank-wood or wood form) must be stamped very well. This portion of the inside wall of the kiln, if not stamped properly, will collapse inward. The other 70 cm until the outside of the wall should also be stamped well, but not as well as the first 30 cm. Level unstamped clay first before stamping, especially near the plywood.

Fig. 15. Adding clay/soil for wa(

Fig. 16. The final traditional wa(

formed

ImportantTo conduct this work requires at least 6-8 people and norma(y it wi( take between 4-7 days. This work

is one of the most difficult in constructing the Iwate Kiln



E1. Redrawing the dimensions after the wa(s are stamped and smoothed

When the wall is completely finished, the following steps can be done:

a. Lay a board across the top and mark the exact center of the 115 cm circle.b. Mark the circumference of the circle again on the top of the wall.c. Measure the second, smaller, front circle again and mark its perimeter on the top. d. Remove the forms inside and all the wood. e. Draw the center line again from back to front on the ground with a string.

Measure from the exact center of the chimney mouth entrance, over the center post and through the mouth. Measure exactly 300 cm from the chimney mouth to the front of the kiln and place a stake at this point. Take the measurements of the kiln mouth again, drawing it out on top of the clay walls The length of the kiln mouth corridor should be 60 cm, measured from the inside wall. The width at the back or inside of the mouth should be 60 cm and the front side should be 48 cm. From the 48 cm measure in front, the mouth can slowly widen from the walls to the out-side.

E2. Shaving and shaping the wa(s

a. Lay any kind of sheet or plywood on the ground inside the kiln before shaving off the excess dirt to maintain a level base.

b. Begin cutting away the extra soil/clay from the inside of the wall. Take the measurements of the kiln mouth again, drawing it out on top of the clay walls

c. Remove the now exposed bamboo stakes, all dirt and the center post. d. Some of the wall may fall off when the forms are removed (note that the traditional kiln us-

ing all wood forms has stronger walls and fewer pores because the strength of the wood allows for harder stamping).

Fig. 17. Marking the completed wa(



e. If some parts of the wall fall off leaving holes in the wall: Make a plaster mixture of 60% clay, 35% sand, and 5% cement or ash and water. This mixture should be adhesive and has very low water content. Mix well and form small balls in your hands and throw them straight against the holes to fill them. Throwing them is important because they will stay. If you apply them directly with a trowel, the “patch” will fall off. Fill all holes and use a trowel to finish the surface until smooth.

f. Re-stamp the kiln floor to level it off and smooth the surface from the holes left by posts.

E3. Drying the wa(s When the wall has already been shaped and all holes are filled, it must be dried to release water content in the wall. If the walls have high water content, they will crack or break.

a. Stack a small pile of wood mixed with and surrounded by 2 large sacks of charcoal dust/powder, sawdust, rice husk, or any burning material inside the kiln.

b. Keep burning continuously for 2 days (3 days is even better), adding the burning material when needed.

c. On the last day of drying the wall, the chimney mold should be burned out by making a fire in front of the chimney mouth. Then clean up the inside of the chimney from charcoal and ask.

d. After 2 or 3 days of continuous burning, put it out and remove all the ash.e. Patch all the holes and cracks with plaster mixture (60% clay, 35% sand, 5 % cement or

ash, and some water).

Fig. 18. Patch the holes with clay, sand and cement

F. Making the Ceiling



The ceiling must be made with a special soil mixture because it must stand up to intense heating during the charcoal making process. The ceiling must be of good materials and it must be mixed well so that the ceiling won’t break. (see Soil Mixture). The ceiling should be smooth. To construct a good ceiling, one must take into consideration the following criteria.

Material mixture must be homogenous Good stamping is necessary to get even compactness in the entire ceiling

It should have proper thickness and follow the parabolic law The ceiling should have a smooth surface both inside and outside

Some large kilns have holes in their ceiling to control carbonization. But since a kiln of the size presented in this manual will only produce 500 kg of charcoal, there is no real need to make the holes.

Ceiling construction will only be done once when making a new kiln. If this is done properly, it will last for 2 – 10 years of operation. However, if the ceiling is broken, simply reconstruct a new ceiling. Ceiling construction can only be done after loading the wood.

Loading the wood has two purposes: as a working step before constructing the ceiling (to act as a support to the ceiling that will be constructed) and as raw material for charcoal making. The first wood loading into the new kiln is aimed more at creating supporting mate-rial for ceiling construction than as raw material to make good charcoal.

Fig. 19. Drying the wa(



F1. Loading the woodWood must be loaded evenly and regularly. Wood character (diameter, length, quality, and species) and heat distribution must be taken into consideration. To be able to construct a good ceiling, wood loading must be arranged as follows:

a. Line the floor of the kiln with small diameter (3 cm) waste wood or branches (see figure 2.1).

It is important to line a few pieces horizontally in front of the chimney mouth, longer than 56 cm. Arrange all the rest lengthwise. This layer of wood allows air to circulate better and allows for more even carbonization by helping the heat move down and around.

b. Choose straight woodc. Wood should stand vertically, with the larger end up.d. Stand the first pieces of wood in the back of the kiln at a slight angle, leaning away from

the chimney mouth (see figure 24).e. The best wood should go in the back of the kiln. f. Load the thickest pieces of wood in the middle. g. The wood loaded in the front can be a 50-50 mix of good and trash wood (wood that is

not straight, etc.) because it becomes ash.

Fig. 20. Line sma( diameter of wood at the kiln floor



h. Choose 2 pieces of average size wood to be control pieces to test the carbonization rate. Mark them both with saw cuts, measure their weight, length, and circumference in the middle. Place these two in the center of the kiln.

i. Once the standing wood is in, begin laying long pieces of larger diameter wood across the top (see figure 23). Then cover them with smaller diameter pieces while maintaining the dome shape, since this will be the inner surface of the kiln ceiling. The top of the dome must be exactly 136 cm from the kiln floor.

j. Cover with grass (about 3 cm thickness) then jute bags or any kind of sheet material.k. Then fill in to shape the ceiling with 2-3 cm diameter of wood, 10, 20, and 30 cm long. l. Shape the ceiling carefully so it is smooth and no large pieces are sticking out.

Fig. 21. Wood loading, put upside-down, best wood placed closed to chimney

Put at the center

Load best wood in this middle



Fig. 23. make the ceiling into a dome shape and cover with grass and jute bags

Fig. 22. Fi( to dome shape ceiling with sma(er woods, twigs, etc.



F2. Soil mixture preparation and testing for kiln ceilinga. Soil mixture

Choosing the correct soil and mixture for the ceiling is very important. The inside ceiling surface temperature reaches 750 - 800°C. If the mixture is not heat resistant, the ceiling will crack. The best mixture is fire-proof, “sticky” (cohesive because it doesn’t decompose during heating and doesn’t fall apart), hard, and economical.If good clay is not available locally, it can be substituted by the mixture of 50% baked soil and 50% fresh soil. A small amount of cement can be put into the mixture (maximum 6%). Sand and ash can also be added in adequate volume.

b. Soil mixture testingThe mixture must first be tested. The mixture test is conducted at around 850°C or by testing on an open bed of burning charcoal. The test should be done as follows:

Use a tennis ball size sample (around 5-6 cm diameter) and bar shape (1 X 2X 12 cm) and mark it with a 10 cm grove line. The sample must be fairly dry. Burn at a temperature above 500°C for at least 60 minutes. Drop it from a standing height to a normal hard soil surface. If it doesn’t break, it’s OK. Measure the shrinkage of the bar shape sample. If the shrinkage is less than 3% it will be fine.

c. If cracks occur. Cracking is often occurred by soil shrinkage. There are two types of kiln soil shrinkage:

Dry shrinkage – Water evaporates at 100°C, which causes shrinkage. Heating shrinkage (dissolving) – This happens during charcoal making above 500°C, when some chemical compounds are lost.

Fig. 24. Drop & shrinkage test



If cracking is vertical, then the ceiling is still OK (see illustration). If rings or horizontal cracks occur, this is very dangerous. The ceiling may fall, so it must be hung. These severe cracks may be caused by a poor clay mixture, poor stamping, and/or a temperature rise that is too rapid. Soil or sand with lots of calcium or lime should be mixed with baked bricks and baked at 500-600°C. Calcium should burn away but this soil should only be used on the out-side walls of the kiln, away from the fire/charcoal

Fig. 25. Types of kiln ceiling cracks possibly occured

d. Types of cracking Cracking after first shrinkage, at 100°C, is due to a loss of water, and can be patched by stamping Cracking after the second shrinkage, at 500-600°C, can be repaired by adding new material (mud mixture). If cracking is very bad after the second shrinkage, the ceiling may need to be hung, and the cracks filled with a mixture of clay and ash



d. Hanging the ceiling. This is necessary only if the kiln is large and/or the ceiling is in danger of collapsing.

Make an iron cross out of 30 cm pieces of iron rod 1.5 cm in diame-ter. From the cross section attach a hanger out of the same material, about 60 cm long. Install the cross 1 cm from the in-side surface. At this point, the temperature can reach 350°C and it is safe for iron bar. If installed on the inside surface of the ceiling, cover the cross with clay/soil to protect it.

Install a pair of posts (3m in height), one on each side of the kiln. Connect the tops of each post to a strong bar. Then connect the hangers to the bar with a piece of strong wire. If necessary, more than one post can be installed on each side of the kiln.

F3. Stamping

When all material for the ceiling is ready, the ceiling construction can begin. Make sure the work can be finished in one day. Stamping and maintaining the thickness on every section of the ceiling, as well as the shape, requires careful attention.

Add the mixture on top of the wall, about 6 cm thick. Stamp well until it is 3 cm thick. This must be done layer by layer, moving around and following the kiln pattern. The next layer can be started when the first layer is finished, well stamped, and compact. To control the thickness of the ceiling, use a small iron stick to measure the thickness periodically and frequently. (see figure 29).

Stamping direction should be done as shown in figure 29 to achieve a strong ceiling. To finish this work in one day usually requires 8-10 people. The day after the ceiling is build, stamping needs to have a more compact surface, using a smaller stamper.

To mark the top of the ceiling, hang a stone on a small wire just above the top (highest point) of the ceiling.

Fig. 26. Ceiling hanger made of

iron rod



To make the dome of the Iwate kiln, there are several different techniques used in Thailand and the Philippines:

1. For attaching the bricks

This technique has been used successful in Pakchong, Thailand. This technique uses raw, unfired bricks. The size of the bricks should be around 25 x 18 cm and about 5 cm thick. The raw bricks can easily be shaped as necessary using a large knife blade. It may be necessary for some bricks to have a pointed shape so that they can be stacked in a circle.

Arrange the wood and twigs on top of the kiln to form a dome shape. It will be-come the “mold” for the dome shape. The glue used to attach the bricks together should be clay; the same substance the bricks are made from. This is to make sure that the shrinkage factor will be uniform throughout the structure. However, the section above the kiln mouth should be made with refractory bricks supported by an iron elbow.

Fig. 27. Kiln ceiling is completed

F4. Another technique to insta( the dome



Raw bricks are stacked along the desired contour. The bricks are glued together with clay – the same clay used to make the bricks. Some bricks wi( need to be cut with a knife to form the curved shape of the dome.

Re"actory bricks are used for the upper part of the kiln mouth. An iron elbow is used to support the bricks

Stack the bricks until they reach the top of the dome.



2. For iron reinforcement: This technique has been used with satisfactory results in Pontianak, Indonesia as well as Davao, Philipines. Materials used include 10 mm diameter reinforced steel and wire mesh. Basically, the reinforced steel is arranged to form a frame in the shape of an arch. Then the wire mesh is attached to the frame. To provide a smooth shape for the dome, use the following steps. Arrange a pile of wood and twigs on top of the kiln and cover it with a sheet of plastic or jute sacks that have been sprinkled with water to make them more flexible. Then spread fine sand on top of the plastic sheet or jute sacks. Using a trowel or thin board, shape the layer of sand in an arch. It will later become the ‘mold’ for the Iwate kiln dome. After that, place the iron frame with wire mesh on top of the pile, so that it is ready for wet cement to be poured on top. Use castable cement with specifications ap-propriate for the temperature that will be reached inside the kiln.

Arrange a pile of wood and twigs in a circular shape

Cover the pile with a plastic sheet and then cover the sheet with damp paper. After that spread find sand on top. Smooth and shape the sand to form the desired dome shape. This pile wi( func-tion as the dome mold.

Iron Reinforcement



A metal "ame that has been reinforced with wire mesh is attached above the dome.

Castable cement is then spread on top of the metal "ame.

Shape and smooth the surface of the dome

G. Mouth of the KilnConstruct the mouth of the kiln with bricks or stones, and carefully adhere to the dimensions given above (see illustration).

The mouth has two holes

Wood fuel is added through the top hole, which must be kept closed. The size of the hole depends on the size of the wood used.

The bottom hole allows air to enter. Airflow should be controlled at this hole.

H. Maintenance



Construct the mouth of the kiln with bricks or stones, and carefully adhere to the dimensions After the kiln has been completely built, it will need continual maintenance. Building a kiln may consume a certain amount of investment and labor. For some areas, the traditional kiln introduced in this manual may not be affordable. Proper maintenance will ensure that the kiln can be operated for a long period of time. To maintain the kiln, follow the guidelines listed below.

Always build a shelter to cover the kiln to protect it from rain and direct sun. Always prepare good drainage around the kiln to protect it from floods caused by rain water.

Choose a location for the kiln away from heavy traffic to prevent people from walk-ing around it.

Keep the working area around the kiln tidy. All the equipment and tools to support the operation should be placed properly.

Patch all cracks and holes that appear. Never wait until the cracks become wider as it will be very difficult to repair.

Fig. 28. Front view of kiln mouth

Kiln Operation

Good kiln operation is another key to high quality charcoal. A good charcoal producer can te( "om the smoke what level the carbonization process is at, and how to adjust the chimney and feeding mouth accordingly. The temperature in the chimney also helps a charcoal producer control the kiln temperature accordingly.

Knowing how much the chimney or mouth should be opened or closed is the art of the charcoal maker and requires a lot of experience. If the holes are too open, carbonization wi( happen too fast and the charcoal produced wi( have lower quality and lesser quantity. On the fo(owing page is a chart with the kiln temperatures and corresponding su2ested opening for both the chimney and the feeding mouth.



A. Taking the temperature

10 cm below the chimney outlet, measure the chimney temperature with a normal thermome-ter

Place a recording note book and a writing pad close to the chimney to note the temperature of the chimney every hour.

B. Smoke. The smoke will change in character during different stages of the carbonization process. Early on the smoke is white and billowing, and will disappear 1-2 cm above the chimney hole.

As carbonization starts, the smoke becomes thinner, more continuous, and long. It will drift 15-30 meters from the chimney before it disappears.

As carbonization continues towards completion, the smoke becomes thinner, dark blue, and transparent.

A. Firing and Control



A. Ignition begins in the lower hole of the kiln mouth, with the chimney totally open (re-fer to the chart). Cover the chimney hole with bamboo or rattan basket to protect it from wind for around 7 hours. Simply add starter wood and a little kerosene to get the fire going, especially in the first 30 minutes. During the first days, because there is still a lot of water, the smoke will be billowing and white. The smoke temperature is around 60°C.

B. The most important temperature is when the chimney temperature reaches 78°C. At this point, temperature should be controlled and gradually raised to 82°C by slowly opening the chimney over a period of 6 hours. This is when carbonization starts and should occur around 30-48 hours after the ignition. At this stage, the taste of smoke should be bitter and drift 15-30 meters away from the chimney be-fore it disappears.

C. After the carbonization has started, gradually close the chimney again. Add some fuel wood for the last time and slowly adjust the kiln mouth. Let the opening of the kiln mouth be as high as a four finger gap.

Since wood is already burning on its own, there is no need to feed fuel wood any longer. Keep this process up to the next morning.

When closing the chimney, always close from the front section backwards so as not to disturb the flow of the exiting smoke.

Close the chimney three quarters or less but make sure the temperature is not higher than 82°C.

Fig. 29. Temperature taking and ceiling monitor stone



D. When the ceiling is completely dry, around 150°C, some cracks may appear. If this happens, immediately mend with mud and a trowel, but do not stamp the ceiling too hard. At this stage observe the shrinkage of the kiln ceiling by measuring the dis-tance between the hanging stone. If the shrinkage is more than 10 cm, just stop fir-ing by closing the chimney and kiln mouth totally. After is has cooled down, recon-struct the kiln ceiling.

E. By the next morning, if the temperature has dropped below 80°C, simply add more fuel wood to raise the temperature. If necessary, widen the chimney opening little by little. However, if the temperature rises above 82°C, close the chimney hole again gradually. After the temperature becomes stable on 82°C for 12 hours, then the air hole on the kiln mouth should be adjusted to a three finger gap opening, and remain that way until the next morning. If the temperature reaches 120°C, reduce the chimney opening slightly to prevent over-burning on the inside of the kiln. At this stage the kiln mouth opening must have a one finger gap opening (around 19 X 2 cm).

F. During the first firing, when the chimney temperature reaches 150°C, closing the kilns should be anticipated.

The smoke will become blue and thin. After several hours, when smoke that is 15-20 cm above the chimney becomes transparent, it is time to close the kiln.

When closing the kiln, the chimney and mouth are opened completely, causing a lot of smoke at first, then slowly clearing and becoming transparent. After 1 hour, close the mouth again causing thin smoke to appear. After another hour, close the chim-ney. At this point, the kiln is totally sealed and carbonization is complete

G. If the temperature reaches 150°C on the second and following operations, antici-pate closing the kiln. The temperature will increase every hour up to 300°C, then the refining process can begin. First, start by opening the chimney to 6 X 12 cm and leave it for 1 – 2 hours. Repeat these steps until the chimney and kiln mouth are totally opened.

Some charcoal producers wait for more than 1 hour after full opening before clos-ing the mouth, and up to 4 hours before closing the chimney. This is because when the mouth is closed, the temperature inside becomes more balanced. This is the process of refining.



To do this, open all holes just before closing them completely. This causes Oxygen to enter and the temperature to rise very high. Because of the increased combus-tion, the front wood becomes ash and supplies heat for the middle and back of the kiln. Because gas is produced by opening all the holes, the front is closed. The gas circulates on its way out of the chimney, helping the carbonization process of the wood on the ground which has not carbonized yet. The temperature at the top of the kiln drops from 800 to 600°C and the temperature at the bottom rises from 400 to 500°C. This balance means that more complete, even, and thorough carboniza-tion is taking place. The longer this balance is maintained, the better the quality of charcoal produced. For the first firing of the kiln, the temperatures and smoke description given in the table might not hold true. This is because the kiln is still wet. For example, during the first firing, at 150°C, the smoke may already be thin and blue. But during normal operation, after 4 to 5 firings, the temperature should be around 250°C.

Fig. 30. Maintaining kiln operation



Fig. 31. Opened and closed kiln

ImportantIn the newly constructed kiln, the refining process wi( usua(y cause cracks in the ceiling. If a crack is wider than 1 cm, stop the process. A crack should be mended. Sometimes, refining can be made we( after 4-5 firing operations.



B. Opening the Kiln and Unloading the Charcoal



A. After cooling the kiln for a sufficient time, check inside the door to make sure the burning has completely stopped.

Open the door slightly to check if there are any live coals

If there are many live coals, re-cluse and wait a few days while repairing all the cracks.

If there are only a few, extinguish them with a little water, but do not use too much.

B. If and when the coals are dead, leave the mouth open for a few hours to release the poisonous gases.

Prepare some water

Listen for the cracking sound of the charcoal inside the kiln and feel the heat inside the kiln with your hand.

C. The burnt clay from the mouth of the kiln should always be collected in a box for use in the next firing. This clay should be mixed well with water and a little ash and put back. Burnt clay should also be used to repair cracks.

D. After taking out the charcoal, it should not be stacked higher than 15 cm

It is always better to spread it out, but keep it away from flammable materials

Always check the charcoal to make sure it’s not burning

Sort the different types of charcoal, i.e. broken, whole, dust, etc.

Fig. 32. Unloading the charcoal

C. Yield Calculations

D. Reloading for the Next CycleAfter the first cycle of charcoal production, it can be continued with the next cycle. The second cycle does not need any complicated work, just loading the wood and firing control. The loading for the second cycle (and the following) are different from the first firing in a newly constructed kiln. They are as follows:

Clean the chimney holes and kiln floor from dust, ash, and other material

Repair the inner surface of the kiln and patch them to get a smooth surface wall, floor, and ceiling. To stick the patch, moisturize the groove/crack with a little water

When the kiln is ready for loading, lay a small diameter of wood (3-5 cm) lengthwise as the base for the other wood to stand on, and to facilitate air circulation

Load the wood one by one, stand them in the kiln, and arrange as previously mentioned



A. Recover the standard wood from the kiln carefully.

B. Measure the standard wood weight diameter, length after firing, and compare it to the pre-firing figures.

C. Calculate the shrinkage as a percentage of the original. In Japan, the average is: shrinkage in length 10-15%; shrinkage is diameter 35-40%.

Fig. 33. Yield calculation and packaging for further storaging or marketing

To fill the space between the top end of the wood and the ceiling, use bent or undersized wood, or whatever is available. This part will mostly become ash during carbonization

After reloading is completely done, prepare the fuel wood in the front-most section of the kiln for ignition purposes

Close the kiln mouth using bricks or stone

When it is ready, the next cycle of charcoal production can be started by igniting the fuelwood.



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