Investigation on efficiency improvement of a Kalina cycle by sliding condensation pressure method

Conventional Kalina cycle-based geothermal power plants are designed with a fixed working point determined by the local maximum ambient temperature during the year. A previous study indicated that the plant’s annual average thermal efficiency would be improved if the ammonia mass fraction of the Kalina cycle could be tuned to adapt to the ambient conditions. In this paper, another sliding condensation pressure method is investigated. A theoretical model is set up and then a numerical program is developed to analyze the cycle performance. The condensation pressure adjustment in accordance to the changing ambient temperature has been numerically demonstrated under various ammonia-water mixture concentrations. The results indicate that the Kalina cycle using sliding condensation pressure method can achieve much better annual average thermal efficiency than a conventional Kalina cycle through matching the cycle with the changing ambient temperature via controlling condensation pressure. Furthermore, the sliding condensation pressure method is compared with the composition tuning method. The results show that the annual average efficiency improvement of the sliding condensation pressure method is higher than that of the composition tuning method

A dynamic organic Rankine cycle using a zeotropic mixture as the working fluid with composition tuning to match changing ambient conditions

Air-cooled condensers are widely used for Organic Rankine Cycle (ORC) power plants where cooling water is unavailable or too costly, but they are then vulnerable to changing ambient air temperatures especially in continental climates, where the air temperature difference between winter and summer can be over 40 °C. A conventional ORC system using a single component working fluid has to be designed according to the maximum air temperature in summer and thus operates far from optimal design conditions for most of the year, leading to low annual average efficiencies. This research proposes a novel dynamic ORC that uses a binary zeotropic mixture as the working fluid, with mechanisms in place to adjust the mixture composition dynamically during operation in response to changing heat sink conditions, significantly improving the overall efficiency of the plant. The working principle of the dynamic ORC concept is analysed. The case study results show that the annual average thermal efficiency can be improved by up to 23% over a conventional ORC when the heat source is 100 °C, while the evaluated increase of the capital cost is less than 7%. The dynamic ORC power plants are particularly attractive for low temperature applications, delivering shorter payback periods compared to conventional ORC systems

Dynamic control strategy of a distillation system for a composition-adjustable organic Rankine cycle

Using zeotropic mixtures as working fluids can improve the thermal efficiency of Organic Rankine cycle (ORC) power plants for utilising geothermal energy. However, currently, such ORC systems cannot regulate the composition of zeotropic mixtures when their operating conditions change. A composition-adjustable ORC system could potentially improve the thermal efficiency by closely matching the cycle to the changing ambient conditions provided that the composition of the working fluid mixture can be adjusted in an economic way. In this paper, a dynamic composition control strategy has been proposed and analysed for such a composition-adjustable ORC system. This method employs a distillation column to separate the two components of the mixture, which can then be pumped back to the main ORC system to adjust the composition of the zeotropic mixture to the required level according to the ambient temperature. The dynamic composition control strategy is simulated using an optimisation algorithm. The design method of the distillation column is presented and its dynamic response characteristics have been analysed using Aspen Plus Dynamics. The results indicate that the average power output can be significantly improved using a composition-adjustable ORC system when the ambient temperature decreases. The size of the distillation system is relatively small and its energy (mainly thermal) consumption is only around 1 percent of the system’s input heat. The research results also show that the dynamic response characteristics of the distillation system can satisfy the requirements of the ORC system

Identification and characterization of protein phosphatase 2A mutants in Arabidopsis thaliana

Reversible protein phosphorylation is a highly regulated process that affects almost all cellular activities. Phosphorylation involves two groups of enzymes: protein kinases and protein phosphatases. Considering the central role of these enzymes in cells, elucidating their function is extremely important. My research focuses on protein phosphatase 2A (PP2A) C subunits. PP2A is one of the most abundant types of serine/threonine phosphatases in all eukaryotic cells. Compared with animals, PP2A function is not well known in plants. Early studies using protein phosphatase inhibitors are not useful to demonstrate the function of individual PP2A subunits. A reverse genetic approach can be helpful to gain insight into the function of PP2A in plants since a resulting phenotype is due to the lack of function of a single protein and provides direct evidence to elucidate function. In this study, 13 homozygous mutant lines generated by the insertion of foreign DNA (T-DNA) in all five Arabidopsis PP2A C subunit genes were identified by the polymerase chain reaction. The precise location of the insertion was determined from DNA sequencing, expressed sequence tags and cDNA data. The presence of a full-length mRNA was not detected from five of the 13 mutant alleles (cl-1, c3-1, c3-3, c4-1 and c4-2) as determined by the reverse transcriptase-polymerase chain reaction. Wild type and mutant plants were compared under different growth conditions and chemical treatments to characterize the effect of the mutations. There was no obvious difference between mutant and wild type plants except in one case: growth in the presence of NaCl. At greater than 50 mM supplemental NaCl, roots of c4 mutant seedlings grown on vertically-oriented plates had a strong right-skewing growth pattern (when viewed from top of the plate) while wild type seedlings showed only a slight right skewing. Complementation confirmed that the c4 mutant phenotype was due to loss of PP2A C4 function. The c4 mutant phenotype did not appear when seedlings were grown in the presence of KCl, LiCl or CaCl2. Additional experiments showed that Ca2+ and auxin transport might also be involved in the NaCl-induced skewing phenotype of the PP2A c4 mutants

A regenerative supercritical-subcritical dual-loop organic Rankine cycle system for energy recovery from the waste heat of internal combustion engines

Organic Rankine cycle (ORC) system is considered as a promising technology for energy recovery from the waste heat rejected by internal combustion (IC) engines. However, such waste heat is normally contained in both coolant and exhaust gases at quite different temperatures. A single ORC system is usually unable to efficiently recover energy from both of these waste heat sources. A dual loop ORC system which essentially has two cascaded ORCs to recover energy from the engine’s exhaust gases and coolant separately has been proposed to address this challenge. In this way, the overall efficiency of energy recovery can be substantially improved. This paper examines a regenerative dual loop ORC system using a pair of environmentally friendly refrigerants, R1233zd and R1234yf, as working fluids, to recover energy from the waste heat of a compressed natural gas (CNG) engine. Unlike most previous studies focusing on the ORC system only, the present research analyses the ORC system and CNG engine together as an integrated system. As such, the ORC system is analysed on the basis of real data of waste heat sources of the CNG engine under various operational conditions. A numerical model is employed to analyse the performances of the proposed dual loop cycle with four pairs of working fluids. The effects of a regenerative heat exchanger and several other key operating parameters are also analysed and discussed in detail. The performance of the integrated engine-ORC system is then analysed under actual engine operating conditions which were measured beforehand. The performance of the proposed system under off-design conditions has also been analysed. The obtained results show that the proposed dual loop ORC system could achieve better performance than other ORC systems for similar applications

A numerical analysis of a composition-adjustable Kalina cycle power plant for power generation from low-temperature geothermal sources

The Kalina cycle is believed to be one of the most promising technologies for power generation from low temperature heat sources such as geothermal energy. So far, most Kalina cycle power plants are designed with a working fluid mixture having a fixed composition, and thus normally operate at a fixed condensing temperature. However, the ambient temperature (i.e., heat sink) varies over a large range as the season changes over a year, particularly in continental climates. Recently, a new concept, i.e., composition-adjustable Kalina cycle, was proposed to develop power plants that can match their condensing temperature with the changing ambient conditions, aiming at improving the cycle’s overall thermal efficiency. However, no detailed analysis of its implementation and the potential benefits under various climate conditions has been reported. For this reason, this paper carried out a comprehensive numerical research on its implementation and performance analysis under several different climate conditions. A mathematical model is firstly established to simulate the working principle of a composition-adjustable Kalina cycle, based on which a numerical program is then developed to analyse the cycle’s performance under various climate conditions. The developed numerical model is verified with some published experimental data. The 2 dynamic composition adjustment in response to the changing ambient temperature is simulated to evaluate its effect on the plant’s performance over a year. The results show that a composition-adjustable Kalina cycle could achieve higher annual-average thermal efficiency than a conventional one with a fixed mixture composition. However, such an improvement of thermal efficiency strongly depends on the heat source temperature, climate conditions, etc. The composition-adjusting system introduces extra capital and operation costs. The economic viability of a composition-adjustable Kalina cycle power plant depends on the balance between these extra costs and the increase of thermal efficiency

Parametric optimization and heat transfer analysis of a dual loop ORC (organic Rankine cycle) system for CNG engine waste heat recovery

In this study, a dual loop ORC (organic Rankine cycle) system is adopted to recover exhaust energy, waste heat from the coolant system, and intercooler heat rejection of a six-cylinder CNG (compressed natural gas) engine. The thermodynamic, heat transfer, and optimization models for the dual loop ORC system are established. On the basis of the waste heat characteristics of the CNG engine over the whole operating range, a GA (genetic algorithm) is used to solve the Pareto solution for the thermodynamic and heat transfer performances to maximize net power output and minimize heat transfer area. Combined with optimization results, the optimal parameter regions of the dual loop ORC system are determined under various operating conditions. Then, the variation in the heat transfer area with the operating conditions of the CNG engine is analyzed. The results show that the optimal evaporation pressure and superheat degree of the HT (high temperature) cycle are mainly influenced by the operating conditions of the CNG engine. The optimal evaporation pressure and superheat degree of the HT cycle over the whole operating range are within 2.5–2.9 MPa and 0.43–12.35 K, respectively. The optimal condensation temperature of the HT cycle, evaporation and condensation temperatures of the LT (low temperature) cycle, and exhaust temperature at the outlet of evaporator 1 are kept nearly constant under various operating conditions of the CNG engine. The thermal efficiency of the dual loop ORC system is within the range of 8.79%–10.17%. The dual loop ORC system achieves the maximum net power output of 23.62 kW under the engine rated condition. In addition, the operating conditions of the CNG engine and the operating parameters of the dual loop ORC system significantly influence the heat transfer areas for each heat exchanger

A Hybrid Energy Storage System for a Coaxial Power-Split Hybrid Powertrain

A hybrid energy storage system (HESS) consisting of batteries and supercapacitors can be used to reduce battery stress and recover braking energy efficiently. In this paper, the performance of a novel coaxial power-split hybrid transit bus with an HESS is studied. The coaxial power-split hybrid powertrain consists of a diesel engine, a generator, a clutch, and a motor, whose axles are arranged in a line. A mathematical model of the coaxial power-split hybrid powertrain with an HESS is established and the parameters are configured using experimental data. Subsequently, to estimate the system performance, a program is designed based on Matlab and Advisor. A rule-based control strategy is designed and finely tuned for the coaxial power-split hybrid powertrain. Then, using the Chinese Transit Bus City Driving Cycle (CTBCDC), the system characteristics and energy efficiencies of the designed coaxial power-split hybrid powertrain with an HESS are analysed. The results indicate that the proposed coaxial power-split hybrid powertrain with an HESS can fulfil the drivability requirement of transit bus and enhance the energy efficiency significantly compared with a conventional powertrain bus as well as reduce the battery stress simultaneously. Using an HESS is a good solution for the coaxial power-split hybrid transit bus

Thermodynamic analysis of a dual-loop organic Rankine cycle (ORC) for waste heat recovery of a petrol engine

Huge amounts of low-grade heat energy are discharged to the environment by vehicular engines. Considering the large number of vehicles in the world, such waste energy has a great impact on our environment globally. The Organic Rankine Cycle (ORC), which uses an organic fluid with a low boiling point as the working medium, is considered to be the most promising technology to recover energy from low-grade waste heat. In this study, a dual-loop ORC is presented to simultaneously recover energy from both the exhaust gases and the coolant of a petrol engine. A high-temperature (HT) ORC loop is used to recover heat from the exhaust gases, while a low-temperature (LT) ORC loop is used to recover heat from the coolant and the condensation heat of the HT loop. Figure 1 shows the schematic of the dual-loop ORC. Differing from previous research, two more environmentally friendly working fluids are used, and the corresponding optimisation is conducted. First, the system structure and operating principle are described. Then, a mathematical model of the designed dual-loop ORC is established. Next, the performance of the dual-loop cycle is analysed over the entire engine operating region. Furthermore, the states of each point along the cycle and the heat load of each component are compared with the results of previous research. The results show that the dual-loop ORC can effectively recover the waste heat from the petrol engine, and that the effective thermal efficiency can be improved by about 20 ~ 24%, 14~20%, and 30% in the high-speed, medium-speed, and low-speed operation regions, respectively. The designed dual-loop ORC can achieve a higher system efficiency than previous ORCs of this structure. Therefore, it is a good choice for waste heat recovery from vehicle engines