Biodiesel resources and production technologies – A review

The environmental concern and availability of fuels are greatly affecting the trends of fuels for transportation vehicles. Biodiesel is one of the options as alternative transport fuel. This can be produced from straight vegetable oils (SVOs), oils extracted from various plant species and animal fats. Amongst many resources, availability and cost economy are the major factors affecting the large scale production of the biodiesels. The transesterification is one of the production processes for biodiesel, but incomplete esterification of all fatty acids in the starting material, lengthy purification methods such as water washing, relatively long reaction times, contamination and separation difficulties associated with co-production of glycerol and saponification of the starting material under certain reaction conditions are still being major challenges in the biodiesel production. Technological advancement and enhanced production methods are the demand of present time for large scale and sustainable production of biodiesel. In the present paper, comprehensive review on its production process, feed stock and its applications have been made. From many case studies it was concluded that engine performance with B20 biodiesel blends, and mineral diesel were found comparable.     

Coal-fired oxy-fuel power unit – Process and system analysis

As oxy-fuel power generation is currently on the pre-demonstration stage of development many studies dealing with optimization and simulation aspects are still in progress. This paper is focused on the development of a simulation model of the integrated oxy-fuel system and cumulative energy analysis of an oxy-unit operation in separated national economy. The analyzed oxy-fuel system consists of a steam boiler, steam cycle, air separation unit, as well as a CO₂ purification and compression island. The built model is based on physical relations. It has been developed as a set of modules modelling isolated devices (e.g. combustion chamber or flue gas dehumidifier). Interconnections between these devices can be easily changed, which permits to analyse different oxy-fuel structures and operating parameters. The simulation model has been partially verified on the basis of literature data. Results of oxy fuel energy analysis have been presented for one selected structure and compared with an air combustion power unit, assuming the same steam cycle parameters. For both cases indices of cumulative primary energy consumption have been calculated. The obtained results show that the increase of oxy-fuel primary energy consumption (compared with air-based combustion) can be significantly reduced if by-produced nitrogen will be used for external applications.     

Li-N-H system – Reversible accumulator and store of hydrogen

The statistical theory of phase transformations in the course of chemical reactions on hydrogen absorption–desorption in the lithium nitride with the formation of lithium amide and hydride has been developed. The calculation of free energies of all constituent phases of chemical reactions has been performed on the basis of molecular-kinetic notions, their dependences on temperature, pressure, hydrogen concentration and energetic parameters have been ascertained. The hydrogen solubility in phases has been estimated, it has been ascertained the possibility of manifestation of peculiarities of its temperature dependence. The constitution diagram for the system being investigated has been constructed. The actual conditions of manifestation of hysteresis effect has been justified. The calculation results have been compared with experimental literature data for the examined system.     

Hydrogen production from methane and solar energy – Process evaluations and comparison studies

Three conventional and novel hydrogen and liquid fuel production schemes, i.e. steam methane reforming (SMR), solar SMR, and hybrid solar-redox processes are investigated in the current study. H₂ (and liquid fuel) productivity, energy conversion efficiency, and associated CO₂ emissions are evaluated based on a consistent set of process conditions and assumptions. The conventional SMR is estimated to be 68.7% efficient (HHV) with 90% CO₂ capture. Integration of solar energy with methane in solar SMR and hybrid solar-redox processes is estimated to result in up to 85% reduction in life-cycle CO₂ emission for hydrogen production as well as 99–122% methane to fuel conversion efficiency. Compared to the reforming-based schemes, the hybrid solar-redox process offers flexibility and 6.5–8% higher equivalent efficiency for liquid fuel and hydrogen co-production. While a number of operational parameters such as solar absorption efficiency, steam to methane ratio, operating pressure, and steam conversion can affect the process performances, solar energy integrated methane conversion processes have the potential to be efficient and environmentally friendly for hydrogen (and liquid fuel) production.     

Hydrogen from biomass – Present scenario and future prospects

Hydrogen is considered in many countries to be an important alternative energy vector and a bridge to a sustainable energy future. Hydrogen is not an energy source. It is not primary energy existing freely in nature. Hydrogen is a secondary form of energy that has to be manufactured like electricity. It is an energy carrier. Hydrogen can be produced from a wide variety of primary energy sources and different production technologies. About half of all the hydrogen as currently produced is obtained from thermo catalytic and gasification processes using natural gas as a starting material, heavy oils and naphtha make up the next largest source, followed by coal. Currently, much research has been focused on sustainable and environmental friendly energy from biomass to replace conventional fossil fuels. Biomass can be considered as the best option and has the largest potential, which meets energy requirements and could insure fuel supply in the future. Biomass and biomass-derived fuels can be used to produce hydrogen sustainably. Biomass gasification offers the earliest and most economical route for the production of renewable hydrogen.     

Anaerobic digestion of maize and cellulose under thermophilic and mesophilic conditions – A comparative study

The aim of this study was to advance in understanding of digestion process of energy crops. Cellulose and maize silage were fermented in batch mode at mesophilic (38 °C) and thermophilic (55 °C) conditions and corresponding organic loads of 5.5 ± 0.2 kgVS/m³, 11.2 ± 0.3 kgVS/m³ and 16.7 ± 0.4 kgVS/m³.For both substrates more stable and faster digestion took place at 38 °C. Due to complex structure maize degradation was characterized by varying digestion rate and longer total digestion time resulting form breakdown of hard-degradable fractions. The digestion retard at increased OLRs of cellulose and lower degradation level obtained for all cellulose series confirm a higher overloading potential for systems dealing with single-component-substrates but also the enhanced sensitivity of such systems to any inconvenient digestion conditions.Based on observed patterns of volatile fatty acids and oxidation-reduction potential, different fermentation mechanisms can be concluded for cellulose and maize, but also for different temperature modes. Conversion of maize at highly reductive conditions with increased concentrations of butyric acid was accompanied by much higher activity of hydrogenotrophic methanogens than for cellulose digestion.Two factors showed a strong potential to influence test results: an insufficient VS content of inoculum, which caused reduced biogas yields, and a high natural biodiversity of maize silage, resulting in higher biogas yields than calculated based on the maize composition.     

Optimization of hybrid – ground coupled and air source – heat pump systems in combination with thermal storage

Ground coupled heat pumps are attractive solutions for cooling and heating commercial buildings due to their high efficiency and their reduced environmental impact. Two possible ideas to improve the efficiency of these systems are decoupling energy generation from energy distribution and combining different HVAC systems. Based on these two ideas, we present several HVAC configurations which combine the following equipments: a ground coupled heat pump, an air to water heat pump and a thermal storage device. These HVAC configurations are linked to an office building in a cooling dominated area in order to evaluate in these conditions the total electrical consumption of each configuration to obtain which one satisfy the thermal demand more efficiently. The results of our simulations show that the electrical energy consumption obtained when the system employs a suitable configuration is of around the 60% compared with an HVAC system driven by an air to water heat pump and around the 82% compared with an HVAC system driven by a ground coupled heat pump.     

Combustion chemical kinetics of biodiesel and related compounds (methyl and ethyl esters): Experiments and modeling – Advances and future refinements

The motivation for and challenges in reducing the world's dependence on crude oil while simultaneously improving engine performance through better fuel efficiency and reduced exhaust emissions have led to the emergence of new fuels and combustion devices. Over the past ten years, considerable effort has gone into understanding combustion phenomena in relation to emerging fuel streams entering the market. The present article focuses specifically on one typical emerging transportation fuel dedicated to the diesel engine, biodiesel, with an emphasis on ethyl esters because of recently renewed interest in its use as a completely green biofuel. Based on a review of the research developments over the past ten years in advanced experimental and kinetic modeling related to the oxidation of biodiesel and related components, the main gaps in the field are highlighted to facilitate the convergence toward clean and efficient combustion in diesel engines. After briefly outlining the synergy between “feedstocks – conversion process – biodiesel combustion”, the combustion kinetics of methyl and ethyl biodiesels are reviewed with emphasis on two complementary aspects: mechanism generation based on a detailed chemical kinetic approach that leads to predictive combustion models and experimental combustion devices that generate the data required during the development and validation of the predictive models.     

Spark spread – A screening parameter for combined heating and power systems

Combined heating and power (CHP) systems may be considered for installation if they produce savings over conventional systems with separate heating and power. For a CHP system with a natural gas engine as the prime mover, the difference between the price of natural gas and the price of purchased electricity, called spark spread, is an indicator as to whether a CHP system might be considered or not. The objective of this paper is to develop a detailed model, based on the spark spread, that compares the electrical energy and heat energy produced by a CHP system against the same amounts of energy produced by a traditional, or separate heating and power (SHP) system that purchases electricity from the grid. An expression for the spark spread based on the cost of the fuel and some of the CHP system efficiencies is presented in this paper as well as an expression for the payback period for a given capital cost and spark spread. The developed expressions allow determining the required spark spread for a CHP system to produce a net operational savings over the SHP in terms of the performance of system components. Results indicate that the spark spread which might indicate favorable payback varies based on the efficiencies of the CHP system components and the desired payback period. In addition, a new expression for calculating the payback period for a CHP system based on the CHP system capital cost per unit of power output and fuel cost is proposed.     

Onboard motorcycle plasma-assisted catalysis system – Role of plasma and operating strategy

Hydrogen as a supplementary fuel can be blended with gasoline/diesel to improve engine performance and reduce pollutant emission. A compact plasma-assisted catalysis (PAC) reformer designed as an onboard device for motorcycle was used to convert methane into a hydrogen-rich gas which then mixed with gasoline to fuel motorcycle engine. Performance of the PAC reformer for motorcycle operated in the cold start, normal idle and normal cruising periods were evaluated experimentally. In the cold start period, the catalyst-bed temperature can rise from 25 °C to >500 °C in 14 s with the assistance of plasma. In the normal operation mode, the goal is to achieve either a high power output in the cruising mode or a low energy consumption in the idle mode. With the power consumption of 32.4 W for plasma, the reforming efficiency was increased by 2%–16% at given conditions. Engine test results showed that the PAC reformer not only reduced CO and HC concentrations by 42% and 21%, respectively, but also enhanced the engine performance, e.g., the brake power increased by 14% and the gasoline consumption by 33%. This study confirmed that in the idle mode, the plasma can be turned off without sacrificing the PAC's performance. Overall speaking, the plasma plays a great role in the cold start, be minor in the cruising mode, and trivial in the idle mode.     

Development of small-scale and micro-scale biomass-fuelled CHP systems – A literature review

A review is carried out on the development of small- and micro-scale biomass-fuelled combined heat and power (CHP) systems. Discussions have been concentrated on the current application of Organic Rankine Cycle (ORC) in small- and micro-scale biomass-fuelled CHP systems. Comparisons have been made between ORC and other technologies such as biomass gasification and micro-turbine based biomass-fuelled CHP systems. The advantages and disadvantages of each technology have been discussed. Recommendations have been made on the future development of small- and micro-scale biomass-fuelled CHP.     

Diesel oxidation catalyst and particulate filter modeling in active – Flow configurations

A one-dimensional transient model is developed in order to carry out theoretical investigations on the active flow diesel aftertreatment configurations. Simulations are carried out to predict the thermal response of particulate filters during active flow regeneration operations. Results indicate that the active flow-control strategies can achieve higher energy efficiency in aftertreatment operations. The energy efficiency analysis is carried out using various active-flow configurations. The theoretical model is validated using the experimental results. Further empirical investigation is carried out in order to study energy efficiency of supplemental fuel in the active-flow configurations. Different engine operating modes are also investigated with the active-flow configurations. It is observed that diesel aftertreatment with active flow can significantly improve in the supplemental energy efficiency.     

Fuel cell systems for long-endurance autonomous underwater vehicles – challenges and benefits

Autonomous underwater vehicles (AUVs) are programmable, robotic vehicles that can drift, drive, or glide through the ocean without real-time control by human operators. AUVs that also can follow a planned trajectory with a chosen depth profile are used for geophysical surveys, subsea pipeline inspection, marine archaeology, and more. Most AUVs are followed by a mother ship that adds significantly to the cost of an AUV mission. One pathway to reduce this need is to develop long-endurance AUVs by improving navigation, autonomy and energy storage. Long-endurance AUVs can open up for more challenging mission types than what is possible today. Fuel cell systems are a key technology for increasing the endurance of AUVs beyond the capability of batteries. However, several challenges exist for underwater operation of fuel cell systems. These are related to storage or generation of hydrogen and oxygen, buoyancy and trim, and the demanding environment of the ambient seawater. Protecting the fuel cell inside a sealed container brings along more challenges related to condensation, cooling and accumulation of inert gases or reactants. This paper elaborates on these technical challenges and describes the solutions that the Norwegian Defence Research Establishment (FFI) has chosen in its development of a fuel cell system for long-endurance AUVs. The reported solutions enabled a 24 h demonstration of FFI's fuel cell system under water. The remaining work towards a prototype sea trial is outlined.     

Fuel cell micro-CHP techno-economics: Part 1 – model concept and formulation

This article presents the concept and mathematical treatment for a techno-economic modelling framework designed to enable exploration of fuel cell micro combined heat and power (micro-CHP) system design and control. The aim is to provide a tool that can help to focus research and development attention on the system characteristics critical for commercial success of these technologies, present cost targets for developers, and to ensure policy makers provide appropriate instruments to support commercialisation. The model is distinctive in that it applies mixed integer unit commitment formulation to link design and control decisions for micro-CHP, and explicitly characterises stack degradation in a techno-economic framework. It is structured to provide depiction of the fuel cell stack and balance-of-plant, supplementary thermal-only system (e.g. tail gas burner), thermal energy storage, and electrical power storage. Technically, the fuel cell stack is characterised by steady-state thermal and electrical efficiencies for full and part-load operation, its nameplate capacity, minimum operating set-point, and stack degradation via performance loss rate proportional to power density and thermal cycling rate. The dynamics of operation are emulated via ramp limits, minimum up-time and minimum down-time constraints, and start-up and shutdown costs and energy consumptions. The primary performance evaluation metric adopted is the maximum additional capital cost a rational investor would pay for the fuel cell micro-CHP system over and above what they would pay for a competing conventional heating system. The companion article (Part 2) applies the developed model to consider the impact of stack degradation on economic and environmental performance.     

Redirection of sunlight by microstructured components – Simulation,fabrication and experimental results

This paper presents a non-tracking microstructured light redirecting device, which can be integrated into architectural glass. When fixed in the upper area of a window above eye level it redirects the light from solar altitudes between 15° and 65° and illuminates a room without causing glare.Ray-tracing calculations are employed as a tool for identifying suitable configurations and geometries. The results of the simulations show the advantage of combinations of lens-like with prism-like geometries in comparison to conventional microprism arrays regarding the overall light redirection efficiency as well as the producibility. The redirecting device is more lightweight, gives better integration options and is producible in a more economic manufacturing process as systems with similar performance. Measurements of cast silicone prototypes (100 mm × 100 mm × 4 mm) confirmed the simulation results. By now the performance has also been shown by large scale industrially produced acrylic panels with dimensions of 1500 mm × 400 mm × 4 mm.     

Packed-bed thermal storage for concentrated solar power – Pilot-scale demonstration and industrial-scale design

A thermal energy storage system, consisting of a packed bed of rocks as storing material and air as high-temperature heat transfer fluid, is analyzed for concentrated solar power (CSP) applications. A 6.5 MWh_th pilot-scale thermal storage unit immersed in the ground and of truncated conical shape is fabricated and experimentally demonstrated to generate thermoclines. A dynamic numerical heat transfer model is formulated for separate fluid and solid phases and variable thermo-physical properties in the range of 20–650 °C, and validated with experimental results. The validated model is further applied to design and simulate an array of two industrial-scale thermal storage units, each of 7.2 GWh_th capacity, for a 26 MW_el round-the-clock concentrated solar power plant during multiple 8 h-charging/16 h-discharging cycles, yielding 95% overall thermal efficiency.     

Human capital and energy in economic growth – Evidence from Chinese provincial data

This paper investigates the cointegration and Granger causal relationship between economic growth and total energy consumption as well as disaggregate energy such as coal, coke, crude oil, petroleum products, natural gas and electricity in China for a period of 1995–2014. Different from limited existing provincial studies on China, we use a multivariate framework that considers per capita human capital on top of physical capital in the neoclassical production function and advanced panel econometric methodologies such as CupFM estimators and bootstrapped panel Granger causality tests that allow for cross-sectional dependence and provincial heterogeneity. Our results suggest that human capital exerts 2–3 times the effect of physical capital on the economy and energy also plays a significant role. Furthermore, the rich bootstrap panel Granger causality test results for both the panel and individual provinces provide substantial insights and suggest that it is important to examine the causal effects of both the total energy use and various disaggregate energy consumption before local governments make specific energy and economic policies.     

Dimethyl ether synthesis from Victorian brown coal through gasification – Current status,and research and development needs

Victorian brown coal, one of the largest and cheapest energy sources in the world, is currently used in mine-mouth coal-fired power plants. These power plants have low efficiency and high CO₂ emission. Alternative process paths leading to electricity generation and chemical production can provide more energy efficient and environment friendly applications of brown coal. Synthesis of dimethyl ether (DME) from brown coal is an attractive option because of its environmentally benign properties and wide range of applications. This article first reviews the current and likely future applications of brown coal. In the latter part of the article emphasis has been given on DME, since it stands out as a suitable option from both environmental and economic point of view. Finally research needs for the development and commercialisation of DME production process from brown coal has been identified.     

Supercritical water gasification of sewage sludge and combined cycle for H2 and power production – A thermodynamic study

An integrated system of supercritical water gasification (SCWG) and combined cycle has been developed for H₂ production and power generation. Sewage sludge and lignite coal were selected as raw material in this simulation. The effects of feed concentration (10–30 wt%) and lignite coal addition (0–50 wt%) on syngas yield and H₂ yield were also investigated in the temperature range of 500 °C–700 °C. Several heat exchangers were considered in the proposed integrated system to minimize energy loss. High pressure syngas was expanded by using turbo-expander to produce electricity, resulting in the improvement of the total efficiency. The results showed that the minimum feed concentrations of 14.25 wt%, 18.75 wt%, and 25.50 wt% were required to achieve self-sufficient energy at 500 °C, 600 °C, and 700 °C, respectively. However, the lower feed concentration and higher temperature were preferable for syngas production. The highest syngas and H₂ yield were obtained at 700 °C and 10 wt% feed concentration. The SCWG could produce 178.08 kg syngas from 100 kg feed and 9.06 kg H₂ were obtained after H₂ separation. The total power generation from turbo-expander and combined cycle module was 48.37 kW. By combining SCWG and combined cycle, the total efficiency could reach 63.48%. It worth mentioning that the addition of lignite coal could help reduce the minimum feed concentration to achieve autothermal condition, but did not have significant improvement on H₂ production.