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Biogas produced from anaerobic digestion of organic waste is composed of methane (CH4) and carbon dioxide (CO2) as the major constituents with trace amounts of other components like water vapor, hydrogen sulfide, ammonia, and nitrogen. Scrubbing of CO2 is essential for upgradation of biogas, which increases the calorific value of the treated gas and enhances its efficiency for power production and cooking. This study was conducted to investigate and compare the effects of different concentrations of KOH (0.1, 0.3, 0.5, 0.7, and 1.0 M) and natural base ash solutions prepared from different parts of banana plant, viz. banana pseudostem (BPS), Musa balbisiana Peel (MBP), and Musa acuminata Peel (MAP) for scrubbing of CO2 from biogas. The methane content of the untreated biogas analyzed in a gas chromatograph was found to be 56.9%. The scrubber with natural base solution from MBP could enrich the methane content in biogas from 56.9% to 86.3% followed by MAP (78.4%) and BPS (76.8%). The experiments revealed that banana peel ash base solutions have nearly equivalent potential as KOH for CO2 absorption from biogas. The highest CO2 absorption of ~ 68% was achieved with MBP with saturation time of 19 min approximately at a flow rate of 200 ml/min. The study also indicated that CO2 absorption by different natural as well as chemical base solvents is transient and has to be replenished after saturation. Natural bases have the added advantage of being easily available, cheap production method, environment friendly and require no treatment for disposal.

This study presents a thermal performance comparative study of three shell-and-tube latent heat storage (LHS) models. With the help of the optimization technique, 19 tubes are chosen with an internal and external diameter of 17 mm and 20 mm, respectively. In the first case, the LHS model is considered without fins. In the second case, the LHS model is also modeled without fins, but the phase changing materials (PCM) are mixed with 5% volume fraction of Cu nanoparticles. In the third case, every HTF tube is supported by four fins. In order to maintain the same volume of PCM in all the models, shell diameter of the first LHS model is 235 mm and for the second and third cases, the diameter is set to be 240 mm. Commercial sugar alcohol known as Erythritol (C4H10O4) is considered as PCM. ANSYS Fluent environment is employed for the numerical modeling and solution of the governing equations representing PCM. The performance study of LHS units is evaluated using parameters, such as transient temperature and liquid fraction. In order to account buoyancy impact of liquid PCM, Boussinesq approximation method is applied to the model. The inner walls of the HTF tubes are maintained at 138 °C as inlet temperature. The numerical estimations are validated against experimental results. LHS model in the third case, which is supported by fins, becomes fully charged after 80 min, whereas, LHS models in the first and second cases take 120 and 136 min, respectively, for complete melting.

Tea has become an important crop in a many regions of the world. India is one of the best quality tea producers in the world. Despite of being an important cash crop, much research has not been made on tea, due to which modern drying technologies have not been employed in this regard. This work reflects the drying characteristics for tea in a bubbling conical bed dryer. Fresh Assam tea leaves have been processed into crush, tear, and curl (CTC) tea initially, followed by fermentation and drying in a conical bubbling fluidized bed dryer. The effect of various parameters, such as drying air temperature, superficial air velocity, inventory, and cone angle, on moisture removal rate from CTC tea in the conical bed dryer has been experimentally investigated and analyzed in this present work. Drying temperature and superficial air velocity are found to be the major parameter that affects the moisture removal rate from tea. The moisture removal rate from tea varies proportionally with the increase in drying temperature, but the quality deteriorates after a certain limit of temperature. Different cone angles of 0°, 5°, and 10° for the conical bubbling fluidized bed dryer are also inquired into for a static inventory bed height of 15 cm. It is found that moisture removal rate is highest for the case 10° cone angle of the dryer.

Hydrodynamics plays an essential role in the flow of gas-solid characteristics in the fluidized bed (FB) unit. The present paper deals with the hydrodynamic study of biomass (sawdust, mean diameter dp = 400 µm and particle density Pp = 410 kg/m3) in a pressurized fluidized bed (PFB) having an internal diameter 100 mm and height 3000 mm. The Experiment has been carried out, at four different inventory of sawdust 500, 750, 1000, and 1250 g and each inventory at four different working pressure 1, 2, 3, and 4 bar. The effect of the operating condition has been analyzed for voidage profile, suspension density, and drop of pressure in the riser. The results show that at the lower part of the riser section, bed voidage reduces with an enhancement in operating pressure whereas at the upper part of the riser section bed voidage increases with a rise in operating pressure. It also can be observed that the bed voidage along the peak of riser decreases with a rise in solid inventory. The bed voidage is found minimum (e = 0.51 at a distance 720 mm from distributor plate) at 1250 g of inventory having operating pressure 4 bar. Solid inventory and operating pressure having a positive effect on suspension density and suspension density found an increasing trend with an enhancement of pressure and bed inventory. At the inlet of riser minimum suspension density was found 59.3 kg/m3 at a pressure of 1 bar having 500 g inventory whereas maximum suspension density was found 124.7 kg/m3 at a pressure of 4 bar having 1250 g inventory.

Pressurized Circulating Fluidized Bed (PCFB) has earned appreciation in using low-grade coal for gasification and combustion applications because of its built-in capacity to capture sulphur and NOx. It becomes more attractive due to its compactness and elevated heat release rate. Whether the fluidized bed is used to separate or react, the key objective is to operate the bed at a flow rate that optimizes the application. Accurate models would help a great deal but modelling continues to challenge engineers and researchers even at a qualitative level. In this present investigation, numerical simulation is carried out in two conical risers and one columnar riser by considering coal as a bed inventory. The simulation is performed at a superficial velocity of 4 m/s for an inventory of 1 kg. The model k–e is used as a turbulence model. The simulation is performed to investigate the optimum parameters for the efficient use of the pressurized circulating fluidized bed. From the simulation, the variation of bed voidage, suspension density and pressure over the riser height are calculated at the operating pressure of 1, 2, 5 and 10 bar and results have been compared among the three risers. It is observed that pressure drop decreases up to a certain height and then increases with the height of the riser. Suspension density is also found to be decreasing with height. The pressure drop in the conical bed is found to be lower than that of columnar bed.

Biogas is mainly composed of methane (CH4) and carbon dioxide (CO2) with trace amounts of hydrogen sulfide (H2S), of which CO2 and H2S are impurities. Scrubbing of these two impurities are crucial for purification and upgradation of biogas, which would simultaneously also increase the calorific value of the treated biogas and address the issue of corrosion. Several studies have used expensive and environmentally harmful chemicals for the purification of biogas. This study reports a simple biogas purification system that utilizes biomass biochar and biochar–clay composites to remove CO2 and H2S from biogas by the process of adsorption. The biomass biochar could enrich the methane content of raw biogas from 59.7 to 84.6%, which shows the potentiality and applicability of biomass biochar for the removal of CO2 and H2S from biogas. This simultaneously enhanced the calorific value of the biogas and retarded the corrosiveness due to H2S. The study also indicated that CO2 adsorption by biomass biochar and biochar–clay composite is transient and has to be reloaded after saturation. Biochar and clay have the added advantage of being environment friendly and require no treatment for disposal. Observed results indicated that similar degree of enrichment, compared to commonly used chemical, could be achieved by application of biomass biochar and biochar–clay at a much lesser cost.

A rotating fluidized bed with static geometry (RFB-SG) drying is a promising technique that is useful for various operations, such as agglomeration, food grain drying, particle coating, separation, and combustion. The advantage of this technique is that a large volume of hot air is circulated across the particles in a very small geometry, which results in higher heat and mass transfer. The higher heat and mass transfer through the RFB-SG dryer makes the drying process faster. Initially, the high-velocity air is injected into the vortex chamber through multi-air inlets, and then the solid particles are inserted into the vortex chamber. The high-velocity air injected into the reactor forces the solid particle to rotate in the form of a solid bed. The air entering into the vortex chamber carries away the moisture of food grains via a centrally located chimney outlet. In the present work, performance of scaled-up RFB-SG dryer has been evaluated considering parameters, such as temperature (55–65 °C), airflow rate (600–800 m3/h), inventory (400–1000 g), and drying time. The RFB-SG dryer is found to be more efficient than the conventional fluidized bed (CFB) dryers as this dryer works on a higher airflow rate. Drying efficiency is improved by better utilization of the drying air at a temperature of 65 °C.

Growing concern about the rapid depletion of fossil fuels, current environmental conditions, energy challenges and new environmental regulations has encouraged the researchers worldwide for new environmentally compatible alternatives from natural resources. In this context, biogas produced from anaerobic digestion of organic resources may be considered as a significant bioenergy with the potential to address these concerns. Biogas is a mixture of methane and carbon dioxide as the major constituents with other trace components like water vapor, hydrogen sulfide, ammonia, carbon monoxide and nitrogen. Uses of biogas can be seen in heating, cooking, lighting and power production. However, cleaning of biogas from its impurities, mainly CO2 and H2S, can extend its scope of applications. There are numerous physico-chemical (viz. cryogenic, adsorption, membrane separations and absorption) and biological (in situ and ex situ) technologies for biogas upgradation. These operations are aimed at enriching the methane content of biogas above 90% and thereby enhancing the calorific value up to 35.3 MJ/m3. The purpose behind such upgrading is generally focused to meet the fuel standards to be used in vehicles, for injection in the natural gas grid, and to be used as substrate for the production of chemicals or for fuel cell applications. Enriched biogas is compressed and stocked in gas cylinder and transported to the desired location for utilization. Additionally, use of enriched biogas reduces greenhouse gas emissions. This chapter aims at meticulously evaluating the existing and emerging biogas production and upgradation technologies and confers the outlook for overcoming the challenges associated with them.

The velocity distribution in the axial direction of a conical fluidized bed is not uniform due to the expansion of cross-sectional area along the height. As such, the hydrodynamic and heat transfer characteristics of a tapered fluidized bed differ from that of the columnar fluidized bed. Various operating parameters have a significant effect on these characteristics. In this paper, the effect of bed inventory and airflow rate on the hydrodynamic and heat transfer characteristics in a columnar and conical are investigated and compared both experimentally and numerically. A Eulerian-Eulerian model is employed to investigate the hydrodynamics and heat transfer behaviour for both the types of bed. The Syamlal-O’Brien model is used as a drag model. The pressure drop across the bed is found to higher for the columnar bed. The heat transfer is also found to be better for the conical bed. Results obtained by experiments are seen to be excellent agreement with the numerical results.

The concept of rotating fluidized bed with static geometry (RFB-SG) is highly beneficial in drying operations. The present work is focused on the drying of granular particles (paddy) in the developed RFB-SG dryer. In this RFB-SG, the tangential injection of fluidizing gas via several inlets induces rotary motion to the solid particles and forms a solid-bed. In the entire process of fluidization, the solid particles experience a radially outward centrifugal force, whereas the gas is forced to move inward towards the chimney. The RFB-SG is expected to operate more efficiently at higher gas flow rates as compared to the conventional fluidized bed reactor. Experiments were carried to dry paddy of initial moisture ranging 23–37% (wb) to 14% (wb) with drying air inlet temperature of 55 and 60 °C and mass flow 250 m3/h. A better air utilization decreased the drying time by 20% on increasing the air inlet temperature by 9%. Air inlet temperature of 60°C is better for drying paddy as compared to 55°C.

In the present investigation a single cylinder, four-stroke, water-cooled, spark ignition (SI) engine was modified to operate as a raw biogas fueled SI engine. The engine was operated at wide-open throttle condition and at three deferent compression ratios (CR 8:1–CR 10:1) over a speed range of 1400–1700 rpm. The spark timing of the engine was set to MBT timing. The effect of CRs on the performance, combustion and emission characteristics of the engine was investigated and presented in this paper. It was observed that with increasing CR, the brake torque (BT), brake power (BP) and brake thermal efficiency (BTE) of the engine were increased. The maximum BT, BP and BTE of the engine were found to be 19.96 N-m, 2.92 kW and 28.68%, respectively, at CR 10:1. With increasing CR, the peak cylinder pressure increased and shifted toward the TDC. The maximum peak cylinder pressure at CR 10 was found to be 23.66 bar. With increasing CR, the rate of flame front propagation became faster and was higher at CR 10 for the biogas fueled SI engine. With increasing CR, the UHC emission was reduced, whereas the CO and NOx concentration were increased.

Power generation from solar photovoltaic (PV) plants depends on multiple factors such as solar radiance and ambient temperature. Effective monitoring and control of the energy generated with the solar PV plants may augment the complete performance of the system. The local controllers regulate switching between solar PV, local battery, community battery, and grid according to the availability of power in each system. The sensor data and user information are stored in the cloud that can be accessed with the Internet of Things (IoT) device for further computation. A Web-based graphical user interface (GUI) has been developed for appropriate monitoring and control of energy flow and also to enable the power pooling. The app gets information from the cloud on which various sensor’s data regarding energy pooling are stored by the local/community controllers, and it displays the information that is stored in the cloud. The primary task is to design and develop a Web-based application with sufficient data security. To secure the user data in the cloud, multi-factor authentication and symmetric key encryption are used for authorized access and data encryption. The basic model of the Web-based application is presented in this paper.

Owing to the non-uniform availability of solar radiation, designing of a latent heat storage found necessary so as to bridge the supply and demand gap. In the current investigation, the charging and discharging characteristics of a 10 MJ capacity, paraffin wax-based latent heat storage are analyzed numerically. Validations with experimental results showed reasonably good agreement following which parametric studies are conducted and detailed discussion on results are presented.

The austenitic stainless steels are widely used in chemical, metallurgical, conventional, nuclear power plants and industrial applications due to their excellent corrosion resistance and formability. For welding plates of higher thickness, the submerged arc welding is a suitable technique, as it offers higher deposition rate, good bead shape and deeper penetration. To get a sound welded joint without defects, suitable welding parameters should be carefully chosen to weld austenitic stainless steel as they are sensitive to heat input. In this study, austenitic stainless steel plates were joined using double-sided submerged arc welding, and key welding parameters such as voltage, current and welding speed were established to get a defect-free joint. The effectiveness of double-sided welding is evaluated from microstructural and mechanical characterization. From the macroscopic examination, the two weld seams, i.e. initial run and second run intersect at the middle, which is an indication of the defect-free weld. The microstructure of the fusion zone consists of dendritic grains and coarse columnar grains. The microhardness tends to increase in the weld zone for initial weld run followed by second weld run and lowest in the middle of the weld seam. The result of the tensile test indicates that elongation of the welded joint surpasses that of parent metal elongation, and fracture occurs at base zone. The field emission scanning microscopy examination of the broken surfaces of the tensile sample reveals the nature of fracture mode is ductile. In this paper, heat input controlling method was successfully introduced for welding of austenitic stainless steels of higher thickness with a simple double-sided submerged arc welding (DSSAW).

The submerged arc welding (SAW) is an automated process that is capable to weld thick and thin plates of steel and non-ferrous materials due to its ease of operation, less spatter and high deposition rates. SAW is extensively used to fabricate bridges, pipe lines, pressure vessel construction, ship building and surface cladding. In present study numerical simulation on effect of welding speed on residual stresses for SAW with square butt geometry of austenitic stainless steel is explored. A moving heat source model considering heat generation is used in this present study. The element birth and death technique is used to incorporate the effects of filler metal deposition. The peak temperatures observed in experimentation were correlated with that of numerical results and the variation was observed to be 4.77%. At higher welding speeds the low peak temperatures were observed which is due to less heat penetrating into the joint. It was observed in the present study at higher welding speeds the residual stress and von Mises stress were in increasing trend whereas normal and transverse stresses are negligible along the weld line.

Conversion of woody biomass, animal waste such as cattle dung, chicken litters, pig manure, municipal solid, and agricultural wastes to methane gas under oxygen-free environment and favorable temperature range is called anaerobic digestion. But achieving the required temperature range under normal condition is difficult which necessitates the development of a heating system for better digestion process. The endeavor of the present investigation was developing 1.8 m2 solar collectors intended to heat biogas digester and investigating its performance. The solar collector was tested experimentally and numerically for heating water before implementing in actual model. A three-dimensional computational fluid dynamics model was developed by taking a single straight tube attached with an absorber plate at the bottom to predict outlet water and absorber plate temperature. The developed model predicted the outlet water temperature and absorber plate temperature with a reasonable accuracy. Moreover, 53 °C of outlet water temperature and 44% daily average efficiency were achieved at a flow rate of 0.021 kg/s. As the obtained temperature was found to be good enough for anaerobic digestion, the developed solar collector could be regarded as an alternate option.

Electricity generation through coal–thermal route is one of the highest contributors to environment pollution through greenhouse gas emission, which has given rise to issue of climate change risk. Among different alternatives of renewable energy, an important source is biomass-based energy. Utilization of biomass for energy production in coal-fired power plants is essentially in terms of partial substitution of coal feed with biomass. Major challenge in this route is fluctuating supply and varying compositions of biomass. It can be overcome by adopting co-gasification technology (using mixed feed of biomass and low-grade coal) for power generation. In this chapter, we have presented a critical review and analysis of the literature in the area of co-gasification of biomass and coal. Analysis in this paper touches upon several facets of co-gasification process such as effect of biomass/coal ratio, the composition (proximate/ultimate analyses of biomass/coal), gasification media, temperature and heating rates on the gasification kinetics, producer gas composition, and yield. The synergistic effects between gasification of coal and biomass have been reviewed. The alkali/alkaline earth metal content in the ash of biomass catalyzes the kinetics of the gasification of coal char. However, if coal has high silica content, adverse reaction between silica and potassium oxides can deactivate the catalytic effect. Actual chemical mechanisms related to this synergy have also been described and discussed. Finally, a brief review of the literature on gasification of coal/biomass blends in bubbling/circulating fluidized bed gasifiers has also been presented.

Biomass gasifiers with capacities exceeding 1 MW have large biomass consumption, and mixture of biomasses need to be used as feedstock in these gasifiers. In this chapter, we have presented a review of our studies in gasification of biomass blends using approaches of non-stoichiometric equilibrium, semi-equilibrium, and kinetic models. Initially, gasification of biomass mixtures has been assessed using thermodynamic equilibrium and semi-equilibrium (with limited carbon conversion) model employing Gibbs energy minimization. Influence of operating parameters such as equivalence ratio, temperature of gasification, and composition of the biomass mixture has been evaluated using two criteria, viz net yield and LHV of the producer gas. Interestingly, optimum operating conditions for all biomass mixtures have been established as equivalence ratio ~0.3 and gasification temperature ~800 °C. The kinetic model analysis of gasification of biomass based on a circulating fluidized bed gasifier. A series of chemical reactions was considered for obtaining complete mass balance. Although the profiles of molar composition, net yield and LHV of the producer gas predicted by kinetic model matched with equilibrium models qualitatively, significant quantitative difference was evident. The processes of char gasification and tar oxidation have slow kinetics that adversely affects the carbon conversion in the riser of the circulating fluidized bed gasifier.

Before the mining of fossil fuels, biomass was the main source of energy for heating and cooking including hot fuel gas production. With rapid industrialization and use of fossil fuels with high calorific values, use of biomass decreased rapidly. However, in the present context of both climate change and energy security, importance of biomass is regaining as a sustainable energy solution. Life cycle of CO2 emission during the secondary energy production from biomass is lesser than that of the fossil fuels. It is even negative, say for bioenergy with carbon capture. Biomass with good calorific value is abundantly available in countries with rapidly increasing energy demands like India, China, Brazil. Utilization of biomass may increase energy access in rural areas and long-term energy security in India. However, proper selection of biomass, their logistics, and conversion pathways will play an important role. Sustainability of the biomass-based energy system should be assessed for its future feasibility. In this chapter, role of biomass for sustainable energy is assessed specifically for India. Present challenges of energy generation are reviewed. Availability of different types of biomass and logistics are explored. Then, various possible conversion technologies for the conversion of biomass for fuels, electricity are discussed. Possible energy system design for biomass inputs including direct firing, co-firing, gasification and polygeneration are discussed in this chapter. Sustainability assessment of these energy systems is discussed in this chapter. Finally, challenges and prospects related to biomass-based distributed energy solution are presented.