Duty Requirements Research Articles

Optimizations and heat integrations on the separation of toluene and 1-butanol azeotropic mixture by pressure swing distillation

ABSTRACTIn this study, optimizations on separation of Toluene and 1-Butanol mixture is carried out by pressure swing distillation process. New heat integration methods are applied and compared to conventional PSD process by using vapor recompression technique combined with pressure swing distillation process. New heat integration methods show positive results to decrease the utilities used in the process. A simulator Aspen HYSYS V8.4 is used for simulating all processes. Cost analysis is also performed and Aspen HYSYS V8.4 optimizer program is used for optimizing profit for the process. Pressure is also optimized for minimum heat duty requirements in the process and the ultimate concern is to minimize the total reboiler heat duties and overall operating cost for the system which results into increasing profit.

Can Virtue Ethics Account for Supererogation?

In his classical article, ‘Saints and Heroes’, James Urmson single-handedly revived the idea of supererogation from it astonishingly long post-Reformation slumber. During the first two decades after its publication, Urmson's challenge was taken up almost exclusively by either utilitarians or deontologists of some sort. On the face of it, neither classical utilitarianism nor Kant's categorical imperative makes room for action which is better than the maximizing requirement, on the one hand, or beyond the requirement of duty, on the other. Nevertheless, both utilitarians and Kantians, as well as deontic logicians, offered more flexible and sophisticated versions of their respective theories which could accommodate supererogatory action. In my 1982 book on supererogation I tried to address the question whether virtue ethics could capture that new category of actions which are praiseworthy though not strictly required. But the focus of my discussion was mostly Aristotle (and Seneca) and accordingly more interpretive in nature. However, that was just before the tremendous surge of interest in virtue ethics and the vast literature debating the merits of agent-based vs. action-based approaches in moral theory. It turned out that fitting supererogation into virtue-based moral theory proved to be a more difficult task than doing so in consequentialist and deontological theories. Some argued that supererogation could nevertheless be accounted for in aretaic terms; others held that it could not and that this fact attested to either a theoretical weakness – even if not a refutation – of virtue-based ethics, or to the incoherence of the concept of supererogation.

Performance evaluation of integrated gasification combined cycle (IGCC) utilizing a blended solution of ammonia and 2-amino-2-methyl-1-propanol (AMP) for CO2 capture

IGCC is an emerging clean coal technology with the potential to produce electricity without damaging the ecosystem. However, efficiency enhancement of the IGCC when pollutant emissions are included in the system is a critical issue that should be evaluated further. In this paper, a large-scale IGCC system is modeled and simulated in three configurations: IGCC without CO2 capture, IGCC with pre-combustion capture, and IGCC with post-combustion capture. The validated model of CO2 capture based on a blended solution of ammonia and AMP is integrated with the IGCC to evaluate system performance in terms of net power produced, efficiency penalty due to CO2 capture, and energy losses in various sections of the IGCC. Moreover, an exergy analysis is carried out to investigate the loss of useful work in major sections of the IGCC for three cases (IGCC without capture, IGCC with pre-capture and IGCC with post-capture). The results indicated that the chemical absorption-based blended solution of AMP and NH3 is an attractive option due to its high CO2 loading capacity and low heat duty requirement; it can also be applied to both the IGCC with pre-combustion capture and IGCC with post-combustion capture. However, IGCC with post-combustion capture is more efficient because the net power produced from IGCC with post-combustion capture (561MW) is greater than the power obtained from IGCC with pre-combustion capture (518MW). The efficiency loss due to CO2 was 1.1% for post-combustion capture and 4.3% for pre-combustion capture. Furthermore, about 65% of the total exergy loss was observed in the gasifier and gas turbine combustor only, whereas 41.5% of the total power produced was consumed in the gas turbine compressor and air separation unit.

Solar repowering of PCC-retrofitted power plants; solar thermal plant dynamic modelling and control strategies

Solar repowering of high pressure side feed water preheaters of post combustion carbon capture (PCC) retrofitted power plants offers a promising capability to offset the power plant output penalty due to capture plant reboiler duty. In this work, a model based approach is used to investigate the technical, operational and control aspects of the solar thermal installation of the super structure (power plant+PCC+solar thermal plant). The base case is a 660MWe PCC-retrofitted power plant operating at 100% capacity and 90% capture rate in Australia. This is repowered by a solar thermal plant consisting of (a) a parabolic trough solar collector field with 806,520m2 aperture area, (b) a thermal storage system with 8 full load hours of thermal storage and (c) an auxiliary gas heating unit, ensuring the solar thermal plant provides the high pressure side feed water preheating duty at all times without requirement to withdraw any steam from the power plant turbine circuit. A total of 230MWth is provided from the solar thermal plant installation, being 100% supply for high pressure and intermediate feed water preheaters duty plus a surplus of 30% for maintaining the deaerator operation. A key feature here is trying to eliminate the frequent changes to the steam flow rate in the turbine circuit for solar feed water preheating and thus promoting ease of retrofit of repowering technology to PCC-retrofitted power plants. Details of the component sizing and modelling of solar thermal installation are provided and control and operating schemes are identified and analysed. A comprehensive dynamic model in TRNSYS dynamic modelling software is developed and used to analyse the solar thermal plant dynamic responses to external disturbances including climatic changes (Typical Meteorological data for Sydney is used). The analysis limitations and capabilities are highlighted. The model performance for month December is assessed showing its full capability to track the changes from power plant duty requirement and meteorological data within the time lapse of 0.01s.

Application of a novel calcium looping process for production of heat and carbon dioxide enrichment of greenhouses

Greenhouses typically employ conventional burner systems to suffice heat and carbon dioxide required for plant growth. The energy requirement and carbon dioxide emissions from fossil fuel burner are generally high. As an alternative, this paper describes a novel greenhouse calcium looping process which is expected to decrease the energy requirements and associated carbon dioxide emissions. The conceptual design of greenhouse calcium looping process is carried out in the ASPEN Plus v 7.3 simulator. In a greenhouse calcium looping process, the calcination reaction is considered to take place during day time in order to provide the required optimum carbon dioxide between 1000 and 2000ppm, while the carbonation reaction is occurred during night time to provide required heat. The process simulations carried out in ASPEN indicates that greenhouse calcium looping process theoretically attributes to zero emission of carbon dioxide. Moreover, in a scenario modelling study compared to the conventional natural gas burner system, the heat duty requirements in the greenhouse calcium looping process were found to reduce by as high as 72%.

Flexible dynamic operation of solar-integrated power plant with solvent based post-combustion carbon capture (PCC) process

This paper examines flexible operation of solvent-based post-combustion carbon capture (PCC) for the reduction of power plant carbon emissions while minimizing revenue loss due to the reduced power plant electricity output. The study is conducted using a model superstructure enveloping three plants; a power plant, a PCC plant and a solar thermal field where the power plant and PCC plant are operated flexibly under the influence of hourly electricity market and weather conditions. Reduced (surrogate) models for the reboiler duty and auxiliary power requirement for the carbon capture plant are generated and applied to simulate and compare four cases, (A) power plant with PCC, (B) power plant with solar assisted PCC, (C) power plant with PCC and solar repowering – variable net electricity output and (D) power plant with PCC and solar repowering – fixed net electricity output. Such analyses are conducted under dynamic conditions including power plant part-load operation while varying the capture rate to optimize the revenue of the power plant. Each case was simulated with a lower carbon price of $25/tonne-CO2 and a higher price of $50/tonne-CO2. The comparison of cases B–D found that optimal revenue generation for case C can be up to 42% higher than that of solar-assisted PCC (case B). Case C is found to be the most profitable with the lowest carbon emissions intensity and is found to exhibit a constant capture rate for both carbon prices. The optimal revenue for case D is slightly lower than case C for the lower carbon price ($25/tonne-CO2) while it is considerably lower in the higher carbon price ($50/tonne-CO2) scenario. The highest revenue to electricity ratio is found to be for the case where solar repowering is used for power boosting. This study highlights the significant potential of dynamic flexible operation toward deeper reductions in carbon capture costs. This analysis is based on the presence of a carbon pricing scheme currently not present in the Australian market, but which could be realised in the future.

Energy Minimization and Ammonia Abatement for CO2 Capture Using a Blend of Ammonia and 2-Amino-2-Methyl-1-Propanol Solution

An aqueous ammonia based CO2 capture offers several advantages over the conventional monoethanolamine (MEA) solvent, including a high CO2 loading capacity, low stripper heat duty, a lower degradation rate of solvent, low equipment corrosion, and the ability to capture multipollutants. However, in order to make an aqueous, ammonia-based CO2 capturing process economically feasible, attention must be paid to the following issues: ammonia slip due to the high evaporation rate of ammonia, energy input for CO2 regeneration, and CO2 removal efficiency improvements. In conventional, aqueous ammonia-based CO2 capture, the process either needs to operate at very low temperatures or must include wash-water columns to mitigate ammonia slips, which increase the capital and operational costs of the system. In this paper, a blended solution of 2-amino-2-methyl-1-propanol (AMP) and ammonia was used to analyze the CO2 capture efficiency, ammonia slip, and stripper heat duty. Our results show that, using the blended (30 wt.% AMP + 3 wt.% NH3) solution for CO2 capture, the ammonia slip was reduced by 64% at a lean CO2 loading of 0.07, CO2 capture efficiency was increased by 17.2%, and the heat duty requirement for CO2 regeneration was reduced by 80% at a stripper inlet temperature of 60°C. Moreover, the loss of AMP due to evaporation was 0.042 kg/day.

Reactive-Distillation Process for Direct Hydration of Cyclohexene to Produce Cyclohexanol

Cyclohexanol is an important precursor in synthesizing intermediates of Nylons and also plasticizers. In this paper, a plantwide reactive-distillation process for the production of cyclohexanol by direct hydration of cyclohexene with water has been studied. Design with excess water is needed to economically increase conversion of cyclohexene to 99.9%. The optimal design of the proposed flowsheet also makes use of the natural liquid–liquid splitting of the binary cyclohexanol–water azeotrope. Realistic fresh cyclohexene feed with impurity of cyclohexane was also considered. This inert is designed to leave the system in the organic outlet stream of a decanter on top of the reactive-distillation column. The reboiler duty requirement of the proposed design flowsheet is compared with existing processes in open literature. It is found that significant energy savings can be realized by using this design.

Optimization of a plate-fin heat exchanger design through an improved multi-objective teaching-learning based optimization (MO-ITLBO) algorithm

Teaching-learning-based optimization (TLBO) is a recently developed heuristic algorithm based on the natural phenomenon of teaching-learning process. In the present work, multi-objective improved teaching-learning-based optimization (MO-ITLBO) algorithm is introduced and applied for the multi-objective optimization of plate-fin heat exchangers. The basic TLBO algorithm is improved to enhance its exploration and exploitation capacities by introducing the concept of number of teachers, adaptive teaching factor, tutorial training and self-motivated learning. The MO-ITLBO algorithm uses a grid-based approach to adaptively assess the non-dominated solutions maintained in an external archive. Minimizing total annual cost and the total weight of heat exchanger as well as minimization of total pressure drop and maximization of heat exchanger effectiveness for specific heat duty requirement are considered as objective functions. Two application examples are presented to demonstrate the effectiveness and accuracy of the proposed algorithm.

Energy minimization in monoethanolamine-based CO2capture using capacitive deionization

Post-combustion CO2 capture using monoethanolamine (MEA) is a mature technology; however, the high energy input requirements for solvent regeneration are still a challenge for MEA-based CO2 capture. In this paper, a novel approach is presented in which a conventional CO2 absorption–desorption system is integrated with capacitive deionization (CDI) in such a way to minimize the heat duty requirement of the stripper. The CO2-rich solution drawn from the absorber column is first sent to CDI where ionic species are adsorbed at oppositely charged electrodes during the charging cycle, and an ion-free solution is sent back to the absorber. The adsorbed ions released during the regeneration cycle are sent to the stripper column. The concentrated solution from the CDI process that was sent to the stripper required low heat duty to regenerate the solvent because of the high CO2 loading of the solution. The feasibility of the suggested modelling technique is verified at various stripper inlet temperatures and lean CO2 loadings. The results indicate that 10–45% of the total energy supplied to the stripper can be conserved at a lean CO2 loading of 0.0000–0.0323 using the suggested process model. Moreover, the required size of the stripper column will be small due to the small volume of the concentrated ionic solutions from the CDI cell, eliminating the initial cost of the CO2 capture system. Copyright © 2014 John Wiley & Sons, Ltd.

Process integration of hydrolysis and electrolysis processes in the Cu–Cl cycle of hydrogen production

Process integration of the hydrolysis and electrolysis processes is one of the most important engineering challenges associated with the Cu–Cl cycle of hydrogen production. The kinetics of the hydrolysis reaction indicates the reversibility of this process which requires H2O in excess of the stoichiometric quantity, which significantly decreases the overall thermal efficiency of the Cu–Cl cycle. Moreover, the HCl concentration in the produced gas mixture of H2O and HCl in the hydrolysis reaction is in much lower concentration of the electrolysis reaction requirement for an effective electrolytic cell performance. This paper simulates an integrated process model of the hydrolysis and electrolysis processes by introducing intermediate heat recovery steam generator (HRSG) and HCl–H2O separation process consisting of rectification and absorption columns. In the separation processes, the influence of operating parameters including reflux ratio, mole fraction of HCl in the feed stream, solvent flow rate and temperature, and column configuration variables such as the location of feed stage and number of stages on the heat duty requirements and the composition of products are investigated and analysed. It is shown that the amount of steam generated in the HRSG unit satisfies the extra steam requirement of the hydrolysis reaction up to 14 times more than its stoichiometric value and the separation process effectively provides HCl acid up to the concentration of 22 mol% for the electrolysis reaction.

Master physician scheduling problem

We study a real-world problem arising from the operations of a hospital service provider, which we term the master physician scheduling problem. It is a planning problem of assigning physicians’ full range of day-to-day duties (including surgery, clinics, scopes, calls, administration) to the defined time slots/shifts over a time horizon, incorporating a large number of constraints and complex physician preferences. The goals are to satisfy as many physicians’ preferences and duty requirements as possible while ensuring optimum usage of available resources. We propose mathematical programming models that represent different variants of this problem. The models were tested on a real case from the Surgery Department of a local government hospital, as well as on randomly generated problem instances. The computational results are reported together with analysis on the optimal solutions obtained. For large-scale instances that could not be solved by the exact method, we propose a heuristic algorithm to generate good solutions.

Quantifying Fatigue Risk in Model-Based Fatigue Risk Management

The question of what is a maximally acceptable level of fatigue risk is hotly debated in model-based fatigue risk management in commercial aviation and other transportation modes. A quantitative approach to addressing this issue, referred to by the Federal Aviation Administration with regard to its final rule for commercial aviation "Flightcrew Member Duty and Rest Requirements," is to compare predictions from a mathematical fatigue model against a fatigue threshold. While this accounts for duty time spent at elevated fatigue risk, it does not account for the degree of fatigue risk and may, therefore, result in misleading schedule assessments. We propose an alternative approach based on the first-order approximation that fatigue risk is proportional to both the duty time spent below the fatigue threshold and the distance of the fatigue predictions to the threshold--that is, the area under the curve (AUC). The AUC approach is straightforward to implement for schedule assessments in commercial aviation and also provides a useful fatigue metric for evaluating thousands of scheduling options in industrial schedule optimization tools.

Wearing long pants while working outdoors in the tropics does not yield higher body temperatures

To compare the thermoregulatory demands of outdoor workers wearing long or knee-length pants while working in situ in a tropical environment. Fifteen male (35.8 ± 10.5 yr) outdoor Council workers completed their daily occupational duties (construction or gardening) in trials conducted six days apart: once wearing knee-length shorts (SHORTS) and once wearing full-length pants (PANTS). Body mass and hydration were assessed prior to and following each trial with core body (T(C) ) and mean skin temperature (MST; weighted from sites: chest, arm, thigh and calf) assessed at 30-minute intervals throughout each trial. No significant differences between SHORTS and PANTS for T(C) , maximum T(C) , heart rate, MST or body mass changes. Skin temperature at the calf was greater for PANTS (33.8 ± 0.4°C) compared to SHORTS (32.9 ± 0.4°C; p<0.05). Hydration assessments identified 36.7% of participants commenced work hypohydrated while the average body mass lost throughout the workday was 2.5 ± 1.5%. Main effects of time were observed for heart rate and MST but no other assessed variable. The additional exposed surface area available for heat exchange when wearing shorts is insufficient to elicit differences in thermoregulatory demands of outdoor employees under the assessed conditions. These results suggest the use of SHORTS or PANTS can be determined by occupational duty requirements rather than risk of heat-related illness during very-light to moderate workloads completed under warm and humid environmental conditions.

Improved Plastic-Al Pipe Based System for Refrigeration of Energy Existed in Urban Sewage

In order to recover the urban sewage energy ,a lab-scale equipment for the sewage energy recovery based on water source heat pump was developed and researched experimentally .The technique of indirect heat exchange by the plastic-Al pipe to recover the urban sewage energy, i.e., the corrosion of the heat exchanger, laying the foundation for the practical utilization of sewage energy. The experimental results show that the developed system is favorable to the environment protection and energy conservation, satisfying the cooling duty requirement with the average coefficient of performance 4.15 in the open cycle system and the average coefficient of performance 3.64 in the close cycle system.

Microstructure and Mechanical Properties of New Type Bainitic Carburized Steel for Gear

This paper presents the microstructure, mechanical properties and carburized behavior of new type bainitic carburized steel. The results show that after new carburized steel is normalized at 920°C and tempered at 300°C, its microstructure consists of bainitic ferrite and residual austenite, and belongs to the carbide-free bainite or atypical bainite. Large or small cross-section size new carburized steel bar all have reached the performance requirements of Cr-Ni carbonized steel. The microstructure of new carburized steel surface consists of high carbon martensite and residual austenite after carburized and air-cooled, It retains austenite fraction of the new carburized steel and 18Cr2Ni4WA steel are about 18% and 38%, respectively. Carbon concentration gradient of new carburized steel changes smoothly and have ideal carbon concentration distribution. Effective carburizing surface depth of new carburized steel is about 0.6mm and is smaller than 18Cr2Ni4WA steel. The gear entities made of new carburized steel meet the technical requirements of heavy duty carburized gear.

Optimization of Steam Pressure Levels in a Total Site Using a Thermoeconomic Method

The present study aims to develop a thermoeconomic-based approach for optimization of steam levels in a steam production and distribution system by use of the specific exergy costing (SPECO) method for determining optimum steam levels to minimize the cost caused by exergy destruction. In the field of total site optimization, incremental cost of the utility system caused by exergy destruction has been selected as an objective function and the result is compared with the case that energy minimization has been selected as the prime objective. The steam levels are optimized considering steam demand at each level, output power generated by turbines, boiler duty, fuel and cold utility requirements as well as capital cost of equipments. The analysis showed that thermoeconomic (exergoeconomic) approach in optimization not only can change the optimum structure of steam levels but also may reduce the total cost of utility system up to 8%.

An Observational Study of Junior Neurosurgery Resident Call at a Large Teaching Hospital

To -date, few studies have attempted to understand resident workload while on call by quantifying individual duty requirements, such as new patients seen, procedures performed, distance walked, or pages received. Theoretically, residents who are required to return more pages, walk greater distances, see more new patients, and sleep less while on call are more likely to suffer from fatigue than those who have less intense responsibilities, regardless of the length of shift. From a practical perspective, it can be argued that increased workload may stimulate residents while on duty and help prevent the performance effects of fatigue. There are few published studies that have attempted to characterize resident fatigue while on call by quantifying workload, scope, and contextual factors. From April to June 2011, the primary author (a postgraduate year-3 neurosurgery resident) recorded workload data during 15 consecutive call shifts in a large neurosurgery program. The author wore a pedometer to record the total number of miles walked during the shift. An average 24-hour neurosurgical call shift at our institution entailed walking 9.6 miles, being responsible for an inpatient census of 62 patients, evaluating 8 new patients, returning 65 pages, performing one minor procedure, eating one sit-down meal, and sleeping 35 minutes with a median sleep time of zero minutes. This report from an individual resident is a first attempt at quantifying the experiences of overnight resident call at a large program to further understand the rigors facing neurosurgical trainees. There are few recent data evaluating the workload of residents or fellows, and only a few studies have quantified the distance walked while on call.1,2 Although these data are limited given their single-center, single-resident origin, we believe the study is interesting, particularly with regard to long distances walked during call (one call period entailed 13 miles of walking). This suggests a need for further investigation into the call experiences of resident physicians, to more fully understand the relationship between the physical demands of call, resident fatigue, and the quality of care that is provided. We encourage other centers to engage in similar, yet more robust, efforts so that we can obtain a broader understanding of the relationship between workload and physician fatigue while on call.

The Cost and Challenges of Facial Trauma: AAO‐HNS Survey

Objective: 1) Define practice patterns and perceptions of young otolaryngologists treating maxillofacial trauma. 2) Identify manners in which the AAO-HNS can meet future maxillofacial trauma needs. Method: A 26-question survey was designed to identify demographic factors, practice patterns, perceptions of facial trauma, and areas for improvement in trauma care. It was distributed anonymously to AAO-HNS members who completed residency from 2005 to 2009 and analyzed using descriptive statistics. Results: A total of 444 of 1378 (32%) otolaryngologists responded. A total of 85% treat maxillofacial trauma (&lt;1 case/month). A total of 64% identify trauma as part of their ideal practice. Sense of duty (54%) and institutional requirement (33%) are the most common reasons for trauma participation. Major deterrents: patient noncompliance (60%) and lifestyle limitations (47%). While insufficient reimbursement is a major deterrent (52%), only 35% would increase their volume if reimbursement improved. Sixteen (3.7%) have had a trauma-related lawsuit. Increased education represents the most common request to the AAO-HNS (59%), followed by focus on improved reimbursement/tort reform (28%). Topics proposed: practice guidelines, pediatric, laryngeal, and midface trauma. Conclusion: Most otolaryngologists treat facial trauma, but do so infrequently. A total of 64% of young otolaryngologists identify trauma as a component of their ideal practice. However, universal concerns include inadequate reimbursement, limited pool of treating physicians, and lack of practice guidelines.

New Duty-Hour Rules Present Challenges

New Duty-Hour Rules Present Challenges