Results 1 - 10 of 171
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[en] An LPE (low-pressure economizer) based waste heat recovery system for a CFPP (coal-fired power plant) is investigated thermodynamically. With the installation of LPE in the flue before the FGD (flue gas desulfurizer), the heat contained in the exhaust flue gas can be recovered effectively and the water consumption can be reduced in the FGD resulted from the temperature dropped flue gas. The impacts on the related apparatuses after installing LPE in a CFPP are analyzed and the internal relationships among correlated parameters are presented. The efficiencies of LPE installed in a CFPP evaluated by the first law, the second law and the thermal equilibrium efficiencies are also compared and analyzed. A detailed case study based on a 350 MW CFPP unit is presented and the variations of the thermal performance after the installation of LPE are investigated. The results show that the second law and the thermal equilibrium efficiencies are increased which can be indicators to evaluate the performance of the LPE system while the first law efficiency is decreased after installing LPE. Results also show that the saving of SCE (standard coal equivalent) is 3.85 g/(kW·h) for this CFPP unit under full load after installing LPE. - Highlights: • An evaluation method of the LPE (low-pressure economizer) system is established. • Impacts on the original thermal system by installing LPE are investigated. • A theoretical guideline is provided to improve the thermal system efficiency by LPE. • A detailed case is presented to demonstrate the energy saving of the LPE system
[en] Oil and gas platforms in the North Sea region are associated with high power consumption and large CO2-emissions, as the processing and utility plants suffer from significant changes in production rates and performance losses over the field lifespan. In this paper, a generic model of the overall offshore system is described: its thermodynamic performance is assessed by performing an exergy accounting and rules of thumb for oil and gas platforms are derived. Simulations are built and conducted with the tools Aspen Plus®, Dynamic Network Analysis and Aspen HYSYS®. 62–65% of the total exergy destruction of an offshore platform is attributable to the power generation and waste heat recovery system, and 35–38% to the oil and gas processing. The variability of the feed composition has little effect on the split of the thermodynamic irreversibilities between both plants. The rejection of high-temperature gases from the utility and flaring systems is the major contributor to the exergy losses. These findings suggest to focus efforts on a better use of the waste heat contained in the exhaust gases and on the ways in which the gas compression performance can be improved. - Highlights: • North Sea oil and gas platforms are investigated and a generic model is developed. • Exergy analysis of these offshore facilities is performed. • Most of the total exergy destruction is attributable to the utility systems producing the electrical power required onsite. • Rejection of the exhaust gases from the utility systems is the major exergy loss of this system. • The highest thermodynamic performance is reached with low well-fluid content of water and gas
[en] Low-grade waste heat source accounts for a large part of the total industrial waste heat, which cannot be efficiently recovered. The ORC (Organic Rankine Cycle) system has been proved to be a promising solution for the utilization of low-grade heat sources. It is evident that there might be several waste heat sources distributing in different temperature levels in one industry unit, and the entire recovery system will be extremely large and complex if the different heat sources are utilized one by one through several independent ORC subsystems. This paper aims to design and optimize a comprehensive ORC system to recover multi-strand waste heat sources in Shijiazhuang Refining and Chemical Company in China, involving defining suitable working fluids and operating parameters. Thermal performance is a first priority criterion for the system, and system simplicity, technological feasibility and economic factors are considered during optimization. Four schemes of the recovery system are presented in continuous optimization progress. By comparison, the scheme of dual integrated subsystems with R141B as a working fluid is optimal. Further analysis is implemented from the view of economic factors and off-design conditions. The analytical method and optimization progress presented can be widely applied in similar multi-strand waste heat sources recovery. - Highlights: • This paper focuses on the recovery of multi-strand waste heat sources. • ORC technology is used as a promising solution for the recovery. • Thermal performance, system simplicity and economic factors are considered
[en] This study presents fundamental research on the development of a new boiler that is expected to have a higher efficiency and lower emissions than existing boilers. The thermodynamic efficiency of exhaust gas recirculation-condensed water recirculation-waste heat recovery condensing boilers (EGR-CWR-WHR CB) was calculated using thermodynamic analysis and was compared with other boilers. The results show the possibility of obtaining a high efficiency when the temperature of the exhaust gas is controlled within 50–60 °C because water in the exhaust gas is condensed within this temperature range. In addition, the enthalpy emitted by the exhaust gas for the new boiler is smaller because the amount of condensed water is increased by the high dew-point temperature and the low exhaust gas temperature. Thus, the new boiler can obtain a higher efficiency than can older boilers. The efficiency of the EGR-CWR-WHR CB proposed in this study is 93.91%, which is 7.04% higher than that of existing CB that is currently used frequently. - Highlights: • The study presents the development of a new boiler expected to have a high efficiency. • Thermodynamic efficiency of EGR-CWR-WHR condensing boiler was calculated. • Efficiency of EGR-CWR-WHR CB is 93.91%, which is 7.04% higher than existing CB
[en] Carbonation of magnesium silicates offers an interesting option for CO2 emission mitigation in Finland, a country with large resources of serpentine-type minerals. Wet processes using aqueous solutions show reasonable chemical kinetics combined with poor energy economy. A dry, gas-solid process with slower chemical kinetics (demonstrated previously), but better energy economy could be an alternative. This paper addresses the energy economy of a two- or three-stage gas-solid process for magnesium silicate carbonation. It involves production of reactive magnesium as magnesium oxide or hydroxide in an atmospheric pressure step, followed by carbonation at elevated pressures that allow for reasonable carbonation reaction kinetics under conditions where magnesium carbonate is thermodynamically stable. For a feasible large-scale process the kinetics in the individual reactors must be fast enough, while the heat produced in the carbonation step must be sufficient to compensate for energy inputs to the preceding step(s). Results give reactor temperature combinations that allow for operation at a negative or zero energy input, for given carbonation reactor pressure and degree of carbonation conversion, and other process energy requirements. Softwares used were HSC and Aspen Plus. Also, some results from gas-solid kinetics studies with magnesium oxide-based materials at the pressures considered are included. (author)
[en] This work describes three different configurations of syngas production processes using a combination of SMR (steam methane reforming) and DRM (dry reforming of methane). The ideal SMR + DRM process ensures the maximum product yield, the heat-integrated SMR + DRM process fulfills the maximum heat recovery, and the stand-alone SMR + DRM process effectively suppress net CO2 (carbon dioxide) emissions. Through specific optimization algorithms, the syngas production systems subject to almost net-zero CO2 emissions are successfully verified by simulations in Aspen Plus environment. - Highlights: • A new syngas production process is composed of SMR (steam methane reforming) and DMR (dry reforming of methane). • The ideal SMR + DRM process can reduce greenhouse gas emissions and increase syngas yield. • The heat-integrated SMR + DRM process can effectively reduce energy consumption. • The stand-alone SMR + DRM process can completely remove external energy supply. • Through design, optimization, and simulation, the proposed system configurations are successfully verified
[en] A detailed chemical kinetic mechanism based on the Appel-Bockhorn-Frenklach (ABF) model was established to describe acetylene decomposition, ethylene formation, and soot formation during quenching in coal pyrolysis to acetylene process. The predictions agreed well with the reported acetylene pyrolysis experimental data. Numerical simulations were then performed to deeply understand the reaction behaviors during quenching of coal pyrolysis in thermal plasma, and to optimize the quenching design for better heat recovery. Two key operating parameters of quenching, i.e., the temperature after quenching and the quenching rate, were studied in detail and optimized after the kinetics were validated. The simulation results also proved that hydrogen can promote the formation of ethylene and inhibit the condensation of acetylene during quenching. In particular, in-depth discussion of acetylene decomposition and ethylene formation using this detailed kinetic mechanism combined with thermodynamic method provided a comprehensive understanding of the thermodynamics and kinetics interpreting pilot plant experimental data. - Highlights: • A detailed kinetic model for C_2H_2 decomposition and soot formation is established. • Two key operating parameters of quenching are studied in detail and optimized. • Effects of H_2 on C_2H_4 formation and C_2H_2 condensation during quenching are discussed. • A comprehensive understanding of the pilot plant experimental data is achieved.
[en] In this paper an exergy analysis of thermochemical ethanol production from biomass is presented. This process combines a steam-blown indirect biomass gasification of woody feedstock, with a subsequent conversion of produced syngas into ethanol. The production process involves several process sections, including biomass drying and gasification, syngas cleaning, reforming, conditioning, and compression, ethanol synthesis, separation of synthesis products, and heat recovery. The process is simulated with a computer model using the flow-sheeting software Aspen Plus. The exergy analysis is performed for various ethanol catalysts, including Rh-based and MoS2-based (target) catalysts as well as for various gasification temperatures. The exergetic efficiency is 43.5% for Rh-based and 44.4% for MoS2-based (target) catalyst, when ethanol is considered as the only exergetic output. In case when by-products of ethanol synthesis are considered as the additional output the exergetic efficiency for Rh-based catalyst increases to 58.9% and 65.8% for MoS2-based (target) catalyst. The largest exergy losses occur in biomass gasifier and ethanol synthesis reactor. The exergetic efficiency for both ethanol catalysts increases with decreasing gasification temperature. -- Highlights: ► Thermochemical ethanol production from biomass via biomass gasification and ethanol synthesis has been modeled. ► Exergy analysis is performed for various process conditions and ethanol catalysts. ► Exergetic efficiencies biomass-to-ethanol range from 43.5% for Rh-based catalyst to 44.4% for MoS2-based catalyst. ► The largest exergy losses take place in the biomass gasification. ► Exergy losses in gasification can be reduced at lower gasification temperatures.
[en] This paper investigates a thermal system that absorbs waste heat from an internal combustion (IC) engine in order to raise the temperature of a working fluid to a saturated state using thermosyphonic flow, non-intrusive of the engine operations. The absorbed heat is rejected to an enclosed space, suitable for in-transit drying. The thermal system comprises a cross-flow heat exchanger connected to a radiator which preheats the working fluid from an insulated (storage) tank. The preheated fluid flows through a radiant heat absorber which absorbs radiant heat from the exhaust manifold. To ensure that the system efficiently performs, a temperature differential is maintained by the heated space while the fluid is cyclically delivered to the tank. The system’s operations are described using a novel flow cycle, and the results indicate a significant heat recovery potential. - Highlights: • This paper investigates a thermal system that absorbs waste heat from an internal combustion (IC) engine. • The absorbed heat is used to raise the temperature of a working fluid employing thermosyphonic flow. • The preheated fluid flows through a radiant heat absorber which absorbs radiant heat from the exhaust manifold. • To ensure that the system efficiently performs, a temperature differential is maintained by a heated space. • The system's operations are described using a novel flow cycle
[en] Energy intensive industries face strong challenges due to rising electricity costs and environmental limitations, therefore, developing methods for energy efficiency improvement is becoming an increasingly important issue. With an estimated 30% of industrial energy input being lost as waste heat, its recovery represents an interesting energy efficiency solution potentially providing for a zero-emission, low cost and abundant resource. This study presents an innovative technology for low-grade waste heat recovery based on advanced adsorbent materials, specifically applied to the drying process of alimentary pasta. Warm and humid air flow resulting from the drying process represents a high-enthalpy waste heat source that, if recovered, can significantly improve the process efficiency. This can be achieved by means of high specific surface materials among which Metal Organic Framework (MOF) compounds represent a promising solution. In this work, the industrial pasta production process has been studied and possible plant design options identified, including an innovative adsorption cycle to recover waste heat from the drying process. The thermodynamic processes involved in pasta drying plants have been quantitatively analysed to assess the energy savings that can be achieved by using adsorbent materials such as MOFs. Results point to thermal energy savings in the range 40–50%. - Highlights: • An innovative open adsorption cycle for industrial pasta drying plants is proposed. • Metal Organic Frameworks (MOFs) are identified as promising adsorbent materials. • Medium-grade waste heat is recovered from MOF regeneration and reused in the process. • Adsorption allows to recover latent enthalpy from humid drying air. • Energy savings of 40–50% compared to conventional processes are demonstrated.