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.     

关于国产大型热电两用机组某些问题的探讨

为了大力推进节能减排工作,近来我国启动了"十大重点节能工程",其中区域热电联产工程进展迅速。国家大力倡导优选大型采暖、发电两用机组,三北地区有条件集中供热的大中城镇都在筹建或建设中,某些不采暖地区也将纯发电大型机组改造成热电联产机组。本文探讨对优先选用300MW及以上大型热电联产机组是有条件的,不宜过分强调;在大型火电机组再热器前(后)打孔抽汽改造,供热参数不匹配,不宜大力推广,这些机组改造仅做过渡措施,应积极开发新型大型高效热电联产机组。     

Transposition of the EU cogeneration directive: A vision for Portugal

The potential for new, small-scale and micro-cogeneration installations in Portugal is very considerable due to the number of potential host buildings. In this work, we discuss the legal framework of the Portuguese energy market, and some modifications to accommodate the Directive, 2004/8/EC are stressed. A practical case of cogeneration is also presented, showing the application of the Annex III (b) and (c) of the Cogeneration Directive. The practical case presented shows that micro CHP can be considered highly efficient, with parameters calculated with the Directive rules. Two main improvements in Portugal's energy policy are important: improvement on the permission to access grid system and improvement on support mechanisms indexing it to PES. The Cogeneration Directive transposition is an excellent opportunity to induce a less restrictive framework for the installation of new cogeneration systems, reducing the technological barriers, namely allowing medium-voltage connection with the grid, and improving the revenues provided from these small cogeneration systems. These modifications can improve significantly the number of potential hosts for small-scale cogeneration systems.     

Evaluating livestock manures for biogas production: a GIS based method

The Animals (data)Base for Energy Potential Estimation (ABEPE), presented in this paper, is a GIS based biomass resource assessment application using a relational database management system to estimate biogas production from livestock manures. Energy and biogas potential of livestock residues of all major groups of stock-raising animals (cattle, pigs, sheep/goats, poultry, etc.) were evaluated. The calculations were based on geographical and time-depending data of Greece. Typical input data included population of animal groupings, by-product factors, availability factors, energy factors, etc. for the period 1970–1998. Output included manure production, available energy and biogas quantities. Furthermore, ‘ABEPE’ can perform time-depending prediction of all types of output, based on past and present trends. As a case example, the prediction results for the year 2010 are herein presented. The possibility of biogas upgrading in order to be distributed through the national natural gas network is also discussed.     

Solar assisted biogas plant IIA: Experimental validation of the mathematical models for floating drum type biogas plant

The theoretical predictions presented in an earlier paper for the performance of solar assisted biogas plants are compared with experimental measurements made on four separate systems. There is good agreement between the results and the theoretical predictions.     

净气沼气技术在高速公路服务区生活污水处理中的应用

文中主要介绍了净化沼气池工艺,并就其工艺原理、技术特点、运行管理、投资效益上进行具体的分析。通过工艺设计实例详细地介绍了工程运行情况,并得出结论：净化沼气技术在高速公路服务区生活污水处理中的应用在节约能源和改善服务区卫生条件等方面都取得了良好的效果。     

Power-to-SNG technologies by hydrogenation of CO2 and biomass resources: A comparative chemical engineering process analysis

Power to Synthetic-Natural-Gas (SNG) technology consists of two main steps: water electrolysis and methanation; the primary energy input is usually surplus power from renewable energy sources, while the electrolytic hydrogen and carbon oxides from different CO_x sources are converted into methane that can be fed in the natural gas grid. We focus on methanation technology, where the main criteria are the complexity of process setup and reactor sizes to achieve production and SNG quality for gas-grid injection. The processes are simulated using a plug-flow model for the reactors and a pseudo-homogeneous kinetic law describing the reaction of CO₂ (that is rate limiting). The results show that feeding biogas or syngas (instead of CO₂) for methanation has remarkable effects regarding the operation and design of the processes; it is concluded that Power-to-SNG technologies that use methane rich streams are favorable in terms of biogas upgrading, H₂ requirements, reactor volumes and process simplicity, as far as these resources are available: e.g., using a typical composition (60% CH₄) the required inputs are 0.96 kmol of biogas, 1.54 kmol of H₂ and 0.26 m³ of reactors (two adiabatic beds with recirculation, R/F = 0.695) per kmol/min of pipeline quality dry gas product (95% CH₄), which means 60% hydrogen saving, less than 26% reaction volumes and near 62% reduction of process throughput, when compared to the methanation process that uses pure CO₂; conversion of syngas can be also favorable, but it requires high recirculation due to the large proportions of CO_x; e.g. for syngas (47.3%H₂-25.9%CO-17.2%CO₂-9.6%CH₄), the required values mean a 53% hydrogen saving and less than 25% reaction volumes, but only 11% reduction of process throughput.     

Biogas reforming for hydrogen production over nickel and cobalt bimetallic catalysts

Ni/Co bimetallic catalysts supported by commercial γ-Al₂O₃ modified with La₂O₃ for biogas reforming were prepared by conventional incipient wetness impregnation. The catalysts were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET surface area and porosity analysis (BET), H₂ temperature-programmed reduction (H₂-TPR), transmission electron microscopy (TEM) and thermogravimetry coupled to differential scanning calorimetry (TG–DSC). XRD and XPS analysis revealed that a Ni/Co alloy was formed in the bimetallic catalysts. The Ni/Co ratio could be adjusted to improve pore textural properties, which enhanced the metal particle dispersion and resulted in smaller metal particle size, and thus increased the catalytic activity and resistance to carbon deposition. The activity and stability of the catalysts for biogas reforming was tested at 800 °C, ambient pressure, GHSV of 6000 ml g_cat⁻¹ h⁻¹ and a CH₄/CO₂ molar ratio of 1 without dilute gas. Experimental results showed that the catalytic activity could be closely related to the Ni/Co ratio. The bimetallic catalyst 7Ni3Co/LaAl exhibited better catalytic and anti-coking performance due to smaller metal particles, higher metal dispersion, uniform pore distribution, surface enrichment of Co, as well as the synergetic effect between Ni and Co. During a 290 h stability test over the catalyst 7Ni3Co/LaAl, the average conversion of CH₄ and CO₂, selectivity to H₂ and CO, and ratio of H₂/CO were 93.7%, 94.0%, 94.9%, 97.8%, and 0.97, respectively. The average coking rate was 0.0946 mg g_cat⁻¹ h⁻¹.     

Use of waste for heat,electricity and transport—Challenges when performing energy system analysis

This paper presents a comparative energy system analysis of different technologies utilising organic waste for heat and power production as well as fuel for transport. Technologies included in the analysis are second-generation biofuel production, gasification, fermentation (biogas production) and improved incineration. It is argued that energy technologies should be assessed together with the energy systems of which they form part and influence. The energy system analysis is performed by use of the EnergyPLAN model, which simulates the Danish energy system hour by hour. The analysis shows that most fossil fuel is saved by gasifying the organic waste and using the syngas for combined heat and power production. On the other hand, least greenhouse gases are emitted if biogas is produced from organic waste and used for combined heat and power production; assuming that the use of organic waste for biogas production facilitates the use of manure for biogas production. The technology which provides the cheapest CO₂ reduction is gasification of waste with the subsequent conversion of gas into transport fuel.