Energy analysis of algae-to-biofuel production chains integrated with a combined heat and power plant

ABSTRACT

This study examines the energy and mass balances of algae cultivation and different post-processing pathways. Flue gases and excess heat from a combined heat and power (CHP) plant are used in algae cultivation, with nutrients from municipal wastewater. In the studied pathways, algae are cultivated in open ponds and photobioreactors with or without artificial lighting. Algal mass is used for methane, biodiesel or ethanol production, or it is combusted in a boiler. Results show that in most process pathways energy output exceeds the energy consumption in processing, and the energy returns are approximately twice as large as the electricity input. A large fraction of input energy is low-temperature heat, while the products have a higher value. Energy outputs from different pathways are similar, but heat and electricity consumption in processing vary significantly. Supercritical water gasification pathway is identified as a possible future option, whereas lipid extraction pathways are suggested to be the most likely candidates for industrial scale operations.     

System dynamics modelling of hybrid renewable energy systems and combined heating and power generator

The role of energy in the present world is critical in terms of both economical development and environmental impact. Renewable energy sources are considered essential in addressing these challenges. As a result, a growing number of organisations have been adopting hybrid renewable energy system (HRES) to reduce their environmental impact and sometimes take advantage of various incentives. When a HRES is being planned, the ability to model a HRES can provide an organisation with numerous benefits including the capability of optimising sub-systems, predicting performances and carrying out sensitivity analysis. In this paper, we present a comprehensive system dynamics model of HRES and combined heating and power (CHP) generator. Data from a manufacturing company using HRES and CHP generator are used to validate the model and discuss important findings. The results illustrate that the components of a HRES can have conflicting effects on cost and environmental benefits; thus, there is a need for an organisation to make trade-off decisions. The model can be a platform to further simulate and study the composition and operating strategies of organisations that are venturing to adopt new or additional HRESs.     

Preliminary analysis of single flash combined with binary system using thermodynamic assessment: a case study of Dieng geothermal power plant

This paper addressed the performance of single flash combined with a binary system that was proposed in the Dieng geothermal power plant by applying thermodynamic assessment methods. A set of mathematical equations from the plant was developed and solved iteratively using engineering equation solver. The results showed that the available exergy of the produced fluid from production wells is 66,204 kW. The performance of an existing single-flash power plant indicated 24,300 kW of net power output. The proposed design of single flash combined with a binary system improves the power output by 17.16% to 27,786 kW. The second law efficiency increases from 36.7% to 41.97% while the first law efficiency increases from 11.62% to 13.61%.     

Comparison of the energetic performance of a binary cycle and a flash evaporation binary cycle,using low-enthalpy geothermal energy

In this article, the comparison of the energetic performance of a binary cycle and a modified binary cycle with flash evaporation is presented, both using a low-enthalpy geothermal resource. The comparative analysis is based on two main discourses: the first one evaluates a conventional binary cycle (CBC) with isopentane as working fluid in order to validate and compare the generated data with those reported in similar studies; the second one uses the same input parameters for both cycles, obtaining the cases in which the modified binary cycle is the most viable choice to use. In addition to the above, several aspects are considered when selecting the most suitable working fluid, and the use of water as working fluid is introduced. When the temperature of the geothermal resource is below 140 °C, and the ambient temperature is 25 °C, the flash evaporation binary cycle, using water as working fluid, shows an improved performance compared to a CBC, with a theoretical output over 1000 kWe. This may encourage new areas of opportunity for power generation, not only with low- and medium-enthalpy geothermal energy, but also with other renewable energy sources such as solar.     

Forty years of atmospheric radiocarbon monitoring around Bohunice nuclear power plant, Slovakia

Radiocarbon variations in the atmospheric CO(2) with attenuating amplitudes and decreasing mean values with typical maxima in summer and minima in winter have been observed since 1967 in two localities of Slovakia, in Bratislava and Zlkovce, situated about 60 km NE from Bratislava, only 5 km from the Bohunice Nuclear Power Plant (NPP). The (14)C record in Bratislava has been influenced mainly by fossil CO(2) emissions, in contrast to the Zlkovce record which has been more variable, as it has clearly been affected by operation of the Bohunice NPP. However, during specific meteorological conditions with NE transport of air masses to Bratislava, the effect of the Bohunice NPP has been visible in Bratislava as well. Maximum (14)C concentrations (up to 120% above a natural background) were observed around A1 NPP which used CO(2) with admixture of air as a cooling agent. The (14)C concentrations around four pressurized light water reactors were up to 30% above the background. The Delta(14)C values in the heavily polluted atmosphere of Bratislava were up to 10% and at Zlkovce up to 5% lower than the European clean air represented by the Jungfraujoch Delta(14)C data. Later the Delta(14)C values were similar at both sites, and from 2003 they were close to the European clean air levels. The observed Delta(14)C behaviour in the atmosphere provides a unique evidence of decreased fossil fuel CO(2) emissions in the region, as well as the long-term effect of the Bohunice NPP on the Bratislava and Zlkovce stations. The estimated annual radiation doses to the local public due to digestion of radiocarbon contaminated food have been estimated to be around 3 microSv.     

Experimental investigation and modelling of tritium washout by precipitation in the area of the nuclear power plant of Paks, Hungary

Tritium occurs in nature in trace amounts, but its concentration is changing due to natural and artificial sources. Studies focusing on natural tritium have to take into account the effect of artificial sources. Also, the impact of tritium is an important issue in environmental protection, e.g. in connection with the emissions from nuclear power plants. The present work focuses on the rain washout of tritium emitted from the Paks nuclear power plant in Hungary. Rainwater collectors were placed around the plant and after a period of precipitation, rainwater was collected and analysed for tritium content. Samples were analysed using low-level liquid scintillation counting, with some also subject to the more accurate ³He ingrowth method. The results clearly show the trace of the tritium plume emitted from the plant; however, values are only about one order of magnitude higher than environmental background levels. A washout model was devised to estimate the distribution of tritium around the plant. The model gives slightly higher concentrations than those measured in the field, but in general the agreement is satisfactory. The modelled values demonstrate that the effect of the plant on rainwater tritium levels is negligible over a distance of some kilometres.     

基于LCA的废旧资源循环利用节能减排效果评估模式与方法研究——以吉林省某钢铁企业为例

促进废旧资源循环利用是加快推进我国生态文明建设,完成节能减排目标的必然选择。本文基于生命周期评价模式,从微观企业层面入手,构建产品全生命周期基准流程,引入能量输入与环境输出参数,建立废旧资源循环利用节能减排效果量化核算模型,评估再生产品的节能减排经济成效,并以吉林省某钢铁企业为例,评估"废钢-电炉"短流程和"铁矿石-高炉-转炉"长流程的能源、环境、成本差异,辨识影响废钢再循环节能减排效果的主要因素和重要环节。结果显示,再生钢铁全生命周期与原生钢铁全生命周期相比,节能588.48kgce/t,节能率为84%;主要污染物中SO2减排率最高,达92%;CO2总减排1 180.92 kg/t,减排率为67%;总成本却高出198元/t。其中,炼铁工序的节能量和减碳量最大,烧结工序SO2、NOx和烟(粉)尘减排量最大,焦化工序COD和氨氮减排量最大,回收、加工处理、炼钢环节节能量和减碳量以及SO2、NOx和烟(粉)尘减排量均为负。成本方面,再生钢铁生产成本高于原生钢铁308元/t,虽然再生钢铁由于污染减排可节省56元/t的排污费并获取54元/t的碳交易收益,但都不足以扭转电炉炼钢费用较高的现状。因此,国家应在电炉炼钢方面给予钢企及相关企业适当的财税扶持政策,在电价方面给予钢企一定的优惠或补贴,并完善废钢回收加工体系等,以促进废钢循环利用。基于LCA的废旧资源循环利用节能减排效果评估可以实现对产品生命周期全过程的资源、环境、成本的优化管理。     

Dynamic simulation of a decentralized polygeneration plant providing SNG,steam and power

The behaviour of a decentralized polygeneration plant providing synthetic natural gas (SNG), steam and electrical power is simulated in three scenarios in this study. The plant size is based on an assumed capacity of decentralized polygeneration plants processing 1070 m³ h^?1 (STP) of syngas. 396 m³ h^?1 (STP) of raw SNG, 0.4 t h^?1 of steam at 5 bar and 670 kW of electrical power can be generated by the plant at the reference scenario. Methanation reactor and steam generator are modelled in detail. Further results indicate that such a polygeneration plant can provide positive and negative operation reserves for the electricity network to the extent of 100% of the reference power output, while the amount of generated steam varies by less than 40%. At the same time, the generated SNG quality keeps constant. Lower variations in the amount of generated steam are applicable when reducing the operation reserve capacity.     

An experimental and a numerical study of horizontal earth-air heat exchanger in a hot climate

Earth-air heat exchangers (EAHE) are devices used in the geothermal technique in order to reduce energy consumption in buildings. In this study, a simulation was conducted through the computational fluid dynamics platform FLUENT 6.3 for the prediction of thermal performance of the EAHE that describes the variation of the air temperature inside the tube. For this, it was necessary to design the heat exchanger while respecting the design and the actual dimensions of the experimental set-up, and stating that the temperature of the wall of the horizontal tube of the exchanger is equal to that of ground at 3 m depth. It should be noted that in assessing the temperature along the two sections vertical (input and output) of the exchanger, opting for a function (UDF) the user define function. Finally, noting a good agreement between both experimental and numerical study, and showing that a significant reduction in temperature at the outlet of the exchanger to a difference of 20 °C, confirming the effectiveness of the heat exchanger.     

Comparative experimental analysis of the effect of convective heat losses on the performance of parabolic dish water heater

This paper reveals comparative experimental analysis of the effect of variation of natural and forced convection heat losses on the performance of prototype parabolic dish water heater with coated and non-coated receivers. With the above-described system, hot water needs in domestic applications can be fulfilled instantly. A parabolic dish collector was used for instant water heating. Design of solar parabolic dish collector consists of truncated cone-shaped helical coiled receiver made up of copper at focal point. Instantaneous efficiency of 63% and 48% has been achieved with coated and non-coated receivers. This prototype has been evaluated for its performance with water flow rate of 0.0076 kg/s during the months of April and May 2010 at Shivaji University, Kolhapur, Maharashtra, India (latitude: 16.42° North, longitude: 74.13° West).     

Comparing environmental product footprint for electronic and electric equipment: a multi-criteria approach

Electronic and electric devices are now applied in most human activities: their diffusion is increasing worldwide; furthermore, most of them are characterized by a high replacement rate due to technological obsolescence. Consequently, environmental problems due to their diffusion are increasing; several aspects are involved from the energy consumption derived from their manufacturing processes and their use phases to their end-of-life (EOL) management. Such legislative (e.g. the European Energy Efficiency directive for household appliances) or voluntary interventions (e.g. based on the ISO standards) have been introduced for such devices: the aim is to incorporate environmental considerations in product design and manufacturing in order to benefit the environment. Some attempts are focusing on defining standardized models for the overall lifecycle including waste management. The aim of this paper is to introduce a reference model for comparing environmental product footprint of electrical and electronic equipment (EEE). All life cycles of EEE will be evaluated: a specific focus is on the EOL management process as their waste management represents a complex problem for developed and developing countries. A multi-criteria decision-making model will be developed based on the well-known analytical hierarchy process (AHP) method: differently from traditional AHP applications, an absolute model has been proposed in order to compare EEE effectively from an environmental point of view. A case study validation regarding large household appliances is proposed.     

Performance analysis of a new sustainable evaporative cooling pad made from coconut coir

This paper reports a performance analysis for a new sustainable engineering application to beneficially reuse an abundant agricultural waste, coconut coir (Cocos nucifera), in evaporative cooling pads. Two small coconut coir pads of different configurations were fabricated and tested using a laboratory‐scale experimental arrangement. The air supply velocity was controlled and varied between 1.88 and 2.79 m s^?1. Heat and mass transfer coefficients, evaporative cooling efficiency and pressure drop across the two types of coconut coir pad were analysed and compared with those of a commercial rigid media paper pad. Results show that the cooling efficiency of the manufactured coconut coir evaporative cooling pad was fairly good (about 50%) and close to that of the commercial paper pad (about 47%). The average pressure drop across the two coconut coir pads was 1.5 and 5.1 Pa respectively. Correlations for heat and mass transfer coefficients expressed using Nusselt and Sherwood numbers are also reported. In addition, the cooling potential of the coconut coir pads was analysed using the average climatic conditions of the central region in Thailand throughout the year. The analysis showed that the air temperature leaving the coconut coir pad varied from 23 to 28°C. Commercial development appears feasible given the coconut coir pad's good performance, lower cost and its availability throughout the country.     

Evaluation of sustainability using an integrated approach at process and product level: a case study

The present world is facing problems like rapid depletion of natural resources and undesired environmental changes on a global scale. Manufacturing organisations are realising the importance of mitigating the present crisis and are adopting sustainable manufacturing principles. Since it is important to achieve sustainable manufacturing, sustainability assessment models were developed. Sustainability assessment models have their own drawbacks and may not provide clear scope for complete sustainable development. A system approach has been developed to overcome this shortcoming by integrating various sustainability assessment models that are already in practice. This article reports the advantages of collecting the advantages of individual sustainability assessment models and how the implementation of the integrated approach has helped to identify the current sustainability level and the scope for future developments in an automotive industry.     

Energy and temperature performance analysis of geothermal (ground source) heat pumps integrated with permeable pavement systems for urban run-off reuse

Geothermal (ground source) heat pumps (GHP) and permeable pavement systems (PPS) have demonstrated their effectiveness in both industry and academic research during recent decades. To meet the rising demand for sustainable, recyclable and energy efficient techniques, research has focused on the combination of techniques to enhance existing or develop new applications.

This paper reports on an experimental programme that combined GHP with PPS for nutrient removal and system energy balancing. Experimental data collected over a 3-year period have provided evidence of highly efficient removal rates of up to 99% for ammonia–nitrate and biochemical oxygen demand; and 96% removal rates were obtained for orthophosphate–phosphorus. This paper also contains energy efficiency ratio (EER) and coefficient of performance (COP) calculations. Cyclic heat removal and heat rejection allowed for stable temperature and pump COP and EER sustainability. The results prove that PPS systems are appropriate for GHP installation, delivering high and stable pollutant removal with EER efficiencies between 1.5 and 5.5.

The combination of GHP with PPS has the potential to provide a new sustainable and eco-friendly practice.     

基于央地分权视角的环境规制策略演化博弈分析

当前,我国环境的根本问题是由粗放式的经济发展模式所引起的,而这一发展模式的根源在于"中国式央地分权"下的政府行为。这种具有中国特色的分权模式的独特之处在于中央政府对地方经济放权的同时,仍然保持政治上的集权控制,上级政府根据绩效考核提拔地方官员,即"经济分权、政治集权"特性。中国式分权下,我国的环境治理体制依据行政区域的划分来设置管理权限,按照政府层级的构成进行垂直式领导,即中央政府统一制定环境政策,地方政府负责各辖区内环境政策的执行。在全国范围内,央地两级政府的关系表现为动态的重复博弈。针对我国现行环境规制执行策略,借助演化经济学研究工具,基于央地分权的视角,将地方政府与中央政府两大主体同时纳入分析框架。根据复制动态方程探讨参与主体的行为演化特征和行为演化稳定策略,在模型求解的基础上,利用MATLAB仿真工具,分析不同情形下参与主体演化稳定策略的走向及其收敛趋势。研究发现,央地两级政府在环境规制策略执行过程中的动态演化,很大程度上取决于地方政府环境规制执行力度、成本、收益和损失以及中央政府监管力度、成本和处罚力度等因素的大小。因此,针对地方政府环境策略激励设计,应重点改革政绩考核机制,引入市场机制,并通过环保补贴、财政转移支付等手段降低地方政府环境规制执行成本;中央政府应通过调节政绩考核体系中的经济发展指标和环境指标的权重系数来加强对地方政府环境规制执行情况的监管力度,建立第三方监管机制以降低中央政府监管成本,制定合理的奖惩机制以提高监管效率;以期推动我国环境规制策略的高效执行,促进环境绩效向经济绩效的良性转换,实现双重帕累托改进。     

基于能源类型的中国反弹效应测算及其分解

能源问题是实现可持续发展的重大战略问题。能效改进所引起的能耗反弹问题已成为能源经济学领域的一个重要议题。针对已有研究基于复合能源维度探讨反弹效应的不足,本文通过构建一个引入反弹效应测算模块的中国静态CGE模型,研究不同类型能源效率改进的节能效果和反弹差异,并将其在生产侧和消费侧进行分解。在分别提高所有生产部门一次能源使用效率和二次能源使用效率两种情景下,我们发现提高二次能源使用效率对经济的促进作用更大,带来的能源节约也更多。就反弹效应而言,两种情景的反弹效应在9.6%-27.9%范围间,但提高一次能源使用效率带来的反弹效应要普遍大于提高二次能源使用效率带来的反弹。这意味着,能效改进的能源类型选择将关系到政策的实施效果。对反弹效应在生产侧和消费侧的分解则显示,生产侧的能效改进会刺激消费侧能耗增加,而且来自消费侧的能耗增加在二次能源品种的反弹效应中扮演了重要角色,尤其是成品油和燃气。综上,我们认为不论从经济表现还是反弹效应来看,提高二次能源使用效率都是比较理想的能源类型选择,这是以往研究未曾注意到的。同时,由于反弹效应的存在确实降低了能效政策的有效性,因此政府在制定能效政策时可通过对冲能效改进带来的能源服务价格下降来减缓能耗反弹。引导和规范居民的用能观念和用能行为也是减缓反弹效应的一个重要途径,这一点对能源需求远未饱和的发展中国家尤其重要。     

Energy and exergy analysis of a PCM-based solar powered winter air conditioning using desiccant wheel during nocturnal

In this paper, heating and humidification of air for space have been carried out by using a phase change material (PCM)-based solar-powered desiccant wheel air conditioning (SPDWAC) in winter. The analysis of the setup has been done at different air flow rates. At low and high air flow rates, system has mean thermal coefficient of performance of 0.121 and 0.172, respectively, and mean exergy efficiency of 0.0787 and 0.0846, respectively. The mean thermal coefficient of performance of the system at high air flow rate (127.23 kg h-1) is 1.42 times the low air flow rate (63.62 kg h-1) and average exergy efficiency of the system at high air flow rate is 1.07 times the low air flow rate. It is observed that with an increase in air flow rate, efficiency of the evacuated tube solar air collector (ETSAC) increases. The average efficiency of the ETSAC at high air flow rate is 15.60%. The maximum average energy efficiency (17.80%) and exergy efficiency (17.08%) of the PCM storage system have been obtained at high air flow rate. The overall performance of the system showed that the use of PCM storage is feasible to run the system in winter during the hours of darkness.     

Application of TISM and MICMAC for analysis of influential factors of sustainable development of tablet devices: a case study

Abstract

With the advancements in technology and increase in demand for eco-efficient products, manufacturers are focusing on sustainable development of products. Enticing a huge demand over the recent years, sustainable development of Information and Communication Technology (ICT) products are a subject of interest for most practitioners and academicians. A number of factors are found to influence the sustainable development of ICT products. It is necessary to identify the most important factors and determine the dependencies of factors among themselves. In this regard, a case study has been conducted in the context of sustainable development of tablet devices. The most influential factors have been identified from literature and with experts input. The factor dependencies are established using Total Interpretive Structural Modelling (TISM) methodology. MICMAC analysis is used to classify the factors based on their ability to influence other factors. The output of TISM forms the input for MICMAC analysis. From the study, it was found that the factors, ‘Customer pressure’, ‘Government regulations’, ‘Competitiveness’, ‘Organization initiative’ and ‘Technological advancements’ are the most driving factors. Factors ‘Environmental impact’, ‘Energy efficiency’ and ‘Opportunities to upgrade’ were found to be dependent.     

水土匹配、空间效应及区域农业经济增长——基于中国2003-2013的经验分析

水资源和土地资源是非常重要的自然资源,是农业经济发展不可或缺的物质要素。水资源与土地资源的合理匹配能够促进区域的资源优势转化为经济增长,从而促进区域农业经济发展。我国是一个人口众多的农业大国,同时也存在水资源与土地资源短缺的问题。本文结合我国农业水土资源自然禀赋与实际利用情况,首先利用中国2003-2013年的分省数据,选取单位耕地面积的广义农业水资源量测度方法和当量系数描述了我国农业水土资源匹配的现实,发现我国农业水资源与土地资源在空间上匹配程度不高,农业生产受到水土资源约束较强,农业水土资源的形成区域与消耗区域在空间上不相匹配;然后,在邻接权重矩阵下采用Moran’s I指数验证我国区域农业经济增长的空间关联性,结果显示我国各省农业经济增长存在显著的空间关系,呈现出高度的集聚性和非均质性。为避免估计结果有偏,本文在此基础上采用空间计量建模及估计方法,加入农业生产人、财、物等控制变量,测度水土匹配度对区域农业经济增长的空间溢出效应。结果显示,水土匹配度对区域农业经济发展的区域内和区域间的溢出效应都显著为正,总体上水土匹配度对区域农业经济发展具有正向的溢出效应,即水土匹配度对本地区农业经济增长具有促进作用;同时,由于相邻区域的水土资源自然禀赋条件类似,而且农业生产中存在"示范效应"和"模仿效应",水土匹配度对相邻地区农业经济增长也具有一定的促进作用。因此,采取相关措施优化农业水土资源匹配关系,对促进我国区域农业经济增长,保障我国粮食安全非常重要。