Modular tool for the simulation of compressor trains for oil and gas applications

AbstractRecently, in the oil and gas extraction and transportation field, much attention has been paid both to increase efficiency and to reduce the environmental impact of the extraction techniques that, by now, consists mainly on Enhanced Oil Recovery processes based on gas or water injection into the reservoirs. Thus, compressor trains are a crucial part of the overall plant, and they require precise performance estimation during the whole oilfield lifespan, when production rates and compression demands significantly change. For this reason, in compression plant design and in-service behavior prediction, modular simulation codes turns out to be the best choice respect to tools for specific plant configuration, since they provide flexibility without losing accuracy.In this paper, a new modular tool for compression plant simulation is described; it is based on a wide database of centrifugal compressors and a library of elementary components that can be freely assembled to build any plant's configuration, regardless of its layout. The code's numerical solver is the implementation of a trust-region Gauss-Newton method, called TRESNEI, which possess a larger convergence region than standard Newton methods.The performance of the code has been tested on two compression train arrangements with both series and parallel-mounted compressors; comparison with the solution of the test cases obtained with a dedicated pre-existing in-house code, shows a good matching between the results. Computational speed and robustness of the new code is also shown

On affine scaling inexact dogleg methods for bound-constrained nonlinear systems

Within the framework of affine scaling trust-region methods for bound constrained problems, we discuss the use of a inexact dogleg method as a tool for simultaneously handling the trust-region and the bound constraints while seeking for an approximate minimizer of the model. Focusing on bound-constrained systems of nonlinear equations, an inexact affine scaling method for large scale problems, employing the inexact dogleg procedure, is described. Global convergence results are established without any Lipschitz assumption on the Jacobian matrix, and locally fast convergence is shown under standard assumptions. Convergence analysis is performed without specifying the scaling matrix used to handle the bounds, and a rather general class of scaling matrices is allowed in actual algorithms. Numerical results showing the performance of the method are also given

TRESNEI, a Matlab trust-region solver for systems of nonlinear equalities and inequalities

The Matlab implementation of a trust-region Gauss-Newton method for bound-constrained nonlinear least-squares problems is presented. The solver, called TRESNEI, is adequate for zero and small-residual problems and handles the solution of nonlinear systems of equalities and inequalities. The structure and the usage of the solver are described and an extensive numerical comparison with functions from the Matlab Optimization Toolbox is carried out

Synthesis of organofluorine compounds using a falling film microreactor : process development and kinetic modelling.

Master of Science in Chemical Engineering. University of KwaZulu-Natal, Durban 2016.South Africa is rich in valuable ore, including fluorspar (calcium fluoride), a principle feedstock used to synthesize hydrofluoric acid and a wide range of other fluorochemicals. As part of a wider initiative to promote local beneficiation of fluorspar, the primary purpose of this investigation was the synthesis of two valuable fluorochemicals, namely 1,1,2,3,3,3-hexafluoropropyl methyl ether (HME) and methyl-2,3,3,3-tetrafluoro-2-methoxypropionate (MTFMP). A secondary objective was to develop and identify suitable kinetic models as well as the associated kinetic parameters for the systems by means of least squares regression of experimental data. Two reactors were used in this study: the first, a gas-liquid continuously stirred semi-batch glass reactor was used for preliminary investigations (prior to the commencement of this work) to investigate the synthesis of HME. The second, a falling film microreactor (FFMR), a much more efficient medium for gas-liquid reactions, was used for the kinetic study. The FFMR was chosen as it has remarkable high rates of heat and mass transfer allowing for stringent control of reaction conditions as well as allowing for continuous process operation to be achieved. HME was produced by the reaction of methanol and hexafluoropropene in the presence of potassium hydroxide. MTFMP was similarly synthesized by the reaction of methanol and hexafluoropropene oxide in the presence of potassium and sodium hydroxide. The HME system was initially investigated in the gas-liquid glass reactor where the presence of HME as well as by-products of the reaction were successfully identified and quantified using gas chromatography-mass spectroscopy and gas chromatography (with the internal standard method), respectively. Results revealed that the reaction was rapid and highly exothermic and brought about negligible solid formation which deemed the system suitable for a FFMR. The yield of HME in the glass reactor varied between 19.21 and 53.32% with respect to moles of hexafluoropropene gas introduced into the system. The yields of the by-products were also quantified and the yield of alkenyl ether was found to vary between 0.07 and 1.03% while alkyl tetrafluoropropionate varied from 2.42 to 5.10%. These experiments were conducted at reactor temperatures between 12 and 28 °C, hexafluoropropene mole fractions in the feed between 0.41 and 0.83 and an inlet potassium methoxide concentration between 0.40 and 0.80 mol∙L-1. The novel synthesis of HME and MTFMP using a FFMR was then undertaken with the reactor operating in counter current mode. A 4 factor circumscribed Box-Wilson central composite design was used to design experiments, the four factors of interest being reaction temperature, liquid flowrate, either potassium or sodium hydroxide concentration, and finally, hexafluoropropene (for the HME system) and hexafluoropropene oxide (for the MTFMP system) mole fraction in the reactant gas. HME yields were found to be greater in the FFMR varying from 11.60 to 71.47% with the yields of the by-products varying from 0.11 to 6.99% for the alkenyl ether and 0.75 and 6.24% for the alkyl tetrafluoropropionate. Experiments were conducted at temperatures between 2 and 22 °C, hexafluoropropene mole fraction in the feed of 0.17 and 0.88, potassium methoxide concentration of 0.25 and 0.61 mol∙L-1 and a liquid flow rate of 0.50 and 5.50 mL∙min-1. The MTFMP system was handled similarly with its presence in the product being identified and quantified using gas chromatography-mass spectroscopy and gas chromatography (with the internal standard method), respectively. The yield of MTFMP was found to vary between 0.00 to 23.62% with respect to the moles of hexafluoropropene oxide introduced over the reaction period. The low yields were due to an inherently slower reaction which was not ideal for a FFMR given its low liquid residence time. Experiments were conducted at temperatures between 30 and 40 °C, hexafluoropropene oxide mole fraction in the feed of 0.16 and 0.84, potassium methoxide concentration of 0.15 and 0.65 mol∙L-1 and a liquid flow rate of 0.50 and 5.50 mL∙min-1. Results of the experiments showed that the MTFMP system was not suitable for the FFMR due to the low residence time of the reactant in reactor. A kinetic model was then developed for both the reactive systems from fundamental principles and executed in the MATLAB® environment (version R2012b, The MathWorks, Inc.). The kinetic model proposed for the HME system consisted of five reactions for which reference kinetic rate constants and activation energies were successfully identified. The resultant model did not predict HME concentrations adequately with an average absolute relative deviation percentage (AARD %) of 34.12 %. The reaction mechanism proposed for the MTFMP system was a two step reaction sequence which described the system satisfactorily well, the kinetic parameters required for this system was a reference kinetic rate constant, activation energy and Sechenov coefficient which were all successfully identified. The effect of reaction order on the pertinent reactions was also investigated and it was found that a second order description best fit the experimental data. The MTFMP model fit experimental data less agreeably with an AARD % of 170.00 % which was heavily weighted by data points with errors in excess of 500%, analysing the results exclusive of these points lead to an AARD % of 17.80 %