Low Temperature Heat Sources Research Articles

Energy Performance Comparison between Power and Absorption Refrigeration Cycles for Low Grade Waste Heat Recovery

Power cycles converting waste heat to electricity and absorption refrigeration cycles converting waste heat to cooling are widely used for low grade waste heat recovery in the process industry. It is significant to choose an appropriate cycle to recover waste heat at different temperatures. In this paper, a comparison is performed between a Kalina cycle and a LiBr-H2O absorption refrigeration cycle considering low-temperature waste heat sources at different temperatures, and the optimal conditions of these two waste heat utilization technologies are determined. Because power and cooling are different kinds of energy with different energy levels, a novel indicator, the amount of mechanical work, is used to evaluate the cycles to reasonably compare the energy performance of the cycles. The cooling generated by an absorption refrigeration cycle is converted into mechanical work required by a compression refrigeration cycle under the same cooling output. Results show that when the waste heat source temperature is from 100 to 175 °C, it is proper to choose a LiBr-H2O absorption refrigeration cycle; when temperature range is 175 to 200 °C, the Kalina cycle is preferable.

A novel geothermal combined cooling and power cycle based on the absorption power cycle: Energy, exergy and exergoeconomic analysis

Energy, exergy, and exergoeconomic analysis of a novel combined cooling and power (CCP) system for producing cooling and power outputs are presented based on the absorption power cycle (APC), using geothermal energy as low-temperature heat source. A comprehensive thermodynamic modeling of the proposed CCP system is carried out leading to determine the main source of irreversibility and performance characteristics of the system for a better thermal design purpose. In the parametric study, the effect of key thermodynamic parameters (i.e., generator hot pinch point temperature difference (PPTD), generator cold PPTD, ammonia concentration, absorber minimum temperature difference, condenser minimum temperature difference, evaporator temperature, and geothermal temperature) on the key performance parameters (i.e., net output power, cooling capacity, thermal efficiency, exergy efficiency, and sum unit cost of product (SUCP) of system) are investigated. It is found that the proposed system can produce cooling capacity and net output power of 221.4 kW and 161.2 kW, respectively, under supplying 2333 kW heat from the geothermal source. In this case, the overall thermal efficiency, exergy efficiency, and SUCP of system are calculated by 16.4%, 28.95% and 93.87 $/GJ, respectively. From exergy analysis it is understood that among all components, absorber accounted for the largest contribution of exergy destruction which constituted around 39.89% of the overall exergy destruction of system. In addition, the highest cost of exergy destruction corresponded to the absorber which is followed by the condenser. Finally, parametric study revealed that the exergy efficiency of the proposed system can be maximized based upon the ammonia concentration and evaporator temperature. Moreover, it is shown that the thermal efficiency of system can be increased by increasing of the generator hot PPTD and evaporator temperature or decreasing ammonia concentration, absorber and condenser minimum temperature differences, and geothermal temperature. While, it is also found that the SUCP of system can be decreased by increasing the generator cold PPTD, condenser minimum temperature difference, and geothermal temperature or decreasing the generator hot PPTD, absorber minimum temperature difference, and evaporator temperature.

Performance analysis of low temperature heat source of organic Rankine cycle for geothermal application

Indonesia has a high potential energy resources from geothermal activities. Base on the report of Asian Development Bank and World Bank, the estimated of Indonesian hydrothermal geothermal resource considered to be the largest among the world. If it’s can be utilized to produce the electric power, it’s can contribute to increasing the electrification rates in Indonesia. In this study, an experimental studied of electric power generation, utilizing the Organic Rankine Cycle (ORC) system to convert the low level heat of hydrothermal as an energy source. The temperature of hydrothermal was modelled as hot water from water boiler which has a temperature range from 60 °C – 100 °C to heat up the organic working fluid of ORC system. The system can generated 1,337.7 watts of electricity when operated using R134A with hot water inlet temperature of 100 °C. Changing system working fluid to R245fa, the net power obtained increase to 1,908.9 watts with the same heat source condition. This study showed that the ORC system can be implemented to utilize low temperature heat source of hydrothermal in Indonesia.

Correction to: Parametric study and working fluid selection of modified combined power and refrigeration cycles (MCPRCs) using low-temperature heat sources

Correction to: Parametric study and working fluid selection of modified combined power and refrigeration cycles (MCPRCs) using low-temperature heat sources

Energy recovery from natural gas pressure reduction stations: Integration with low temperature heat sources

Energy recovery from Natural Gas (NG) distribution networks is a promising strategy in order to pursue energy sustainability in urban areas. The NG pressure reduction process, normally achieved by means of conventional throttling valves, can be upgraded by implementing turbo expander technology, which allows recovery of energy from the NG pressure drop. As commonly known, in this process the NG must be preheated in order to avoid methane-hydrate formation. The preheating temperature represents a key parameter of the process, on which depends the possibility of integrating low enthalpy heat sources into the system and of exploiting more efficient technologies and renewable energies as well. In this work, the possibility of integrating a pressure reduction station with low temperature heat sources is studied. In particular, a novel plant configuration consisting of a two-stage expansion system is presented and its energy performances are investigated by means of numerical dynamic simulations. The risk of formation of methane hydrate is assessed for different operating conditions and for transient behavior. Finally, the energy efficiency of PRSs with high and low temperature configuration is compared, showing how the two stage expansion can achieve higher energy performance and be effectively integrated with low enthalpy heat sources.

Testing the lab-scale “Heat from Cold” prototype with the “LiCl/silica – methanol” working pair

Adsorptive transformation of heat is an energy and environment saving technology, which allows effective utilization of low temperature heat sources. Recently, a new adsorption cycle (the so-called “Heat from Cold” or HeCol) has been suggested for amplification of the ambient heat in cold regions up to higher temperature, suitable for heating. In this paper, at first we analyzed which adsorbent is needed for practical realization of the HeCol cycle. Then, the composite sorbent, based on LiCl and silica gel, was selected for the comprehensive study, and its sorption equilibrium with methanol was analyzed keeping in mind the requirements of the HeCol cycle. Finally, a first lab-scale HeCol prototype was tested with the LiCl/silica sorbent to evaluate the feasibility of the new cycle. The effects of the heat source temperature and the rate of heat transfer fluid on the prototype performance were studied. It was shown that at heat source temperature of 20–30 °C, the maximum temperature of the released heat reaches 34–53 °C, which is suitable for warm floor and hot water systems. The maximum specific heating power varies from 6.0 to 10.8 kW/kg and the sorbent heating capacity reaches 620 kJ/kg. The results obtained clearly demonstrate that the use of the LiCl/silica sorbent allows quite compact HeCol units to be designed.

Parametric study and working fluid selection of modified combined power and refrigeration cycles (MCPRCs) using low-temperature heat sources

This paper presents a theoretical analysis of various combined power and refrigeration cycles (CPRCs) as well as the working fluid selection used in these cycles based on the first law of thermodynamics. These proposed cycles include a combination of organic Rankine cycles (ORCs) and an ejector refrigeration cycle (ERC) to produce more power and refrigeration, simultaneously. In all the proposed cycles, the ejector is driven by the exhausts of the turbine. The performance of the proposed cycles for five appropriate working fluids (i.e., isobutane, isobutene, butene, R236fa, and R245fa) is evaluated by the means of their corresponding thermal efficiency and power/refrigeration ratio. It has been demonstrated that among all the proposed working fluids, isobutane is a good candidate with a thermal efficiency of 39.03–44.52%, which is enhanced through these modifications, successively. In this study, simple CPRC and modified regenerative CPRC with an IHE have the minimum and maximum thermal efficiencies, respectively. Thermal efficiency is improved by 8.27, 6.76, 5.63, 5.33, and 5.49%, in the case of R245fa, R236fa, butene, isobutene, and isobutane, respectively. Throughout these state-of-art modifications, rejecting heat has also been decreased. Moreover, the effects of key parameters such as evaporator, condenser, and generator temperatures on each cycle are also investigated.

Estimation of microalgae resource potential for bio-oil production and sustainable rural development in the climatic conditions of Russia (the Republic of Dagestan)

The work is devoted to the estimation of microalgae resource potential for bio-oil production. We propose a method of climate and infrastructural factors spatial analysis for estimations of resource and the possibility of bio-oil production facilities construction in the study region. The resource potential depends on the area of the territory that can be used to produce biomass as feedstock for biofuel production, and equal to the amount of microalgae biomass that can be obtained on this territory. For the case study we selected the territory of the Republic of Dagestan (Russia) and microalgae Arthrospira platensis and Dunaliella salina. As an infrastructural factors, which may reduce the cost of bio-oil production we considered the following sources of cheap material resources and energy: seawater (as a source of macro- and microelements), geothermal water (as low-temperature heat source), CO2 emissions of cement plants and combined heat and power plants (as carbon source and to reduce CO2 emission). The analyses of these factors using the technology of geoinformation systems allowed to find the most suitable territories for microalgae plant allocation and therefore estimate resource potential for biooil production with maximum profit.

Experimental study for a high efficiency cascade heat pump water heater system using a new near-zeotropic refrigerant mixture

Single-stage water-source heat pumps have some disadvantages such as high pressure ratio and lower coefficient of performance at high water outlet temperature, and normally the temperature promotion cannot exceed 50 °C. To surmount these disadvantages, a high temperature water-source cascade heat pump (HTWSCHP) was suggested; the HTWSCHP system demonstrates a much more competitive performance at high water outlet temperature of 142 °C and the temperature promotion can reach 90 °C. Lots of researches have been performed to analyze the cascade heat pump system, but they are normally about the low ambient temperature and there is very little information about the high water -outlet temperature. In this study, a HTWSCHP system was investigated experimentally. The high and low refrigerant cycle employed BY-3(A&B) and R245fa respectively. The experimental test was performed under different conditions: different electronic expansion valve opening ratio combination for low and high cycle, different refrigerants for the low cycle, different temperature for low-temperature heat source, different heating capacity, and varying water-outlet temperature. The final results shows that the water-outlet temperature of 142 °C can be achieved which is the highest level in the open literature with the total coefficient of 1.669, and the pressure ratio for low and high cycle are 3.9 and 3.4 respectively.

Performance investigation of Kalina cooling cogeneration cycles

The power and cooling demands are increasing drastically with increase in living stands and population. Kalina cycle system (KCS) is a power cycle and vapor absorption refrigeration (VAR) is a refrigeration cycle operating with zeotropic mixture. In this work, the common features of KCS and VAR are identified and developed a new Kalina cooling cogeneration cycle (KCCC) to generate combined power and cooling from a single plant configuration. The total output from cogeneration is compared with the total generation from the individual plants (KCS and VAR) at low temperature heat source (155−180 °C). To justify the merit of proposed configuration, thermodynamic simulation has been conducted through critical investigation applied to flexible KCCC under varying operating conditions viz. strong solution concentration, source temperature, separator vapor concentration and dephlegmator effectiveness. The generated results are power, refrigeration, combined power and cooling, cycle energy utilization factor (ENUF) and plant ENUF. The power to total output ratio in KCCC once through cycle is considered as a reference to the other cooling cogenerations for the comparison. The highest cycle ENUF (0.39) is resulted with KCCC once through cycle. KCCC split cycle is not recommended because of its lower efficiency (0.18) compared to the non-integrated efficiency (0.21).

Conceptual design and performance evaluation of a hybrid concentrating photovoltaic system in preparation for energy

Concentrating sunlight and focussing it on smaller sized solar cells increases the device's power output per unit active area. However, this process tends to increase the solar cell temperature considerably and has the potential to compromise system reliability. Adding a heat exchanger system to regulate this temperature rise, can improve the electrical performance whilst simultaneously providing an additional source of low temperature heat. In this study the performance of a low concentrator photovoltaic system with thermal (LCPV/T) extraction was conceptualised and evaluated in depth. An experimental analysis was performed using a first-generation prototype consisting of 5 units of Cross Compound Parabolic Concentrators (CCPC) connected to a heat extraction unit. A bespoke rotating table was used as experimental apparatus to effectively evaluate the optical performance of the system, as a function of its angular positions to replicate the motion of actual sun. Key design performance parameters for the LCPV/T collector are presented and discussed. This work also provides a useful technique to effectively calculate system performance, as a function of the orientation-dependant electrical characterisation parameters data. Finally, a Computational Fluid Dynamics (CFD) model was also applied to investigate the efficacy of the heat exchanger and hence estimate the overall co-generation benefit of using such optimisation techniques on realistic CPV systems. It was highlighted through these simulations that the water flow rate had the potential to be a critical power-generation optimisation criterion for LCPV-T systems. The maximum power output at normal incidence with concentrators and no water flow was found to be 78.4 mW. The system was found to perform with an average electrical efficiency ranging between 10 and 16% when evaluated at five different geographic locations. Experimental analysis of the data obtained showed an increase in power of 141% (power ratio 2.41) compared to the analogous non-concentrating counterpart. For example, in the case of London which receives an annual solar radiation of 1300 kWh/m2 the system is expected to generate 210 kWh/m2. This may reduce further to include losses due to temperature, reflectance/glazing losses, and electrical losses in cabling and inverter by up to 36% leading to an annual power output of 134 kWh/m2 of module.

Novel classification of pure working fluids for Organic Rankine Cycle

Power generation from low-temperature heat sources (80–300 °C) like thermal solar, geothermal, biomass or waste heat has been becoming more and more significant in the last few decades. Organic Rankine Cycle (ORC) uses organic working fluids, obtaining higher thermal efficiency than with water used in traditional Rankine Cycles, because of the physical (thermodynamic) properties of these fluids. The traditional classification of pure (one-component) working fluids is based on the quality of the expanded vapour after an isentropic (adiabatic and reversible) expansion from saturated vapour state, and distinguishes merely three categories: wet, dry and isentropic working fluids. The purpose of this paper is to show the deficiencies of this traditional classification and to introduce novel categorisation mostly to help in finding the thermodynamically optimal working fluid for a given heat source.

Thermodynamic and economic assessments of a novel CCHP cycle utilizing low-temperature heat sources for domestic applications

Abstract This paper presents thermo-economic analysis of a novel combined cooling, heating, and power (CCHP) cycle based on the first and second laws of thermodynamics and economic point of view. The proposed CCHP cycle includes an organic Rankine cycle, an ejector refrigeration cycle and a domestic water heater to produce the desired electrical power, cooling and heating, simultaneously. The basic CCHP (BCCHP) system is modified by regenerative method (RCCHP). Four different dry working fluids R123, R236fa, R245fa and R600a are employed. Both systems are analyzed thermo-economically and their performance, total cost rate and unit cost of products are compared. Moreover, parametric study is conducted to investigate the effect of key parameters. Under given condition, thermodynamics analysis of proposed systems is conducted in which the maximum energy and exergy efficiencies corresponded to the BCCHP system using R123 as working fluid. The exergy analysis results show that, vapor generator has a major contribution in the overall exergy destruction, which is followed by the domestic water heater. Also, minimum total cost rate belongs to the proposed RCCHP system utilizing R123. Furthermore, a multi-objective optimization is performed for both systems. The optimization results show that RCCHP system has the smaller total cost rate compare to the BCCHP while their thermodynamic performances are approximately the same.

Energetic investigation of a new combined ORC-VCC system for cogeneration

The present study, deals with a novel combined ORC-VCC system. In fact, the main purpose of this study is to analyze the performance of the proposed cycle, which combines Rankine-vapor compression cycle for the cogeneration of electricity and refrigeration. This system uses a low-temperature heat sources such as solar energy, industrial waste heat and biomass. Particular attention is paid to the effect of parameters system, including the evaporation temperature, the mass flow, the temperature and the pressure of the heating source on system performances, such as refrigeration capacity efficiency Thermal and the COP.

ORC cogeneration systems in waste-heat recovery applications

The performance of organic Rankine cycle (ORC) systems operating in combined heat and power (CHP) mode is investigated. The ORC-CHP systems recover heat from selected industrial waste-heat fluid streams with temperatures in the range 150 °C – 330 °C. An electrical power output is provided by the expanding working fluid in the ORC turbine, while a thermal output is provided by the cooling water exiting the ORC condenser and also by a second heat-exchanger that recovers additional thermal energy from the heat-source stream downstream of the evaporator. The electrical and thermal energy outputs emerge as competing objectives, with the latter favoured at higher hot-water outlet temperatures and vice versa. Pentane, hexane and R245fa result in ORC-CHP systems with the highest exergy efficiencies over the range of waste-heat temperatures considered in this work. When maximizing the exergy efficiency, the second heat-exchanger is effective (and advantageous) only in cases with lower heat-source temperatures (< 250 °C) and high heat-delivery/demand temperatures (> 60 °C) giving a fuel energy savings ratio (FESR) of over 40%. When maximizing the FESR, this heat exchanger is essential to the system, satisfying 100% of the heat demand in all cases, achieving FESRs between 46% and 86%.

R1234yf and R1234ze as alternatives to R134a in Organic Rankine Cycles for low temperature heat sources

This paper compares the predicted organic Rankine cycle performance of two low global warming potential working fluids, R1234yf and R1234ze, alternatives to R134a over a wide range of evaporating temperatures and condensing temperatures for a given thermal power input. The results show that R1234yf would require 18.3% to 25.8% higher pump power and would enable up to 13.9% lower net cycle efficiencies than R134a over the range of cycle conditions examined in this work. In the other hand, R1234ze would require 15.7% to 20.2% lower pump power and would enable up to 13.8% higher net cycle efficiencies than R134a, over the range of cycle conditions analyzed. Both alternative fluids net cycle efficiency is benefitted substantially by a recuperator. The differences with R134a in net cycle efficiency are accentuated for high evaporating and condensing temperatures.

Thermo-economic evaluation of low global warming potential alternatives to HFC-245fa in Organic Rankine Cycles

In the present work, a thermo-economic evaluation of the low global warming potential fluids HCFO-1233zd-E, HFO-1336mzz-Z and HFO-1234ze-Z as alternatives to HFC-245fa in organic Rankine cycle systems for low temperature heat sources is carried out. A thermodynamic organic Rankine cycle model is extended with the overall cost of the system, and it is used to identify the system parameter values for each working fluid considered that minimize the specific investment cost at a given set of the heat source and sink inlet temperatures. Thereby, the results show that HCFO-1233zd-E and HFO-1336mzz-Z present higher efficiencies than HFC-245fa, while HFO-1234ze-Z presents lower efficiency than HFC-245fa. The low global warming potential working fluids result in lower specific investment cost values than HFC-245fa. HFO-1336mzz-Z presents the lowest specific investment cost and highest efficiency values among the working fluids of interest throughout the range of operating conditions studied.

Exergoeconomic analysis and comparison between ORC and Kalina cycles to exploit low and medium-high temperature heat from two different geothermal sites

The Organic Rankine (ORC) and Kalina (KC) Cycles represent two different technologies suitable to exploit low and medium temperature geothermal heat resources. In this work, the performances of KC, CO2 and ORC cycles, the latter using different working fluids, for power generation from two geothermal fluid reservoirs are compared from an energy and exergoeconomic perspective.Two different case studies are discussed: the first one referred to a medium-temperature heat source of 212 °C (Mt. Amiata, Italy), the second one to a low-temperature heat source of 120 °C (Pomarance geothermal basin, Italy).For each case study, cost rate balances and auxiliary equations for all components were evaluated, as well as the flow rate and unit exergy cost for each stream.The results for the medium temperature case study showed that, among the considered cycles, an ORC with R1233zd(E) achieves the best exergoeconomic performance. The cost of the produced electricity was found to be 8.85 c€/kW h, which is 3% lower than that of the KC. On the other hand, for the low temperature case study, the KC shows the best performance, being able to produce 22–42% more net power than the ORC; in this case, the cost of electricity produced by the KC was found at 12.5 c€/kW h, which is 24–34% lower than the typical value for an ORC with different working fluids.

Hybrid heating system for increased energy efficiency and flexible control of low temperature heat

This study presents the evaluation of functionality and potential of a hybrid heating system (H2S) prototype. This technology is designed for retrofitting thermal treatment plants to use hot water (HW) and steam in controlled ratios. In the food industry, steam with a temperature above 140 °C usually indirectly supplies the thermal production processes, but most of them only require temperatures below 100 °C. Total site heat integration is applied on a cheese and whey powder plant to show the potential for low-temperature heat (below 100 °C) that could be supplied more appropriately by hot water cogeneration, heat recovery and heat pumps. These low-temperature heat sources can only be combined with the rigid steam system if the demand structure is changed to a hybrid use of HW and steam. The H2S increases the energy efficiency and flexibility by integrating low-temperature heat and responding to sudden changes in the demand and supply structure, like demand response strategies on intermittent renewable energies and the changing availability of HW and steam. The technical implementation is realised by a hydraulic interconnection of heat exchangers and valves. A smart control algorithm acutely determines the share of HW and steam. Prerequisite for functional verification on a laboratory scale is a hardware-in-the-loop (HIL) testbed, in which load profiles and relevant process parameters are passed in real time between hardware components and simulation. The results show that the H2S is a feasible solution for maintaining product quality and safety while also increasing energy efficiency and energy flexibility.

Proposal and assessment of a novel geothermal combined cooling and power cycle based on Kalina and ejector refrigeration cycles

This paper aims at introducing a new combined cooling and power (CCP) cycle, using geothermal energy as low-temperature heat source. The proposed cycle is integrated from a Kalina cycle (KC) and an ejector refrigeration cycle (ERC) to produce a simultaneous refrigeration and power outputs. To enhance performance operation of the proposed CCP cycle, turbine exhaust is extracted for more power production purposes by employing a feed fluid heater (FFH). Energy and exergy assessments of the proposed CCP cycle are conducted using Engineering Equation Solver (EES) software. In addition, considering the thermal efficiency and exergy efficiency as objective functions, single- and multi-objective optimizations are carried out by genetic algorithm (GA), leading to determination of the optimum design variables including basic ammonia concentration, geothermal inlet temperature, evaporator temperature, turbine inlet pressure, mass extraction ratio (MER), FFH pressure, terminal temperature difference (TTD) of vapor generator, and pinch point temperature differences of vapor generator and recuperators. In this case, the optimum net output power, refrigeration, thermal efficiency and exergy efficiency are calculated 2319 kW, 1133 kW, 15% and 47.8%, respectively. Moreover, among all components condenser 1 accounts for the biggest exergy destruction rate (589.6 kW) followed by vapor generator (422.1 kW). To better understand the effect of various parameters on system performance, a comprehensive parametric study of some key parameters (including turbine inlet pressure, geothermal inlet temperature, feed fluid heater pressure, evaporator temperature, basic ammonia concentration, and mass extraction ratio) on the performance criteria is carried out. It is shown that the exergy efficiency of system can be maximized based on the turbine inlet pressure, feed fluid heater pressure, basic ammonia concentration, and mass extraction ratio. In addition, the thermal efficiency of system can be maximized by feed fluid heater pressure, while refrigeration output can be maximized by mass extraction ratio. Also, it is shown that a higher power output can be obtained at lower turbine inlet and feed fluid heater pressures as well as higher geothermal inlet temperature, basic ammonia concentration, and mass extraction ratio. Moreover, a higher refrigeration output can be resulted at higher turbine inlet pressure and evaporator temperature, as well as lower feed fluid heater pressure and basic ammonia concentration.