The design of a highly efficient gas generating plant with a direct­flow gas generator was proposed for gasification of low­grade fuels. The design includes a gas­air recuperator and an evaporator for preliminary preparation of air­steam mixture. The gasification process is fully controlled since operation of the evaporator is coordinated with operation of the blast gas supply system due to which humidity of the mixture fed to the gasification zone is programmed 10 mm pellets produced of rape stems were used as fuel. Two­factor experiments have been carried out to estimate the effect of volume and humidity of blast air on the lower heat value of the generator gas and the mass fuel consumption in the gasification process. The effect of air volume and humidity on temperature of the air­steam mixture required for the gasification process was also investigated. It has been established that the optimum temperature of the air­steam mixture was 550...570 o N and was achieved at the volume of blast gases entering the gas generator in the range of 37...42 m 3 /h and air humidity of 55...65 %. Under these conditions, the lower calorific value of the generator gas was 12.3 MJ/m 3 , which was 15.1 % higher than that of the gas obtained without the use of air­steam blast in the gasification process. Consumption of pellets for the gasification process was reduced by 14.7 % and the volume of gas produced from a kilogram of pellets increased by 18 % to 3.2 m 3 /kg. The total energy efficiency of using the given flowsheet in production of generator gas from pellets produced of rape stems was 23.5 %. The innovative procedure of compiling heat balance for the process of air­steam gasification of plant materials was presented. According to the results of experimental studies, a heat balance has been compiled for the developed design of the gas generating plant. This balance has demonstrated high efficiency of the process of air­steam gasification. Efficiency factor of the direct­flow gas generator was 79 % and that of the gas generating plant as a whole was 74.6 %. The presented studies can be used as a basis for modernized methodologies of thermal calculation of mobile and stationary gas generating plants