scholarly journals USING EXERGY LOSS PROFILES AND ENTHALPY-TEMPERATURE PROFILES FOR THE EVALUATION OF THERMODYNAMIC EFFICIENCY IN DISTILLATION COLUMNS

2005 ◽  
Vol 4 (1) ◽  
pp. 76 ◽  
Author(s):  
S. H. B. Faria ◽  
R. J. Zemp
Keyword(s):  
Energy Balance ◽  
Distillation Column ◽  
Enthalpy Of Solution ◽  
Exergy Loss ◽  
Thermodynamic Efficiency ◽  
Consistency Test ◽  
Distillation Columns ◽  
Water Distillation ◽  
Ideal Solutions ◽  
Thermodynamic Excess

In this work the temperature-enthalpy profile and the exergy loss profile are used together to improve thermodynamic efficiency of distillation columns, by identifying possible benefits of using side exchangers. The method proposed is to compute the exergy loss profile and to analyse the distribution of the losses across the column stages. The present work aims at applying the stage-by-stage exergy analysis to the distillation of non-ideal mixtures, e.g. methanol/water. For these systems the use of thermodynamic excess properties is required: Gibbs free energy for phase equilibrium and enthalpy of solution for energy balance. Initial studies showed that the enthalpy of solution has a small effect on the overall energy balance of the distillation column, but a significant impact on the exergy loss profiles. Some profiles even showed a violation of the second law of thermodynamics, with entropy being destroyed on some stages, clearly indicating that a wrong approach to exergy calculation was being used.A model for exergy calculations of non-ideal solutions is presented. The exergy values so computed are then checked by a consistency test, using the reversible column profile. Finally, the exergy procedures are used to study a typical methanol/water distillation columns, where the exergy profiles are used to identify scope for intermediate heat exchange.

scholarly journals USING EXERGY LOSS PROFILES AND ENTHALPY-TEMPERATURE PROFILES FOR THE EVALUATION OF THERMODYNAMIC EFFICIENCY IN DISTILLATION COLUMNS

2005 ◽  
Vol 4 (1) ◽  
Author(s):  
S. H. B. Faria ◽  
R. J. Zemp
Keyword(s):  
Energy Balance ◽  
Enthalpy Of Solution ◽  
Second Law Of Thermodynamics ◽  
Exergy Loss ◽  
Excess Properties ◽  
Thermodynamic Efficiency ◽  
Consistency Test ◽  
Distillation Columns ◽  
Water Distillation ◽  
Ideal Solutions

In this work the temperature-enthalpy profile and the exergy loss profile are used together to improve thermodynamic efficiency of distillation columns, by identifying possible benefits of using side exchangers. The method proposed is to compute the exergy loss profile and to analyse the distribution of the losses across the column stages. The present work aims at applying the stage-by-stage exergy analysis to the distillation of non-ideal mixtures, e.g. methanol/water. For these systems the use of thermodynamic excess properties is required: Gibbs free energy for phase equilibrium and enthalpy of solution for energy balance. Initial studies showed that the enthalpy of solution has a small effect on the overall energy balance of the distillation column, but a significant impact on the exergy loss profiles. Some profiles even showed a violation of the second law of thermodynamics, with entropy being destroyed on some stages, clearly indicating that a wrong approach to exergy calculation was being used.A model for exergy calculations of non-ideal solutions is presented. The exergy values so computed are then checked by a consistency test, using the reversible column profile. Finally, the exergy procedures are used to study a typical methanol/water distillation columns, where the exergy profiles are used to identify scope for intermediate heat exchange.

scholarly journals Integrated Multiscale Latent Variable Regression and Application to Distillation Columns

2013 ◽  
Vol 2013 ◽  
pp. 1-17 ◽  
Author(s):  
Muddu Madakyaru ◽  
Mohamed N. Nounou ◽  
Hazem N. Nounou
Keyword(s):  
Feature Extraction ◽  
Latent Variable ◽  
Prediction Accuracy ◽  
Distillation Column ◽  
Selection Criterion ◽  
Process Data ◽  
Distillation Columns ◽  
Latent Variable Regression ◽  
Multiscale Filtering ◽  
Modeling Algorithm

Proper control of distillation columns requires estimating some key variables that are challenging to measure online (such as compositions), which are usually estimated using inferential models. Commonly used inferential models include latent variable regression (LVR) techniques, such as principal component regression (PCR), partial least squares (PLS), and regularized canonical correlation analysis (RCCA). Unfortunately, measured practical data are usually contaminated with errors, which degrade the prediction abilities of inferential models. Therefore, noisy measurements need to be filtered to enhance the prediction accuracy of these models. Multiscale filtering has been shown to be a powerful feature extraction tool. In this work, the advantages of multiscale filtering are utilized to enhance the prediction accuracy of LVR models by developing an integrated multiscale LVR (IMSLVR) modeling algorithm that integrates modeling and feature extraction. The idea behind the IMSLVR modeling algorithm is to filter the process data at different decomposition levels, model the filtered data from each level, and then select the LVR model that optimizes a model selection criterion. The performance of the developed IMSLVR algorithm is illustrated using three examples, one using synthetic data, one using simulated distillation column data, and one using experimental packed bed distillation column data. All examples clearly demonstrate the effectiveness of the IMSLVR algorithm over the conventional methods.

Why is the thermodynamic efficiency of carbon uptake by terrestrial vegetation so low despite its optimal functioning?

2021 ◽  
Author(s):  
Axel Kleidon
Keyword(s):  
Energy Balance ◽  
Gas Exchange ◽  
Surface Energy ◽  
Surface Energy Balance ◽  
Thermodynamic Efficiency ◽  
Carbon Uptake ◽  
Terrestrial Vegetation ◽  
Strong Constraint ◽  
Vegetation Activity ◽  
Evaporative Flux

<p>Optimality concepts have been used to successfully infer ecophysiological properties and functioning of terrestrial vegetation from the leaf- to ecosystem scale.<span>  </span>In many cases this implies, roughly speaking, that vegetation is as productive as it can possibly be.<span>  </span>However, when vegetation activity is looked at in terms of its energy conversion from the radiant energy in sunlight to the chemical energy stored in carbohydrates, it has a very low conversion efficiency of about 1% or less.<span>  </span>This is much less than what would be expected from thermodynamics applied to the photochemical conversion process.<span>  </span>How do these two seemingly contradictory views fit together?<span>  </span>Here I suggest that thermally-driven gas exchange between vegetation canopies and the lower atmosphere represents the major bottleneck, explaining the low thermodynamic efficiency of carbon uptake and setting a strong constraint to any form of vegetation optimality.<span>  </span>Gas exchange intimately links the carbon taken up by vegetation from the atmosphere for photosynthesis during the day with the water loss by evaporation, with evaporation being a major component of the surface energy balance.<span>  </span>The magnitude of this exchange is, however, not externally set by atmospheric conditions, but predominantly determined by the local heating of the surface, creating buoyancy and thus this exchange.<span>  </span>Thermodynamics sets a strong constraint on the magnitude of this locally generated exchange by the maximum power that can be derived from the absorption of solar radiation to generate the associated kinetic energy.<span>  </span>I use global, observation-based radiation and precipitation datasets and this thermodynamic constraint to quantify surface energy balance partitioning over land as well as the associated rate of evaporation at the climatological scale.<span>  </span>I then use a typical value for the water use efficiency observed in vegetation to convert this evaporative flux to a carbon uptake flux by vegetation and show that the derived fluxes of water and carbon compare very well to observation-based estimates across regions.<span>  </span>This means that the low thermodynamic efficiency of terrestrial carbon uptake should not be attributed to an inefficient use of light, but rather to the low efficiency by which radiative heating generates gas exchange that is needed to supply canopies with carbon dioxide and that maintains evaporation.<span>  </span>This interpretation has broad implications for the role of vegetation in the Earth system.<span>  </span>It implies that physically-driven gas exchange with the atmosphere - and not energy directly - is a major constraint on vegetation activity, shaping its geographic patterns.<span>  </span>Given this constraint, vegetation may then maximize its carbon uptake for the given evaporative flux, but it has comparatively little control over evaporation and surface energy balance partitioning if sufficient water is available.<span>  </span>Applied to global warming, this then implies that the response of evaporation is mostly determined by changes in the radiative forcing and water availability, and not by stomatal responses.</p>

scholarly journals Separative Analyses of Packed Water Distillation Column with Channeling Stage Model

2000 ◽  
Vol 37 (3) ◽  
pp. 273-280 ◽  
Author(s):  
Takahiko SUGIYAMA ◽  
Youichi ENOKIDA ◽  
Ichiro YAMAMOTO
Keyword(s):  
Distillation Column ◽  
Stage Model ◽  
Water Distillation

Reducing Energy Consumption in Propylene-Propane Separation with Heat Coupled Distillation

2011 ◽  
Vol 225-226 ◽  
pp. 500-503
Author(s):  
Lan Yi Sun ◽  
Jun Li ◽  
Xue Nuan Liu ◽  
Qing Song Li
Keyword(s):  
Energy Consumption ◽  
Distillation Column ◽  
Pressure Ratio ◽  
Internal Heat ◽  
Thermodynamic Efficiency ◽  
Total Annual Cost ◽  
Heat Integration ◽  
Internal Heat Integration ◽  
Vapor Recompression ◽  
Reducing Energy

The heat coupled distillation column which applies the principle of internal heat integration between the rectifying section and the stripping section of a distillation column by increasing the temperature of the rectifying section with a compressor attracts extensive attention worldwide for its high thermodynamic efficiency. In this study, the economic features of a heat coupled distillation column (HCDC) are investigated and compared to a conventional column and a commercial column with vapor recompression system (VRC) for the separation of propylene-propane mixture. The economic analysis indicates that HCDC has 10 – 20 % total annual cost (TAC) saving associated with VRC, which appeared to be strongly sensitive to the pressure ratio.

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