Fly Ash Characterization from Cynara cardunculus L. Gasification

Abstract

This study analyzes the characteristics of fines produced during the air-blown gasification of Cynara cardunculus L. in a bubbling fluidized bed. These fines are collected by means of two hot cyclones and a hot filter. The gasification temperature is varied from 700 to 800 ºC using olivine and magnesite as bed materials, with an equivalence ratio (ER) of 0.2. Relatively high carbon content is found in the entrained fines for all experiments. The lower heating value (LHV) of the elutriated fines varies from 5.2 to 9.4 MJ/kg db . Around 75 % of the fines are The final composition of fly ash depends also on the atmosphere, reducing or oxidative, at which the conversion process is carried out 3 . Dong et al. 4 found that a reducing atmosphere promotes the evaporation of Cd and Zn while Pb, Cu, Ni, and Cr volatilization is enhanced under an oxidative atmosphere. In addition, presence of chlorine promotes the evaporation of heavy metals in form of metal chlorides that tend to condense on fine particles, leading into the corrosion of the different parts of the installation 5-8 . Belevi and Moench 9 , on the other hand, found that during the incineration of (household waste) the content of Al, and Ti in fly ash is not much influenced by chemical conditions (temperature or redox conditions) whereas Cu and Zn are favored by oxidative conditions.In the case of biomass combustion, there is an extensive library of literature which deals with ash characterization and utilization 10-14 . However, the information regarding biomass gasification fly ash is very limited 15-17 and its composition is also quite different from that of combustion plants, containing high amounts of unburned carbon, polycyclic aromatic hydrocarbons (PAHs), chlorine and heavy metals. All these features make the use of gasification fly ashes more complicated and suggest that coal combustion fly ash utilization options are not suitable for biomass gasification ash, giving rise to the requirement for some pretreatment 18,19 . Different studies have been performed within the GASASH project 15 , trying to find sustainable and economic methods for gasification ash management. When the carbon content is high, combustion is the most promising method to reduce the un-reacted carbon and the amount of undesirable compounds such as the PAHs, chlorine and some heavy metals as well as recovering energy. This reduces the volume of the fly ashes and applications such as construction products can be considered for the new ash generated 15 .

Fluidized bed gasification of biomass from plant-assisted bioremediation: Fate of contaminants

“…circumstance was already analysed in the paper of Serrano et al [42], that studied the FBG of Cynara Cardunculus, by using olivine and magnesite as bed materials.They noticed a relevant release of Mg, Fe and Cr from the bed. However they did not measure the metal concentration in the bottom ashes and then the extent of their analysis remained limited.…”