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2017 - 20192
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Author: Gurpreet Singh × Type: Thesis × Thesis Type: M.Tech. ×
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    ThesisItemOpen Access
    Development and evaluation of system for torrefaction of paddy straw
    (Punjab Agricultural University, Ludhiana, 2019) Gurpreet Singh; Soni, Rajesh
    The disposal of surplus paddy straw is a serious problem in North-West India. About two-third of the 22 MT paddy straw produced in Punjab is openly burnt in fields. All the existing onsite and offsite methods to manage paddy straw have met with limited success. Biomass co-firing with coal in large thermal power plants is a promising technology for its utilization. Agricultural residues including paddy straw are herbaceous type of biomass. This herbaceous biomass have several unfavorable characteristics that hinder their use in power plants. These include low bulk density, hydrophobicity, high moisture content, and degradation during storage, and low energy density. Pre-treatment of biomass through torrefaction (followed by pelletization) can resolve most of these problems. In this study, the paddy straw was torrefied in an oven at various temperatures viz 230, 240 and 250°C and various durations viz 20, 30 and 40 minutes. The effect of torrefaction on paddy straw properties were studied. Thereafter, a bench scale reactor for torrefaction of around 0.8 kg of paddy straw was designed and fabricated. The unique feature of this reactor was the division of the reactor into four vertical zones. The lower most zone was meant for combustion of the paddy straw to provide additional heat to the upper zones and to assist heat transfer to the upper zones. On the basis of lab studies done earlier, the duration and temperature of 30 minutes and 250°C respectively were selected for bench scale studies. With proper insulation of the reactor, the desired torrefaction condition could be achieved in the lower 10 cm of the reactor. The studies show that with the existing mode of heating, the height of the torrefaction reactor should be limited to 10 cm only. The grinding energy reduced to 6-7 kW/kg. The average particle size decreased, moisture content of straw also decreased to less than 6.4% while the gross heating value increased to 17.07 MJ/kg, mass yield and energy yield of torrefied paddy straw was 0.87 and 1.05 respectively. Thus torrefied straw acquired more coal like properties. This improves the suitability of torrefied straw co-firing with coal in unmodified thermal power plants.
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    Effect of angle of attack on heat transfer and friction characteristics of inclined rib roughened solar air heater duct
    (Punjab Agricultural University, Ludhiana, 2017) Gurpreet Singh; Hans, V.S.
    Thermal performance of solar air heaters is very low due to formation of laminar sublayer over the heat transferring surface. By use of artificial roughness in the form of wires, thermal performance of solar air heaters can be increased considerably. This study represents an experimental investigation carried out to examine the effect of angle of attack on heat transfer and friction characteristics of inclined rib roughened solar air heater duct. The various parameters related to roughness geometry and flow were Reynolds number in the range of 2000 to 16000, relative roughness height (e/D) in the range of 0.02 to 0.043, relative roughness pitch (P/e) in the range to 6 to 14 and angle of attack (α) in the range of 45o to 75o: The results obtained from this experimental investigation suggested that ribs inclined at 67o, having relative roughness pitch and relative roughness height value of 10 and 0.043 respectively outperformed the other rib configuration in terms of thermal and thermo-hydraulic performance. Correlations for Nusselt number and friction factor in terms of roughness geometry parameters and flow parameters have also been developed from experimental data.