What is the inorganic content, “ash forming matter”, of biomass and wastes?
All solid fuels contain an inorganic, not combustible fraction, constituted by elements such as Cl, S, K, Na, Mn, Cd, Cr, Zn, Si, Mg, etc. Elements are present in the fuel in different phases and minerals. During thermal conversion the inorganic matter present in the fuel undergoes chemico-physical transformations, changing its association, form, phase and forming an etherogenours matter called generally “ash”.
What is ash?
Ash, the transformed inorganic matter, stays in the plant in solid/liquid phase or is released to the environment in gaseous phase. Ash can often be splitted in bottom ash and fly ash. Fly ash is composed by a fine and a coarse fractions.
What are bed materials and combustion additives?
Bed materials are inert which are used to increase the inertia of the bed, in fluidized bed combustion, allowing to convert the fuel at low temperatures. Example of bed materials are: sand, feldspar, dolomite. Additives are materials injected in the plant or premixed with the fuel, in order to capture critical inorganic elements and promote specific interactions. Examples are: aluminosilicates (kaolin), Ca-based (gypsum), S-based (ammonium sulphate).
Which are ash-related problems in thermal processes for bio-waste fuels?
Ash agglomeration (fluidized beds): rapid formation of agglomerates, which causes improper fluidization till interruption of operations.
Ash slagging: deposition of partially molten ash particles on the furnace water walls, bottom grid/roof, refractories and more in general on radiant heat exposed surfaces (high temperatures).
Ash fouling: deposition of condensed and impacting compounds on the upper, medium or low temperature sections of the boiler (convective heat exposed surfaces). Deposits are often (partially) removed with sootblowers, cleaning devices which use steam or water.
Corrosion: metal wastage mechanisms occurring in high and low temperature sections.
Erosion: metal wastage due to the presence of hard compounds in the ash and increasing with increased materials velocities.
Flue gas conditioning disturbances: ash can influence the operation of the flue gas cleaning systems, e.g. by deactivation of catalysts or sorbents.
Those problems affect the thermal efficiency of the plant and increase maintenance costs therefore reducing the system’s profitability.
Why to use BIOFACT?
BIOFACT provides, at low cost, a confidence on results comparable to combustion pilot testing. It is easy to use and rapid to apply for a quick fuel screening. The best use of BIOFACT is in a funnel strategy to screen and compare fuels. The tool generates results to aid fuel selection, design and boiler operational decisions. It helps preventing the sourcing of unsuitable fuels and premature plant outages.