10:30
Session 1C: CHP's Multi Generation
Chair: Dieter Brüggemann
10:30
20 mins
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Optimisation of Biomass-fired Cogeneration Plants Using ORC Technology
Jacek Kalina, Mateusz Świerzewski
Abstract: Biomass-fired cogeneration projects are usually initiated in locations where a heat market exists and therefore most of the biomass-fired ORC systems had been installed in district heating systems. The biomass-fired modules are added to existing fossil-fuel-fired heating plants within either backfitting or modernisation projects focused on using locally available feedstock and making profits out of electricity generation and emission reduction. The critical issue of such projects is optimal design of the biomass-fired block and its integration with the existing heat only plant. The energy, ecological and economic performance of the integrated technological system depends on a set of decision variables concerning plant’s components and structure, working fluid selection, construction and operational parameters. The optimisation task must be properly formulated under site-specific economic and ecological constraints including different strategies to sell electric energy generated in cogeneration.
In this paper the municipal heating plant in Krosno (Poland) is taken into account as the reference case. In 2013 there was commissioned the biomass biomass-fired cogeneration system with the Turboden T14 CHP SPLIT unit of 1255 kW net electric power. Basing on the operational experiences from this unit an optimisation study is performed in order to examine the influence of current economic and legal conditions on the optimal design characteristics of the plant. New structure of the plant is determined and compared with the existing one. There are taken into account different structures of the ORC unit (simple, with regeneration, with split heat exchanger), different working fluids, exhaust gas latent heat recovery unit, heat storage vessel and network water cooler. Different electricity, biomass and coal prices are taken into account as well as the influence of the EUA (European Emission Allowance) price is examined. The results reveal importance of the optimisation of design parameters as well as the dependence of the plant’s size and structure on local economic conditions.
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10:50
20 mins
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Combining an Organic Rankine Cycle and a Heat Pump Cycle in a Test Plant for Reversible Storage of Energy
Daniel Steger, Christoph Regensburger, Bernd Eppinger, Stefan Will, Jürgen Karl, Eberhard Schlücker
Abstract: The heat pump cycle is a well-known concept to lift the temperature of a medium by using electricity and waste heat. The ORC-process on the other side offers the possibility to gain electrical energy out of thermal energy. Combining these two processes and adding a thermal storage enables an innovative and reversible energy storage concept called “Combined Heat Pump – Organic Rankine Cycle (HP-ORC)” [1]. As both processes use similar components, it is a consequent step to combine these in one single cycle with two operation modes.
The combination on the one hand, reduces the investment costs, as the most expensive components (e.g. heat exchangers) pare down to the minimum. On the other, it poses difficulties, which have to be countered by finding the best compromises in process properties and apparatus designs. Crucial factors are the upper and lower storage temperature as they determine the storage capacity and influence the overall efficiency (power-to-power-efficiency). Methods of multi-criteria decision-making, such as Pareto-Optimization, identify favourable combinations of upper and lower storage temperature. The selection of the working fluid has also a critical influence on the combined process, as apparatus properties alter, in some cases effecting significant increase in costs
The biggest challenge of the combined cycle is to realise the compressor of the heat pump and the expander of the ORC in one single machine. A lot of preliminary planning was done to find the best working principle for this diverse task. As the temperatures differ according to the mode (ORC or HP), the mechanical load situation is complex. Additionally the lubrication system has to fulfil the demands of both modes, requiring an innovative design of the oil supply and separation.
To evaluate the concept, a pilot plant is built at the Institute of Process Machinery and Systems Engineering at FAU. This paper describes preliminary considerations, design methods and the development of a HP-ORC-pilot-plant.
[1] Staub, S.; Bazan, P.; Braimakis, K.; Müller, D.; Regensburger, C.; Scharrer, D.; Schmitt, B.; Steger, D.; German, R.; Karellas, S.; Pruckner, M.; Schlücker, E.; Will, S. & Karl, J. Reversible heat pump-organic rankine cycle systems for the storage of renewable electricity, Energies, 2018, 11
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11:10
20 mins
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Absorption Power Cycle with Libr Solution Working Fluid – Design of the First Proof of Concept
Vaclav Novotny, David Szucs, Jan Spale, Vaclav Vodicka, Jakub Mascuch, Michal Kolovratnik
Abstract: The most common technology for utilizing low temperature and low power heat sources in a decentralized power system is the organic Rankine cycle (ORC). Nevertheless, there are appearing new alternative concepts providing theoretically higher efficiency, but they are far behind the technological maturity level of the ORC. One such concept is an absorption power cycle (APC) working with an aqueous solution of lithium bromide (LiBr) as a working fluid.
According to our findings and theoretical studies, the perspective application of APC is in low power output of no more than a few dozens of kW, and for heat sources at temperatures below 150 °C. Other features of APC include a high temperature glide across heat exchangers resulting in high exergy efficiency, and large volumetric flow rate of the vapour allowing to build an efficient turbine for small power output.
This cycle has, however, to the best knowledge of the authors, never been experimentally explored. To assess the possibilities of the actual application, a proof-of-concept APC unit is designed. This work is a methodological design analysis of an experimental unit based on a thermodynamic model presented. The design of the APC unit is adapted for the following heat source: heat input 20 kW from a topping ORC unit, in 90 °C water (intermediate cycle). Calculation and sizing model results in expected <0.5 kW turbine output with high and low pressures 13 kPa and 6 kPa respectively. Alongside with the calculation methodology, the final design of the APC unit is presented. The equipment consists of a custom shell & tube desorber (evaporator) and absorber (condenser) with a design described, an axial impulse turbine made by additive manufacturing from plastic and micro gear pumps. The construction of these components and of the whole apparatus is, at the time of writing this article, underway. Commissioning, experimental results, and a subsequent proof of application potential of the APC concept will be a subject of future work.
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11:30
20 mins
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Small-scale Organic Rankine Cycle for Domestic Biomass Fueled Combined Heat and Power Applications
Joaquín Navarro-Esbrí, Marta Amat-Albuixech, Adrián Mota-Babiloni, Francisco Molés, Carlos Mateu-Royo, Manuel González, José Pascual Martí
Abstract: Environmental concerns have made increase the interest on energy efficiency and renewable energy sources. Domestic buildings are one of the main fields of energy consumption, mainly in the form of electricity and heating systems. Therefore, the use of Combined Heat and Power systems and renewable energy sources in domestic applications is a very interesting option to reduce fossil fuels consumption. Organic Rankine Cycle is one of the most attractive technologies in terms of low temperature and small-scale applications, producing not only electricity but also useful heat through the exploitation of the condensation thermal power. This paper presents the preliminary tests of a small-scale ORC for domestic biomass fueled Combined Heat and Power applications using commercial biomass boilers. This system has been conceived to operate as a CHP technology, using the thermal energy provided by the condenser for domestic heating, with outlet water temperatures up to 45ºC. The main characteristics on the ORC will be presented with a basic cycle configuration and using HFC-245fa as working fluid. The system has been designed for a maximum electrical output of 1.5 kW.
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11:50
20 mins
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A Novel Micro-cogeneration Unit for Market Applications Based on a Biomass-fired ORC System
Gianluca Carraro, Viola Bori, Andrea Lazzaretto, Giuseppe Toniato, Piero Danieli
Abstract: In the transition towards smart grid systems, a problem of increasing importance is the distributed generation of thermal and electric power at low cost and low environmental impact. This work proposes a novel cogeneration system based on a biomass boiler and a micro-Organic Rankine Cycle (ORC) unit. The biomass boiler heats up an unpressurised thermal oil circuit, which, in turn, supplies heat to an ORC unit that produces electricity and hot water for the users. The ORC system is based on a single-pressure regenerative cycle that works in the subcritical region. The goal of this study is twofold: i) the analysis of the design choices that were made to achieve a good compromise between efficiency and cheapness of the micro-CHP system, and ii) the performance evaluation of the system for variations of key parameters, such as temperature and flow rate of the thermal oil, mass flow rate of the cooling water and operational assets of the ORC unit. An in-depth experimental campaign has been carried out, where the rotational speeds of the pump and expander of the ORC unit have been varied to choose first the best operating asset, and then investigate the influence of the other key parameters. The best combination of the speeds has been identified as 2250 rpm for the pump and 2300 rpm the expander. In these conditions, maximum values of electrical efficiency (7.4%) and total energy utilization factor (62%) are found. With an oil temperature of about 150°C, the achieved power production is 2530 W, the ORC utilization factor 93% and the expander global efficiency 57%. Simplicity and low specific cost contribute to increase the efficiency-to-cost ratio, making this novel system appealing for the customer.
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12:10
20 mins
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ORC Conversion of Solar Heat to Electricity and Low Temperature Heat for Domestic use
Gael Leveque
Abstract: The concept of the European project Innova MicroSolar is based on a novel flat Fresnel mirror solar concentrating collector, connected to a Thermal Energy Storage (TES) composed of Phase Change Material (PCM) and reversible heat pipes, and an Organic Rankine Cycle (ORC). The target is for the whole system to supply 60% of a household’s energy requirements, 18 KW of low grade heat and 2 kW of electricity.
An extensive test period at ENOGIA facilities allowed highlighting areas of improvement of the ORC in early 2018 (results presented at the ICSEF). A thorough upgrade of the system was then realized, including the change of the working fluid and related components before installation of the complete system at the demo site of Almatret.
The presentation will detail the results obtained during real condition tests, and assess the performance increase compared to the first version of the ORC. Key criterion for the evaluation of the performance of the installation will be its capacity to regulate the power and temperature on the cold source (domestic hot water production mode, already demonstrated with the first prototype) and to reach the targeted electricity output (83% of the target reached with the first prototype).
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