Chapter 8

What techniques are available for harvesting switchgrass?

Why would debarking be advantageous when the wood will be burned for energy recovery?

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 \(0.8 \mathrm{wt} \% \mathrm{Cl}\) (ar basis). When taken out of the water, the straw is very wet with a moisture content of \(80 \mathrm{wt} \%\) but a \(\mathrm{Cl}\) content of only \(0.03 \mathrm{wt} \%\). What is the partitioning coefficient of \(\mathrm{Cl}\) when this is defined as the mass fraction of \(\mathrm{Cl}\) in the water phase divided by the \(\mathrm{Cl}\) mass fraction in the wet biomass before submerging? What do you assume?

Give an example of smart blending in a biomass-to-energy supply chain; which purpose(s) can it serve?

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 \(29 \mathrm{wt} \%\) dry matter can be obtained. About 700 households produce \(125 \mathrm{~kg}\). 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?

What is accomplished by biomass washing? For which types of biomass do you think this is relevant? List advantages and disadvantages of washing as a pretreatment technique.

Which particle properties change when size reduction is applied?

List advantages and disadvantages of direct comilling of biomass with coal. Is this always possible?

A wood drying system consists of boiler in which dried wood (with 25 wt\% moisture content) is burned with ambient air \(\left(25^{\circ} \mathrm{C}\right)\) and hot water is generated. The flue gas available at \(130^{\circ} \mathrm{C}\) (immediately after the boiler) is used to dry the wood from \(55 \mathrm{wt} \%\) moisture content in an integrated manner. The wood enters the dryer at \(25^{\circ} \mathrm{C}\). The initial LHV of the wood is \(9.5 \mathrm{MJ} \cdot \mathrm{kg}^{-1}\) (ar) and the wet wood feed rate is \(250 \mathrm{~kg} \cdot \mathrm{h}^{-1}\). Consider a combustion system in which combustion with \(25 \%\) excess air is applied. Use the wood composition for pellets (daf basis) presented in Table \(2.3\). The boiler and dryer may be assumed to have no heat losses. The \(\mathrm{c}_{\mathrm{p}}\) value of wood can be assumed to be constant at \(1200 \mathrm{~kJ} \cdot \mathrm{kg}^{-1} \cdot \mathrm{K}^{-1}\). a. Which type of dryer do you prefer for this system and why? b. What must be the capacity of the air fan (in \(\mathrm{kg} \cdot \mathrm{h}^{-1}\) )? c. What is the amount of heat transferred per unit of time to the water system in the boiler? d. What is the end temperature of the flue gas after the dryer? e. Is the temperature at the dryer exit above the dew point of the water?

How can particle size distributions be determined? Which average particle sizes can you name? Why are they needed?

In practice, is screening always needed for biomass processing?

Miao et al. (2011) show a correlation between the bulk density of biomass and the screen size as a power law expression. Why is the correlation characterized by a negative sign in the power of the characteristic size?

What are advantages and disadvantages of compacting biomass?

What are limits in the application of mechanical dewatering of biomass?

List advantages and disadvantages of direct and indirect drying techniques.

Describe the pros and cons of direct drying using flue gas and steam.

Is microwave heating an economically viable option for large-scale drying of biomass for heating purposes?

Which factors cause emissions of VOCs to increase when using direct drying techniques?