Insights into the production potential and trends of China's rural biogas

China, one of the countries in the world abundant in agricultural wastes, has a great potential for rural biogas production. As a strategy for building a new socialist countryside and sustainable agriculture in rural China, the development of biogas is an important means to convert agricultural wastes to clean and safe energy, thereby reducing the need for fossil fuel and alleviating environmental pollution. This study presents an assessment of the biogas production potential, its current development state, and perspectives of agricultural wastes in rural China. Estimated data show that annual biogas potential from agricultural wastes is approximately (3350.58 ± 669.28) × 10⁸ m³ (equal to 239.22 ± 47.78 million tons of equivalent standard coal); such potential has been underutilized in the past. By analyzing and summarizing the direction for future development and various benefits of rural biogas in China, we present burning questions and countermeasures for biogas development and recommend that the future development of rural biogas in China should focus on both household‐scale and large‐scale development, giving priority to the establishment of large‐scale biogas engineering and biogas plants, improvement of biogas comprehensive utilization level, and construction of a reticular model of systemized green agricultural engineering linked with biogas to solve completely the problem of agricultural waste accumulation and improve the living conditions in rural China. Copyright © 2015 John Wiley & Sons, Ltd.     

Energy-efficient cooking methods

Energy-efficient new cooking techniques have been developed in this research. Using a stove with 649?±?20 W of power, the minimum heat, specific heat of transformation, and on-stove time required to completely cook 1 kg of dry beans (with water and other ingredients) and 1 kg of raw potato are found to be: 710 (±24)?kJ, 613 (±20)?kJ, and 1,144?±?10 s, respectively, for beans and 287?±?12 kJ, 200?±?9 kJ, and 466?±?10 s for Irish potato. Extensive researches show that these figures are, to date, the lowest amount of heat ever used to cook beans and potato and less than half the energy used in conventional cooking with a pressure cooker. The efficiency of the stove was estimated to be 52.5?±?2 %. Discussion is made to further improve the efficiency in cooking with normal stove and solar cooker and to save food nutrients further. Our method of cooking when applied globally is expected to contribute to the clean development management (CDM) potential. The approximate values of the minimum and maximum CDM potentials are estimated to be 7.5?×?10¹¹ and 2.2?×?10¹³?kg of carbon credit annually. The precise estimation CDM potential of our cooking method will be reported later.     

Personal power using metal-supported solid oxide fuel cells operated in a camping stove flame

A complete stand-alone product prototype providing combined cooking and power is fabricated by retrofitting a commercial camping stove with a stack of metal-supported solid oxide fuel cells (MS-SOFCs) delivering power to microelectronic LED driver and voltage boost circuits. The 5-cell stack produces 2.7 W (156 mW cm^?2) while cooking on the stove, and is demonstrated to produce LED lighting and mobile phone charging while operating outdoors. Cooking efficiency is minimally impacted by the presence of the MS-SOFCs. It is found that vertical orientation of the cells is critical to maintain separation of fuel and air when a pot is placed on the stove.     

Optimal sizing of a solar–biogas-based cooking system for a cluster of villages

Energy supplies particularly in remote and far-flung rural areas are in pathetic situation. Leave aside other needs, most of the rural communities still use wood as a source of energy for cooking. Burning of wood is not only an inefficient method, but also hazardousness for the person working on the stove. People have been working for cleaner and efficient means of cooking for decades. Solar cooker- and biogas-based cook stoves are two of the successfully implemented technologies in this area. Although solar cooker requires no maintenance, the initial investment is quite high for a cluster of villages. In addition to this, the intermittency involved in solar energy makes this an unreliable source.

In this paper, a cluster of villages of Narendra Nagar block of Tehri Garhwal district of Uttarakhand, India, has been studied in terms of their thermal requirements. The potential of solar energy and biomass energy has been estimated. An integrated solar–biogas system has been proposed to satisfy this cooking demand. To obtain the optimal sizes of solar cooker and biogas generator, MATLAB codes have been developed. It was found that this system is more economical and much reliable than the other two cases.     

An Application of Solar Energy Storage in the Gas: Solar Heated Biogas Plants

Abstract

Temperature is an important factor that may affect the performance of anaerobic digestion. Therefore, biogas plants without heating system work only in warmer regions for the whole year. In regions with extreme temperature variations, for instance in Turkey, the biogas plant should be built with heating system. One of the methods is to use solar energy to increase the reactor temperature. In this study, solar heated biogas plants were reviewed. Furthermore, the optimization of insulation thicknesses and solar energy systems for 5 m³ biogas reactor were carried out for two different cities for three different climatic zones in Turkey. Based on the obtained results, the ratio of annually produced biogas used for reactor heating was calculated for each city, with and without solar heating system. Obtained results indicate that the biogas consumption for reactor heating is decreased by approximately 19% for average of six cities when solar heating system is used. This means that available biogas potential would be increased.     

Anaerobic treatment of wastewater using an upflow anaerobic sludge blanket reactor

An upflow anaerobic sludge blanket (UASB) reactor of volume 0.03 m³ was designed and fabricated to treat wastewater. The initial organic loading rate (OLR) of the wastewater estimated to be 4.8 gVS/l.d was later reduced to 0.96 gVS/l.d to control the observed acidity in the medium while the reactor was operated continuously for 64 days. The percent biological oxygen demand (BOD) and volatile solid (VS) removal were calculated over a period of 5 weeks to measure the efficiency of the reactor. The mean VS, total solid (TS), and BOD for the influent substrate were 0.43 g/kg, 0.84 g/kg, and 0.020 mg/m³, respectively, while for the treated wastewater, the VS, TS, and BOD were 0.30 g/kg, 0.59 g/kg, and 0.013 mg/m³, respectively. The estimated energy produced by the biogas was 5.8 kWh and 0.001 m³ of the biogas raised the temperature of 20 ml of water by 11.8°C in 40 s. The study concluded that the UASB reactor designed could treat the wastewater and the biogas generated could also serve as a source of renewable energy for cooking. However, the start-up OLR should be monitored in the course of operation to prevent souring of the digester and to achieve optimum performance of the reactor.     

Biogas production from municipal sewage sludge (MSS)

Biogas is produced by anaerobic (oxygen free) digestion of organic materials such as sewage sludge, animal waste, and municipal solid wastes (MSW). As sustainable clean energy carrier biogas is an important source of energy in heat and electricity generation, it is one of the most promising renewable energy sources in the world. Biogas is produced from the anaerobic digestion (AD) of organic matter, such as manure, MSW, sewage sludge, biodegradable wastes, and agricultural slurry, under anaerobic conditions with the help of microorganism. Biogas is composed of methane (55–75%), carbon dioxide (25–45%), nitrogen (0–5%), hydrogen (0–1%), hydrogen sulfide (0–1%), and oxygen (0–2%). The sewage sludge contains mainly proteins, sugars, detergents, phenols, and lipids. Sewage sludge also includes toxic and hazardous organic and inorganic pollutants sources. The digestion of municipal sewage sludge (MSS) occurs in three basic steps: acidogen, methanogens, and methanogens. During a 30-day digestion period, 80–85% of the biogas is produced in the first 15–18 days. Higher yields were observed within the temperature range of 30–60°C and pH range of 5.5–8.5. The MSS contains low nitrogen and has carbon-to-nitrogen (C/N) ratios of around 40–70. The optimal C/N ratio for the AD should be between 25 and 35. C/N ratio of sludge in small-scale sewage plants is often low, so nitrogen can be added in an inorganic form (ammonia or in organic form) such as livestock manure, urea, or food wastes. Potential production capacity of a biogas plant with a digestion chamber size of 500 m³ was estimated as 20–36 × 10³ Nm³ biogas production per year.     

Biogas production in low-cost household digesters at the Peruvian Andes

Low-cost tubular digesters originally developed in tropical regions have been adapted to the extreme weather conditions of the Andean Plateau (3000-4000 m.a.s.l.). The aim of this study was to characterise biogas production in household digesters located at high altitude, operating under psychrophilic conditions. To this end, two pilot digesters were monitored and field campaigns were carried out in two representative digesters of rural communities. Digesters’ useful volume ranged between 2.4 and 7.5 m³, and hydraulic residence time (HRT) between 60 and 90 days. The temperature inside the digester’s greenhouse ranged between 20 and 25 °C. Treating cow manure, a specific biogas production around 0.35 m³ kg_VS⁻¹ was obtained, with some 65% CH₄ in biogas. In order to fulfil daily requirements for cooking and lighting, biogas production should be enhanced without increasing implementation costs as not to impede the expansion of this technology at household scale. In this sense, HRT below 60 days and OLR above 1 kg_VS m⁻³ day⁻¹ should be investigated to decrease digesters’ volume (i.e. costs) and increase biogas production rate. The adaptation of conventional gas burners to biogas characteristics can also contribute in improving the efficiency of the system.     

Design of 3 kW integrated power generation system from solar and biogas

Energy/Power is an important element of social and economic development. Without availability of energy at a reasonable price, there is little prospect of developing the country's economy and people's living conditions. A quarter of Pakistani population have no access to electricity, and currently a shortage of 5.0–7.0 GW power supply causes load shedding/blackout problems. In Pakistan, most of the power is generated from non-renewable sources like natural gas etc. Pakistan receives almost 15.525 × 10¹⁴ kW-hour of solar energy per year and sunshine duration is normally 8.0–10.0 h per day. Animal/farm wastes are readily available in Pakistan. Residues from these sources produce 103.0 billion m³ of biogas per year that is equivalent to 63.20 TWh. The objective of this study is energy production by using easily available indigenous resources. In this study a 3.0 kW integrated solar/biogas power generation system consist of 2.84 kW solar system and 4.0 m³ biogas system is designed and installed. This paper also present simulation model of system. A hybrid inverter is used to convert DC power of photovoltaic modules and the battery bank in to AC power and combines with the output power of biogas generator. Performance of the hybrid system are analysed from May 1, 2018 to June 15, 2018. During the test maximum power produce by the integrated system is 1.10 kW in morning, 2.14 kW in noon and 1.16 kW in afternoon.     

Enhancement of the quality of syngas from catalytic steam gasification of biomass by the addition of methane/model biogas

In this study, methane and model biogas were added during the catalytic steam gasification of pine to regulate the syngas composition and improve the quality of syngas. The effects of Ni/γ-Al₂O₃ catalyst, steam and methane/model biogas on H₂/CO ratio, syngas yield, carbon conversion rate and tar yield were explored. The results indicated that the addition of methane/model biogas during biomass steam gasification could increase the H₂/CO ratio to about 2. Methane/model biogas, steam and Ni/γ-Al₂O₃ catalyst significantly affected the quality of syngas. High H₂ content syngas with H₂/CO ratio of about 2, biomass carbon conversion >85% and low tar yield was achieved under the optimum condition: S/C = 1.5, α = 0.2 and using Ni/γ-Al₂O₃ catalyst. According to ANOVA, methane and catalyst were the key influencing factors of the H₂/CO ratio and syngas yield, and the tar yield mainly depended on the Ni/γ-Al₂O₃ catalyst. Biogas, as a more environmentally friendly material than methane, can also regulate the composition of syngas co-feeding with biomass.     

Solar assisted biogas plants III: Energy balance of fixed dome biogas plants and enhancement of production in winters

This paper presents a thermal model of a fixed dome biogas plant, with or without hot charging and having the ground surface above the plant, blackened and glazed. The rate of energy transfer, between the ground and the plant has been determined by electrical simulation experiments, using a small scale model of the plant (made of copper), suspended in copper sulphate solution. For hot charging a shallow solar pond, built on the ground has been considered. The monthly variation of the slurry temperature, corresponding to 1, 4, 8, 15 and 30 m³ plants have been evaluated for Madras, New Delhi and Srinagar, which correspond to typical hot, composite and cold climates; the following cases have been considered:

• 1 Bare plant, without hot charging and blackening/glazing of the ground, above the plant.
• 2 Plant, charged with hot slurry from a shallow solar pond.
• 3 Plant, with ground above blackened and glazed.
• 4 Plant, with ground above blackened and double glazed and also provision for heating the slurry by burning a part of the produced biogas.

It is seen that blackening and single glazing of the ground above the plant is able to maintain the slurry temperature between 28 and 35°C throughout the year in composite climate such as Delhi; in cold climates even double glazing alone is not enough for that purpose. Hot charging from a shallow solar pond alone is not sufficient to maintain satisfactory slurry temperatures in winters of Delhi and of course Srinagar. In hot climates the slurry temperature is sufficiently high, except for a couple of months, when either hot charging from a shallow solar pond or blackening/glazing of the ground above is sufficient to have the slurry temperature in the desirable range. In cold climates such as Srinagar, the desired slurry temperatures can be maintained if a part of the gas produced is burnt for heating the slurry, in addition to blackening and double glazing of the ground above the dome. Theoretical predictions of slurry temperatures have been compared with the field data recorded for an 8 m³ digester at the Energy Complex, Masoodpur, Delhi; the agreement is satisfactory.     

Effect of PVC greenhouse in increasing the biogas production in temperate cold climatic conditions

This paper presents an investigation on a new concept of greenhouse coupled biogas plant for enhancing the biogas yield during winter months when the slurry temperature decreases considerably. Using this concept, two of the biogas units (having a capacity of 8 m³ and 85 m³, respectively) at Masoodpur Village (near New Delhi), were experimented upon in January 1984. Continuous observations for about 1 week, 1 yr after installation of the greenhouse over the biogas units, have indicated that the biogas yield has increased by almost 100%. Subsequently, an analytical model has also been developed to validate the experimental observations and to predict the thermal performance of biogas plants, with and without greenhouse, under any climatic conditions. It has been observed from a comparative study of the conventional and the solar-assisted greenhouse coupled biogas plant that the temperature of the slurry can be raised from 20°C (in the conventional plant) to nearly 35°C, the optimal temperature for anaerobic fermentation.     

Hydrogen sulfide removal from biogas by biotrickling filter inoculated with Halothiobacillus neapolitanus

Hydrogen sulfide (H₂S), a highly corrosive gas, is found in biogas due to the biodegradation of proteins and other sulfur containing organic compounds present in feed stock during anaerobic digestion. The presence of H₂S is one of the biggest factors limiting the use of biogas. It should be removed prior to application of biogas in an electric generator or industrial boiler. The present research evaluated the performance of biotrickling filter inoculated with Halothiobacillus neapolitanus NTV01 (HTN) on the H₂S removal from synthetic biogas. HTN, isolated and purified from activated sludge, is a sulfur oxidizing bacteria able to degrade H₂S and thiosulfate to elemental sulfur and sulfate, respectively. Operational parameters in a short term operation were varied as following; gas flow rate (0.5–0.75 LPM); EBRT (40–120 s); the inlet H₂S concentrations (0–1500 ppmv); liquid recirculation rate (3.6–4.8 L/h). EBRT showed a greater effect to the removal efficiency than increasing H₂S concentration. Longer EBRT resulted higher removal efficiency. The changes of liquid recirculation rates did not significantly affect the removal efficiency. In long term operation, the gas flow rate and liquid recirculation rate were fixed at 0.5 LPM (120 s EBRT) and 3.6 L/h; and H₂S concentrations were varied (0–2040 ppmv). The maximum elimination capacity was found as 78.57 g H₂S/m³ h, which had greater performance than the previous studies.     

Biogas production from thermophilic codigestion of air‐dried rice straw and animal manure

In order to evaluate the effects of organic loading rate (OLR) on thermophilic codigestion of air‐dried rice straw (RS) with pig manure (PM), cow manure (CM), and chicken manure (CHM), continuous bench experiments (40 L) were carried out at OLRs of 3.0, 3.6, 4.2, 4.8, 6.0, 8.0, and 12.0 kg VS/(m³ · d). Stable biogas production without inhibition by volatile fatty acids (VFA) or ammonia and foaming was achieved at OLRs of 3–12, 3–6, and 3–4.8 for the codigestions of RS + PM, RS + CM, and RS + CHM, respectively. Maximum average volumetric biogas production rates of 4.98, 2.64, and 2.03 m³/(m³ · d) were obtained at OLRs of 12, 6, and 4.8 kg VS/(m³ · d) for the codigestions of RS + PM, RS + CM, and RS + CHM. Foaming was occurred at OLRs of 8 kg VS/(m³ · day) for the codigestions of RS + CM. The codigestion of RS + CHM was inhibited by the accumulation of ammonia instead of VFA when the OLR was ≥6 kg VS/(m³ · d). This study provided references for the engineering application of codigestion of RS and animal manure. Copyright © 2016 John Wiley & Sons, Ltd.     

Novel solar cookers: suitable for small families

This paper presents the fabrication details and on-field experimental studies of two novel solar cookers, suitable for cooking requirements of small families; these are named as small family solar cookers (SFSC-1 and SFSC-2). Small size, good thermal performance, light weight, low-cost and short payback periods are some important features of these cookers. The values of some essential thermal performance parameters, first figure of merit (F₁), second figure of merit (F₂) and standard cooking power suggested by Bureau of Indian Standards and International Standard for box-type solar cookers, have been evaluated by experimental studies and found to be 0.116°C m²/W, 0.466, 30 W and 0.118°C m²/W, 0.488, 50 W for SFSC-1 and SFSC-2, respectively. A comparative analysis of the thermal performances of SFSCs with the solar cookers, developed by many authors, has also been presented here. The payback periods with respect to different cooking fuels for SFSCs have been found to be reasonably short.     

Production of bio‐energy from organic waste: effect of temperature and substrate composition

This article presents the influence of temperature and influent substrate composition on the produced biogas volume in an anaerobic co‐digestion process. Four cases of anaerobic digestion were considered. Digestion of waste sludge only and anaerobic co‐digestion of sludge mixed with solid waste in mesophilic (T = 35 °C) and thermophilic (T = 55 °C) phases. The obtained results show that thermophilic co‐digestion gives the best results; although the temperature has an effect on biogas production, it remains however quite relative compared to the effect of solid waste. They confirm, surely, that the combined effect of temperature and solid waste improves considerably the biogas production rate (GPR). Changing conditions from mesophilic to thermophilic ones for waste sludge alone and for waste sludge mixed with solid waste results in an increase of the GPR from 0.18 to 0.39 m³/m³.d and from 0.29 to 0.96 m³/m³.d, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Syngas production by steam and oxy-steam reforming of biogas on monolith-supported CeO2-based catalysts

In this study, the syngas production by steam reforming (SR) and oxy-steam reforming (OSR) of clean biogas over cordierite monoliths (400 cpsi) lined with Ni, Rh, or Pt on CeO₂ catalyst was deeply investigated. Structured catalysts were prepared by using an alternative method to traditional washcoating based on the combination of the solution combustion synthesis (SCS) with the wetness impregnation (WI) technique. TEM and SEM analysis were used to study the morphology of the catalytic layer and to determine its thickness, while the quality of the coating in terms of adhesion on the monolith was evaluated by ultrasonic treatment in isopropyl alcohol solution. The performance and the stability of the structured catalysts were investigated at different process parameters, namely temperature (700–900 °C), steam-to-carbon (S/C = 1–5) and oxygen-to-carbon (O/C = 0.1–0.2) molar ratios, and weight space velocity (WSV = 30,000–250,000 NmL g_cat^?1 h^?1). The SCS + WI deposition method allowed obtaining a uniform and thin coated layer with high mechanical strength. The following order of activity was exploited: Rh > Pt > Ni for biogas SR and Rh > Pt ≈ Ni for biogas OSR. The Rh-based catalyst exhibited higher activity and long-lasting stability towards biogas SR and OSR reactions for syngas production.     

Experimental and Numerical Analysis of Heat Transfer in a Tall Vertical Concentric Annular Thermo-siphon at Constant Heat Flux Condition

The present work deals with the numerical and experimental analyses to study the detailed behavior of the thermally induced flow of water in an open vertical annulus, circulating through a cold leg forming a closed loop thermo-siphon. Spatio-temporal behavior of fluid flow is also studied for variety of heat fluxes. The annuli in the present study have a radius ratio of 1.184 and aspect ratio (length to annular gap) equal to 352. The objective of the present work is to quantify the effect of heating on design parameters such as liquid and wall temperatures, mass flow rate, and heat transfer coefficient. Experiments have also been conducted on a similar system with water at constant heat flux of 1 kW/m², 2.5 kW/m², 5 kW/m², 7.5 kW/m², 10 kW/m², 12.5 kW/m² and 15 kW/m². For numerical purpose, a two-dimentional solver has been developed for direct numerical simulation of the essential thermally induced flow dynamics The numerical solution was thus performed for Rayleigh numbers ranging between, 4.4 × 10³ and 6.61 × 10⁴ which correspond to the given heat flux, respectively.     

The fixed dome digester: An appropriate design for the context of Sub-Sahara Africa?

The fixed dome digester design is the most deployed small scale biogas technology in sub-Sahara Africa (SSA). This design is deployed on mono-feedstock-wet anaerobic digestion (WAD) principle. Little or nothing has been reported in the literature on the sustainability in terms of the actual field operation and performance of this design within the SSA context. This study aims at bridging this gap and bringing additional insights to the scientific literature by investigating the sustainability of the Nepali–type fixed dome digester within the context of rural Cameroon. The investigations were evaluated in terms of operating parameters, biogas production, production rate and productivity of the digester. In addition the local investment cost of the design was analyzed. The design was operated on multiple-locally-available feedstock mixed with water at an average of 3:1 ratio resulting in a higher than design TS of 16%. The design, thus was operated towards the dry anaerobic digestion principle, highlighting insufficient mono-feedstock and water scarcity for a sustainable operation of the design within the context of rural SSA. The average biogas production was 1.2 m³_biogas/day, giving average volumetric production rate of 0.16 m³_biogas/m³_digester day⁻¹ and yields of 0.18 m³_biogas/kg VS respectively. This low performance compared with the potential mesophilic biogas production rate of 0.27 m³_biogas/m³_digester day⁻¹ could be linked to insufficient mixing of digester content and low operating temperatures. Gas storage facility (dome), skilled labour and cement made significant contributions to the investment cost of the digester. The Levelized cost of Energy from the digester was less than 1 € cents/MJ.     

Experimental investigation of high temperature congregating energy solar stove with sun light funnel

A solar stove which uses a light funnel to guide light and congregate solar energy has been designed. Its structure and operation principle have been introduced. The performance tests under the real weather have been carried out and the graphic lines of experiment have been given. The experimental result shows that the maximum temperature inside the stove is as high as 250 °C under the condition of 1.5 m² of lighting area, 70% reflectivity of reflecting aluminum foil inside surface of concentrator and no load (without water inside the coil pipe). When reflectivity is 86% the heat collecting efficiency of the device is about 43%. The collecting power that the stove receives can be up to 500 W. It is an ideal medium and high temperature solar energy congregating device suitable for industrial usage or cooking and other domestic usage.