Search

Combustion of fossil fuels is one of the major sources of greenhouse gas CO2, it is therefore necessary to develop technologies that will allow us to utilize the fossil fuels while reducing the emissions of greenhouse gases. Pressure swing adsorption (PSA) is a potential technique for removing CO2from high-pressure fuel gas streams. Zeolites are suitable candidate sorbents for use in the PSA process. Studies of the gas adsorption of CO2onto zeolite 13X and zeolite 4A were conducted at a temperature of 25 °C, 35 °C, 45 °C and 60 °C up to a pressure of 1 bar. The data fitting is accomplished with the Toth and Sips adsorption models which are generally used for micro-porous adsorbents such as zeolites. Moreover, regeneration studies have been conducted in order to verify the possibility of adsorbents reutilization, to determine its CO2adsorption capacity within consecutive cycles of adsorption–desorption. Zeolite with higher surface area showed higher CO2adsorption capacity. There is no full reversibility for the two zeolites.

The present study involves the preparation and characterization of the biomass briquettes made from saw dust and rice husk. Five samples with different compositions were prepared using the old news papers as the binder for both the biomass. Ultimate analysis, proximate analysis, heating value and handling characteristic of all the samples were determined. It was observed that the compositions of the biomass sawdust (BMS)-15 and biomass rice husk (BMR)-15 are suitable for the downdraft gasifier.

This paper presents the study of carbonization systems for the production of Bamboo Charcoal which is formed on dry distillation of raw bamboo. The paper mentions the drawbacks of the conventional practices of production of Bamboo Charcoal. Design of a new charcoal production unit is aimed at eliminating the identified drawbacks in the present methodology of production making the process of production faster and more efficient by minimizing heat loss during the production process. Designing is attempted with strong consideration for manufacture, operational cost and ease of operation of the furnace as the process finds application amongst rural people with little or no technical knowhow, making simplicity of design absolutely critical for implementation of the developed technology. Results of testing and experimentation presented in this paper describe the working prototype confirming qualitative and quantitative improvements in the bamboo charcoal being produced as compared to the conventional method of production.

Biodiesel from sunflower oil using lipase chemically immobilized on silk-cocoon matrix in a packed-bed bioreactor was investigated. The immobilization was demonstrated by field-emission scanning electron microscopy and activity study. The lipase loading was 738.74 U (~0.01 g lipase powder)/g-lipase-immobilized matrix. The (Michaelis-Menten constant) of the free and the immobilized lipase was 451.26 μM and 257.26 μM, respectively. Low value of the immobilized lipase is attributed to the hydrophobic nature of the matrix that facilitated the substrate diffusion to the enzyme surface. The biodiesel yield of 81.62% was obtained at 48 hours reaction time, 6 : 1 methanol : oil ratio (v/v), and 30°C. The immobilized lipase showed high operational stability at 30°C. The substrate conversion was only marginally decreased till third cycle (each of 48 hours duration) of the reaction since less than even 5% of the original activity was decreased in each of the second and third cycle. The findings demonstrated the potential of the silk-cocoon as lipase immobilization matrix for industrial production of biodiesel.

Low-grade coal and biomass waste such as bamboo dust, sawdust, rice husk, etc. are abundantly available in India. Utilization of such resources to generate electricity is a challenging task with conventional methods. Atmospheric circulating fluidized bed (ACFB) is considered to be one of the potential devices to utilize coal or biomass or both for power production through gasification or combustion routes. In this paper, the effect of various operating parameters such as bed inventory, particle size, superficial velocity, blends of coal with sawdust (percentage by weight) and operating pressure on bed hydrodynamics, i.e., bed voidage, suspension density, and solid circulation rate were studied experimentally in a pressurized circulating fluidized bed (PCFB). The bed voidage decreases with an increase in operating pressure and increases with an increase in particle size. Maximum of 8.2% decrement in bed voidage is observed as operating pressure varies from atmospheric to 4 bar. Further, the suspension density is found to increase with an increase in inventory weight. Peak increment of 28.3% in suspension density is perceived with an increase in inventory weights at a pressure of 4 bar.

The present research is focused on the hydrodynamics and gasification studies of a pressurized circulating fluidized bed (PCFB) gasifier considering saw dust as a bed inventory. The operating pressure range of the PCFB gasifier is maintained in between 1 to 4 bar and the suspension density, syngas composition, lower heating value (LHV), gas yield, carbon conversion efficiency (CCE) and cold gas efficiency (CGE) were calculated and presented in this paper. The suspension density increases with rise in operating pressure and decreases with rise in superficial velocity. The concentration of CH4 in the syngas was found to be increasing with rise in bed pressure and is found to be 4.78 % at 4 bar. However, no significant effect of operating pressure on H2 concentration is observed and is found to vary between 8.3 to 7.95 %. The CO concentration increases up to 2 bar pressure and decreases gradually afterwards. The LHV, gas yield, CCE and CGE has a positive response to the rise in operating pressure and found maximum at 4 bar. The CCE and CGE of the PCFB gasifier are increased by 57 % and 58 %, respectively when the operating pressure is changed from 1 to 4 bar.

The desulfurization process to a two-dimensional (2-D) and three-dimensional (3-D) Eulerian–Eulerian computational fluid dynamic (CFD) model of a coal bubbling fluidized gasifier is introduced. The desulfurization process is important for the reduction of harmful SOx emissions; therefore, the development of a CFD model capable of predicting chemical reactions involving desulfurization is key to the optimization of reactor designs and operating conditions. To model the process, one gaseous phase and five particulate phases are included. Devolatilization, heterogeneous, and homogeneous chemical reactions as well as calcination and desulfurization reactions are incorporated. A calcination-only model and a calcination plus desulfurization model are simulated in 2-D and 3-D and the concentrations of SO2 leaving the reactors are compared. The simulated results are assessed against available published experimental data. The influence of the fluidized bed on the desulfurization is also considered. © 2013 American Institute of Chemical Engineers AIChE J, 59: 1952–1963, 2013

Biogas is a mixture of methane, carbon dioxide and traces of numerous trace of elements. It is produced by anaerobic digestion of organic matters including cattle dung which depend upon various factors affecting the population and activity of microorganisms producing biogas. Among the various factors temperature is one of them which play a significant role in biogas production from cattle dung. Biogas production from cattle dung was studied at temperatures 35°C to 55°C at a step of 5°C to study the effect of temperature on biogas production from cattle dung. In this work a mathematical model is developed for evaluating the effect of temperature on the rate of biogas production from cattle dung. The new mathematical model is derived by adding the effect of temperature on the modified Gompertz model. The new model is found to be suitable for predicting the biogas production from cattle dung in the temperature range 35°C to 55°C. The results from the new model are found to be highly correlated to the experimental data of present study.

Pressurised circulating fluidised bed (CFB) technology is a potentially promising development for clean coal technologies. The current work explores the hydrodynamics of a small-scale circulating fluidised bed at elevated operating pressures ranging from 0.10 to 0.25 MPa. The initial experiments were performed at atmospheric pressure with air and O2/CO2 environments as the fluidisation gas to simulate the hydrodynamics in a CFB. A comparison between the effects of air and O2/CO2 mixtures on the hydrodynamics was outlined in this paper for particles of 160 μm diameter. A small but distinct effect on axial voidage was observed due to the change in gas density in the dense zone of the bed at lower gas velocity, while only minimal differences were noticed at higher gas velocities. The hydrodynamic parameters such as pressure drop and axial voidage profile along the height were reported at two different bed inventories (0.5 and 0.75 kg) for three mean particle sizes of 160, 302 and 427 μm and three superficial gas velocities. It was observed that the operating pressure had a significant effect on the hydrodynamic parameters of bed pressure drop and axial bed voidage profiles. The effect of solids loading resulted in an exponential change in pressure drop profile at atmospheric pressure as well as at elevated pressure. The experimental results on hydrodynamic parameters are in reasonable agreement with published observations in the literature.

In the present investigation, the effects of particle size, solid inventory and operating pressure on bed hydrodynamics and heat transfer in a pressurized circulating fluidized bed has been studied. Three different particle sizes of mean diameter of 278, 307 and 469 μm are considered. Experiments have been conducted at five different solid inventories such as 400, 500, 600, 800, and 1000 g, and at three different operating pressures such as 1, 3 and 5 bar. All the above studies have been made at three different superficial velocities of 5, 6 and 7 m/s. The axial variation of heat transfer coefficient with various percentage blending of sawdust in sand has also been studied. Results show that, with the increase in operating pressure and solid inventory, the bed voidage decreases. The solid circulation rate is found to increase with an increase in superficial velocity as well as with an increase in solid inventory. The heat transfer coefficient decreases with an increase in particle size, while it increases with operating pressure from the bottom to the top of heat transfer probe. The heat transfer coefficient is also found to increase with the increase in % blending of sawdust in sand and the operating pressures. The overall uncertainties in calculating solid circulation rate and heat transfer coefficient are estimated to be ±5.32% and ±3.90%, respectively.

In the present work, a pressurized circulating fluidized bed (PCFB) unit of 54 mm inner diameter and riser height of 2000 mm has been fabricated to investigate the effect of pressure on suspension density and heat transfer. The effects of blending of biomass in sand, and superficial velocity on bed hydrodynamics and heat transfer has also been studied. Experiments have been conducted at four different percentage blending of biomass such as 2.5%, 7.5%, 15% and 20% in sand with two different weight composition ratios and at a superficial velocity of 5 m/s. Operating pressure is varied from 1 to 5 bar in a step of 2 bar. Results show that, the axial heat transfer coefficient increases from the bottom to the top of heat transfer probe with the increase in operating pressure. The radial variation of heat transfer coefficient decreases from the wall to the core of the heat transfer probe. The heat transfer coefficient is also found to be higher in between the 7.5 to 15% biomass blending in sand. The overall uncertainty in calculating heat transfer coefficient is found to be 3.90%.

In the present investigation, the effect of aeration rate on bed hydrodynamics in the riser of a pressurized circulating fluidized bed (PCFB) has been studied. Experiments are conducted with two different bed inventories, viz. 500 and 750 g. Aeration superficial velocities, U sup = 0.65, 1.94, and 3.23 m/s respectively are used to observe the change of bed hydrodynamics of the PCFB. Operating velocities of 2.72, 3.4 and 4.08 m/s and pressures of 100, 200, and 250 kPa are maintained for each inventory and aeration rate. It has been observed that the suspension density increases along the riser height with the decrease in aeration rate. The solid circulation rate increases with the increase in aeration rate as well as primary air flow rate. The present study will help in optimizing the aeration rate for smooth operation of the non-mechanical valve or the stand pipe without obstruction of inventory material.

Carbon nitride thin films were deposited by RF plasma enhanced chemical vapor deposition using acetylene (C2H2) and nitrogen (N-2) mixture on Si (1 0 0) substrates. The films were deposited at 400 degrees C substrate temperature, 600 W RF power with 5 sccm C2H2 and different flow ratio of N-2 (5, 15, 30, 60) sccm. The deposition rate was characterized by surface profilometer, composition and bonding structure were characterized by EDS, Raman spectroscopy and Fourier transform infrared spectrometry (FTIR) and microstructure by Atomic Force Microscopy (AFM). The deposition rate decreased with the increase in nitrogen content. Nitrogen content of 15 atom% could be incorporated in the film at 60 sccm N-2. Deposition rate and roughness was found to decrease with the increase of nitrogen ratio. Spectroscopic studies confirmed the incorporation of nitrogen (C=N, C N) in the film and the amount of CN bonding was found to increase with increase of nitrogen content. AFM studies showed decrease of particle size with increase of nitrogen content in the precursor gas. All films were found to be X-ray amorphous. The atomic resolution picture from AFM of films confirmed the formation of C3N4 phase in the carbon nitride film.

In the villages of developing countries, use of electricity or petroleum fuel is expensive for drying the agricultural products. In the current scenario, drying through “natural convection grain dryer” is an important alternative. This paper proposes the development and evaluation of the natural convection grain dryer in drying performance of paddy. The proposed system is capable of generating an adequate and continuous flow of hot air with range of 60-70 degree centigrade. Paddy was successfully dried from 33% moisture content to 14% (w.b). Woodchips (biomass) were burnt to heat the incoming air in the dryer. Experiments were conducted with fixed amount of sensible heat storage material with varying the amount of latent heat storage material. Increase in the latent heat of storage material indicates the improvement in standard drying temperature, time and enhancement in amount of paddy dried. Re-firing further enhances the duration of optimum temperature range for quality drying.

In the present work a comparative study of steady state wall-to-bed heat transfer was conducted along the risers of height 2.85 m of three different circulating fluidized beds (CFBs) with bed cross sections of 0.15 m × 0.15 m, 0.20 m × 0.20 m, and 0.25 m × 0.25 m, respectively. Experiments were conducted on each CFB unit for five superficial air velocities ( U = 2.5 m/s, 2.75 m/s, 3 m/s, 3.3 m/s, and 4 m/s) and two different weights of sand inventory per unit area of the distributor plate ( P = 1750 N/m 2 and P = 3050 N/m 2 ) with average sand particle size of 460 μm. Bed temperature distributions across the three risers were measured and compared at different heights (1.04 m, 1.64 m, and 2.24 m above the distributor plate). Axial distribution of heat transfer coefficient along the height of riser was evaluated and compared for the three bed cross sections. Effect of superficial velocity of air, sand inventory, and bed cross section on bed temperature and heat transfer coefficient was investigated. An empirical correlation was developed for the bed Nusselt number as a function of various non-dimensional parameters based on the parametric study. The correlation was compared with available literatures.

SUMMARY Biomass gasification has been a viable alternative for decentralized electricity generation in developing countries. The efficiency of the biomass gasification process for operation of the engine-generator set is mapped in terms of quality and quantity of the producer gas. In this study, we have attempted to devise generalized correlations for four principal parameters that form the benchmark for the performance of the gasifier. These parameters are lower heating value and net yield (per unit biomass) of producer gas, and volume fractions of CO and CO2 in the gas resulting from biomass gasification process. The correlations have been constituted using simulations of gasification of three common biomass feedstocks (viz. rice husk, saw dust and corn cobs) using semi-equilibrium non-stoichiometric thermodynamic model. The independent variables used in the simulations are air ratio, carbon conversion, gasification temperature and three elemental ratios in the gasification mixture, viz. H/C, O/H and O/C. As many as eight expressions of linear and non-linear type have been evaluated to best fit the simulations data for each performance parameter. On the basis of statistical indicators, the compatibility of the correlations for best fit of the data has been assessed. Finally, the predictions of the correlation have been tested against experimental data on gasification of different biomass. The best correlation for each performance parameter was chosen on the basis of least average absolute error and highest (absolute) regression coefficient. It was found that the set of best correlations could predict the values of performance parameters within engineering accuracy of ± 10–20%. The correlations proposed in this work are independent of the type of biomass gasifier. These correlations can form a useful tool for design and optimization of fixed or fluidized bed gasifier for any biomass feedstock. Copyright © 2011 John Wiley & Sons, Ltd.

In the present work, a comparative study of steady-state wall-to-bed heat transfer was conducted along the lower and middle splash region located in the riser of height 2.85 m of three different circulating fluidized beds (CFBs) with bed cross-sections of 0.15 m×0.15 m, 0.20 m×0.20 m, and 0.25 m×0.25 m. Experiments were conducted under similar operating conditions on above-mentioned three CFB set-ups using the same weight of sand per unit area of the distributor plate, non-dimensional superficial velocity ( U∗), heat flux, and sand particle size. Further, experiments were conducted on all the three CFB set-ups for five different non-dimensional air velocities ( U∗ = 5, 5.5, 6, 6.6, and 8) and two different weights of sand inventory per unit area of the distributor plate with average particle size of 460 μm. Bed temperature distributions across the lower and middle splash regions were measured and compared for the three bed cross-sections. Axial distributions of heat transfer coefficient along the height of lower and middle splash region of risers were evaluated and compared for the three bed cross-sections. The effect of superficial velocity, sand inventory, and bed cross-section on temperature and heat transfer coefficient was investigated. Based on the present study, correlations were developed for the bed Nusselt number as a function of various non-dimensional numbers for lower and middle splash regions of the riser. The non-dimensional area parameter ( A∗) was found to be a significant number. Predictions of these correlations are in agreement (±16 per cent) with experimental data.

Present work deals with the development of butanol−diesel−biodiesel blends to substitute for petrodiesel. These blends were tested for physical stability and various fuel properties conforming to ASTM standards. Subsequently engine performance and emission tests were conducted with each blend. Observations revealed the blends to be thermally and physically stable, and they showed good resemblance to the properties of diesel, with the exception of flash point only. Brake power showed marginal decrease and fuel consumption an increase in the range of 4.9%−10.7% as compared to diesel for identical performance. Exhaust gas temperature showed a drop in the range of 3.3%−9.4% due to quenching effect of butanol, whereas brake thermal efficiency showed a reduction of 6.3%−10% to that over petrodiesel. Exhaust gas emissions showed a significant decrease in CO (42%) at medium and higher loads, whereas NO showed an average increase of 2.4%−11% as compared to diesel.

In recent years, biomass gasification has emerged as a viable option for decentralized power generation, especially in developing countries. Another potential use of producer gas from biomass gasification is in terms of feedstock for Fischer–Tropsch (FT) synthesis – a process for manufacture of synthetic gasoline and diesel. This paper reports optimization of biomass gasification process for these two applications. Using the non–stoichometric equilibrium model (SOLGASMIX), we have assessed the outcome of gasification process for different combinations of operating conditions. Four key parameters have been used for optimization, viz. biomass type (saw dust, rice husk, bamboo dust), air or equivalence ratio (AR = 0, 0.2, 0.4, 0.6, 0.8 and 1), temperature of gasification (T = 400, 500, 600, 700, 800, 900 and 1000 °C), and gasification medium (air, air–steam 10% mole/mole mixture, air–steam 30%mole/mole mixture). Performance of the gasification process has been assessed with four measures, viz. molar content of H2 and CO in the producer gas, H2/CO molar ratio, LHV of producer gas and overall efficiency of gasifier. The optimum sets of operating conditions for gasifier for FT synthesis are: AR = 0.2–0.4, Temp = 800–1000 °C, and gasification medium as air. The optimum sets of operating conditions for decentralized power generation are: AR = 0.3–0.4, Temp = 700–800 °C with gasification medium being air. The thermodynamic model and methodology presented in this work also presents a general framework, which could be extended for optimization of biomass gasification for any other application.

This article attempts to highlight the technical and economical issues related to decentralized power generation in India using biomass gasification. Biomass-based energy has several distinct advantages such as wide availability and uniform distribution that puts it ahead among the renewable energy options for India. The estimated potential of power generation through renewable sources in India is 85 GW with biomass power contributing approximately 20 GW. Especially, in the remote areas and hilly terrains of India, biomass gasification-based power generation offers a highly viable solution for meeting energy demands of small villages and hamlets, which would not only make them independent but will also reduce burden on state electricity boards. This paper reviews various technical options for biomass gasification-based low-, medium- and large-scale power generation. We essentially discuss the merits and demerits (operational and other problems) of different systems. Further, we also deal with economics of these systems and discuss principal factors influencing the viability of the biomass-based power generation. Finally, we review some case studies of biomass-based power generation for meeting energy needs, both thermal and electrical.

Lipase was immobilized in silk fibers through glutaraldehyde cross-linking to a maximum loading of 59 U/g silk-fiber and the immobilized lipase was utilized for the hydrolysis of sunflower oil (Helianthus annuus). The hydrolytic activity of the lipase, which was poor in biphasic oil in water system, was increased significantly when the sunflower oil was emulsified in aqueous medium. The hydrolytic activities of the immobilized lipase were 48.73 +/- 1.26 U, 36.11 +/- 0.96 U, and nil when the substrate sunflower oil was used as emulsion created by a rhamnolipid biosurfactant, Triton X100, and ultrasonication, respectively. Although the efficiency of the immobilized lipase was less than 12% than the corresponding free lipase, the immobilized lipase could be reused for the biosurfactant-mediated hydrolysis of sunflower oil up to third cycle of the reaction. The yield of the fatty acids in the second, third, and fourth cycles were 49.45%, 22.91%, and 5.09%, respectively, of the yield obtained in the first cycle.

Fluoride contaminated drinking water is a severe problem in many parts of the world because of fluoride-related health hazards, which are considered to be a major environmental problem today. The present work is aimed at utilizing solar energy for removal of fluoride from drinking water by using a “solar still”. Also tests have been conducted with the “solar still” to find out hourly output rate and “still efficiencies” with various test matrixes. It is observed that the distillate from “solar still” showed a fluoride reduction of 92–96%. Further, the efficiency of “solar still” got increased by 11% when capacity of water in the solar basin was raised from 10 to 20 L. Upon suitable modification of the solar basin with appropriate base liner and insulation, this efficiency of the “solar still” is found to be further increased by 6% with a 20 L basin capacity.

The present work investigates the suitability of mesua ferrea (nahar) oil seed as a source of alternative fuel in CI engines. Non-edible straight vegetable oil obtained from mesua ferrea seeds was extracted using a solvent extraction technique. A significant amount of unsaturated fatty acids was found from a gas chromatography test, which was further ascertained by measuring the acid value. The thermo-physical and chemical properties of straight mesua ferrea oil were determined. The flash point, kinematic viscosity, and density of the straight mesua ferrea oil were found to be much higher than diesel, though the calorific value was found to be lower. The variation in thermo-physical and chemical properties of various blends of straight mesua ferrea oil and diesel were studied. The straight mesua ferrea oil blend up to 15% with the diesel met the standard specification. Based on the present study, it was concluded that due to higher viscosity and density and low volatility of straight mesua ferrea oil, it ...

Gasification is the thermochemical conversion of solid fuel into the gas which contains mainly hydrogen, carbon monoxide, carbon dioxide, methane and nitrogen. In gasification, fluidized bed technology is widely used due to its various advantageous features which include high heat transfer, uniform and controllable temperature and favorable gas–solid contacting. Modeling and simulation of fluidized bed gasification is useful for optimizing the gasifier design and operation with minimal temporal and financial cost. The present work investigates the different modeling approaches applied to the fluidized bed gasification systems. These models are broadly classified as the equilibrium model and the rate based or kinetic model. On the other hand, depending on the description of the hydrodynamic of the bed, fluidized bed models may also be classified as the two-phase flow model, the Euler–Euler model and the Euler–Lagrange model. Mathematical formulation of each of the model mentioned above and their merits and demerits are discussed. Detail reviews of different model used by different researchers with major results obtained by them are presented while the special focus is given on Euler–Euler and Euler–Lagrange CFD models.

Present work deals with testing a performance of a compression ignition (CI) engine with different blends of non-edible oil as well as their methylesters with petrodiesel. Various blends of a non-edible vegetable oil, commonly known as honge ( Pongamia pinnata L.) in India, were prepared and tested over a wide range of engine load. Results obtained from the study showed that 15–20 per cent pongamia methylester-diesel blend (B15 and B20) could be a better fuel in terms of fuel efficiency and power developed. Further, the blend can be used in any existing CI engine without modification and preheating. The pongamia oil is transesterified by using base catalysed transesterification process in a batch type transesterification reactor. Transesterification shows improvement in fuel properties of pongamia oil. Results obtained with B15 and B20 show improvement in brake thermal efficiency and reduction in brake specific fuel consumption, especially at higher load. Emission results show significant reduction in percentage of CO and HC for B15 and B20 at medium and higher power output.

Application of the discrete transfer method is extended to solve transient radiative transport problems with participating medium. A one-dimensional gray planar absorbing and anisotropically scattering medium is considered. Both boundaries of the medium are black. The incident boundary of the medium is subjected to pulse-laser irradiation, while the other boundary is cold. For radiative parameters such as optical thickness, scattering albedo, anisotropy factor, transmittance, and reflectance at the boundaries are found. Results obtained from the present work are compared with those available in the literature. The discrete transfer method has been found to give an excellent agreement.

In the present paper, CFD simulations using ANSYS-Fluent 14.5 were accomplished to study the effect of bed or sand inventory and effect of scale-up of riser on heat transfer characteristics like temperature and heat transfer coefficient. To accomplish the scale-up study, 3D CFD simulations were performed on the Circulating Fluidized Bed (CFB) risers of cross section 0.15 × 0.15 m, 0.30 × 0.30 m, and each of height 2.85 m. CFD simulations to predict heat transfer characteristics were accomplished under same operating conditions on heated portion (heater) of both risers. The walls of heater were maintained at the constant heat flux q″ = 1,000 (W/m2). Modeling and meshing were done using ProE and ANSYS ICEM CFD software, respectively. RNG k-e model was used for turbulence modeling. Eulerian model with Gidaspow phase interaction scheme was used to simulate the two phase flow (air + sand mixture flow). Computational (CFD simulation) data was compared with experimental data for the validation purpose. After validation, further simulations were conducted on riser of cross section 0.30 × 0.30 m. Based on scale-up study, empirical correlation has been developed to predict the heat transfer coefficient.

In the present study, a new method is proposed for temperature controlling by combustion staging. Two combustion stages can be used with two stages of fuel feeding. A high stoichiometric ratio (SR) gimel > 1 is used at the first stage to mitigate adiabatic flame temperature (AFT) in case of high O2% in the oxidant. For validation, a series of experiments are conducted using mini-CFB (circulating fluidized bed), and an oxidant of 100% O-2 concentration is used with three SR ratios, i.e. gimel = 1.25, 2.0 and 3.0. The resulting average temperatures along the riser for biomass are 1031 degrees C, 950 degrees C and 798 degrees C; and for coal 1129 degrees C, 1051 degrees C and 961 degrees C respectively. The controlling of AFT with pure oxy-fuel combustion eliminates the recycled flue gas in oxy-fuel CFB combustion and flue gas recirculation section; this simplifies design, fabrication and installing-operating costs of the power plants. Familiarizing this concept can accelerate adapting oxy-fuel combustion in CFB power plants for carbon capturing and sequestration. This study can help commercialize the third generation of oxy-fuel CFB combustion with zero RFG. Finally, the concept of controlling AFT by SR is validated experimentally.

The objective of this paper is to investigate the effect of temperature on anaerobic digestion of different lignocellulosic biomasses such as bamboo dust and saw dust. Bamboo dust and saw dust were mixed with cattle dung in 1:3 ratio in batch type anaerobic digesters of volume 1000 ml at 35°C, 45°C and 55°C temperatures. At five day interval, 10 ml of digested slurry was taken out from the digesters and tested for total solid and volatile solid contents. Effect of temperature on kinetic rate constant was also studied. It was observed that biogas production increases with temperature. The kinetic rate constant plays a significant role to indicate the digestion process.

In recent years, biomass gasification has emerged as a viable option for decentralized power generation, especially in developing countries like India. In this chapter, we have given an overview of the energy scenario in India with statistics of electricity generation through various sources along with data on coal deposits and agro-residues, which are potential feedstock for electricity production through thermal route. Moreover, using the non-stoichiometric equilibrium and semi-equilibrium models, we have assessed the outcome of gasification process for different combinations of operating conditions and various biomass as feedstock, either single biomass or their mixtures. Four key parameters have been used for optimization, viz. biomass type, air or equivalence ratio, temperature of gasification, and gasification medium. The gasification medium has been taken to be either pure air or air–steam mixture. It is revealed that the biomass mixtures also form potential feedstock for gasifiers, and the performance of gasifier is very similar to that with single biomass as feedstock. On the basis of simulations results, we have also attempted to optimize the operating conditions for biomass gasifier operation. The optimum sets of operating conditions for gasifier for application of decentralized power generation are: Air Ratio = 0.3–0.4, Temperature = 700–800°C with gasification medium being air.

Introduction C OLLAPSED dimensionmethod (CDM) is one of the ray tracing methods used for the solution of radiative transfer problems. Development of this method is partly based on the works of Shih and Chen1 and Shih and Ren2 on the discretized intensity method. Some light on the method was thrown by Blank. Subsequent developmentof the method was made by Blank andMishra.4 Detailed description of this method is available in Ref. 5. In CDM, three-dimensionalradiative information is mapped into a two-dimensionalsolutionplane in terms of effective intensity (EI) andoptical thicknesscoefŽ cient (OTC). Thus, unlikeothermethods, analysis and computations in this method are performed in a twodimensional solution plane instead of three-dimensionalspace. CDMhas beenused for the solutionof radiativetransferproblems with highaccuracy.4;5 Thismethodhasbeenfoundtowork for awide rangeof optical thickness (very low to high optical thickness). Furthermore, CDM has also been found to work well for the conjugate mode heat transfer problems. In CDM, for determinationof heat  ux and temperature information, at each point of interest EIs have to be integrated over planar angle in the solutionplane.Theseangularintegrationsareperformed by dividing the planar angle into intervals of equal sizes. In each subinterval, EI is assumed isotropic. Hence, for higher accuracy, CDM requiresmore EIs and, thus, higher computational time. In the presentwork,with the objectiveofmakingCDMmore economical, the method is modiŽ ed. In the modiŽ ed CDM (MCDM), angular integrations of the EIs are performed differently. The discretizationand integrationsperformed in thismethod originatefrom the concept of the discrete ordinate method (DOM). Here, the planar angle is divided into a Ž nite number of subintervals according to the number of Gaussian quadraturepoints considered.Hence, in MCDM, angular subintervals are unequal and instead of considering average values of interval, the weighted mean corresponding to the Gauss points is considered. With this, the method becomes more realistic, and it derives computational efŽ ciency with a more realistic representationof the radiative transfer process. In the present work, improvements in MCDM over CDM are tested by solving radiative transfer problems in oneand twodimensional Cartesian enclosures with gray and homogeneous, absorbing, emitting, and anisotropically scattering medium. Both radiative and nonradiative equilibrium situations are considered. MCDM and CDM results are compared with results from the exact method and DOM.

Present study involves characterisation and thermal analysis of rice husk as a potential source for gasification. Both the thermogravimetric (TG) analysis and differential scanning calorimetry were used to study the influence of heating rate on the degradation of rice husk. Experiments were carried out at three different heating rates of 10, 30, and 80 K min−1. The kinetic parameters, viz. pre-exponential factor, activation energy, and order of reaction were evaluated for both first and second reaction zones, which are categorized based on the degradation of cellulose, hemicelluloses, and lignin content present in the biomass. The degradation of mass with temperature obtained from TG curve was validated numerically. The thermal response of rice husk undergoing decomposition has also been modelled by using a one dimensional (1-D) transient thermal model with an nth order approximation for the rate of decomposition. Kinetic parameters, heat of decomposition, and thermal properties are taken as input to the model. The model was validated by measuring the transient temperature profiles during decomposition using Heisler chart at heat transfer coefficient of 20 W/m2 K. The data for specific heat and thermal conductivity of the biomass were taken from the literature and the values of heat of decomposition and kinetic parameters were taken from the experiments. Model results were compared well with the result obtained by using Heisler chart.

Biomass has great potential as a clean, renewable feedstock for producing modern energy carriers. Low density biomass, such as rice husk, sawdust, bamboo dust, etc., can provide a continuous supply of liquid and gaseous fuels through thermochemical conversion processes. In the present study, kinetics of the thermal decomposition of three biomasses such as rice husk, sawdust, and bamboo dust were evaluated under air atmosphere from ambient temperature to 1000 °C at a heating rate of 10 °C min−1. Two distinct reaction zones were observed for all the three biomasses. From the thermogravimetric (TG) and differential TG curves, the activation energies, pre-exponential factors, and order of reaction were determined for both the reaction zones. Experimental results were validated numerically and these results are found to be very close to the numerical results. As observed, thermal decomposition rates in the first reaction zone were found to be significantly higher than those in the second reaction zone.

Combustion of fossil fuels is one of the major sources of greenhouse gas (GHG) CO2, it is therefore necessary to develop technologies that will allow us to utilize the fossil fuels while reducing the emissions of GHG. Removal of CO2 from flue gasses has become an effective way to mitigate the GHG and adsorption is considered to be one of the methods. Adsorption of CO2 on zeolite 13X, zeolite 4A and activated carbon (AC) have been investigated at a temperature ranging from 25 to 60 °C and pressure up to 1 bar. The experimental data were fitted with isotherm models like Langmuir and Freunlich isotherm model. The Langmuir model fit well with the two zeolites and Freunlich model fit well with AC. The thermodynamics parameters were calculated and found to be exothermic in natures for all three adsorbents. Moreover, regeneration studies have been conducted in order to verify the possibility of activated carbon reutilization, to determine its CO2 adsorption capacity within consecutive cycles of adsorption–desorption. Temperature swing adsorption was employed as the regeneration method through heating up to a temperature of approximately 100 °C. There is no full reversibility for zeolites while AC can achieve complete regenerations.

The Indian Government's National Biogas and Manure Management Programme (NBMMP) seeks to deliver renewable energy services to households across the country by facilitating the deployment of family-sized ( 3 ) anaerobic (biogas) digesters. NBMMP policy is implemented at three levels, from government and state nodal agency, via private contractors to households, creating multiple institutional arrangements. We analysed the scheme in Assam, north-east India, focusing on how policy was implemented across two districts and interviewing stakeholders in rural households, state and non-state institutions. The top-down, supply-side approach to policy enables government to set targets and require individual states to deploy the scheme, which benefits households who can afford to participate. NBMMP delivered improved energy service outcomes to a majority of households, although the level of knowledge and understanding of the technology amongst users was limited. Training and education of householders, and particularly women, is needed in relation to the maintenance of digesters, feedstock suitability and the environmental and potential livelihood benefits of digestate. A revised bottom-up approach to policy, which highlights the contextual and demand-side issues around adopting the technology, may deliver monetary benefits from market competition and enable development of community-focused microfinance schemes to improve the affordability of biogas systems.