A study on energy saving in residential PEFC cogeneration systems

We have been developing technologies for energy saving in the residential sector. Recently, we have been concentrating our resources specifically into the development of polymer electrolyte fuel cell (PEFC) cogeneration systems. The system has excellent energy saving characteristics. However, the total amount of energy saved depends on how the system is operated. The characteristics of residential energy consumption are more complicated than in industrial use and depend on individual living patterns. It is therefore not easy to develop a control method for a system that can be generally applied across a wide variety of residential use.In this paper, we propose a system configuration and operation planning method developed for a residential PEFC cogeneration system. Using an operation planning method we developed, we demonstrate that our system provides higher energy savings than the conventional method. The energy saving rates are 15.9% under a large heat demand, 18.4% under a relatively high electrical demand and low heat demand, 1.3% under relative low electrical and heat demands.     

Performance of an innovative 120 kWe natural gas cogeneration system

The paper deals with an innovative (120 kWe, 195 kWt) natural gas (NG) combined heat and power (CHP) system, at present under development, which has been set up at the FIAT Centre of Research (CRF), Turin, Italy. The main characteristics of the CHP system are: the use of an automotive derived internal combustion engine, a high part load electrical efficiency due to a variable speed operation strategy and an advanced exhaust gas after-treatment to meet the most stringent pollutant emission regulations.     

Applying a non-intrusive energy-management system to economic dispatch for a cogeneration system and power utility

Non-intrusive energy-management (NIEM) techniques are based on energy signatures. While such approaches lack transient energy signatures, the reliability and accuracy of recognition results cannot be determined. By using neural networks (NNs) in combination with turn-on transient energy analysis, this study attempts to identify load demands and improve recognition accuracy of NIEM results. Case studies are presented that apply various methods to compare training algorithms and classifiers in terms of artificial neural networks (ANN) due to various factors that determine whether a network is being used for pattern recognition. Additionally, in combination with electromagnetic transient program (EMTP) simulations, calculating the turn-on transient energy facilitate load can lead to identification and a significant improvement in the accuracy of NIEM results. Analysis results indicate that an NIEM system can effectively manage energy demands within economic dispatch for a cogeneration system and power utility. Additionally, a new method based on genetic algorithms (GAs) is used to develop a novel operational strategy of economic dispatch for a cogeneration system in a regulated market and approach the global optimum with typical environmental constraints for a cogeneration plant. Economic dispatch results indicate that the NIEM system based on energy demands can estimate accurately the energy contribution from the cogeneration system and power utility, and further reduce air pollution. Moreover, applying the NIEM system for economic dispatch can markedly reduce computational time and power costs.     

Design and performance evaluation of an innovative small scale combined cycle cogeneration system

This paper deals with an innovative natural gas (NG) combined cycle cogeneration system (150-kW_e, 192 kW_t). The system is made up of a combination of two interconnected combined heat and power (CHP) systems: a reciprocating internal combustion engine cogenerator (ICE CHP) as the topping cycle and a Rankine cycle cogenerator (RC CHP) which operates as the bottoming cycle on the exhaust gases from the ICE. The expander technology chosen for the Rankine cycle prime mover is a reciprocating single expansion steam engine with three cylinders in a radial architecture. The ICE is an automotive derived internal combustion engine with a high part-load electrical efficiency, due to a variable speed operation strategy and reduced emissions.     

CPH systems for cogeneration of power and hydrogen from coal

Three layouts with an integrated coal gasifier hydrogen production and a small powerplant section have been modelled using a computer code (ASPEN PLUS^TM${\mathrm{PLUS}}^{\mathrm{TM}}$). The integration allows to eliminate or to reduce the losses at the condenser of the powerplant: the steam is reheated and fed to the gasifier. The resulting counterpressure operation of the powerplant is justified like in a co-generator of heat and power (CHP). In this case we have a co-generation of power and hydrogen (CPH). Therefore the efficiency of the power plant is not high, but it shows an “apparent” efficiency very high. Even if the concept has been demonstrated, further work is required because power generation is very small with respect to the hydrogen production.     

Exergetic analysis of an innovative small scale combined cycle cogeneration system

The purpose of this paper has been to carry out an exergetic analysis of an innovative natural gas (NG) combined cycle cogeneration system (150-kW_e, 192-kW_t). The combined cycle is composed of a reciprocating Internal Combustion Engine (ICE), which is used as the topping cycle, and a water Rankine cycle (RC), which operates on the exhaust gases from the ICE, as the bottoming cycle.     

Numerical based design of exhaust gas system in a cogeneration power plant

Among the various aspects that have to be analysed in a cogeneration and combined cycle plant design, the exhaust gas stack design can represent a critical aspect, in particular when a by-pass stack, which allows the modulation of heat-to-power generation, is present, since it may influence the entire system working condition. To properly take into account the large number of the different requirements which enter in an exhaust gas system design, a multidisciplinary analysis involving numerical integrated approaches can be adopted in order to obtain an optimally designed stack system. In this paper, the design of the exhaust gas system in a cogeneration plant is analysed. The design is performed numerically through a three-dimensional integrated numerical code. Different design solutions are simulated and the results discussed in detail.     

Global and local emission impact assessment of distributed cogeneration systems with partial-load models

Small-scale distributed cogeneration technologies represent a key resource to increase generation efficiency and reduce greenhouse gas emissions with respect to conventional separate production means. However, the diffusion of distributed cogeneration within urban areas, where air quality standards are quite stringent, brings about environmental concerns on a local level. In addition, partial-load emission worsening is often overlooked, which could lead to biased evaluations of the energy system environmental performance.     

Expanding photovoltaic penetration with residential distributed generation from hybrid solar photovoltaic and combined heat and power systems

The recent development of small scale combined heat and power (CHP) systems has provided the opportunity for in-house power backup of residential-scale photovoltaic (PV) arrays. This paper investigates the potential of deploying a distributed network of PV + CHP hybrid systems in order to increase the PV penetration level in the U.S. The temporal distribution of solar flux, electrical and heating requirements for representative U.S. single family residences were analyzed and the results clearly show that hybridizing CHP with PV can enable additional PV deployment above what is possible with a conventional centralized electric generation system. The technical evolution of such PV + CHP hybrid systems was developed from the present (near market) technology through four generations, which enable high utilization rates of both PV-generated electricity and CHP-generated heat. A method to determine the maximum percent of PV-generated electricity on the grid without energy storage was derived and applied to an example area. The results show that a PV + CHP hybrid system not only has the potential to radically reduce energy waste in the status quo electrical and heating systems, but it also enables the share of solar PV to be expanded by about a factor of five.     

Sustainability assessment of cogeneration sector development in Croatia

The effective and rational energy generation and supply is one of the main presumptions of sustainable development. Combined heat and power production, or co-generation, has clear environmental advantages by increasing energy efficiency and decreasing carbon emissions. However, higher investment cost and more complicated design and maintenance sometimes-present disadvantages from the economical viability point of view. As in the case of most of economies in transition in Central and Eastern Europe, Croatia has a strong but not very efficient co-generation sector, delivering 12% of the final energy consumption. District heating systems in the country's capital Zagreb and in city of Osijek represent the large share of the overall co-generation capacity. Besides district heating, co-generation in industry sector is also relatively well developed. The paper presents an attempt to assess the sustainability of Croatian co-generation sector future development. The sustainability assessment requires multi-criteria assessment of specific scenarios to be taken into consideration. In this respect three scenarios of Croatian co-generation sector future development are taken into consideration and for each of them environmental, social and economic sustainability indicators are defined and calculated. The assessment of complex relationships between environmental, social and economic aspects of the system is based on the multi-criteria decision-making procedure. The sustainability assessment is based on the General Sustainability Index rating for different cases reflecting different criteria and their priority. The method of sustainability assessment is applied to the Croatian co-generation sector contributing to the evaluation of different strategies and definition of a foundation for policy related to the sustainable future cogeneration sector development.     

Government policy and industrial investment in cogeneration in the USA

This paper presents an economic analysis of investment in cogeneration in selected industries and assesses the impact of investment tax credits policy directed at cogeneration. We use a dynamic partial equilibrium model that is derived under the assumption that investment in cogeneration occurs if and when the annualized cost of the incremental investment is less than the annualized benefits of avoiding electricity purchase from the utilities. Policy simulations show that investment in cogeneration is economically feasible even without the tax credits; the tax credit policy marginally increases investment in cogeneration. The welfare distortions and revenue loss to the US Treasury are also estimated. External benefits required per barrel of oil to offset distortion costs would come to $2.83.     

Effect of power interchange operation of multiple household gas engine cogeneration systems on energy-saving

The effect of power interchange operation of multiple household gas engine cogeneration systems (H-GCGS) on the energy-saving is investigated using an optimization approach based on the mixed-integer linear programming. In this power interchange operation, electricity generated by H-GCGS is shared among households in a housing complex without transmitting to a commercial electric power system so that the operating time of these systems may increase. This paper numerically analyzes optimal operational strategies for 20 households and three types of household energy supply configurations: the power interchange operation of the H-GCGSs (IC), stand-alone operation of each H-GCGSs (SA), and conventional energy supply system without the H-GCGSs. A numerical result clarifies the effectiveness of the power interchange operation from the energy-saving viewpoint and a dominant parameter for evaluating the energy-saving effect.     

Exergy analysis of cogeneration power plants in sugar industries

In this paper, exergy analysis of a heat-matched bagasse-based cogeneration plant of a typical 2500 tcd sugar factory, using backpressure and extraction condensing steam turbine is presented. In the analysis, exergy methods in addition to the more conventional energy analyses, are employed to evaluate overall and component efficiencies and to identify and assess the thermodynamic losses. The analysis is carried out for a wide range of steam inlet conditions selected around the sugar industry’s export cogeneration plant. The results show that, at optimal steam inlet conditions of 61 bar and 475 °C, the backpressure steam turbine cogeneration plant perform with energy and exergy efficiency of 0.863 and 0.307 and condensing steam turbine plant perform with energy and exergy efficiency of 0.682 and 0.260, respectively. Boiler is the least efficient component and turbine is the most efficient component of the plant.     

Feasibility of small-scale gas engine-based residential cogeneration in Spain

Nowadays all countries are developing their own policies to promote cogeneration in the small-scale residential sector. In this paper the feasibility of small-scale gas engine-based residential cogeneration plants under the current Spanish regulation is studied. A unitary thermal load profile is obtained to characterised the thermal demand of residential applications in Spain. This unitary profile is used to analyse the potential of cogeneration in the small-scale range of powers (100–1000 kW). A complete characterisation of the gas fuelled engines in the market is performed and subsequently used to evaluate the economic feasibility within the selected range by means of a self-tailored simulation model. It is underlined how the thermal storage is a crucial element that should be suitably included in a residential cogeneration plant and the distortions that the actual pricing system adds to the profitability of residential plants of different sizes. Finally a sensibility study is carried out in order to evaluate how the Spanish regulation is able to deal with future variations in the energy prices. It is shown that a rise in the price of the natural gas increases the current feasibility of a plant while a decrease descends the profitability.     

An estimation of cogeneration potential by using refinery residuals in Mexico

Electric power generation in Mexico is mainly based on fossil fuels, specifically heavy fuel oil, although the use of natural gas combined cycles (NGCC) is becoming increasingly important. This is the main destination that has promoted growing imports of natural gas, currently accounting for about 20% of the total national annual consumption. Available crude oil is becoming heavier; thus refineries should be able to process it, and to handle greater quantities of refinery residuals. If all refinery residuals are used in cogeneration plants serving petroleum refineries, the high heat/power ratio of refinery needs, leads to the availability of appreciable quantities of electricity that can be exported to the public utility. Thus, in a global perspective, Mexican imports of natural gas may be reduced by cogeneration using refinery residuals. This is not the authors’ idea; in fact, PEMEX, the national oil company, has been entitled by the Mexican congress to sell its power leftovers to The Federal Electricity Commission (CFE) in order to use cogeneration in the way described for the years to come. A systematic way of determining the cogeneration potential by using refinery residuals from Mexican refineries is presented here, taking into account residual quantities and composition, from a national perspective, considering expected scenarios for Maya crude content going to local refineries in the years to come. Among different available technologies for cogeneration using refinery residuals, it is believed that the integrated gasification combined cycle (IGCC) would be the best option. Thus, considering IGCC plants supplying heat and power to refineries where it is projected to have refinery residuals for cogeneration, the expected electric power that can be sent to the public utility is quantified, along with the natural gas imports mitigation that may be attained. This in turn would contribute to a necessary fuel diversification policy balancing energy, economy and ecology.     

Evaluating the role of cogeneration for carbon management in Alberta

Developing long-term carbon control strategies is important in energy intensive industries such as the oil sands operations in Alberta. We examine the use of cogeneration to satisfy the energy demands of oil sands operations in Alberta in the context of carbon management. This paper evaluates the role of cogeneration in meeting Provincial carbon management goals and discusses the arbitrary characteristics of facility- and product-based carbon emissions control regulations. We model an oil sands operation that operates with and without incorporated cogeneration. We compare CO₂ emissions and associated costs under different carbon emissions control regulations, including the present carbon emissions control regulation of Alberta. The results suggest that incorporating cogeneration into the growing oil sands industry could contribute in the near-term to reducing CO₂ emissions in Alberta. This analysis also shows that the different accounting methods and calculations of electricity offsets could lead to very different levels of incentives for cogeneration. Regulations that attempt to manage emissions on a product and facility basis may become arbitrary and complex as regulators attempt to approximate the effect of an economy-wide carbon price.     

Condition and development of the cogeneration facilities based on autoproduction investment model in Turkey

Turkey, with its young population and growing energy demand per person, its fast growing urbanization, and its economic development, has been one of the fast growing power markets of the world for the last 20 years. It is expected that the demand for electric energy in Turkey will be 294 billion kWh by the year 2010 and 556 billion kWh by the year 2020. Turkey’s electric energy demand is growing 7% yearly. Because a substantial amount of Turkey’s energy need has been met by cogeneration facilities in recent years. Cogeneration facilities have an important role in Turkey’s energy strategy. While there were only four cogeneration facilities and the total capacity of them was 30 MW_e in 1994, in 1999, 10.6% of total electric production was produced by these facilities. In accordance with the governmental decree numbered 85/9799, cogeneration is the technology which produces electricity and heat synchronously and autoproduction is the name of the firm which was founded for the purpose of producing electricity and heat. In this study, the development of autoproduction facilities in Turkey, which are the most convenient legal investment model for cogeneration investors, has been investigated.     

Dynamic behavior of PEM fuel cell and microturbine power plants

This paper presents a comparison between the dynamic behavior of a 250 kW stand-alone proton exchange membrane fuel cell power plant (PEM FCPP) and a 250 kW stand-alone microturbine (MT). Dynamic models for the two are introduced. To control the voltage and the power output of the PEM FCPP, voltage and power control loops are added to the model. For the MT, voltage, speed, and power control are used. Dynamic models are used to determine the response of the PEM FCPP and MT to a load step change. Simulation results indicate that the response of the MT to reach a steady state is about twice as fast as the PEM FCPP. For stand-alone operation of a PEM FCPP, a set of batteries or ultracapacitors is needed in order to satisfy the power mismatch during transient periods. Software simulation results are obtained by using MATLAB^®, Simulink^®, and SimPowerSystems^®.     

Power and cogeneration technology environomic performance typification in the context of CO2 abatement part II: Combined heat and power cogeneration

This is the second of a series of two articles, dealing with a new approach of environomic (thermodynamic, economic and environmental) performance ‘Typification’ and optimization of power generation technologies. This part treats specifically of combined heat and power (CHP) cogeneration technologies in the context of CO₂ abatement and provides a methodology for a flexible and fast project based CHP system design evaluation. One of the aspect of the approach is the post-optimization integration of the operating and capital costs, in order to effectively deal with the uncertainty of the project specific design and operation conditions (fuel, electricity and heat selling prices, project financial conditions such as investment amortization periods, annual operating hours, etc). In addition the approach also allows to efficiently evaluate the influence of the external cost such as the CO₂ tax level under a tax scheme or the CO₂ permit price in the emission trading market.