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Poster Presentation 1-30
Post-Harvest Processing Methods for Reduction of Silica and Alkali Metals in Wheat Straw
David N. Thompson, Jeffrey A. Lacey and Peter G. Shaw
Idaho National Engineering and Environmental Laboratory Biotechnology Department, P.O. Box 1625, Idaho Falls, ID 83415-2203
Telephone: (208) 526-3977; Fax: (208) 526-0828; E-mail: thomdn@inel.gov
High silica and alkali metal levels in wheat straw limit its use for power generation and pulp production. In boilers and fluidized bed combustors, slag deposits occur via the eutectic melting of SiO2 with K2O, and corrosion caused by chlorides trapped by slag deposition in contact with metal surfaces contributes to lowered efficiency and high downtime. When pulp is made from straw via alkaline processes, significant SiO2 dissolves in the black liquor. Effluent is later treated to recover alkali, and SiO2 melts in the lime kiln, slagging and producing alkali-laden glass beads.
A minimum melting point of 950ºC (preferably > 1100ºC) is desirable, corresponding to SiO2:K2O ratios of about 3:1 to 4:1. Mild chemical treatments were used to remove SiO2, K, and Cl. Temperature, concentration, and time were varied to optimize SiO2, K, and Cl removal while minimizing degradation of plant biopolymers. Our results indicate that treatment at moderate temperatures with dilute acid was more effective at removing potassium and chlorine, while dilute alkali was more effective at removing silica. In a distributed system, reduction of silica and alkali metal contents in this manner may prove economical for increasing utilization of the straw for combustion or production of paper pulp.
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