Filetype PDF | Posted on 16 Sep 2022 | 3 years ago
Authentication
digital resources
161x Filetype PDF File size 2.14 MB Source: www.tropicaltimber.info
A PRACTICAL GUIDE
FOR THE DETERMINATION OF
MOISTURE CONTENT
OF WOODY BIOMASS
A Practical Handbook of Basic Information,
Definitions, Calculations, Practices and Procedures
for Purchasers and Suppliers of Woody Biomass
Developed by:
Robert Govett, University of Wisconsin-Stevens Point
Terry Mace, Wood Utilization and Marketing, Wisconsin DNR
Scott Bowe, University of Wisconsin-Madison
A PRACTICAL GUIDE FOR THE
DETERMINATION OF
MOISTURE CONTENT OF
WOODY BIOMASS
Overview
Use of woody biomass such as mill residues and
forest residues is not a new practice by any stretch
of the imagination. There is a long and widespread
tradition of the use of woody biomass in energy appli-
cations such as a boiler fuel, and it represents a very
large fraction of the total renewable energy produced
in Wisconsin and across the United States. Interest
in increased use of woody biomass has grown signifi-
cantly in recent years, particularly in the Lake States, With the expanded use of woody biomass, loggers,
with increased conversion or replacement of fossil foresters and others within the industry (and some
fuel fired boilers to the use of woody biomass and people from outside the industry) are now being
with consideration of woody biomass as a feedstock forced to understand and deal with wood moisture
for the production of biofuels. While many sectors content issues. For example, loggers or foresters that
within the forest industry, such as sawmills, veneer may have sold woody biomass on a green ton basis
operations, chip mills, pulp mills and all types of sec- may soon need to understand the practical aspects of
ondary manufacturers routinely deal with moisture selling the same woody biomass on a dry ton basis.
content of wood, other sectors of the industry such Also boiler operators outside of the industry need an
as loggers and practicing foresters have typically had understanding of wood moisture determination in
much less need to concern themselves with moisture fuel acquisition and testing. This paper is designed to
content determination. Additionally, the basis and serve as a practical guide for anyone in the Wisconsin
methods of determining moisture content are quite industry in understanding the issues related to deter-
variable depending on the products being dealt with mination of moisture content of woody biomass and
and the sector of the industry being represented. reasonable methods that can be used to determine
moisture content of woody biomass in an industrial
setting.
Woody biomass can be composed of wood (in the
form of some kinds of mill residues such as sawdust,
trim ends, etc.), or bark (typically that has been
removed in a debarking process), or a combination
of wood and bark (such as cull logs or bolts, chipped
tree trimmings etc.). Also the forms of the material
can vary considerably, ranging from roundwood of
various sizes and lengths, slabs, edgings, sawdust,
hogged fuel, and whole-tree-chips and also in the
form of recovered residue such as branchwood that
may include some fraction of needles. For purposes
of simplicity in this paper, the term “wood” in discus-
sion will be used as a generic term for woody biomass
in all its various forms in calculations and discussions
for which the calculation would be the same for wood
(xylem) or woody biomass.
3
The basis on which moisture content % is It is important to note that both of these
determinded (i.e. MC as a % of what?) methods of determining moisture content are appro-
priate and are commonly used. There is good reason
There are two common ways in which the moisture to use the ovendry basis for measuring moisture
content percentage (MC%) of wood is content in solid wood products. For example, where
routinely expressed. calculations may need to be made regarding chang-
GREEN BASIS: ing moisture contents over time using periodically
In the green or wet basis (usually ab- measured sample pieces (such as sample board in a
breviated “Green basis”) method, the percent mois- dry kiln), in using the ovendry basis method, the de-
ture in the wood is expressed as a percentage of the nominator in the equation would not change for the
TOTAL weight of the wood, including both the dry piece for the string of calculations to estimate mois-
wood material and the water. This method is most ture content at various times in the drying process. In
commonly used for pulp chips and hogged fuel and a similar vein, there is good reason to use the green
this method is generally the method used to deter- basis method for pulp chips and fuel, where it is used
mine the MC of woody biomass. It is computed as for a one-time point estimate of what fraction of the
follows: whole is usable fiber (or fuel) and what fraction is wa-
MC% (Green basis) =( weight of water ) 100 ter. As you will note, in the example provided above,
weight of water + dry weight of wood * the OD basis moisture content can (and will) exceed
100% on occasion – this is NOT an error – it simply re-
OVENDRY BASIS: In the ovendry basis (usually ab- flects that the weight of water in the sample exceeds
breviated “OD basis”) method, the % moisture in the the weight of dry material (this is quite common in
weight of water many circumstances in Wisconsin, such as with aspen
wood is expressed as a percentage of the dry weight
MC% (OD basis) =(dry weight of wood )*100 in the winter, and for many softwoods and some
of wood. This method is the standard method used
weight of water lower density hardwoods). In any context regard-
in this country to express moisture content for solid
MC% (Green basis) =( )*100
weight of water + dry weight of wood ing the expression of moisture content of woody
wood products of all kinds including lumber, veneer,
51 biomass in an industrial setting it is essential that
plywood, OSB, particleboard and other panel
MC% (Green basis) = *100 =51% MC (Green basis)
( )
products. 100 all parties concerned understand the basis on which
the moisture content is determined and expressed.
MC% (OD basis) =( weight of water ) 100 For this reason, it is highly desirable (if not essential)
dry weight of wood *
weight of water to clearly express the basis on which the moisture
MC% (Green basis) =( weight of water )*100
MC% (Green basis) = weight of water + dry weight of wood 100
( )*
weight of water + dry weight of wood content was determined. It is so easy to succinctly,
51
In terms of an example, assume you have taken a clearly and accurately express “MC (OD basis)” or
MC% (OD basis) = 100 = 104% MC (OD basis)
( )51
49 *
sample of woody biomass equal to 100 grams in
MC% (Green basis) = *100 =51% MC (Green basis)
( ) “MC (Green basis)” - which are two very different
100
total weight, and you are able to determine that the things – that it would be utterly foolish to simply
weight of water
MC% (OD basis) = weight of water
sample consists of 49 grams of dry woody biomass
( )*100 express “moisture content” or “MC” (without any
MC% (OD basis) = dry weight of wood 100
(dry weight of wood )*
material (after water equal to 51 grams is removed), expressed basis) and create the potential for con-
the moisture contents would be calculated as follows: fusion. This potential for confusion (and contract
MC% (OD basis) = 51 MC % (OD basis)
( ) 100 = 104% MC (OD basis)
MC% (Green basis) = * 100
( )
49 * disputes, disagreements etc.) can largely be avoided
51
100% + MC% (OD basis)
MC% (Green basis) = 51 *100 =51% MC (Green basis)
( )
MC% (Green basis) = 100 *100 =51% MC (Green basis)
( ) by simply specifying the basis being used to express
100
the percentage moisture content. In almost all cases
And, for THE SAME SAMPLE: in transactions regarding woody biomass it will prob-
MC % (OD basis) ably be the case that using the Green basis moisture
MC% (Green basis) = 100
( )*
51 100% + MC% (OD basis) content would be used – but there are circumstances
MC% (OD basis) = 51 100 = 104% MC (OD basis)
( )
MC% (OD basis) = 49 * MC % (Green basis)
( ) 100 = 104% MC (OD basis)
49 *
MC% (OD basis) = ( )*100 where MC may be determined using the OD basis and
100% - MC% (Green basis) conversion could be required, prompting confusion.
4
MC % (Green basis)
MC% (OD basis) = MC % (OD basis) 100
( MC % (OD basis) )*
MC% (Green basis) = 100% - MC% (Green basis) 100
( )*
MC% (Green basis) = 100% + MC% (OD basis) 100
( )*
100% + MC% (OD basis)
MC % (Green basis)
MC% (OD basis) = ( MC % (Green basis) )*100
MC% (OD basis) = 100% - MC% (Green basis) 100
( )*
100% - MC% (Green basis)
no reviews yet
Please Login to review.
