Small Combined Heat And Power Research Articles

Reserve Provision by CHP Units and Its Impact on Equilibria in Spot and Reserve Markets

There is a broad consensus that the energy transition planned in Europe, along with an increasing share of renewable energy sources, demands a sufficient number of flexibility providers. The established flexibility procurement mechanisms, notably the reserve markets, are expected to reflect the cost of flexibility provision. As more flexibility is needed – given a higher resulting uncertainty of residual load levels – prices for such provision are expected to rise. In recent years, however, reserve provision prices in Germany have shown a decreasing tendency, with overall reserve demand remaining constant. This contribution proposes to analyse first the equilibrium pricing of reserve power against the electricity spot market in a stylized setting. A fundamental market model is used to analyse the price effects of reserve flexibility from Combined Heat and Power (CHP) entering both markets, using 2016 data as input. Four cases are analysed to assess the effects of different reserve market characteristics. In Case 1, CHP plants may not provide secondary reserve for the reserve market and a stylized heat demand curve is considered as operating restriction of CHP plants in the spot market. Case 2 allows reserve provision by CHP plants, but models these plants without heat restrictions. Case 3 considers the combination of the stylized heat demand curve and reserve from CHP plants. Case 4 extends Case 3 by 100 small CHP power plant pools, analysing their additional effect on reserve prices. From June 2018 on, secondary reserve in Germany will be auctioned in four-hour tenders, instead of the current weekly peak/off-peak auction design. We therefore compare the results to such an alternative auction regime with the same demand, but four-hour reserve provision tenders to reflect upcoming market design changes. Our approach leads to spot prices at a similar mean level compared to historical data, with MAE values in a range from 5.91-6.64 €/MWh for all cases. The positive reserve price levels in this approach also compare to mean historical price levels. The price lowering effect of flexibility provision from CHP is clearly identifiable, underscoring the importance of explicit modelling of heat demand restrictions. A change of the reserve tender regime towards 4-hour tenders further lowers positive reserve prices in all cases. As a result, low reserve price levels may be expected to persist in the medium term despite the expected increase of intermitting generation.

Statistical method for the determination of the minichannel heat exchanger’s thermal characteristics

The paper presents a new statistical method for the determination of the experimental thermal characteristics of mini- and microchannel heat exchangers. These exchangers are suitable for small scale ORC (Organic Rankine Cycle) installations, CHP (Combined Heat and Power) generation or other applications like electronic equipment. It is not possible in practice to measure the temperature inside mini- and microchannels and only statistical methods may be used to determine the exchanger’s characteristics. There are many such methods which are the modifications of the Wilson plot method. However, the presented method has some advantages. Both fluid flows are treated symmetrically and flow rates and temperature values may be changed simultaneously. In many other methods it is necessary to stabilize one fluid flow while changing the second one. The correlations for Nusselt number may easily be chosen without changing the method itself. The linear coefficients are calculated analytically, but in the case of additional nonlinear coefficients, the numerical method may easily be used. The presented statistical method was verified based on the experimental data of the prototype minichannel heat exchanger.

Modeling and techno-economic analysis of the integration of a FC-based micro-CHP system for residential application with a heat pump

This work aims to analyse the techno-economic performance of an integrated system for a residential CHP (Combined Heat and Power) application, based on the integration of a Fuel Cell (FC) micro-cogeneration device coupled with an Heat Pump (HP).The main components of the system are: the Fuel Cell unit, the Heat Pump and the thermal storage – required to cover the thermal peaks, mainly due to the domestic hot water demand. The analysis will be focused on the most diffused FC technologies for residential applications: a low temperature Polymer Electrolyte Membrane Fuel Cell (PEMFC) and a high temperature Solid Oxide Fuel Cell (SOFC).FC-based cogeneration systems usually produce an electric power surplus respect to the thermal production, because of their high electrical efficiency. Currently, however, the households heating load exceeds significantly the electricity requirements, thus making difficult the sizing of a FC system for a single family house without including large electrical and thermal storages or high grid/boiler integration. The combination of a Fuel Cell and an Heat Pump has been found to be an optimal solution to manage this problematic while achieving a reduction in the primary energy consumption and avoiding energy overproduction.In the proposed scenario the heat is exploited by feeding both the domestic hot water and a low-temperature radiant floor heating system operating between 35 °C and 45 °C.An energy and economic analysis has been performed to understand and to evaluate the plant feasibility.Results have pointed out that the best economic choice, with the current energy tariff scenario, is related to a small size FC-based CHP system able to produce enough electrical power to feed the HP plus a low electrical consumption (<1 kW electrical size), which corresponds to the base electrical household consumption (the electrical power which is near-always requested by the house). The electrical load is in fact deeply changing during the day (with one-minute variable peaks) and with a higher electrical production from the FC, most of the electrical power would be sold to the grid without no energy advantages.The best PEMFC configuration was able to reach a total efficiency of 75%: if compared to the case with separated energy generation (electricity from the grid and heat from a boiler) the saving is estimated in three years of payback for the current scenario (2015).With the SOFC system, thanks to its higher total efficiency equal to 81%, the primary energy consumption was reduced (−30% respect to PEMFC) with a consequent reduction in the operating costs. However, from an economic point of view, the payback still results extended because of its not competitive investment cost.

Prototype of the domestic CHP ORC energy system

Abstract The Institute of Fluid-Flow Machinery (IMP PAN) in Gdansk pursues its own research in fields such as technologies that use renewable energy sources efficiently, including in particular the small-scale combined heat and power (CHP) systems. This article discusses the design concepts for the prototype of small CHP ORC (organic Rankine cycle) energy system, developed under the research project. The source of heat is a boiler designed for biomass combustion. Electricity was generated using specially designed oil-free vapour micro-turbine. The turbo-generator has compact structure and hermetical casing thanks to the use of gas bearings lubricated by working medium. All energy system components are controlled and continuously monitored by a coherent automation and control system. The article also discusses selected experimental results conducted under laboratory conditions. Thermal-flow tests were presented that allow for an assessment of the operation of energy system components. Additionally, energy performance results of the turbo-generator were given including power obtained at various cycle parameters. The achieved results have shown that the developed energy system operated in accordance with design solutions. Electricity derived from the energy system prototype was around 2 kW, with boiler’s thermal power of 25 kW. The research has also confirmed that this system can be used in a domestic environment.

Small scale biomass CHP: Techno-economic performance of steam vs gas turbines with bottoming ORC

Small scale Combined Heat and Power (CHP) plants present lower electric efficiency in comparison to large scale ones, and this is particularly valid when biomass fuels are used. In most cases, the use of both heat and electricity to serve on site energy demand is a key to achieve acceptable global energy efficiency and investment profitability. However, the heat demand follows a typical daily and seasonal pattern and it is influenced by climatic conditions. During low heat demand periods, a lot of heat produced by the CHP plant is discharged. In order to increase the electric conversion efficiency of small scale biomass CHP plants, a bottoming ORC system can be coupled to the cycle, however this decreases the temperature and quantity of cogenerated heat available to the load. In this perspective, the paper proposes a thermo-economic analysis of small scale CHP plants based on steam turbine (ST) or externally fired micro gas turbine (EFGT) coupled to different typologies of bottoming Organic Rankine Cycles (ORC). The research assesses the influence of the thermal energy demand and CHP plant operational strategies on the global energy efficiency and profitability of the proposed cogeneration options, taking into account the part load efficiency and the heat to electricity ratio flexibility that could be achieved through a switch on-off of the bottoming ORC. The thermodynamic cycles and their part load efficiency are modeled by Gate-Cycle (Brayton cycles) and Cycle-Tempo (Rankine cycles). The research explores the profitability of bottoming ORC in view of the higher efficiency and electricity generation revenues but higher costs and reduced heat available for cogeneration in the case of bottoming ORC. The results indicate the optimal CHP technology and configuration for each energy demand segment and the relative key technical and economic factors in the Italian legislative framework.

Thermo-Economic Assessment of a Olive Pomace Gasifier for Cogeneration Applications

Abstract A thermo-economic analysis of a combined heat and power (CHP) plant fed by syngas produced through the gasification of dry olive pomace is presented. The plant is composed by a 800 kWt downdraft gasifier, a gas clean-up system, a 200 kWe microturbine (MGT) and a heat recovery system to cogenerate hot water. Surplus heat is used to dry olive pomace from 50% to 17% wb moisture content. The plant is modeled in ASPEN Plus. Real data from experimental tests are used to calibrate the gasifier model, while the technical specification and performance of the CHP plant are collected from commercial plants in operation and data from manufacturers. Mass and energy balances are reported throughout the paper. The thermodynamic simulation of the biomass gasifier coupled to the MGT, the thermal and electrical conversion efficiency and temperature of cogenerated heat available are also presented. A thermo-economic assessment is then proposed, to investigate the economic profitability of this small scale CHP plant in the Italian energy policy scenario and considering the subsidies available for renewable electricity in the form of feed-in tariffs. For this purpose, the case study of base load CHP plant operation and heat supplied to different typologies of energy end user is assumed. The results allow quantifying the most influencing economic and technical factors that affect the performance and profitability of such investment and the bottlenecks that should be faced to facilitate a broader implementation of such CHP schemes for on site generation.

Efektywność energetyczna i ekonomiczna perspektywicznych technologii wytwarzania energii elektrycznej

The paper presents the analysis of energy and economic effectiveness of electricity generation technologies of the future in: system power plants, large and medium scale combined heat and power (CHP) plants, and small scale power plants and CHP plants (distributed sources). For particular generation technologies were determined the quantities characterizing their energy effectiveness, unitary emission of CO2 (kg CO2/kWh) and unitary discounted electricity generation costs of 2013. DOI: 10.12736/issn.2300-3022.2014214

Comparative economic analysis of gas turbine-based power generation and combined heat and power systems using biogas fuel

We evaluated the economic feasibility of small CHP (combined heat and power) and CC (combined cycle) systems using a 5 MW-class gas turbine fueled with biogas. The significance of this study is that we used practical hourly and seasonal variations of the CHP and CC performance based on detailed performance analysis. Using the investment and running costs of the entire facilities and the prices of electricity and heat, economic indices such as the annual gross margin, the net present value of the cash flow and the payback period were estimated. Two kinds of heat demand patterns were compared in the CHP system. Major findings are as follows. A strong dependence of the project economics on heat sales was observed. Both of the CHP cases showed an economic benefit over both the CC system and the gas turbine-only system. Another important finding is that the CHP system would be more beneficial than the CC system in terms of the total net present value after twenty years as long as the annual heat demand is over thirty percent of the annual electricity supply. The effect of increasing prices and costs was also simulated, and improvements in project economics were estimated.

Small scale biomass CHP plant: An assessment for an animal feed industry

This paper describes a technical, economic and exergoeconomic assessment to verify the feasibility of a combined heat and power (CHP) plant implementation in an animal feed industry to attend its electric power demands. A small-scale Rankine cycle was defined for the CHP plant. Plant operation was simulated at steady state condition, taking into account heat and electric power demands under two considerations: electric power selling to the grid and burning wood chips or charcoal as fuel. In order to get the feasibility assessment, a cash flow was elaborated. The thermoeconomic structural theory was applied for the exergoeconomic assessment. The results show that the feasibility of the CHP plant implementation was achieved by using charcoal as fuel. The consideration of electric power selling to the grid was shown to be the most interesting.

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.

The impact of lignocellulosic ethanol yields in polygeneration with district heating – A case study

The development towards high energy efficiency and low environmental impact from human interactions has led to changes at many levels of society. As a result of the introduction of penalties on carbon dioxide emissions and other economic instruments, the energy industry is striving to improve energy efficiency and climate mitigation by switching from fossil fuels to renewable fuels. Biomass-based combined heat and power (CHP) plants connected to district heating networks have a need to find uses for the excess heat they produce in summer when the heat demand is low. On the other hand, the transport sector makes a substantial contribution to the increasing CO 2 emissions, which have to be reduced. One promising alternative to address these challenging issues is the integration of vehicle fuel production with biomass-based CHP plants. This paper presents the configuration and operating profits in terms of electricity, heat and ethanol fuel from cellulosic biomass. A case study of a commercial small scale CHP plant was conducted using simulation and modeling tools. The results clearly show that electricity production can be increased when CHP production is integrated with cellulosic ethanol production. The findings also show that the economic benefits of the energy system can be realized with near-term commercially available technology, and that the benefits do not rely solely on ethanol yields.

Development of a 3 kW Microturbine for CHP Applications

Combined heat and power (CHP) concepts for small-scale distributed power generation offer significant potential for saving energy and reducing CO2 emissions. Microturbines are an interesting candidate for small CHP systems with advantages in terms of performance, size, noise, and costs. MTT is developing a 3 kW recuperated microturbine for micro CHP applications for large households and for truck combined APU-heating systems. To minimize costs, off-the-shelf automotive turbocharger technology has been used for the turbomachinery. During recent years, turbocharger turbomachinery performance and efficiencies have significantly increased, even for very small sizes. At the same time, efficient high-speed motor-generators have become available at relatively low prices. The development of a concept demonstrator started in May 2008. This program phase included a cycle analysis and component selection study around off-the-shelf turbomachinery, design of a custom combustor, recuperator and generator, and a test program. In this paper, results of the cycle definition, conceptual design and component matching study are presented. Next, the development of a detailed performance model is described and performance prediction results are given. Also, results of the test program and test analysis work are presented. Finally, from the conclusion of the demonstrator phase an outlook is given on the prototype design and performance, which will be the next phase of the development program.

Do liberalised electricity markets help or hinder CHP and district heating? The case of the UK

This paper investigates whether and how Danish-style combined heat and power (CHP) and district heating (DH) can be implemented in the UK in the context of a liberalised electricity market. There is currently an absence, in the UK, of the Danish system of planning rules and also good tariffs for CHP electricity exports to the grid that led to the development of the Danish system of CHP and DH. However, there are some changes in UK planning practice that may help CHP and DH. These would need to be strengthened, but it is also the case that the way the liberalised electricity market operates in the UK effectively discriminates against small CHP plant selling their electricity to the grid. A Danish system of ‘aggregating’ CHP–DH plant using thermal stores could help to overcome this problem. However, an alternative strategy would be to establish feed-in tariffs for CHP units that are linked to DH modelled on the Danish ‘triple tariff’. This could help the UK's long-term objective of absorbing high levels of fluctuating renewable energy sources.

Corn Grain Drying Using Corn Stover Combustion and CHP Systems

Post-harvest drying of shelled corn grain requires large amounts of fossil fuel energy. In 2004, it was estimated that the upper Midwest consumed more than $1.4 billion of fossil fuels to dry $19.7 billion of corn grain. Over the long term, drying corn with fossil fuels may become cost prohibitive due to limited fuel reserves. To address future energy concerns for grain dryers, this study evaluated the potential use of combined heat and power (CHP) systems that use the combustion of corn stover both to produce heat for drying and to generate electricity for fans, augers, and control components. Net present value (NPV) cost estimates were determined for two continuous-flow dryers: a relatively small on-farm dryer (8.9 Mg h-1), and a larger dryer more common to grain elevators (73 Mg h-1). For each dryer, three levels of assumed stover price were used: $15, $25, and $35 per dry Mg for the small dryer, and $30, $45, and $60 per dry Mg for the larger dryer (includes payments to farmer and off-farm transport costs). Compared to equivalently sized fossil fuel-fired dryers, both the small and large CHP dryers were found to be more economical over the long term. Twenty-year NPV cost savings and breakeven points were estimated to be $63,523 and 14.3 years for the small CHP dryer ($25 Mg-1 stover) and $1,804,482 and 7.5 years for the large dryer ($45 Mg-1 stover). Sharing CHP infrastructure with other processes requiring heat that extend seasonal use can reduce payback periods significantly and provide broader efficiency benefits. Sensitivity analysis found cost savings to be most sensitive to fluctuations in fossil fuel costs, followed by annual use of dryer equipment.

Increased power to heat ratio of small scale CHP plants using biomass fuels and natural gas

Abstract In this paper, we present a systematic study of process changes for increased power production in 1–20 MW e combined heat and power (CHP) plants. The changes are simulated, and their economic feasibility evaluated by using existing small scale CHP case plants. Increasing power production in decentralised CHP plants that operate according to a certain heat demand could reduce the fuel consumption and CO 2 emissions per power unit produced and improve the feasibility of CHP plant investments. The CHP plant process changes were simulated under design and off design conditions and an analysis of power and heat production, investment costs and CO 2 emissions was performed over the whole annual heat demand. The results show that using biomass fuels, there are profitable possibilities to increase the current power to heat ratios, 0.23–0.48, of the small scale CHP plants up to 0.26–0.56, depending on the size of the plant. The profitable changes were a two stage district heat exchanger and the addition of a steam reheater and a feed water preheater. If natural gas is used as an additional fuel, the power to heat ratio may be increased up to 0.35–0.65 by integrating a gas engine into the process. If the CO 2 savings from the changes are also taken into account, the economic feasibility of the changes increases. The results of this work offer useful performance simulation and investment cost knowledge for the development of more efficient and economically feasible small scale CHP processes.

New CHP partnerships offering balancing of fluctuating renewable electricity productions

Combined heat and power (CHP) as well as intermittent renewable energy sources (RES) are key elements in future cleaner electricity production systems. This article presents solutions which will integrate fluctuating renewable electricity supplies, such as wind power, into electricity systems using small and medium-sized combined heat and power plants (CHP). Such solutions call for a new organisational setup of partnerships and software tools. The software tools will allow the new partnerships to offer services which are currently only offered by big power plants to electricity markets. The article presents recent results of the development and implementation of such partnerships and focuses on the methodologies and computer tools necessary in order to allow the partnerships to optimise their behaviour on the market. The use of such tools and methodologies makes groups of small CHP plants able to replace large power stations and, at the same time, allows for the integration of a higher share of RES in the electricity supply, resulting in a decrease in both fossil fuels and CO2 emissions.

Large-scale integration of wind power into different energy systems

The paper presents the ability of different energy systems and regulation strategies to integrate wind power. The ability is expressed by the following three factors: the degree of electricity excess production caused by fluctuations in wind and Combined Heat and Power (CHP) heat demands, the ability to utilise wind power to reduce CO 2 emission in the system, and the ability to benefit from exchange of electricity on the market. Energy systems and regulation strategies are analysed in the range of a wind power input from 0 to 100% of the electricity demand. Based on the Danish energy system, in which 50% of the electricity demand is produced in CHP, a number of future energy systems with CO 2 reduction potentials are analysed, i.e. systems with more CHP, systems using electricity for transportation (battery or hydrogen vehicles) and systems with fuel-cell technologies. For the present and such potential future energy systems different regulation strategies have been analysed, i.e. the inclusion of small CHP plants into the regulation task of electricity balancing and ancillary grid stability services and investments in electric heating, heat pumps and heat storage capacity. The results of the analyses make it possible to compare short-term and long-term potentials of different strategies of large-scale integration of wind power.

Technical, economic and environmental analysis of energy production from municipal solid waste

Four technologies are investigated which produce energy from municipal solid waste (MSW): incineration, gasification, generation of biogas and utilisation in a combined heat and power (CHP) plant, generation of biogas and conversion to transport fuel. Typically the residual component of MSW (non-recyclable, non-organic) is incinerated producing electricity at an efficiency of about 20% and thermal product at an efficiency of about 55%. This is problematic in an Irish context where utilisation of thermal products is not the norm. Gasification produces electricity at an efficiency of about 34%; this would suggest that gasification of the residual component of MSW is more advantageous than incineration where a market for thermal product does not exist. Gasification produces more electricity than incineration, requires a smaller gate fee than incineration and when thermal product is not utilised generates less greenhouse gas per kWh than incineration. Gasification of MSW (a non-homogenous fuel) is, however, not proven at commercial scale. Biogas may be generated by digesting the organic fraction of MSW (OFMSW). The produced biogas may be utilised for CHP production or for transport fuel production as CH 4-enriched biogas. When used to produce transport fuel some of the biogas is used in a small CHP unit to meet electricity demand on site. This generates a surplus thermal product. Both biogas technologies require significantly less investment costs than the thermal conversion technologies (incineration and gasification) and have smaller gate fees. Of the four technologies investigated transport fuel production requires the least gate fee. A shortfall of the transport fuel production technology is that only 50% of biogas is available for scrubbing to CH 4-enriched biogas.

Technical/economic/environmental analysis of biogas utilisation

Biogas may be utilised for Combined Heat and Power (CHP) production or for transport fuel production (CH 4-enriched biogas). When used to produce transport fuel either electricity is imported to power the plant or some of the biogas is used in a small CHP unit to meet electricity demand on site. The potential revenue from CH 4-enriched biogas when replacing petrol is higher than that for replacing diesel (Irish prices). Transport fuel production when replacing petrol requires the least gate fee. The production of greenhouse-gas is generated with cognisance of greenhouse-gas production with the scheme not in place; landfill of the Organic Fraction of Municipal Solid Waste (OFMSW) (20% of biomass) with and without combustion of landfill gas is investigated. The transport scenario with importation of brown electricity generates more greenhouse-gas than petrol or diesel, when the ‘do-nothing’ case involves combustion of landfill gas. The preferred solution involves transport fuel production with the production of CHP to meet electricity demand on site. A shortfall of this solution is that only 53% of biogas is available for export.

00/00848 Combined heat and power economic dispatch by improved ant colony search algorithm

The development of industrial ecology has led company managers to increasingly consider their company's niche in the regional system, and to develop optimization plans. We used emergy-based, ecological-economic synthesis to evaluate two optimization plans for the Jiufa Combined Heat and Power (CHP) Plant, Shandong China. In addition, we performed economic input–output analysis and energy analysis on the system. The results showed that appropriately incorporating a firm with temporary extra productivity into its regional system will help maximize the total productivity and improve ecological-economic efficiency and benefits to society, even without technical optimization of the firm itself. In addition, developing a closer relationship between a company and its regional system will facilitate the development of new optimization opportunities. Small coal-based CHP plants have lower-energy efficiency, higher environmental loading, and lower sustainability than large fossil fuel and renewable energy-based systems. The emergy exchange ratio (EER) proved to be an important index for evaluating the vitality of highly developed ecological-economic systems.