Conventional Combined Heat And Power Research Articles

Commercial building integrated energy system: sizing and energy-economic assessment

Abstract Integrated energy systems are one of the potential options for buildings that can reduce emission. In this research study, the energetic and economic performance of a micro-gas turbine combined heating and cooling plant coupled with a solar PV is analyzed for an office building in Iran. For each analysis, two different scenarios have been performed. System sizing parameters defined in a way that renewable to fossil fuel share is correlated to plant performance and economy. To model the studied system, a time-dependent method is used, which is the inherent characteristic of renewable energies. The renewable energies used here are solar heaters and solar panels. Contours of Net Present Value (NPV) are evaluated as a function of solar heating share and different economic parameters. In addition, optimal system sizing for a typical building is obtained and the results are provided. Effect of various major parameters shows that under the current condition and despite the supportive incentive for renewable energies, strategies and plans even without solar energy are not economically viable due to the high discount rates. In addition, results provide that, in reasonable and normal discount rate, fuel and grid electricity prices, governmental subsidization for conventional combined heat, and power (CHP) and combined cooling, heat, and power(CCHP) is not necessary, and only in this condition solar electricity selling price (i.e. governmental support program) is effective to increase renewable penetration. The results show that if the interest rate is less than 5%, the NPV becomes positive. Also, when the electricity price reaches $0.07/kWh or higher, the NPV becomes positive.

Performance assessment of new energy-saving schemes for combined heat and power plants

A new energy-saving scheme is proposed for the combined heat and power (CHP) retrofitting in a coal-fired power plant by combining the high back-pressure (HBP), the absorption heat pump (AHP) and the absorption heat exchanger (AHE). Compared to the conventional CHP retrofitting scheme, the proposed new scheme reduces the exergy loss during heat transfer and the waste heat to environment, enabling more power output with the same heat supply amount. When the proposed new scheme is effectively applied in dual unit systems by system integration, the additional power loss caused by the off-design condition of the low-pressure turbine could be reduced or even eliminated, which further improves the overall performance. Detailed thermodynamic, exergy and techno-economic analyses are conducted to compare the proposed new scheme with the conventional scheme in a 2 × 350 MWe coal-fired power plant. With the same heat supply amount of 237.56 MWth, the power efficiency is increased by 3.55% in total. Techno-economic analysis results show that the dynamic payback period (DPP) to offset the total investment increase of the proposed new scheme is 1.59 years, and the net present value (NPV) increase for a 25-year lifespan can reach 48,805 thousand USD.

Simulation study on a novel solar aided combined heat and power system for heat-power decoupling

To guarantee the space heating in the heating season, conventional combined heat and power (CHP) plants operate in a heat-controlled operation mode, resulting in restricted peak-shaving ability (PSA). To improve the CHP plant’s PSA, a novel solar aided CHP (SA-CHP) system is proposed and simulated in this paper. In the new system, solar heat could be flexibly used to generate power or to supply heat according to the heating and power demands, thereby realizing the heat-power decoupling. A set of models for the SA-CHP system is developed and validated. The PSA, the standard coal consumption (SCC) and the techno-economic performances of a 330 MWe SA-CHP system are comprehensively analyzed in this paper. The results show that the SA-CHP system can significantly improve (up to double) the PSA compared with the CHP plant under the same rated heating power. The feasible operation region area of the SA-CHP system is 74.7% larger than that of the CHP plant. The annual SCC of the SA-CHP system are 17378.23 t less than that of the CHP plant. The net annual revenue of the SA-CHP system is $2.24 M. Besides, techno-economic performances of SA-CHP systems with two different heat storage systems are compared.

Combined heat and power operational modes for increased product flexibility in a waste incineration plant

The expected strong expansion of wind power may cause challenges for the electricity system in terms of grid stability, power balance, and increased electricity price volatility. This paper analyses how the new market conditions impact the operational pattern and revenue of a combined heat and power (CHP) plant. The work focuses on product flexibility that enables varied ratios between products; and thermal flexibility, to shift load in time given the differing timescales of heat and power demand. Product flexibility is given by five operational modes: conventional CHP, heat-only, CHP plus frequency response, condensing, and condensing plus frequency response. Optimization and process modeling are combined to study the plant dispatch in current and future electricity market scenarios and with thermal flexibility. The results indicate that load-shifting of heat generation together with condensing operation can increase revenue up to 4.5 M€ and plant utilization up to 100% for a 50 MWel waste-fired plant; but requires a thermal energy storage to meet hourly heat demand. The electricity price profile impacts both the revenue and operational patterns, with low-price periods favoring increased heat generation and frequency response delivery. High average electricity price and price volatility results in increased profitability of product and thermal flexibility.

District Heating Technologies: Is it Chance for CHP Plants in Variable and Competitive Operation Conditions?

District heating system with power generation is integrated in the electricity system since combined heat and power (CHP) plants are used for heat supply. Nowadays, the changes happen in the electricity system and conventional CHP plant operation. They are caused by wide integration of renewable energy sources (RES) in energy production process, feed-in tariffs for RES, the implementation of market mechanisms, and the incremented requirement in energy efficiency and flexibility of power plants. This creates new opportunities and conditions for district heating (DH) and power system cooperation though the use of DH flexible technologies, i.e., power-to-heat (P2H) technologies (electric boilers (EB) and heat pumps). The use of P2H technologies is limited and they are not costs-efficient due to electricity tariff formed components. Two Targets of EB use at power plant are evaluated, omitting these components, to show the usefulness and significant of these technologies for conventional generation.

Investigation of Subsystems for Combination into a SOFC-Based CCHP System

This paper presents the development of the subsystems for stationary biogas powered solid oxide fuel cell (SOFC)-based combined cooling, heat and power (CCHP). For certain applications, such as buildings, a heat-driven operation mode leads to low operating hours per year for conventional combined heat and power (CHP) systems due to the low heat demand during the summer season. The objectives of this study are the evaluation of an adsorber, a steam reformer, a SOFC, and an absorption chiller (AC). Biogas, however, contains impurities in the form of hydrogen sulfide (H2S), hydrogen chloride (HCl), and siloxanes in different concentrations, which have a negative effect on the performance and durability of the SOFC and, in the case of H2S, also on the catalyst of the steam reformer. This paper describes different experimental sections: (i) the biogas treatment with its main focus on H2S separation and steam reforming, (ii) the setup and start-up of a 10 cell SOFC stack, and (iii) test runs with an AC using a mixture of NH3 (ammonia)/H2O (water). The components required for the engineering process of the subsystem's structure are described in detail and possible options for system design are explained. The evaluation is the basis to reveal the improvement potentials, which have to be considered in future product developments. This paper aims at comparing experimental data of the test rigs to develop an understanding of the requirements for a stable and continuous operation of a SOFC-based CCHP operated by biogas.

Integrated Dispatch Model for Combined Heat and Power Plant With Phase-Change Thermal Energy Storage Considering Heat Transfer Process

Combined heat and power (CHP), with its limited flexibility, is one of the leading causes for the curtailment problem of variable renewable energy source (VRES) in Northern China. To increase the flexibility for CHP, thermal energy storage (TES) is considered to be an effective solution, and a phase-change TES demonstration pilot project is now being constructed in Northern China. Almost all the previous studies have modeled the TES device without considering the heat transfer process, which is a main constraint in thermal system analysis. Thus, in this contribution, we consider the heat transfer process for the phase-change TES device installed in a CHP plant based on the steam's three-stage heat transfer model and the entransy dissipation-based thermal resistance theory. An integrated electrical-thermal dispatch model concerning conventional thermal units, VRESs, and CHP units with phase-change TES device is given, and an iteration method for solving this nonlinear programming problem is proposed. Case studies show that it is vital to consider the heat transfer process in the modeling of CHP plant with phase-change TES device, and it has significant influence on the flexibility that the TES device can provide when the working conditions vary.

Selection of a Combined Heat and Power (CHP), and CHP Generation Compared to Buying of Electrical Power from the National Grid and Separate Thermal Heat Production

In this work, Combined Heat and Power (CHP) is critically discussed and its application analytically compared with alternative energy source.CHP efficiency was first compared with the conventional generation and realised that, for equivalent heat and power production, CHP exhibits a higher efficiency than conventional generation. For example, energy input of 215J and 170J for Conventional generation and CHP respectively produces equal amounts of heat and power with CHP having efficiency of 76.5% which is 16.5% more efficient than the conventional type with 60%. Factors influencing the choice of a CHP plant such as financial considerations, Environmental and Compliance considerations, Site Specific considerations and Technical parameters Considerations are vastly discussed. Since the choice of a CHP and its application depends on the type of the prime mover, different types of the CHPs and their applications were then discussed to understand their working principles and the choice of the fuel used. Two typical case scenarios were analytically compared to look into the most economical way of acquiring heat and power for a plant. Cogeneration (A) was compared with buying of electrical power from the national grid and at the same time producing thermal energy in the plant using natural gas fired boiler(B). From cost analysis of the case scenarios, it is confirmed that cogeneration (A) is the most economical aspect compared to alternative B. Finally, the advantages and the disadvantages of a CHP are explored.

Multi-criteria analysis of district heating system operation strategy

The contemporary energy system is faced with new challenges on the energy market. Both the rising share of renewable-based electricity (characterised by intermittent production) and increasing energy efficiency in buildings induce a reconsideration of the traditional role of conventional power plants coupled with district heating systems along with its impact on the energy system. Moreover, the price of electricity determined by the merit-order system additionally decreases the load factor of such plants, making them less competitive or even inflicting financial loss in operation. Research presented in this paper focuses on a novel approach towards conventional combined heat and power (CHP) plants coupled with district heating systems. It involves an analysis of dynamical performances of the district heating system – capability of energy accumulation and thermal inertia – in order to assess its potential to become part of ancillary services. It is concluded that the district heating system, i.e. network of pipelines can be considered as dynamical thermal energy storage in which excess energy can be stored during operation of the CHP plant. A comprehensive analysis of dynamic behaviour of the district heating system has been performed by means of a mathematical model developed as a part of this research. The model is implemented on a theoretical case consisting of a simplified district heating system with three final users and the pipeline network of 9000m in length. The simulation has shown that the storage capacity of the network depends on the thermal load in the network and in such circumstances specific thermal capacity of the network amounts to 10.1Wh/(km). If the thermal load is decreased by 13% at the peak the accumulation capability is decreased by 40%. Moreover, the thermal capacity of the network increases up to 13.7Wh/(km) as the pipeline length declines to 1000m which is characteristic of densely populated areas. The capability of energy accumulation is explored for different parameters, such as: external temperature, distance of the network, supply water temperature etc. It is shown that distance of final users from CHP plant has certain impact on the operation strategy as well. Final users closer to the CHP plant determines operation strategy in the case of short-term disturbances in heat supply, while the farther ones in the case of long-term disturbances.

Electricity Market Liberalisation and Flexibility of Conventional Generation to Balance Intermittent Renewable Energy – Is It Possible to Stay Competitive?

Abstract Intermittent generation (solar PV and wind energy) integration in power production portfolio as well as electricity price fluctuations have changed the running manner of conventional combined heat and power (CHP) plants: the shift from base load operation to running in cyclic modes. These cogeneration power plants are not adapted to new running conditions. The level of CHP plant flexibility should be improved to operate profitably and efficiently from both technical and fuel usage point of view. There are different ways to increase the flexibility of power plants. Before any improvements, the situation at power plants should be evaluated and the weakest points defined. In this publication, such measures are presented on Riga CHP-2 plant example: installation of heat storage tank; extension of operation rang; acceleration of start-ups.

Renewable energy from biogas with reduced carbon dioxide footprint: Implications of applying different plant configurations and operating pressures

Renewable energy from biogas has the potential to decarbonise energy systems. For example, biomethane derived from raw biogas may partially displace fossil fuels in the transportation sector. The implemented renewable energy actually decarbonises energy systems only if its life cycle CO2 footprint is lower than that of displaced conventional technologies, which is sometimes uncertain. Therefore, this study has been undertaken to review and synthesise knowledge available in the academic literature on the CO2 footprint of renewable energy from biogas. The typical life cycle CO2 footprint of biogas reported in literature is between 50 and 450kgCO2/MWhel. The review analyses three phases associated with biogas: (i) biomass production, (ii) biomass-to-biogas conversion, and (iii) biogas end use. It is found that remarkable CO2 footprint reduction can be achieved by innovating the biomass-to-biogas phase through limiting the amount of CO2 liberated to biogas. The mechanism for reducing CO2 footprint is proposed and suitable solutions are discussed and evaluated. The literature review is followed by a case study that improves the practical understanding of CO2 footprint reduction potentials. In the case study anaerobic digestion (AD) and pressurised anaerobic digestion (PAD) are compared in terms of their biomethane, power and heat generations, and CO2 emissions. Six plant configurations involving AD, biogas upgrading and combined heat and power (CHP) generation are modelled and simulated. The results show that due to the methane enrichment in biogas (94% CH4 at the self-sustained digester pressure of 5MPa) CO2 footprint is reduced. It is revealed that PAD based biogas plants may generate high purity biomethane with the extremely low direct CO2 footprint of about 13kgCO2/MWhf which contrasts with conventional CHP systems achieving about direct CO2 footprint of 700kgCO2/MWhel. The study also explores the fundamentals of PAD which is one of emerging biogas technologies.*Corresponding author.

Grid-interactivity of a Solar Combined Heat and Power District Heating System

Abstract In this paper the performances regarding grid-interactivity of a conventional combined heat and power (CHP) district heating system and a solar CHP district heating system – with decentralized solar thermal systems and heat storages in the buildings – are investigated and compared for a future scenario of the energy system. For this, simulations were carried out and the subsequent results evaluated applying a recently introduced method (load-grid matching coefficient) for quantifying grid-interactivity. It is shown that the solar CHP district heating system has better grid-interactivity compared with the conventional CHP district heating system. It is also quantitatively and visually shown that there is still potential to improve the grid-interactivity of both concepts by, for instance, applying more sophisticated control strategies. Furthermore, it is shown that in the summer period the CHP unit is not required for long periods of time. This allows temporal decommissioning of the district heating station and the district heating grid and thus an avoidance of the distribution losses which are relatively high when compared with the actual heat used during this period.

Study on a heat recovery system for the thermal power plant utilizing air cooling island

A new heat recovery system for CHP (combined heat and power) systems named HRU (heat recovery unit) is presented, which could recover the low grade heat of exhausted steam from the turbine at the thermal power plant directly. Heat recovery of exhausted steam is often accomplished by recovering the heat of cooling water in current systems. Therefore, two processes of heat transfer is needed at least. However, exhausted steam could be condensed in the evaporator of HRU directly, which reduce one process of heat transfer. A special evaporator is designed condense the exhausted steam directly. Simulated results are compared to experiments, which could include the calculation of heat transfer coefficients of different parts of HRU. It is found that about 25Mw of exhausted steam is recovered by this system. HRU could be promising for conventional CHP systems, which could increase the total energy efficiency obviously and enlarge the heating capacity of a built CHP system.

A domestic CHP system with hybrid electrical energy storage

CHP (combined heat and power) is widely regarded as one of the most promising technologies to resolve energy-related problems, such as primary energy saving, emission reducing etc. Domestic CHP is the energy system applied to the household sector to supply both electric and heat energy to users. Due to the dissimilar characteristics between household electricity and heat demands, conventional off-grid CHP systems may not satisfy both of the demands simultaneously. This study developed a domestic CHP system in which an engine-based CHP fuelled by biofuels was integrated with a hybrid electric energy storage system and operated under FEL (following electric load) energy management strategy. Experimental tests validate the feasibility of this application and the results show that the system can satisfy the fluctuant energy demands in a domestic dwelling. The overall energy efficiency has been improved by 47.86% compared to conventional CHP.

The cost of reducing CO 2 emissions–methodological approach, illustrated by the Danish energy plan

Within the last years development of greenhouse gas reduction strategies has become a vital part of both international and national planning. When developing energy and environmental strategies it is highly relevant to gain an insight into how to prioritise among various technology options available. One of the tools available for this purpose is the construction of cost-reduction curves, relating the marginal cost of CO 2 reduction and the quantity of the reduced emission to specific technology options. This paper outlines different approaches for establishing cost-reduction curves for CO 2 emissions, and a case based on the Danish Energy21-plan is analysed illustrating one of these approaches. The analysis is carried out from the broad perspective of the overall energy system, but with the main emphasis on renewable energy technologies, especially the use of wind energy and biomass in the Danish system. The paper concludes that the construction of reduction cost curves is helpful in two ways: (1) to decompose existing energy strategies (scenarios) into individual reduction options and (2) to compare new options with an existing strategy. In both cases the reduction cost curve highlights those technological options that have the highest reduction potential and the lowest marginal costs, and vice versa. Based on the case of the Danish energy plan, the results of the analyses show that a number of reduction options with significant reduction potentials are available at relatively low marginal costs. Among others can be mentioned increased use of combined heat and power (CHP), substituting conventional coal-fired CHP plants with biomass ones and the development of offshore wind turbines.

Commercialisation of fuel cells for combined heat and power (CHP) application

Combined heat and power or co-generation is an ideal application for the fuel cell. This paper has been written from the perspective of a current designer, builder and operator of small-scale (i.e. sub 1 MW) combined heat and power. Conventional current CHP is described together with typical applications. The perceived advantages of fuel cells are also discussed together with the potential for fuel cells opening up currently unapproachable markets. Various matters relevant to the application of fuel cells are also described including: initial and life costs for fuel cells CHP systems; maintenance requirements, security of supply requirements. In addition to these commercial aspects, technical issues including interfacing to building systems, control, protection, monitoring, operating procedures and performance are also discussed.