Development of a thermoelectric self-powered residential heating system

Self-powered heating equipment has the potential for high overall energy efficiency and can provide an effective means of providing on site power and energy security in residential homes. It is also attractive for remote communities where connection to the grid is not cost effective. Self-powered residential heating systems operate entirely on fuel combustion and do not need externally generated electricity. Excess power can be provided for other electrical loads. To realize this concept, one must develop a reliable and low maintenance means of generating electricity and integrate it into fuel-fired heating equipment. In the present work, a self-powered residential heating system was developed using thermoelectric power generation technology. A thermoelectric module with a power generation capacity of 550 W was integrated into a fuel-fired furnace. The thermoelectric module has a radial configuration that fits well with the heating equipment. The electricity generated is adequate to power all electrical components for a residential central heating system. The performance of the thermoelectric module was examined under various operating conditions. The effects of heat transfer conditions were studied in order to maximize electric power output. A mathematical model was established and used to look into the influence of heat transfer coefficients and other parameters on electric power output and efficiency.     

Harvesting of PEM fuel cell heat energy for a thermal engine in an underwater glider

The heat generated by a proton exchange membrane fuel cell (PEMFC) is generally removed from the cell by a cooling system. Combining heat energy and electricity in a PEMFC is highly desirable to achieve higher fuel efficiency. This paper describes the design of a new power system that combines the heat energy and electricity in a miniature PEMFC to improve the overall power efficiency in an underwater glider. The system makes use of the available heat energy for navigational power of the underwater glider while the electricity generated by the miniature PEMFC is used for the glider's sensors and control system. Experimental results show that the performance of the thermal engine can be obviously improved due to the high quality heat from the PEMFC compared with the ocean environmental thermal energy. Moreover, the overall fuel efficiency can be increased from 17 to 25% at different electric power levels by harvesting the PEMFC heat energy for an integrated fuel cell and thermal engine system in the underwater glider.     

Methanol decomposition fuel processor for portable power applications

A new fuel processor approach for portable fuel cell power sources significantly improves upon microreformers by overcoming the difficulties with heat deficiencies and contaminants in the product hydrogen. Instead of reforming, the processor uses methanol decomposition to enable the byproduct, carbon monoxide (CO), to be used as the heat source. A hydrogen permselective membrane segregates the CO for combustion in an integrated burner, maximizes the decomposition conversion, and provides pure hydrogen for a fuel cell. Discharging the CO-rich retentate through an ejector to draw combustion air into the burner greatly simplifies the system. High and stable hydrogen yields are attained with optimized catalysts and fuel compositions. The resultant simple, efficient, and self-heating processor produces 85% of the hydrogen content of the fuel. A 20 W autonomous power source based on this novel fuel processor demonstrates a fuel energy density >1.5 Wh g^?1_(electrical), nearly twice as high as microreformer power sources.     

Catalytic combustion of hydrogen for residential heat supply application

Hydrogen can be converted to thermal energy by combustion or to electricity energy by fuel cells. Considering the stringent requirements for safety from fire hazards and elimination of pollutants, the flameless catalytic combustion of hydrogen is favorable over conventional flame combustion for residential heat supply application. This paper reported an industrial‐scale heat acquisition system based on hydrogen catalytic combustion. The 1 wt% Pt‐loaded glass fiber felts prepared by an impregnation process were used as the combustion catalyst, and a catalytic combustion burner with a capacity of 1 kW was designed. It was found that 100% hydrogen conversion rate could be obtained during the stable combustion stage, and the stable combustion could be achieved by adjusting hydrogen flow rate. The change in H₂/air ratio would influence the initial combustion stage but has little impact on the stable combustion stage. A heat efficiency of 80% for hot water supply was obtained based on the present catalytic hydrogen combustion burner. Copyright © 2016 John Wiley & Sons, Ltd.     

Design and evaluation of hybrid propulsion ship powered by fuel cell and bottoming cycle

Fuel cells are a promising power source in the electric propulsion systems for zero-emission vessels. The electric efficiency of fuel cells can be increased to 55% practically, but significant amounts of remaining energy from the electrochemical reaction are wasted as heat. This article proposes a hybrid propulsion system for ships that utilizes both the electric energy and thermal energy generated by fuel cells. The electric power capacity of fuel cells and the steam generation capacity of recovered heat from fuel cell systems are calculated, and then the propulsion power of the hybrid system is simulated by MATLAB Simulink. The overall energy efficiency of the proposed ship propulsion system is compared with that of conventional systems by comparing fuel consumption rate. Simulation results indicate that the proposed hybrid propulsion system can increase energy efficiency by 22.5% by additional utilization of the recovered heat from fuel cells.     

Performance simulation of a low‐swirl burner for a Stirling engine

A new type of gas burner for Stirling engine that can recover adequate heat from exhaust gas was designed based on the plate heat exchanger and low‐swirl combustion technology, which consists of three components: a cyclone, a burner, and a circular plate heat exchanger. The circular plate heat exchanger tightly wound around the combustion chamber plays a high efficiency of heat recovery role. In consideration of the radial symmetry of the burner, a three‐dimensional numerical simulation was carried out by Ansys15. The velocity distribution, temperature distribution, and pressure distribution of the combustion gas were presented respectively. Strong backflow that came from the exhaust gas around the root of the flame in the combustion chamber and a vortex below the inlet of the exhaust gas channel were found, which were beneficial for the combustion and improving the uniformity of temperature distribution. Combustion behaviors of the burner under standard operating conditions were obtained, the highest temperature was about 2200 K in burner and the exhaust gas entered the plate heat exchanger at the temperature of 1375 K and exited at 464 K, with the waste heat recovery efficiency over 65.8%. And, the air‐fuel ratio and combustion power had negligible effect on the waste heat recovery efficiency.     

Energy efficiency analysis and impact evaluation of the application of thermoelectric power cycle to today’s CHP systems

High efficiency thermoelectric generators (TEG) can recover waste heat from both industrial and private sectors. Thus, the development and deployment of TEG may represent one of the main drives for technological change and fuel substitution. This paper will present an analysis of system efficiency related to the integration of TEG into thermal energy systems, especially Combined Heat and Power production (CHP). Representative implementations of installing TEG in CHP plants to utilize waste heat, wherein electricity can be generated in situ as a by-product, will be described to show advantageous configurations for combustion systems. The feasible deployment of TEG in various CHP plants will be examined in terms of heat source temperature range, influences on CHP power specification and thermal environment, as well as potential benefits. The overall conversion efficiency improvements and economic benefits, together with the environmental impact of this deployment, will then be estimated. By using the Danish thermal energy system as a paradigm, this paper will consider the TEG application to district heating systems and power plants through the EnergyPLAN model, which has been created to design suitable energy strategies for the integration of electricity production into the overall energy system.     

Electric power generation by super-adiabatic combustion in thermoelectric porous element

A new system for converting combustion heat into electric power was proposed on the basis of reciprocating-flow super-adiabatic combustion in a catalytic and thermoelectric porous element. Self-sustaining combustion of an extremely low-calorific gas was successfully achieved in the element; because a reciprocating flow in the porous element recirculated energy, effectively regenerating combustion gas enthalpy into an enthalpy increase in the low-calorific gas. In the combustion system, a trapezoidal temperature distribution was established along the flow direction, resulting in a steep temperature gradient in the thermoelectric porous element. Numerical simulation showed that 94% of the combustion heat was transferred through the thermoelectric element by conduction. As a result, the total thermal efficiency, which was defined as the ratio of the electric power generated to the combustion heat, attained a value close to the conversion efficiency of the thermoelectric device itself.     

Characterization of confined hydrogen-air jet flame in a crossflow configuration using design of experiments

Hydrogen combustion has many industrial applications and development of new hydrogen burners is required to fulfil new demands. A novel configuration of hydrogen burner utilizing crossflow injection of fuel jets into swirling combustion air is characterized empirically in this work. It is intended as a first step in the development of new burner technologies having reduced emission levels and improved efficiency. Experiments were designed using the full factorial design method. Operating parameters were varied simultaneously and the NO_X emissions from the flame stabilized on the burner were measured. Statistical analysis of the experimental data showed that overall equivalence ratio is the dominant factor and lower NO_X emissions are observed at low equivalence ratios, irrespective of the burner power level. The analysis yielded an empirical relationship among NO_X emission, overall equivalence ratio, and power level that is useful in the design activity for a future combustion system based on the proposed configuration.     

Development of a powerful miniature hydrogen catalytic combustion powered thermoelectric generator

Rapid development of portable electronics promotes the R&D of micro/miniature power sources with high energy density. The high mass energy density and zero emission characteristic of hydrogen show a huge potential to develop powerful portable hydrogen-based power sources. A miniature hydrogen catalytic combustion powered thermoelectric generator (CCP-TEG) is designed and tested in detail. An outstanding catalytic core is prepared with a newly proposed method on the basis of combining H₂PtCl₆ solution and foamed transition metal. Such catalytic core is demonstrated to provide high combustion temperature, complete combustion, and sufficient heat flux for power generation. Several parameters including input power, equivalent ratio, cooling mode, and load resistance are investigated to clarify their influences on the combustion temperature, electric power, and various efficiencies (combustion, heat collection, TE, and overall efficiencies) of the hydrogen CCP-TEG. The developed hydrogen CCP-TEG is able to generate an electric power of 20.7 W with an overall efficiency of 2.04%, filling the research gap of generating large electric power (>10 W) with sufficiently high overall efficiency (>2%) in the research field of hydrogen CCP-TEG. The generated electric power and overall efficiency are much higher than those in previous hydrogen CCP-TEGs. The prepared catalytic core remains excellent functionality after running for 30 h, and the combustion temperature is as high as 918 K, which ensures the sufficiently high temperature difference for powerful power generation. This study is conducted to illustrate a concrete method on developing a powerful hydrogen CCP-TEG, and to identify further research directions.     

Optimization and efficiency analysis of methanol SOFC-PEMFC hybrid system

In order to improve the power generation efficiency of fuel cell systems employing liquid fuels, a hybrid system consisting of solid oxide fuel cell (SOFC) and proton exchange membrane fuel cell (PEMFC) is proposed. Utilize the high temperature heat generated by SOFC to reform as much methanol as possible to improve the overall energy efficiency of the system. When SOFC has a stable output of 100 kW, the amount of hydrogen after reforming is changed by changing the methanol flow rate. Three hybrid systems are proposed to compare and select the best system process suitable for different situations. The results show that the combined combustion system has the highest power generation, which can reach 350 kW and the total electrical efficiency is 57%. When the power of the tail gas preheating system is 160 kW, the electrical efficiency can reach 75%. The PEM water preheating system has the most balanced performance, with the electric power of 300 kW and the efficiency of 66%.     

Numerical studies on the combustion of ultra-low calorific gas in a divergent porous burner with heat recovery

This study presents the idea of heat recovery through recirculating walls to enhance the combustion stability for ultra-low calorific gas in a porous burner. Numerical studies on the combustion of ultra-low calorific gas of CO/H₂ with CO₂ and N₂ in a developed divergent porous burner with annular channel is conducted using two-dimensional axis symmetrical model with detailed kinetics. The heat recovery efficiency is defined as the ratio of heat recovery by the fresh mixture in the annular channel to burner power. It is shown that the heat recovery has significant effect on the minimal inlet gas temperature (MIGT) for stable combustion. It is confirmed that the heat recovery enhances the combustion and the stability limits are enlarged by preheating the fresh mixture, but it also leads to an extra pressure loss across the burner compared to that without heat recovery. Results show that heat recovery efficiency reaches up to 0.18 for all the investigated parameters and it reduces linearly from 0.32 to 0.18 as the mass flow ratio increases from 0.8 to 1.5. The MIGT for the burner with heat recirculating channel is always smaller than that without heat recovery. As a result, the combustion is greatly improved by the heat recovery in the divergent burner. Meanwhile, it is shown that pressure loss is increased significantly when the heat recirculating annular channel is added.     

Performance and emission studies on port injection of hydrogen with varied flow rates with Diesel as an ignition source

Automobiles are one of the major sources of air pollution in the environment. In addition CO₂ emission, a product of complete combustion also has become a serious issue due to global warming effect. Hence the search for cleaner alternative fuels has become mandatory. Hydrogen is expected to be one of the most important fuels in the near future for solving the problems of air pollution and greenhouse gas problems (carbon dioxide), thereby protecting the environment. Hence in the present work, an experimental investigation has been carried out using hydrogen in the dual fuel mode in a Diesel engine system. In the study, a Diesel engine was converted into a dual fuel engine and hydrogen fuel was injected into the intake port while Diesel was injected directly inside the combustion chamber during the compression stroke. Diesel injected inside the combustion chamber will undergo combustion first which in-turn would ignite the hydrogen that will also assist the Diesel combustion. Using electronic control unit (ECU), the injection timings and injection durations were varied for hydrogen injection while for Diesel the injection timing was 23° crank angle (CA) before injection top dead centre (BITDC). Based on the performance, combustion and emission characteristics, the optimized injection timing was found to be 5° CA before gas exchange top dead centre (BGTDC) with injection duration of 30° CA for hydrogen Diesel dual fuel operation. The optimum hydrogen flow rate was found to be 7.5 lpm. Results indicate that the brake thermal efficiency in hydrogen Diesel dual fuel operation increases by 15% compared to Diesel fuel at 75% load. The NO_X emissions were higher by 1–2% in dual fuel operation at full load compared to Diesel. Smoke emissions are lower in the entire load spectra due to the absence of carbon in hydrogen fuel. The carbon monoxide (CO), carbon dioxide (CO₂) emissions were lesser in hydrogen Diesel dual fuel operation compared to Diesel. The use of hydrogen in the dual fuel mode in a Diesel engine improves the performance and reduces the exhaust emissions from the engine except for HC and NO_X emissions.     

Investigation of the influence of fuel type on energy indicators of an electrochemical generator as a PART of a cogeneration unit

The influence of the type of fuel such as hydrogen, methane, motor diesel fuel, ethanol, motor gasoline and methanol on the fuel utilization ratio, the specific consumption per unit of electrical and heat power generated, the efficiency of the catalytic burner, the solid oxide fuel cell battery and the electrochemical generator has been studied. It has been shown that hydrogen is the best fuel in terms of energy indicators, and methanol is the worst one. For hydrogen, the fuel utilization ratio and specific fuel consumption for the production of electrical power and heat power supplied to heat networks are equal to 1; 0.122 kg r.f./kW·h and 34 kg r.f./GJ, respectively, while for methanol these indicators are 0.359; 0.275 kg r.f./kW·h and 83.7 kg r.f./GJ, respectively. For other types of fuels studied the energy indicators lie between the specified values.     

Performance characteristics of a Diesel engine power plant

Performance of an actual Diesel engine power plant with a rated output of 120 MW is analyzed based on the first and second laws of thermodynamics. The plant consists of seven identical Diesel engines and various subsystems including turbochargers, fuel heating units and heat exchangers performing various useful tasks. The engine runs on heavy fuel oil, and the pollutant emissions from the engine are greatly reduced by effective treatment systems. The characteristics and performance parameters of the internal combustion engines of the plant are evaluated. The mass, energy and exergy balances are verified for each flow stream in the power plant. The work and heat interactions, the exergy losses and the efficiencies of various components based on both energy and exergy concepts are evaluated. The thermal and the exergy efficiencies of the plant are determined to be 47% and 44%, respectively. The engine irreversibilities are due mostly to the irreversible combustion process and account for 32% of the total exergy input and 57% of the total irreversibilities in the plant. Most of the remaining irreversibilities in the plant occur in the desulphurization, intercooler, compressor and lubrication oil cooler units. The results should provide a realistic and meaningful ground for the performance evaluation of Diesel engine power units, and it may be used in the design and analysis of such systems.     

Thermophotovoltaic power generation systems using natural gas-fired radiant burners

Thermophotovoltaic (TPV) power generation in gas-fired furnaces is attracting technical attention. Considerable work has been done in the area of low bandgap GaSb cell-based TPV systems as well as silicon solar cell-based TPV systems. Previous investigations have shown that a radiant burner with a high conversion level of fuel to radiation energy must be developed to realize an efficient TPV system. In our work, we investigated different natural gas-fired radiant burners in order to raise the conversion of fuel energy to thermal radiation. These burners were used as radiation sources to establish and test two TPV prototype systems. It was found that for a non-surface combustion radiant burner, the radiation output can be enhanced using a thermal radiator with a porous structure. Also, we developed a cascaded radiant burner that generates two streams of radiation output. One stream illuminates silicon concentrator solar cells while the other drives low bandgap GaSb cells. In this way, useful radiation output and thus TPV system efficiency are significantly increased due to the cascaded utilization of combustion heat and optimized thermal management.     

Fuel cycle CO2-e targets of renewable hydrogen as a realistic transportation fuel in Australia

The claim of catastrophic man made climate change or global warming through anthropogenic CO₂ has presently focused the interest on the tailpipe emissions of CO₂ per km, with recent legislations obsessively targeting these emissions of CO₂ with defectively implemented procedures. With a variety of different propulsion solutions (electric, hybrid electric, hybrid mechanic, conventional) and different fuels (Diesel, Petrol, alternative fossil, alternative renewable) available in the near future, a more comprehensive approach based on the full fuel cycle, and eventually also the full life cycle of the vehicle appear to be necessary. The paper is a contribution to trigger further improvement to currently implemented procedures. The paper discusses the CO₂ emission data in the present form, some simple but effective measures to improve the accuracy of the data collection procedure, and propose results of fuel cycle CO₂-e analysis of vehicles with electric and thermal engines having different fuels. Vehicles with advanced internal combustion engines and power trains fuelled with Diesel may reach CO₂-e values of 100 g/km in Australia. Use of bio-ethanol in these vehicles may deliver in Australia a significant reduction of CO₂-e emissions to values below 36 g/km. Emission factors for Victoria are presently 1.23 kg CO₂-e/kWh for the purchased electricity and vehicles powered by electric motors will need a significant reduction of this indirect CO2-e emission to become competitive. Values below 0.5 kg CO₂-e/kWh are needed to make electric cars competitive with Diesel cars while values below 0.1 kg CO₂-e/kWh are needed to make electric cars competitive with bio-ethanol cars. Compared with all these alternatives, renewable hydrogen may possibly compete with Diesel when produced with renewable energy sources and made available at the pump for less than 0.1 kg CO₂-e/MJ of fuel energy, and with bio-ethanol if produced and distributed at a cost below 0.02 kg CO₂-e/MJ of fuel energy.     

Frontiers in combustion techniques and burner designs for emissions control and CO2 capture: A review

The use of fossil fuel is expected to increase significantly by midcentury because of the large rise in the world energy demand despite the effective integration of renewable energies in the energy production sector. This increase, alongside with the development of stricter emission regulations, forced the manufacturers of combustion systems, especially gas turbines, to develop novel combustion techniques for the control of NO_x and CO₂ emissions, the latter being a greenhouse gas responsible for more than 60% to the global warming problem. The present review addresses different burner designs and combustion techniques for clean power production in gas turbines. Combustion and emission characteristics, flame instabilities, and solution techniques are presented, such as lean premixed air‐fuel (LPM) and premixed oxy‐fuel combustion techniques, and the combustor performance is compared for both cases. The fuel flexibility approach is also reviewed, as one of the combustion techniques for controlling emissions and reducing flame instabilities, focusing on the hydrogen‐enrichment and the integrated fuel‐flexible premixed oxy‐combustion approaches. State‐of‐the‐art burner designs for gas turbine combustion applications are reviewed in this study, including stagnation point reverse flow (SPRF) burner, dry low NO_x (DLN) and dry low‐emission (DLE) burners, EnVironmental burners (including EV, AEV, and SEV burners), perforated plate (PP) burner, and micromixer (MM) burner. Special emphasis is made on the MM combustor technology, as one of the most recent advances in gas turbines for stable premixed flame operation with wide turndown and effective control of NO_x emissions. Since the generation of pure oxygen is prerequisite to oxy‐combustion, oxygen‐separation membranes became of immense importance either for air separation for clean oxy‐combustion applications or for conversion/splitting of the effluent CO₂ into useful chemical and energy products. The different carbon‐capture technologies, along with the most recent carbon‐utilization approaches towards CO₂ emissions control, are also reviewed.     

Partial oxidation of methane in a reciprocal flow porous burner with an external heat source

A reciprocal flow porous burner with an external heat source in the middle section was studied numerically to access the reactor efficiency for synthesis gas generation. The temperature and species profiles were predicted using a two temperature model with a detailed chemical mechanism. The effect of the variation of the power of the external heat source on the hydrogen and carbon monoxide yields was studied. The energy conversion efficiencies of the system with various power levels of the external heat source were evaluated. It is found that H₂ and CO yields increase significantly with the addition of the external heat source due to the temperature increase in the middle section of the burner. The CO₂ emissions remain small. The methane conversion ratio increases with increase of the power of the external heat source reaching 97%. The H₂ and CO conversion ratios yields are nearly doubled as the power of the external heat source increases from 0 to 750 W. The cold gas energy conversion efficiency decreases as the power of the external heat source increases. At the same time, the syngas energy conversion efficiency increases from 41% to 70%, while hydrogen energy conversion efficiency increases from 28% to 46%.     

A fibre‐mat catalytic burner for the heating system of PVC tiles

This study aims to develop the low‐temperature catalytic burner using Al₂O₃ fibre and Pt catalyst as a substrate and an active material, respectively, and then to apply it to the heating system of PVC tiles. Three types of fibre‐mat catalytic burners—natural diffusion catalytic burner, forced diffusion catalytic burner and premixed catalytic burner—were tested. For the natural diffusion catalytic burner, the combustion efficiency was significantly affected by the installation method. Its combustion efficiency was above 99.5% when it was placed vertically and upward, whereas the combustion efficiency rapidly deteriorated to less than 80% when it was installed in downward position. When the forced diffusion combustion mode was employed, the combustion efficiency of the fibre‐mat catalytic burner was successively improved over 99.5%. The optimal operation condition of the premixed fibre‐mat catalytic burner was obtained when the excess air ratio is 4.3 and the heat load is 3.0 kcal h^?1 cm^?2. The heat load of the premixed catalytic burner was found to be twice as much as those of the natural and forced diffusion catalytic burner, meaning that the size of the catalytic burner can be reduced to its half if the premixed catalytic burner is used. We also performed the field test of the fibre‐mat catalytic burner in the heating system of the PVC tiles. The combustion efficiency of the catalytic burners appeared to be satisfactory, above 99.5%, and the energy saving by replacing the existing electrical heaters with the fibre‐mat catalytic burners were shown to be 27.7%. Copyright © 2002 John Wiley & Sons, Ltd.