Low Temperature Heat Sources Research Articles

Adsorption cycle “heat from cold” for upgrading the ambient heat: The testing a lab-scale prototype with the composite sorbent CaClBr/silica

Adsorptive transformation of heat is an emerging technology that is especially promising for low-temperature heat sources. Recently, an adsorption cycle (the so-called “Heat from Cold” or HeCol) has been suggested for upgrading the ambient heat in cold countries. This paper addresses the selection of composite sorbents of methanol specialized for this cycle and the study of their sorption properties. First, we analyzed which adsorbent is optimal for the HeCol cycle and how its properties depend on the HeCol cycle boundary temperatures. Then, three composite sorbents, based on CaCl2, CaBr2 and their mixture confined inside the silica gel mesopores, were prepared and their sorption equilibrium with methanol was analyzed keeping in mind the HeCol cycles with various boundary temperatures. It was shown, that these composite sorbents exchange up to 0.48 g of methanol per 1 g of the composite that far exceeds this value for common activated carbons. Finally, a first lab-scale HeCol prototype was built and tested with one of the studied sorbents, namely CaClBr/SiO2, to evaluate the feasibility of the cycle.

Employing thermoelectric generator for power generation enhancement in a Kalina cycle driven by low-grade geothermal energy

The Kalina Cycle (KC) is one of the most promising options for power generation from renewable energy and low temperature heat sources such as geothermal energy. Also, employing thermoelectric generators (TEGs) is widely developed recently to convert heat into electricity directly. The possibility of employing thermoelectric generators to utilize the waste heat of a Kalina cycle is investigated in the present paper. The proposed system performance is modeled, analyzed and compared with the conventional Kalina cycle performance. To assess the systems’ performances, thermodynamic and economic models are developed and a parametric study is carried out. The results indicated an enhancement of around 7.3% for net output power and energy and exergy efficiencies for the proposed system as compared to the conventional Kalina cycle, at a typical operating condition. In addition, an economic evaluation of integrating thermoelectric generators with the Kalina cycle is conducted and the conditions are indicated under which the proposed system is profitable.

Energy, exergy and thermoeconomic analysis of a novel combined cooling and power system using low-temperature heat source and LNG cold energy recovery

This paper deals with the energy, exergy, and economic analysis of a novel ammonia-water combined cooling and power cycle using waste heat as low-temperature heat source and LNG cold energy as thermal sink. For this purpose, thermodynamic modeling of the proposed system is presented and the performance of the cycle is investigated based on the following performance criteria: net power output, cooling output, first-law efficiency, second-law efficiency, and sum unit cost of the products (SUCPs) of the system. In this respect, the simulation revealed that the net power output, cooling output, first-law efficiency, second-law efficiency, and total SUCP of the system can be calculated 1379kW, 1736kW, 43.25%, 22.51%, and 133.7 $/GJ, respectively, showing a considerable enhancement through this integration. In addition, the irreversibility of each component and overall system are presented showing that heat exchanger 2 accounts for the highest exergy destruction among all components which is followed by the throttling valve 1. Moreover, a comprehensive parametric study is conducted to investigate the effects of considered key parameters, namely, vapor generator pressure, LNG turbine inlet pressure, evaporator temperature, condenser temperature, heat source temperature, and ammonia concentration on the performance criteria. It is observed that one can obtain a higher first-law efficiency at higher ammonia concentrations, heat source temperatures and LNG turbine inlet pressures or at lower condenser temperatures and vapor generator pressures, while a higher second-law efficiency can be obtained at lower ammonia concentrations, heat source temperatures and condenser temperatures or at higher vapor generator pressures, evaporator temperatures as well as LNG turbine inlet pressures.

High Temperature ORC Systems

ORC systems are well known as the best available technology for electricity production from low temperature heat sources -such as geothermal ones - and continuous technical development is done to optimize performances by means of finding new working fluids and improved design criteria and thermodynamic cycles.With regard to medium and high temperature heat sources exploitation for electric power production, ORC technology and Steam Rankine Cycle solutions are competing in terms of power production, capital expenditures and O&M costs to become the preferred choice on a case-by-case basis.Commercially available ORC technology is currently limited to a maximum working fluid operating temperature of about 300°C, leading to a strong limitation on performances achievable. Finding new working fluids that could operate at Higher Temperatures and developing the related technical solutions, will enable to improve ORC technology competiveness also in other niches that now are Steam Rankine Cycles territory. Very High Temperature ORC technology will lead to new solutions for both power only production and cogeneration, allowing ORC technology to enter market segments traditionally belonging to other technologies (e.g. Steam Rankine Cycles, Otto Cycles, Bryton Cycles, etc.).The paper will present the technical and industrial development on High Temperature ORC systems, potential market development and a technology comparison to other generation technologies.

Sensitivity analysis of the conception of small scale district heating networks on the thermal conductivity of the surrounding soil

Heat distribution via pre-insulated plastic bonded piping systems will become of major importance for covering the primary energy consumption of EU and will be of vital importance for the energy and heat turnaround. Utilizing efficiency potentials of combined heat and power (CHP) and integrating (industrial) waste heat and renewable energy contents within these grids, low temperature (and low-ex) heat sources might be exploited. Thus, energetic contents unsuitable for electrical energy supply are utilized in order to diminish greenhouse gas emissions and minimize primary energy needs.Distribution of heat requires accurate planning and network design for the expected service time of several decades. This applies for existing networks as well as for future networks. During planning and conception different load scenarios (of today and in future) must be considered. Since the design of existing networks was done in the past, this paper focusses on the requirements for the conception and planning of heating networks in the near future. Because of low temperature (and low-ex) heat sources, the expansion of district heating networks in EU will be linked to modifications in the network design and planning. A sensitivity analysis was carried out for relevant input parameters in low temperature networks. The analysis showed a significant influence of the conductivity of the bedding material as well as the overburden height on heat losses. For the given set of reference parameters, the energy efficiency potential of systems for heat distribution is approximately 10 %.

Overview of the Activities on Heavy Duty Diesel Engines Waste Heat Recovery with Organic Rankine Cycles (ORC) in the Frame of the ECCO-MATE EU FP7 Project

The ECCO-MATE Project is a European Union funded project aimed to develop a synergistic framework for cutting edge research on novel engine technologies for higher energy efficiency and lower emissions.The project partners, Ricardo plc, an engineering consulting company, and the University of Trieste, focus the research attention on waste heat recovery systems, such as Organic Rankine Cycles (ORC), which are gaining increasing interest by engine manufacturers, vehicles and ships fleet operators, because of their potential for further increasing engine efficiency and decreasing fuel consumption. In particular, in the frame of the developed research activity, the 1-D Ricardo engine simulation software WAVE has been used in order to assess novel engine concepts, both in the commercial vehicles and marine sectors.A combined engine-ORC system First and Second Law of Thermodynamics analysis has been proposed in order to study where system inefficiencies are concentrated and propose improvements, with particular focus on commercial vehicle heavy duty diesel engines. A thermo-economic analysis has been also considered.Furthermore, in collaboration with the project partners National Technical University of Athens (NTUA) and Winterthur Gas & Diesel (WinGD), an innovative low pressure Exhaust Gas Recirculation (EGR) configuration for low speed 2-stroke ship propulsion units has also been studied with the aim of reducing NOx in order to meet IMO Tier III emissions limits. ORC systems are, in this application also, a promising technology that can be used, in synergy with emission reduction systems, to recover, in particular, low temperature heat sources such as engine coolant and scavenging air, always with the aim of improving overall system efficiency while respecting new stringent emission reduction targets. The first results of the research activity show that a fuel consumption improvement up to 10% could be achieved both for commercial vehicles off-highway applications and in the marine sector, depending on the type of ORC and waste heat recovery architecture chosen and the engine considered.

Narrow-Bandgap Interband Cascade Thermophotovoltaic Cells

We report on the characterization of narrow-bandgap ( Eg ≍ 0.4 eV, at 300 K) interband cascade thermophotovoltaic (TPV) devices with InAs/GaSb/AlSb type-II superlattice absorbers. Two device structures with different numbers of stages (two and three) were designed and grown to study the influence of the number of stages and absorber thicknesses on the device performance at high temperatures (300–340 K). Maximum power efficiencies of 9.6% and 6.5% with open-circuit voltages of 800 and 530 mV were achieved in the three- and two-stage devices at 300 K, respectively. These results validate the benefits of a multiple-stage architecture with thin individual absorbers for efficient conversion of infrared radiation into electricity from low-temperature heat sources. Additionally, we developed an effective characterization method, based on an adapted version of Suns - V oc technique, to extract the device series and shunt resistance in these TPV cells.

Two-phase chamber modeling of a twin-screw expander for Trilateral Flash Cycle applications

Low temperature (<100°C) streams have the largest share of waste heat recovery potential and may represent an attractive opportunity for a sustainable economy. Among the bottoming thermodynamic approaches that have been proposed to convert this waste heat into electricity, the Trilateral Flash Cycle (TFC) proved to be theoretically capable to recover more heat from a low-temperature single-phase heat source than any simple Rankine cycle. However, the commercialization of TFC recovery units has been so far prevented by the lack of an expander technology that should efficiently operate with high mass flow rates of a two-phase flashing flow. A promising candidate to tackle these challenges is the twin-screw technology thanks to its positive displacement nature and the capability to run at high revolution speeds without remarkable efficiency drops.In the current research work, a twin-screw expander has been modeled in the commercial software GT-SUITE™. The modeling activity resulted in a two-phase chamber model based on the coupling of the conservation equations and the REFPROP library to calculate the thermophysical properties of the liquid-vapor mixture of the R245fa working fluid at each time step. Using pre-processed geometrical data, the model includes a detailed breakdown of the leakage paths and allows to retrieve key information for a future optimization of the machine such as the indicator diagram and the quality-angle diagram. Parametric analyses were eventually carried out to assess the expander behavior at different operating conditions, namely manometric expansion ratio, revolution speed and inlet quality.

Experimental investigation on power generation with low grade waste heat and CO2 transcritical power cycle

In this study, a small-scale test rig of CO2 transcritical power cycle (T-CO2) system driven by low-grade heat has been developed and investigated experimentally. The test rig consists of a number of essential components including a CO2 turboexpander with high speed generator, finned-tube air cooled condenser, liquid receiver, CO2 liquid pump and CO2 gas generator. The CO2 is heated in the plate-type gas generator by hot thermal oil flow which is circulated and heated by exhaust flue gases from an 80kWemicroturbine CHP unit. The test rig has been fully commissioned, instrumented, controlled and is ready to operate experiment as required. Subsequently, at constant heat sink (ambient) and heat source (thermal oil) temperatures, a series of experiments have been carried out to examine the effects of various important parameters on the T-CO2 system performance. These include thermal oil flow rate and CO2 mass flow rate etc. Preliminary experimental results show that the CO2 TPC is applicable for the low temperature heat sources to generate power although further efficiency improvements are needed. In addition, the experimental outcomes can instruct future optimal system design and controls.

Field operation of a 125kW ORC with ship engine jacket water

Improving ship system efficiency is a growing concern for the marine industry. New regulations imposed by the International Maritime Organization (IMO) have set efficiency targets for new and existing ships. These targets are outlined in the energy efficiency design index (EEDI) and will reach a maximum of 30% by 2025. In order to satisfy the regulations, ship owners are exploring new methods to improve the efficiency of existing systems. One such method is to capture and repurpose engine waste heat.Many ships employ exhaust steam boilers to recover heat from engine exhaust. This represents a source of high quality heat (≥ 200°C). At these temperatures, it is relatively easy to extract thermal energy. In contrast, low quality heat sources, such as engine jacket water (≤ 100°C), have been largely ignored. Steam production is impractical at such low temperatures. A new technology was needed to take advantage of low temperature heat sources on the ship.Calnetix Technologies, in conjunction with Mitsubishi Heavy Industries (MHI), developed an Organic Rankine Cycle (ORC) specifically designed to utilize engine jacket water as a heat source. The first prototype was successfully built, tested, and certified by Lloyd’s Registry (LR) and Nippon Kaiji Kyokai (NK) in March 2015. The system generates up to 125 kW from a heat source with temperature range 80°C to 95°C.This prototype was installed, commissioned, and placed into service on the Arnold Maersk container ship in April 2016. This paper will discuss difficulties which arose during the installation. It will also present and discuss data collected by the ORC’s sensors during its first several months of operation. Finally benefits of the ORC operation in conjunction with auxiliary ship systems will be explained.

Thermodynamic Optimization of a Double-pressure Organic Rankine Cycle Driven by Geothermal Heat Source

Geothermal energy, as a typical low-temperature heat source, has been exploited for decades to generate electricity. Organic Rankine cycle (ORC) system has a high energy conversion efficiency due to the good performance of organic fluids under the geothermal water temperature. In this study, a double-pressure organic Rankine cycle system driven by geothermal heat source is used to generate electricity. The double-pressure ORC system achieves the cascaded utilization of energy, which can improve the efficiency of energy conversion. Mathematical model is established based on thermodynamic laws, and the overall system performance has been evaluated. A parametric analysis is conducted to examine the effects of some key thermodynamic parameters, namely turbine high-level inlet pressure, turbine low-level inlet pressure, turbine high-level inlet temperature, on the system performance. Parametric optimization is conducted by means of genetic algorithm (GA) to find the maximum system performance. At the same time, the performances of three organic working fluids are examined. Results indicate that R245fa has a better performance among the three organic fluids. The exergy efficiency of overall system exceeds 5.8% under the supply water of 120℃, and it produce more than 800kW electricity with the geothermal water at the mass flow rate of 250t/h. It is also found that the exergy efficiency has peak value under the effect of turbine high-level inlet pressure and turbine low-level inlet pressure. In addition, increasing turbine high-level inlet temperature brings a positive effect to the system performance. Exergy analysis is also conducted and the result shows that the main exergy loss occurs in high-pressure evaporator. By system optimization, the double-pressure organic Rankine cycle has a better performance in utilizing geothermal energy than single-pressure system.

Area optimization of solar collectors for adsorption desalination

Adsorption desalination is an emerging method to address the shortage of fresh water. To achieve its energy-saving potentials, a renewable low-temperature heat source is the key. This paper focuses on the area optimization of solar collectors in combined solar heating systems that supply heat for adsorption desalination, aiming at achieving the maximum economic benefits during the lifespan of a project. The optimum tilt angle was discussed and the corresponding daily radiation data were calculated with HDKR (Hay, Davies, Klucher, Reindl) model. The area optimization function was proposed with the unit costs of fresh water as the optimization objective. A reference area calculated according to annual solar radiation was employed to describe the optimization results. Then the influences of the price of auxiliary energy sources, the performance ratio of adsorption desalination, and the heat loss of solar heating on the optimization results were studied with an actual adsorption desalination project in Tianjin. It has been found that the optimal area is positively associated with the auxiliary energy price, however approximately inversely proportional to the performance ratio of desalination and the energy efficiency of solar heating. The unit costs of producing fresh water can be reduced up to 20% after collector area optimization when the auxiliary energy is expensive. Besides, the overall costs of utilizing solar heating to supply heat for adsorption desalination is around 0.03–0.04 CNY/MJ which is lower than conventional energy sources. We also tested the optimization results with an altered precision of radiation data and different meteorological conditions. Findings in this paper proved the advantages of incorporating solar heating in adsorption desalination and provided instructions for designing solar adsorption desalination projects.

Improved thermodynamic design of organic radial-inflow turbine and ORC system thermal performance analysis

The Organic Rankine Cycle (ORC) has obvious advantages in the utilization of low-temperature heat source (80–300°C). Based on specific heat source, this paper determines design conditions of radial-inflow turbine with six kinds of dry working fluids. This paper presents a new method for modeling of ORC based on radial-inflow turbine with the novel selection of initial design parameters. In the selection procedure of the initial design parameters, the properties of organic working fluids should be taken into consideration to control the increase of υ2/υ1, which can lead to the large relative velocity ratio and the poor performance of the radial–inflow turbine. The study shows that the applicable selection area of initial design parameters differentiates from that recommended in the literature for organic working fluids. The lowest cycle ideal efficiency with R123 results in the minimums of the cycle thermal efficiency and the cycle net power, which reaches 8.33% and 67.24kW, respectively. Although the relative internal efficiency of the radial-inflow turbine with R600a is in the middle level, the highest cycle thermal efficiency and cycle net power reach 9.17% and 74.59kW, respectively. The results show that the ORC systems with R600 and R600a both have better cycle performance with smaller geometric dimensions and more excellent thermal matching with specific heat source.

High potential of employing bentonite in adsorption cooling systems driven by low grade heat source temperatures

In this research article a new modified adsorbent has been presented to be used in thermally driven adsorption systems for renewable energy applications. Bentonite is introduced as a cheap adsorbent with high potential for use in heat pumps or chillers driven by renewable energy. A simple acid activation procedure increases the inner surface of the material and also enhances the water adsorption capacity markedly. The raw bentonite is activated with different concentrations (0.2, 0.4, 0.6 mol L−1) of HCl. FT-IR, XRD, N2 adsorption, water adsorption and heat capacity measurements have been carried out for the raw and HCl activated bentonite. The acid activation process increased the surface area of the bentonite from 64 m2 g−1 to a level of 500 m2 g−1. In that respect the maximum adsorption capacity has markedly increased by the acid activation. Experimental and theoretical studies for the adsorption isotherms and kinetics at different adsorption temperatures of water vapor onto 0.6 HCl treated bentonite have been conducted. A simulation for an adsorption cooling system employing treated bentonite has been presented. The performance of the modeled system has been also studied to be driven by low grade heat source temperatures at different operating conditions.

Study of a Combined Power and Ejector Refrigeration Cycle with Low-temperature Heat Sources by Applying Various Working Fluids

A power and cooling cycle which combines the organic Rankine cycle and the ejector refrigeration cycle supplied by waste heat energy sources is discussed in this paper. Thirteen working fluids including one wet, eight dry and four isentropic fluids are studied in order to find their performances on the combined cycle. First and second law analysis has been performed by using a computer program in order to investigate various operating conditions’ effects on the proposed cycle by fixing power/refrigeration ratio and varying waste heat source and evaporator temperature. According to the results, in general, dry and isentropic ORC fluids have better performance compared with wet fluids. The increase in evaporator temperature leads to the decrease in exergy efficiency. On the other hand, exergy efficiency rises with the turbine inlet temperature decrease and an increase of heat source temperature. Rising expansion ratio and inlet temperature of the turbine causes an increase in the thermal efficiency of the cycle.

A modified ammonia-water power cycle using a distillation stage for more efficient power generation

An ammonia-water power cycle with a distillation stage is proposed, two Kalina cycles and one Organic Rankine Cycle (ORC) are selected for comparisons under two scenarios: medium (346 °C) and low (146 °C) heat source temperatures. The optimization efforts are aimed at maximizing net power production for all concerning cycles, the results show that the proposed cycle can produce 9% and 8% more power than the reference Kalina cycles, while a better thermal performance is achieved for thermal efficiency and exergy efficiency. When the proposed cycle compares with ORC, the amount of net power can be produced is improved by 9% and 3%, respectively. On the other hand, the thermal performance of Kalina cycles and ORC are largely relied on the design of internal heat exchangers, requiring relatively larger size of internal heat exchangers. The proposed cycle, however, is much more compact because of less amount of internal heat transfer needed, leading to less irreversibilities. The proposed cycle can be further simplified by using a solution cooled absorber which eventually decreases the system complexity. A parametrical study shows that the proposed cycle has a better capability of adaptation to a wider temperature range of heat source conditions while maintaining a better performance.

Constrained multi-objective optimization of radial expanders in organic Rankine cycles by firefly algorithm

Organic Rankine Cycles are viable energy conversion systems in sustainable energy systems due to their compatibility with low-temperature heat sources. In the present study, one dimensional model of radial expanders in conjunction with a thermodynamic model of organic Rankine cycles is prepared. After verification, by defining thermal efficiency of the cycle and size parameter of a radial turbine as the objective functions, a multi-objective optimization was conducted regarding tension and vibration constraints for 4 different organic working fluids (R22, R245fa, R236fa and N-Pentane). In addition to mass flow rate, evaporator temperature, maximum pressure of cycle and turbo-machinery design parameters are selected as the decision variables. Regarding Pareto fronts, by a little increase in size of radial expanders, it is feasible to reach high efficiency. Moreover, by assessing the distribution of decision variables, the variables that play a major role in trending between the objective functions are found. Effects of mechanical and vibration constrains on optimum decision variables are investigated. The results of optimization can be considered as an initial values for design of radial turbines for Organic Rankine Cycles.

Performance analysis on a novel compact two-stage sorption refrigerator driven by low temperature heat source

A novel two-stage sorption refrigeration system is established and analyzed, which is driven by heat source with the temperature lower than 100 °C. CaCl2-BaCl2-NH3 is selected as working pair whereas matrix of expanded natural graphite treated with sulfuric acid (ENG-TSA) is used for the improved heat and mass transfer performance of composite sorbent. The non-fin filling technique is adopted to decrease mass and volume of sorption reactor, which further improves system compactness. Results show that two-stage sorption refrigeration system is flexibly adapted to different heat source with temperature below 100 °C. COP and SCP of the novel system range from 0.185 to 0.22 and from 50 W kg−1 to 76 W kg−1, respectively under the condition of 70 °C–90 °C heat source temperature and 5 °C–10 °C evaporation temperature. Performance of novel two-stage sorption refrigeration system is also compared with that of previous type by using the conventional fin tube sorption reactor based on mass and volume of the whole system. It is indicated that the highest improvement of SCPsys and VCPsys for the novel system are able to reach 28.1% and 32.5%, respectively when heat source temperature is 70 °C.

A two-stage liquid desiccant dehumidification system by the cascade utilization of low-temperature heat for industrial applications

Cooling dehumidification driven by power is widely used in industrial processes to obtain dry air, but the main drawback is its large power consumption. In these processes, large amounts of low-temperature waste heat are released to the environment directly, so there is a great energy-saving potential to recover low-temperature waste heat and generate dry air. A new two-stage liquid desiccant dehumidification system with the cascade utilization of low-temperature heat is proposed. The waste heat is used in a cascade manner. The higher-temperature heat is used to generate a strong desiccant solution, which will be used in the first-stage dehumidifier. The lower-temperature heat is used to drive a single-effect absorption refrigerator and provide cooling energy to the second-stage dehumidifier. Simulation results showed that the proposed system can reduce electricity consumption by 92.29% compared with the conventional cooling dehumidification system driven by power. The ratio of electricity savings to absorbed heat can reach 7.35%. The advantage of the cascade utilization of the low-temperature heat was further illuminated by studying the driving force in the dehumidifiers, and a preliminary economic and environmental analysis was performed. The increased initial investment can be recovered in only 3.39years. Approximately 11,028 tons of standard coal are saved per year, and a reduction of 27,488 tons CO2 can also be realized per year. Finally, a parametric sensitivity analysis was conducted to optimize the system performance. This study may provide a new method to perform dehumidification by efficiently using a low-temperature heat source.

New performance maps for selecting suitable small-scale turbine configuration for low-power organic Rankine cycle applications

This paper aims to deliver new performance maps for small-scale organic Rankine cycle (ORC) turbines (<20 kW) by assessing the impact of single and two stage turbine configurations on the ORC’s performance driven by low-temperature (<100 °C) heat source. Small-scale axial, radial-inflow and radial-outflow turbines are designed and compared with their single and two stage configurations with the aim of improving the performance of the ORC’s system by increasing its expansion ratio. Therefore, the preliminary mean-line design is coupled with three-dimensional CFD analysis and ORC modelling for all turbines’ configurations to deliver the performance maps for low-power applications. Due to the complex and 3D nature of flow across the turbine stage, CFD analysis was used to investigate in more detail five candidates of small-scale turbines, in single and two stage configurations with three working fluids (R141b, R245fa and isopentane). ANSYS®17-CFX was used to perform 3D CFD analysis of all turbine configurations. RANS equations for three-dimensional steady state and viscous flow were solved with a k-ω SST turbulence model. The performance maps in terms of turbine isentropic efficiency and power output for each turbine configuration are presented according to the operating conditions in terms of expansion ratio, working fluid mass flow rate, and rotational speed with turbine size.The results revealed that the two-stage axial and radial-outflow turbines’ configurations exhibited a considerably higher turbine performance, with overall isentropic efficiency of 84.642% and 82.9% and power output of 15.798 kW and 14.331 kW respectively, with R245fa as a working fluid. Also, the results exhibited that the maximum ORC thermal efficiency for both two-stage configurations was 13.96% and 12.80% for axial and radial-outflow turbines respectively working with R245fa. These results indicated the potential advantages of a two-stage turbine configuration in a small-scale ORC system for the conversion of a low-temperature heat source into electricity as a useful power.