Synthesis of Light Hydrocarbons from Biogas and Hydrogen: Investigation of a Fe-Mn-K/MgO Catalyst

Fischer-Tropsch synthesis of the CO₂ in biogas aims at producing light hydrocarbons and increasing its calorific value for feeding into the grid. Fe catalysts with Mn and K as promoters are supposed to yield high amounts of light hydrocarbons. Using a Fe-Mn-K/MgO catalyst, a parameter screening and long-term experiments were carried out. The catalyst shows, within the examined range, the highest selectivity to C₂–C₄ hydrocarbons at 450 °C, 8 bar(a), and a gas hourly space velocity of 350 h⁻¹. Calcination of the catalyst resulted in a significant drop of activity and an almost complete loss of selectivity to hydrocarbons. Admixture of steam to the reactant gas lowers the tendency to carbon deposition but also promotes the water-gas shift reaction and results in lower yields of hydrocarbons.     

Study of MW-scale biogas-fed SOFC-WGS-TSA-PEMFC hybrid power technology as distributed energy system: Thermodynamic,exergetic and thermo-economic evaluation

Advanced biogas power generation technology has been attracting attentions, which contributes to the waste disposal and the mitigation of greenhouse gas emissions. This work proposes and models a novel biogas-fed hybrid power generation system consisting of solid oxide fuel cell, water gas shift reaction, thermal swing adsorption and proton exchange membrane fuel cell (SOFC-WGS-TSA-PEMFC). The thermodynamic, exergetic, and thermo-economic analyses of this hybrid system for power generation were conducted to comprehensively evaluate its performance. It was found that the novel biogas-fed hybrid system has a gross energy conversion efficiency of 68.63% and exergy efficiency of 65.36%, indicating high efficiency for this kind of hybrid power technology. The market sensitivity analysis showed that the hybrid system also has a low sensitivity to market price fluctuation. Under the current subsidy level for the distributed biogas power plant, the levelized cost of energy can be lowered to 0.02942 $/kWh for a 1 MW scale system. Accordingly, the payback period and annual return on investment can reach 1.4 year and about 20%, respectively. These results reveal that the proposed hybrid system is promising and economically feasible as a distributed power plant, especially for the small power scale (no more than 2 MW).     

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2002年AAPG年会于3月10－13日在美国休斯顿隆重召开。根据会议论文，介绍了国外天然气勘探与研究最新进展及发展趋势，其中包括：生物气、海域及深水区有利含气区带、际上新老气区带等常规天然气，以及煤层气、深盆气、天然气水合物等非常规天然气的最新勘探与研究进展。     

Optimal size,hydraulic retention time and volatile solids loading rate of biogas unit using water hyacinth

With a view to evaluate the effects of hydraulic retention time and volatile solids loading rate on methane production using water hyacinth, experiments were conducted in a 160 dm³ capacity, well-mixed continuous digestion unit at ambient temperature. The optimal design of biogas plant using water hyacinth was elucidated, to provide a unit giving a maximum methane yield of 0.16 nm³ kg^?1 volatile solids added, which was 60% greater than the conventional plant using cowdung. The calculations of optimal design factors were based on reactor size, hydraulic retention time and volatile solids loading rate; considerations were made of capital cost, running costs and operational revenue.     

A dynamic linear programming approach to market allocation of renewable resources in the italian energy system: The case of solar thermal and biogas technologies

In Italy solar thermal energy and energy from biogas are two possible means of reducing dependence on energy imports. Using a multiperiod LP model (MARKAL) the authors assessed the likely potential of both technologies under various circumstances. The study covered the period 1980–2005, in five segments of five years. It focused only on the subsystem of the energy end-uses which can be substituted for by solar thermal and biogas technologies. The overall non-renewable sources which can be saved in 20 years by these technologies total 450 PJ (1 PJ = 10^{1 5} J) if the fuel prices rise at 0 per cent average annual, 1450 PJ if the fuel prices rise at 4.2 per cent average annual, 1860 PJ if the fuel prices rise at 7.2 per cent average annual and 3780 PJ if the fuel prices rise at 15 per cent average annual. However the most competitive technologies appear to be solar water heaters used mainly in the private and commercial sectors and biogas systems used mainly in the agricultural sector. The study was carried out by APRE under ENEA (formerly CNEN) contract and was intended to serve as an analytical basis for establishing an overall development and demonstration strategy for end-use renewable technologies in Italy.     

Combined Ozone Pretreatment and Anaerobic Digestion for the Reduction of Biological Sludge Production in Wastewater Treatment

The ever-increasing amount of solid waste generated by wastewater treatment plants highlights emerging economic and environmental issues. In order to develop new processes producing less sludge, the use of ozone combined with anaerobic digestion was investigated for waste activated sludge treatment. This paper was aimed at evaluating the impact of ozone pretreatment on anaerobic digestion and particularly the enhancement of biogas production. Sludge solubilization was estimated in terms of modification of chemical oxygen demand, solids and nitrogen. Batch anaerobic digestion highlighted the enhancement of ozonated sludge biodegradability. Ozonation led to an increase in biogas production. The ozone dose of 0.15 g O₃/g total solids resulted in a considerable increase in the soluble COD ratio from 4% to 37%. This ozone dose achieved the highest increase in biogas production: 2.4 times greater than without chemical pretreatment.     

Maximizing biogas production from the anaerobic digestion

This paper presents an optimal control law policy for maximizing biogas production of anaerobic digesters. In particular, using a simple model of the anaerobic digestion process, we derive a control law to maximize the biogas production over a period T using the dilution rate as the control variable. Depending on initial conditions and constraints on the actuator (the dilution rate D(·)), the search for a solution to the optimal control problem reveals very different levels of difficulty. In the present paper, we consider that there are no severe constraints on the actuator. In particular, the interval in which the input flow rate lives includes the value which allows the biogas to be maximized at equilibrium. For this case, we solve the optimal control problem using classical tools of differential equations analysis. Numerical simulations illustrate the robustness of the control law with respect to several parameters, notably with respect to initial conditions. We use these results to show that the heuristic control law proposed by Steyer et al., 1999 [20] is optimal in a certain sense. The optimal trajectories are then compared with those given by a purely numerical optimal control solver (i.e. the “BOCOP” toolkit) which is an open-source toolbox for solving optimal control problems. When the exact analytical solution to the optimal control problem cannot be found, we suggest that such numerical tool can be used to intuiter optimal solutions.     

Effects of the German Renewable Energy Act on structural change in agriculture – The case of biogas

The strong political support for biogas production in Germany over the past decade has greatly affected agricultural production, farms and land markets. This paper analyzes the effects of Germany's biogas policies on agricultural development by using the agent-based simulation model AgriPoliS. Particular focus is placed on the effects of the previous German Renewable Energy Act (REA, German “EEG”) of 2012, as well as the latest amendments, which were added in 2014. Our results show that under the previous REA and its predecessors, biogas production provided an attractive investment opportunity, especially for large farms, which led to a boost in biogas production. However, this policy also caused distortions within the agricultural sector, including increasing land rental prices. These effects particularly threatened farms that were not able to invest in biogas, as well as smaller biogas farms. On average, biogas farms could not increase their profitability. The main reason for this effect can be seen in the fact that a significant share of the value added is transferred via increased rental prices to land owners. The amendment of the REA in 2014, which reduced support levels substantially, partly attenuates some of these effects, though the previous policy will cast a long shadow.     

Co-digestion of poultry manure and residues from enzymatic saccharification and dewatering of sugar beet pulp

This study investigates the co-digestion of poultry manure (PM) with sugar beet pulp residues (SBPR) obtained from saccharification and dewatering of sugar beet pulp. The laboratory-scale experiments were conducted under batch and semi-continuous conditions at mesophilic temperatures (35 °C). Batch tests gave specific biogas and methane yields of 590 dm³/kgVS_fed and 423 dm³CH₄/kgVS_fed, respectively for SBPR, whereas the corresponding values for PM were 434 dm³/kgVS_fed and 300 dm³CH₄/kgVS_fed. The co-digestion of PM with SBPR was found to increase biogas and methane yields compared to the manure alone. In semi-continuous reactor experiments, the highest methane yield of 346 dm³ CH₄/kgVS_fed was achieved for the mixture containing poultry manure with 50% SBPR (weight basis) and a solids retention time (SRT) of 20 days. However, when poultry manure was digested as a sole feedstock, the biogas production was inhibited by ammonia, whereas the co-digestion of PM with 25% SBPR was slightly affected by volatile fatty acids, which concentrations exceeded 4000 g/m³.     

Nutritional assessment of different greenhouse by-products for biogas production

Intensive vegetable production in greenhouse systems has been largely developed in southeast Spain in the past 40 years, thus the elimination of tonnage amounts of by-products inherent to this economic activity constitutes a major problem to solve. To discern the suitability for biogas production of the different by-products generated, a study about their proximate composition was carried out in fresh and ensiled material. The output of the analyses indicates a chemical composition similar to medium-high quality forages, since all exhibited high protein and digestible fiber content, and a low amount of lignin, showing the applied model an optimal potential for methane production.