Low Temperature Heat Sources Research Articles

Research and Application of Air Source Heat Pump Technology at Rd. 60-10 Oil Delivery Site

The heating methods currently used at oil delivery sites and transfer stations on North China Oilfield include electric bar heating, fuel oil heating, gas heating, etc. The traditional heating methods have adverse effect on energy conservation and environmental protection. They have low energy efficiency of heating and produces great pollution to the environment. The air source heat pump technology uses the heat in the air as the low-temperature heat source and transforms it to the high-temperature hot water, which will later serve as a heat tracing for crude oil gathering and transportation. No combustion effluent is produced in operation and the energy-saving effect is outstanding with high social-benefit.

A Steady-State Evaluation of Simple Organic Rankine Cycle (SORC) with Low-Temperature Grade Waste Heat Source

The low-grade heat source recovery is usually constrained by the physical characteristics of the hot fluid medium. The present work focuses on the importance of energy recovery from low-temperature waste energy sources and its conversion to useful electrical power. The thermal performance analysis is based on the utilization of R-123, R-134a, R-290, R-245fa, R-1234ze-E, and R-1233zd-E fluids in a simple organic Rankine cycle (SORC). A waste energy source from an industrial sector is suggested to be available at a temperature greater than 110 °C. A hypothetical organic Rankine cycle of 10 kW nominal heat recovery was implemented to evaluate the cycle performance. It operates at evaporation and condensation temperatures of 90 °C and 45 °C, respectively. The selected vapor superheat degree at the expander entrance was 5 °C - 15 °C, and the liquid was subcooled by 5 °C at the discharge port of condenser. The estimated first law cycle thermal efficiency fell in the range of 6.4% - 7.7%. The results showed that the thermal efficiencies of R-134a, R-123, R-245fa, R-1233zd-E, and R-1234ze-E were higher than that of R-290 by 10% - 14%, 11% - 12%, 9% - 12%, 4% - 7% and 1% - 3%, respectively. R-1233zd-E, R-1234ze-E, and R-290 showed close thermal efficiency values, and it fell in the range of 6.7% - 7% for the (SORC) at a superheat degree of 15 °C. At the same superheat degree, the corresponding range of thermal efficiency for R-134a, R-123 and R-245fa fell within 7.5% - 7.7%. R-134a possessed the highest net power output of the (SORC); it reached a value of 0.91 kW as predicted at 15 °C superheat degree. Increasing the expander volumetric efficiency value by 10% improved the cycle thermal efficiency by 10% - 12%.

Thermo-Chemical Engines: Unexploited High-Potential Energy Converters

Thermal engines, and in particular closed power cycles, are currently a focus of attention of many researches mainly because they represent the only way to exploit renewable thermal energies. To contribute to boosting the exploitation of available thermal sources, this work investigates the higher potential offered by a complementary technology, based on the use of reactive working fluids instead of inert ones: the here-called “thermo-chemical” engine. Such a power cycle enables the simultaneous conversion of thermal and chemical energies into power. With a theoretical approach, we analyse engine performances considering different stoichiometries and thermodynamic characteristics of reactive fluids and different operating conditions. It is shown that the use of specific equilibrated reactions occurring in the gaseous phase might lead to extremely powerful and highly efficient energy conversion systems, in the whole current domain of application of power cycles. Moreover, we demonstrate that, differently from classical thermal machines, a thermo-chemical engine allows for the efficient and powerful exploitation of low temperature heat sources and high temperature cold sinks which in general characterize renewable thermal energies.

Drinking water supply as low-temperature source in the district heating system: A case study for the city of Copenhagen

This paper explores the potential for using large-scale heat pumps (HPs) to extract energy from Copenhagen’s drinking water network and deliver it to its district heating system. The system involves certain losses in terms of additional heat and power consumption for end-use water heating. The net potential for energy extraction was analysed by means of an EPANET model to simulate system-wide temperatures in a piped distribution network. The model was validated against measured data from the network. Heat transfer in service lines was computed analytically and included in the net potential for energy extraction, which was determined to be 21 MW in Copenhagen. Around 38% of the HP source demand was harnessed from the ground. With HP COPs between 2.8 and 3.2, the System COP was only 1.7, thus suggesting that the choice of drinking water as a low-temperature heat source should depend on the available alternatives. Drinking water HPs have the side-benefit of preventing high drinking water temperatures; if operated in the summer they increased the share of supplied water complying with a recommended upper temperature limit of 12 °C from 42% to 81%.

Experimental analysis of defrosting and heating performance of a solar‐assisted heat pump integrated phase change energy storage

This thesis investigates a novel solar-assisted heat pump integrated phase change energy storage system. The defrosting performance of this system was studied experimentally and the results were compared with two traditionally used methods: reverse cycle defrosting (RCD) method and hot gas bypass defrosting (HGBD) method. The results show that the phase change energy storage system has superior performance compared with traditional defrosting methods. The indoor temperature drop recorded was relatively small and the defrosting time was 75% of the RCD system and 53% of HGBD system. The phase change energy storage system increased the condensation temperature which consequently increased the temperature difference of heat transfer resulting in higher conductivity in the defrosting progress. Compared with the method of RCD and the method of HGBD, the recovery time of the system was shortened by 90 and 160 seconds, respectively. The system works with low-temperature heat source and circulating water, which considerably reduces energy consumption, thereby improving the performance of the defrosting system. A further experimental study was also conducted on the heating performance and the results also indicated that the value of COP can reach up to 3.6 in daytime, and the indoor temperature can be stably maintained above 18°C throughout the day. Novelty Statement A new defrosting method for energy storage defrosting is proposed, and the defrosting performance is compared with two common defrosting methods. In addition, the performances of the heating system over the day were experimentally investigated. The experimental results show the system meets the heating needs of the building. Finally, the influence of the outdoor temperature on the exergy efficiency of the system was discussed. It shows that this system can improve the operational stability, the system economy and energy saving.

Multi-effect distillation plants for small-scale seawater desalination: thermodynamic and economic improvement

The growing global demand for fresh water coupled to the increasing interest in renewable energies and waste heat recovery has resulted in flourishing attention to the multi-effect distillation process for seawater desalination. The low operating temperature makes this technology attractive in the case of low temperature heat sources such as geothermal, solar or waste heat recovery. The low energy density of these heat sources requires small-scale desalination systems whose layout and operation may differ from large-scale plant. In this work, new plant configurations for a small-scale multi-effect distillation system are proposed and analyzed from a thermodynamic and economic point of view. Each configuration tends to better exploit the energy content of the various streams by improving heat recovery, according to an increasing layout complexity. These configurations were studied in two layouts, differing in the way seawater and brine fed the various effect. The feed mass flow in each effect was varied to maximize the recovery ratio by imposing the maximum salt concentration in the brine related to calcium sulphate precipitation. Numerical simulations were conducted in Aspen Plus environment by varying the top brine temperature with a fixed bottom brine temperature of 40 °C. The electrolyte non-random two liquid equation of state was adopted to evaluate saltwater properties and an inter-model comparison with a validated algebraic model was carried out. The configurations implementing seawater preheating increased the performance ratio up to 10% due to the better exploitation of the energy content of distillate streams. The proposed solutions with the maximization of the recovery ratio demonstrated to be cost-effective with respect to the base multi-effect distillation configuration when thermal energy cost became relevant. In the case of negligible thermal energy cost (waste heat recovery) the base configuration was the preferable solution in terms of water cost, despite the lower performance ratio.

Comparison of the Trilateral Flash Cycle and Rankine Cycle with Organic Fluid Using the Pinch Point Temperature

Low-temperature heat utilization can be applied to waste heat from industrial processes or renewable energy sources such as geothermal and ocean energy. The most common low-temperature waste-heat recovery technology is the organic Rankine cycle (ORC). However, the phase change of ORC working fluid for the heat extraction process causes a pinch-point problem, and the heat recovery cannot be efficiently used. To improve heat extraction and power generation, this study explored the cycle characteristics of the trilateral flash cycle (TFC) in a low-temperature heat source. A pinch-point-based methodology was developed for studying the optimal design point and operating conditions and for optimizing working fluid evaporation temperature and mass flow rate. According to the simulation results, the TFC system can recover more waste heat than ORC under the same operating conditions. The net power output of the TFC was approximately 30% higher than ORC but at a cost of higher pump power consumption. Additionally, the TFC was superior to ORC with an extremely low-temperature heat source (<80 °C), and the ideal efficiency was approximately 3% at the highest work output condition. The TFC system is economically beneficial for waste-heat recovery for low-temperature heat sources.

Organic Rankine Cycle (ORC) in geothermal power plants

Organic Rankine Cycle is a technology that convert low-temperature heat sources into a mechanical energy, and it can be used to produce electrical energy in a closed system. The heat sources can be received from renewable energy such as geothermal, solar, and biomass. Furthermore, the ORC system can also be used to increase energy efficiency in the industry by utilizing the waste heat produced. Therefore, there are two classification of the ORC system, namely a heat recovery system and binary power plant. Recently, the ORC system has made a thrive in the geothermal power plant. The ORC system can be applied to resources with low to medium temperature characteristics (<90°C - 150°C). This paper will present an overview of the implementation, model, and innovation of ORC system technology in geothermal resources.

Thermodynamic and thermoeconomic analysis of innovative integration of Kalina and absorption refrigeration cycles for simultaneously cooling and power generation

The energy consumption and the emission of greenhouse gases have been motivated researchers toward using renewable energy sources for the development of a sustainable society. Low-temperature heat sources like geothermal sources can be a desirable option to produce the demanded power, cooling, heating, and other byproducts. In the present literature, a novel combined cooling and power generation system is presented which is an internal integration of the Kalina Cycle and the absorption refrigeration cycle. The system operates using the low-temperature heat source. The thermodynamic and thermoeconomics analysis is carried out using Engineering Equation Solver software. Besides, considering the mathematical modeling, the parametric investigation is implemented to evaluate the effect of the key parameters on the sum unit cost of the products. Based on the obtained results, the cooling and power generation system can provide the net output power of 158.3kW and the cooling capacity of 1084kW. The results indicate that the system is most appropriate for cooling provision rather than for power generation aims. The energy and the exergy efficiencies and the net power of the combined cycle obtained 41.33%, 27.47%, and 158.3kW respectively. The sum unit cost of the product cooling, power, and total system are respectively evaluated 148.5$/GJ, 97.16$/GJ, and 19.44$/GJ. The minimum and maximum values for the rate of exergy destruction cost belong to the pump and absorber, respectively. The parametric analysis delivered some valuable results such as a drop in the sum unit cost of the net power, cooling output, and overall system by increasing the generator hot pinch point temperature difference, an increase in the overall system sum unit cost of the products with increment in the low-temperature heat source inlet temperature, and rising in the sum unit cost of the net power, cooling output, and the overall system with an increase in the evaporator temperature.

Bi2Te3/Sb2Te3 thermophotovoltaic cells for low temperature infrared radiation

The thermophotovoltaic cells which convert the low temperature (below 500 K) infrared radiation into electricity are of significance due to their potential applications in many fields. In this work, narrow bandgap Bi2Te3/Sb2Te3 thin film thermophotovoltaic cells were fabricated, and the formation mechanism of Bi2Te3/Sb2Te3 p-n heterojunctions was investigated. At room temperature, the heterojunctions are formed through the diffusion of electrons and holes along the same direction from n-type Bi2Te3 thin films to p-type Sb2Te3 thin films rather than conventional bi-directional diffusion. Because the strong intrinsic excitation generates a large number of intrinsic carriers which weaken the built-in electric field of the heterojunctions, their I-V curves become similar to straight lines. It is also demonstrated that Bi2Te3/Sb2Te3 thermophotovoltaic cells can output electrical power under the infrared radiation from a low temperature heat source. Although the open-circuit voltage and the short-circuit current of the cells are low, this work provides a possible way to utilize the low temperature radiation.

Thermodynamic modelling of hybrid adsorption system

The ability of adsorption based desalination system to cogenerate distilled fresh water and cooling effect provides an increasing attention in the field of cooling and desalination technologies. Eco-friendly adsorption cycles are capable of producing the hybrid effects (desalination& cooling) with low temperature heat source having temperature range from 50°C to 90°C. Adsorption characteristics (isotherm) of silica gel-water and zeolite-water have been presented in this study. Dubinin-Astakov (D-A) and Dubinin-Radushkevich (D-R) adsorption equilibrium equations are used for comparing the performance of silica gel and zeolite. Results show that maximum water production rate in the case of silica gel adsorbent is stabilised at lower regeneration temperature, ranges from 80°C to 120°C, where as in zeolite it is in the higher range from 150°C to 250°C. Maximum COP of the system obtained is 0.65 for silica gel-water at a regeneration temperature of 80°C where as 0.35 for zeolite-water at 110°C. Study concluded that the performance of the system using silica gel-water adsorbent is comparatively better than zeolite-water pair.

Enhanced sorption heat transportation cycles with large concentration glide

Sorption heat transportation is promising in low-grade thermal energy transportation over long distance due to its small energy transportation loss. However, to compete with the sensible heat transportation from economic aspect, energy transportation density and efficiency of sorption heat transportation still need to be further improved. In this paper, two novel sorption heat transportation cycles with double-stage input or output are proposed. Compared with the conventional cycle, larger concentration glide is achieved by the novel cycles for cycle improvement. Performance of the conventional cycle and novel cycles are calculated and compared using mathematical models developed in software Engineering Equation Solver. Results show that higher energy transportation density could be achieved by the enlargement of concentration glide. The improvement in energy density is stronger with lower heat source temperature, higher heat output temperature, or lower cooling temperature. In addition, the performance of novel cycles is more stable under the same temperature range. The improved sorption heat transportation system could be used as an effective way to transport the low-grade industrial excess heat, which is an efficient connection between the heat source and end user.

Experimental study on steam side vacuum capillary concentrated ethylene glycol aqueous solution

ABSTRACT The separation system is designed to separate and concentrate the aqueous glycol solution under a low-temperature heat source. The experiment found that the pore size of the capillary wick, the verticality of the evaporator, as well as the degree of vacuum and the inlet flow rate of the working fluid are important factors for the success of the experiment. At a vacuum of 10 kpa and a flow rate of less than 5 mL/min, the ethylene glycol aqueous solution was separated and concentrated at a temperature between 90 and 105℃, and the ethylene glycol content in the condensate was less, reducing the loss of ethylene glycol. The steam side vacuum capillary evaporation system proposed in this paper utilizes the difference of the surface force between the metal porous structure and the binary solution, thereby causing excess increase of the relative volatility of the two solution components, and strengthening the separation effect of the binary solution, meanwhile, the system can uses industrial waste heat as heat source, which has great potential to be a new kind of binary solution separation method.

Recent Developments in Solar and Low-Temperature Heat Sources Assisted Power and Cooling Systems: A Design Perspective

Abstract Even though the renewable technologies are getting a gradually increasing share of the energy industry, the momentum of its growth is far away from outweighing the dominance of fossil fuel. Due to the concern for ozone depletion, global warming, and many more environmental hazards caused by fossil fuels, it is essential to substitute the conventional energy sources with renewables. Since this replacement cannot be done overnight, the conventional energy technologies should be integrated with renewables to minimize the pace of adverse effects on fossil fuel–based industries in the meantime. This way, the industries can be more efficient by utilizing waste heat, which accounts for 50% of the total energy generated now. This review paper outlines the role of solar energy in the generation of power and cooling systems that are capable of utilizing low-temperature heat sources below 400 °C. The review is primarily concentrated on line-focused concentrated solar power (CSP)-assisted solar technologies to be integrated with organic Rankine cycle (ORC) and absorption cooling systems. Photovoltaic and similar multigeneration systems are also discussed in brief.

Performance investigation of the heat pump and power generation integration system

A novel heat pump and power generation integration system (HPPGIS) using solar energy as a low temperature heat source was presented in this study. This system could be operated in both an organic Rankine cycle power generation (ORC-PG) mode and a reverse Carnot cycle heat pump (RCC-HP) mode. Compared with a single heat pump and power generation system, this system improved the utilization efficiency of solar energy, thus showing potential for the generation of economic benefits. Contrastive analyses of different working fluids using ORC-PG and RCC-HP systems were conducted first, leading to the selection of R142b and R245fa as optimal fluids. Then, an experimental investigation of the system was carried out under different conditions. A heat pump and ORC system model was proposed and validated by comparing experimental and simulated values. The experimental results indicated that the HPPGIS had good feasibility and stability in both modes. In the ORC-PG mode, HPPGIS had a power output of 1.29 kW and a thermal efficiency of 4.71% when the water inlet temperature of the evaporator was 90.03°C. In the RCC-HP mode, HPPGIS had a COP of 3.16 and a heat capacity of 33.24 kW when the water outlet temperature of the condenser was 106.23°C.

Effect of Inlet Air Heating on Gas Turbine Efficiency under Partial Load

A novel heating technology is presented to analyze the influence of inlet air heating on gas turbine efficiency under partial load. This technology uses the waste heat of a low-temperature heat sources, which includes but is not limited to the exhaust gas of a combined-cycle heat-recovery steam generator or a single-cycle gas turbine. A calculation model of the equilibrium running point is used for the given load and the characteristic curves of the compressor and the turbine to study the mechanism of the inlet air heating technology. Then, the equilibrium running line is calculated and drawn in the characteristic curves of the compressor and the turbine. The factors for gas turbine efficiency are discussed through the calculated equilibrium running line. The results show that an increase in inlet air temperature has considerable potential for improving gas turbine efficiency due to the increase in compressor and turbine efficiency. This finding is different from traditional viewpoints. Meanwhile, each partial load has an optimum heating temperature which becomes higher when the load is lower.

Preliminary design of radial inflow turbine and working fluid selection based on particle swarm optimization

Organic Rankine cycle (ORC) is an efficient technique to recycle the low temperature heat sources. The design method of the critical component, radial inflow turbine, is a main focus of research. A preliminary design method was developed to optimize eight critical parameters based on particle swarm optimization (PSO) algorithm. The isotropic efficiency was the objective function of the algorithm. Six working fluids were selected to conduct turbine design based on the design method. The turbine with R245fa was determined to be optimal due to its small geometry size, high exergy efficiency (0.929) and high load coefficient (1.1027). The off-design performance of R245fa turbine was investigated with the variation of pressure ratio (PR), stator inlet temperature and power output. The results indicate that the turbine efficiencies increase with the reduction of PR and turbine inlet temperature and the increase of power output. The exergy efficiency and isotropic efficiency drop slightly with the increase of turbine inlet temperature. So the turbine with R245fa exhibited good off-design performance.

Thermal Optimization of a Dual Pressure Goswami Cycle for Low Grade Thermal Sources.

This paper presents a theoretical investigation of a new configuration of the combined power and cooling cycle known as the Goswami cycle. The new configuration consists of two turbines operating at two different working pressures with a low-heat source temperature, below 150 °C. A comprehensive analysis was conducted to determine the effect of key operation parameters such as ammonia mass fraction at the absorber outlet and boiler-rectifier, on the power output, cooling capacity, effective first efficiency, and effective exergy efficiency, while the performance of the dual-pressure configuration was compared with the original single pressure cycle. In addition, a Pareto optimization with a genetic algorithm was conducted to obtain the best power and cooling output combinations to maximize effective first law efficiency. Results showed that the new dual-pressure configuration generated more power than the single pressure cycle, by producing up to 327.8 kW, while the single pressure cycle produced up to 110.8 kW at a 150 °C boiler temperature. However, the results also showed that it reduced the cooling output as there was less mass flow rate in the refrigeration unit. Optimization results showed that optimum effective first law efficiency ranged between 9.1% and 13.7%. The maximum effective first law efficiency at the lowest net power (32 kW) and cooling (0.38 kW) outputs was also shown. On the other hand, it presented 13.6% effective first law efficiency when the net power output was 100 kW and the cooling capacity was 0.38 kW.

Investigation on the performance of R1234ze(E) in absorption refrigeration and ejection refrigeration systems

To mitigate greenhouse warming and ozone depletion, trans-1,3,3,3-tetrafluoropropene (R1234ze(E), a kind of hydrofluoroolefin) has been developed by researchers as an environment-friendly refrigerant. To investigate which kind of refrigeration is suitable for R1234ze(E), the performance of R1234ze(E) in both the absorption refrigeration and ejection refrigeration systems was simulated. It was found that R1234ze(E) is more suitable for ejection refrigeration and the COP reaches to 0.38 (Tb = 373 K, Te = 278 K, Tc = 303 K). However, R1234ze(E) performs poorly in the absorption refrigeration system, reaching its peak (COP = 0.29) at Tg = 363 K. To top it off, the circulation ratio is too high so that absorption refrigeration is unacceptable for R1234ze(E). Even though an ejector can increase the absorber pressure, it cannot promote the performance except that the system can be driven by lower temperature heat source.

Analysis on the change of coal consumption of low-pressure (low temperature) economizer unit

This paper discusses the calculation of coal consumption for power generation when the unit uses steam extraction as a low-pressure (low temperature) heat recovery source. The calculation of coal consumption for power generation when the unit uses low-pressure (warm) economizer as a low-pressure (low-temperature) heat source, the heat source is not recovered. At the same time, the coal consumption of power generation was compared, and finally the reduction of the heat rate of the turbine was discussed as a decrease in coal consumption.