Compared with common industrial coal gasification technology, solar CO2 coal gasification has the advantages of reducing CO2 emissions, high purity of product gas, which is also easy to be separated and be stored. One of the major problems affecting solar gasifier' performance is the coal particle contaminating on the glass. So keeping the reactor quartz glass clean is the key to increase reactor efficiency and safety. CO_2 replaces another std inert gas as sweep gas which is recyclable in solar CO_2 coal gasification. This paper establishes a three dimensional mathematical model of a directly-irradiated cyclone-flow solar thermochemical reactor to investigate the effects of sweeping glass inlet positions, the transported pulverized coal particles inlet positions and different inlet flow velocity of the cleanliness of the quartz glass. The numerical results are validated by comparing with the experimental and numerical results of ETH 5 kW cyclone reactor. The results show that keeping the glass clean mainly depends on increasing the inlet flow velocity of the sweeping glass. Increasing the flow velocity can effectively reduce the coal particles contaminating the glass. However, there is an optimal flow velocity for avoiding coal depositing on the window glass. In the determined reactor structure, when the mass flow rate of the sweeping glass is 13.6%~18.2% of the total intake gas, the coal particle track is limited to the opening aperture area and the glass window can keep clean.
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