Optimum design of multi-stage isotope separation process by exergy analysis

A separation process of carbon isotopes, ¹²C (98.9%), ¹³C (1.1%) and ¹⁴C (trace), by the chemical exchange reactions between CO₂ and amine carbamate was designed by the exergy analysis technique and the applicability of the exergy analysis to the design of isotope-separation process is discussed. The exergy loss (EXL) for the single-column process was increased exponentially toward the product end, because of the mixing of isotopes between gas and liquid flows. By the application of ideal cascade without the mixing of ¹⁴C and ¹²C, the EXL value was reduced to 10% of that for the single-column process. The ideal cascade gives the minimum volume of separation column reasonably, however, is impracticable as an industrial process, because of the complexity of process configuration and operation. From the viewpoint of practical use, a squared-off cascade with three columns, whose diameters were reduced toward the product end, was designed under the condition that the difference of EXL between the squared-off cascade and the ideal one was minimized. The EXL value of this process was evaluated as about 12% of that of single-column process and the separation performance was similar to that for the ideal cascade. These results suggest that the process design method based on exergy analysis is very useful as a tool to design an optimum squared-off cascade.     

Optimum operating conditions for a laser uranium enrichment plant

Operating conditions of the laser uranium enrichment plant to obtain cheaper enriched uranium are optimised by using the standard optimisation procedure. A simple kinetic model is given to obtain the ion production rate as a function of the laser energy density, ultraviolet light energy density, atomic density and depth and height of the reaction region. The unit cost of enriched uranium is chosen as a value function instead of the unit cost of the separative work. The construction cost is expressed by means of an exponential function to take the scale merit into account.

Two numerical results are given. In case 1, the laser power and efficiency are subject to the restraints determined by the present technical levels and in case 2, they are free. The unit cost of the enriched uranium is higher than those of the gaseous diffusion and gas centrifuge methods by a factor of 2 11. Results indicate that laser uranium enrichment is probably competitive with the other uranium enrichment methods, provided that the laser efficiency is improved by up to 1% and the laser lifetime is extended several times.     

Hydrogen enrichment and separation from synthesis gas by the use of a membrane reactor

One of the objectives of the CHRISGAS project was to study innovative gas separation and gas upgrading systems that have not been developed sufficiently yet to be tested at a demonstration scale within the time frame of the project, but which show some attractive merits and features for further development. In this framework CIEMAT studied, at bench scale, hydrogen enrichment and separation from syngas by the use of membranes and membrane catalytic reactors.In this paper results about hydrogen separation from synthesis gas by means of selective membranes are presented. Studies dealt with the evaluation of permeation and selectivity to hydrogen of prepared and pre-commercial Pd-based membranes. Whereas prepared membranes turned out to be non-selective, due to discontinuities of the palladium layer, studies conducted with the pre-commercial membrane showed that by means of a membrane reactor it is possible to completely separate hydrogen from the other gas components and produce pure hydrogen as a permeate stream, even in the case of complex reaction system (H₂/CO/CO₂/H₂O) under WGS conditions gas mixtures.The advantages of using a water-gas shift membrane reactor (MR) over a traditional fixed bed reactor (TR) have also been studied. The experimental device included the pre-commercial Pd-based membrane and a commercial high temperature Fe–Cr-based, WGS catalyst, which was packed in the annulus between the membrane and the reactor outer shell. Results show that in the MR concept, removal of H₂ from the reaction side has a positive effect on WGS reaction, reaching higher CO conversion than in a traditional packed bed reactor at a given temperature. On increasing pressure on the reaction side permeation is enhanced and hence carbon monoxide conversion increases.     

Advances in materials process and separation mechanism of the membrane towards hydrogen separation

The increased demand for a reliable and sustainable renewable energy source encourages the hydrogen-based economy. For the same, membrane separation approaches were reviewed as an advantageous process over contemporary techniques due to the environmentally friendly nature, economically viable pathway, and easily adaptable technology. A comprehensive assessment for the advancements in the type of membranes namely, polymeric and mixed matrix membranes (MMMs) has been delineated in the present article with the fabrication methodologies and associated mechanism for hydrogen separation. In hydrogen separation mechanism of the membrane, depends on the morphology of the membrane (dense or porous). The existence of pores in membranes offers various gas transport mechanisms such as Knudsen diffusion, surface diffusion, capillary condensation, molecular sieving mechanisms were observed, depending on the pore size of membranes and in dense membrane gas transport through the solution-diffusion mechanism. In polymer membrane, hydrogen separation occurs mainly due to solubility and diffusivity of gases. The hydrogen separation mechanism in MMMs is very complex due to the combining effect of polymer and inorganic fillers. So, the gas separation performance of MMMs was evaluated using the modified Maxwell model. Moreover, adequate polymeric material and inorganic fillers have been summarised for MMMs synthesis and highlighting the mechanism for gas transport phenomena in the process. Several types of materials implemented with polymeric matrix examined in the literature, amongst these functionally aligned CNTs with Pd-nanoparticles dispersed in polymer matrix were observed to reveal the best outcome for the hydrogen separation membrane due to the uniform distribution of inorganic material in the matrix. Henceforth, the agglomeration gets reduced promoting hydrogen separation.     

Energy and exergy analyses of OMW solar drying process

The energy and exergy analyses of the drying process of olive mill wastewater (OMW) using an indirect type natural convection solar dryer are presented. Olive mill wastewater gets sufficiently dried at temperatures between 34 °C and 52 °C. During the experimental process, air relative humidity did not exceed 58%, and solar radiation ranged from 227 W/m² to 825 W/m². Drying air mass flow was maintained within the interval 0.036–0.042 kg/s. Under these experimental conditions, 2 days were needed to reduce the moisture content to approximately one-third of the original value, in particular from 3.153 g_water/g_{dry matter} down to 1.000 g_water/g_{dry matter}.Using the first law of thermodynamics, energy analysis was carried out to estimate the amounts of energy gained from solar air heater and the ratio of energy utilization of the drying chamber. Also, applying the second law, exergy analysis was developed to determine the type and magnitude of exergy losses during the solar drying process. It was found that exergy losses took place mainly during the second day, when the available energy was less used. The exergy losses varied from 0 kJ/kg to 0.125 kJ/kg for the first day, and between 0 kJ/kg and 0.168 kJ/kg for the second. The exergetic efficiencies of the drying chamber decreased as inlet temperature was increased, provided that exergy losses became more significant. In particular, they ranged from 53.24% to 100% during the first day, and from 34.40% to 100% during the second.     

Dynamic optimization of cryogenic distillation operation for hydrogen isotope separation in fusion power plant

Stable operation of a hydrogen isotope separation system is one of the most important issues in the sustainable operation of fusion power plants. Owing to the present limitation in retention time of fusion reaction, fusion reactors are run in repeated batch operations, causing large fluctuating flows in the system. Hence, to reliably produce required products, counteractive operational strategies must be devised. To this end, we perform dynamic optimization in this paper to derive an optimal control policy that can minimize the tritium inventory and satisfy the product quality specifications. In addition, a rigorous dynamic model for packed columns is developed to simulate realistic behaviors of cryogenic distillation. We demonstrate that the optimization results yield vital operational strategies, such as operation mode switching, without any expertise provided.     

Storage and separation of hydrogen with the metal steam process

The chemical reaction of metals and metal oxides with steam at elevated temperatures produces pure hydrogen. Therefore certain metals can be used as gas purification and hydrogen storage material. Storage and transport of metals are basic operations, free from safety issues and hydrogen is produced on demand whenever it is needed by passing steam over the solid reactant.     

A novel magnetic separation oxygen-enriched method and the influence of temperature and magnetic field on enrichment

A novel oxygen-enriched method is presented.Using two opposite magnetic poles of two magnets with certaindistance forms a magnetic space having a field intensity gradient near its borders.When air injected into themagnetic space outflows from the magnetic space via its borders,oxygen molecules in air will experience the in-terception effect of the gradient magnetic field,but nitrogen molecules will outflow without hindrance.Therebythe continuous oxygen enrichment is realized.The results show that the maximum increment of oxygen concen-tration reaches 0.49% at 298 K when the maximum product of magnetic flux density and field intensity gradientis 563T~2/m.The enrichment level is significantly influenced by the gas temperature and the magnetic field.Themaximum increment of oxygen concentration drops to 0.16% when the gas temperature rises to 343 K,and dropsto 0.09% when the maximum product of magnetic flux density and gradient is reduced to 101 T~2/m from 563T~2/m.     

Process Study and Exergy Analysis of a Novel Air Separation Process Cooled by LNG Cold Energy简

In order to resolve the problems of the current air separation process such as the complex process, cumbersome operation and high operating costs, a novel air separation process cooled by LNG cold energy is proposed in this paper, which is based on high-efficiency heat exchanger network and chemical packing separation technology. The operating temperature range of LNG cold energy is widened from 133K-203K to 113K-283K by highefficiency heat exchanger network and air separation pressure is declined from 0.5MPa to about 0.35MPa due to packing separation technology, thereby greatly improve the energy efficiency. Both the traditional and novel air separation processes are simulated with air handling capacity of 20t·h 1. Comparing with the traditional process, the LNG consumption is reduced by 44.2%, power consumption decrease is 211.5 kWh per hour, which means the annual benefit will be up to 1.218 million CNY. And the exergy efficiency is also improved by 42.5%.     

Idea,process and analyses of hydrogen production from atmospheric pollutant

With the considerable amounts of Sulfur dioxide (SO₂) discharged from the sulfuric acid production unit of the Tunisian Chemical Group (TCG), questions have arisen regarding the treatment of this very dangerous atmospheric pollutant which is crucial. Here, we used SO₂ to produce hydrogen. Sulfur dioxide was fed into a PEM electrolysis, the dissolved SO₂ was oxidized at the anode to produce sulfuric acid, whereas hydrogen was produced at the cathode. By measurements on site complemented by mass balances, we determined the quantities of sulfur dioxide regenerated in the atmosphere. We focused on the startup stage which is the most polluting as the amount of sulfur dioxide generated during this step is enormous. By simulation with Aspen Plus we found that two processes were possible to realize this idea; one with absorption and the other with compression. The same software was used to determine the operating parameters that can run the processes, taking into account the permissible level of SO₂ released into the atmosphere and the production of the highest amount of hydrogen. After a comparative study between the two processes, we selected the process with absorption. An exergetic study was conducted. The exergy loss of the absorption process was equivalent to 563 kJ/mol of H₂. This amount is low compared to other methods. The results show that the new process has the highest exergy efficiency (η_Ex = 90%). This was achieved through Life Cycle Analyses (LCA) which showed that the process with absorption had the highest impact on marine aquatic Eco-toxicity, whereas other impact categories were relatively insignificant.     

Effects of various factors on the hydrogen isotope separation efficiency of a novel hydrophobic platinum-polytetrafluoroethylene catalyst

The application of platinum supported on polytetrafluoroethylene (Pt/PTFE) as a composite catalyst for the separation of hydrogen isotopes holds much promise but warrants further refinement for improved performance. The objective of the present study was to examine the performance of a new hydrophobic Pt/PTFE catalyst during hydrogen-water exchange-based deuterium separation. The influence of diverse factors such as flow rate, column height, temperature, the volume ratio of filler to catalyst, and flow mode (co-current or counter-current), and so on, on catalytic performance was investigated. The deuterium conversion rate from co-current exchange was superior to that from counter-current exchange. Decreasing the hydrogen flow rate, increasing the feed water flow rate, and decreasing the molar flow ratio of hydrogen to water improved the deuterium conversion rate. In terms of layered filling of the catalyst column, adding more hydrophilic fillers improved the deuterium conversion rate. The characterization results highlight the high catalytic activity of the Pt/PTFE catalyst for hydrogen-water exchange, as well as its high stability in water.     

Novel process for preparation of metal-polymer composite membranes for hydrogen separation

In the present work, a new preparation method for metal-polymer composite materials for hydrogen separation which consist of hydride-forming intermetallic compound LaNi₅ and polyethylene was developed. According to this technique, the mechanical activation of the initial powder mixtures was employed to provide good interface between the phases. A series of composite membranes with various filler concentrations was synthesized and characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. The gas transport properties of the obtained materials in relation to H₂, O₂, N₂, CO₂ and CH₄ were tested. The results indicate that the addition of the hydride-forming intermetallic compound to the barrier polymer leads to significantly improved selectivity with respect to hydrogen. The proposed method can be considered as a promising approach to producing of high performance composite membranes for hydrogen separation.     

Elevated temperature hydrogen/carbon dioxide separation process simulation by integrating elementary reaction model of hydrotalcite adsorbent

An elementary reaction kinetics model related with Elovich equation is developed to predict the CO₂ adsorption capacity and adsorption kinetic behavior for potassium promoted hydrotalcite-like compound (K-promoted HTlcs). The elementary reaction kinetics model is comprehensively validated by experimental data from both atmosphere pressure thermo gravimetric analysis (TGA) and a high pressure adsorption apparatus. The elevated temperature pressure swing adsorption s(PSA) system modeling framework is then developed on the gPROMS commercial simulation platform by further considering comprehensive coupling effects from mass, momentum and energy transport processes, integrated with dynamic boundary condition and realistic operating procedures. The effects of adsorption time, residence time, purge to feed ratio, working pressure and adsorbents capacity on PSA cycling gas separation performance are studied with the proposed modeling framework based on a four-bed two-pressure-equalization PSA process.     

Application of residual correction method to laser heating process

In this study, the residual correction method is employed to predict the temperature distribution during laser heating process. The energy transfer induced by laser irradiation in the solid is described by Fourier’s law of conduction with an energy source modeled by Beer’s law. The approximate solution of temperature field is obtained by residual correction. Using the residual correction method, the precise average value of upper and lower approximate solutions is obtained and the error range between the analytical solution and the numerical solution can be analyzed. The results reveal that this method is an effective numerical method with satisfactory accuracy.     

New technologies for solar energy silicon: Cost analysis of BCL process

New technologies for producing polysilicon are being developed to provide lower cost material for solar cells which convert sunlight into electricity. This article presents results for the BCL Process (Battelle Columbus Laboratories), which produces the solar-cell silicon by reduction of silicon tetrachloride with zinc vapor. The UCC Silane Process (Union Carbide Corporation) was reported in a previous article.Cost, sensitivity and profitability analysis results are presented based on a preliminary process design of a plant to produce 1000 metric tons/year of silicon by the BCL Process. Profitability analysis indicates a sales price of 12.1–19.4$/kg of silicon (1980 dollars) at a 0–25 per cent DCF rate of return on investment after taxes. These results indicate good potential for meeting the goal of providing lower cost material for silicon solar cells.     

Energy and exergy analyses in drying process of porous media using hot air

In this paper the energy and exergy analyses in drying process of porous media using hot air was investigated. Drying experiments were conducted to find the effects of particle size and thermodynamics conditions on energy and exergy profiles. An energy analyses was performed to estimate the energy utilization by applying the first law of thermodynamics. An exergy analyses was performed to determine the exergy inlet, exergy outlet, exergy losses and efficiency during the drying process by applying the second law of thermodynamics. The results show that energy utilization ratio (EUR) and exergy efficiency depend on the particle size as well as hydrodynamic properties. Furthermore, the results of energy and exergy presented here can be applied to other porous drying processes which concern effect of porosity as well as grain size.     

Energy and exergy analyses in convective drying process of multi-layered porous packed bed

This paper is concerned with the investigation of the energy and exergy analyses in convective drying process of multi-layered porous media. The drying experiments were conducted to find the effects of multi-layered porous particle size and thermodynamics conditions on energy and exergy profiles. An energy analysis was performed to estimate the energy utilization by applying the first law of thermodynamics. An exergy analysis was performed to determine the exergy inlet, exergy outlet, exergy losses during the drying process by applying the second law of thermodynamics. The results show that the energy utilization ratio (EUR) and the exergy efficiency depend on the particle size as well as the hydrodynamic properties and the layered structure, by considering the interference between capillary flow and vapor diffusion in the multi-layered packed bed.     

New technologies for solar energy silicon—Cost analysis of dichlorosilane process

New technologies for producing polysilicon are being developed to provide lower cost material for solar cells which convert sunlight into electricity. This article presents results for a process to produce dichlorosilane (DCS) as a silicon source material for solar energy silicon. Major benefits of dichlorosilane include faster chemical vapor deposition of silicon and higher chemical equilibrium yield for silicon production. Hemlock Semiconductor Corporation has recently demonstrated that under comparable conditions and for rods up tp 42 mm dia., deposition rates and conversions for dichlorosilane are approximately twice those for trichlorosilane. Cost, sensitivity and profitability analysis results are presented based on a preliminary process design of a plant to produce dichlorosilane by the DCS process. Profitability analysis indicates a sales price of $1.29–$1.47/kg of dichlorosilane (1980 dollars) at a 0–15 per cent discounted cash flow rate of return after taxes. These results indicate good potential for dichlorosilane as a silicon source material to provide lower cost material for solar cells.     

An electrical resistance tomography technique for the monitoring of a radioactive waste separation process

An electrical resistance tomography (ERT) technique is suggested to monitor a radioactive waste separation process. This paper presents analytical results for a simple model problem to estimate the boundary between two distinct waste streams in a rotating separator as well as the conductivity value of each stream. To solve this highly non-linear identification problem, the particle swarm optimization (PSO) algorithm is successfully introduced. The results show the feasibility of the ERT for monitoring the separation process.