Energy recovery from effluents of supercritical water oxidation reactors (original) (raw)
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Applied Sciences
Supercritical water gasification (SCWG) has been shown to be an effective technology to valorize a wide range of organic waste by transforming them into gases with high energy potential, such as hydrogen and methane. However, the industrial implementation of these processes is rarely extended due to the huge energy requirements during plant start-up and operation. The purpose of this study is to explore feasible ways of energy integration by hybridizing SCWG processes with combined heat and power technologies, such as exhaust gases coming from (i) internal combustion engines or (ii) gas turbines. The analysis focuses on energy consumption with the aim of optimizing the operation and design of plants. System configurations are simulated with Aspen Plus considering data from the literature for the gasification of glycerol and using typical plant capacities on an industrial scale. Results show the thermal power required in heat exchangers and the electricity generation from residual en...
Energy integration of high pressure processes using gas turbines and internal combustion engines
2016
High pressure processes (e.g. sustainable hydrothermal manufacturing of nanomaterials [1], supercritical water oxidation (SCWO) [2] and biomass hydrolysis [3]) require high operational conditions. Water at high pressure and temperature conditions improves kinetic, selectivity and efficiency of these processes but entail high-energy operational expenditure. Use of fluids at high operational conditions makes necessary to supply heat of high quality, as well as power. Because of this, it is necessary to study reasonable solutions for energy recovery and integration in order to achieve the energy self-sufficiency of the process and, if possible, the net power production and with a viable efficiency [4]. In this work, the energy integration of supercritical water oxidation process is being studied. One solution that has been recently proposed is the integration of supercritical processes with energy production in cogeneration or Combined Heat and Power (CHP) cycles. Cogeneration is defin...
2018
Waste heat to power conversion is a promising approach to reduce the carbon intensity in industry and manufactured goods. In this framework, bottoming thermodynamic cycles using supercritical carbon dioxide as working fluid (sCO2) might be a suitable and efficient technology to consider especially for heat sources characterized by streams at high temperatures (>300°C). The compactness of sCO2 turbomachinery is one of the advantages of sCO2 systems over the conventional technologies; on the other hand, the reduced dimensions limits the bottom end of the power size achievable with such systems. The scarce amount of scientific and industrial literature for electrical power sizes between 50 and 100 kW further demonstrates this. The current research work summarizes the design procedure as weil as the technical and technological challenges involved in the design of a single-shaft compressor, generator, turbine unit (CGT) for a sCO2 system with a 50kWe nominal power output. First an ove...
Super- and Transcritical Fluid Expansions for Next-Generation Energy Conversion Systems
The next generation of thermodynamic power cycles offers great potential as the conceptual basis for sustainable energy converters. Examples are the supercritical and superheated Organic Rankine cycle, the transcritical condensation cycle, the supercritical Brayton cycle, the Organic Stirling cycle and the transcritical vapor compression cycle. They can be considered the next generation of well-known thermodynamic cycles, since they work with different working fluids and operate at different thermodynamic conditions, namely, close to or above the critical point of the working fluid or, at slightly lower pressures, in the dense-gas region. The anomalous thermodynamic behavior at these conditions and for these fluids offers various advantages, such as expansion across a reduced number of turbine stages, reduced compression work and a better match between the heating trajectory of the working fluid and the cooling trajectory of the heat source in the heat exchanger. This new generation...
A process for generating power from the oxidation of coal in supercritical water
Fuel, 2004
A theoretical study of power generation from oxidation of coal by supercritical water oxidation (SCWO) is presented. Two versions of SCWO power plant are compared to two of the most efficient conventional power plant processes: pulverised coal power plants and pressurised fluidised bed power plant. The effects of steam pressure and temperature on produced ðW p Þ; consumed ðW c Þ and net work ðW N Þ are calculated in order to compare the efficiency of these power plants for the same steam conditions. Enthalpies have been calculated using residual enthalpies by Peng -Robinson equation of state. Calculated results show that net work in SCWO power plant is 5% higher than in other power plants, due to the fact that no air surplus is necessary for complete combustion and because steam is produced by direct heating. Energetic efficiency of SCWO increases more quickly with temperature than for the other power plants. The effect of steam pressure is different: until 30 MPa power plant efficiencies increase more quickly in SCWO power plants than in conventional plants, but when steam pressures increases beyond 30 MPa, efficiencies decrease in SCWO power plants. q
Advanced Thermodynamic Analysis and Evaluation of a Supercritical Power Plant
Energies, 2012
A conventional exergy analysis can highlight the main components having high thermodynamic inefficiencies, but cannot consider the interactions among components or the true potential for the improvement of each component. By splitting the exergy destruction into endogenous/exogenous and avoidable/unavoidable parts, the advanced exergy analysis is capable of providing additional information to conventional exergy analysis for improving the design and operation of energy conversion systems. This paper presents the application of both a conventional and an advanced exergy analysis to a supercritical coal-fired power plant. The results show that the ratio of exogenous exergy destruction differs quite a lot from component to component. In general, almost 90% of the total exergy destruction within turbines comes from their endogenous parts, while that of feedwater preheaters contributes more or less 70% to their total exergy destruction. Moreover, the boiler subsystem is proven to have a large amount of exergy destruction caused by the irreversibilities within the remaining components of the overall system. It is also found that the boiler subsystem still has the largest avoidable exergy destruction; however, the enhancement efforts should focus not only on its inherent irreversibilities but also on the inefficiencies within the remaining components. A large part of the avoidable exergy destruction within feedwater preheaters is exogenous; while that of the remaining components is mostly endogenous indicating that the improvements mainly depend on advances in design and operation of the component itself.
The Journal of Supercritical Fluids, 2015
Supercritical water oxidation (SCWO) has the potential to be considered a clean energy generation process, as the process effluent is a high temperature, high pressure stream with a high enthalpy content that can be converted to heat and shaft work. In this work the state of the art of SCWO has been reviewed, focusing on energy production. For the description of thermodynamic and transport properties, there are some methods recommended for pure substances, but the applicability of those methods for mixtures at supercritical state is yet not clear. Most of the work found in literature use cubic equations of state and linear mixing rules. The design of reactors has evolved in order to reduce the drawbacks of corrosion and salt deposition, in general, through the dilution of reaction products. In order to make the process profitable energetically different strategies must be used to keep the products at the highest temperature without compromising the safety, and the hydrothermal flames if correctly stabilized are a good choice. Reactors and reaction systems able to process feeds consisting of suspension with high inorganic contents without diluting the effluent reducing its temperature must be developed. On the other hand, the systems of energy recovery must be improved, especially the expanders, in order to recover the pressure work as well as the thermal energy. Modeling tools can help in both aspects. But for developing good models a good comprehension of thermal and transport properties of mixtures at supercritical state, as well as oxidation kinetics under that condition are essential data that must be further investigated in order to find energetically efficient processes.