Steady state simulation and exergy analysis of supercritical coal-fired power plant with CO₂ capture

Integrating a power plant with CO₂ capture incurs serious efficiency and energy penalty due to use of energy for solvent regeneration in the capture process. Reducing the exergy destruction and losses associated with the power plant systems can improve the rational efficiency of the system and thereby reducing energy penalties. This paper presents steady state simulation and exergy analysis of supercritical coal-fired power plant (SCPP) integrated with post-combustion CO₂ capture (PCC). The simulation was validated by comparing the results with a greenfield design case study based on a 550 MWe SCPP unit. The analyses show that the once-through boiler exhibits the highest exergy destruction but also has a limited influence on fuel-saving potentials of the system. The turbine subsystems show lower exergy destruction compared to the boiler subsystem but more significance in fuel-saving potentials of the system. Four cases of the integrated SCPP-CO2 capture configuration was considered for reducing thermodynamic irreversibilities in the system by reducing the driving forces responsible for the CO₂ capture process: conventional process, absorber intercooling (AIC), split-flow (SF), and a combination of absorber intercooling and split-flow (AIC + SF). The AIC + SF configuration shows the most significant reduction in exergy destruction when compared to the SCPP system with conventional CO₂ capture. This study shows that improvement in turbine performance design and the driving forces responsible for CO₂ capture (without compromising cost) can help improve the rational efficiency of the integrated system

Exergetic and Economic Evaluation of a Transcritical Heat-Driven Compression Refrigeration System with CO2 as the Working Fluid under Hot Climatic Conditions

The purpose of this research is to evaluate a transcritical heat-driven compression refrigeration machine with CO2 as the working fluid from thermodynamic and economic viewpoints. Particular attention was paid to air-conditioning applications under hot climatic conditions. The system was simulated by Aspen HYSYS® (AspenTech, Bedford, MA, USA) and optimized by automation based on a genetic algorithm for achieving the highest exergetic efficiency. In the case of producing only refrigeration, the scenario with the ambient temperature of 35 °C and the evaporation temperature of 5 °C showed the best performance with 4.7% exergetic efficiency, while the exergetic efficiency can be improved to 22% by operating the system at the ambient temperature of 45 °C and the evaporation temperature of 5 °C if the available heating capacity within the gas cooler is utilized (cogeneration operation conditions). Besides, an economic analysis based on the total revenue requirement method was given in detail

Energetic and exergetic analysis of combined cycle power plant: Part-1 operation and performance

Energetic and exergetic analyses are conducted using operating data for Sabiya, a combined cycle power plant (CCPP) with an advanced triple pressure reheat heat recovery steam generator (HRSG). Furthermore, a sensitivity analysis is carried out on the HRSG using a recent approach to differentiate between the sources of irreversibility. The proposed system was modelled using the IPSEpro software and further validated by the manufacturer’s data. The performance of the Sabiya CCPP was examined for different climatic conditions, pressure ratios, pinch point temperatures, high-pressure steam, and condenser pressure values. The results confirmed that 60.9% of the total exergy destruction occurs in the combustion chamber, which constitutes the main source of irreversibilities within a system. The exergy destruction was significantly affected by both the pressure ratio and the high-pressure steam, where the relation between them was seen to be inversely proportional. The high-pressure stage contributes about 50% of the exergy destruction within the HRSG compared to other stages and the reheat system, due to the high temperature difference between the streams and the large number of components, which leads to high energy loss to the surroundings. Numerous possibilities for improving the CCPP’s performance are introduced, based on the obtained results

New Trends in Enhanced, Hybrid and Integrated Geothermal Systems

Geothermal energy is a renewable, sustainable, and ecologically friendly resource of energy that can be captured with shallow or deep installations, or a combination of both—alone or integrated with other technologies. It can then be employed for a variety of purposes, for example, electricity generation, space heating and cooling, agriculture, and aquaculture. Given the nature/features of this green energy resource—such as being a local, climate-independent, potentially constant, robust, generally available, resilient, almost greenhouse gas-free, and long-lived energy source—geothermal solutions can and should make a more prominent contribution to the future global energy supply mix, in addition to helping lessen humanity’s environmental footprint and enabling it to attain its sustainable development goals. This Special Issue, “New Trends in Enhanced, Hybrid and Integrated Geothermal Systems”, addresses existing knowledge gaps and aids advance deployment of geothermal energy globally. It consists of eight peer-reviewed papers that cover a range of subjects and applications related to geothermal energy

천연가스 공급망 내 초구조 최적화 및 다중모듈방식을 이용한 공정설계 및 운전

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 화학생물공학부, 2019. 2. 이원보.본 논문은 공정시스템 분야의 최신기술 수요에 상응하는 최적 공정설계 및 운전기술 개발을 주목적으로 한다. 최근 셰일가스 등 변화하는 천연가스 자원으로부터 지속적인 부가가치 창출과 플랜트의 내재적 안전성을 제고할 수 있는 설계 및 운전을 도모하였다는 점에서 실제 산업에의 응용가치가 매우 높다. 첫 번째로 천연가스 가솔린회수 및 액화 통합공정에 질소회수공정을 추가하여, 저품질 천연가스로부터 지속적인 액화천연가스 생산이 가능한 공정을 설계하였다. 열교환망 및 분리공정 최적화를 위해 공정요소들의 엑서지를 최소화할 수 있는 초구조를 설계함으로써 기존의 연구가 찾지 못하였던 새로운 최적 구조 및 운전조건을 결정하였다. 나아가 서로 다른 천연가스 조성에 따라 각기 적용이 가능한 대안공정을 추가 설계·최적화함으로써 변화되는 천연가스 자원에 지속적인 가치창출을 위한 해답을 제시하고 있다. 두 번째로 공정의 예비설계단계에서 내재적 안전성의 개념을 도입하여, 경제성과 안전성의 균형을 유지하기 위한 새로운 다목적최적화 알고리즘을 개발하였다. 잠재적 위험도가 높은 천연가스 액화공정을 대상으로 액화사이클에 따른 초구조를 모사하여 두 가지 목적함수의 가중치에 따른 최적해를 결정함으로써 기존 최적화의 한계를 보완하였다. 마지막으로 플랜트 안전운전을 위해 공정이상에서부터 사고의 발생 및 전파과정을 실시간으로 구현할 수 있는 시뮬레이션 모듈을 개발하였다. 동적공정시뮬레이션 및 사고시뮬레이션의 두 가지 독립된 모듈을 객체연결매입 기법을 이용하여 연동함으로써 사고상황에서 운전원의 임의조치가 모듈에 실시간 반영되도록 하였다. 해당 모듈은 임의의 사고상황에서 제어실 및 현장 운전원의 적절한 대응을 효과적으로 유도할 수 있으며 나아가 플랜트 안전시스템설계에 객관화된 지표를 제시할 수 있었다. 본 논문은 위와 같이 실제 산업의 기술적 수요를 충족시키고 이를 발전시킴으로써 공정시스템 학술분야에 기여하였다.Recently in the field of process systems engineering in natural gas processing, various researches trying to make changes in the existing framework of process design and operation have been studied with the emerging need of sustainability and safety in the chemical processes. These two considerations of sustainability and safety either result in a totally new solution for a certain decision making or require far different methods or technologies for it. Especially for a natural gas supply chain broadly from drilling of the gas/oil reservoirs to distributing the product gas to end-users like households or offices, new frameworks of process design and operation critically influence the way of producing desired products and supplying them to the users in the associated industries. Then it determines the structure, operating conditions, and operation procedures of chemical processes which are economically powerful and good in operability. Recently, as the natural gas sources becomes unconventional varying from mid-to-small size reservoirs or shale gases, this change makes the offshore natural gas plants emerge as an alternative and vital site of producing LNG (liquefied natural gas) with strict requirements of safety. It also makes additional processing units like a cryogenic nitrogen recovery be necessary for sustainable production of LNG with leaner feed natural gases. Among various processes in the overall natural gas supply chain, this thesis dealt with largely three parts including gas pre-treatment, liquefaction, and distribution to the end-users, attempting to design new processes or develop new methods of decision making in the context of the new framework considering sustainability and safety in process systems engineering. In this thesis, I will discuss the process synthesis, intensification, and optimization for sequential units, multi-objective optimization for economic feasibility and inherent safety, and multi-modular approach for interactive simulation of dynamic process and 3D-CFD (computational fluid dynamics) accident models. First of all, for designing a sustainable process of producing LNG from feed natural gases with high amounts of nitrogen, two cryogenic nitrogen recovery processes integrated with LNG production and NGL (natural gas liquid) recovery were designed and optimized based on the structural analysis of components separation: one for integrated nitrogen recovery unit and the other for standalone one. The difference of each process is the way the nitrogen is removed from the natural gas. The former recovers nitrogen in the integrated heat and mass transfer structure with natural gas liquefaction while the latter separates the nitrogen recovery unit into an independent structure apart from the liquefaction section. These sophisticated nitrogen recovery solutions follow the recent demand of highly efficient electric motors as alternative compressor drivers which require less or no fuel gas, the major sink of nitrogen in the feed gas. These two processes were compared with each other in terms of specific power (kWH/kg_LNG), which is equivalent to the overall process efficiency, with respect to the nitrogen content in the feed gas from 0mol% to 20mol%. Consequently, as the nitrogen content in the feed gas increases, the specific power of each process also increases while the standalone solution has a priority over the other until around 17mol% of nitrogen and after that point the integrated solution becomes relatively more efficient. It should be noted that all of the optimization results of each configuration were improved with the reduced specific power by up 38.6% compared to those from previous studies which have similar configurations. The way this study aimed could be reasonable guidelines for other chemical process designs as well as nitrogen recovery in natural gas processing. Secondly, for designing a safer process of natural gas processing, two different systematic approaches were newly proposed in this study: one for risk reduction method based on rigorous QRA (quantitative risk assessment) results through process design modification of an existing plant which already finished up to the detailed design stage, and the other for deciding an optimal process design through multi-objective optimization for minimizing both the TAC (total annual cost) and the risk (fatality frequency) at the preliminary design stage. This latter approach could largely lower the cost required for finalizing the design as it doesnt need to follow the general QRA procedure where the recursive loop is recycled until the risk is reduced to an acceptable level. But before this approach starts to be applied, the suitability of its method should be verified as it has to make some assumptions in assessing the safety level of the process with limited information. Also the computation load would be higher as it needs to simultaneously consider the economic feasibility and inherent safety in designing a process. Despite the differences these two approaches have each other, however, they are essentially in the same context in that they share the same purpose of deciding a process design which is safer and/or even cheaper than the existing processes. Consequently, for the former approach of which the target process is the GTU (gas treatment unit) of an existing GOSP (gas oil separation plant) for processing associated natural gas, the modified design with different operation conditions reduced the total risk integrals by 27% at the expense of only the additional $50,000 for capital cost. In addition, sensitivity analysis of total risk with respect to probability of success for safety barriers was carried out in order to show the preferences of process design modification, this study proposed, over the improvement of safety systems. Meanwhile, the latter approach of superstructure formulation and multi-objective optimization for designing an optimal heat transfer structure and operating conditions was applied to the natural gas liquefaction processes, deciding that the SMR (single-stage mixed refrigerant process) structure with the TAC of 626.6MM$/yr and fatality frequency of 1.28E-03/yr has the highest priority over all possible solutions. Finally, with the aim of safely operating a chemical plant, a new operator training module which mainly targets the interactive cooperation of control room operators and field operators was developed through using multi-modular approach with advanced simulations and data processing technologies. This interactive simulation modeling delivers the online simulation results of process operation to the operators and induces them to take proper actions in case of a random accidental situation among pre-identified scenarios in a chemical plant. Developed model integrates the real-time process dynamic simulations with the off-line database of 3D-CFD accident simulation results in a designed interface using OLE (Object Linking and Embedding) technology so that it could convey the online information of the accident to trainees which is not available in existing operator training systems. The model encompasses the whole process of data transfer till the end of the training at which trainees complete an emergency shutdown system in a programmed model. The developed module was applied to a natural gas pressure regulating station where the high pressure gas is depressurized and distributed to the end-users like households or offices. An overall scenario is simulated in the interactive simulation model, which starts from an abnormal increase of the discharge (2nd) pressure of the main valve due to its malfunction, spreads to an accidental gas release through the crack of a pressure recorder, and ends with gas dispersion and explosion. Then the magnitude of the accident outcomes with respect to the lead time of each trainees emergency response is analyzed. Consequently, the module could improve the effectiveness of operator training system through interactively linking the trainee actions with the model interface so that the associated accident situations would vary with respect to each trainees competence facing an accident.Abstract i Table of Contents vii List of Figures x List of Tables xiv CHAPTER 1. Introduction 1 1.1. Research motivation 1 1.2. Research objectives 4 1.3. Outline of the thesis 6 1.4. Associated publications 11 CHAPTER 2. Process Intensification 12 2.1. Introduction 13 2.2. Conceptual Design of the Nitrogen Recovery 17 2.3. Design Improvement and Optimization 26 2.3.1. Integrated Nitrogen Recovery Unit 26 2.3.2. Optimization of the Base Case 32 2.3.3. Design Improvement 40 2.4. Alternative Process Design and Optimization 65 2.4.1. Standalone Nitrogen Recovery Unit 65 2.4.2. Optimization of Standalone Nitrogen Recovery Unit 74 2.4.3. Comparison between End-flash and Stripping Options 78 2.5. Varying Feed Composition and Optimization 95 2.6. Concluding Remarks 105 CHAPTER 3. Safer Process Design 107 3.1. Introduction 109 3.2. Risk Reduction through Process Design Modification 112 3.2.1. Risk Assessment for the Target Process 113 3.2.2. Risk Reduction to ALARP 141 3.3. Multi-objective Optimization Including Inherent Safety 154 3.3.1. New Decision Making Schemes for Inherent Safety 159 3.3.2. Superstructure for Natural Gas Liquefaction Processes 168 3.3.3. Multi-objective Optimization 187 3.3.4. Decision Making for Final Optimal Solution 203 3.3.5. Future Works 208 3.4. Concluding Remarks 210 CHAPTER 4. Safe Operation with Multi-modular Approach 212 4.1. Introduction 213 4.2. Interactive Simulation Modeling 218 4.2.1. Model Structure 218 4.2.2. Dynamic Process and Accident Simulation Engine 221 4.2.3. Real-time 3D-CFD Data Processing Method 225 4.3. Case Study – Pressure Regulating Station 231 4.3.1. Developing a Program Prototype 231 4.3.2. Prototype Test and Training Evaluation 252 4.4. Concluding Remarks 256 CHAPTER 5. Conclusion 257 Nomenclature 261 Reference 263 Abstract in Korean (국문초록) 270Docto

Modelling and operational analysis of coal-fired supercritical power plant integrated with post-combustion carbon capture based on chemical absorption under UK grid requirement

Fossil-fuel fired power plants are subjected to stringent operational regime due to the influx of renewable resources and the CO2 emission reduction target. This study is aimed at modelling and analysis of supercritical coal-fired power plant (SCPP) integrated with post-combustion CO2 capture (PCC) and its response electricity grid demand constraints. Current status of dynamic modelling of SCPP integrated with PCC was reviewed to identify the gaps in knowledge. It was observed that no accurate dynamic model of an SCPP integrated with PCC had been reported in open literature. A steady state model of the SCPP integrated with PCC was developed with Aspen Plus®. The model was validated with the reference plant and it was found that the relative error is about 1.6%. The results of the conventional and advanced exergetic analysis showed that the energy/exergy consumption and the efficiency of the integrated system can be improved by recovering the avoidable exergy destruction in the whole system.Dynamic models of SCPP once-through boiler based on lumped parameter and distributed parameter approaches were compared. The distributed parameter model gave a more accurate prediction of the SCPP boiler dynamics at different load levels. Analysis of the strategies for operating the SCPP under the UK grid requirement as regards to primary frequency response was performed using the validated SCPP model. The results show that using turbine throttling approach, extraction stop or condensate stop individually was not sufficient to meet the grid requirement. A combination of turbine throttling, extraction stop and/or condensate stop can achieve a 10% increase in maximum continuous rating (MCR) of the power plant within 10 seconds to 30 seconds of primary frequency change as required by the UK grid.The dynamic model of SCPP was integrated with a validated and scaled-up model of PCC. Analysis of the strategies for operating the SCPP integrated with PCC under the UK grid requirement as regards to primary frequency response was undertaken. The results show that the stripper stop mechanism is not sufficient for the 10% MCR required for the primary response. The results show that the combination of stripper stop mechanism with extraction stop can meet the 10% MCR requirement for integrated plant operating at above 75% of its full capacity. The throttling and stripper stop configuration only barely meets the demand at full load capacity. The condensate stop combination with the stripper stop mechanism on the other hand could not meet the frequency response requirement at any load level

Energy, exergy, and economic evaluation of integrated waste incineration facility with a thermal power plant

Increased waste production and poor waste management have created severe negative environmental impacts. Waste incineration is a way to produce energy and decreases environmental impacts; however, this technique cannot be considered independently as a source of power generation because of its low performance. This study aims to evaluate the integration of a waste incineration system with a natural gas-fired power plant in terms of energy, exergy, and economic points. As a result of the proposed configurations, in addition to promoting efficiency and net power production, some equipment is removed from power plants. Efforts are made to increase the accuracy of simulation results by paying attention to the combustion process in boilers and predicting the actual working condition of feed water heaters. Results showed that the hybrid scheme improves electricity generation by up to 2.87 MW and boosts energy, and exergy efficiency by up to 0.32%, and 0.3%, respectively

Energetic and exergetic study for cross-corrugated membrane-based total recovery exchanger for ventilation

Indoor air quality is an important component of the air conditioning of buildings due to its major effect on the health of the occupants, thus the air supplied to these buildings by the ventilation system should be sufficient, clean and healthy. A most promising development was the heat recovery system which offers better thermal energy efficiency and comfort with adequate fresh air. An energetic and exergetic analysis has been conducted on a cross-corrugated membrane based total heat exchanger core for ventilation of single dwellings. In order to enhance the sensible and latent effectiveness of the heat and mass transfer intensification was achieved by selecting Polyethersulfone for the membrane material, and a cross-corrugation arrangement of different dimensions for the primary surface exchanger. The design was tested against a ventilation air volume flow rate for an individual household; from 85 to 100 m³/hr. The dimensions of the exchanger were based on the polymer core being developed by Redring-Xpelair, Peterborough UK, with core dimensions of width and length both 250 mm, and a range of heights 100 – 500 mm. The cross-corrugated design of the test core had triangular openings with pitch lengths of 5, 10 and 25 mm. The ambient conditions were for a cold and humid winter in the UK. The ambient temperature test values were 2, 4, 6, 8 and 10 °C, and the inlet air velocities in the core were 0.5, 1.0, 1.5 and 2 m/s, with Reynolds numbers not exceeding 2200. CFD studies were conducted to investigate the thermal-fluid performance of the core, the Transition-SST model was used in the simulations within ANSYS Fluent 17.1 software and was validated using experimental data in the literature. The proposed model performed successfully in this study and proved that it was compatible with the test conditions. The exergetic analysis was conducted using the IPSEpro modelling software, by creating a system consisting of membrane core, a domestic dwelling, fresh air and exhaust fans. The energetic analysis results were the basis of the IPSEpro modelling to determine the exergy, the exergetic efficiency and exergy destruction in the system. The study concluded from both the energetic and the exergetic analysis that the membrane based exchanger core showed promising performance as a total heat and moisture recovery application with sensible and latent effectiveness values varying from 65% to 82%; and exergetic efficiency values varying from 30% to 60%, depending on core geometry and ambient conditions. The chemical exergy was the dominant factor in the performance in all cases, and the membrane core had the highest exergy destruction percentage comparing to the other system components. Decreasing the pitch length of the exchanger core intensified its performance, the 5 mm case showed the best performance, but there are likely to be difficulties in manufacturing such a compact core. But, and more directly, its use would mean unpleasant compromises due to the extremely higher pressure drop across such a core even at low Reynolds numbers. The 10 mm case gave a better performance than the 25 mm, but not substantially different, therefore, the optimum choice lies between the better heat and mass transfer performance of the 10 mm case and the lower pressure drop and relative ease of manufacture of the 25 mm