Small-scale Power Generation Research Articles

O-202 小型バイオマスガス化発電装置の開発(セッション2:技術2,口頭発表)

O-202 小型バイオマスガス化発電装置の開発(セッション2:技術2,口頭発表)

5-6.スターリングエンジンを用いたバイオマス資源からの小型発電システムの実証研究((2)燃焼・蒸発,Session 5 燃焼・熱利用)

5-6.スターリングエンジンを用いたバイオマス資源からの小型発電システムの実証研究((2)燃焼・蒸発,Session 5 燃焼・熱利用)

CFD simulations of compressed air two stage rotary Wankel expander – Parametric analysis

A small scale volumetric Wankel expander is a powerful device for small-scale power generation in compressed air energy storage (CAES) systems and Organic Rankine cycles powered by different heat sources such as, biomass, low temperature geothermal, solar and waste heat leading to significant reduction in CO2 emissions. Wankel expanders outperform other types of expander due to their ability to produce two power pulses per revolution per chamber additional to higher compactness, lower noise and vibration and lower cost. In this paper, a computational fluid dynamics (CFD) model was developed using ANSYS 16.2 to simulate the flow dynamics for a single and two stage Wankel expanders and to investigate the effect of port configurations, including size and spacing, on the expander’s power output and isentropic efficiency. Also, single-stage and two-stage expanders were analysed with different operating conditions. Single-stage 3D CFD results were compared to published work showing close agreement.The CFD modelling was used to investigate the performance of the rotary device using air as an ideal gas with various port diameters ranging from 15mm to 50mm; port spacing varying from 28mm to 66mm; different Wankel expander sizes (r=48, e=6.6, b=32)mm and (r=58, e=8, b=40)mm both as single-stage and as two-stage expanders with different configurations and various operating conditions. Results showed that the best Wankel expander design for a single-stage was (r=48, e=6.6, b=32)mm, with the port diameters 20mm and port spacing equal to 50mm. Moreover, combining two Wankel expanders horizontally, with a larger one at front, produced 8.52kW compared with single-stage which gave 4.75kW power output at the same operating conditions. Also, a maximum isentropic efficiency of 91% was calculated with inlet pressure of 6bar and inlet temperature of 400K at 7500rpm for the two-stage compared to the 87.25% for the single-stage.

Graphene Ink Laminate Structures on Poly(vinylidene difluoride) (PVDF) for Pyroelectric Thermal Energy Harvesting and Waste Heat Recovery.

Thermal energy can be effectively converted into electricity using pyroelectrics, which act as small scale power generator and energy harvesters providing nanowatts to milliwatts of electrical power. In this paper, a novel pyroelectric harvester based on free-standing poly(vinylidene difluoride) (PVDF) was manufactured that exploits the high thermal radiation absorbance of a screen printed graphene ink electrode structure to facilitate the conversion of the available thermal radiation energy into electrical energy. The use of interconnected graphene nanoplatelets (GNPs) as an electrode enable high thermal radiation absorbance and high electrical conductivity along with the ease of deposition using a screen print technique. For the asymmetric structure, the pyroelectric open-circuit voltage and closed-circuit current were measured, and the harvested electrical energy was stored in an external capacitor. For the graphene ink/PVDF/aluminum system the closed circuit pyroelectric current improves by 7.5 times, the open circuit voltage by 3.4 times, and the harvested energy by 25 times compared to a standard aluminum/PVDF/aluminum system electrode design, with a peak energy density of 1.13 μJ/cm3. For the pyroelectric device employed in this work, a complete manufacturing process and device characterization of these structures are reported along with the thermal conductivity of the graphene ink. The material combination presented here provides a new approach for delivering smart materials and structures, wireless technologies, and Internet of Things (IoT) devices.

Gasification: An alternative solution for energy recovery and utilization of vegetable market waste.

Vegetables waste is generally utilized through a bioconversion process or disposed of at municipal landfills, dumping sites or dumped on open land, emitting a foul odor and causing health hazards. The presents study deals with an alternative way to utilize solid vegetable waste through a thermochemical route such as briquetting and gasification for its energy recovery and subsequent power generation. Briquettes of 50 mm diameter were produced from four different types of vegetable waste. The bulk density of briquettes produced was increased 10 to 15 times higher than the density of the dried vegetable waste in loose form. The lower heating value (LHV) of the briquettes ranged from 10.26 MJ kg-1 to 16.60 MJ kg-1 depending on the type of vegetable waste. The gasification of the briquettes was carried out in an open core downdraft gasifier, which resulted in syngas with a calorific value of 4.71 MJ Nm-3 at the gasification temperature between 889°C and 1011°C. A spark ignition, internal combustion engine was run on syngas and could generate a maximum load up to 10 kWe. The cold gas efficiency and the hot gas efficiency of the gasifier were measured at 74.11% and 79.87%, respectively. Energy recovery from the organic vegetable waste was possible through a thermochemical conversion route such as briquetting and subsequent gasification and recovery of the fuel for small-scale power generation.

Thermo-economic evaluation of water-injected air bottoming cycles hybridization using heliostat field collector: Comparative analyses

A possible solution to intermittency and storage difficulties associated with solar energy utilization is power plant hybridization. Additionally, air bottoming cycle is an alternative plant configuration which is more economical for small scale power generation than conventional combined cycle. To further improve the air bottoming cycle thermo-economic performance, water injection in the bottoming cycle air is proposed. In this paper, a detailed thermo-economic optimization is conducted for a hybrid air bottoming cycle power plant with water injection in the bottoming cycle air. Analyses are accomplished by utilizing three thermo-economic assessment approaches comprising levelized cost of electricity, payback period and life cycle savings. The acquired results indicate the advantages of water injection to improve the bottoming cycle heat recovery capability and plant's levelized cost of electricity. Noting that the plant's levelized cost of electricity is improved by 0.7 US$/MWh from 77.8 US$/MWh to 77.1 US$/MWh as water injection in the bottoming cycle is implemented. Therefore, 2.940 MUS$ can be saved during 25 years of plant operation.

Combustion Characterization and Model Fuel Development for Micro-tubular Flame-assisted Fuel Cells.

Combustion based power generation has been accomplished for many years through a number of heat engine systems. Recently, a move towards small scale power generation and micro combustion as well as development in fuel cell research has created new means of power generation that combine solid oxide fuel cells with open flames and combustion exhaust. Instead of relying upon the heat of combustion, these solid oxide fuel cell systems rely on reforming of the fuel via combustion to generate syngas for electrochemical power generation. Procedures were developed to assess the combustion by-products under a wide range of conditions. While theoretical and computational procedures have been developed for assessing fuel-rich combustion exhaust in these applications, experimental techniques have also emerged. The experimental procedures often rely upon a gas chromatograph or mass spectrometer analysis of the flame and exhaust to assess the combustion process as a fuel reformer and means of heat generation. The experimental techniques developed in these areas have been applied anew for the development of the micro-tubular flame-assisted fuel cell. The protocol discussed in this work builds on past techniques to specify a procedure for characterizing fuel-rich combustion exhaust and developing a model fuel-rich combustion exhaust for use in flame-assisted fuel cell testing. The development of the procedure and its applications and limitations are discussed.

Dynamic modelling and experimental validation of scroll expander for small scale power generation system

This work presents a detailed and generic dynamic modelling and simulation method of scroll expander for small scale power generation system. The geometric models of the scroll were built step by step, including the scroll involute, scroll dimensions, chamber areas and volumes, the scroll profile modifications and so on. The valve model, internal leakage model, motion equation, heat transfer equation and energy balance equation were combined with the geometric models to complete the scroll expander modelling. A mathematic model of a direct current generator or an experimentally determined correlation of generated power against rotational speed of the used generator was integrated to the expander model as the power output unit. To enhance the adaptability of the current model, an overall dynamic friction coefficient of the scroll expander and the generator was innovatively proposed and introduced as one of the key parameters in the present study. The accurate value of this coefficient should be experimentally determined for a specific expander – generator system; with the knowledge of such a parameter, the mechanical friction loss can be accurately and easily calculated in the simulation study. The present modelling and simulation method have been validated by several sets of experimental results based on different scroll expanders studied by different researchers, and the corresponding overall dynamic friction coefficient was found in the order of magnitude of 10−3Nms.

Premixed combustion of methane–air mixture stabilized over porous medium: A 2D numerical study

The advancing development of small portable devices and miniaturization of electronic components such as smartphones, laptops, Global Positioning Systems (GPS), Unmanned Aerial Vehicles (UAVs) and sensors have led to an increasing demand for small scale power generators, such as the Ultra Micro Gas Turbine (UMGT). This study focuses on the two dimensional numerical investigation of premixed methane–air flames stabilized over a porous medium in a cylindrical combustion chamber which is a fundamental part of an UMGT. A reduced skeletal mechanism of methane combustion including 17 species and 73 reactions was employed for the simulations. The main objective of the present work is to investigate the effect of important parameters such as incoming mixture mass flow rate, equivalence ratio, reactants’ initial temperature, thermal conductivity and porosity of flame holder on the combustion process. Results show that combustion can be considerably affected by the flame holder, especially because under certain conditions it could lead to considerable heat losses and eventually flame quenching. Generally when the burning velocity is much higher than the incoming flow velocity, the flame lays on the surface of the porous medium and heat is lost through the flame holder causing a decrease in the flame temperature. On the other hand, when the flame is slightly lifted from the flame holder, heat is dispersed to the outer wall and through axial conduction the porous medium is heated up, allowing the mixture to increase its temperature before combustion. Finally the effect of the thermal conductivity and porosity of the porous medium are analysed, showing that the more insulating the flame holder is, the less heat losses occur.

The development of a thermoelectric power generator dedicated to stove-fireplaces with heat accumulation systems

A significant part of the world’s population (about 40%) cooks their meals and provides heating for their homes using wood-burning heating devices. Due to the relatively low cost of fuel and their aesthetic design, solid fuel stoves capable of heat accumulation are convenient and common. The use of dedicated small-scale power generators provides also additional benefits.This paper presents the results of a study conducted to verify the possibility of generating power using stove-fireplaces with heat accumulation systems. In such units, the temperature of the flue gas should be kept at a certain level for the purposes of storing heat, which results from certain limitations of the thermoelectric generators. To verify the possibility of applying thermoelectric modules in such heating devices, a dedicated system with thermoelectric generators was selected from among various microcogeneration systems and implemented. Three types of heat exchangers were studied and the most efficient unit was selected for further testing. Two types of generators, with maximum operating temperatures of 320 and 175°C, were compared. Subsequently, the characteristics of the latter were determined. The conducted tests allowed to determine the performance and the total efficiency of the generators that were used. It has been demonstrated that the maximum power of the generator would not exceed ca. 30We and that there is no economic justification for such a device. However, providing a self-powered and self-sufficient operation of stove-fireplaces with heat accumulation systems remains an important goal.

Multiobjective Optimization Design of Small-Scale Wind Power Generator With Outer Rotor Based on Box–Behnken Design

In this paper, the finite-element method (FEM) based on 2-D numerical analysis was used for the basic design and characteristics analysis of a small-scale 3-kW wind power generator to which a permanent-magnet generator was applied. A prototype was manufactured, and a characteristics experiment was performed to verify the designed generator. In addition, the optimization design in order to satisfy required power of a generator while minimizing the cogging torque and the back electromotive force (EMF) total harmonic distribution (THD) on the basis of the designed initial model generator was conducted using the Box-Behnken design (BBD), which is a response surface method (RSM). The cogging torque, the back EMF THD, and the output power for each level of the design factors selected by the BBD were derived by the FEM based on 2-D numerical analysis. As a result, the optimal design model was derived in consideration of the RSA among each factor and the main effect and the interaction effects of each factor. This demonstrated the validity of the optimized design of the urban small-scale wind power generator design using the BBD.

Simulation and experimental study of the Otto and Stirling combined cycle

Gasoline engines currently reject up to 40% of the total fuel energy in their exhaust. Because of increasing petroleum costs, there is a growing interest in techniques that can use this waste heat to improve the overall system efficiency. In this paper, a combined cycle system is proposed where a high-speed gasoline engine acts as the topper of the combined cycle with exhaust gases used for a bottoming cycle based on a Stirling cycle. This paper describes a mathematical model of the Stirling engine to evaluate the combined performance of the gasoline engine and the Stirling engine driven by waste heat. Simulation and experimental studies of the combined cycle system of the gasoline engine and Stirling engine reveal that the Stirling engine is a good candidate for small-scale power generation. Maximum shaft power of 535 W is recovered when the temperature of the exhaust gas reaches approximately 1000 K and the gasoline engine operates at 3000 RPM and 90% load with 50.7 kW output power. The operating pressures and temperatures of the Stirling engine are monitored in the experiment by placing three pressure sensors and 34 thermocouples in the heat exchangers.

A methodology to identify potential markets for small-scale solar thermal power generators

This paper presents an innovative methodology to perform market analysis of a new solar power generation technology based on parabolic dish and micro gas turbine engines. Technical, economic, social and political parameters of influence are combined together into a single figure of merit: index of market potential. This index is an original approach enabling the identification of the potential markets for this technology, tackling the inverse problem (from technology to market identification) in lieu of the usual direct problem (determining the interest of a technology in a predefined region).The paper takes into account the availability of solar energy, population distribution, intensity of the electricity consumption, economic indicators, business environment and legal framework for a set of more than twenty countries. Risk assessment tools at various levels are also built into the numerical tool, which is not the case in similar works reviewed by the authors.Finally, the methodology includes a probabilistic approach to handling uncertainty in the input data. The result of this confirms that the methodology is robust and is not very affected by changes in the initial assumptions.

Sensorless fuzzy‐logic‐based maximum power point tracking control for a small‐scale wind power generation systems with a switched‐mode rectifier

This study proposes a sensorless maximum power point tracking (MPPT) control using an improved variable-speed small-scale wind power generation system (WPGS) with a permanent magnet synchronous generator. The passive elements of a small-scale WPGS that use a conventional boost converter suffer from disadvantages that result in power losses, increased costs, and increased system size. Therefore, to eliminate the passive elements, the proposed system performs MPPT control to vary the duty ratio of a switched-mode rectifier. To evaluate the MPPT algorithms, a comparison was made between a fuzzy-logic-based perturb-and-observe (P&O) control with variable step size and a conventional P&O control with fixed-step size. A wind turbine model is investigated using a squirrel-cage induction motor, and the variable torque is controlled by varying the generator speed. The presented system and algorithm are verified by the simulations and experiments.

Determination of Sectional Constancy of Organic Coal-Water Fuel Compositions

To use widespreadly the waste of coals and oils processing in the great and the small-scale power generation, the key parameter, which is sectional constancy of promising organic coal-water fuels (OCWF), was studied. The compo-sitions of OCWF from brown and bituminous coals, filter cakes, used motor, turbine and dielectrical oils, water-oil emul-sion and special wetting agent (plasticizer) were investigated. Two modes of preparation were considered. They are with homogenizer and cavitator. It was established that the constancy did not exceed 5–7 days for the compositions of OCWF with brown coals, and 12–15 days for that compositions with bituminous coals and filter cakes. The injection of used oils in a composition of OCWF led to increase in viscosity of fuel compositions and their sectional constancy.

A brief study on the economic and technical feasibility of a small biomass power plant - the case of Morretes, Paraná, Brazil

Brazil is one of the biggest agricultural producers in the world, and the uncontested leader in sugarcane production. One main by-product of sugarcane is bagasse which has a high energy potential and is used as fuel in large thermal power generation stations located within sugar and ethanol plants. However, this is not the reality of small sugarcane producers, which use just a fraction of bagasse as animal feed, improperly discarding outdoors all the rest, thus causing many environmental problems. The objective of this paper is, from a case study conducted in a small town in Paraná (Southern Brazil), to check the technical and financial feasibility of implementing local-level small-scale thermal power generation stations, which could use the surplus sugarcane biomass. The conclusion not only indicates it is feasible, but also that there are benefits that go beyond the financial sphere, regarding the environment and the national energy deficit.

A brief study on the economic and technical feasibility of a small biomass power plant - the case of Morretes, Paraná, Brazil

Brazil is one of the biggest agricultural producers in the world, and the uncontested leader in sugarcane production. One main by-product of sugarcane is bagasse which has a high energy potential and is used as fuel in large thermal power generation stations located within sugar and ethanol plants. However, this is not the reality of small sugarcane producers, which use just a fraction of bagasse as animal feed, improperly discarding outdoors all the rest, thus causing many environmental problems. The objective of this paper is, from a case study conducted in a small town in Parana (Southern Brazil), to check the technical and financial feasibility of implementing local-level small-scale thermal power generation stations, which could use the surplus sugarcane biomass. The conclusion not only indicates it is feasible, but also that there are benefits that go beyond the financial sphere, regarding the environment and the national energy deficit.

Design of disk type PM synchronous generator based on halbach

This paper expounds the application merits of disk type PM synchronous generator in small-scale wind power generation .The characteristics of the disk type PM synchronous generator were analyzed and 8P, 200W disk type generator with 90 degree Halbach magnet structure was designed. Simulation and calculation are carried out by using finite element method. By comparing the 90 degree Halbach magnet structure and the traditional magnet structure of the disk type generator, the results shows that the 90 degree Halbach magnet structure can improve the air gap magnetic density, reduce the leakage of main magnetic circuit and the loss.

Integration of Hybrid PV/Wind Generation System Using Fuzzy MPPT in Grid Connected System for Remote Area

Photovoltaic and wind are renewable energy resources that widely used and grow rapidly in fulfilling electricity demand. Powers from both technologies depend on sunlight intensity and wind speed. For small scale power generation, DC voltage from both technologies is low and requires step-up converter to raise DC voltage ratio before converted into AC voltage. To optimize this system, step-up converter must have high ratio and efficiency to a distance of wide voltage input. This paper proposed an operation simulation and arrangement of DC-DC converter along with DC-AC from hybrid source PV-Wind which integrated to grid utilities without using storage device. High Gain Integrated Cascade Boost (HGICB) is DC-DC converter that has quadratic voltage ratio and used in this research. Then DC link connected to Voltage Source Inverter (VSI) which interconnected with utility grid and controlled by current control method. The total installed capacity of hybrid source is 4.4 kW. Wind turbine uses PMSG along with full bridge rectifier. To maximize and stabilize the generated power, MPPT fuzzy is used. Result from the simulation shows that converter capable to maintain maximum power whether from PV and wind turbine which canalized to utility grid in various irradiation condition, wind speed, and grid load alteration.

Experimental Tests on a Pre-Heated Combustion Chamber for Ultra Micro Gas Turbine Device: Air/Fuel Ratio Evaluation

Current portable power generators are mainly based on internal combustion engine since they present higher values of efficiency comparing to other engines; the main reason why internal combustion engine is not convenient for micro power generation (5 - 30 kW) is because of their heaviness. Micro and ultra micro gas turbine devices, based on a micro compressor and a micro turbine installed on the same shaft, are more suitable for this scope for several reasons. Micro turbine systems have many advantages over reciprocating engine generators, such as higher power density (with respect to size and weight), extremely low emissions and few, or just one, moving part. Those designed with foil bearings and air-cooling operate without oil, coolants or other hazardous materials. Micro turbines also have the advantage of having the majority of their waste heat contained in their relatively high temperature exhaust. Micro turbines offer several potential advantages compared to other technologies for small-scale power generation, including: a small number of moving parts, compact size, lightweight, greater efficiency, lower emissions, lower electricity costs, and opportunities to utilize waste fuels. The object of this study is the experimental tests on a stand-alone gas turbine device with a pre-heated combustion chamber (CC), to validate the fuel consumption reduction, compared to an actual and commercial device, used on air models.