Browsing by Subject "Petroleum -- Refining"
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Item Modeling of a hydrogenated vacuum gas oil hydrocracker(Texas Tech University, 2003-05) Govindhakannan, JagannathanHydrocracking is used in the petroleum industry to convert low-quality feedstocks into highly-valued fransportation fuels such as gasoline, diesel, and jet fiiel. Hydrocracking is usually carried out in two stages. The first stage decomposes sulfurand nifrogen-containing compounds and hydrogenates the aromatics. The liquid fraction from the first stage is hydroisomerized and hydrocracked in the second stage. The primary objective of the present research is to develop a very detailed, fundamental, and molecular-level model for the second stage hydrocracking process. The modeling methodologies reported in the literature for the hydrocracking process thus far, describe the feed and product compositions based on the boiling range and the actual reaction network is reduced to a smaller number of reactions between the lumped species. The present approach applies the concept of single event kinetics to the hydrocracking process. In this approach, the various reactions involved in hydrocracking are considered in terms of fiindamental elementary steps involving carbocations. A computer algorithm, in which feed and product molecules, carbocations, and olefinic intermediates are represented by means of Boolean relation matrices and characterization vectors has been developed to generate the elementary reaction networks for paraffinic, naphthenic, and aromatic feed components. The standardized labeling algorithms for acyclic and cyclic hydrocarbon stmctures are developed. The network generation leads to a very large network of elementary reactions (>10^). However, due to the molecular nature of the approach, the number of rate parameters is kept within the tractable limits (<30) and the rate parameters are independent of the feedstock composition. Since the number of chemical species generated in the reaction network is very large, a certain degree of lumping is required to reduce the number of continuity equations for the components to be integrated along the reactor. The lumps should be chosen in terms of the present day analytical capabilities. The single event kinetic model, in the present work, considers the pure components and lumps according to the carbon number. Each lump is defined by its carbon number and the type of chemical structure that represents that lump. The type of chemical structures considered here are n-paraffins, iso-paraffins, mono-, di-, tri-, and tetra-naphthenes, mono-, di-, tri-, and tetra-aromatics, and naphtheno-mono-, naphtheno-di-, and naphtheno-tri-aromatics. Some lumps are individual molecules while most are collection of molecules. For the lump involving a collection of molecules, the properties of the lump are determined by averaging of the properties of each individual molecule comprising the lump. The model parameters are estimated from the synthetic product distribution data obtained from an industrial organization. A partially hydrogenated vacuum gas oil (VGO) is considered as the feedstock. The single event kinetic model is inserted into a homogeneous reactor model and the resulting continuity equations are integrated numerically along the length of the catalyst bed. The reactor simulation results are the temperature profile, composition profiles, and hydrogen consumption profile through the catalyst bed. The hydrogen consumption is calculated in a very rigorous way in the single event model, which is not possible with the lumped models. The reactor simulation results are consistent with industrial practice and published information. A profit optimization study is carried out to evaluate the aspects of the single event approach for process optimization. The molecular nature of the single event approach provides a framework to calculate important properties such as Reid vapor pressure (RVP) and octane number that are difficult to estimate using the lumped models.Item Refinery-wide optimization(Texas Tech University, 2000-05) Li, XuanA fuel-oriented refinery converts crude oil into various fuel products which are used for transportation and heating. It also provides feedstock for petrochemical plant. Based on a real refinery in the Gulf coast, a first-principle, nonlinear, plant-wide model was developed by integrating several single-unit models into an overall model. Detailed models were developed for two major units, crude unit and gasoline blending. The crude unit model is a non-stage-by-stage, steady-state model based on material balance and energy balance. The model calculates the yields and properties of the products based on the feed information and product specifications. The gasoline blending model calculates the complete set of gasoline specifications of three grades of gasoline from the information of gasoline blending stocks. Existing detailed models of fluidized catalytic cracking (FCC) unit and catalytic reformer were used in this work after minor modification. Simplified first-principle models were developed for other units in the refinery. Each single-unit model was benchmarked against the industrial data obtained from the refinery. In the refinery-wide model, the outputs of models of upstream units are used as the inputs to the models of downstream units. The intermediate streams are characterized in the overall model to provide necessary information for the models of downstream units. Detailed composition information of feeds to FCC unit and catalytic reformer is calculated. General properties, volume, weight, and specific gravity are calculated for other intermediate streams. A constrained nonlinear optimization was carried out using the developed refinery-wide model. The objective of the optimization is to maximize the daily revenue of the whole refinery. The decision variables are the collection of the process variables of each unit that has significant influence on the economy of whole refinery operation. The nonlinear and linear constraints in the optimization are the summation of constraints of each unit. Two operation modes, Summer Mode and Winter Mode, were studied. The optimal solutions obtained from refinery-wide optimization show that the revenue increase over the normal operating conditions is 4.5% for Summer Mode and 3.6%) for Winter Mode. The revenue from refinery-wide optimization is about 1.6% over single-unit optimization.Item Review of paraffin control and removal in oil wells using Southwestern Petroleum Short Course searchable database(Texas Tech University, 2000-12) Shahreyar, NomanThe SWPSC Association, Inc. is a non-profit educational organization. The objective of the SWPSC is to disseminate technical knowledge about existing oil field problems, innovations/improvements in different areas of petroleum engineering, on-going research projects, and field-proven techniques to efficiently and economically solve various field problems. As of date, forty-six volumes of the SWPSC conference proceedings have been published over the past 46 years, comprising of 1641 conference proceedings. An initiative is undertaken to archive the SWPSC conference proceedings in the electronic format. A detailed methodology is outlined to archive the SWPSC conference proceedings from paper to the electronic format and to develop the SWPSC searchable database with the use of previously available computer software. The SWPSC database, developed in this work, is tested for its efficiency to retrieve the technical papers on paraffin control and removal methods that have been presented over the past 46 years of the SWPSC annual conferences. An overview of mechanical thermal, chemical, and other published methods for paraffin treatment is provided after reviewing the 24 out of 36 retrieved SWSPC papers. In addition, the Society of Petroleum Engineers (SPE) image library is used to retrieve technical papers on paraffin treatment methods from the SPE collection of technical papers. After reviewing 19 out of 310 SPE technical papers, a summary of thermal, and chemical methods for paraffin control is outlined. The paper retrieval efficiency of both of these technical paper databases is compared and analyzed for retrieving papers related to paraffin control and removal methods.