Role of a district-heating network as a user of waste-heat supply from various sources – the case of Göteborg

District-heating (DH) networks can utilise heat that would otherwise be of limited use. This study analyses a municipal DH system, which uses waste heat from industries and waste incineration as base suppliers of heat and is currently investing in a natural-gas fired combined heat-and-power (CHP) plant. An important assumption in this study is of the establishment of an integrated European electricity-market, which means higher electricity prices than are traditional in Sweden. The study shows that there is space in the DH system for all three energy carriers; heat from industries, waste incineration and CHP plants. The new CHP plant replaces mainly other heat sources, i.e., hot water boilers and heat pumps. The new CHP plant’s operating time is strongly dependent on the electricity price.     

燃气轮机热电联供系统性能评估案例

对某供热厂的燃气轮机热电联供系统进行了研究,将燃煤分产和燃气分产进行了全方面的比较,其性能评价对合理应用CHP有重要作用。在热电分产的节能性方面,以燃气-蒸汽联合循环电厂和燃气锅炉作为比较的基准线,全年平均节能率为8.9%;在运行经济性方面,燃气轮机系统与燃煤锅炉分产相比,每年节省46万元,与燃气锅炉分产相比,每年节省182万元,且节省费用随着电价的增加而增加,随着气价的增加而减少。另外,与燃煤锅炉分产相比时,还随着煤价的增加而增加;在排放物方面,燃气轮机联供系统与燃煤分产和燃气分产对比,NOx减排量并不显著,而其余排放物有明显地减少。燃气轮机系统与燃煤以及燃气锅炉相比具有一定的优越性,在设计合理的情况下具有良好的前景。     

Implementation strategy for small CHP-plants in a competitive market: the case of Lithuania

Within five years from now, Lithuania is going to close down Ignalina, the only nuclear-power plant in the country. Since Ignalina generates more than 75% of the Lithuanian electricity production, new generation capacities are needed. Traditional steam-turbines, fuelled with fossil fuels, would mean further imports of fuel as well as a rise in CO₂ emissions. At the same time, several small district-heating companies one suffering from high heating-prices. Typically, the price in small towns is 20–50% higher than the price in large urban areas. Consequently, alternative strategies should be considered. This article analyses the conditions for one such strategy, namely the replacement of boilers in the existing district-heating supplies with combined heat-and-power production (CHP). Compared with new power stations, fuel can be saved and CO₂-emissions reduced. Also this strategy can be used to level the difference between low heating prices in the large urban areas and high prices in small towns and villages.     

The role of policy instruments for promoting combined heat and power production with low CO2 emissions in district heating systems

Policy instruments clearly influence the choice of production technologies and fuels in large energy systems, including district heating networks. Current Swedish policy instruments aim at promoting the use of biofuel in district heating systems, and at promoting electric power generation from renewable energy sources. However, there is increasing pressure to harmonize energy policy instruments within the EU. In addition, natural gas based combined cycle technology has emerged as the technology of choice in the power generation sector in the EU. This study aims at exploring the role of policy instruments for promoting the use of low CO₂ emissions fuels in high performance combined heat and power systems in the district heating sector. The paper presents the results of a case study for a Swedish district heating network where new large size natural gas combined cycle (NGCC) combined heat and power (CHP) is being built. Given the aim of current Swedish energy policy, it is assumed that it could be of interest in the future to integrate a biofuel gasifier to the CHP plant and co‐fire the gasified biofuel in the gas turbine unit, thereby reducing usage of fossil fuel. The goals of the study are to evaluate which policy instruments promote construction of the planned NGCC CHP unit, the technical performance of an integrated biofuelled pressurized gasifier with or without dryer on plant site, and which combination of policy instruments promote integration of a biofuel gasifier to the planned CHP unit. The power plant simulation program GateCycle was used for plant performance evaluation. The results show that current Swedish energy policy instruments favour investing in the NGCC CHP unit. The corresponding cost of electricity (COE) from the NGCC CHP unit is estimated at 253 SEK MWh^?1, which is lower than the reference power price of 284 SEK MWh^?1. Investing in the NGCC CHP unit is also shown to be attractive if a CO₂ trading system is implemented. If the value of tradable emission permits (TEP) in such as system is 250 SEK tonne^?1, COE is 353 SEK MWh^?1 compared to the reference power price of 384 SEK MWh^?1. It is possible to integrate a pressurized biofuel gasifier to the NGCC CHP plant without any major re‐design of the combined cycle provided that the maximum degree of co‐firing is limited to 27–38% (energy basis) product gas, depending on the design of the gasifier system. There are many parameters that affect the economic performance of an integrated biofuel gasifier for product gas co‐firing of a NGCC CHP plant. The premium value of the co‐generated renewable electricity and the value of TEPs are very important parameters. Assuming a future CO₂ trading system with a TEP value of 250 SEK tonne^?1 and a premium value of renewable electricity of 200 SEK MWh^?1 COE from a CHP plant with an integrated biofuelled gasifier could be 336 SEK MWh^?1, which is lower than both the reference market electric power price and COE for the plant operating on natural gas alone. Copyright © 2005 John Wiley & Sons, Ltd.     

Gas turbines in district heating combined heat and power systems: influence of performance on heating costs and emissions

Much work is currently focussed on identifying economically and environmentally optimal strategies for increasing gas turbine based combined heat and power (CHP). In many such studies, only a few fixed parameters are used to describe the CHP plant. These are typically total and electrical efficiencies, investment and running costs, minimum and maximum acceptable size, and minimum acceptable part-load. However, for gas turbine based systems these characteristics are clearly functions of the operating conditions, especially for part-load operation. This study examines the effects of varying performance of the gas turbine on the overall heat production costs and CO₂ emissions of a medium sized community district heating plant. Both single and double-shaft engines are considered in the study. The results show that the assumption of constant efficiencies for all operating conditions leads to an overestimation of the optimal CHP plant size, thereby underestimating the heat production costs and overestimating the CO₂ emissions of the plant. The results also show marked differences according to the type of gas turbine used and part-load operating strategy adopted. In particular, the paper discusses the part-load operating difficulties for CHP plants running gas turbines equipped with low emissions burners.     

An economic analysis of a clean-development mechanism project: a case introducing a natural gas-fired combined heat-and-power facility in a Chinese industrial area

A case study of the installation of a combined heat-and-power (CHP) facility as a potential clean-development mechanism (CDM) project in an industrial area in China was undertaken using a newly developed mathematical programming model. The model was developed to optimize the installation capacity of the CHP under constraints on electricity-and-heat supply and demand balances, etc. Energy cost and emissions of CO₂ and SO_x were also calculated with the model. Parametric surveys were carried out for natural gas and CHP capital prices, which inherently include large uncertainties; the resultant calculations revealed that in some cases the CHP would be voluntarily (i.e., without financial support from an investor's country) introduced in China, and that in some cases the CHP could be certified as a CDM project with financial support by the investor country. In some combinations of parameters, the value of CO₂ emission reduction credit offsets the CHP capital price, although shared allocation of economic profits yielded by the CDM project between the two countries greatly mitigated the restraints on the project, while at the same time qualifying it for the CDM.     

Domestic-scale combined heat-and-power system incorporating a heat pump: analysis of a prototype plant

This paper introduces an innovative domestic scale combined heat-and-power plant (CHP), incorporating a heat pump (HP) for single-dwelling applications. The incorporation of a heat pump enhances the flexibility of a domestic scale CHP plant to satisfy domestic energy demand economically. The development, testing and subsequent thermodynamic analysis of the prototype plant are presented. First law thermodynamic analysis of experimental results is compared to equivalent second law analysis. Analysis of experimental results practically demonstrates that heat-pump incorporation satisfies extremely low domestic electrical requirements economically, whilst delivering relatively high thermal output, without resorting to electricity export.     

Long-term optimization of cogeneration systems in a competitive market environment

A tool for long-term optimization of cogeneration systems is developed that is based on mixed integer linear-programming and Lagrangian relaxation. We use a general approach without heuristics to solve the optimization problem of the unit commitment problem and load dispatch. The possibility to buy and sell electric power at a spot market is considered as well as the possibility to provide secondary reserve. The tool has been tested on a demonstration system based on an existing combined heat-and-power (CHP) system with extraction-condensing steam turbines, gas turbines, boilers for heat production and district-heating networks. The key feature of the model for obtaining solutions within reasonable times is a suitable division of the whole optimization period into overlapping sub-periods. Using Lagrangian relaxation, the tool can be applied to large CHP systems. For the demonstration model, almost optimal solutions were found.     

Testing activity‐based costing to large‐scale combined heat and power plant using bioenergy

This paper deals with the energy production and economics of a large‐scale biomass‐based combined heat and power (CHP) plant. An activity‐based costing model was developed for estimating the production costs of the heat and power of the bio‐CHP. A 100 MW plant (58 MW heat, 29 MW electricity) was used as reference. The production process was divided into four stages: fuel handling, fluidized bed boiler, turbine plant, and flue gas cleaning. The boiler accounted for close to 50% of the production costs. The interest rates and the utilization rate of the CHP had a significant effect on the profitability. We found that below 4000–4500 h per year utilization, the electricity production turned unprofitable. However, the heat production remained profitable with high interest rate (10%) and a low utilization rate (4000 h). The profitability also depended on the type of biomass used. We found that, e.g. with moderate interest rates and high utilization rate of the plant, the bio‐CHP plant could afford wood and Reed canary grass as fuel sources. Copyright © 2013 John Wiley & Sons, Ltd.     

某热电厂实施冷热电联产的节能分析

通过对热电联产冷分产及冷热电联产能源消耗的计算分析比较,进一步论述在热电厂热电联产基础上发展冷热电联产的可行性和合理性,结合实例说明发展冷热电联产所产生的经济性、节能性和环保性,并为其他热电厂的节能改造提出建议,     

Exergetic comparison of efficiency indicators for combined heat and power (CHP)

Legislative regulations in favor of combined heat and power (CHP) production have been implemented in many countries. Although these regulations put different emphasis on power production vs. process heat production, they are based on energy quantities and not on exergy. In order to analyze and compare the exergetic consequences of the various legislations, a relative avoided irreversibility (RAI) is defined. This can be regarded as the exergy loss that is avoided when reference plants with separate production are replaced by an actual CHP plant. Some series of industrial and district heating CHP plants, under varying operational conditions, are used as test cases. It is seen that some, but not all, CHP cases are exergetically beneficial to separate generation. Comparison with the RAI allows a quantitative assessment of the various performance indicators. It is seen that exergetic improvements were only captured to a limited degree by the various energy-based efficiency indicators. Some legislatively defined indicators even appear to discourage thermodynamic improvements.     

Analysis of advanced energy chain typologies

A method for estimating the effectiveness and CO₂ emissions of advanced energy conversion systems from primary to final energy is presented. A traditional condensing power plant for electricity production and a fuel boiler for heat production based on natural gas were used as the reference system. Several potentially better energy chains were analysed including CHP, tri‐generation, heat pumps and efficiency improvements in final energy use. All above solutions could provide clear reductions in primary energy use and emissions, in most cases tens of per cents, but the results are sensitive to operational conditions. In a heat pump system, the primary energy savings are considerable but emission reductions may turn out to be marginal or even negative whereas in co‐generation the emission reductions are higher than energy savings. Striving for high conversion efficiencies would ensure sustained benefits from the advanced energy chain typologies over the reference system even in the less favourable cases. Copyright © 2007 John Wiley & Sons, Ltd.     

Techno-economic analysis of using corn stover to supply heat and power to a corn ethanol plant – Part 2: Cost of heat and power generation systems

This paper presents a techno-economic analysis of corn stover fired process heating (PH) and the combined heat and power (CHP) generation systems for a typical corn ethanol plant (ethanol production capacity of 170 dam³). Discounted cash flow method was used to estimate both the capital and operating costs of each system and compared with the existing natural gas fired heating system. Environmental impact assessment of using corn stover, coal and natural gas in the heat and/or power generation systems was also evaluated. Coal fired process heating (PH) system had the lowest annual operating cost due to the low fuel cost, but had the highest environmental and human toxicity impacts. The proposed combined heat and power (CHP) generation system required about 137 Gg of corn stover to generate 9.5 MW of electricity and 52.3 MW of process heat with an overall CHP efficiency of 83.3%. Stover fired CHP system would generate an annual savings of 3.6 M$ with an payback period of 6 y. Economics of the coal fired CHP system was very attractive compared to the stover fired CHP system due to lower fuel cost. But the greenhouse gas emissions per Mg of fuel for the coal fired CHP system was 32 times higher than that of stover fired CHP system. Corn stover fired heat and power generation system for a corn ethanol plant can improve the net energy balance and add environmental benefits to the corn to ethanol biorefinery.     

Energetic and exergetic analysis of steam production for the extraction of coniferous essential oils

Bioenergy production is optimal when the energy production process is both efficient and benefits from local resources. Energetic and exergetic analyses are applied to highlight efficiency differences between small-size systems that are based on the co-generation of heating and power (CHP) versus the co-generation of heating and power with steam production (CHP-S). Both systems use the Organic fluid Rankine Cycle (ORC).The recovery of heat from flue gases is considered to be a way of increasing energy efficiency. In the CHP-S case, steam (at low pressure) is used to extract essential oils from fresh twigs and needles of coniferous trees throughout a steam distillation process. When the systems work at a thermal combustion power of 1350 kW, energetic analysis shows that the energy efficiency of the CHP-S plant (89.4%) is higher than that of the CHP plant (77.9%). Exergetic analysis shows that the efficiency of the CHP-S plant is 2.2% higher than that of the CHP plant.     

Biomass gasification in district heating systems – The effect of economic energy policies

Biomass gasification is considered a key technology in reaching targets for renewable energy and CO₂ emissions reduction. This study evaluates policy instruments affecting the profitability of biomass gasification applications integrated in a Swedish district heating (DH) system for the medium-term future (around year 2025). Two polygeneration applications based on gasification technology are considered in this paper: (1) a biorefinery plant co-producing synthetic natural gas (SNG) and district heat; (2) a combined heat and power (CHP) plant using integrated gasification combined cycle technology. Using an optimisation model we identify the levels of policy support, here assumed to be in the form of tradable certificates, required to make biofuel production competitive to biomass based electricity generation under various energy market conditions. Similarly, the tradable green electricity certificate levels necessary to make gasification based electricity generation competitive to conventional steam cycle technology, are identified. The results show that in order for investment in the SNG biorefinery to be competitive to investment in electricity production in the DH system, biofuel certificates in the range of 24–42 EUR/MWh are needed. Electricity certificates are not a prerequisite for investment in gasification based CHP to be competitive to investment in conventional steam cycle CHP, given sufficiently high electricity prices. While the required biofuel policy support is relatively insensitive to variations in capital cost, the required electricity certificates show high sensitivity to variations in investment costs. It is concluded that the large capital commitment and strong dependency on policy instruments makes it necessary that DH suppliers believe in the long-sightedness of future support policies, in order for investments in large-scale biomass gasification in DH systems to be realised.     

Cogeneration plant in a pasta factory: Energy saving and environmental benefit

Italy produces approximately 4,520,000 tons of pasta annually, which is about 67% of its total productive potential. As factories need electric and thermal energy simultaneously, combined heat and power (CHP) systems are the most suitable. This paper describes a feasibility study of a CHP plant in a pasta factory in Italy while analyzing energy saving and environmental benefits. Commercially available CHP systems suitable for the power range of energy demand in pasta production use reciprocating engines or gas turbines. This study demonstrates how their use can reduce both energy costs and CO₂ equivalent greenhouse gas emission in the environment. An economic analysis was performed following the methodology set out by Italian National Agency for Technology, Energy and Environment (ENEA) based on a discounted cash flow (DCF) method called “Valore Attuale Netto” (VAN), which uses a cash flow based on the saving of energy when using different energy processes.     

System behaviour of compressed-air energy-storage in Denmark with a high penetration of renewable energy sources

In 2005, wind power supplied 19% of the 36 TWh annual electricity demand in Denmark, while 50% was produced at combined heat-and-power plants (CHP). The installed wind-turbine capacity in Western Denmark exceeds the local demand at certain points in time. So far, excess production has been exported to neighbouring countries. However, plans to expand wind power both in Denmark and in its neighbouring countries could restrain the export option and create transmission congestion challenges. This results in a need to increase the flexibility of the local electricity-system. Compressed-Air Energy-Storage (CAES) has been proposed as a potential solution for levelling fluctuating wind-power production and maintaining a system balance. This paper analyses the energy-balance effects of adding CAES to the Western Danish energy-system. Results show that even with an unlimited CAES plant capacity, excess power production is not eliminated because of the high percentage of CHP production. The optimal wind-power penetration for maximum CAES operation is found to be around 55%. The minimum storage size for CAES to fully eliminate condensing power plants operation in the optimized system is over 500 GWh, which corresponds to a cavern volume of around 234 Mm³ at an average pressure of 60 bar. Such a storage size would be technically and economically unfeasible. The analysis, however, did not include the potential role of a CAES plant in regulating the power services.     

Cost effectiveness of decentralized energy supply systems taking solar and wind utilization plants into account

In this article, results are presented of annual simulations of a decentralized (regional) plant for the power and heat supply of a residential complex. This complex consists of four houses with 40 flats all in all. The annual power consumption of the complex is 157 MWh and the heat requirement is 325 MWh. The concrete dynamics of the energy demands over the year is taken into consideration. The energy supply system is composed of a power-controlled combined heat and power (CHP) plant (55 kW), a photovoltaic plant (PV array or PV plant) array for power generation as well as a field of solar thermal collectors with a short-term accumulator for water heating and a long-term accumulator for supplying heat for domestic heating purposes. Simulation results demonstrate that synergetic effects result from the combination of a CHP plant with wind power and PV plants of varying sizes, which have an effect on the cost effectiveness of the plant as a whole with the different dynamics of energy sources (wind and solar energies) and of the consumption of power and heat being the decisive factors. The power deficits of wind power and PV plants are compensated through the application of a natural gas-operated CHP plant. In almost all variants, the demand for fossil energy carriers is distinctly less than in conventional energy supply plants.     

Optimal day-ahead energy planning of multi-energy microgrids considering energy storage and demand response

Due to the environmental and economic advantages of combined heat and power (CHP) units, their use in power grids has expanded. The entry of CHP into power systems increases the complexity of the economic power flow problem. This complexity is due to the introduction of multiple constraints into problem. A mere electricity supply is not optimal in today's networks, and energies such as heat, power and gas must be planned and managed simultaneously as an energy hub. Therefore, in this paper, an intelligent multi-energy microgrid (MG) consisting of power generation units, CHP units and gas units is modeled for day-ahead energy management (DAEM). The economic distribution problem focuses on the amount of power generation, heat and gas of the units in the system. In contrast, the total generation cost of the system is minimized, and all the equality and inequality constraints of the problem are observed. The proposed microgrid includes various energy-dependent equipment such as CHP units, gas boilers, electricity-to-gas units, power and heat storage units and electric heat pumps. Also, price-based load management was included to reduce costs due to the transfer of information between the consumer and the generator in the context of smartization. Since the above problem is difficult to solve due to various constraints and decision parameters, a newly developed optimization method based on water flows was proposed. The simple movement of water flows on the ground is efficient and optimal and always follows the shortest and fastest path to reach the deepest point. In the proposed algorithm, simple movements of water in routing, a change of direction and even the creation of rapids and vortices were simulated as various mathematical operators. Finally, the proposed model and method were examined in different scenarios. The numerical outcomes demonstrated that, the proposed modeling framework is superior to hub-based multi-carrier microgrid models in terms of power system security. The sensitivity of operational expenses to changes in initial values of energy storage systems (ESS) and thermal storage system (TSS) is proved that the cost of operation reduces as the baseline values of ESS and TSS are reduced to 0.2% of the maximum capacity. Because DAEM performance is less flexible when the primary values are reduced by 0.2% of the maximum value, the system running expenses increase marginally.     

Development of cogeneration in Germany: A mean-variance portfolio analysis of individual technology’s prospects in view of the new regulatory framework

The Integrated Energy and Climate Protection Program of the German government includes the political target of doubling the share of combined heat and power generation (CHP) in Germany from currently about 13% to 25% by 2020. In order to reach this goal, a new CHP law was enacted to improve the framework conditions for CHP generation. In this paper, we aim at identifying which CHP technologies are most likely to be installed in the near future to reach the CHP target stipulated by the German government. In our model, we apply Mean-Variance Portfolio (MVP) theory to consider return- and risk-related aspects of various CHP technologies. The analysis pays tribute to specific characteristics of CHP generation, such as promotion via guaranteed feed-in tariffs, additional revenues from heat sales, specific operational features, and specifics concerning the allocation of CO₂ allowances. The investigation is based on four generic standard CHP technologies currently available on a commercial basis: large coal-fired CHP plants, combined-cycle gas turbines (CCGT-CHP), engine-CHP and micro-turbine CHP. As selection criteria for the portfolio performance we take, independently from each other, the net present value (NPV) of investment in CHP and the expected annual portfolio return, and compare the results obtained from both approaches. Irrespective of the chosen selection criteria, the analysis shows that CCGT-CHP and engine-CHP are the most attractive CHP technologies from a return perspective. A diversification of the portfolio with other kinds of CHP technologies can contribute to stabilizing portfolio returns. In view of the results obtained we conclude for the further development of CHP generation in Germany that a large portion of additional new CHP capacity will probably be built in the industrial sector.