Rice husk bubbling fluidized bed combustion for amorphous silica synthesis

Published Date
June 2016, Vol.4(2):2278–2290, doi:10.1016/j.jece.2016.03.049

• Author 

• Gabriel M. Faé Gomes ^a,b,,,
• Caterina Philipssen ^c
• Eduardo K. Bard ^a
• Leandro Dalla Zen ^b
• Guilherme de Souza ^a

• aFundação de Ciência e Tecnologia do Estado do Rio Grande do Sul (CIENTEC). Av das Indústrias, 2277, Distrito Industrial, Laboratory of Combustion, Cachoeirinha, RS, Brazil
• bUniversidade do Vale do Rio dos Sinos (UNISINOS). Av Unisinos, 950, Cristo Rei, Politecnic School, São Leopoldo, RS, Brazil
• cPrograma de Pós-Graduação em Engenharia de Minas, Metalúrgica e Materiais, Universidade Federal do Rio Grande do Sul (UFRGS). Av. Bento Gonçalves, 9500, Setor 6, Centro de Tecnologia, Laboratório de Siderurgia, Sala 222, Porto Alegre, RS, Brazil

Received 18 November 2015. Revised 11 March 2016. Accepted 30 March 2016. Available online 7 April 2016.

Highlights

• Rice husk combustion on bubbling fluidized bed with different conditions was applied.
• •
  Rice husk ashes characteristics were related to combustion conditions.
• •
  Velocities up to 0.30 m/s produced ashes with better characteristics.
• •
  Amorphous silica was synthetized from rice husk combustion ashes.
• •
  Different purification methods showed statistically the same silica yield.

Abstract 

Rice husk combustion generates ashes that consist basically of SiO₂ and can be used in several and important applications on its amorphous form. When using bubbling fluidized bed combustion for rice husk ash generation, process variables, like temperature, fluidization velocity, combustion efficiency and elutriation behavior, influence ashes characteristics for synthesis step as well as silica purity. In this way, this work analyses the relations among rice husk fluidized bed hydrodynamics and combustion variables, rice husk ashes’ characteristics and yield of silica synthesis according to ashes purification. Rice husk combustion was applied in a 250 kWth bubbling fluidized bed pilot plant on temperatures of 700, 750, 800 and 850 °C together with fluidization velocities of 0.3, 0.4 and 0.5 m/s. One bench scale fluidized bed was also used to observe elutriation behavior. Rice husk ashes were characterized according to their crystallinity, particle diameter and composition. Silica was synthesized with NaOH impregnation from the different ashes, without purification, with acid purification and water purification. Low carbon content, up to 1.89%, was obtained in the combustion ashes. Combustion efficiency increased with combustion temperature but showed some decrease tendency as fluidization velocity increases. Rice husk ash crystallinity showed values up to 15.7%, which was associated with the presence of quartz and attributed to rice husk contamination, not with bed elutriation. Concerning silica yield, the three different purification procedures prior to NaOH impregnation, although presenting different carbon removals on ash, statistically did not show different values.

Graphical abstract

Keywords

• Combustion
• Rice husk
• Fluidized bed
• Amorphous silica

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  Corresponding author at: Fundação de Ciência e Tecnologia do Estado do Rio Grande do Sul (CIENTEC). Av das Indústrias, 2277, Distrito Industrial, Laboratory of Combustion, Cachoeirinha, RS, Brazil.

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