Fluidization of extremely large and widely sized coal particles as well as its application in an advanced chain grate boiler

A pyrolysis combustion technology (PCT) was developed for high-efficiency and environment-friendly chain grate boilers (CGBs). The realization of the PCT in a CGB requires that extremely large and widely sized coal particles should be first pyrolyzed in a semi-fluidized state before being transported into the combustion chamber of the boiler. This article was devoted first to investigating the fluidization of 0–40 mm coal particles in order to demonstrate the technical feasibility of the PCT. In succession, through mixing 0–10 mm and 10–20 mm coal particles in different proportions, multiple pseudo binary mixtures were prepared and then fluidized to clarify the effect of particle size distribution. With raw steam coal used as the feedstock, the superficial gas velocity of about 2.0 m/s may be suitable for stable operation of the fluidized-bed pyrolyzer in the CGB with the PCT. In the fluidization of widely sized coal particles, approximately half of the coal mass is segregated into the bottom section of the bed, though about 15% of 10–20 mm large particles are broken into 0–10 mm small particles because of particle attrition. The experimental results illustrate that an advanced CGB with the PCT has a high adaptability for various coals with different size distributions.

Integrating a semi-fluidized pyrolyzer into a conventional coal-fired chain grate boiler not only increases combustion and thermal efficiency but also reduces NOx and SOx emissions. In order to demonstrate the technical feasibility of the idea and provide a quantitative basis for the design of the advanced boilers, the fluidization and the segregation of 0–40 mm stem coal were investigated experimentally. Figure optionsDownload as PowerPoint slide