Combustion Characteristics of Spent Catalyst and Paper Sludge in an Internally Circulating Fluidized-Bed Combustor

Abstract

Combustion of spent vacuum residue hydrodesulfurization catalyst and incineration of paper sludge were carried out in thermo-gravimetric analyzer and an internally circulating fluidized-bed (ICFB) reactor. From the thermogravimetric analyzer-differential thermo-gravimetric curves, the pre-exponential factors and activation energies are determined at the divided temperature regions, and the thermo-gravimetric analysis patterns can be predicted by the kinetic equations. The effects of bed temperature, gas velocity in the draft tube and annulus, solid circulation rate, and waste feed rate on combustion efficiency of the wastes have been determined in an ICFB from the experiments and the model studies. The ICFB combustor exhibits uniform temperature distribution along the bed height with high combustion efficiency (Ͼ90%). The combustion efficiency increases with increasing reaction temperature, gas velocity in the annulus region, and solid circulation rate and decreases with increasing waste feed rate and gas velocity in the draft tube. The simulated data from the kinetic equation and the hydrodynamic models predict the experimental data reasonably well. INTRODUCTIONRecently, most refinery companies installed desulfurization processes to produce light oils from cracking of heavy oils. Consequently, large amounts of catalysts in the crackers are deactivated because of the deposition of vanadium and coke during the cracking reaction. Nickel (Ni), vanadium (V), and coke in the raw oil are deposited on the hydrodesulphurization catalyst or inside pore of the catalyst, and the weight is increased Ͼ50%. In Korea, spent hydrodesulphurization catalysts are producing Ͼ4500 t/yr from hydrodesulphurization processes, and it must be treated properly without environmental pollution. To treat this spent catalysts, there are three methods available, including regeneration of spent catalyst for additional use, recovery of valuable metals (Co, V, and Ni) after combustion of coke in the catalyst, and solidification after melting of the catalyst for landfilling. During the regeneration of the deactivated catalyst, it is necessary to remove coke and sulfur from the combustion of spent catalysts.The production of paper sludge has been also increased because of the large quantity of industrial wastewater from paper mills. Typical wastewater treatment processes generate great quantities of sludge from either primary (clarifiers) or secondary treatments (anaerobic and aerobic biological processes). As an example in the mechanical pulping industry, the removed primary and secondary sludge, ϳ25 and 12 kg/t processed pulp, respectively, that make up sludge disposal is a major environmental problem. 1 Until now, sludge landfill is a preferred disposal method; however, landfill is no longer a viable solution because of the decrease in space available for landfills, the rising tipping fees, and the growing concern about their impacts on the environment. Thermal utilization of sludge may be an economic and sustainable disposal solution. I...

Metal recovery from spent hydrodesulfurization catalysts using a combined acid-leaching and electrolysis process

“…However, HDS catalysts may be deactivated by fouling the active surface with element (e.g., S, C, V, Fe, Ni, Si, Zn, and As) deposits during the cracking reactions [3][4][5]. As a result, large amounts of deactivated HDS catalysts become spent catalysts that need to be treated to meet environmental regulations because the predominant elements, such as V, Ni, Mo, and Co, in the catalysts are toxic and can be easily leached out with water to cause secondary pollution [3,6].…”

“…Studies on treatments of spent HDS catalysts have used different approaches, such as hydrometallurgy, stabilization and encapsulation, conversion of spent catalysts into useful products [9], and regeneration of spent catalysts with nitrogen-air or steam-air [3][4][5][6]. Among these methods, the hydrometallurgy process is an approach that has a good commercial potential to extract valuable metals due to the large amount of spent HDS catalysts and the high content of valuable metals (e.g., >11% Mo, >5% Ni, and >11% V) in the catalysts.…”

Heat transfer process in gas–solid fluidized bed combustors: A review

“…Therefore, ICFBs have been widely used for various processes, such as coal combustion and co-combustion [53,56], coal gasification [57], incineration of solid wastes, and continuous adsorption and desulfurization [58]. No information is available in the literature on the combustion efficiency and heat transfer characteristics in the ICFB comparing with that in case of bubbling fluidized bed and circulating fluidized bed.…”

Hydrodynamic behaviors of an internally circulating fluidized bed with wide-size-distribution particles for preparing polysilicon granules

“…To solve this problem, a new structure of internally circulating fluidized bed (ICFB) with separate heating and reaction zones divided by a centrally located draft tube was proposed [5,6]. The ICFB has many advantages such as reduced height and construction cost, smaller heat loss and longer residence time of particles, and therefore has been widely utilized in coal combustion [7,8], coal gasification [9], incineration of solid wastes [10,11] and desulfurization [12,13]. When the ICFB is used for polysilicon production, the reactant gas (SiHCl 3 and H 2 ) is pumped into the reaction zone (draft tube) and the fluidizing gas (H 2 ) is pumped into the heating zone (annulus), thus the wall deposition can be significantly reduced due to the absence of SiHCl 3 in the heating zone.…”