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14:00   Poster Session and Sponsors Exhibition
Tri Handayani, Adam Harvey, David Reay
Abstract: Recent developments in ORCs have heightened the need for choosing the optimum working fluids which are critical to the successful performance of Organic Rankine cycles (ORC). Currently, the working fluid is defined as optimum if it is fulfils some specific requirements relating to its thermodynamic, economic, safety and environmental characteristics. However, research has consistently shown that no working fluids are able to achieve all those requirements. Therefore, studies continue searching for the best strategies for selecting the working fluids. So far, selection methods are based on traditional approaches, which are firstly select several working fluid candidates, secondly, set the objective of the design (net power output, thermal efficiency, irreversibility), lastly, select the working fluid based on maximum or minimum objective. This paper seeks to remedy this trial and error method by a fuzzy logic approach which enables the user to filter out the near optimum working fluids at the first level. This approach begins with the selection of a number of working fluids commonly tested in previous studies. Secondly, setting up some optimum working fluid rules such as low molecular weight, high latent heat, low cost, high critical temperature, high flow rate, low volumetric flow rate, high availability, low boiling point, low global warming potential, low ozone depletion potential, low toxicity, low flammability etc.. Next, the working fluids' variables related to the defined rules are simulated using the fuzzy Matlab toolbox. Finally, the results of this simulation are sorted and the highest value is chosen as the highly recommended working fluid. The highly recommended working fluid is expected to achieve maximum net power output, high thermal efficiency, low cost, low irreversibility, high safety and low environmental effect.
Piero Colonna, Mauro Gallo, Emiliano Casati, Tiemo Mathijssen, Paolo Repetti
Abstract: The Flexible Asymmetric Shock Tube setup has been designed and built at the Process and Energy Laboratory of the Delft University of Technology in order to study non-classical gasdynamic phenomena in flows of dense organic fluid vapors [1]. It operates according to the Ludwieg tube principle. One of the main objectives is the detection of rarefaction shock waves, which are theoretically predicted to occur at operating conditions close to the vapour-liquid critical point in the superheated vapor thermodynamic region of so called BZT fluids [2]. Fluids of the siloxanes family qualify as BZT fluids therefore they are employed in the FAST setup [3]. Siloxanes are also working fluids for organic Rankine cycle power plants [4]. Gasdynamic measurements performed with the FAST setup are therefore also relevant especially for the aerodynamic design of ORC expanders. The FAST can be operated at temperatures up to 400 °C and pressures up to 30 bar. The current status with respect to the commissioning of the setup is illustrated. In addition the FAST laboratory has been recently equipped with Laser-based diagnostics for flow visualization and measurements. The experience gained in handling siloxanes and the FAST setup triggered interest into the design of a new test rig for flow measurements in transonic flows around blade shapes, with the objective of accurately validating an in-house CFD code for flows of dense organic vapors in conditions typical of ORC turbo-expanders. Preliminary results of the initial design process are described and discussed.
Dariusz Mikielewicz, Jaroslaw Mikielewicz, Jan Wajs, Eugeniusz Ihnatowicz
Abstract: The parallel path for searching of the expansion device to operate within the domestic micro heat and power plant encompasses activities related to adaptation and modification of existing devices available on the market to adjust them to operate as expansion machines. Authors accomplished already adjustments of three of such devices, namely the scroll compressor, pneumatic drill and pneumatic wrench. Some experiences from operation of these devices on the specially designed for that purpose experimental rig will be presented in the paper. Experiments showed the superiority of both “pneumatic devices” over the scroll expander, indicating the possible internal efficiencies in the range of 6182%. Such efficiencies are very attractive, especially at the higher end of that range. The volume of these devices is much smaller than the scroll expander which makes it again more suitable for a domestic micro CHP. Small rotational velocities enable to conclude that connection to electricity grid will also be simpler in the case of “pneumatic devices”.
Aleksandra Borsukiewicz-Gozdur, Wladyslaw Nowak
Abstract: During recent years the research activity in the area of the ORC power plants has been growing also in the Polish scientific institutions. This is motivated especially by the need to utilize low and moderate temperature heat sources of renewable origin like geothermal water, biomass or the sun collectors. The research work is being carried out at the Polish Academy of Science, Institute of Turbomachinery in Gdansk, at the Technical Universities in Wroclaw, Gdansk and Lodz, and at the West Pomeranian University of Technology in Szczecin. Covered research problems refer in particular to the question of the energy and exergy effectiveness of the single cycle ORC power plant, as well as to the question of their effectiveness improvement by means of application of the evaporators with an internal working fluid circulation. Experimental work is carried out at the West Pomeranian University of Technology on the first in Poland fully operational small ORC power plant built by the Turboservice Company of Lodz. The research on the area of the ORC power plant applications is further extended to cover utilization of the waste heat encountered in various industrial branches like chemical, cement or ceramic plants. The works published by the Polish scientific institutions refer also to some other types of the power plant solutions. They include double and triple cycle power plant schemes with sequential supply of the economizers and evaporators, as well as power plants for which the conventional saturated or superheated steam cycle functions as the upper temperature cycle. On the basis of the works published by the institutions quoted above the most interesting, valuable and novel research results will be presented.
Mohammad Mehdi Rashidi, Nicolas Galanis, Amin Habibzadeh
Abstract: In this paper a power and cooling cycle which combines the organic Rankine cycle (ORC) and the ejector refrigeration cycle supplied by geothermal heat energy sources is analyzed. The thermodynamic and physical properties of thirteen working fluids, including wet, dry and isentropic fluids are investigated in the proposed combined cycle, and their performances are compared. With a fixed power/refrigeration ratio, the effects of the various operating conditions on the cycle performance are examined. The proposed model is validated with the results of the combined power and ejector refrigeration cycle using R245fa as the working fluid presented by Zheng et al. [1] and Hasan et al. [2]. Also it is validated with the results of Dai et al. [3] in which R123 was selected as the working fluid. The main conclusions from this study are as follows: 1- The results confirm the thermodynamic superiority of dry and isentropic ORC fluids over the wet fluids. 2- Exergy efficiency decreases with increasing evaporator temperature but increases with decreasing turbine inlet temperature and increasing heat source temperature. 3- Thermal efficiency increases with the increase in the turbine inlet temperature and expansion ratio of the turbine. 4- Entrainment ratio of the ejector decreases as the evaporator temperature rises.
Piotr Klonowicz, Pawel Hanausek
Abstract: The ORC power plants require essentially their turbines to be individually designed for each power plant case. This is due to the varying parameters (temperature, capacity) of the heat sources to be utilized by a prospective ORC power plant. Moreover, selected cycle working fluid and its critical parameters, as well as certain design constraints (like in the case of the hermetic turbogenerators), are all affecting the final design of the turbine that should yield the maximum power output. Occurrence of the transonic and supersonic flows in the turbine channels is another difficulty to reach the optimum turbine design. Several basic turbine designs will be discussed in this contribution. Their final form was achieved with support of the numerical 3D viscous flow simulations by using the ANSYS CFX code. The thermodynamic parameters of the organic fluids were taken from the REFPROP library. The discussed turbine solutions will refer mainly to application of HFC 227ea as the organic cycle fluid.
Renzo Molinari, Ernesto Benini
Abstract: In this paper, an in-depth comparative analysis between the Organic Rankine Cycle (ORC) and the classical Water Rankine Cycle (WRC) technologies is carried out. For this purpose, the behavior of a cogenerative power plant fed by the output gases of a micro-gas turbine at a temperature of 300°C was considered where the net electrical power level requested was 30kW. Through this comparative analysis we have picked out the advantages of ORC technology in terms of thermal efficiency (i.e. more electric power can be produced from a given heat source) and feasibility of the turbine. In order to deepen the characterization of the ORC we have simulated the plant performance for three different organic fluids: N-pentane, Cyclohexane and Toluene. Thanks to this approach we have parameterized the main subjects of the power plant as a function of the thermophysical properties of the organic fluid. The work is divided into two parts. In the first part we have investigated, after an appropriate choice of evaporation and condensation temperatures, the cycle thermal efficiency. Great attention has been given towards the heat exchange behavior and the volume flow rates of the plant. From this first analysis we have demonstrated that the ORC technology makes it possible to obtain higher thermal efficiencies when low enthalpy heat sources are available. In this way, we have shown the dependence of efficiency from the properties of fluid and then important guidelines to choose the suitable fluid are given. In the second part, a preliminary design of the turbine is carried out. From the temperature-enthalpy diagrams for organic fluids you can see, contrarily to water, a positive slope of satur-vapour curve. This fundamental characteristic allows organic fluids an expansion in a superheated vapor region. Otherwise, if you spare a superheating process, water expands in a two phase region whit a great disturbance of the flow field and the consequent decrease of the turbine expansion efficiency. With the purpose to realize a preliminary study of the main geometrical and functional parameters of the turbine we have developed a dedicated computational code. In this case we have parameterized, as a function of the fluid, the dimension of the rotor inlet blade and other main turbine parameters. Great attention has been given towards the behavior of the flow field at the exit of the turbine nozzle. In the last part of this paper we have matched, for each fluid, thermodynamic efficiency and feasibility of the turbine. In this way some considerations arose about the selection of suitable organic fluid in accordance with plant power level and heat source temperature. As a consequence you can understand the reason why some companies are looking for new organic fluids or mixtures of them. The importance of this work is related to the general approach utilized and the results obtained represent an important preliminary guideline to design ORC systems.
Hyun Jin Kim, Je Seung Yu
Abstract: Application of an organic Rankine cycle to a passenger car has been considered to improve fuel consumption by recovering engine coolant heat, which usually amounts to about one third of the fuel energy. The high-side and low-side temperatures of the ORC were limited by the engine coolant and radiator temperatures, respectively. The evaporator and condenser temperatures of the ORC were set at TH=93oC and TL=60oC, respectively, for the vehicle speed of 120km/hr. At this temperature condition, theoretical efficiency of the Rankine cycle with R1234yf as the working fluid was 7.23%. A scroll expander was designed for energy conversion from thermal energy of the working fluid in the ORC to useful shaft power. For axial compliance, a back pressure chamber was provided on the rear side of the orbiting scroll. Lubrication oil was to be delivered by a positive displacement type oil pump driven by the expander shaft. Performance analysis on the designed scroll expander showed that the expander efficiency was 68.6%. It extracts the shaft power of 1.7 kW out of engine coolant waste heat (plus some portion of the exhaust gas heat) of 32.1 kW. This amount of the expander output is equivalent to the fuel consumption improvement of about 8% for the passenger car under consideration at the vehicle speed of 120km/hr. With decreasing vehicle speed, the scroll expander efficiency was calculated to decrease accordingly: it turned out to be 38.4% at 60km/hr, resulting in about 4.5% improvement in the fuel consumption. REFERENCES Endo T., Kawajiri S., Kojima Y., Takahashi K., Baba T., lbaraki S., Takahashi T., Shinohara M., 2007, Study on Maximizing Exergy in Automotive Engines, 2007 SAE 2007-01-0257. Diego A., Arias, Timothy A., Shedd and Ryan K., Jester, 2006, Theoretical Analysis of Waste Heat Recovery from an Internal Combustion Engine in a Hybrid Vehicle, 2006 SAE 2006-01-1605.
Johann Fischer, Martin Wendland, Ngoc Anh Lai
Abstract: For conversion of medium or low temperature heat to power one may think of using besides organic Rankine cycles (ORC) also trilateral cycles (TLC). In the TLC the liquid working fluid is pressurized and heated to its boiling point. Then it undergoes a flash expansion into the wet vapour region whereby it delivers work. Finally, the fluid is condensed. The advantage of the TLC is a very good match between the heating up curve of the working fluid and the cooling down curve of the heat carrier. The advantage of the ORC is that its cycle is closer to the Carnot cycle. Hence one would expect that the exergy efficiencies of both cycle types are similar. Recent papers, however, claimed that the efficiency of the TLC is 1.5 to 3 times higher than that of the ORC and hence we decided to reinvestigate that question. We consider optimized TLC- and ORC-systems which include the heat transfer from the heat carrier to the working fluid, the cycle process, and the heat transfer from the working fluid to the cooling agent. Optimization criterion is the exergy efficiency of the system for power production p being the ratio of the net power output to the incoming exergy flow of the heat carrier. Model calculations were made for five cases I to V specified by the inlet temperature of the heat carrier and the inlet temperature of the cooling agent. The inlet temperature pairs are for I (350°C, 62°C), II (280°C, 62°C), III (280°C, 15°C), IV (220°C, 15°C), V (150°C, 15°C). For TLC we use water throughout as working fluid and hence the only parameter for optimization is the boiling temperature. For the ORC we use different working fluids depending on the temperature interval. Their thermodynamic properties are obtained from the molecular based BACKONE and PC-SAFT equations of state. First, we searched for optimal ORC working fluids for the cases I and II considering alkanes, aromates and linear siloxanes in subcritical cycles (p/pc = 0.9) with and without superheating and supercritical cycles (p/pc = 1.2), all with internal heat exchange. Rankings based on the exergy efficiency p, the cycle thermal efficiency th and on the volume and the heat flow rates show cyclopentane to be the best working fluid for all studies of cases I and II which is caused by its only slightly overhanging dew line in the T,s-diagram. Moreover its autoigintion temperature is more than 100 K higher than the maximum cycle temperature considered. Hence, we used in the comparison between TLC and ORC as ORC working fluid for cases I to III cyclopentane, for case IV n-butane and for case V propane. It is found that the exergy efficiency p is larger for the TLC than for the ORC betwen 14% and 20% for cases I to IV and by 29% for case V. On the other hand, the outgoing volume flows from the expander are larger for the TLC than for the ORC by a factor ranging from 2.8 for case I to 70 for case V which is caused by the low vapour pressure of water for the low temperatures.
Andrea Spinelli, Vincenzo Dossena, Paolo Gaetani, Matteo Pini, Franco Marinoni
Abstract: A blow-down, closed-loop wind tunnel for real gas applications has been designed, validated by means of dynamic simulation and finally constructed. The facility is aimed at characterizing an organic vapour stream, representative of expansions taking place in Organic Rankine Cycles (ORC) turbines, by independent measurements of pressure, temperature and velocity. ORC turbine performances are expected to strongly benefit from characterization of such a flow and from design tools validation provided by experimental data, which still lack in scientific literature. A straight axis planar convergent-divergent nozzle represents the test section for early tests, but the test rig can also accommodate linear blade cascades. A wide variety of working fluids can be tested with adjustable operating conditions up to maximum temperature and pressure of 400 °C and 50 bar. The test rig is batch-operating; the working liquid is stored and evaporated in a high pressure vessel (HPV), the vapour is then discharged through the test section (where the flow field is measured) and is collected and condensed within a low pressure vessel (LPV). The liquid compression to the HPV finally closes the loop. Despite the test rig operational mode is unsteady, the inlet nozzle pressure can be kept constant by a control valve. The work presented here discusses the commissioning of the facility, namely the performance of preliminary tests using air as working fluid and an orifice plate in place of the convergent-divergent nozzle. Even though the ordinary tests require the facility to be operated with organic compounds, the use of air allow a simpler operation of the plant; in fact, the fluid can be exhausted to the atmosphere with no need of vapour collection and condensation and tests can be performed at moderate temperatures. No measurement of the flow field through the orifice are performed. Indeed, the present work only aims at testing the plant sealing, the correct operation of the main plant components (with the exception of the pumps and of the condensing system), at verifying the simulated behaviour for the control system and finally at setting-up the control loop software. In order to perform this validation and, in particular, to test the operation of the control valve, the orifice plate design is such that the dynamics of the HPV air emptying mimics the one obtained by using the organic vapour taken as reference for the first actual experiment. The pressurized air required to carry out the commissioning tests has been provided by a reservoir array (fed by a compression station) storing about 6000 kg of dry air at the pressure of 200 bar. Several tests have been performed, allowing a satisfactory adjustment of the control loop and in particular the tuning of the parameters characterizing the PID regulators of both the heating system and the control valve.
Mohammed Khennich, Nicolas Galanis
Abstract: Subcritical and transcritical Rankine cycles operating between a low temperature heat source (Ts,in = 100, 165 and 230 °C) of fixed volume flowrate (1.2 106 m3/h, idealized as atmospheric air at Ps = 101 kPa) and a fixed temperature heat sink (water at Tp,in = 10 °C) have been analyzed using the principles of classical and finite-size thermodynamics. The model of the system and its validation have been presented elsewhere [1]. Optimum operating conditions (pressure of the working fluid during heat addition, Pev, and temperature difference DT between the working fluid and the two external fluids) and the corresponding values of several system characteristics have been determined for different net power outputs using the variable metric method for each of the following objectives: maximum thermal efficiency, minimum total exergy destruction, minimum total thermal conductance of the two heat exchangers UAt and minimum turbine size SP. Typical results with R134a as the working fluid are presented. For this fluid the cycle is subcritical for Ts,in = 100 °C and transcritical for the other two values of the heat source temperature. At the turbine outlet the fluid is always superheated vapor. The lowest exergy losses as well as the smallest total conductance and turbine are obtained with Ts,in = 100 °C while the highest thermal efficiencies are obtained with Ts,in = 230 °C. The combinations of Pev and DT which maximize the thermal efficiency and minimize the exergy destruction are essentially identical. For these conditions the net power output has no effect on the thermal efficiency. On the other hand the exergy losses as well as the size of the turbine and heat exchangers increase with the net power output, albeit at different rates (the variation of the exergy losses, UAt and SP with the net power output is not linear). In all these cases the pinch in the high temperature heat exchanger occurs at the heat source inlet. The combinations of Pev and DT which minimize UAt and SP are different from each other and from those which maximize the thermal efficiency. The conditions which minimize UAt give turbine sizes not much bigger than the corresponding minimum size; on the other hand, the conditions which minimize SP give a thermal conductance significantly bigger than the corresponding minimum values.
Thierry Bouchet, Brice Hermant
Abstract: DCNS has both a strong experience and an outstanding know-how in the field of engineering of complex naval systems. The group is now investing into ocean energy technologies such as tidal turbines, floating offshore wind turbines, wave energy and OTEC (Ocean Thermal Energy Conversion). OTEC principle is a thermodynamic cycle based upon the use of the temperature difference between the cold deep seawater and the warm surface seawater to deliver steady baseload electrical flow of power to the grid using refrigerating fluid in a Rankine cycle (for example: organic fluid). DCNS roadmap ensures at minimizing the technical risks associated to the development of this technology. Thus, DCNS recently achieved an OTEC landbased prototype using heating pump in place of cold and warm seawater supply. Measurements on this one are currently underway and will be used in order to modify if necessary the various models of cycle and exchangers behavior developed on software named Equation Engineering Solver. Furthermore this one ensures to have a best understanding of the control of this type of cycle and will enable to qualify various equipments for a 10MW full-scale OTEC power plant. In same time, regarding the use of seawater in this application, DCNS analyzes risks and adapted solutions for corrosion and bio-fouling problems with DCNS group's expert with the ability to test in seawater environment exchangers specimens or cold seawater pipes specimens.
Guoquan Qiu, Gang Pei
Abstract: Biomass-fired or solar-driven micro-scale combined heat and power (micro-CHP) systems with organic Rankine cycle (ORC) have been highly concerned in the latest decade because the electric output (1-10kWe) and the heat output (20-50kWth) generated by the micro-CHP system are very applicable for a household or a little enterprise. The ORC-based micro-CHP system mainly consists of a heat source (e.g. a biomass boiler, solar collectors), an evaporator, an ORC expander, an alternator, a heat recuperator and a condenser. The expander plays a vital role in the ORC-based micro-CHP system; however the lack of commercially available micro-scale expanders (rated 1-10kW) applicable to ORC-based micro-CHP systems has hindered the development of these novel CHP systems. Qiu [1] reviewed various state-of-the-art kinds of micro-scale expander and concluded that scroll expanders and vane expanders are likely the good choices for 1-10 kWe micro-CHP systems. The vane expanders modified from air motors have been applied by Qiu [2]. The micro-CHP system with a 50kWth biomass-pellet boiler can generate 937W electricity (12.52VDC and 74.86ADC) and 47kWth heat which are more or less sufficient to meet the domestic electrical and heating demands [2]. The vane expanders modified from air motors may be feasible in both economic sector and technical sector. Compared with other kinds of expanders, the rotary vane expanders have simpler structure, easier manufacturing and thus lower cost [3]. Air motors are designed to replace electric motors and applied in special spark-prohibited environments [4], accordingly leaking of the air motor-modified vane expanders with ORC fluids is inevitable since they are subject to sealing problems over the big variations of temperature and pressure with the ORC. The leaking may be avoided after the sealant is applicable for the working ORC fluid and the casing of the rotor is designed with less bolt fixing (leaking occurs along the bolts or sealants). So specific mechanical designs and sealing skills may be developed to manufacture the vane expanders with ORC fluids, which should be feasible in technology. This paper presents some leaking problems occurring in applying air motor-modified vane expander and some methods of solving leaking problems. Vane expanders are feasible for ORC-based micro-CHP systems. REFERENCES [1] G. Qiu, H. Liu and S.B.Riffat, “Expander for micro-CHP systems with organic Rankine cycle”, Applied Thermal Engineering, DOI:10.1016/j.applthermaleng.2011.06.008. (Accepted) [2] H. Liu, G. Qiu, Y. Shao, F. Daminabo and S.B. Riffat, “Preliminary experimental investigations of a biomass-fired micro-scale CHP with organice Rankine cycle”, Intl J. of Low-Carbon Technol. Vol. 5, pp.81-87, (2010). [3] B. Yang, X. Peng, Z. He, B. Guo and Z. Xing,“Experimental investigation on the internal working process of a CO2 rotary vane expander”, Applied Thermal Engineering, Vol. 29, pp.2289-2296, (2009). [4] Y.R. Hwang, Y.T. Shen and M.S. Chen, “Dynamic analysis and fuzzy logic control for the vane-type air motor”, J. of Mech. Sci. and Technol. Vol. 23,pp.3232-3238, (2009).
Piotr Klonowicz, Wojciech Klonowicz
Abstract: Organic Rankine Cycles (ORC) are used in an increasing number of applications in the field of the distributed electricity generation. There is also a tendency to convert heat of lower and lower temperature, i.e. such as 100 OC and below that value. However, the thermodynamic efficiency of the energy conversion is very low at this temperature level. To overcome that situation several hybrid systems were considered within which the low temperature heat would be in various ways coupled with additional high temperature heat. Irrespectively from the energy conversion efficiency in those systems (the high temperature heat source requires application of the conversion technology that is different from ORC) this kind of approach calls for a high temperature heat source to be provided at the location of the existing low temperature heat source, which in most cases might be not feasible. Now, a requested positive effect in the efficiency of the energy conversion results when two low temperature heat sources (of different temperature values) are engaged in one hybrid ORC system, and the cycle generates saturated vapour to drive the turbine. An example discussed in the presentation refers to the case of low enthalpy geothermal water (with the temperature of, say, 70 OC) and heat delivered by a biomass fired water boiler (water output at 100 – 120 OC). It appears that, with properly adjusted heat streams of those two heat sources, the power output of such hybrid ORC system is up to 40 % greater than the sum of the power outputs of the two ORC units utilizing the respective individual heat sources at the equivalent heat stream capacities. The synergy effect comes from a thermodynamically better utilization of the upper heat source.
Aleksandra Borsukiewicz-Gozdur, Wladyslaw Nowak, Slawomir Wisniewski
Abstract: A schematic diagram and description of the ORC installation incorporating a single turbine will be presented for the case where the saturated dry vapour is produced in evaporators with an internal circulation of the individual energy carrying fluids. In the case of the heat sources of different temperature the internal circulation coefficients of the evaporators can be selected for each energy carrying fluid in such a way that the saturated dry vapour at the outlet of evaporators will have equal values of pressure and temperature. An algorithm of calculations will be also presented to enable the determination of the output power and efficiency of the power plant that works according to the subcritical Clausius-Rankine cycle. Calculation results will be shown for the cases of one, two and three energy carrying fluids of different temperature. On that basis, final conclusions will be given in respect to the possibility of application of the heat sources of different temperature to co-fuel the ORC power plant.
Amin Habibzadeh, Mohammad Mehdi Rashidi, Nicolas Galanis
Abstract: Recently, there is a strong interest toward exploiting renewable energies and waste heat instead of fossil fuel sources. The main reason is that the renewable energy sources are environment friendly, cheap and abundant. On the other hand the use of waste heat improves energy efficiency. Several studies have investigated the performance of cycles using low temperature heat sources [1, 2]. The present paper presents a thermodynamic study and optimization of a combined organic Rankine cycle (ORC) and ejector refrigeration cycle driven by low-temperature waste heat. The performance of different working fluids (R123, R141b, R245fa, R600a, R601a) was investigated. The analysis has been performed for a case for which the power/refrigeration ratio is 2, the pinch point temperature difference is fixed, the waste heat source temperature varies between 393 and 443 K, and the evaporator temperature varies between 258 and 278 K. Results show that the inlet pressure of the pump and inlet pressure of the turbine can be optimized to get a minimum total thermal conductance. The main results from this study at the defined ranges are as follows: 1- Inlet pressure of the pump and inlet pressure of the turbine can be optimized to get a minimum total thermal conductance. 2- Working fluid R601a is the suitable working fluid if the cycle is optimized according to the turbine inlet pressure, because it has the highest thermal efficiency (18.67%) and the lowest total thermal conductance (1479 kW/K). On the other hand, if the cycle is optimized according to the pump inlet temperature, R141b is the best choice because it has the lowest exergy destruction rate (911.8 kW) and the highest thermal efficiency (19.02 %). 3- Total exergy destruction of the proposed cycle increases as the heat source temperature and evaporator temperature increase but decreases as the condenser temperature and turbine expansion ratio increase. 4- Thermal efficiencies of the working fluids increase as the heat source temperature and expansion ratio of the ejector goes up.
Teemu Turunen-Saaresti, Antti Uusitalo, Juha Honkatukia, Jaakko Larjola
Abstract: The Organic Rankine Cycle (ORC) consists at least of a turbine, a pump, a condenser and an evaporator. The optimal operation of all process components is important to the efficient performance of the ORC. This is especially true in a case of a small electrical output and a low evaporation temperature processes where initial conditions are not supporting the high efficiency. The turbine efficiency can vary widely and it is affected by many factors e.g. the operation point, size, design and type of the turbine. Also when optimum operation of the turbine is sought, the maximum efficiency of the turbine is obtained using highly laborious and complex techniques. Therefore, it is important to study the necessity of achieving the top efficiency. In this study, the sensitivity of the ORC process to the turbine efficiency is evaluated. The ORC process is designed to produce about 10 kW of electric power and the heat source temperature is about 400 degree of centigrade. The working fluid of the cycle is siloxane, MDM. The effects of the turbine efficiency on the ORC process electric efficiency and on the measure of the ORC process quality are presented in this paper. The electric efficiency of the ORC process is rather insensitive for the turbine efficiency. The change in the electrical efficiency of the process is about 0.2 percent while the isentropic efficiency of the turbine changes one percent. Therefore, benefits improving the turbine efficiency using laborious methods and resulting complex geometry are not economically essential in units where the electric power is small. The financial benefit increasing the turbine isentropic efficiency by 5 percent is 174€ - 347€ per year with the electric price varying from 60€/MWh to 120 €/MWh and 5000 operation hours per year in the unit studied in this article. The financial benefits of the higher turbine efficiency are larger when the unit size is larger but in units with the small electric power the financial benefits are very low. Therefore, the main focus should be paid to the manufacturing costs of the turbine/unit rather than to optimize the turbine efficiency. REFERENCES: [1] J.P. van Buijtenen, J. Larjola, T Turunen-Saaresti, J Honkatukia, H. Esa, J. Backman and A. Reunanen: “Design and validation of a new high expansion ratio radial turbine for ORC application” 5th European conference on Turbomachinery, Prague, March 17-22, 2003 [2] J. Harinck, T. Turunen-Saaresti, P. Colonna, S. Rebay, and J. P. van Buijtenen, “Computational Study of a High-Expansion Ratio Radial Organic Rankine Cycle Turbine Stator”, Journal of Engineering for Gas Turbines and Power, 2010, 132, 054501
Christopher Steins, Martin Habermehl, Reinhold Kneer
Abstract: The use of geothermal energy for power generation at brine temperatures of less than 200°C is usually achieved by the Organic-Rankine-Cycle (ORC). Thereby, the choice of a suitable fluid results in another level of complexity in the design of such a process. The study analyses criteria for the evaluation of an ORC related to a given brine flow. Due to the given temperature and the given heat capacity rate, the aim for ORC design is to maximize the power output. Since the heat flow and the heat capacity rate from the geothermal source are limited, a simple efficiency consideration for the ORC based only on the Carnot efficiency will not lead to the maximum power output. The heat transfer between the brine and the working fluid must also be included into efficiency considerations. Using the concept of power maximization [1] to characterise the process temperatures, the choice of the fluid is used as a design parameter to optimise the heat transfer into the ORC. Based on a preliminary developed theoretical concept, the study analyses eight different working fluids, which have been chosen by their thermodynamic properties in relation to the maximum temperature of the brine. Within under-critical conditions the simple power cycle is then calculated over an interval of process power. As a reference, the conditions for a prospected geothermal power station in the German Upper Rhine Valley are taken. It is shown how the choice of the fluid influences the power output and the ability of the ORC to transfer the brine’s heat into work. Furthermore, considerations for a consistent efficiency definition are presented.
Michele Bianchi, Lisa Branchini, Andrea De Pascale, Sonia Di Nocco
Abstract: The organic Rankine cycle (ORC) is an emerging technology for power generation by recovering heat from different thermal sources. The most common applications are biomass power plants, recovery of wasted heat from industrial process and engine flue gases; applications under investigation are also geothermal, solar desalinization, biogas applications and heat recovery from waste-to-energy power plants. The ORC adopts a simple thermodynamic concept and is based on the use of particular organic fluids as working medium and their characteristics have a strong influence on the cycle performance. The general aim of the study started on the ORC at the University of Bologna is to perform different thermodynamic investigations on the potentiality of this kind of energy system, considering specific applications. The starting point for the analysis described with this paper/poster is the study of subcritical cycles, by considering fourteen fluids as working medium, including aromatics, linear siloxanes, refrigerants and hydrocarbons. This paper/poster represents a preliminary numerical study to assess the relevance of the main cycle parameters and to calculate the performance in term of heat recovery efficiency. To improve the recovery efficiency and the net power output of the ORC different cycle modifications are evaluated, such as superheated cycle, supercritical conditions and other cycle modifications. A parametric analysis of these cycles has been carried out at different evaporation pressure values, to identify the best operating condition. Preliminary results of the investigation will be provided.
Stefano Clemente, Diego Micheli, Mauro Reini, Rodolfo Taccani
Abstract: The paper presents the simulation model of a small-scale Organic Rankine Cycle (ORC), conveniently usable to recover electrical power from low-temperature heat sources, such as the exhaust gases of internal combustion engines, solar panels or biomass boilers. Aim of the paper is to achieve an overall knowledge of the expected performance of the experimental test bench currently under development at the Energy Systems Laboratory (EneSysLab) of the Department of Mechanical Engineering and Naval Architecture of the University of Trieste. The global model has been implemented with Aspen® simulation software, taking into account the real behavior of the system components in design and off-design conditions. All the heat exchangers have been modeled referring to the geometrical data provided by the manufacturer, and have been validated by comparing the simulated performances with the declared ones. Detailed one-dimensional models have been developed to predict the behavior of the expander, since it represents the most critical component of the cycle in terms of efficiency: MatLab® codes have been implemented for both a scroll expander [1-3] and an alternative (piston-type) machine [4, 5]. Several working curves (at various operating conditions and with reference to R245fa and isopentane as working fluids) have been obtained and used in the global model. In such a way, main dissipative phenomena in all components - like heat transfers toward ambient, pressure drops, expander leakages, etc. - can properly be taken into account in different applications and operating conditions, and the relative weight of each dissipative phenomenon and of each heat transfer irreversibility, affecting the cogenerator behavior, can be separately evaluated, highlighting possible design improvements for some components and for the whole system. REFERENCES [1] M. Kane, D. Larrain, D. Favrat, Y. Allani, “Small hybrid solar power system”, Energy, Vol. 28 (14), pp. 1427-1443 (2003). [2] V. Lemort, S. Quoilin, C. Cuevas, J. Lebrun, “Testing and Modeling of a Scroll Ex-pander Integrated into an Organic Rankine Cycle”, Appl. Therm. Eng., Vol. 29, pp. 3094-3102, (2009). [3] S. Clemente, D. Micheli, M. Reini, R. Taccani, “Numerical Model and Performance Analysis of a Scroll Machine for ORC Applications”, Proceedings of ECOS2010, June 14-17, Lausanne (CH), (2010). [4] M. Badami and M. Mura, “Preliminary design and controlling strategies of a small-scale wood waste Rankine Cycle (RC) with a reciprocating steam engine (SE)”, Energy, 34, pp. 1315-1324, (2009). [5] S. Clemente, D. Micheli, M. Reini, R. Taccani, “Performance analysis and modelling of different volumetric expanders for small-scale Organic Rankine Cycles” Proceedings of ESFuelCell2011, August 7-10, Washington DC ( USA) (2011).
Gang Pei, YunZhu Li, Jing Li, Jie Ji
Abstract: An ORC platform has been built to investigate its performance. In this platform, heated oil and circulating cooling water are used as heat source and sink respectively, organic fluid R123 is selected as the working medium, and a fabricated micro turbo-expander of high speed is employed as the heat engine. A DC motor-generator is attached to the turbo-expander via a gearbox, electricity is produced and then consumed by a series DC bulbs. Preliminary experiments were executed to examine the performance of the platform as well as the turbo-expander. In these tests, heat source temperature was regulated by a heat oil controller, and the turbo-expander inlet pressure was adjusted and controlled by the pump. The output power of the generator was regulated by adjusting the number of the bulbs manually. The experimental results show that the system works well. While the heat source and sink temperature were fixed at 108 ℃ and 31 ℃ respectively, the peak rotational speed of the turbo-expander reached to 24000 r/min, and the corresponding isentropic efficiency was 0.65.
Dariusz Mikielewicz, Jan Wajs, Michal Glinski, Jaroslaw Mikielewicz
Abstract: In the paper the application of ORC in the installation of heat recovery from the power unit is described. Presented works form a part of the national strategic project underway for one year. The analysis of possible configurations of waste recovery is done in several stages. In the first stage it is assumed that the ORC evaporator is supplied with hot water of temperature equal to 80 oC. Such temperature of working medium is coming from the energy conversion of all identified and possible to use waste energy sources in the power plant. Next, attention is focused on the possibility of increasing the upper temperature of the cycle. That could be done, for example by incorporation of absorption heat pumps or solar collectors in the cycle. Next, attention is focused on the possibility of designing the exhaust gas-working fluid heat exchanger where the exergetic losses would be limited and therefore the efficiency would increase. Some preliminary tests of the prototype of such heat exchanger have been conducted in the laboratory showing promising results.
Wijittra Hongsiri, Wiebren de Jong
Abstract: Green platform chemicals and biofuels(s) can be produced from wet biomass pretreatment integrated with supercritical water gasification. This is a novel biorefinery concept. However, the utilization of low grade heat to improve economics has been a challenge. This article describes a process model and simulations in which an Organic Rankine Cycle (ORC) was combined with Supercritical water gasification (SCWG) system. The working fluid used in this study is CO2. It has many advantages, low cost, low toxicity, is non-flammable and has no environmental impact. In this modeling, water temperature in the range of 170 - 200 ºC and a flow of 7200 kg/hr was used as the low-grade heat source. CO2 is biomass derived in the same process which can be produced about 1800 kg/hr. Aspen PlusTM process modeling software is used to model this system. The economics and efficiency of the process are evaluated.
Srikanth Santhanam, Daniel Baldacchino, Pauline Bozonnet, Lu Zheng
Abstract: The increasing need for clean, renewable energy is causing a renewed interest in Ocean Thermal Energy Conversion (OTEC). This concept developed at the beginning of the 20th century aims at generating electricity through a thermodynamic cycle, using the temperature difference between the hot surface water and the cold deep water in the ocean. The main advantage of OTEC, compared to other renewables like wind and solar energy, is the fact that it is a so-called baseload source of energy, available day and night. Furthermore, in addition to electricity production, OTEC also offers the possibility of co-generating other products like clean drinking water and enhancing agriculture and aquaculture productivity. However the available temperature difference found in tropical oceans of little more than 20°C highlights the true difficulty but exciting opportunity in harnessing ocean energy. Few successful demonstration power-plants have already been built worldwide, nevertheless research and investors are still lacking in this field. Thus to fill this gap and demonstrate the validity of the OTEC principle we are currently designing and building a small-scale (150W) working power-extraction cycle, an ‘OTEC Demo’. A thorough study of current practice and an evaluation of the available cycles have led to the choice of the Kalina cycle as extraction-cycle. The latter has been selected based on its (claimed) high efficiency for low-grade, large capacity thermal resources, like the ocean. Using Cycle Tempo [1], a software for thermodynamic analysis and optimization, the cycle has been modeled and the different components have been sized. A detailed comparison of the modeled Kalina cycle based OTEC prototype and an ORC based OTEC prototype is made with a view point of efficiency and economics is performed and greater efficiency for the Kalina based OTEC is expected. If the prototype proves to be successful it would be the first OTEC power plant based on this cycle in the world.
Zbigniew Gnutek, Piotr Kolasiński
Abstract: Works in the field of the ORC`s with mechanical power of 1-2 kW were carried out at the Institute of Power Engineering and Fluid Mechanics of Wrocław University of Technology since the early 1990s. Then the test stand of the ORC using as expander vane rotary machine was designed and built. Working medium was R-11. At the test stand, series of experiments were carried out, and the results have been collected by Mr Stanislaw Biernacki in his PhD thesis. The need for the withdrawal of R-11 from use was associated with the exploration of new working mediums and analysis of their property and properties of thermodynamic systems using different rotary vane expanders. New organization of a low potential heat conversion process to mechanical work has been proposed. Also the methodology of working medium selection has been designed. That methodology was then developed by Dr. ing. Piotr Kolasiński. CHP ORC systems that can be used in households and small workshops were designed, analyzed and tested. Works in ORC area are still carried out.
Bruno Vanslambrouck, Ignace Vankeirsbilck, Sergei Gusev, Michel De Paepe
Abstract: On renewable energy installations such as biogas-, landfill gas- and bio oil engines and even at all kinds of industrial plants lots of waste heat is dissipated into the atmosphere. On the other hand, there is a proven, commercially available technology to convert it (partially) into electricity. This is the Organic Rankine Cycle (ORC), used since several decades within f.i. geothermal plants. Applications of the same technology for waste heat recovery are rather premature. To transfer this technology to such applications, practical research in collaboration with industry was performed with as output : technology review (used working fluids to replace water/steam, expander types...), a market overview, view on technical and economical feasibility, simulation models, comparison between the steam cycle and ORC and selection criteria, industrial case studies (landfill- and biogas engines, steel, glass, paper, automotive, chemical, clay, water treatment....industry). As a conclusion, ORC-projects were found being very attractive on renewable energy applications with the help of green certificates. On non renewable industrial cases, economic feasibility strongly depends from integration costs and electricity prices. A test and demonstrational facility for ORC has been build. As a result of industrial collaboration, an unique 11 kWe ORC unit is composed and integrated as a scale model of the 50 and 250 kWe units that are commercially available.
Matthew Lehar, Guillaume Becquin
Abstract: As the demand grows for low-temperature waste heat recovery systems, ORCs (Organic Rankine Cycles) and other alternatives to traditional steam Rankine cycles are becoming more common in industry. Although analytical tools exist that can predict the performance of a steam cycle in a given waste-heat application, the development of a similar tool for ORCs has been hampered by the large choice of possible working fluids. In this paper, two methods are presented with the aim of providing an estimate of the best performance possible for any ORC in a given industrial application. The first is a purely analytical approach assuming an idealized fluid, and the second compares real fluids through cycle simulations to select the most appropriate parameters for the application. The analytical approach provides a rough baseline for performance, while the simulation method refines the estimate to give predictions that are more consistent with the documented performance of ORC plants currently in operation. Together, the two approaches represent a robust means of quickly estimating the capability of an ORC plant, to allow quick comparisons with other technologies.
Emilie Sauret, Andrew S. Rowlands, Carlos A. Ventura
Abstract: Optimisation of Organic Rankine Cycles (ORCs) for binary-cycle geothermal applications could play a major role in the competitiveness of low to moderate temperature geothermal resources. Part of this optimisation process is matching cycles to a given resource such that power output can be maximised. Two major and largely interrelated components of the cycle are the working fluid and the turbine. Both components need careful consideration. Due to the temperature differences in geothermal resources a one-size-fits-all approach to surface power infrastructure is not appropriate. Furthermore, the traditional use of steam as a working fluid does not seem practical due to the low temperatures of many resources. A variety of organic fluids with low boiling points may be utilised as ORC working fluids in binary power cycle loops. Due to differences in thermodynamic properties, certain fluids are able to extract more heat from a given resource than others over certain temperature and pressure ranges. This enables the tailoring of power cycle infrastructure to best match the geothermal resource through careful selection of the working fluid and turbine design optimisation to yield the optimum overall cycle performance. This paper presents the rationale for the use of radial-inflow turbines for ORC applications and the preliminary design of several radial-inflow turbines based on a selection of promising ORC cycles using five different high-density working fluids: R134a, R143a, R236fa, R245fa and n-Pentane at sub- or trans-critical conditions. Numerous studies published compare a variety of working fluids for various ORC configurations. However, there is little information specifically pertaining to the design and implementation of ORCs using realistic radial turbine designs in terms of pressure ratios, inlet pressure, rotor size and rotational speed. Preliminary 1D analysis leads to the generation of turbine designs for the various cycles with similar efficiencies (77%) but large differences in dimensions (139289 mm rotor diameter). The highest performing cycle (R134a) was found to produce 33% more net power from a 150°C resource flowing at 10 kg/s than the lowest performing cycle (n-Pentane).
Shengjun Zhang, Huaixin Wang, Tao Guo
Abstract: Kalina cycle, sub- and trans-critical ORC are three promising cycles to use low-temperature (i.e. 80-100°C) geothermal sources. However, little studies were published on the economic performance comparison of the three systems under their optimized operation parameters. The objective of this study is to provide favorable cycle and fluids as well as the corresponding optimum operation conditions for low-temperature (i.e. 80-100°C) geothermal ORC power system. And the minimum cost of geothermal power plant should be the determining factor of both choices. The LECplant value of the geothermal power plant can be divided into LECsystem and LECfield. The exploration, transmission, drilling, piping, control system, land use costs, etc, which almost const for a specific geothermal source, are indicated by LECfield. And the costs of refrigerant pump, turbine and heat exchangers are revealed by LECsystem and almost the same by our previous study [1] for both cycles when the optimum working fluids and parameters were used. So the fluids with maximum power output will be favored in this study. The power output of the system is used the objective function. The simulation is performed by using a program written in Matlab referred to our previous study [1]. The inlet temperature of the heat source and sink is 90oC and 20oC, respectively. The pinch temperature difference is 5oC and flow rate of the heat source is 1kg/s. And saturated vapor was assumed at the turbine inlet in subcritical ORC system. Aside from the 16 different working fluids considered in our previous study [1], the mixtures of ammonia/water with four solutions (Ammonia/Water mole fraction: 0.78/0.22, 0.82/0.18, 0.92/0.08, 0.98/0.02) are included. The results indicate that the R227ea exhibits the highest power output in subcritical ORC and the R218 is the excellent fluid by the highest power output of 12.3kW in transcritical ORC. The power output of Kalina cycle increases with the increasing of ammonia concentration in the mixture. The power output of the R218 is 30.2% larger than that of R227ea and 5% larger than that of ammonia/water (mole fraction: 0.98/0.02) mixture in Kalina cycle. In conclusion, the transcritical power cycle with R218 as the working fluid is a cost effective approach for the low-temperature geothermal ORC system. REFERENCES [1] Zhang Shengjun, Wang Huaixin, Guo Tao. Performance comparison and parametric optimization of subcritical Organic Rankine Cycle (ORC) and transcritical power cycle system for low-temperature geothermal power generation. Appl Energy 2011, 88, 2740-2754
Diego Acevedo, G.A. van Dorp, K.D. Kruit, C.L. van Zuijlen
Abstract: Combined heat and power (CHP) is an interesting application in which low-grade waste heat from combustion can be used to drive a turbine to produce electrical power. This article describes a simple model in which combustion of biomass (i.e. demolition wood) in a bubbling fluidized bed (BFB) is combined with an Organic Rankine Cycle (ORC) of 800 kWthermal operating on toluene. The advantage of using an organic fluid is that the turbine can efficiently operate at lower temperatures than with steam. Toluene as a working fluid, furthermore, has an extremely low global warming potential. The thermal input of the fluidized bed combustor is 1.1 MW (HHV based) and complete combustion is assumed with an excess air ratio of 20% at 1 bar and 850 °C. Furthermore, the system is designed in such a way that the temperature of the freeboard zone does not exceed 350 °C in view of the stability of the thermal oil. For optimal efficiency of the 800kW ORC system and under particular assumptions of fuel utilization and heat exchanger efficiency, a fuel flow rate of 229 kg/h (with a moisture content of 9.1% for demolition wood) and an air flow rate of 1614 kg/h lead to a flue gas flow rate of 1818 kg/h. A model is set up to calculate the heat capacity and flow rates of the flue gas, and it is found that the inlet air must be preheated to an optimum of 133 °C. Part of the stack heat lost could be used to preheat the air to the optimum temperature, therefore increasing the system efficiency. Heat losses through the reactor walls are neglected. Heat released during combustion is transferred to the ORC via heat exchangers on the bed and the freeboard section. The two separate flows are combined to a single flow to transfer the heat to the ORC generator. The heat exchangers are assumed to have an isentropic efficiency of 85% and a heat transfer coefficient of 400 W/m²K for the bed heat exchanger, and 50 W/m²K for the freeboard heat exchanger. A heat exchanging area of 3.3 m² for the bed heat exchanger, and 53.4 m² for the freeboard heat exchanger is sufficient to transport the heat, due to the temperature difference between the freeboard entrance and the thermal oil. This leads to a total flow rate of 3276 kg/h for the thermal oil. The model estimates a boiler thermal efficiency of 80.7% and electricity is produced with a system efficiency of 10.2%, which is in accordance with other studies [2]. A MATLAB model is implemented in which the efficiency and other parameters can be easily changed to obtain more precise temperature requirements and fluid flows. Key performance factors of the BFB and the ORC are identified and discussed. A considerable degree of uncertainty is found on the heat exchanger efficiencies. A change in the heat exchanger efficiency of +/- 5% can yield a difference in preheat temperature of 60-100 °C. Also, a cost benefit analysis of the cost of heat exchangers vs. efficiency of the complete system should be performed. A more sophisticated model can be designed to produce more a more accurate model. References: [1] P. Basu, Combustion and Gasification in Fluidized Beds, Taylor & Francis Group LLC, 2006. [2] A.A. Khan, Combustion and co-combustion of biomass in a bubbling fluidized bed boiler, Faculty 3mE, Delft University of Technology, Delft, 2007, p. 200.
Sylvain Quoilin, Clément Gantiez, Laurent Sanchez, Ahmed Berkane, Gilles David, Vincent Lemort
Abstract: This papers presents the design of 1 MWe biomass ORC for isolated grid operation and using Solkatherm as working fluid. Special attention is paid to the control of the system: a dynamic model of the ORC is developed and coupled to several control strategies in order to evaluate their respective performance under different load profiles on the isolated grid.
Erhard Perz, Michael Erbes
Abstract: Organic Rankine Cycles (ORCs) are often integrated in more complex systems such as geothermal plants, biomass combustion and gasification plants, solar power plants or industrial processes. To optimize the performance of the resulting system, accurate models of the thermodynamic system are of great value. This paper describes the process modeling system IPSEpro and its application to ORCs. With IPSEpro, process models are created from individual components. The user can set up the process scheme graphically by arranging components appropriately and entering the required data in the flowsheet. IPSEpro is a open framework: Components and physical property calculations are not coded into the system. All application specific information is contained in model libraries. A model library for modeling ORC processes is available. The user can combine the ORC library with other existing libraries, like libraries for power processes, for solar power or for biomass gasification. Additionally the user can modify libraries and create new ones using a Model Development Kit (MDK). The paper illustrates the capabilities of the ORC library and presents results obtained. Once a process model exists, its usage is not limited to normal performance calculations. With additional modules, the model can be used for parameter optimization as well as for the validation of measured data. The paper show examples for this usage.
Laura Alonso, Joan Carles Bruno, Alberto Coronas
Abstract: Cement manufacturing is an energy intensive process, in which a large part of the consumed energy is emitted as waste heat. The BREF reference document [1] reports waste heat recovery for electricity generation as one of the Best Available Techniques for the cement industry. In this paper, integration of two Organic Rankine Cycles (ORC) using two different working fluids is proposed and analyzed. Electricity generation potential of the cycle is very closely related to the availability of the heat source. In the cement manufacturing process two waste heat sources mainly exist: the preheater exhaust and clinker cooler exhaust gases, which have different temperature levels. Energy recovery from both heat sources has been analyzed, considering typical values of exhaust gases flow and temperature. Efficiency of ORC depends mainly on the thermodynamic properties of the working fluid and its operating conditions. Therefore, selection of the working fluid plays a key role in ORC systems, and is determined by the waste heat level. For this particular application, where waste heat at two different temperature levels is available, the use of two Organic Rankine Cycles is analyzed, by using suitable fluids for each heat source. The analysis and comparison of several integrated configurations is presented. Integration of both cycles is optimized in order to maximize heat recovery. The proposed configuration is also compared with a more conventional ORC making use of both waste heat sources but with a single fluid.
Dariusz Mikielewicz, Jaroslaw Mikielewicz, Jan Wajs, Tomasz Muszynski, Eugeniusz Ihnatowicz
Abstract: In the paper the idea of a novel microjet heat exchanger is shown together with the flow and thermal experimental results of the prototype. Two flow cases are studied, namely water-water and air-air. In case of measurements of such complex geometries recording of wall temperatures is impossible and hence determination of heat transfer coefficient difficult. Therefore the Wilson technique was used for determination of the heat transfer coefficient. The results of accomplished measurements are satisfactory with the view of developing effective heat exchangers.
Katja Kruit, Diego Acevedo, Bert van Dorp, Christine van Zuijlen
Abstract: Combined heat and power (CHP) is an interesting application in which low-grade waste heat from combustion can be used to drive a turbine to produce electrical power. This article describes a simple model in which combustion of biomass (i.e. demolition wood) in a bubbling fluidized bed (BFB) is combined with an Organic Rankine Cycle (ORC) of 800 kWthermal operating on toluene. The advantage of using an organic fluid is that the turbine can efficiently operate at lower temperatures than with steam. Toluene as a working fluid, furthermore, has an extremely low global warming potential. The thermal input of the fluidized bed combustor is 1.1 MW (HHV based) and complete combustion is assumed with an excess air ratio of 20% at 1 bar and 850 °C. Furthermore, the system is designed in such a way that the temperature of the freeboard zone does not exceed 350 °C in view of the stability of the thermal oil. For optimal efficiency of the 800kW ORC system and under particular assumptions of fuel utilization and heat exchanger efficiency, a fuel flow rate of 230 kg/h (with a moisture content of 9.1% for demolition wood) and an air flow rate of 1600 kg/h lead to a flue gas flow rate of 1800 kg/h. A model is set up to calculate the heat capacity and flow rates of the flue gas, and it is found that the inlet air must be preheated to an optimum of 133 °C. Part of the stack heat lost could be used to preheat the air to the optimum temperature, therefore increasing the system efficiency. Heat losses through the reactor walls are neglected. Heat released during combustion is transferred to the ORC via heat exchangers on the bed and the freeboard section. The two separate flows are combined to a single flow to transfer the heat to the ORC generator. The heat exchanger system is assumed to have an overall efficiency of 85% and a heat transfer coefficient of 400 W/m²K for the bed heat exchanger, and 50 W/m²K for the freeboard heat exchanger. A heat exchanging area of 3.3 m² for the bed heat exchanger, and 53.4 m² for the freeboard heat exchanger is sufficient to transport the heat, due to the temperature difference between the freeboard entrance and the thermal oil. This leads to a total flow rate of 3300 kg/h for the thermal oil. The model estimates a boiler thermal efficiency of 80.7% and electricity is produced with a system efficiency of 10.2%, which is in accordance with other studies [2]. If the heat from the flue gas is used to preheat the incoming air, the thermal efficiency could be raised up to 84%. A MATLAB model is implemented in which the efficiency and other parameters can be easily changed to obtain more precise temperature requirements and fluid flows. Key performance factors of the BFB and the ORC are identified and discussed. A considerable degree of uncertainty is found on the heat exchanger system efficiency. A change in the heat exchanger efficiency of +/- 5% can yield a difference in preheat temperature of 60-100 °C. Also, a cost benefit analysis of the cost of heat exchangers vs. efficiency of the complete system should be performed. A more sophisticated model can be designed to produce more a more accurate result. References: [1] P. Basu, Combustion and Gasification in Fluidized Beds, Taylor & Francis Group LLC, 2006. [2] A.A. Khan, Combustion and co-combustion of biomass in a bubbling fluidized bed boiler, Faculty 3mE, Delft University of Technology, Delft, 2007, p. 200.
Alexander Nikolskiy, Sergey Ryabokon, Grigory Tomarov, Valery Semenov, Andrey Shipkov
Abstract: Modern technologies for the exploitation of geothermal energy in power plants or heating systems have been developed in Russia since the late 60's [1]. In 1967, the first binary cycle geothermal power plant in the world was built in Russia, at Paratunsky . This plant used hot water at 90о C for electricity generation. In 1999 the 12 MW Verkhne-Mutnovsky geothermal power plant (V-M GeoPP) in Kamchatka was put into operation. The Mutnovsky GeoPP (50 MW) was commissioned in October 2002 and has been in successful operation despite of severe climate conditions. Currently a new generation of geothermal binary power plants is being developed in Russia. This new technology is aimed at the production in series of smaller systems for the conversion of low-enthalpy heat sources into electricity and/or heating. JSC “RusHydro Engineering Center of Renewable Energy” with the scientific and technical assistance of SC “Geotherm-EM” have designed and are building a pilot plant at the Pauzhetsky site [2, 3]. Research and development activities include system design, fluid selection, experimental investigation of several aspects, components selection and development of the control system.. The Pauzhetsky installation will include: the turbo-unit and its auxiliaries, condenser, heat exchangers (heater, evaporator and super-heater share a common housing), feed pumps, auxiliaries of the power unit (including storage tank for waste working fluid), corrosion-protection and salt-sedimentation-protection devices, and cooling water pumps. The project is at the stage of pre-commissioning. Various aspects of the design, construction and commissioning are discussed. REFERENCES [1] G. Tomarov, A. Nikolsky, V. Semenov, A. Shipkov, “Recent Geothermal Power Projects in Russia”, Proceedings World Geothermal Congress (2010). [2] M. Boyarskiy, O. Povarov, A. Nikolskiy, A. Shipkov. “Comparative Efficiency of Geothermal Vapor-Turbine Cycles”, Proceedings World Geothermal Congress (2005). [3] G. Tomarov, A. Nikolsky, V. Semenov, A. Shipkov, “Construction of Russia’s Pilot Binary Power Unit at the Pauzhet Geothermal Power Station”, Thermal Engineering, Vol. 57, No. 11, pp. 925–930 (2010)
Athanasios Papadopoulos, Mirko Stijepovic, Patrick Linke, Panos Seferlis, Spyros Voutetakis
Abstract: Power generation from low enthalpy heat sources requires the use Organic Rankine Cycle systems (ORC), where organic fluids such as hydrocarbons or refrigerants are utilized to facilitate efficient heat extraction. The economic, operating and environmental performance of the ORC depends on the properties of the selected working fluids, the design and operating characteristics of the ORC process and the characteristics of the heat source (e.g. hot fluid temperature, flowrate etc.). This raises the challenge of selecting working fluids and ORC process features that will result in an integrated system of optimum performance for a particular heat source. Available works address the selection of ORC fluids based on fluid- and process-related properties by testing various available fluids in ORC simulation models, sometimes combined with optimization of process operating parameters. A common characteristic shared among all these approaches is the use of a data set containing several available working fluid options. Although useful, this approach limits the search for efficient working fluids that exhibit favourable properties to an often empirically compiled dataset containing ‘‘the usual suspects”. Such a small set is extremely limiting in view of the vast number of molecules that could be considered as candidate ORC working fluids. Instead, this work proposes a systematic approach combining computer-aided molecular design (CAMD) methods with process optimization to enable the design of working fluid options and ORC processes of optimum performance. CAMD tools utilize a database containing a few chemical groups that are used to generate and search a vast number of conventional or novel molecular structures to identify those working fluids that offer the best performance with respect to the properties of interest. The evaluation of the investigated working fluids is based on multi-objective optimization technology to identify a broad set of options with optimum physical, chemical, environmental and safety characteristics. The generated working fluids are subsequently introduced to ORC optimization in order to identify process and molecular features resulting in optimum economic performance [1]. Several ORC design stages are considered incorporating increasing modelling and design detail to enable fast and efficient screening of working fluid candidates in view of varying heat source conditions. The proposed developments are illustrated with applications in power or heat and power cogeneration from low enthalpy geothermal fields. Important working fluid properties are considered such as toxicity, flammability, ozone depletion and global warming potential, in conjunction to economic ORC performance. REFERENCES [1] A. I. Papadopoulos, M. Stijepovic, P. Linke. On the systematic design and selection of optimal working fluids for Organic Rankine Cycles, Applied Thermal Engineering, 30, 760-769 (2010)