MIL-HDBK-1003/6
Wood. Today, the use of wood for steam generation is largely
5.1.4
confined to wood chip burning and is generally used in locations where it is
available as a by-product or waste from the lumber or paper industry. The
moisture content can vary widely to the extent that handling and combustion of
the fuel can be difficult. Refer to Table 11. Ash content is lower than ash
in coal and ash disposal can be less of a problem.
Table 11
Available Energy in Wood
+))))))))))))))))))))0)))))))))))))))))))))))))))0)))))))))))))))))))))))),
*
*
*
*
Moisture, %
Heating value, Btu/Lb
Lb Water/Lb Wood
/))))))))))))))))))))3)))))))))))))))))))))))))))3))))))))))))))))))))))))1
*
*
*
*
0
8,750
0.00
*
*
*
*
20
7,000
0.25
*
*
*
*
50
4,375
1.00
*
*
*
*
80
1,750
4.00
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Source:
Marks' Standard Handbook for Mechanical Engineers, Baumeister,
Avalone & Baumeister, 1978.
Chipped Wood. Fresh timber contains 45 to 55 percent moisture,
5.1.4.1
mostly in the cell structure of the wood. After air drying, the moisture
content reduces to 18 to 25 percent. Kiln-dried wood contains about 8 percent
moisture. Some impurities found in wood fuel are sand in bark and dirt from
the harvesting operation. The heating value of chipped wood as harvested
averages about 4,200 Btu/lb (9 770 kJ/kg) although the heating value of dry
wood averages approximately 8,800 Btu/lb (20 504 kJ/kg). Refer to Table 12.
Bark. Bark is a common waste product in paper mills from debarking
5.1.4.2
of tree trunks. Bark received from barking drums often contains sand and dirt
and as much as 65 percent moisture and has very little fuel value unless this
material is dried. Once dried, this fuel has essentially the same heating
value as the wood. Bark readily absorbs moisture from the air and even if
dried, it soon has reabsorbed moisture in storage. Bark is not considered as
a suitable fuel because of the difficulty in its burning, handling, and
storage.
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