PHYSICAL PRETREATMENT OF BIOMASS - Biomass as a Sustainable Energy Source for the Future - page 242

Risks associated with storing biomass in general are (see, e.g., Kaltschmitt
et al., 2001):

￿ Loss of material by bacterial activity

￿ Fungi growth

￿ Self-heating and ignition

￿ Stench

￿ Renewed wetting and absorption

￿ Agglomeration/structure change by means of frost

￿ Demixing and loss of fines

￿ Release of water from a pile

￿ Dust issues with explosion risks

Systems for storing biomass can be subdivided into two types: outdoor and indoor
storage. Outdoor storage is accomplished either without using cover or by using a
simple cover (e.g., plastic) or below a shed. For indoor storage, a barn can be used,
or storage can take place in a bunker or silo.
The type of biomass packing morphology mainly determines the storage solution.
As occupation of space is costly, often, a precompaction is chosen, e.g., baling or
pelletizing and loading big bags with the pellets. We will not deal with bulk material
handling and transportation in detail as we focus on physical and chemical transfor-
mation processes. The reader is referred to general textbooks in this area (e.g., Mason,
1988; McGlinchey, 2008).

8.4 WASHING

Sometimes, it is worthwhile to extract mineral matter from the harvested biomass to
prevent issues related to thermochemical processing. Especially for biomass contain-
ing high concentrations of both alkali metal ions (Na + and K + ) and chlorine, which is
the case in particular for herbaceous biomasses, such as grasses and straw (Arvelakis
and Koukios, 2002), thermochemical processing can become cumbersome due to
agglomeration/sintering phenomena (fluidized beds), slagging and fouling of heat
exchanger surfaces, as well as corrosion and erosion (see Chapters 9 and 10 for a more
detailed description of these phenomena). This washing procedure (also called leach-
ing) has been studied and suggested by many authors (e.g., Arvelakis et al., 2001;
Jenkins et al., 1996, 1998; Turn et al., 1997) to be an efficient, quick, and cheap
way to substantially diminish the ash content of a biomass material by eliminating
alkali metals (K, Na), chlorine, and sulfur in the first place and secondly calcium
and also minerals extraneously added to the biomass (such as clays), resulting in a
material with improved ash thermal behavior. Leaching can be performed with water,
which is most simple, or with acid and ammonia. Water ensures leaching of alkali
sulfates, chlorides, and carbonates, while ammonia leaches out Mg, Ca, K, and Na,