Characterization of biomass using instruments – Measurement of forest and crop residues - Biomass as Energy Source: Resources, Systems and Applications - page 66

might not require a high precision if the measurement result is used for a large number of ship-
ments. However, whereas a small bias has lesser importance for logistic purposes, systematic
measurement errors would cause a corresponding error in the prices paid.
A large number of instrumental methods deliver indicative measurements of moisture content.
Possibly, buyers and sellers could agree on anymeasurement method that they are comfortablewith
it. However, since unbiasedness is an important for price settlement, performance requirements
are likely to high for systems that will determine the price of a shipment. To facilitate trade,
methods for large-scale use are likely to be subject to accreditation The Bestwood BAS-700 was
the first method to receive such an accreditation in Sweden.
3.5.3 Logistics
Access to real-time moisture information facilitates a large number of applications. One obvious
application is the rejection of shipments that do not meet the specified quality requirements.
However, a fully automatic system for price settlement will also have economic benefits in terms
of avoiding manual labor. Other applications include automatic handling of invoices, real-time
inventory control and order systems that adapt to changes in the production targets.
Access to real-time feedback also has benefits for the supplier since it will be easier to adapt
to deviations in terms of contracted energy content or changes in production forecasts. On-site
measurement at a terminal would also allow for delivery of a biomass that is more optimal
with respect to the moisture content and variation required by the energy producer. In this case,
measurement costs have to be weighed against the price premium paid by the customer. Another
aspect is that rising demand is likely to increase the use of biomass that is considered inferior
today. With an adequate measurement system, it is possible to deliver a more stable product
despite the lower quality of the biomass.
3.5.4 Fuel mixing
There are several applications for fuel mixing on the site of the energy producer. The general
theme is to direct material flows in a way that reduces the variation in moisture content and
to reach an average moisture content that is optimal for the configuration of the boiler and the
production targets with respect to power and heat.
The potential in this respect will depend on the possibilities in mixing fuel at the respective
plants. In Sweden, some plants have large areas to store fuel. It is then possible to store biomass
in different piles, depending on moisture content, and mix an appropriate fraction when the fuel
is to be used. However, the majority of the plants have a small storage area or no storage area
at all. If there are several entry points where the biomass is tipped into a silo, one strategy is to
direct trucks to appropriate entry points depending on the moisture content. This strategy is used
by a large producer on the Swedish West coast.
3.5.5 Boiler control
Boiler control utilizes information about the moisture content of the fuel on its way to the boiler.
Being able to compensate for fluctuations in fuel moisture, it is possible to stabilize the fuel feed
and combustion process and slightly increase capacity and overall efficiency.
Precision is more important than accuracy since the control loops act on relative changes
where the presence of a systematic and constant bias has less importance. An indicative precision
requirement for on-line control might be approx. 2%-units of moisture, which is of the same
magnitude as the gravimetric method in a lab.
3.6 FUTURE PERSPECTIVES
Today, the measurement technology is developing rapidly. Some examples of hardware were
shown in section 3.4. New systems are likely to enter the market and the range of products might
change in the near future. Certain trends are already more or less visible.