Which factors influence the solid fuels inorganic composition?

The composition of ash forming matter in the biomass fuels is largely varying and depends on multiple factors, not only the biomass type. For example, for biomass, poor-in-nutrients soils can reduce the plant’s capacity to uptake inorganic substances. It was demonstrated that, in spruce, tree branches and twigs contain a higher content of inorganic matter (especially K, Na, Si) than stem wood. It is also known that delayed harvest in spring can result in a reduced inorganic content (especially K).

In this overview, a summary of twelve factors which can influence the biomass fuels inorganic composition is proposed.

Biomass type

1.     The plant species, e.g. variety, genotype.

2.     The state of the plant development or age, the plant growth cycles/season.

3.     The part of the plant considered (and mixes) such as leaves, bark, stem, fibres, tops.

Soil, climate and agricultural practises

4.     The soil characteristics: type, pH, nutrients or composition, pollutants, water quality.

5.     The type of fertilization or pesticides applied.

6.     The climate of the location: rains, atmospheric pollutants and external environmental factors (E.g. road side vegetation contaminated with salt (road de-icing); biomass from river maintenance; driftwood.)

Harvesting, transport, pre-treatment

7.     The selected harvest date and season.

8.     The collection method, harvesting operations (soil and dust incorporation, machines pollution, biological contamination) and transport conditions (ships, trucks potential contaminations).

9.     The storage type/time, if any, and the drying (or other pre-treatment/upgrading) type/duration, if any.

10.  The size reduction e.g. the fineness of the fuel or particles size distribution.

Analyses of the samples

11.  The material sampling method and its representativeness (sampling standards).

12.  The ashing method and the ashing temperatures (production of the ash sample to analyse) as well as the analytical instrumentation used for the ash composition analyses (errors theory).

These factors can influence the inorganic matter content of each biomass, that is why each fuel is different.

It might be complex for producers to control those factors, especially for low-grade or opportunity fuels. Detailed compositional data for the specific fuel to be processed are needed and it is not recommended to consider literature data.

In our thermochemical simulations, we study the ash behaviour of the specific fuel sample, mixture or portfolio, processed in each specific energy plant.

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