Hydrogen production by sorption enhanced steam reforming of propane: A thermodynamic investigation

Thermodynamic features of hydrogen production by sorption enhanced steam reforming (SESR) of propane have been studied with the method of Gibbs free energy minimization and contrasted with propane steam reforming (SR). The effects of pressure (1-5 atm), temperature (700-1100 K) and water to propane ratio (WPR, 1-18) on equilibrium compositions and carbon formation are investigated. The results suggest that atmospheric pressure and a WPR of 12 are suitable for hydrogen production from both SR and SESR of propane. High WPR is favourable to inhibit carbon formation. The minimum WPR required to eliminate carbon production is 6 in both SR and SESR. The most favourable temperature for propane SR is approximately 950 K at which 1 mol of propane has the capacity to produce 9.1 mol of hydrogen. The optimum temperature for SESR is approximately 825 K, which is over 100 K lower than that for SR. Other key benefits include enhanced hydrogen production of nearly 10 mol (stoichiometric value) of hydrogen per mole of propane at 700 K, increased hydrogen purity (99% compared with 74% in SR) and no CO₂ or CO production with the only impurity being CH₄, all indicating a great potential of SESR of propane for hydrogen production.     

Optimization of two bio-oil steam reforming processes for hydrogen production based on thermodynamic analysis

Thermodynamics of hydrogen production from conventional steam reforming (C-SR) and sorption-enhanced steam reforming (SE-SR) of bio-oil was performed under different conditions including reforming temperature, S/C ratio (the mole ratio of steam to carbon in the bio-oil), operating pressure and CaO/C ratio (the mole ratio of CaO to carbon in the bio-oil). Increasing temperature and S/C ratio, and decreasing the operating pressure were favorable to improve the hydrogen yield. Compared to C-SR, SE-SR had the significant advantage of higher hydrogen yield at lower desirable temperature, and showed a significant suppression for carbon formation. However excess CaO (CaO/C > 1) almost had no additional contribution to hydrogen production. Aimed to achieve the maximum utilization of bio-oil with as little energy consumption as possible, the influences of temperature and S/C ratio on the reforming performance (energy requirements and bio-oil consumption per unit volume of hydrogen produced, Q_D/H2 (kJ/Nm³) and Y_Bio-oil/H2 (kg/Nm³)) were comprehensively evaluated using matrix analysis while ensuring the highest hydrogen yield as possible. The optimal operating parameters were confirmed at 650 °C, S/C = 2 for C-SR; and 550 °C, S/C = 2 for SE-SR. Under their respective optimal conditions, the Y_Bio-oil/H2 of SE-SR is significant decreased, by 18.50% compared to that of C-SR, although the Q_D/H2 was slightly increased, just by 7.55%.     

Hydrogen production by glycerol steam reforming with in situ hydrogen separation: A thermodynamic investigation

Thermodynamic features of hydrogen production by glycerol steam reforming with in situ hydrogen extraction have been studied with the method of Gibbs free energy minimization. The effects of pressure (1–5 atm), temperature (600–1000 K), water to glycerol ratio (WGR, 3–12) and fraction of H₂ removal (f, 0–1) on the reforming reactions and carbon formation were investigated. The results suggest separation of hydrogen in situ can substantially enhance hydrogen production from glycerol steam reforming, as 7 mol (stoichiometric value) of hydrogen can be obtained even at 600 K due to the hydrogen extraction. It is demonstrated that atmospheric pressure and a WGR of 9 are suitable for hydrogen production and the optimum temperature for glycerol steam reforming with in situ hydrogen removal is between 825 and 875 K, 100 K lower than that achieved typically without hydrogen separation. Furthermore, the detrimental influence of increasing pressure in terms of hydrogen production becomes marginal above 800 K with a high fraction of H₂ removal (i.e., f = 0.99). High temperature and WGR are favorable to inhibit carbon production.     

Hydrogen production via steam and autothermal reforming of beef tallow: A thermodynamic investigation

A thermodynamic analysis of hydrogen production via steam and autothermal reforming of beef tallow has been carried out via the Gibbs free energy minimization method. Equilibrium calculations are performed at atmospheric pressure with a wide range of temperatures (400–1200 °C), steam-to-beef tallow ratios (1–15) and oxygen-to-beef tallow ratios (0.0–2.0).     

A novel method for measuring the coarse water droplets in wet steam flow in steam turbines

IntroductionWetoess in last stages Of LP steam ~es has beenlmown for a long time as a cause of efficiency loss anderosion of bladeslll. It comprises fine dIDPlets (also fogdrOPletS or Primal droplets) less than about 2 11 m indiameter and coarse water (big drOPlets or secondsdropletS), with diameter ~ about 10 11 m up tO sevedhundreds inicmns.For the fine droplet, the global method, known aSthe extinction method has been chosen tO Obtain itS sizedistribution and concentalon (weiness). …     

Reforming of vegetable oil for production of hydrogen: A thermodynamic analysis

The vegetable oils are one of the promising renewable feedstock for production of hydrogen suitable for application in hydrogen based fuel cells for electrical power generation. In the present work, a thermodynamic equilibrium analysis of steam reforming (SR) and autothermal steam reforming (ATSR) of vegetable oils to synthesis gas was investigated by Gibbs free energy minimization method. The thermodynamic equilibrium analysis was performed considering the vegetable oils as a mixture of triglycerides containing three same fatty acid groups in the structure. The property method used for equilibrium analysis was first regressed using available physical and chemical properties of the considered triglycerides. The regressed property method was then used to calculate the equilibrium products composition. The effects of various parameters of SR of vegetable oils, temperature and steam-to-carbon ratio (SCR), on hydrogen yield and selectivity of CO and methane was studied in a broad range of temperature (573-1273 K) and SCRs (1-6). The optimum conditions for SR of vegetable oils were then determined for maximum hydrogen yield with very low selectivity of methane. The thermodynamic equilibrium analysis of ATSR of vegetable oils was then performed at different oxygen-to-carbon ratios and thermoneutral conditions were then determined for various operating conditions.     

Correlations for fast computation of thermodynamic properties of saturated water and steam

An important issue in the engineering analysis and design of thermodynamic cycles is the calculation of saturation properties with enough speed without sacrificing accuracy. A set of correlations to reproduce tabulated thermodynamic saturation properties to engineering accuracy is given. They are fast to compute and become adequate for use whenever several thousands to millions of property evaluations are required. Then, they can be applied in thermodynamic cycle design optimization, in dynamic simulations of power cycles and in other industrial flow calculations. In addition, they can be incorporated into programmable calculators. For most saturation properties, the whole range from triple point to the critical point is dealt with by a single equation. Such equations can approximate tabulated values to within a small error. The correlations presented here were developed for water substance.     

A general method for the optimum design of heat recovery steam generators

The optimization of the heat recovery steam generator (HRSG) is one of the key elements for increasing the efficiency of combined plants. According to the current technical practice, it can be organized at different levels of complexity with objectives sequentially defined: operating parameters, geometrical details and technological elements.

According to this point of view, in the paper a complete strategy for the optimum design of the HRSG is outlined. The optimization is organized at two levels: the first one enables to obtain the main operating parameters of the HRSG, while the second involves the detailed design of the component concerning the geometric variables of the heat transfer sections. The output of the first-level optimization is the input of the second level. In particular, the second level of the optimization can be articulated in two different steps. The first step can be aimed to the minimization of the pressure drop for a given heat flow. The second step leads to a reduction of the overall dimensions, maintaining the imposed performance of the HRSG in terms of heat flow and pressure drop. The whole procedure is tested with reference to a case of existing HRSG structures; it shows the possibility of improving performance maintaining a constrained packaged size.     

A thermodynamic study of propanol reforming in presence of hydrazine for hydrogen production

Thermodynamic analysis of hydrogen production from propanol reforming reactions, by decomposition and steam reforming, in presence of hydrazine was evaluated as a function of temperature (300–900 K) at a constant pressure of 1 atm. The molar ratio of reactants were varied to identify the conditions leading to hydrogen rich product stream with low carbon formation. Steam reforming of propanol displayed higher hydrogen production and a gradual decrease in carbon content with an increase in the steam/propanol ratio. Addition of hydrazine leads to a further enhancement in hydrogen amount along with a suppression in coking. A similar trend was observed in case of propanol decomposition reaction. Addition of hydrazine leads to a favorable condition for hydrogen production along with a decrease in carbon formation. In both, steam reforming and decomposition, methane and water seem to be the stable products at low temperature, which react together at elevated temperatures following steam reforming of methane to generate CO and hydrogen. Hydrazine, on the other hand diminishes carbon at low temperature and produces ammonia, which decomposes at higher temperature to generate hydrogen and nitrogen. It is clear that steam assists in eliminating carbon at higher temperature whereas hydrazine is helpful in removing carbon formation at lower temperature. Also, a considerably high ratio of H₂/CO can be maintained in both the reactions, propanol steam reforming and propanol decomposition, by introducing a hydrazine stream in the feed.     

Combination of thermodynamic analysis and regression analysis for steam and dry methane reforming

Hydrogen is predominantly produced via methane reforming. In this study, thermodynamic analysis and regression analysis of the steam reforming of methane (SRM) as well as dry methane reforming (DRM) are conducted. The method of Gibbs free energy minimization is applied for investigating the effect of factors, such as temperature, pressure, and inlet composition, on the performance of hydrogen production. Notably, this study is not restricted to the effect of a single factor, but to the combined results of all independent variables. Then, regression analysis is adopted for examining the quantitative relationship between response observed and conditions. As a result, different mathematical expressions are attempted, such as linear regression, second-order polynomial, and logarithmic form, for finding the optimal form to preferably illustrate the manner in which factors affect performance. In this process, the forms are compared in several ways from the perspective of not only regression parameters but also error bars on graphs curve images. Finally, a three-pieces-logarithmic model is proposed as the final form to explain the relation between factors and response with maximum error 7% and the most deviations range between 0% and 2%.     

Thermodynamic analysis of steam reforming and oxidative steam reforming of propane and butane for hydrogen production

Thermodynamic analyses of cracking, partial oxidation (POX), steam reforming (SR) and oxidative steam reforming (OSR) of butane and propane (for comparison) were performed using the Gibbs free energy minimization method under the reaction conditions of T = 250–1000 °C, steam-to-carbon ratio (S/C) of 0.5–5 and O₂/HC (hydrocarbon) ratio of 0–2.4. The simulations for the cracking and POX processes showed that olefins and acetylene can be easily generated through the cracking reactions and can be removed by adding an appropriate amount of oxygen. For SR and OSR of propane and butane, predicted carbon formation only occurred at low S/C ratios (<2) with the maximum level of carbon formation at 550–650 °C. For the thermal-neutral conditions, the TN temperatures decrease with the increase of the S/C ratio (except for O/C = 0.6) and the decrease of the O/C ratio. The simulated results for SR or OSR of propane and butane are very close under the investigated conditions.     

Thermodynamic analysis of the efficiency of high-temperature steam electrolysis system for hydrogen production

High-temperature steam electrolysis (HTSE), a reversible process of solid oxide fuel cell (SOFC) in principle, is a promising method for highly efficient large-scale hydrogen production. In our study, the overall efficiency of the HTSE system was calculated through electrochemical and thermodynamic analysis. A thermodynamic model in regards to the efficiency of the HTSE system was established and the quantitative effects of three key parameters, electrical efficiency (η_el), electrolysis efficiency (η_es), and thermal efficiency (η_th) on the overall efficiency (η_overall) of the HTSE system were investigated. Results showed that the contribution of η_el, η_es, η_th to the overall efficiency were about 70%, 22%, and 8%, respectively. As temperatures increased from 500 °C to 1000 °C, the effect of η_el on η_overall decreased gradually and the η_es effect remained almost constant, while the η_th effect increased gradually. The overall efficiency of the high-temperature gas-cooled reactor (HTGR) coupled with the HTSE system under different conditions was also calculated. With the increase of electrical, electrolysis, and thermal efficiency, the overall efficiencies were anticipated to increase from 33% to a maximum of 59% at 1000 °C, which is over two times higher than that of the conventional alkaline water electrolysis.     

Positioning of PV panels for reduction in line losses and mismatch losses in PV array

Partial shading decreases the power output of PV arrays due to mismatch losses. These losses are dependent on the shading pattern and the relative positions of shaded modules in the array. Various static and dynamic reconfiguration techniques have earlier been proposed to mitigate these losses. In an earlier proposed static reconfiguration technique, the power generation is enhanced by altering the physical location of the PV panels using a random Sudoku configuration without modifying the TCT (Total-Cross-Tied) based electrical connections. However, this arrangement faces drawbacks due to ineffective dispersion of shade and significant increase in wiring required. In this work, an optimal Sudoku arrangement to overcome these drawbacks is formulated. Further analysis indicate that the global peak of the optimal Sudoku based PV array occurs as the right most peak in the curve for most shading conditions, thus evidently obviating the need for complex MPPT (Maximum-Power-Point-Tracking) algorithms. The proposed configuration is compared with various other existing reconfiguration schemes in terms of power output and the comparison is presented. In addition, a general formulation is proposed to expand this pattern to any generic array. A strategy is also proposed to make such an interconnection practicable for very large size PV arrays.     

宝钢中压蒸汽管网疏水系统的节能研究

工业企业内的节能工作已经成为企业可持续发展的主题,作为能源消耗中的蒸汽系统,目前在宝钢内部的损失率居高不下。介绍了宝钢中压蒸汽疏水器的现状,通过试验对节能型疏水器与普通疏水阀的性能进行了对比,并对节能型疏水阀的经济性进行分析,并提出了宝钢中压蒸汽疏水系统改造方案。     

Experimental Studies on The Mechanism and Control of Secondary Flow Losses in Turbine Cascades

This paper summarizes the results of the authors' 4 year experimental studies on the secondary flow losses in turbine cascades. Cascade wind tunnel experiments were carried out concerning the influence of aspect ratios, incidence, turning angles and outer endwall divergent angles in order to unveil the evolution mechanism of secondary flow losses in turbine cascades without end clearance. Some methods for controlling the secondary flows are investigated including the blade leaning, blade cambering, endwall convergence and leading edge extension at two ends of the blade.     

汽轮机及热装置性能评估系统研究

以某石化电厂双抽凝汽式汽轮机及热系统为研究对象,开发了以“热力参数诊断”为中心的旋转机械热力性能评估体系。通过对该汽轮机组运行性能和经济性能的计算分析,实时显示汽轮机组工作状态、当前热经济指标、当前工况下的节能潜力及热设备能损诊断结果,提出优化运行建议,并从热力学角度为电站设备的状态监测和预知性维修提供科学依据,实时指导汽轮机组经济运行。     

电厂主蒸汽流量测量与计算方法分析比较

介绍了目前获取发电机组主蒸汽流量的几种常用方法,对它们进行了分析比较,指出影响主蒸汽流量测量精度的几个主要因素,并提出了提高发电机组主蒸汽流量测量精度的相应对策。     

Comparative thermodynamic analysis of adsorption,membrane and adsorption-membrane hybrid reactor systems for methanol steam reforming

The thermodynamic analysis of steam reforming of methanol without and with fractional removal of H₂ and CO₂ in adsorption, membrane and adsorption-membrane hybrid reactor systems to produce fuel cell grade H₂ with minimal carbon formation is investigated. The results indicate that the removal of undesired CO₂ by CO₂ adsorbent is most effective process for the production of high purity H₂ than H₂ removal by membrane. However, the membrane is effective only above 30% H₂ removal. It is possible to obtain H₂ yield of 2.6 with negligibly small amount of CO and carbon formation at T = 405 K, P = 1 atm, 80% removal of CO₂ and 100% methanol conversion. Identical results are achieved even at lower temperature of 345 K in adsorption-membrane hybrid reactor system at 80% removal of H₂ and CO₂. Thus high grade H₂ can be produced by single step process and further processing to reduce CO by PROX reactor is not necessary.     

Thermodynamic analysis of ethanol steam reforming using Gibbs energy minimization method: A detailed study of the conditions of carbon deposition

In this paper, a thermodynamic analysis of ethanol/water system, using the Gibbs energy minimization method, has been carried out. A mathematical relationship between Lagrange's multipliers and carbon activity in the gas phase was deduced. From this, it was possible to calculate carbon activities in both stable and metastable systems. For the system that corresponds to ethanol steam reforming at very low contact times, composed mainly of ethylene and acetaldehyde, carbon activities were always much greater than unity over the whole temperature range, changing from 1.2 × 10⁷ at 400 K to 1.1 × 10⁴ at 1200 K. Furthermore, there was practically no effect of the inlet steam/ethanol ratio on carbon activity values. These results indicate that such a system is highly favorable to carbon formation. On the other hand, by considering a more stable system, in order to represent high contact times, it was observed that carbon activities are much lower and depend greatly on the inlet steam/ethanol ratio employed. Besides, the complete conversion of ethylene and acetaldehyde into other species, such as CO, CO₂, CH₄ and H₂, lowers the total Gibbs energy of the system. By computing carbon activities in experimental systems, it was also possible to explain deviations between thermodynamic analysis and experimental results regarding carbon deposition.     

A thermodynamic equilibrium analysis of hydrogen and synthesis gas production from steam reforming of acetic acid and acetone blends as bio-oil model compounds

Thermodynamic analysis of steam reforming of blends of two model oxygenates, acetic acid and acetone, representing carboxylic acids and ketones in bio-oil is performed to investigate the effects of their potential interactions on hydrogen yield, synthesis gas composition and progress of reaction network. The results show that both acetic acid and acetone reach complete conversion at all operating conditions. Higher S/C molar ratio results in higher H₂ and CO₂ yields for both acetic acid and acetone. With the increase in pressure, H₂ and CO yields are diminished whereas CH₄ and CO₂ yields are enhanced. H₂ and CO₂ yields increase with the decrease in acetone concentration in the feed blend. CO and CH₄ production are affected adversely for acetic acid rich blends. The maximum H₂ yield values are 75.54%, 78.34%, 80.09%, 81.78% and 84.17% at 700 °C for acetic acid/acetone blends of 0.0/1.0, 0.3/0.7, 0.5/0.5, 0.7/0.3 and 1.0/0.0, respectively.