Simulation and thermodynamic evaluation of steam cogeneration system configurations for energy recovery from exhaust gases of a carbo-chemical industry

In this paper, the useful concept of energy and exergy utilization is analyzed, and applied to the boiler system. Energy and exergy flows in a boiler have been shown in this paper. The energy and exergy efficiencies have been determined as well. In a boiler, the energy and exergy efficiencies are found to be 89.21% and 45.48%, respectively. A boiler energy and exergy efficiencies are compared with others work as well. It has been found that the combustion chamber is the major contributor for exergy destruction followed by heat exchanger of a boiler system. Furthermore, Modifications are examined to increase gas-fired steam power plant efficiency by reducing irreversibilities in the steam generator, including Decreasing the fraction of excess combustion air, and/or the stack-gas temperature. Overall-plant energy and exergy efficiencies both increase by 0.19%, 0.37% respectively when the fraction of excess combustion air decreases from 0.4 to 0.15, and by 0.84%, 2.3% when the stack-gas temperature decreases from 137°C to 90°C Keywords. Exergy efficiency, energy efficiency, super critical thermal power plant, excess air, stack gas temperature

In this paper, a new integrated system of solid oxide fuel cell (SOFC)–gas turbine (GT)–steam Rankine cycle (SRC)–exhaust gas boiler (EGB) is presented, in which ammonia is introduced as a promising fuel source to meet shipping decarbonization targets. For this purpose, an SOFC is presented as the main power-generation source for a specific marine propulsion plant; the GT and SRC provide auxiliary power for machinery and accommodation lighting, and steam from the waste heat boiler is used for heating seafarer accommodation. The combined system minimizes waste heat and converts it into useful work and power. Energy and exergy analyses are performed based on the first and second laws of thermodynamics. A parametric study of the effects of the variation in the SOFC current density, fuel utilization factor, superheat temperature, and SRC evaporation pressure is conducted to define the optimal operating parameters for the proposed system. In the present study, the energy and exergy efficiencies of the integrated system are 64.49% and 61.10%, respectively. These results serve as strong motivation for employing an EGB and SRC for waste heat recovery and increasing the overall energy-conversion efficiency of the system. The SRC energy and exergy efficiencies are 25.58% and 41.21%, respectively.

This paper deals with parametric of thermodynamic analysis of a gas power plant has 165.1 MW rated power capacity. This plant established as a gas power plant in Mosrata, (Libya) to feed an iron and steel factory. The thermodynamic analysis energy and exergy analysis indicate how much power has been rejected in the exhaust gases in case of gas power plant only. In order to enhance the exergy and energy efficiencies, this study propose a steam unit as a (combined power plant). The gas plant was designed to work under different part load of 0.2, 0.4, 0.6, 0.8, and at full load. Then, the thermodynamic energy and exergy analysis of the plant has been carried out. The energy and exergy efficiencies were calculated according to the first and the second laws of thermodynamics. It is concluded that the overall thermal efficiency can be improved by 9.835% and the exergy can be enhanced by 9.34% at full load.

In recent years, the increment of pollutants emissions in the environment, global warming concerns, and governmental restrictions on fossil fuel consumption have necessitated the prevention of the spread of pollution in various industries, such as waterborne transport. In this study, new electricity and cooling cogeneration system is proposed for waste heat recovery of exhaust gas from the combustion of a marine diesel engine. The proposed system encompasses a combination of an absorption power cycle and an ejector refrigeration cycle to supply the cooling and electricity required for the crew. The performance of the proposed system is evaluated from the perspective of the first and second laws of thermodynamics, and a parametric study is conducted to predict the behavior of the system under the influence of the input parameters. Later, due to the existing conflicting trend between energy efficiency and exergy efficiency, multi-objective optimization is used to merge several optimal design points into a final optimal point. The results indicate that the proposed cogeneration system has a capacity of 49.72 kW and 23.56 kW of electricity and cooling production in the optimal mode. In addition, in this case, the energy and exergy efficiencies of the system are obtained at 17.25% and 28.82%, respectively, which the former has improved by about 9.32% and the latter by 6.9%. Based on the obtained results, the total fuel exergy through exhaust gas is about 174.8 kW, of which 100.3 kW, 24.11 kW, and 50.38 kW are associated with exergy destruction, loss, and product rates.

Thermodynamic analysis of a novel multigeneration energy system based on heat recovery from a biomass CHP cycle

Due to the relatively cheap price of diesel, most Marine engines use diesel as Marine fuel, but its emissions contain a lot of carbon. To reduce carbon emissions, International Maritime Organization (IMO) has established an Energy Efficiency Design Index (EEDI) and Energy Efficiency Existing-Ship Index (EEXI). Currently, a popular way is to reduce EEDI by optimizing the heat transfer performance of exhaust gas boilers on new ships, but there is little research on the EEXI index of existing ships. For operating ships, the thermal conductivity of exhaust gas boiler materials and other parameters has been fixed, so the main factors affecting the heat transfer coefficient of the exhaust gas boiler are exhaust gas temperature and flow velocity. Therefore, this paper studies the influence of engine exhaust temperature and flow rate on boiler heat transfer coefficients and optimizes it to achieve the EEXI value required by IMO. Firstly, based on the conservation of mass and energy as the basic equation, a heat exchange model of the exhaust gas boiler is established by using the hybrid modeling method and lumped parameter method. Secondly, for the given boiler, since other parameters are basically unchanged, the input temperature and flow rate of the model are changed by the control variable method, and the temperature of the boiler outlet is simulated by the test algorithm. Through the simulation operation of an Aalborg OC-type boiler, the results show that when the exhaust gas flow velocity is 15 m/s, 17.2 m/s, 22.4 m/s and 25 m/s, respectively, the heat transfer coefficient at each flow velocity increases first and then slowly decreases with the increase of temperature, and there is an optimal temperature at each velocity, which is 230 °C, 227 °C, 225 °C and 224 °C, respectively. The innovation of this study lies in the research on the inlet temperature and flow rate of the exhaust gas boiler of the operating ship based on the EEXI, and the relevant results are obtained, which provides theoretical guidance for the operation management of the exhaust gas boiler of the operating ship.

The application of waste heat from exhaust gas of ship’s main engines has become widely practiced as early as in the 1930s. Thus the increase of ship’s overall efficiency was improved. Nowadays all newly built ships of the 400 gross tonnage and above must have specified energy efficiency design index, which is a measure for CO2 emissions of the ship and its impact on the environment. Therefore, the design of waste heat recovery systems requires special attention. The use of these systems is one of the basic ways to reduce CO2 emissions and to improve the ship’s energy efficiency. The paper describes the ship’s heating systems designed for the use of waste heat contained in the exhaust gas of self-ignition engines, in which the heat carriers are respectively water vapor, water or thermal oil. Selected results of comparative exergy analysis of simplified steam, water and oil heating systems have been presented. The results indicate that the oil heating system is comparable to the water system in terms of internal exergy losses. However, larger losses of exergy occur in the case of a steam system. In the steam system, a significant loss is caused by the need to cool the condensate to avoid cavitation in boiler feed pumps. This loss can in many cases cause the negative heat balance of ship during sea voyage while using only the exhaust gas boilers.

The objective in this work is to characterize a zero energy and energy efficient solar-house, demonstrating that it can be the basis for sustainable development, where sustainability particularly is measured by the contribution to mitigate global warming, that’s means reducing GHG emissions. In this sense, the systematization of solar-house appears with guidelines that guide its design under the end-use of electricity, environmental conditioning, application of solar systems and other equipment to ensure energy and environmental efficiency in its operation. Quantitative evidence appears securing the residential sector of Brazil as a case study, analyzing the Brazilian energy system and use of electricity by the residential sector, with concomitant evaluation of associated emissions of greenhouse gases. Moreover, it has been as solar house prototype verification as the EkoHouse identified model. The estimated reduction of GHG emissions is related to the use of electricity, and accounting for these emissions are considered photovoltaic generation to replace the power grid, and the adoption of energy efficiency measures. As a result this study presents a model of solar-house; defining strategies for energy and environmental efficiency in dwellings, the accounting of emissions avoided and the analysis of the benefits obtained by the application of solar-house model on a large scale in Brazil. To estimate impacts of these solutions on a larger scale, it is assumed as part of the case study Southeast of Brazil, and is considered the adoption of energy efficiency measures and PV generation to 50 % of homes in this area. The accounting shows a potential to prevent up to 355 tons of CO2. We conclude that solar-house modeled to have zero annual energy consumption and to be energy efficient, contributes to a low environmental impact and to sustainable development throughout mitigation of global warming by reducing GHG emissions.

Modelling the future CO2 abatement potentials of energy efficiency and CCS: The case of the Dutch industry

Energy, exergy and exergoeconomic (3E) evaluation are performed to assess the performance of a NH3/H2O cycle integrated with parabolic trough solar collectors (PTSC). To provide continuous electricity produced by generator when solar beam radiation is insufficient a stabilizer temperature subsystem is utilized. The major thermodynamic parameters and climate conditions variations are selected to investigate, for their effects on the energy efficiency, exergy efficiency and unit cost of electricity of the overall system. The results reveal that the solar collectors exhibit the worst exergy and exergoeconomic performance, so that when system is only fuelled by solar energy, elevation of solar beam irradiation around 40% reduces the efficiencies and electricity production cost within 23% and 0.4%, respectively. It is found that the increment of ammonia basic concentration, turbine inlet pressure, evaporator inlet temperature and evaporator pinch temperature lead to elevation of energy and exergy efficiencies and decrement of electricity production cost. Then, the single and multi-objective optimizations are performed to maximize the energy and exergy efficiencies and minimize the electricity production cost based on genetic algorithm (GA). Results indicate that the electricity production cost obtained through economic optimization is less than around 2% and 2.2% compared to the optimization based on the first and second laws of thermodynamics. Multi objective optimization causes reduction of electricity production cost around 14% and enhancement the energy and exergy efficiencies 8.5% and 6.7%, respectively too.

Energy–exergy analysis and optimisation of a model sugar factory in Turkey

Thermodynamics analysis of a novel designation of LNG solid oxide fuel cells combined system with CO2 capture using LNG cold energy

Electrochemical ammonia synthesis: Mechanistic understanding and catalyst design

In this research, the thermodynamic investigation of the tri-generation system is performed by the first and second law of Thermodynamics. The trigeneration system under study consists of three subsystems including the solar subsystem, Kalina subsystem and lithium bromide-water absorption chiller subsystem. The proposed system generates power, cooling and hot water using solar energy. The system considered is designed and evaluated based on the climate condition in Zahedan, Iran. The calculation results show that the most exergy destruction rate takes place in the solar cycle. The assessment of system is used dynamic and static forms. In dynamic form, that maximum total cost rate, energy and exergy efficiency are equal to 15.1 dollars per hour,by 33% and 36.47%, respectively. The results base-case demonstrate that energy and exergy efficiencies and total cost rates are equal to 9.63 dollars per hour by 17.37% and 18.82% , respectively in static analysis. Furthermore, optimization criteria comparison such as energy efficiency, exergy efficiency and power are discussed in static form. The results of static evaluation revealed that the power is the best criteria for thermodynamics. Moreover, optimization results based on maximum power criterion show that produced power, energy efficiency, exergy efficiency and total cost rate increase by 28%, 12.32%, of 13.97% and 7.68%, respectively in comparison with the base case.

Thermoelectric (TE) generation is becoming a valuable and promising research direction. Many researchers have carried out system analysis and performance optimization of thermoelectric technologies based on the generalized thermoelectric energy balance equations. However, it is assumed that TE legs have no heat exchange with the ambient except at the junctions of the hot and cold ends where heat flows in and out. Based on basic thermoelectric effects and fundamental theories of heat transfer, a detailed derivation of the revised generalized thermoelectric energy equations considering convective heat transfer between TE legs and the ambient has been carried out. Irreversible heat transfer processes have been analyzed by employing energy analysis based on the first law of thermodynamics and exergy analysis based on the second law of thermodynamics. The results show that convective heat transfer leads to a decrease in both energy and exergy efficiencies: the rate and magnitude of the decrease in exergy efficiency are greater than those of the decrease in energy efficiency. The exergy efficiency is relatively high despite the low energy efficiency in operation, revealing the features and advantages of thermoelectric generators (TEGs) in low‐grade energy utilization. For TEG efficient operation, the load resistance value should match the system's internal resistance, or at least be greater than that, to avoid a sharp drop in power output and efficiencies. In an attempt at theoretical analysis, the concept of entransy was first introduced into thermoelectric analysis, yielding two concise relational equations which reflect the intrinsic link between Carnot cycle efficiency, energy efficiency, exergy efficiency, and entransy flow transfer efficiency. The entransy analysis based on the index of entransy flow transfer efficiency, together with energy analysis and exergy analysis, may be a novel and valuable guideline for the operation and optimization of TEGs, which needs to be further investigated.