Energy and exergy analyses of seawater desalination system integrated in a solar heat transformer

Among the numerous options to improve the energy efficiency of desalination plants stands out the absorption heat transformer. A heat transformer is a device, which can deliver heat at a higher temperature than the temperature of the fluid by which it is fed. Solar thermal energy can be used as heat input for single effect heat transformer while the high grade thermal energy delivered by the heat transformer can be used as heat source for water desalination.In this paper, an attempt has been made to study the combination: flat plate solar collectors, a single effect heat transformer and desalination system (distillation process) used to provide a beach house located in Skikda (East of Algeria; Latitude 36.52°N, Longitude 6.57°E) with drinking water. This system produces about 500 l of drinking water per day in July.Mathematical models of the solar flat plate collectors (FPC), absorption heat transformer (AHT) operating with the water/lithium bromide solution and the overall desalination system (WP) were developed to simulate the performance of this combination system. The energy and exergy analyses are carried out for each component of the system. All exergy losses that exist in this solar desalination system are calculated. Energy and exergy efficiencies are estimated.     

Energy,exergy and economic analyses on heat pump drying of lignite

Abstract

Evaporative drying of lignite is an energy intensive process. In this study, the heat pump is integrated with a lignite drying system to decrease the energy consumption rate of lignite drying. The performance of heat pump drying is energetically and exergetically evaluated with developed models. Results show that the power consumption rates to dehydrate 1?kg of water from raw lignite in the heat pump drying system without and with lignite preheater are 660.82 and 585.62?kJ (kg H₂O)^?1, respectively. Exergetic analysis indicates that most exergy is destructed in the condenser and the evaporator in the heat pump drying. The case of lignite-to-electricity process (i.e., a lignite-fired power plant integrated with heat pump drying) is studied to examine additional benefits of heat pump drying to the downstream industrial processes that consume dried lignite. Thermodynamic and economic models are developed. Net efficiency of the lignite-to-electricity process can be increased by 1.4 and 1.57 percentage points for heat pump drying without and with lignite preheater, respectively. Preliminary economic analysis shows that the integration of heat pump drying without and with lignite preheater can earn additional 1.42 and 1.73 million USD, respectively. The influences of drying system and heat pump parameters are also analyzed.     

CO_2汽提法尿素合成装置有效能分析软件设计

根据二氧化碳汽提合成尿素工艺流程，建立了能量分析的“黑箱模型”。在进行物料衡算时，采用Ｄｕｒｉｓｃｈ简化模型，用Ｐｒａｕｓｎｉｔｚ提出的Ｒ─Ｋ修正方程和Ｗｉｌｓｏｎ方程分别校正了汽液相的非理想性热力学行为。用ＢＡＳＩＣ语言编制了能平衡及有效能分析软件，得出了整个流程的能量平衡结果，并对其用能情况进行评价，提出改善用能的主要途径。     

Thermodynamic and economic analysis on a two-stage predrying lignite-fueled power plant

In this study, an improved configuration of lignite-fueled power plant integrated with a two-stage predrying system was proposed. The predrying system mainly consists of two fluidized-bed dryers and an additional feed water heater. Lignite is dried successively in the exhaust gas dryer and steam dryer. With boiler exhaust gas being the heat source of the first stage dryer, waste heat of a fraction of the boiler exhaust gas can be used. The exhaust gas of the second stage dryer was considered to be water vapor and its latent heat can be recovered by the additional feed water heater. The thermodynamic and economic analysis show that with the lignite drying degree being 0.1, 0.2, and 0.3?kg/kg, the power generation efficiency of the proposed power plant is 1.45, 2.12, and 2.81% higher than that of the conventional lignite power plant, respectively. Moreover, the annual net economic benefit will be 1.34, 2.03, and 1.60 M$/a during the lifetime of the drying system. The annual net economic benefit is not necessarily higher with higher power generation efficiency.     

The oxygen production step of a copper-chlorine thermochemical water decomposition cycle for hydrogen production: Energy and exergy analyses

In the copper-chlorine (Cu-Cl) thermochemical cycle water is decomposed into its constituents (oxygen and hydrogen) by a series of chemical reactions. The cycle involves five steps in which three thermally driven chemical reactions and one electrochemical reaction take place. Oxygen is produced during one of the main chemical reactions. In the present study, the O₂ production step is described with its operational and environmental conditions, and energy and exergy analyses are performed. The cycle is assumed driven using nuclear energy. Various parametric studies are carried out on energetic and exergetic aspects of the step, considering variable reaction and reference-environment temperatures. At a constant reference-environment temperature of 25 °C, the exergy destruction of the O₂ production step varies between 4500 and 23,000 kJ/kmol H₂ when the reaction temperature increases from 450 to 1000 °C. At a 500 °C reaction temperature and a 25 °C reference-environment temperature, the exergy destruction for this step is found to be 5300 kJ/kmol H₂. At a reaction temperature of 500 °C and a reference-environment temperature of 25 °C, the exergy efficiency of the step is determined to be 96% and to decrease with increasing reaction temperature and/or reference-environment temperature.     

An integrated computational fluid dynamics-process model of natural circulation steam generation in a coal-fired power plant

A semi-detailed 1D process model for steam generation in a natural circulation boiler (thermosyphon loop) is linked to a detailed 3D computational fluid dynamics (CFD) model of the coal-fired furnace. The CFD model has been validated against typical data from a 500 MW_e subcritical power plant. The heat flux distribution data from the CFD model are regressed into a function of height and used to drive the process model. The complex physics occurring in the furnace are coupled with the thermosyphon steam loop, resulting in circulation flows of around 4 times the feed flow. The steam side heat transfer coefficients are predicted in the process model and so the overall heat transfer coefficient for use in the CFD simulation can be re-evaluated as a function of height. The recalculated heat flux distribution is almost identical to the original, because the dominant resistance to heat flow is on the furnace side.     

Environmental assessment of natural radionuclides and heavy metals in waters discharged from a lignite-fired power plant

Gross alpha, gross beta and ²²⁶Ra activities as well as the concentration of trace metals (V, Cr, Mn, Ni, Cu, Zn, Mo and Pb) in the discharge waters of the major lignite-fired power plant in Greece were measured during the period October 2004 to May 2006. Gross alpha activity of particulate matter in the discharge waters was 0.75 ± 0.40 Bq g⁻¹ (0.3-1.2 Bq g⁻¹) while the beta activity was 1.54 ± 0.50 Bq g⁻¹ (1.2-1.7 Bq g⁻¹). The ranges of water gross alpha, beta and ²²⁶Ra activities were 0.062-0.268 Bq L⁻¹, 0.064-0.268 Bq L⁻¹ and 0.021-0.062 Bq L⁻¹, respectively. The mean concentration of ²²⁶Ra in the discharge waters was at least one order of magnitude higher than in natural water bodies. Soil samples were collected from fields irrigated with discharge waters and 29.2 ± 2.2 Bq kg⁻¹ of ²³⁸U, 1.2 ± 0.2 Bq kg⁻¹ of ²³⁵U, 26.8 ± 0.8 Bq kg⁻¹ of ²²⁶Ra, 36.8 ± 1.5 Bq kg⁻¹ of ²³²Th and 492.6 ± 25.8 Bq kg⁻¹ of ⁴⁰K were determined. The concentration values of dissolved metals in the discharge waters were higher than those usually observed in water streams near coal-fired power plants or rivers due to metal leaching from lignite or/and by-products. However, the leaching at high pH’s as those observed in the discharged waters does not raise the concentration of the studied metals to values higher than the criteria maximum concentrations and criterion continuous concentration (CCC) values of the US EPA water quality criteria. Statistical analysis was further applied to reveal the correlations between the different water components. Hierarchical cluster analysis revealed four different clusters: the first cluster was primarily composed of radioactivity and physicochemical parameters; the second cluster consisted of Cu, Ni and Zn, the third of Mn, Fe, Mo and Pb and the fourth of V and Cr. This clustering agrees with the associations suggested for elements in most coals or with the Goldschmidt classification.     

影响热电厂发电汽耗的因素分析

通过对运行数据的分析和计算,确定了影响发电汽耗的因素,提出了降低发电汽耗的建议。     

Energy analysis of a lignite predrying power generation system with an efficient waste heat recovery system

Lignite has been extensively used for electricity generation in many regions worldwide. However, its high water content has obviously negative effect on plant thermal efficiency. Performance of lignite-fired power plant can be improved by predrying the lignite before combustion. In addition, recovery of waste heat from the dryer and the power generation system will enhance the plant thermal efficiency further. In the present study, a new lignite predrying power generation system integrated with an efficient waste heat recovery system was proposed. Both dryer exhaust waste heat and steam turbine exhaust latent heat were recovered to heat boiler feed water. Energy analysis indicates that system performance is improved significantly. The plant thermal efficiency increases linearly with drying degree and then increases at a lower rate. The generation of unused dryer exhaust changes the variation tendency of system performance with drying degree.     

平煤集团坑口电厂汽轮机快冷装置的安装及运行效果

介绍了平煤集团坑口电厂YQL -II1 2 0型汽轮机快冷装置安装并投入运行的过程 ;运行结果表明 ,汽缸冷却时间及汽轮发电机本体检修时间缩短 ,发电时间增加 ,每年可多创收上百万元。     

Interactions of supported nickel and nickel oxide catalysts with methane and steam at high temperatures

The catalytic performance of cermets made of 10% nickel or nickel oxide supported on YSZ (yttria-stabilized zirconia) for chemical looping combustion (CLC) and steam reforming (SR) of methane at 700 °C is investigated. Steam reforming of methane over the reduced catalyst resulted in a syngas containing more than 70% hydrogen and about 15% carbon monoxide. Chemical looping combustion of methane with insufficient lattice oxygen could potentially lead to 40–65% hydrogen rich gas products. Prolonged induction period (e.g. 30–80 min) in reduction of nickel oxide by methane has been observed in the presence of steam. The span of induction period increases by increasing steam partial pressure. It is hypothesized that the delayed reduction of nickel oxide is related to the retarding effect of steam on autocatalytic reactions of methane and hydrogen with lattice oxygen of nickel oxide and the subsequent reforming reactions.     

Optimal design and operation of a steel plant integrated with a polygeneration system

A process integration approach has been applied to integrate a traditional steelmaking plant with a polygeneration system to increase energy efficiency and suppress carbon dioxide emissions from the system. Using short‐cut models and empirical equations for different units and available technologies for gas separation, methane gasification, and methanol synthesis, a mixed integer nonlinear model is applied to find the optimal design of the polygeneration plant and operational conditions of the system. Due to the complexity of the blast furnace (BF) operation, a surrogate model technique is chosen based on an existing BF model. The results show that from an economic perspective, the pressure swing adsorption process with gas‐phase methanol unit is preferred. The results demonstrate that integration of conventional steelmaking with a polygeneration system could decrease the specific emissions by more than 20 percent. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3659–3670, 2013     

Development of a new soft sensor method using independent component analysis and partial least squares

Soft sensors are used widely to estimate a process variable which is difficult to measure online. One of the crucial difficulties of soft sensors is that predictive accuracy drops due to changes of state of chemical plants. To cope with this problem, a regression model can be updated. However, if the model is updated with an abnormal sample, the predictive ability can deteriorate. We have applied the independent component analysis (ICA) method to the soft sensor to increase fault detection ability. Then, we have tried to increase the predictive accuracy. By using the ICA‐based fault detection and classification model, the objective variable can be predicted, updating the PLS model appropriately. We analyzed real industrial data as the application of the proposed method. The proposed method achieved higher predictive accuracy than the traditional one. Furthermore, the nonsteady state could be detected as abnormal correctly by the ICA model. © 2008 American Institute of Chemical Engineers AIChE J, 2009     

热电厂泵汽蚀原因分析与防止措施

锅炉给水泵的正常运行是确保锅炉安全的第一步。而泵的汽蚀在生产运行中时有发生,不仅对泵本身危害极大,对整个热电厂安全运行也至关重要。本文将对给水泵汽蚀的原因进行分析,指出在给水泵进口压力最低点处,给水压力大于水温所对应的饱和压力,泵就不会产生汽蚀,并对防止给水泵汽蚀进行简要的说明。     

煤矸石电厂节能环保存在的问题及技术改造措施

分析了煤矸石电厂节能和环保的现状 ,指出了煤矸石电厂在除尘、脱硫、锅炉热效率和余热资源利用等方面存在的问题。分析了这些问题产生的原因及危害。结合先进的环保节能技术 ,提出了技术改造措施     

Synthesis of heat exchanger networks at subambient conditions with compression and expansion of process streams

This article presents an optimization formulation for the synthesis of heat exchanger networks where pressure levels of process streams can be adjusted to improve heat integration. Especially important at subambient conditions, this allows for the interconversion of work, temperature, and pressure‐based exergy and leads to reduced usage of expensive cold utility. Furthermore, stream temperatures and pressures are tuned for close tracking of the composite curves yielding increased exergy efficiency. The formulation is showcased on a simple example and applied to a case study drawn from the design of an offshore natural gas liquefaction process. Aided by the optimization, it is demonstrated how the process can extract exergy from liquid nitrogen and carbon dioxide streams to support the liquefaction of a natural gas stream without additional utilities. This process is part of a liquefied energy chain, which, supplies natural gas for power generation while facilitating carbon dioxide sequestration. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Polygeneration of hydrogen and power based on coal gasification integrated with a dual chemical looping process: Thermodynamic investigation

This paper assesses, from a thermodynamic perspective, the conversion of coal to power and hydrogen through gasification simultaneously with a dual chemical looping processes, namely chemical looping air separation (CLAS) and water–gas shift with calcium looping CO₂ absorption (WGS-CaL). CLAS offers an advantage over other mature technologies in that it can significantly reduce its capital cost. WGS-CaL is an efficient method for hydrogen production and CO₂ capture. The three major factors, oxygen to coal (O/C), steam to coal (S/C) and CaO to coal (Ca/C) were analyzed. Moreover, the comparisons of this suggested process and the traditional processes including integrated gasification combined cycle (IGCC), integrated gasification combined cycle with carbon capture and storage (IGCC-CCS) and integrated gasification combined cycle with calcium-based chemical looping (IGCC-CaL) were discussed. And, the exergy destruction analysis of this suggested process has also been calculated.     

Energy transfer and photoluminescent analysis of a novel color-tunable Ba2Y1-xV3O11:xSm3+ nanophosphor for single-phased phosphor-converted white LEDs

Metal nitrates are used to synthesize a series of novel Ba₂Y_1-xV₃O₁₁:xSm³⁺ nanophosphors via urea-assisted solution combustion route. X-ray diffraction (XRD), diffuse reflectance (DR), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy were employed to analyse the structure, morphology, photoluminescent behaviour and energy transfer mechanism. Rietveld analysis over Ba₂Y_0.98Sm_0.02V₃O₁₁ showed that Y³⁺ ions can be well-replaced by trivalent samarium ions without resulting any major alteration in the crystal structure of host lattice. Furthermore, the lattice parameters were determined for both the host as well as the doped composition. The Scherrer equation yielded an average particle size of 44?nm, which in turn was further confirmed by TEM micrographs. The optical band-gap of the host (3.92?eV) was calculated from the diffuse reflectance spectra. Moreover, the photoluminescence spectral studies showed that under near ultra-violet (NUV) excitation of 340?nm, our nanophosphor powder exhibits the characteristic emission peaks of trivalent samarium along with the emission of VO₄^3? (501?nm) group. The excitation energy transfer from vanadate group to Sm³⁺ produced a systematic color tunablity in white region itself. The optimum Sm³⁺ concentration for better luminescence was found to be 2?mol%. The critical distance for energy transfer was calculated to be 29.02?Å, which in turn assisted to shortlist the mechanism responsible for luminescence-quenching (dipole-dipole) arising from the over-doping of the activator. The photoluminescence decay curves revealed the decay kinetics of ⁴G_5/2 electronic state. Finally, the calculation of CIE color coordinates from emission spectra in MATLAB program unveiled a somewhat white-light emitter which may find potential applications in phosphor-converted white light emitting diodes (PC-WLED) under near-ultraviolet (NUV) excitation.     

16万 t／a尿素装置节能技术改造

从高压合成系统、中压系统、蒸发系统、DCS系统、主要动力设备等5个方面分析了16万t/a尿素装置节能技术改造的原因,介绍了尿素装置的主要节能技术改造措施。结果表明：改造后的生产运行情况与原设计及国内相同规模的企业相比,吨尿素的氨耗降低了13 kg,电耗降低了34 kW,优级品率上升,各项指标达到了预期目标。