Improved combustion stability of biogas at different CO_(2) concentrations using inhomogeneous partially premixed stratified flames

Biogas is a renewable and clean energy source that plays an important role in the current environment of lowcarbon transition.If high-content CO_(2) in biogas can be separated,transformed,and utilized,it not only realizes high-value utilization of biogas but also promotes carbon reduction in the biogas field.To improve the combustion stability of biogas,an inhomogeneous,partially premixed stratified(IPPS)combustion model was adopted in this study.The thermal flame structure and stability were investigated for a wide range of mixture inhomogeneities,turbulence levels,CO_(2) concentrations,air-to-fuel velocity ratios,and combustion energies in a concentric flow slot burner(CFSB).A fine-wire thermocouple is used to resolve the thermal flame structure.The flame size was reduced by increasing the CO_(2) concentration and the flames became lighter blue.The flame temperature also decreased with increase in CO_(2) concentration.Flame stability was reduced by increasing the CO_(2) concentration.However,at a certain level of mixture inhomogeneity,the concentration of CO_(2) in the IPPS mode did not affect the stability.Accordingly,the IPPS mode of combustion should be suitable for the combustion and stabilization of biogas.This should support the design of highly stabilized biogas turbulent flames independent of CO_(2) concentration.The data show that the lower stability conditions are partially due to the change in fuel combustion energy,which is characterized by the Wobbe index(WI).In addition,at a certain level of mixture inhomogeneity,the effect of the WI on flame stability becomes dominant.

Numerical Simulation of Turbulent Diffusion Flames of a Biogas Enriched with Hydrogen

Any biogas produced by the anaerobic fermentation of organic materials has the advantage of being an environmentally friendly biofuel.Nevertheless,the relatively low calorific value of such gases makes their effective utilization in practical applications relatively difficult.The present study considers the addition of hydrogen as a potential solution to mitigate this issue.In particular,the properties of turbulent diffusion jet flames and the related pollutant emissions are investigated numerically for different operating pressures.The related numerical simulations are conducted by solving the RANS equations in the frame of the Reynolds Stress Model in combination with the flamelet approach.Radiation effects are also taken into account and the combustion kinetics are described via the GRI-Mech 3.0 reaction model.The considered hydrogen fuel enrichment spans the range from 0%to 50%in terms of volume.Pressure varies between 1 and 10 atm.The results show that both hydrogen addition and pressure increase lead to an improvement in terms of mixing quality and have a significant effect on flame temperature and height.They also reduce CO_(2) emissions but increase NOx production.Prompt NO is shown to be the predominant NO formation mechanism.

Application of 9-component S-wave 3D seismic data to study sedimentary facies and reservoirs in a biogasbearing area:A case study on the Pleistocene Qigequan Formation in Taidong area,Sanhu Depression,Qaidam Basin,NW China

To solve the problems in restoring sedimentary facies and predicting reservoirs in loose gas-bearing sediment,based on seismic sedimentologic analysis of the first 9-component S-wave 3D seismic dataset of China,a fourth-order isochronous stratigraphic framework was set up and then sedimentary facies and reservoirs in the Pleistocene Qigequan Formation in Taidong area of Qaidam Basin were studied by seismic geomorphology and seismic lithology.The study method and thought are as following.Firstly,techniques of phase rotation,frequency decomposition and fusion,and stratal slicing were applied to the 9-component S-wave seismic data to restore sedimentary facies of major marker beds based on sedimentary models reflected by satellite images.Then,techniques of seismic attribute extraction,principal component analysis,and random fitting were applied to calculate the reservoir thickness and physical parameters of a key sandbody,and the results are satisfactory and confirmed by blind testing wells.Study results reveal that the dominant sedimentary facies in the Qigequan Formation within the study area are delta front and shallow lake.The RGB fused slices indicate that there are two cycles with three sets of underwater distributary channel systems in one period.Among them,sandstones in the distributary channels of middle-low Qigequan Formation are thick and broad with superior physical properties,which are favorable reservoirs.The reservoir permeability is also affected by diagenesis.Distributary channel sandstone reservoirs extend further to the west of Sebei-1 gas field,which provides a basis to expand exploration to the western peripheral area.

A Biogas Production Model from the Combination of Pig Manure and Cow Dung in N’Zérékoré City, Republic of Guine

This present research work focuses on the valorization of pig droppings for production of biogas in mono digestion and co-digestion with proportions of cow dung from the urban commune of N’Zérékoré. It was carried out in December 2020 in the Physics laboratory of the University of N’Zérékoré. The anaerobic digestion process took 25 days in an almost constant ambient temperature of 25˚C. Five digesters were loaded on 12/06/2020, two of which with 1 kg of pig dung and 1 kg of cow dung both in mono-digestion. The 3 other digesters in co-digestion with different proportions of pig manure and cow dung. The substrate in each digester is diluted in 2 liters of water, with a proportion of (1/2). The main results obtained are: 1) the evolution of the temperature and pH during digestion process, 2) the average biogas productions 0.61 liters for (D1);1.20 liter for (D2);1.65 liter for (D3);1.51 liter for (D4) and 1.31 liter for (D5). The cumulative amounts of biogas are respectively: D1 (7.95 liters), D2 (15.60 liters), D3 (21.50 liters), D4 (19.65 liters) and D5 (17.05 liters). The total cumulative production is 81.75 liters at the end of the process. The originality of this research work is that the proposed model examines the relation between the daily biogas production and the variation of temperature, pH and pressure. The combustibility test showed the biogas produced during the first week was no combustible (contains less than 50% methane). Combustion started from the biogas produced from the 15th day and it is from the 20th day that a significant amount of stable yellow/blue flame was observed. The results of this study show the combination of pig manure and cow dung presents advantages for optimal biogas production.

Study on Biogas Production Using Anaerobic Fermentation of Rice Straw

[Objective] The aim was to improve the biogas production rate,and improve the use ratio of rice straws to the furthest.[Method] Single-factor method was adopted to analyze the influence of inoculated amount,total solid content and carbon-nitrogen ratio on biogas production in biogas station of Nanjing University of Technology.[Result] It was found that the most optimum condition was：inoculated amount of 34%,total solid content of 6%,and carbon-nitrogen ratio of 25：1.According to the experimental verification,the total biogas yield in experimental group increased by 27.6% over the control group.[Conclusion] The research provided the reference of the further industrialization production of biogas using straw.

Performance of a Combined Energy System Consisting of Solar Collector, Biogas Dry Reforming and Solid Oxide Fuel Cell: An Indian Case Study

An energy production system consisting of a solar collector, biogas dry reforming reactor and solid oxide fuel cell (SOFC) was assumed to be installed in Kolkata, India. This study aims to understand the impact of climate conditions on the performance of solar collectors with different lengths of parabolic trough solar collector (dx) and mass flow rate of heat transfer fluid (m). In addition, this study has evaluated the amount of H2 produced by biogas dry reforming (GH2), the amount of power generated by SOFC (PSOFC) and the maximum number of possible households (N) whose electricity demand could be met by the energy system proposed, considering the performance of solar collector with the different dx and m. As a result, the optimum dx was found to be 4 m. This study revealed that the temperature of heat transfer fluid (Tfb) decreased with the increase in m. Tfb in March, April and May was higher than that in other months, while Tfb from June to December was the lowest. GH2, PSOFC and N in March, April and May were higher than those in other months, irrespective of m. The optimum m was 0.030 kg/s.

Application of Landfill Composed of Biogas Residue and Slurry in Cherry Production

In order to explore the effects of landfill composed of biogas residue and slurry on the improvement of soil nutrients and cherry fruit yield, three treatments： control （no landfill）, landfilling with biogas residue and water （BR）, landfilling with biogas residue and slurry （BS） were conducted in a cherry orchard. The results showed that compared with the control, soil water content around the landfills with a radius of 60 cm within 30 d was increased in BR and BS treatments. The poment- age of short shoots and the total number of shoots of cherry trees were also signif- icantly increased by BR and BS treatments; the cherry fruit yield per tree and the single-fruit weight in BS treatment were increased by 21.76% and 28.89%, respec- tively. In addition, BS treatment obviously improved the contents of soil organic matter, soil available nitrogen, s0il available phosphorus, soil available potassium and other nutrients. The positive effects of BR treatment on the improvement of soil nutrients and cherry fruit yield were lower than those of BS treatment, indicating that the combined use of biogas residue and biogas slurry as landfill can improve the soil water and fertilizer status in orchards, and thus can be promoted in the cultivation of fruit trees.

Effect of Highly Efficient Nutrient Solution of Biogas Slurry on Yield and Quality of Vegetables

[Objective] The paper aimed to study highly efficient utilization of biogas slurry and the effect of highly efficient biogas slurry on vegetables,so as to provide basis for wide and effective application of biogas slurry.[Method] Using secondary aerobic fermentation technology,a small amount of humic acid was added to biogas slurry to enhance the biological activity of biogas slurry.Through greenhouse experiment,the effect of highly efficient nutrient solution of biogas slurry on yield and quality of green pepper,tomato and cucumber was studied.[Result] Compared with control and traditional application of biogas slurry,application of highly efficient nutrient solution of biogas slurry increased the yield of green pepper,tomato and cucumber,and the increase extents were 12.4%,47.4%,19.9% and 2.7%,15.9%,9.1%,respectively.Compared with traditional application of biogas slurry,application of highly efficient nutrient solution of biogas slurry significantly increased Vc content of green pepper and cucumber with the increase extent of 16.8% and 43.8%,respectively.[Conclusion] Application of highly efficient nutrient solution of biogas slurry can effectively promote the yield of green pepper,tomato and cucumber and change the qualities of vegetables,and significantly enhance the biological activity of biogas slurry.

Security Risk Analysis on the Nutrients and Heavy Metals of Biogas Slurry in Agricultural Application

[Objective] This study was to provide scientific basis for the security application of biogas slurry in agriculture through the analysis on the security risk of nu- trients and heavy metals of biogas slurry in agricultural application. [Method] The components of the slurry produced by the anaerobic digestion of straws and manures were systematically analyzed. Different types of biogas slurry with different concentrations were used to conduct the germination test. [Result] The types and proportions of raw materials, and alkali pretreatment affected the compositions and nature of the biogas slurry. Alkali pretreatment could reduce the contents of heavy metals and improved the contents of nitrogen, phosphorous, organic matter and available components. The contents of heavy metals in the biogas slurry were as follows： Cd of 8.76 μg/kg, Cr of 52μg/kg, Pb of 210 μg/kg, Hg of 0.512 μg/kg, As of 140μg/kg, and the contents of Cu and Zn were the highest among the heavy metals, respectively, 279 and 680 μg/kg. All the contents were under the limit standards of the urban wastes for agricultural use. The germination tests of the seeds verified that the slurry with the concentration of lower than 5% could accelerate the germination, while the salt stress could inhibit the growth of seedlings in the slurry. [Conclusion] When the dung are uses as the raw materials for fermentation, appropriate control should be conducted on the feeding proportion or the heavy metals should be pre-removed; when the slurry is used as the liquid fertilizer to apply in the farmland, the dilution or desalting treatment should be conducted at first.

Effects of Crops, Soil Types and Irrigation Methods on Digestion Capacity of Biogas Slurry

In the research, pot experiment and field testing were conducted to study the effect of different crops, soil types, and irrigation modes on biogas slurry diges- tions. The results showed that when silage maize, sweet sorghum and Chinese cabbage were planted in purple soils, the quantities of digested biogas slurry were of 57, 157.5, and 34.5 t/hm2, respectively, while the quantities of digested biogas slurry were 70.5, 157.5 and 40.5 t/hm2 in yellow soils. Besides, the digested biogas slurries reached 36 and 27 t/hm2 as per flood irrigation and sprinkling irrigation when Chinese cabbages were planted in yellow soils. The research indicated crop variety, soil type, and irrigation method all have effects on farmland digestion of biogas slurry.

Design and Implementation of Biogas Plants Geographic Information System

[Objective] A kind of biogas engineering geographic information system was designed and realized.[Method] Based on the data of the investigation of the large and medium-sized biogas projects in Beijing,the system user＇s need and function demand were studied.Sub-system function was divided.By using SuperMap IS.NET,C# and SQL Server 2005 as the database and WebGIS frame,the system spatial and attribute database were designed so as to realize the WebGIS software of biogas project in Beijing.[Result] The system provided application platform for the distribution of biogas project information.User can realize the submission and inquiry the feedback of biogas project information based on system application right etc,so as to visually,fully and precisely inquiry project data.Based on the comprehensive analysis of data,the current state of biogas project and change trend were studied and decided.[Conclusion] The system provided convenience and services to relevant departments＇ planning and management of biogas project.

Design Considerations of a Flexible Biogas Digester System for Use in Rural Communities of Developing Countries

Several challenges are associated with the development, adoption and deployment of biogas digesters in developing countries. Amongst these challenges is a comprehensive and systematic procedure for the design of digesters suitable for rural communities. This paper proposes the Flexible Biogas Digester System (FBDS) as a viable option for rural communities in developing countries and provides a detailed step-by-step procedure for its design. The biogas production process is a function of the digester operating factors which may be grouped into physical, process and performance parameters. The physical design parameters include the digester volume, the volume of the biogas storage tank, and the volume of the installation pit. The process parameters include total solid content of the slurry (TS), organic loading rate (OLR), digester operating temperatures, pH of the slurry inside the digester. The performance parameters include biogas production rate, biogas productivity and biogas quality. The Net Present Value and the Levelised Cost of Energy are presented for simple economic evaluation of the FBDS.

Effects of Continuous Irrigation of Biogas Slurry on Forms and Biological Availability of Pb in Soil of a Tea Garden

Through indoor culture experiments, the effects of continuous irrigation of biogas slurry on the forms and biological availability of Pb in soil of a tea garden were studied. The results show that continuous irrigation of biogas slurry could change the forms of Pb in the soil, and exchangeable Pb, Pb bonded to iron and manganese oxides, and Pb bonded to carbonates transformed to Pb bonded to or- ganic matter and residual Pb in the soil. Among various forms of Pb in the soil, the content of residual Pb was the highest in the soil irrigated with biogas slurry contin- uously in various treatments, accounting for 54.56%, 60.00% and 60.70% in the treatments T1, T2 and T3 respectively. Compared with the CK, the application of bio- gas slurry could decrease the biological activity and biological availability of Pb in the soil obviously, and the reduction of the biological activity was 21.26%-22.83%. In a word, the application of biogas slurry in soil of the tea garden could inhibit the biological activity and biological availability of Pb.

Current Situation and Prospect Analysis of Biogas Project in Scale Farms in Chengdu

In order to implement National Sustainable Development of Agriculture 2015-2030 and supply-side reform of agriculture, and seek the way to replace chemical fertilizer by livestock and poultry manure, the animal breeding scale and the demand space for biogas project were analyzed according to the changes in farm scale and farm quantity, the present situation of livestock breeding, the biogas technical pattern and present project quantity in Chengdu. Furthermore, based on the cultivated land area in Chengdu, a principle that ＂land decides production, pro- duction decides fertilizer, and fertilizer decides livestock＂ was proposed, and a pro- gram for the livestock quantity and biogas projects in Chengdu in ＂The 13th Five- Year＂ was suggested. Suggestions were also made for government to modify the allowance standards for biogas project construction.

Research Development of Control Technology of Hydrogen Sulfide in Biogas Slurry

In order to provide help for the accurate application of biogas slurry in the field, the application of biogas slurry and control technology of hydrogen sulfide in biogas slurry were reviewed. Results of recent researches suggested that source control and end-treatment were the two measures to remove hydrogen sulfide in biogas slurry, including physical method, chemical method and biological method. Some conventional deodorizing methods were introduced and compared.

Effects of Storage Methods and Time on Content of Nutrients in Biogas Slurry of Straw

To study the effects of different storage methods and time on content of nutrients in biogas slurry of straw, two storage methods were carried out on biogas slurry between open storage and airtight storage conditions at normal atmospheric temperature. The contents of N, P, K, and organic matter in biogas slurry of straw were determined in different storage times. The results showed that： during the pro-cess of biogas slurry storage, little change occurred in the content of the organic matter while the total content of N, P, K significantly declined; up to 50 days, the total content of N, P, K reduced to nearly 80%-90%. Because the contents of N, P, K in biogas slurry reduced less in airtight storage conditions so that a better re-sult was found on airtight storage methods than open storage methods in fertilizer field of biogas slurry of straw.

The Current Status, Potential Benefits and Future Prospects of the Australian Biogas Sector

Anaerobic digestion technology provides a new approach to treat organic waste while generating greenhouse gas (GHG) savings. Moreover, the methane gas produced during the process can be used to generate electricity. In order to ensure that Australia stays on its trajectory towards a carbon neutral future, the use of anaerobic digestion technology to treat its abundant organic waste streams should be considered. Thirty million tonnes (Mt) of organic waste was produced in 2017. The use of anaerobic digestion to treat 1 tonne of waste could result in 0.143 tonne of CO2-e in GHG savings. In contrast, other more widely employed waste disposal methods such as landfilling, composting and incineration may generate GHG emissions. Additionally, the use of methane for electricity production also generates the least GHG emissions per MWh. This is approximately 3 times lower than crude oil, 4 times lower than black coal and 5 times lower than brown coal. However, the adoption and implementation of anaerobic digestion technology in Australia face several immediate constraints. Firstly, anaerobic digestion technology is deemed unprofitable, incurring high initial capital cost, operating costs and extremely long payback periods. Secondly, there is a lack of government support in terms of a national target for biogas production via anaerobic digestion. This review will provide an in-depth analysis into the current state of the Australian biogas sector. In addition, the review discusses the opportunities to make anaerobic digestion technology more financially viable and to accelerate the growth of the Australian biogas sector.

Effects of Biogas Slurry Irrigation on Heavy Metal Contents in Soils

[Objective] This study aimed to investigate the effects of biogas slurry irri- gation on heavy metal contents in soils. [Method] A pot experiment was carried out to investigate the effects of biogas slurry irrigation on the accumulation of heavy metals in soils by measuring the contents of Cu, Zn, Pb, Cr and Cd in different soil layers. [Result] The results showed that original and 30-fold biogas slurry increased the contents of Cu, Zn, Pb, Cd and Cr in soils; Cr might partially reach an exces- sive level in a short term. Biogas slurry irrigation increased the downward migration velocity of Cu and reduced the downward migration velocity of Zn in soils. [Conclu- sion] Biogas slurry irrigation influences the contents of heavy metals, and long-term application of biogas slurry will lead to the accumulation of heavy metals in soils.

Small-Scale Household Biogas Digesters as a Viable Option for Energy Recovery and Global Warming Mitigation--Vietnam Case Study

Biogas from livestock waste is considered as clean and renewable energy in Vietnam. In the last 20 years, in rural and remote areas of Vietnam, there has been a significant increase of small-scale household biogas digesters. Biogas digesters create the benefits of replacing energy and mitigation of climate change caused by greenhouse gas （GHG） emission and deforestation for firewood and charcoal. Livestock waste produces approximately 85 million tonnes every year and continues to increase, meaning there are huge feedstocks for biogas digesters to meet the energy demands in households. However, there are also many constraints on the development programme for small-scale household biogas digester. In Vietnam, the socio-economic situation and the lack of a sustainable energy policy for biogas from livestock sector are hindering the growth of the biogas digester industry. Government subsidies are needed to encourage farmers to participate. This paper will be helpful not only for the sustainable development of household biogas in Vietnam, but also for the developing program of biogas generation in developing countries with similar agricultural economies to Vietnam.

Recovery of Nitrogen and Phosphorous as Struvite From Swine Waste Biogas Digester Effluent

Objective To investigate the feasibility of nitrogen and phosphorus recovery from swine waste biogas digester effluent and the effects of pH and NH4^＋： Mg2^＋： PO4^3- molar ratio on its precipitation. Methods Precipitation experiments with swine waste biogas digester effluent were conducted at pH 7.5, 8.0, 8.5, and 9.0 together with NH4^＋： Mg^2＋： PO4^3- molar ratios 1： 0.2： 0.08, 1： 1： 1, and 1： 1.5： 1.5. Chemical and X-ray diffraction （XRD） analysis were done to determine the composition of the precipitate. Results The highest removal and recovery of NH4^＋ and PO4^3- were achieved at pH 9.0 in each experiment. The elevation of pH to 9.0 alone could decrease the initial PO4^3- concentration from 42 mg L^-1 to 4.7 mg L-1 and 89.2% PO4^3- recovery was achieved. The pH-molar ratio combination 9.0-1： 1.5： 1.5 effected 76.5% NH4^＋ and 68.5% PO4^3- recovery. The molar ratio of 1： 1： 1 together with pH elevation to 9.0 was determined to be the optimum combination for both NH4＋ and PO4^3- removal as it recovered over 70% and 97% of the initial NH4^＋ and PO4^3-, respectively. Conclusions Nitrogen and phosphorus can be recovered from biogas digester effluent as struvite.