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Biomass pelletization technology overcame the poor utilization and handling properties of loose materials. The quality of pellets is sensitive to the pelletization conditions. In this work the impact of the operating parameters as pressure, temperature, and moisture content on the mechanical characteristics as the compression strength ( $${\sigma }_{max}$$ ) and durability ( $$Du$$ ) and energy consumption for both production ( $${E}_{c,p}$$ ) and ejection ( $${E}_{c,ej}$$ ) of rice straw (RS) pellets was studied. Furthermore, the synergic effect of these parameters on the pellet characteristics was evaluated at the optimum conditions. The operating parameters were optimized using a multi-objective optimization approach of Response Surface Method (RSM) based on the predicted significant models that describe the physical characteristics of the pellets. The optimization results showed that high quality pellets could be produced at a pressure of 68.4 MPa, temperature of 110.0 °C, and moisture of 8.2% for solid pellets and 63.6 MPa, 110.0 °C, and 8.7% for hollow pellets. Significant individual and interaction effects of all independent parameters on the pellets characteristics were investigated using statistical analysis results, main plot curves and 2D interaction contour plots. New significant empirical dimensionless relationships that correlate the characteristics of pellets were proposed. These relationships can be generalized for any type of pellets that produced under various operating conditions. Hollow pellets are recommended to be used in the industrial sector due to their enhanced heat transfer which resulted from the high surface to volume ratio besides their ease production at normal operating condition similar to that required for solid pellets.

Combustion and emission characteristics of Egyptian sugarcane bagasse and cotton stalks powders were investigated in a bubbling fluidized bed combustor (BFBC) using silica sand as an inert bed material. Mixing and fluidizing characteristics of the two biomass materials and bed material of a certain size distribution were studied. It was found that, the feed rate ranged from 70 to 113 g/min and feed rate of 51 g/min for cotton stalks and sugarcane bagasse, respectively may be suitable for better combustion characteristics in the BFBC. The effect of different operating parameters on the axial temperature and gas concentration profiles (O2, CO2, CO, H2S, SO2 and NOx) was investigated. It was found that the formation of NOX during combustion doesn’t represent a problem as the nitrogen content of fuel is low, the bed temperature of fluidized bed is below 900 °C, and the particle size of the biomass is small. It was found that combustion efficiency ranged from 90 to 100% and from 93 to 98.8% for sugarcane bagasse and cotton stalks, respectively. Thermal efficiency was found to be in the range of (33.7–41%) and (32.5–48.7%) for sugarcane bagasse and cotton stalks, respectively. A verification model for mass and heat balance of combustion experiments was constructed to confirm that the measured values of different parameters were measured accurately with acceptable percent of error.

A TG/DTG and DTA measurements are used to determine the kinetics of the thermal decomposition of two Egyptian biomasses (sugarcane bagasse and cotton stalks powders) at three heating rates of 10, 15 and 20 °C/min. Two distinct reaction zones were observed for the two biomasses. The direct Arrhenius plot method and integral method were applied to (TG/DTG) analysis for determination of kinetic parameters: activation energy, pre-exponential factor, and order of reaction. The weight loss curve showed that pyrolysis of sugarcane bagasse and cotton stalks took place mainly in the range of 200–500 °C. Also, the activation energy of a phase transition can be calculated directly from the DTA thermogram of each biomass material. Heating rates had little effect on the pyrolysis process, but the peak of the weight loss rate in the DTG curves shifted towards higher temperature with heating rate. The activation energy of the sugarcane bagasse powder obtained by the direct Arrhenius plot method are 48.25, 57.15 and 45.35 kJ/mol for the heat rate of 10, 15 and 20 °C/min, respectively. On the other side, the integral method shows larger values of the activation energy for sugarcane bagasse (82.5, 78.5 and 56.7 kJ/mol for the heat rate of 10, 15 and 20 °C/min, respectively). The activation energy of the cotton stalks powder obtained by the direct Arrhenius plot method are 100, 80 and 68 kJ/mol for the heat rate 10, 15 and 20 °C/min, respectively, but the integral method shows larger values of activation energy (100, 107 and 101 kJ/mol for the heat rate of 10, 15 and 20 °C/min, respectively). The calculated activation energy by DTA analysis was found to be 81.77 and 84.75 kJ/mol for sugarcane bagasse and cotton stalks, respectively. These values are, to some extent, in agreement with the data obtained by direct and integral methods. The cotton stalks are more reactive than the sugarcane bagasse.

An investigation was made of relevant physical properties of two types of biomass: bagasse and cotton stalk powders. Three samples of each biomass were analyzed, and the average value of the mass retained in each sieve of the three samples was taken. Any study incorporating grain size analysis must include a clear statement of the measurement technique and the method used in the calculation of any statistics. It will be appropriate to employ more than one method, since comparison of results obtained in different ways may provide additional insight into the processes involved. In this work, the particle size distribution was calculated by three various methods. These methods are sieving analysis, statistical calculations and image analysis (i.e. microscopy). Sieving analysis has been done mechanically using a mechanical sieve shaker and a series of nested sieves. A computer program called GRADISTAT has been used for the rapid analysis of grain size statistics from the standard measuring sieving techniques. Statistical parameters of mean, median, standard deviation, skewness and kurtosis are calculated arithmetically and geometrically (in metric units) and logarithmic (in phi units) using moment and Folk and Ward graphical methods.