Small-scale Combined Heat Research Articles

木質バイオマスの中小規模熱電併給システムの事業性評価

In this paper, the effective woody-biomass utilization system is proposed. In recent year, we are interested in energy security by the Great East Japan Earthquake. In addition, the possibility of renewable energy spread is increasing by the enforcement of FIT (Feed-in tariff). There are abundant wood resources in Japan, but woody biomass is not so popular. Therefore, in this study, we encored the evaluation with a focus on small-scale combined heat and power (CHP) business in which there is a possibility of commercialization. As a result, it was found that CHP business by gasification power generation utilizing the FIT was possible to return on investment in about 10 years. Further, as a result of evaluation by interviews and SWOT analysis of CHP precedents, it was found that only pellets CHP project could achieve.

Performance of U.S. hybrid distributed energy systems: Solar photovoltaic, battery and combined heat and power

Until recently, the relatively high levelized cost of electricity from solar photovoltaic (PV) technology limited deployment; however, recent cost reductions, combined with various financial incentives and innovative financing techniques, have made PV fully competitive with conventional sources in many American regions. In addition, the costs of electrical storage have also declined enough to make PV+battery systems potentially economically viable for a mass-scale off-grid low-emission transition. However, many regions in the U.S. (e.g. Northern areas) cannot have off-grid PV systems without prohibitively large battery systems. Small-scale combined heat and power (CHP) systems provide a potential solution for off-grid power backup of residential-scale PV+battery arrays, while also minimizing emissions from conventional sources. Thus, an opportunity is now available to maximize the use of solar energy and gain the improved efficiencies possible with CHPs to deploy PV+battery+CHP systems throughout the U.S. The aim of this study is to determine the technical viability of such systems by simulating PV+battery+CHP hybrid systems deployed in three representative regions in the U.S., using the Hybrid Optimization Model for Electric Renewable (HOMER) Pro Microgrid Analysis tool. The results show that the electricity generated by each component of the hybrid system can be coupled to fulfill the residential load demand. A sensitivity analysis of these hybrid off grid systems is carried out as a function capacity factor of both the PV and CHP units. The results show that conservatively sized systems are technically viable in any continental American climate and the details are discussed to provide guidance for both design and deployment of PV+battery+CHP hybrid systems to reduce consumer costs, while reducing energy- and electricity-related emissions.

Thermodynamic Performance of a High Efficient Power Plant Based on Faecal Biomass Gasification, Solid Oxide Fuel Cells and Micro Steam Turbine

Affordable sanitation around the world with the recovery of valuable energy and clean water from faecal biomass in an off-grid system is a challenge. A novel small scale combined heat and power (CHP) toilet system concept has been optimized which generate power very efficiently and produce clean water. The system combines a dryer, a plasma gasifier, and a gas cleaning unit with an ambient pressure solid oxide fuel cell (SOFC) stack and a micro steam turbine (MST). The gasifier uses additional heat supplied from the combustion of stack depleted fuel. With this concept, syngas with high heating value can be produced which can be efficiently converted in a SOFC system. This is reflected by the net electrical efficiency of the integrated system configuration of the order of 40%. Additional power is produced combining it with an MST and an efficiency increase of the order of 20% is achieved.

Comparing the life cycle costs of using harvest residue as feedstock for small- and large-scale bioenergy systems (part II)

In part II of our two-part study, we estimate the nominal electricity generation and GHG (greenhouse gas) mitigation costs of using harvest residue from a hardwood forest in Ontario, Canada to fuel (1) a small-scale (250 kWe) combined heat and power wood chip gasification unit and (2) a large-scale (211 MWe) coal-fired generating station retrofitted to combust wood pellets. Under favorable operational and regulatory conditions, generation costs are similar: 14.1 and 14.9 cents per kWh (c/kWh) for the small- and large-scale facilities, respectively. However, GHG mitigation costs are considerably higher for the large-scale system: $159/tonne of CO2 eq., compared to $111 for the small-scale counterpart. Generation costs increase substantially under existing conditions, reaching: (1) 25.5 c/kWh for the small-scale system, due to a regulation mandating the continual presence of an operating engineer; and (2) 22.5 c/kWh for the large-scale system due to insufficient biomass supply, which reduces plant capacity factor from 34% to 8%. Limited inflation adjustment (50%) of feed-in tariff rates boosts these costs by 7% to 11%. Results indicate that policy generalizations based on scale require careful consideration of the range of operational/regulatory conditions in the jurisdiction of interest. Further, if GHG mitigation is prioritized, small-scale systems may be more cost-effective.

An assessment of solar-powered organic Rankine cycle systems for combined heating and power in UK domestic applications

Performance calculations are presented for a small-scale combined solar heat and power (CSHP) system based on an Organic Rankine Cycle (ORC), in order to investigate the potential of this technology for the combined provision of heating and power for domestic use in the UK. The system consists of a solar collector array of total area equivalent to that available on the roof of a typical UK home, an ORC engine featuring a generalised positive-displacement expander and a water-cooled condenser, and a hot water storage cylinder. Preheated water from the condenser is sent to the domestic hot water cylinder, which can also receive an indirect heating contribution from the solar collector. Annual simulations of the system are performed. The electrical power output from concentrating parabolic-trough (PTC) and non-concentrating evacuated-tube (ETC) collectors of the same total array area are compared. A parametric analysis and a life-cycle cost analysis are also performed, and the annual performance of the system is evaluated according to the total electrical power output and cost per unit generating capacity. A best-case average electrical power output of 89W (total of 776kWh/year) plus a hot water provision capacity equivalent to ∼80% of the total demand are demonstrated, for a whole system capital cost of £2700–£3900. Tracking PTCs are found to be very similar in performance to non-tracking ETCs with an average power output of 89W (776kWh/year) vs. 80W (701kWh/year).

Simulations of greenhouse gas emission reductions from low-cost hybrid solar photovoltaic and cogeneration systems for new communities

Recent work has shown that small-scale combined heat and power (CHP) and solar photovoltaic (PV) technologies have symbiotic relationships, which enable coverage of technical weaknesses while providing the potential of significant greenhouse gas emission reductions at the residential level. With the reductions in the cost of PV systems and the increasing maturity of CHP systems an opportunity exists for widespread commercialization of the technology, particularly for new construction. In order to determine the potential for this opportunity and to optimize the design of PV–CHP systems for greatest emission and cost reductions in the residential context a simulation, an optimization model has been developed using multiobjective genetic algorithms called the Photovoltaic-Trigeneration Optimization Model (PVTOM). In this paper, PVTOM is applied to emission-intensive and rapidly growing communities of Calgary, Canada. Results consistently show decreases in emissions necessary to provide both electrical and thermal energy for individual homes of all types. The savings range from 3000–9000kgCO2e/year, which represents a reduction of 21–62% based on the type of loads in the residential household for the lowest economic cost hybrid system. These results indicate that hybrid PV–CHP technologies may serve as replacements for conventional energy systems for new communities attempting to gain access to emission-intensive grids.

Micro gas turbine configurations with carbon capture – Performance assessment using a validated thermodynamic model

The expected increase in distributed power generation, especially in Europe, and the necessity for a reduction in greenhouse gas emissions requires an evaluation of carbon capture application at small-scale combined heat and power plants. In this regard, a micro gas turbine (MGT), a Turbec T100, has been selected for further investigation as a baseline. A thermodynamic model validated against data obtained from a test rig has been extended to enable modeling of a CO2 capture unit. In addition, two innovative cycles, an exhaust gas recirculation (EGR) cycle and a humid air turbine (HAT) cycle, have been investigated using the selected micro gas turbine model with a focus on improved carbon capture efficiency. The thermodynamic performance indicators of all cycles, namely, the baseline MGT cycle, the EGR cycle, and the HAT cycle, all with capture unit, are presented. The results show a considerable improvement in cycle efficiency for the HAT cycle (25.8%), compared to the baseline MGT (23.0%) and EGR (22.5%) cycles. However, the surge margin is reduced markedly for the HAT cycle. It is shown that the effect of EGR on the operation of the micro gas turbine is marginal. The effects of varying ambient air temperature on the performance of all cycles as well as the effect of different recirculation percentages on the performance of the EGR cycle have also been investigated. The results confirm that the performance in the EGR cycle is less sensitive to the change in ambient temperature, compared to the other cycles. The marginal effect of various recirculation percentages on the performance of the EGR cycle is also shown in this paper.

Small-scale combined heat and power as a balancing reserve for wind – The case of participation in the German secondary control reserve

Increasing amounts of intermittent renewable energy sources (RES) are being integrated into energy systems worldwide. Due to the nature of these sources, they are found to increase the importance of mechanisms for balancing the electricity system. Small-scale combined heat and power (CHP) plants based on gas have proven their ability to participate in the electricity system balancing, and can hence be used to facilitate an integration of intermittent RES into electricity systems. Within the EU electricity system, balancing reserves have to be procured on a market basis. This paper investigates the ability and challenges of a small-scale CHP plant based on natural gas to participate in the German balancing reserve for secondary control. It is found that CHP plants have to account for more potential losses than traditional power plants. However, it is also found that the effect of these losses can be reduced by increasing the flexibility of the CHP unit.

Performance analysis of a small-scale combined heat and power system using agricultural biomass residues: The SMARt-CHP demonstration project

A small mobile agricultural residue gasification unit for decentralized CHP (combined heat and power) production is designed and constructed within the framework of the SMARt-CHP LIFE+ project. This unit applies the technology of biomass gasification coupled with an ICE (internal combustion engine) based generator-set for CHP production. The unit is sized for a maximum thermal output of 12 kW in addition to approximately 5 kW electrical output.Four different locations close to biomass feedstock origin in rural areas of Western Macedonia in Greece, two in Ptolemaida and two in Amyntaion, were selected for the demonstrative operation of the unit. Peach, olive and grape residues were utilized as biomass feedstocks while the unit operated continuously on a 24/7 basis.The present paper describes the unit performance in terms of operation stability, application of different agricultural residues as well as the energy output of the process. The results show the effect of different types of biomass feedstock, gasification parameters and engine intake mixture to long-term operation and energy output while the obtained data will aid in the direction of CHP systems scale-up and optimization towards possible commercialization.

The agnion Heatpipe-Reformer—operating experiences and evaluation of fuel conversion and syngas composition

Fluidized bed gasification of solid fuels is considered as one of the core technologies for future sustainable energy supply. Whereas autothermal oxygen-driven gasification is applied in large-scale substitute natural gas (SNG) and Fischer–Tropsch (FT) plants or small-scale combined heat and power (CHP) plants, the allothermal steam-reforming process of the agnion Heatpipe-Reformer is designed for cost- and fuel-efficient syngas generation at small scales for distributed applications. The Heatpipe-Reformer's pressurized syngas generation provides a number of benefits for SNG, biomass to liquid (BTL) and CHP applications. A modified gas engine concept uses the pressurized and hydrogen-rich syngas for increased performance and tar tolerance at decreased capital expenses. Agnion has installed and operated a 500-kW thermal input pilot plant in Pfaffenhofen, Germany, over the last 2 years, showing stable operation over a variety of operating points. The syngas composition has been measured at values expected by thermodynamic models. An influence of the steam-to-fuel ratio and reformer temperature was observed. Tar and sulphur contents have been monitored and correlated to operation parameters, showing influences on stoichiometry and carbon conversion. The mass and energy streams of the plant were balanced. One of the main observations in the monitoring programme is the fact that syngas output, efficiency and syngas quality correlate to high values if the carbon conversion is high. Carbon conversion rates and cold gas efficiencies are comparably high in respect to today's processes, promising economic and fuel-efficient operation of the Heatpipe-Reformer applications.

A study on the optimum arrangement of prime movers in small scale microturbine-based CHP systems

Flexibility in connection methods as well as the capability to be stacked in parallel in order to reliably supply larger demands are amongst the significant features which have attracted considerable interest in microturbines for distributed generation applications. One of the leading applications of microturbines is operating as the prime mover of a Combined Heat and Power (CHP) system. There is an increasing trend towards CHP systems due to their high fuel consumption efficiency as a result of simultaneous production of heat and power. These systems deal more effectively with the environmental issues, since they emit less pollution in comparison with a separate production of the same amount of electricity and heat. In order to optimally benefit from combined heat and power generation, the proper sizing of prime movers is of paramount importance. We have developed a technical-economic approach to selecting the optimum arrangement of microturbines (i.e. number of units and nominal power) and planning its operational strategy in small scale combined heat and power systems (capacities up to 500 kW) for three modes of operation: one-way connection (OWC) mode, two-way connection (TWC) mode, and heat demand following (HDF) mode. The economic decision making is based on Net Present Worth (NPW) method.In addition to the common practice of using identical models, a novel method for stacking microturbines is studied and the results are compared. Performance characteristics of microturbines as well as economic parameters play a crucial role in the proposed sizing procedure; hence appropriate relations are presented to estimate the technical and economic parameters of the system and a detailed sensitivity analysis is conducted. A carbon tax legislation is being considered now in Australia and we have also included in our analysis the impact of this on the economics of the system.

Techno-economic Evaluations of Various Biomass CHP Technologies and Policy Measures Under Norwegian Conditions

This work deals with evaluations of different possible cost-effective small-scale combined heat and power (CHP) solutions based on biomass for the Norwegian market. Many CHP technologies and systems exist and can easily be proposed as candidates for introduction and/or widespread use in the Norwegian market. However, today they may be far from cost-effective given the current energy market and framework situation. These constraints can, however, change relatively fast. Hence, it is important to evaluate the feasibility of small-scale CHP technologies and systems in this perspective. What will the most promising small-scale CHP technologies based on biomass be in the near to medium term future? What are the limiting factors? What can be done to speed up the introduction of small-scale CHP solutions based on biomass in the Norwegian market? This work evaluates techno-economics of various CHP solutions based on biomass in the Norwegian market. Traditional financial indicators such as financial internal rate of return and net present value are used to assess the solutions. The methodology includes the following sequential steps: estimation of the economic production costs of various options for biomass CHP for power and heat generation and sorting these options in ascending order of costs to present the supply curve to meet the national target. Finally, the analysis includes various incentive schemes, feed-in tariffs/green certificates, investment based tax exemptions (8 years for each technology), prolonged tax exemption (+5 years for each technology), investment subsidies (in % for each technology) and low-interest loans (decided for each technology). Based on the evaluations, MSW backpressure turbine, biogas engine and industrial backpressure turbine are profitable without any subsidy under Norwegian framework conditions. With additional subsidy from grid deduction fee and green certificates, district heat ORC, district heat backpressure turbine and gasification with micro gas turbine are feasible with profitability of internal rate of return above 11%. Other gasification technologies are feasible under prevailing market conditions. In addition, a cost supply curve is generated for 10 years framework conditions based on the planned CHP installations.

Reliable overlay topology design for the smart microgrid network

Integration of the advances in information and communication technologies to the power grid technologies is changing the architecture and operation of the traditional grid, leading the grid to gradually evolve into a smart grid. Generation in the smart grid will be different than it is in today's grid, mainly due to the high penetration level of distributed renewable power generators. The distributed generator (DG) is favorable for its low transmission losses and low emissions. On the other hand, control of a high number of DGs is challenging. Almost a decade ago, microgrids were proposed to tackle the challenge of handling the growing number of DGs and fault isolation. A microgrid is a medium voltage or low voltage electrical power system that contains DGs, storage units, controllable loads, small-scale combined heat and power units, and an energy management system. In this article, we revisit the microgrid concept in light of survivability approaches borrowed from high-speed networks. We provide an analogy between survivability in metroaccess networks and reliability of the overlay topology for the smart microgrid network (SMGN). We develop the idea of resource sharing among smart microgrids for the sake of increased reliability. In our case, reliability corresponds to supplying power to the loads using the energy generated in the SMGN, without importing power from the utility grid. We provide a reliable overlay topology design scheme that maximizes the usage of renewable energy in the SMGN.

Dispatch strategy and model for hybrid photovoltaic and trigeneration power systems

The advent of small scale combined heat and power (CHP) systems has provided the opportunity for in-house power backup of residential-scale photovoltaic (PV) arrays. These hybrid systems enjoy a symbiotic relationship between components, but have large thermal energy wastes when operated to provide 100% of the electric load. In a novel hybrid system is proposed here of PV-trigeneration. In order to reduce waste from excess heat, an absorption chiller has been proposed to utilize the CHP-produced thermal energy for cooling of PV-CHP system. This complexity has brought forth entirely new levels of system dynamics and interaction that require numerical simulation in order to optimize system design. This paper introduces a dispatch strategy for such a system that accounts for electric, domestic hot water, space heating, and space cooling load categories. The dispatch strategy was simulated for a typical home in Vancouver and the results indicate an improvement in performance of over 50% available when a PV-CHP system also accounts for cooling. The dispatch strategy and simulation are to be used as a foundation for an optimization algorithm of such systems.

MOTOR BIOFUEL-POWERED CHP PLANTS—A STEP TOWARDS SUSTAINABLE DEVELOPMENT OF RURAL LITHUANIA

This paper focuses on the benefits that can be attained from the correct option of small-scale combined heat and power plant (CHP) relative to fuel availability and sphere of application. The analysis serves as a means of highlighting some of the owners of large-scale farms as well as holders of industrial greenhouses that influence the penetration of small-scale cogeneration plants running on bio-based liquid fuels. The identification of the main influencing factors and their weight is the first step towards the implementation of a more coherent strategy, if the EC (European Commission) and national energy authorities wish for new small-scale cogeneration technologies to have a future in the context of sustainable development of rural Lithuania. Against this background, this paper aims at presenting the technical, environmental and economic aspects of the possibilities of utilizing biodiesel, biodiesel-conventional diesel blends and rapeseed oil in combined heat and power production as an issue for further discussions regarding the formative breakthrough attitude towards a possible path of country's sustainable development.

Biomass from agriculture in small-scale combined heat and power plants – A comparative life cycle assessment

Abstract Biomass produced on farm land is a renewable fuel that can prove suitable for small-scale combined heat and power (CHP) plants in rural areas. However, it can still be questioned if biomass-based energy generation is a good environmental choice with regards to the impact on greenhouse gas emissions, and if there are negative consequences of using of agricultural land for other purposes than food production. In this study, a simplified life cycle assessment (LCA) was conducted over four scenarios for supply of the entire demand of power and heat of a rural village. Three of the scenarios are based on utilization of biomass in 100 kW (e) combined heat and power (CHP) systems and the fourth is based on fossil fuel in a large-scale plant. The biomass systems analyzed were based on 1) biogas production with ley as substrate and the biogas combusted in a microturbine, 2) gasification of willow chips and the product gas combusted in an IC-engine and 3) combustion of willow chips for a Stirling engine. The two first scenarios also require a straw boiler. The results show that the biomass-based scenarios reduce greenhouse gas emissions considerably compared to the scenario based on fossil fuel, but have higher acidifying emissions. Scenario 1 has by far the best performance with respect to global warming potential and the advantage of utilizing a byproduct and thus not occupying extra land. Scenario 2 and 3 require less primary energy and less fossil energy input than 1, but set-aside land for willow production must be available. The low electric efficiency of scenario 3 makes it an unsuitable option.

Modelling of biomass gasifier and microturbine for the olive oil industry

SUMMARY The olive oil industry generates several solid wastes. Among these residues are olive tree leaves, prunings, and dried olive pomace (orujillo) from the extraction process. These renewable energy sources can be used for heat and power production. The aim of this paper consists of modelling and simulation of a small-scale combined heat and power (CHP) plant (fuelled with olive industry wastes) incorporating a downdraft gasifier, gas cleaning and cooling subsystem, and a microturbine as the power generation unit. The gasifier was modelled with thermodynamic equilibrium calculations (fixed bed type, stratified and with an open top). This gasifier operates at atmospheric pressure with a reaction temperature about 800°C. Simulation results (biomass consumption, gasification efficiency, rated gas flow, calorific value, gas composition, etc.) are compared with a real gasification technology. The product gas obtained has a low heating value (4.8–5.0 MJ Nm−3) and the CHP system provides 30 kWe and 60 kWth. High system overall CHP efficiencies around 50% are achievable with such a system. The proposed system has been modelled using Cycle-Tempo software®. Copyright © 2010 John Wiley & Sons, Ltd.

Technological innovation systems for microgeneration in the UK and Germany – a functional analysis

This paper examines the deployment of microgeneration in Germany and the UK from a technological innovation systems (TIS) perspective. Based on the TIS functions approach, we condense supportive and obstructive factors and discuss the differences in the respective national setting for small-scale renewable and combined heat and power (CHP) technologies. The findings underline the relevance of legitimation and of institutional and financial support. High degrees of legitimacy were achieved in both the UK and Germany. In Germany, early institutional and financial support reduced uncertainty for new market entrants and consumers, and fuelled a self-reinforcing diffusion dynamic for small renewables. In the UK, by comparison, microgeneration enjoys little support. The paper concludes that distributed generation will not be successful without a more focussed and technology-oriented innovation policy.

Dynamic simulation of a solar-driven carbon dioxide transcritical power system for small scale combined heat and power production

Carbon dioxide is an environmental benign natural working fluid and has been proposed as a working media for a solar-driven power system In the current work, the dynamic performance of a small scal ...

Improved load control for a steam cycle combined heat and power plant

The problem of optimum load control of steam power plants has been dealt within many technical papers during the last decades. Deregulation of the power markets and close to the (bio-) fuel source thinking has lead to a trend of small scale combined heat and power plants. These plants are usually operated according to the heat demand and therefore they spend a significant time on partial load. The load control of such plants is in general done by partial arc control. This work applies a hybrid control strategy, which is a combination of partial arc control and sliding pressure control. The method achieves further improvement in performance at partial load. Hybrid control itself is not novel and has earlier been used on traditional coal-fired condensing plants. This has, to the author's knowledge, not earlier been applied on combined heat and power plants. The results show that there is a potential for improved electricity production at a significant part of the load range.