Browsing by Subject "Process integration"
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Item A novel approach to process debottlenecking and intensification: integrated techniques for targeting and design(2009-05-15) Al Thubaiti, Musaed MuhammadContinuous process improvement is a critical element in maintaining competitiveness of the process industries. An important category of process improvement is process debottlenecking which is associated with plants that have sold-out products while making a profit. In such cases, market conditions and the prospects for enhancing revenues and profits drive the process to increase production. To overcome the limitation of conventional sequential unit-by-unit debottlenecking approach, this work introduces a new approach. This new approach is simultaneous in nature and is based on posing the debottlenecking task as a process integration task which links all the design and operating degrees of freedom and exploits synergies among the units and streams to attain maximum debottlenecking. Additionally, this new approach considers heat integration of the process while simultaneously performing the debottlenecking. Because of the general nonconvexity of the process model, a rigorous interval-based bounding technique is used to determine the target for maximum extent of debottlenecking aside from the problem nonconvexity. Inclusion isotonicity using interval arithmetic is used to determine a global bound for the maximum extent of process debottlenecking. Focus is given to no/low cost debottlenecking such as modest changes in design and operating degrees of freedom. Two case studies are solved to illustrate the applicability of the new approach and its superior results compared to the conventional sequential approach. Intensification, to debottleneck a process and to improve process safety is also addressed in this work. A new definition and classification of intensification is introduced. This classification distinguishes between two types of intensification: single unit and whole process. Process integration and optimization techniques are used to develop a systematic procedure for process intensification. Focus is given to the interaction among the process units while enhancing the intensification of the process. A case study is solved to illustrate the usefulness of the developed approach.Item Equation-oriented modeling, simulation, and optimization of integrated and intensified process and energy systems(2016-12) Pattison, Richard C.; Baldea, Michael; Edgar, Thomas F.; Rochelle, Gary T; Bonnecaze, Roger T; Biros, GeorgeProcess intensification, defined as unconventional design and/or operation of processes that results in substantial performance improvements, represents a promising route toward reducing capital and operating expenses in the chemical/petrochemical process industry, while simultaneously achieving improved safety and environmental performance. In this dissertation, intensification is approached from three different angles: reactor design and control, process flowsheet design and optimization, and production scheduling and control. In the first part of the dissertation, three novel concepts for improving the controllability of intensified microchannel reactors are introduced. The first concept is a latent energy storage-based temperature controller, where a phase change material is confined within the walls of an autothermal reactor to improve local temperature control. The second concept is a segmented catalyst layer which modulates the rate of heat generation and consumption along the length of an autothermal reactor. Finally, the third concept is a thermally actuated valve, which uses small-scale bimetallic strips to modulate flow in a microchannel reactor in response to temperature changes. The second part of the dissertation introduces a novel framework for equation-oriented flowsheet modeling, simulation and optimization. The framework consists of a pseudo-transient reformulation of the steady-state material and energy balance equations of process unit operations as differential-algebraic equation (DAE) systems that are statically equivalent to the original model. I show that these pseudo-transient models improve the convergence properties of equation-oriented process flowsheet simulations by expanding the convergence basin in comparison to conventional steady state equation-oriented simulators. A library of pseudo-transient unit operation models is developed, and several case studies are presented. Models for more complex unit operations such as a pseudo-transient multistream heat exchanger and a dividing-wall distillation column are later introduced, and can easily be included in the flowsheet optimization framework. In the final part of the dissertation, a paradigm for calculating the optimal production schedule in a fast changing market situation is introduced. This is accomplished by including a model of the dynamics of a process and its control system into production scheduling calculations. The scheduling-relevant dynamic models are constructed to be of lower order than a detailed dynamic process model, while capturing the closed-loop behavior of a set of scheduling-relevant variables. Additionally, a method is given for carrying out these production scheduling calculations online and in "closed scheduling loop,"' i.e., recalculating scheduling decisions upon the advent of scheduling-relevant process or market events. An air separation unit operating in a demand response scenario is used as a representative case study.Item Germanium and epitaxial Ge:C devices for CMOS extension and beyond(2011-08) Jamil, Mustafa; Banerjee, Sanjay; Colombo, Luigi; Register, Leonard F.; Tutuc, Emanuel; Tsoi, MaximThis work focuses on device design and process integration of high-performance Ge-based devices for CMOS applications and beyond. Here we addressed several key challenges towards Ge-based devices, such as, poor passivation, underperformance of nMOSFETs, and incompatibility of fragile Ge wafers for mass production. We simultaneously addressed the issues of bulk Ge and passivation for pMOSFETs, by fabricating Si-capped epitaxial Ge:C(C<0.5%) devices. Carbon improves the crystalline quality of the channel, while Si capping prevents GeOx formation, creates a quantum well for holes and thus improves mobility. Temperature-dependent characterization of these devices suggests that Si cap thickness needs to be optimized to ensure highest mobility. We developed a simple approach to grow GeO₂ by rapid thermal oxidation, which provides improved passivation, especially for nMOSFETs. The MOSCAPs with GeO₂ passivation show ~10× lower Dit (~8×10¹¹ cm⁻²eV⁻¹) than that of the HF-last devices. The Ge (111) nMOSFETs with GeO₂ passivation show ~2× enhancement in mobility (~715 cm²V⁻¹s⁻¹ at peak) and ~1.6× enhancement in drive current over control Si (100) devices. For improved n⁺/p junctions, we proposed a simple technique of rapid thermal diffusion from "spin-on-dopants" to avoid implantation damage during junction formation. These junctions show a high ION/IOFF ratio (~10⁵⁻⁶) and an ideality factor of ~1.03, indicating a low defect density, whereas, ion-implanted junctions show higher Ioff (by ~1-2 orders) and a larger ideality factor (~1.45). Diffusion-doped and GeO₂-passivated Ge(100) nMOSFETs show a high ION/IOFF ratio (~10⁴⁻⁵) , a low SS (111 mV/decade), and a high [mu]eff (679 cm²V⁻¹s⁻¹ at peak). Moreover, diffusion-doped Ge (111) nMOSFETs show even higher [mu]eff (970 cm²V⁻¹s⁻¹ at peak) that surpasses the universal Si mobility at low Eeff. For Beyond CMOS devices, we investigated Mn-doped Ge:C-on-Si (100), a novel Si-compatible ferromagnetic semiconductor. The investigation suggests that the magnetic properties of these films depend strongly on crystalline structure and Mn concentration. On a different approach, we developed LaOx/SiOx barrier for Spin-diodes that reduces contact resistance by ~10⁴, compared to Al₂O₃ controls and hence is more conducive for spin injection. These ferromagnetic materials and devices can potentially be useful for novel spintronic devices.Item Mitigation of municipal biosolids via conversion to biocrude oil using hydrothermal liquefaction : a techno-economic analysis(2015-05) Bond, Cody Ray; Berberoglu, Halil; Greene, DavidIn this techno-economic analysis, we have shown that hydrothermal liquefaction (HTL) technology can be integrated with existing biosolids management facilities that utilize anaerobic digestion and biogas capture. The overall process converts raw sewage sludge to refinery-ready biocrude oil. The Hornsby Bend Biosolids Management Plant (HBBMP) in Austin, TX is used as a case study. First, the operation of the plant without any modification was modeled and validated with field data. A standalone HTL processing unit was then considered as an add-on to the existing infrastructure. Technical and economic parameters were obtained from literature and experimental data. The results showed that savings of about $32 M over current operation with a payback period of 4.35 years were achievable at HBBMP. A nation-wide implementation could result in production of almost 4.5 million barrels of upgraded biocrude oil per year while offsetting about 330,000 metric tons of CO2 equivalent greenhouse gas emissions annually.Item Process Design, Simulation and Integration of Dimethyl Ether (DME) Production from Shale Gas by Direct and Indirect Methods(2014-08-11) Karagoz, SecginAs the energy demand is increasing constantly, sustainable energy resources are needed to meet this demand and enable economic stability. In order to attain this goal, researchers continue to develop new technologies and methods in the field of sustainable energy. Over the last decade, the U.S has witnessed substantial growth in shale gas production. Consequently, shale gas has become a competitive feedstock for usage as energy and production of chemicals and petrochemicals. A valuable product which may be obtained from shale gas is dimethyl ether (DME). Dimethyl ether can be used in many areas such as power generation, transportation fuel, and domestic heating and cooking. Dimethyl ether is currently produced from natural gas, coal and biomass through synthesis gas as an intermediate. Recently, the attention to DME has increased because of its potential in addressing energy security and environmental problems. DME is produced conventionally through two steps (indirect process) which are methanol synthesis and dehydration of the methanol to DME. Another way to produce DME is the direct synthesis of DME from syngas. In order to use DME as a fuel alternative, it must be produced at low cost in large quantities. The purpose of this study is to develop a process synthesis, simulation, and integration of a shale gas-to-DME plant by direct and indirect methods. Techno-economic analysis is carried out to assess the profitability of the base-case processes under current market conditions. A sensitivity analysis is also conducted to evaluate the process profitability under variable market conditions. Finally, the both methods are compared in terms of the fixed capital cost, operating cost, return on investment, and CO_(2) and water impact. Indirect and direct process simulation of commercial DME plant was carried out by Aspen Plus. The shale gas feedstock was taken from one of the wells in Barnett shale play. The DME production capacities of the base cases for the direct and indirect processes were set to 3,250 tonnes per day. The direct and indirect process flowsheets were synthesized using five and seven main processing steps, respectively. Pinch analysis was used to conduct heat integration of the process. As a result of study, it was found that the direct method has advantage over the indirect method in terms of the fixed capital cost, operating cost, return on investment, and CO_(2) impact. The capital investment of the direct production method is 25% less than the indirect method. The direct method is more economically attractive than the indirect method. When a sensitivity analysis is considered, the prices of methanol and shale gas are the most important factors impacting the operating cost. The contribution of energy integration on the ROI of the direct method is approximately 2.25%. The ROI of the indirect method is improved by 1.83% after energy integration. In contrast to the other criteria, the indirect way has significant advantage over the direct way by producing almost 1760 ton/d water. The direct method produces less CO_(2) emission than the indirect method because it uses dry reforming to convert CO_(2) to syngas.