Revamping downdraft gasifier to minimize clinker formation for high-ash garden waste as feedstock

[Display omitted] •Improved design of a downdraft gasifier proposed to accommodate high-ash feedstocks.•Clinker is minimized by manipulating grate movement and changing air feed position.•Grate movement, ER, and air split ratio were optimized to obtain a desired performance.•LHV of producer gas and CGE for best case were found to be 3.59 MJ/Nm3 and 62.61%. The conventional downdraft gasifier, when used with garden waste pellets (ash ∼10%) as feedstock, exhibits formation of clinker due to hardening of softened ash, which results in discontinuous flame and intermittent operation. The design and operation protocol of the gasifier was appropriately modified to circumvent this problem. The effects of parameters such as grate movement, equivalence ratio (ER), and ratio of air entering at combustion and drying zones (split ratio) were systematically studied to maximize the lower heating value (LHV) of gas and minimize the amount of clinker. The grate movement of once in 20 min, ER of 0.32, and air split ratio of 0:100 together proved to be the best for garden waste pellets. The producer gas LHV and cold gas efficiency were 3.59 MJ/Nm3 and 62.61%, respectively, and comparable to the producer gas obtained from other biomass resources such as rice husk, wheat straw, and cotton stalks.