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Biomass has a great potential for production of syngas and chemicals; however, it has stood in the shadow of natural gas (NG) and coal due to technical problems and issues such as tar formation. In this paper, syngas production from catalytic air–steam gasification of biomass in a fluidized bed was investigated. To enhance the yield of produced syngas and reduce its tar content by cracking, limestone, calcined dolomite, and olivine were used as catalyst. The maximum mole fraction of H2 was found to be 49.1 vol% at 1000 °C and a steam/biomass ratio (S/B) of 1.0 with dolomite present. Compared to olivine and dolomite, calcined dolomite was proved to be more effective for gas production and tar destruction. The results also showed that the particle size has a weak influence on gasifier performance, with only a slight decrease in tar content with decreasing biomass particle size.

In the small-scale industrial CFB(SICFB) boiler, the furnace height is limited, the fuel particles can't be burned out in the furnace completely. So the circulating solid particles would combust in the external loop including the cyclone and the external fluidized bed heat exchanger(FBHE). Moreover, there's a macroscopic horizontal movement of circulating solid particles exists in the FBHE from its inlet to outlet. Under the impacts of combustion, heat transfer and particles attrition, parameters such as the bed temperature, combustion products concentrations, solids physical properties and heat transfer coefficient are changed along the solids movement direction. In this research, a one-dimensional cell model along the solids horizontal movement direction was established in the FBHE of a industrial CFB test-rig. The distributions, as well as the variations of the above parameters were calculated and analyzed based on the energy balance and material balance in each cell. The calculation results were compared with the experimental results to be validated. The energy balance and material balance characteristics of the FBHE were obtained accordingly. These results can provide referential materials for design and operation of the FBHE in small-scale industrial CFB system.

In this paper, the pressure fluctuation in a fluidized bed was measured and processed via standard deviation and power spectrum analysis to investigate the dynamic behavior of the transition from the bubbling to turbulent regime. Two types (Geldart B and D) of non-spherical particles, screened from real bed materials, and their mixture were used as the bed materials. The experiments were conducted in a semi-industrial testing apparatus. The experimental results indicated that the fluidization characteristics of the non-spherical Geldart D particles differed from that of the spherical particles at gas velocities beyond the transition velocity U c . The standard deviation of the pressure fluctuation measured in the bed increased with the gas velocity, while that measured in the plenum remained constant. Compared to the coarse particles, the fine particles exerted a stronger influence on the dynamic behavior of the fluidized bed and promoted the fluidization regime transition from bubbling toward turbulent. The power spectrum of the pressure fluctuation was calculated using the auto-regressive (AR) model; the hydrodynamics of the fluidized bed were characterized by the major frequency of the power spectrum of the pressure fluctuation. By combining the standard deviation analysis, a new method was proposed to determine the transition velocity U k via the analysis of the change in the major frequency. The first major frequency was observed to vary within the range of 1.5 to 3 Hz.

Most of the small scale industrial CFB (SICFB) boilers in China work at low operating pressure. Compared with the big scale CFB boiler in power plant, the heat ratio of water evaporation is higher in the SICFB boiler. Consequently, evaporating submerged tubes are always installed in the furnace emulsion zone in order to avoid overheating of flue gas at the furnace outlet. The boiler metal consumption could also be reduced because of the higher heat transfer coefficient of submerged tubes. But serious erosions are brought to the submerged tubes as the furnace emulsion zone always works at turbulent fluidized bed state with higher fluidization velocity. In the study, for alleviating the erosion to the submerged tubes, all the evaporating submerged tubes are set in the loop seal instead of in the furnace emulsion zone, and the loop seal is enlarged accordingly to be an evaporating loop seal (ELS). An 11t/h SICFB boiler with an ELS has been put into industrial application, the design consideration and operating characteristics of the boiler are systematically discussed in the paper.