Báo cáo khoa học nông nghiệp " Improvement of operator skills and technology in small rural sawmills in Vietnam. " doc

There is greatpotential for solar kiln drying technology in Vietnam for furniture manufacturers andsmall sawmillers particularly in the HCM City region and Dak Lak Province, whereair-dry

Collaboration for Agriculture & Rural Development

Project Report

027/06VIE Improvement of operator skills and technology in

small rural sawmills in Vietnam.

Kiln Drying in Vietnam

byGerry Harris, Peter Vinden and Philip Blackwell

October 2009

Wood fired Boilers 19

APPENDIX - FACTORY VISIT REPORTS 21

Factory Visits A - CAXE Environmental & Thermal Engineering Co Ltd 21

Director Mr Bui Anh Viet 21

Factory Visits B - Hoang Thanh Company 23

Factory Visits C - Troung Tai Company 28

Factory Visits D - CHANH HUNG DRYING UNIT 30

Factory Visits E - Nong Lam University 37

Factory Visits F - Thien Hung Company Technologies (THC) 42

THC Factory 43

THC Kilns 44

Factory Visits G - Forest Science Institute of Vietnam – Sth Vietnam Co-Op 50

Factory Visits H - Truong Thanh Wood Processing 57

PART 2 POTENTIAL FOR SOLAR KILNS IN VIETNAM 65

Introduction 65

Background 65

The efficiency of solar drying 68

Climatic Data 70

Calculation Method for Fuel Savings 70

Insolation 71

Kiln types 73

Conclusions 78

REFERENCES 79

SUMMARY AND RECOMMENDATIONS

This report is in two parts Part 1 summarises a number of visits to furnituremanufacturers and sawmills where audits were undertaken of the operation of thekilns The kilns varied in sophistication from being state of the art technology to lowcost, low tech, locally built plant However, without exception improvements could bemade to the operation of each kiln that was audited This report summarises whereimprovements can be made to each of the kilns visited This forms the basis of a

“Wood drying improvement program” that needs to be implemented This is anurgent need given that most of the kiln dried material is destined for furnituremanufacture As a general comment most kilns in Vietnam operate as ovens Whilstthe primary objective of reducing the moisture content of timber to below fibresaturation point (28%moisture content) is achieved, there is a high variability in finalmoisture content This inevitably results in down-stream problems associated withthe quality of joinery or furniture that is manufactured from the timber

Part 2 evaluates the potential for solar kiln drying in Vietnam There is greatpotential for solar kiln drying technology in Vietnam for furniture manufacturers andsmall sawmillers particularly in the HCM City region and Dak Lak Province, whereair-drying is prevalent and where final drying of timber to equilibrium moisturecontent is a requirement of further processing

It is recommended that:

1 A “Wood drying improvement program” is established by the Department ofForestry comprising customised advice and generic training on site at eachprocessing facility where drying is undertaken Some nominal charge should

be made for the provision of this service It is anticipated that the servicewould take approximately 1week and could involve

2 Further research is needed to develop drying and processing methodologiesspecifically for plantation grown acacias for use in furniture production inVietnam This could involve the training of a Masters research student jointly

in Vietnam and Australia, with the objective of training the person forimplementing the “Wood drying improvement program”

3 The development of new drying technology should focus on:

Solar kilns using Australian technology in the first instance, to developdemonstration models for solar drying in Vietnam This could befollowed up by local manufacture

Comparative investigations are needed to determine the best locationsfor solar drying (using the regression analysis models identified in thisreport) throughout Vietnam

4 A model should be developed for the creation of modern drying plants forclusters of small-scale sawmills and/or clustering existing sawmills into larger

PART 1- VIETNAM FACTORY VISITS AND KILN ASSESSMENT

Introduction

The CARD Team visited a number of furniture factories located in the Central andSouth Vietnam, with kiln drying facilities The facilities at these factories ranged fromvery basic, small capacity, in-house built kilns to very large capacity modern units.The Team also visited a number of kiln manufactures in order to gain anunderstanding of the expertise in Vietnam

All kilns assessed by the Team utilised wood waste as the main heat source, either

as direct fire units, suppling heat to the kiln chamber via flue gasses ducted throughthe kiln or as a fuel supply to boilers which inturn supply heat to the kiln via heatexchangers in the form of steam

The Team also inspected the drying facilities at Nong Lam University which hadresearch and commercial drying facilities These facilities were originally establishedand designed by Prof Cac in the 1990’s (see CAXE Section in appendix A for furtherdescription) This design appeared to be the basis of many of the kilns assessed bythe Team throughout Vietnam

Timber is dried mainly:

 To reduce its weight for the purpose of transport,

 To increase strength – dry wood is considerably stronger than green wood,

 To produce a product that is stable and durable and

 That can be painted / stained and glued and

 Can be machined and finished to an acceptable standard (ATSM, 1997)

From a commercial perspective this needs to be done as cheaply and efficiently aspossible and to achieve this goal the timber needs to dried as fast as possiblewithout too much degrade (Walker, 2006) The purpose of drying timber (from acommercial perspective) is to:

 Dry the stack of timber as fast as possible – without excessive degrade

Summary of results

The Team found that there was a general lack of understanding of the basicprinciples of drying lumber by the workers and kiln operators Kiln operators oftenused the rear of the kiln as a place of residence Kiln condition appeared to becontrolled on a set and forget basis

In particular there appeared to be a lack of understanding, by the operators, asregards the relationship between dry bulb (DB) and wet bulb (WB) temperatures,airflow and timber racking and the overall effect that these parameters have on theconditions inside the kiln and the resultant non-uniformity of drying of the lumber ifthey are not correctly monitored and controlled

More specifically it was often found that WB sensors were disconnected (possibly bythe operators) from the kilns control system (fig 1) This meant that the kilns weresolely controlled on DB temperature alone, in effect creating a ‘hot box’, with nohumidity control The operators appeared to have made this decision to control thekilns only by DB temperature, purely to simplify the process through lack ofunderstanding of the actual relationship between DB and WB temperatures It wasreported at one facility that as they had dried using the same schedule (i.e using DBand WB temperatures) that the operator knew from past experience when to changecondition based on the DB temperature alone

Where sensors were correctly installed they were only used for manual control, that

is, the control of kiln conditions relied basically on the operator monitoring thetemperature (i.e WB and/or DB) and making a ‘uneducated’ decision to open orclose the appropriate valve or vent, which was set and forgot until next time hehappened to check the reading

Humidity control was generally based on a random basis depending on the gutfeeling of the operator It was reported at one facility that the humidity controlconsisted of “turning the stop valve, mounted on the external wall, ‘ON’ until waterran out from under the door”

Only one kiln drying facility had fully automated controls ensuring 24 hour control ofthe drying conditions inside the kiln

The use of baffling to restrict by-passing around stacks was nonexistent Also it wasobserved on one occasion that boards were rotated 90° to the airflow in order tostack more material inside the kiln (fig 4a) in order to fill up the remaining spaceinside the kiln which did not allow for a full length board This had the effect ofblocking any cross flow between the boards due to the placement of stickers atregular intervals.

Further it was observed that kilns were generally stacked to ‘maximum capacity’ withlittle regard to leaving sufficient ‘plenum’ space between the edge of the stack andthe side of the kiln wall (fig.4b) This has the effect of creating uneven airflow throughthe stack, from top to bottom On some occasions the plenum space was filled upwith surplus material that required redrying (fig 4c) This practise only leads toreduced efficiency of the kiln

With respect to timber stacking it was found that there was a lack of use of dedicatedmaterial for ‘stickers’ In general boards were racked out using the same materialthat was being dried, by placing the components or boards at right angles in a

‘crosshatched’ fashion (fig 4d) to create the gap between boards in order to allowairflow This meant that often the gap was too wide, consequentially reducing theefficiency of the kiln

Figure 1 Disconnected wet bulb sensor

Figure 2 Typical kiln controls – DB sensors and fan switches

Figure 3 Analogue readout inserted through wall.

Figure 4a Boards stacked at right angles to airflow

Figure 4b Minimum plenum space Figure 4c Excess components stacked in plenum space

Figure 4d Typical example of ‘crosshatch’ stacking.

Temperature Monitoring & Controls

The drying conditions inside a kiln are, in general, monitored by the measurement ofthe dry bulb temperature (DBT) and wet bulb temperature (WBT) These parameterscan in turn be used to determine the relative humidity (RH) (i.e the amount ofmoisture in the air) These three (3) parameters can be used to determine theequilibrium moisture content (EMC) or the dry effort of the environment inside thekiln DBT and WBT are set according to predetermined conditions which are known

as ‘schedules’ or recipes Different schedules are used for specific species and aredetermined through extensive research and consultation with industry And examplespecific schedule maybe DBT = 60° and WBT = 55° giving and EMC = 12.5% If thekiln is controlled only on DBT (i.e no humidity control) may result in the EMC falling

as low as 2-3%, generating an extremely harsh and dry environment which may lead

to drying degrade in the product

The practise of drying lumber, monitoring only the DBT is not recommended as itquestionable as to whether the practice will result in acceptable drying quality,especially for high valued products such as fro furniture This practice can only lead

to moisture content variations in the final product and contribute to drying stress anddegrade This is due to the potentially low EMC’s that may be maintained in thedrying chamber, resulting from the lack of humidity In high value product such as infurniture where components are require to be laminated into larger components, it isessential to have uniform moisture content, both within and between components.Any variation in MC (between pieces or boards) will result in uneven shrinkage,resulting in defects such as splitting or cracking in the finished product Further if theboards are ripped or machined, the inherent drying stresses will result inunacceptable distortion in the finished product

The Team found that WB sensors were not used and they had been deliberatelydisconnected (fig 1) This meant that the kilns were solely controlled on DBtemperature alone, in effect creating a ‘hot box’, with no humidity control Themajority of sensors that were correctly installed were only of a ‘manual’ control type

exhausting of moist air and resulting in an overly dry environment in side the kiln, asthe vents set then left until the operator retuned from other duties Humidity wasgenerally controlled by turning on a stop cock to provide steam or water to the kiln Itwas reported at one facility that the humidity control consisted of “turning the stopvalve, mounted on the external wall, ‘ON’ until water ran out from under the door”.

For the production of ‘high-value’ components with correct moisture content andminimal degrade, it is recommended that kilns should be, at a minimum, fitted withsemi-automatic controls Only one kiln drying facility was observed by the Team tohave been fitted with fully automated controls The utilisation of a fully automatedcontrol system ensures that kiln conditions were controlled on a continuous basisaround the clock, regardless of the kiln operator being in attendance This wouldensure maximum output of lumber at correct moisture content with minimal degrade

As has already been reported WB sensors tended to be disconnected Howeverwhere wet bulb system were fitted these installations were considered to besatisfactory, with appropriate water baths and sensors etc, utilised However theTeam observed on most installations, that excessively ‘thick’ fabric was employed asthe ‘wick’ material (fig 5a) This had the effect of reducing the evaporation and airflowover the sensor and inturn giving an incorrect WBT reading The wet bulb wickshould be made from thin smooth material that readily evaporates moisture from itssurface Therefore it is recommended that a thinner type material be utilised that isable to cover the entire bulb of the sensor and be capable of maintaining acontinuous flow of water This will ensure that a correct reading of WBT is returned.One option is to employ a ‘boot lace’ type material (fig 5b) which ‘snugly’ fits over thesensor bulb The wet bulb sensor should also be located so that the air to bemeasured can freely flow over the wick and not placed in a corner, resulting inreduced air flow The wick should also be kept clean and changed on a regularbasis

Figure 4 Manual vent controls.

Figure 5a Typical wet bulb assemblies with wick attached - too thick

Figure 5b Wet bulb sensor with boot lace wick

In addition it was noted that the humidification system on most kilns consisted only ofgalvanised pipes with small holes drilled along the length (fig 6) This would tend toprovide a ‘stream’ of water, which has the potential to wet the stacks, instead ofproviding a spray or mist into the kiln environment It was observed that the holes inthe spray pipe tended to become blocked, reducing the efficiency of humidificationdelivered to the kiln It was unclear whether the water treatment was utilised

Figure 6 Humidity pipe showing water/steam outlet mounted in front of heat exchanger.

Air Flow

Air is the transfer medium by which heat is transferred to the timber and the medium

to absorb evaporating moisture, therefore adequate airflow or circulation is essential

in order to attain uniform drying and successful seasoning of timber Therefore (in akiln) it is vital that airflow is uniform and adequate through all ‘sticker’ spaces andparts of the stack Drying time and wood quality depends on the air velocity anduniformity of circulation ‘Baffles’ and ‘stickers’ are essential apparatus in creatinguniform air flow around the kiln and through the stack

Baffling

Baffles in kilns are used to stop air by-passing around and over the top of the timberstack and in turn force the circulating heated air, through the sticker spaces betweenthe boards, creating uniform airflow around the kiln Generally a movable or flexiblematerial is used as a baffle, to provide a barrier to the air flow (fig 6) This ensureseven airflow between boards or sticker spaces and in turn leads to uniform drying.Any by-passing of air around the stack means that there is reduced airflow throughthe stack resulting in longer drying times and uneven MC distribution within andbetween the boards Depending on the volume of air by-passing the stack, (i.e thesize of the gaps around and over the top of the stack), has a direct effect on theamount of airflow through the stack and maybe reduced by up 50% This in turn canresult in an increase in drying time of up to 50%

Figure 6 Typical kiln schematic showing baffles at ceiling and floor level.

It was considered that the Type I style kiln had an inherent air by-passing problembetween the heating coils and the fans (i.e air is diverted from the fans directly to theheating coils and visa versa) As the warm air from the heating coils hits the stack,(i.e a significant resistance) a considerable restriction to the flow is created As therewas no effective baffling in the kilns observed, between the top of the fancompartment and the heating coils, a path of lower resistance exists Thereforeinstead of the air flowing through the stack, the majority ‘short circuits’ the system,bypassing the stack and flows back to the fans (fig 7a)

Figure 7a Type I kiln showing bypassing

Figure 7b Use of hinged baffles to block air by-passing.

Figure 7c Simple solution to bypassing using extended layer of boards (see arrow)

Figure 7d Using extra layers to block by-passing over stack (recommended).

This particular problem can be simply solved by placing a baffle at the top of the fancompartment that can be hinged back out of the way during loading and unloading.Another method is shown in Figure 7c where the layer of boards is extended at theheight of the fan compartment creating a simple barrier to the airflow and ensuringthe air flows through the spaces above, providing alternate solution to the problem

In addition an extra layer of boards can be used to fill the space above the stack (fig7d) and therefore stop air by-passing over the top However it is not recommended

to fill this space with ‘off-cuts’ (fig 7e) as was observed by the Team in more thanone occasion

Figure 7e Baffling using excess material above stack – not recommended

Figure 8a and 8b which shows the use of a ‘swing’ baffle supported from the ceiling

of the kiln, could easily be retro-fitted to many kilns to solve the problem of passing over the top of the stack This type of baffle can be raised up out of the waywhen the kiln is being loaded then lowered on to the stack once the loading iscomplete This type of baffle could be made from panels using plywood or aluminium

by-or from flexible material such as ‘conveyby-or belt’ material

Figure 8a Ceiling baffle mounted in top of kiln to stop air bypassing over the stack.

Figure 8b Manual close/release cable for baffle

There was also concern regarding the loading of this type of kiln with side mountedfans as the long pathway which the warm air has to travel through the stack (Fig 8d)may result in moisture gradients being setup in the components, from one side of thekiln to the other This is particularly exacerbated, given that there is no means ofreversing the airflow That is, even if the baffling problem is corrected, warm dry airwould enter the stack (nearest the fans) and travel through the stack giving up heatand collecting moisture as it does so, until it exits on the opposite side cool andmoist This would result in one side of the stack (i.e closest to the heating coils)being dry and the side furtherest away being still ‘wet’ It is recommended that

Baffle

Baffle Close/Release handle

Figure 8c Bypassing around stack – need for baffling.

Figure 8d Long pathway for airflow through stack

Racking Practises

The racking out of timber involves placing small strips of timber know as ‘stickers’ or

‘rack sticks’ between boards to separate one layer of boards from another They areevenly placed along the length to form a stack of timber of specific width and length.The purpose of the stickers are two-fold:

a to provide a gap between boards to allow air circulation between boards toenable drying and

b to provide restraint of the boards to prevent distortion such as twisting andwarping as the timber dries

Poor or careless stacking practices result in distortion and degrade in the boards (fig.9)

Stickers are generally wooden strips of approx 16-20 mm thick and 30-38 mm wide.They should be evenly space along the length of the stack at either 300mm or450mm intervals and should be made from sound timber, seasoned, dry, clean andfree from decay and staining fungi (ATSM, 1997)

Figure 9 Distortion in stack due to poor sticker alignment

Source:(Nolan et al., 2003) Figure 10 Racking guides

The use of racking or stripping guides can improve sticker and stack uniformity while

at the same time improving efficiency of stack construction (fig.10)

Findings

The racking practices in the factories and sawmills visited by the Team weregenerally found to be poor, with little or no use of stacking frames or guides Stickersizes were not consistent and were made from low quality material In addition littleconsideration was given to vertical alignment of stickers within stacks and alignment

of bearers between stacks This resulted in many examples of distorted boards beingobserved (fig 11)

Figure 11 Poor sticker alignment – note distortion in boards

On more than one occasion The Team observed fungi to be growing on timber inside

a kiln (fig 12) This was as a result of poor air flow to certain sections of the kiln due

to poor stacking practices, resulting in the timber to staying wet and not drying

Figure 12 Fungi growing on timber due to poor airflow due bad stacking practises

Wood fired Boilers

All drying facilities visited by the Team operated wood direct fired fuel systemutilising the heat from flue gases to heat the kiln or direct fired steam boilers, utilisingsteam as the heating medium

One company operated a 2,500 kg/hr wood fired steam boiler, which consumedapprox 8m3 of fire wood per day All fire wood was supplied from the on-site sawmilloperation and any excess could be sold at approx US$2/t to the local market There

is a question as to the long term viability of using wood waste as fuel for dryingtimber Currently in Vietnam wood waste attracts a very low return, however ifanother use is found for this material, as in the manufacture of particleboard, it maybecome far more valuable This can be paralleled to the situation in China werewood waste currently is valued at US$40/t making the cost of fuelling kilns fromwood waste very expensive

Figure 13 Wood waste used to fuel boiler.

Figure 14 Truck being loaded with wood waste - US$2/t

APPENDIX - FACTORY VISIT REPORTS

Factory Visits A - CAXE Environmental & Thermal Engineering Co Ltd

Kiln Construction Company

Director Mr Bui Anh Viet

Caxe.ete@gmail.com

The CAXE Company manufactures timber dry kiln equipment, to suit chamberssizes, ranging from 25 to 50 m3 The construction of the kiln chamber is generallyconstructed from brick and rendered with concrete The chamber is generallysupplied by the owner, according to CAXE specifications, with the drying equipment(fans, heat exchangers etc) supplied and fitted by CAXE

Air circulation system consists of up to 7 (dependent on chamber size) axial fans 600

mm in diameter, delivering 9600 m3/hr and powered by 1.5 hp, externally mountedelectric motors

The heating is generally supplied via a wood fired steam boiler delivering 2500 kg/hr,which can also be supplied by CAXE

The control system is manual in the MK I type kiln and semi-automatic in the MKIItype The wet bulb and dry bulb temperatures are measured via analogue sensors inthe MK I model, with externally mounted displays, and a water bath and wickassembly used for the wet bulb determination, although on the kilns that wereinspected, the WB system had all been disconnected Vents are manually openedand closed On the later MK II model electronic WB and DB sensors are employed

Figure A1.In-house kilns at CAXE factory site

Figure A2 Fan controls.

Figure A3 Manual humidity controls & DB sensor inside kiln

Figure A4 Wood fired boiler and dried product

The company has 12 kilns located on their premises located in Ho Chi Minh City.Costings: per 2 kilns

Table A1 Kiln costing

Kiln's dimension: W x D x H 9m x 5m x 5m 5m x 7m x 4m

Total amount USD 21,203.84 17,287.87

Factory Visits B - Hoang Thanh Company

A number of kilns, constructed by CAXE, were assessed at the Hoang ThanhCompany The Company’s drying facilities consisted of 12 kilns, 6 at 50 m3 and 6 at

40 m3 capacity The kilns were constructed from concrete rendered bricks All weremanual controlled with wet and dry bulb sensors fitted at the time of commissioning;however it was found that the wet bulb sensors had been disconnected on all kilns(F

The company operated a 2,500 kg/hr wood fired steam boiler, which consumedapprox 8m3 of fire wood per day All fire wood was supplied from the on-site sawmilloperation and the surplus was sold at approx US$2/t This figure is in contrast to theprice received in China were wood waste currently is valued at US$40/t

Kilns were loaded by hand and stacking practises were found to be reasonable,albeit that ‘cross-hatching’ (Fig B3) method was employed However it was foundthat the kilns tended to be ‘overloaded’ resulting in reduced plenum spaces (Fig B4

& 5) which would result in longer drying times and non-uniformity of moisture content

in the dried product

The kilns appeared to be well constructed with a high level of quality applied to heatexchangers and fans which were mounted over head (Fig B6 & 7) However it wasfound that the humidification system consisted of galvanised pipes with holes drilledalong the length (Fig B8), resulting in blocked pipes and a reduced level of humidity

in the kiln environment It should be noted that spray nossils were not installed.The practice of disconnecting the WB sensor (Fig B10) was of great concern to theTeam as using only DBT to control kilns would result in great difficulty in monitoringand controlling the humidity and overall equilibrium moisture content (EMC)conditions inside the kiln Venting and humidification were also manually controlled(Fig B11) and relied on the operator’s skills at predicting conditions inside the kiln(based only on the DBT), at any point in the drying It was reported that the decision

as to when to change conditions (i.e increase humidity or open / close the vents) inthe kilns, was based on past drying history It is questionable if this practice wouldlead to good drying quality, with minimal degrade, in the final product

Figure B1 Hoang Thanh Factory site

Figure B3 Example of cross-hatch racking.

Figure B4 Example of cross-hatch stacking – note min plenum space

Figure B5 Steam pipe and plenum space (opposite side)

Figure B6 Heat exchangers and fans kilns

Figure B7 Close up of fan housings and external fan motors.

Figure B8 Galvanised steam pipe – no nossils

Figure B9 Fan control box & external gauges for WB & DB sensors

Figure B10 DB sensor mounted on internal wall & WB sensor disconnected.

Figure B11 Manual vent control

Figure B12 Boiler and controls

monitored via a simple analogue thermometer inserted through the wall (Fig C3).This was also a cause for concern to the Team due to heat sinking problemsassociated with the sensor stem being inserted into the brick work, which may result

in an incorrect reading As the kilns did not monitor the WBT there was no waydetermining humidity inside the kiln The owner reported to the Team that at varioustime during the drying schedule, humidity was increased by “throwing a bucket ofwater on the floor”

‘Butterfly’ type vents were mounted in the sides of the kilns (Fig C5) and weremanually opened and closed according to operator’s intuition

Figure C1 Kilns – note clutter Figure C2 Ext fan motors & vents

Figure C3 DB sensor - external mounted

Figure C4 Direct fire heat source

Figure C5 Manually operated butterfly vents

vents

notably wet bulb sensors in installed and working However the kilns were only automatic as the DB and WB sensors were only used for monitoring the kilnconditions That is, the sensors (i.e WB & DB) were read by the operator viaanalogue gauges, externally mounted on the rear wall of the kiln (Fig D8) Theoperated then opened or closed steam valves and vents according to predeterminedconditions set by the specific schedule (Fig D11) that was being used In additionthe material used for the wet bulb wick was considered to be too thick, which wouldhave lead to incorrect readings of the wet bulb temperature (Fig D9).

semi-Stacking of the kiln was done in-situ by hand, and racking practises were generallyfound to be reasonable quality Stickers were of a very high quality, made from KDtimber and machined to size One fault was observed when one of the kilns wasbeing loaded at the time of the Team’s visit This was concerning the in alignment ofthe stack closest to the door (Fig D5) In order to fill the remaining space in the kilnboards were rotated 90° to the direction of air flow This would result in little or no airflow through the front stack as the stickers would effectively create a blockage

The air bypassing between the fans and the heating coils identified in other kilns ofthis type, had been corrected with a simple realignment of the stack at the height ofthe top of the fan compartment, by placing a canter-levered row of boards (Fig D…),creating an effective baffle to prevent any potential air by-pass

The plenum space on the return air side of the kilns was considered to be verynarrow and it is recommended that this be maintained at a minimum of 400mm

Figure D2 Kiln door and overhead opening mechanism.

Figure D3a Kiln with side mounted fans and heat exchangers mounted at 45°

Figure D3b Side mounted fans & close-up of fan

Figure D4 Kilns loaded by hand.

Figure D5 Incorrect alignment of boards

Figure D6 Simple solution to bypassing using canter-levered layer of boards (see arrow)

Figure D7 Good quality stickers.

Figure D8a Controls on rear of kilns

Figure D8b BD & WB readouts

Figure D9 Poor maintained wet bulb wick & wet bulb water supply.

Figure D10 Wood fired steam boiler & specification plate

Figure D11 Chalkboard mounted on rear of - used to display operating condition

Figure D12 Manual vent controls.

Figure D13 Vents in ceiling of kiln & fan compartment

Figure D14 Heat exchanger & steam humidification outlet

Figure D15 Kiln operator accommodation at rear of kiln.

Factory Visits E - Nong Lam University

The Uni kilns were originally designed by Prof Cai There were two styles of kilnobserved The first or older type of kilns were direct fired using flue gases from wastewood, the second or newer type were built in the 1990’s and were used for research

as well as commercial drying It was noted that the plenum space (door side) wasvery narrow, it was explained that this was only for commercial operation and wasincreased to 40cm for research purposes

The fans and heat exchangers were mounted opposite the door and the air flow fromfront to back

Older kiln constructed from brick and concrete

New kilns constructed from pressed metal.

Wood fire providing heat to kiln via ducted flue gases

Heat ducts & fans – note no baffling

Air flow front to back (door view)

Hand loading of kiln

Kiln full loaded – note very small plenum space