Agglomeration mechanism in biomass fluidized bed combustion – Reaction between potassium carbonate and silica sand

Big problem, little answer: overcoming bed agglomeration and reactor slagging during the gasification of barley straw under continuous operation

“…10,[12][13][14][15][16] The transition between adapting uidised beds previously used for coal to biomass waste for power generation is minimal due to the fuel exibility and high combustion efficiency. 10,13,[17][18][19] Fluidized bed reactors provide lower emissions, low temperature operation, better heat transfer, solid/gas mixing and as a result a large surface area for an upward owing gas stream. 10,13,15,18,20 Not without issues, the uidised bed reactor, especially beds made from silica sand, can suffer from 'bed agglomeration'.…”

“…This phenomenon has been reported over the last 30 years for generating energy from lignite. 15,17,[19][20][21] Bed agglomeration occurs when ash components from the biomass feedstock interacts with the bed material, due to lower melting temperature of ash compounds opposed to oxides, layers and agglomerates form restricting gas ow and subsequently reactor bed destabilisation and collapsing as a result of deuidisation. 14,15,[22][23][24] Alkali metals in the biomass waste form eutectic mixtures in the liquid phase that deposit on the surface of the bed material grains and form a physical linkage between the bed particles which leads to bed agglomeration via alkali silicate (molten) bridges, fusing the bed material particles together.…”

“…14,15,[22][23][24] Alkali metals in the biomass waste form eutectic mixtures in the liquid phase that deposit on the surface of the bed material grains and form a physical linkage between the bed particles which leads to bed agglomeration via alkali silicate (molten) bridges, fusing the bed material particles together. 13,[15][16][17]23 As a prelude to de-uidisation there is a decrease in the heat transfer and the bed hydrodynamics which inuence the temperature distribution throughout the reactor. 13,18,25 As a cascade process, a steady or sharp decrease in the reactor pressure can be detected due to an unstable bed temperature.…”

“…As a result of the stopstart behaviour and corrosive nature of some of the inorganic deposits, the lifespan of the equipment and reactor on a whole are radically decreased. 10,17,27 The occurrence of bed agglomeration is highly dependent on the inorganic composition of the biomass feedstock, specically alkali metals, in conjunction with the reactor operating temperature and reaction atmosphere. 13,17,21,22,28,29 The most problematic elements that participate in bed agglomeration are K, S, Cl and P, this is because they can form low melting point compounds with the bed material.…”

New chemical mechanism explaining the breakdown of protective oxides on high temperature steels in biomass combustion and gasification plants

“…K 2 O-SiO 2 silicate formation plays a major role in deposit formation in the furnace (slagging) and in bed agglomeration issues in uidized bed boilers, where silica containing sand is oen used as the bed material. [11][12][13] Formation of K 2 SO 4 plays a major role in aerosol and deposit formation further downstream of the boiler. 14,15 K 2 SO 4 formation may decrease the corrosion rate of the heat exchangers forming a less corrosive deposit than KCl or KOH/ K 2 CO 3 .…”