micro-CHP Research Articles

Feasibility of Hybrid Desalination Plants Coupled with Small Gas Turbine CHP Systems

Nowadays, several technologies for desalination processes are available and widely employed. However, they consume a considerable amount of energy and involve high capital and operating costs. Therefore, the techno-economic analysis of a system coupling different energy sources with the desalination processes is of value. The possibility of coupling a small gas turbine combined heat and power system (GT CHP) with hybrid desalination plants (HDPs) has been assessed in this study. The proposed gas turbine power generation system, based on a single-stage centrifugal compressor and an uncooled centripetal turbine, provides design simplicity and reasonable installation costs for the power generating plant. The hybrid desalination technique, based on the use of two different desalination technologies, i.e., Reverse Osmosis (RO) and a thermal desalination process, has been chosen to better exploit the electrical and thermal energy produced by the mini CHP plant. The proposed solution is numerically investigated from both thermodynamic and economic points of view, and the results of the thermodynamic analysis of the cycle are used as input for the evaluation of the amount of freshwater produced and of costs. The economic assessment of standalone desalination systems is also shown for the comparison with the hybrid solutions here proposed. Results show that the total cost of the water produced by MED + RO was less than the total cost of the water obtained by MSF + RO, and that the energy cost of MED + RO hybrid desalination system was about 15% less than that for stand-alone RO desalination technology. Thus, the MED + RO hybrid desalination system can be considered a promising solution for the coupling with the proposed mini GT CHP plant, which, due to the small size and cost, as well as the easy installation, can be easily applied in off-grid or remote areas.

Micro Combined Heat and Power Systems – Evaluation of a Sample Application

The growing need for a secure, cost-effective, less polluting and efficient form of energy has contributed to an increasing interest in the use of micro combined heat and power (MCHP) systems. In this paper, the environmental performance and economic feasibility of a 1 kWe internal combustion engine (ICE) MCHP system in a one-family house was assessed and compared with the baseline scenario were residential energy demands are met with grid electricity and natural gas fired condensing boilers. The result of the analysis shows that MCHP systems present opportunities for savings in energy costs. Based on a social discount rate (SDR) of 5 % and a calculated 3259 operating hours, a simple payback period of about 4.8 years was derived as the time needed to recover the extra investment cost of the ICE unit. The result of the sensitivity analysis reveals that, both the running hours and price of electricity have significant effects on the payback period of the project. Considering the end of useful life period of the systems, MCHP offer a good replacement for conventional gas boilers of 90 % efficiency. However, their high initial costs (when compared to high efficiency condensing boilers), could be seen as the major factor hampering market diffusion. Also, considering the optimal environmental benefits, MCHP system produced more on-site CO2 emissions in reference to the condensing boiler but generally, annual CO2 emission is reduced by about 38 % when compared to the overall separate generation of heat and power scenario.

Mini CHP based on the electrochemical generator and impeded fluidized bed reactor for methane steam reforming

The paper presents a configuration of mini CHP with the methane reformer and planar solid oxide fuel cell (SOFC) stacks. This mini CHP may produce electricity and superheated steam as well as preheat air and methane for the reformer along with cathode air used in the SOFC stack as an oxidant. Moreover, the mathematical model for this power plant has been created. The thermochemical reactor with impeded fluidized bed for autothermal steam reforming of methane (reformer) considered as the basis for the synthesis gas (syngas) production to fuel SOFC stacks has been studied experimentally as well. A fraction of conversion products has been oxidized by the air fed to the upper region of the impeded fluidized bed in order to carry out the endothermic methane steam reforming in a 1:3 ratio as well as to preheat products of these reactions. Studies have shown that syngas containing 55% of hydrogen could be produced by this reactor. Basic dimensions of the reactor as well as flow rates of air, water and methane for the conversion of methane have been adjusted through mathematical modelling.The paper provides heat balances for the reformer, SOFC stack and waste heat boiler (WHB) intended for generating superheated water steam along with preheating air and methane for the reformer as well as the preheated cathode air. The balances have formed the basis for calculating the following values: the useful product fraction in the reformer; fraction of hydrogen oxidized at SOFC anode; gross electric efficiency; anode temperature; exothermic effect of syngas hydrogen oxidation by air oxygen; excess entropy along with the Gibbs free energy change at standard conditions; electromotive force (EMF) of the fuel cell; specific flow rate of the equivalent fuel for producing electric and heat energy. Calculations have shown that the temperature of hydrogen oxidation products at SOFC anode is 850 °C; gross electric efficiency is 61.0%; EMF of one fuel cell is 0.985 V; fraction of hydrogen oxidized at SOFC anode is 64.6%; specific flow rate of the equivalent fuel for producing electric energy is 0.16 kg of eq.f./(kW·h) while that for heat generation amounts to 44.7 kg of eq.f./(GJ). All specific parameters are in agreement with the results of other studies.

CFD Modelling of a Spark Ignition Internal Combustion Engine Fuelled with Syngas for a mCHP System

Micro Combined Heat and Power (mCHP) powered with biomass is nowadays a technology attracting increasing interest to develop a local supply chain to produce, process and valorise the available material in territorial areas as much as possible circumscribed, with a considerable reduction also of the CO2 related to transportation. Application for biomass powered mCHP produces environmental benefits by reducing primary energy consumption and associated greenhouse gas emissions and complies with the need for increased decentralization of energy supply. Of particular relevance is mCHP based on biomass gasification due to the negligible particulate matter release with respect to combustion.The present work describes a 3D CFD model of the spark ignition (SI) internal combustion engine (ICE) fuelled with syngas installed in the mCHP pilot system ECO20 manufactured by the Italian company Costruzioni Motori Diesel S.p.A. (CMD). The considered system is made of a gasifier combined with proper syngas cleaning devices, an ICE and a generator to deliver a maximum electrical and thermal power of 20 kW and 40 kW, respectively. For the proper initialisation of the 3D CFD model, the syngas composition is experimentally characterised using a gas-chromatograph on samples collected under real operation. The calculated pressure cycle is verified by comparison with the one calculated through a properly developed 1D ICE model. Main goals of the performed numerical analysis are to study into detail the combustion process and to assess the engine performance characteristics related to the use of syngas.

Investigation Of Working Temperature Effect On Micro-Cogeneration Application Of Proton Exchange Membrane Fuel Cells

Investigation Of Working Temperature Effect On Micro-Cogeneration Application Of Proton Exchange Membrane Fuel Cells

MINI CHP BASED ON THE ELECTROCHEMICAL GENERATOR AND IMPEDED FLUIDIZED BED REACTOR FOR METHANE STEAM REFORMING

The paper presents the scheme of mini CHP with methane reformer and planar solid oxide fuel cells (SOFC) stack. The mini CHP produces electricity, superheated steam, hot air and methane for the reformer and it also preheats cathode air used in the SOFC stack as an oxidant. Moreover, the scheme’s mathematical model is constructed. The thermochemical reactor with impeded fluidized bed for autothermal steam reforming of methane (reformer) studied experimentally is the key element in producing synthesis gas – fuel for the SOFC stack. The research indicates that synthesis gas containing 55% of hydrogen can be derived using the reactor. Through mathematical modeling, the entire reactor’s principal dimensions as well as flow rates of air, water and methane were adjusted to the methane reforming for the mini CHP studied. The paper includes the heat balances of the reformer, SOFC stack and waste heat boiler that produces the superheated steam, hot air and methane for the reformer as well as preheated cathode air. These balances were instrumental for calculating the useful product fraction in the reformer, fraction of hydrogen oxidized in the SOFC anode channel, electric gross efficiency, anode temperature, exothermic effect of synthesis gas hydrogen oxidation by air oxygen, excess entropy and Gibbs free energy change at standard conditions, SOFC electromotive force (EMF), specific flow rate of standard fuel for heat, and power generation. The simulation study has shown that the hydrogen oxidation products temperature in the SOFC anode channel is 850ºС, electric gross efficiency 61.0%, single fuel cell EMF 0.985 V, fraction of hydrogen oxidized in the SOFC anode channel 64.6%, specific flow rate of standard fuel for power generation 0.16 kg/(kW·h), for heat generation 44.7 kg/GJ. All the specific parameters are in good agreement with other publications results.

Microcogeneration in buildings with low energy demand in load sharing application

The paper investigates the introduction of a MCHP (Micro Combined Heat and Power) system in buildings with low energy demand with respect to the current building stock. A load sharing approach between a multifamily residential building and an office one is taken into account. Dynamic simulations are carried out in order to evaluate the thermo-economic performance of the analyzed system. Particular attention is given to the estimation of the electric load of the different users, as the economic profitability of a MCHP system is strongly influenced by the amount of self-consumed electricity. In order to analyze the influence of climatic conditions, two different geographical locations in Italy (Naples and Turin, having 1034 and 2617 heating degree days, respectively) are considered. The results of this study indicate that the installation of MCHP systems in buildings with low energy demand allows to increase the percentage of self-consumed electricity reducing the bidirectional electricity flow between the users and the external grid, as well as the impact on the grid itself due to the large diffusion of distributed generation systems.Moreover this study shows that the load sharing approach between users with different load profile leads to better energy, environmental and economic results with respect to a conventional system. The climatic conditions play an important role on the MCHP operational hours and hence on the thermo-economic performance of the system. The primary energy saving of the system located in Turin is equal to 8.8% with respect to 6.2% of the system located in Naples. Also the environmental performance, evaluated in terms of equivalent CO2 avoided emissions, are better in Turin (8.3%) than in Naples (6.7%). The economic analysis shows acceptable values of the pay-back period in presence of economic support mechanisms. The findings of this study show that the introduction of a MCHP system in load sharing approach leads to thermo-economics advantages even considering the lower heating needs of well-insulated buildings.

Control strategies and cycling demands for Li-ion storage batteries in residential micro-cogeneration systems

Energy storage units have become important components in residential micro-cogeneration (MCG) systems. As MCG systems are often connected to single residences or buildings in a wide variety of settings, they are frequently unique and highly customized. Lithium-ion batteries have recently gained some profile as energy storage units of choice, because of their good capacity, high efficiency, robustness and ability to meet the demands of typical residential electrical loads. In the present work, modeled scenarios are explored which examine the performance of a MCG system with an internal combustion engine, photovoltaic input and a Li-ion storage battery. An electricity demand profile from new data collected in Ottawa, Canada is used to provide a full year energy use context for the analyses. The demands placed on the battery are examined to assess the suitability of the battery size and performance, as well as control related functionalities which reveal significantly varying battery use, and led to a quantitative expression for equivalent cycles. The energy use simulations are derived from electrochemical fundamentals adapted for a larger battery pack. Simulation output provides the basis for techno-economic commentary on how to assess large-scale Li-ion batteries for effective electrical storage purposes in MCG systems, and the impact of the nature of the control strategy on the battery service life.

A Review on Microcogeneration National Testing Procedures

Several standard testing procedures were prepared or are in a developing phase in many countries, to provide methods for determining the performance of MCHP (Micro Combined Heat and Power) systems. This is due to the quick diffusion of microcogenerators worldwide, especially in the Japanese, European and North American markets, and to existing supporting mechanisms, that require the achievement of specific minimum energy performance.In the framework of Subtask B of Annex 54 of International Energy Agency, information about national standard testing procedures were gathered. In this paper, the main available national standards are summarized, and a comparison is performed.

Energy, environmental and economic dynamic performance assessment of different micro-cogeneration systems in a residential application

A dynamic performance assessment for a number of micro combined heat and power (MCHP) systems fuelled by natural gas, namely two different internal combustion engines and a reciprocating external combustion Stirling engine, was performed by using a simulation software. The cogeneration units were integrated with an Italian multi-family house compliant with the transmittance values of both walls and windows suggested by the Italian Law. Auxiliary thermal energy was supplied by a natural gas-fired boiler and the heat provided by both the MCHP device and the boiler was accumulated within a combined storage tank. A sensitivity analysis upon varying the hot water storage volume (0.855 m3, 0.738 m3, 0.503 m3) and the set-point temperature (55 °C and 60 °C) of the water within the tank was performed.Detailed dynamic models, developed within Annex 42 of the International Energy Agency (IEA) and calibrated on the basis of experimental results, were used for carefully predicting the performance of the cogeneration devices.The simulated performance of the proposed system were compared with those of a reference system composed of a natural gas-fired boiler (for thermal energy production) and the central grid (for electricity production) in order to assess the suitability of the cogeneration device-based system in comparison to the system based on separate energy production.The comparison was performed from energy, environmental and economic point of views according to the Italian scenario.The comparison showed that, whatever the MCHP unit is, the proposed system allows for reducing the primary energy consumption (up to 13.4%), the carbon dioxide equivalent emissions (up to 18.9%), as well as the operating costs (up to 20.9%) with respect to the conventional system. The largest savings were obtained with the tank characterized by the lowest volume coupled with the internal combustion engines in the case of 55 °C was used as set-point temperature.

Performance analysis of heating systems for low energy houses

The residential sector is responsible for more than 35% of the final energy consumption in the European Union, and is increasingly constrained by thermal regulations, resulting in a significant rise of new efficient heating technologies. This paper presents a comparison of the energetic and environmental performances of six heating systems installed in a low energy house: a gas-fired condensing boiler, a wood pellet boiler, a micro-combined heat and power (MCHP), an air-to-water electric heat pump, an air-to-water gas absorption heat pump and an exhaust air-to-air electric heat pump. The comparison is made with respect to the annual primary energy consumption and the annual greenhouse gas (GHG) emissions, and carried out under various climates and electricity generation mixes. The results indicate that, based on an ideal sizing, the MCHP and the absorption heat pump achieve the highest energy performances. However, both technologies suffer from small size unavailability, leading to significant oversizing which impacts their performances. Based on current size availability, the air-to-water electric heat pump benefits from the previous systems oversizing and thus appears as the most efficient technology. However, current sizing practice also causes significant oversizing which impacts the performances of thermodynamic systems. Without significant sizing practice improvements, the air-to-water electric heat pump merit decreases in favor of the MCHP. In terms of environmental impact, the wood boiler causes the lowest GHG emissions, whatever the electricity generation mix considered.

The mighty micro

Massed ranks of gas central heating boilers, serving as mini CHP plants, are being recruited in the battle against global warming.

Assessment of economical and ecological benefits from deployment of a domestic combined heat and power unit based on its experimental performance

A number of technologies have been embarked upon for combating the problems of escalating energy requirements and the resulting greenhouse gas emissions. Micro or domestic combined heat and power (CHP) has been considered to be one of such technologies. Estimation of the benefits from implementing a pre-commercial prototype of a WhisperGen Mk 3, Stirling engine based, micro CHP (MCHP) unit, in a typical UK semi-detached house with high efficiency electrical appliances and with a typical non-condensing boiler was carried out and some of these results are presented in this article. The initial stage of the investigations focused on mapping thermal and electrical operational performance of the MCHP through physical experimentation on the pre-production unit. Then, to estimate the economical and environmental benefits over a 12-month period, the typical heat and power demand profiles within a household were modelled. In the final stage of the research, the operation of MCHP was simulated within the household, taking into account information on heat and electricity demands and data on the experimental performance of the domestic CHP system. The simulation indicated that with the application of this pre-commercial prototype as a replacement for the typical non-condensing boiler a 9 per cent reduction in both utility bills (using electricity and natural gas prices that were effective in March 2005) and CO2 emissions with a seasonal efficiency of 86 per cent could be achieved assuming that no auxiliary heating system was used to rapidly compensate the hot water deficit in the storage tank in periods of the high hot water demand.

Energy and carbon emission footprint of micro-CHP systems in residential buildings of different energy demand levels

This article summarizes an evaluation of micro-CHP (MCHP) systems in residential buildings. To account for the dynamic interactions between MCHP devices, heat storage and loads, MCHP models integrated into building simulations tools were used, calibrated with either results from laboratory experiments or manufacturer data. Solid oxide and polymer electrolyte membrane fuel cell as well as Stirling and internal combustion engine devices were compared to reference systems with either gas boiler or ground-coupled heat pump, and utility electricity supply. The influence of different energy demand levels for space heating, domestic hot water and electricity, heat storage size, control parameter and MCHP capacity, and combinations with solar thermal collectors were analysed. With the European electricity mix, most MCHP systems showed primary energy and emission reductions in comparison with the gas boiler system. With the combined cycle power plant mix, the largest reductions resulted for the ground-coupled heat pump systems, however.

Energy and CO 2 emissions performance assessment of residential micro-cogeneration systems with dynamic whole-building simulation programs

Micro-cogeneration, also termed micro combined heat and power (MCHP) or residential cogeneration, is an emerging technology with the potential to provide energy efficiency and environmental benefits by reducing primary energy consumption and associated greenhouse gas emissions. The distributed generation nature of the technology also has the potential to reduce losses due to electrical transmission and distribution inefficiencies and to alleviate utility peak demand problems. Detailed MCHP models for whole-building simulation tools, developed in Annex 42 of the International Energy Agency (IEA) Energy Conservation in Buildings and Community Systems Programme, have been used to conduct a performance assessment study for a number of micro-cogeneration systems and residential buildings. Annual non-renewable primary energy (NRPE) demand and CO 2-equivalent (CO 2-eq) emissions were determined by simulation for different cogeneration technologies, namely natural gas-fuelled solid oxide (SOFC) and polymer electrolyte membrane fuel cells, Stirling and internal combustion engines. These were compared to the reference system with a gas boiler and electricity supply from the grid. A ground-coupled heat pump system was also analysed for comparison. The cogeneration units were integrated in single and multi-family houses of different energy standard levels. Two different electricity generation mixes were considered: European mix and combined cycle power plant (CCPP). For the MCHP devices, detailed dynamic component models as well as simplified performance map models were used, developed and calibrated with either results from laboratory experiments or with manufacturer data. The simulations were performed using the whole-building simulation programme TRNSYS, using domestic hot water and electric demand profiles specified in IEA Annex 42. Combinations of three demand levels were analyzed. In NRPE demand, for the European electricity mix, most MCHP systems offered reductions (up to 34%) in comparison with the gas boiler reference system and crediting the electricity exported to the grid. For the CCPP electricity generation mix, the largest NRPE reductions resulted for the ground-coupled heat pump systems (up to 29%). The maximum reduction with a cogeneration system was 14%. In terms of CO 2-eq emissions, most cogeneration systems offered reductions for the European electricity mix (up to 22%). However, maximum reductions resulted for the heat pump system (23%). For the CCPP mix, maximum reductions by far again resulted for the heat pump systems (up to 29%). The maximum reduction for a cogeneration system was achieved with the ICE system in the single-family house (14%).

Assessment of micro-cogeneration potential for domestic trigeneration

Cogeneration is worldwide considered as the major option to achieve considerable energy saving with respect to traditional systems. This paper deals with the application of micro-cogeneration, Micro-Combined Heat and Power (MCHP) (electrical power <15 kW) to small-scale (residential application) users for the assessment of its use in trigeneration; the state of art of this technology is considered, a test facility designed and built to evaluate the performances of MCHP-Electric Heat Pump (EHP) system itself is described and the Energetic, Economic and Environmental (3-E) analysis in some operation mode to match the users loads is proposed.

96/05327 Contours of micro-CHP are becoming visible

96/05327 Contours of micro-CHP are becoming visible

Mini CHP systems — a small price to pay for bigger profits

The use of combined heat and power systems in the UK has traditionally lagged behind that in the United States and the rest of Europe-to some extent due to legislation and to the attitude of the gas and electricity authorities. The 1983 Energy Act created a measure of freedom in the UK so far as electricity was concerned, in that any generator of electricity can contract to sell power to the local network and indeed can use the local network to pass power from one part of the country to another. A company taking advantage of the new situation is Combined Power Systems Ltd. It has developed a neat packaged customer-friendly and yet very sophisticated combined heat and power (cogeneration) set which provides substantial energy savings for the user.