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close this bookDesign of a Suspension Burner System for Forestry and Agricultural Residues (NRI)
close this folderAppendices
View the documentAppendix 1: Lighting and starting procedure
View the documentAppendix 2: Coir dust dewatering trials
View the documentAppendix 3: Results of the timber drying trials

Appendix 3: Results of the timber drying trials

Summary of results

Typical heat balance on suspension burner/timber drying unit

Typical heat balance

Note: * ignoring heat losses from the exposed surfaces of the heat exchanger system.

A heat balance was conducted for each trial so that an assessment of the major heat losses could be made. It served to highlight that the unit is very energy efficient in terms of the transfer of heat generated from the burner to the kiln, and actual losses from the burner are small in comparison to the rest of the unit.

Basic data for typical run

Basic data for typical run (cont.)


* Combustion gas temperature inside the burner were, in general, 100°C higher
* * Average daily ambient temperature 32°C Average nightly ambient temperature 22°C

Calculated results for a typical run


* gross calorific value x feedrate (dry basis). gross calorific value taken as 20,500 kJ/kg
** net calorific value x feedrate (wet basis)
† primary
heat exchanger efficiency =

secondary heat exchanger efficiency =

where Tcg = temperature of suspension burner combustion gas
Tpfg - temperature of primary heat exhanger flue gas
Tsfg - temperature of secondary heat exchanger flue gas
Tamb - temperature of ambient air
‡ using the relationship: W=

where W = mass flowrate of air (kg/h)
NCV = net calorific value of feed (kJ/kg)
FR = feedrate of woodwaste, dry basis (kg/h)
Cp = specific heat of air, calculated at the suspension combustion gas temperature (kJ/kg°C)
DT = temperature differences between suspension burner combustion gas and ambiant (°C)

then, excess air =

where Ws = stoichiometric air requirements, taken as 4.5 kg of air per kg of wet sawdust at 15% moisture content

Calculated heat losses for a typical run


* ambient temperature 27°C (300 K) average
** Using the relationship; Q=CE (Ts4-TA4)
where Q - radiated surface heat loss (kJ/h m2)
C - Stefan Boltzman constant - 2.0142 x 10 7 kJ/h m' K4
E - emissivity
Ts- surface temperature K
TA- ambient temperature K
† Using the following relationships for natural convextion (IHVE Guide 1970); (a) horizontal surfaces facing up ho=2.5
(T) 0.25
(b) vertical surfaces ho= 1.9 (T) 0.25
(c) cylindrical surfaces ho= 1.32 (T/do) 0.25
where ho= heat transfer coefficient for natural convection (kJ/h m2 °C)
T - temperature difference between the surface and ambient, (°C)
do= diameter of cylinder

Record of kiln samples for a typical run

Record of kiln samples for a typical run (cont.)

Notes: moisture content =

estimated dry weight =

Seasonal quality record for a typical run

Notes:Category: 1 - no defect
2 - slight
3 - moderate
4 - severe
5 - very severe
Average timber grade: good
Additional remarks: timber load was weighted to reduce defects; quality assessment is purely subjective