A novel fluidized bed ash cooler called Bi-spouted-bed fluidized bed ash cooler was developed for circulating fluidized bed (CFB) boilers. It consists of chambers that have some characteristics of slot-rectangular spouted bed (SRSB), and the flow structure is similar to a combination bubbling bed and SRSB, thus we call it quasi-slot-rectangular spouted bed (QSRSB). A cold model of quasi-slot-rectangular spouted bed (QSRSB) with a cross-section of 900 mm x 200 mm was built. And a binary mixture of different sized particles was adopted, and the jetsam (bigger) and flotsam (smaller) component were used as tracers and bed material respectively. Experimental investigation on lateral mixing of tracer particles has been conducted. The lateral mixing process of tracer particles was studied. In addition, the effects of particle. size of bed material d(p), superficial gas velocity u, static bed height h and air inlet section width 5 on the effective lateral dispersion coefficient of tracers were investigated. Meanwhile, a comparison of the effective lateral dispersion coefficient of tracers in QSRSBs and the bubbling fluidized bed with the same upper cross-section was conducted. It is found that the tracers disperse from regions of higher tracer concentration to regions of lower tracer concentration. Furthermore, the effective lateral dispersion coefficient of tracers increase with the increase of superficial gas velocity u, static bed height h and air inlet section width 5, but decrease with the increase in size of bed material dp, respectively. Additionally, the effective lateral dispersion coefficient of bubbling fluidized bed appears to be larger than that of QSRSBs when gas velocity at the upper section of bed, U, is greater than 03 m/s. However, the minimum U that ensuring the normal operation of QSRSBs is less than that of bubbling fluidized bed in the present work, which means that QSRSB has a better adaptability to the tracer granularity with the same gas flowrate. (C) 2013 Elsevier B.V. All rights reserved.