PHYSICAL PRETREATMENT OF BIOMASS - Biomass as a Sustainable Energy Source for the Future - page 263

PROBLEMS

8.1 Estimate the fossil carbon footprint of 100 km truck transport (diesel consump-
tion 1 L per 10 km) for the transportation of 30 tonnes of wood chips (moisture
content 25 wt%) from storage location to processing unit. How does the fossil
energy utilization compare to the energy content (LHV basis) of the biomass
transported?

8.2 Under relatively wet conditions, storage of wood might lead to a greenhouse gas
emission load of 144 CO 2eq MWh −1 (Wihersaari, 2005); how does this

compare to emissions of a coal-fired power station or a gas-fired combined cycle
power station? What is your conclusion about the importance of appropriate
storage conditions?

8.3 A certain type of straw (with 15 wt% moisture content) is submerged in water
at a mass ratio of water to straw of 4. The straw initially contains 0.8 wt% Cl
(ar basis). When taken out of the water, the straw is very wet with a moisture
content of 80 wt% but a Cl content of only 0.03 wt%. What is the partitioning
coefficient of Cl when this is defined as the mass fraction of Cl in the water
phase divided by the Cl mass fraction in the wet biomass before submerging?
What do you assume?

8.4 Kratky and Jirout (2011) have summarized literature concerning milling of
biomass and its associated specific energy consumption. For the reported values
for hardwood, try to fit the trends in terms of the presented models of Bond,
Rittinger, and Kick. What do you conclude? Give an estimation of the relative
energy use for the reported finest milling (to 1.6 mm) compared to the heating
value of the hardwood.

8.5 In Table 8.2, a particle size distribution is given for crushed Miscanthus pellets.
Determine the mass average, area average, volume average, area volume

average, and Sauter mean diameter. Compare the values. What do you
conclude?

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8.6 A community intends to use their sewage waste (using urine separation) to
derive energy from it. The material is very wet, however, and even with urine
separation, only about 29 wt% dry matter can be obtained. About 700 house-
holds produce 125 kg day −1 of feces matter, and the combustion process that

is to be applied requires 80 wt% dry matter material.

a. How much water must be removed per second in a continuous process?
b. In case no heat losses occur, what would be the energy needed for this drying
process? Neglect the heating up of the feces, but only consider the water heat
up and evaporation at atmospheric conditions.
c. Would the assumption in (b) lead to a large difference in the calculated heat
supply?