This paper mainly studies the separation mechanism of a square cyclone at high inlet solid concentration. It is shown that the separation mechanism is very different from that at low inlet solid concentration. A phenomenon called two-instantaneous separation exists, which has never been found in square cyclone experiments before. This phenomenon has bearing on the limit load of gas-solid flow, and the part exceeding the limit load will be separated instantaneously after entering the square cyclone. A model called two-instantaneous separation is introduced in this paper as well as the calculations of limit load and separation efficiency, which can be used in the design and research on a square cyclone for circulating fluidized bed boiler. q1999 Elsevier Science S.A. All rights reserved.

Experimental research on cellulose pyrolysis under catalysis of metallic salts was done on a thermo balance and a rapid pyrolysis system. Thermogravimetric analysis showed that K+ catalyzed the formation of active cellulose strongly and decreased the activation energy of cellulose pyrolysis. Experimental results indicated that K+ would promote the formation of char and restrain the production of bio-oil largely. Fe2+ had a similar catalysis effect on cellulose pyrolysis with K+. Fe2+ particularly catalyzed the formation of small molecule gaseous product while K+ the formation of char. The addition of K+ or Fe2+ resulted in a reduction of levoglucosan formation, and enhanced the production of hydroxyacetaldehyde and other small molecule components. Levoglucosan and hydroxyacetaldehyde were formed by the decomposition of active cellulose in a parallel mode. The secondary cracking of levoglucosan would also produce hydroxyacetaldehyde. A modified cellulose pyrolysis mechanism model was proposed based on the B-S model.