Process residues, such as coffee and tea grounds, bagasse, vinegar lees, etc., represent a kind of concentrated biomass resources rich in cellulose. They contain water usually of about 60 wt % and are easy to rot to cause serious pollution to groundwater and air. Conversion of them into energy can not only control their induced pollution but also develop their CO2 neutralization function. The present paper concerns the production of middle caloric producer gas from such cellulose-rich process biomass residues. The involved technical process consisted of fuel drying and in turn gasification of the dried fuel in a dual fluidized bed system. Using coffee grounds containing 65 wt % water as a model high water content process residue, the paper found that with fuel drying calcium hydrate (or oxide) can be well-impregnated onto fuel to remarkably increase the gasification reactivity of the fuel and suppress tar evolution with producer gas. Thermal gravitational analysis clarified further that the increase in the gasification reactivity of the fuel was due to enhanced char gasification exclusively. In both scanning electron microscopy-energy dispersive X-ray (SEM-EDX) photographs and X-ray diffraction (XRD) spectrums, it was identified that the impregnated Ca species were present at micro sizes and dispersed uniformly on the matrix of fuel as well as char particles made from the fuel. This indicates essentially the necessary precondition for Ca-base material to catalyze biomass fuel gasification.