Simulation and calculations of processing and transportation of hydrocarbon streams in spreadsheets

Transcription

1 Energy Producton and Management n the 21st Century, Vol Smulaton and calculatons of processng and transportaton of hydrocarbon streams n spreadsheets O. A. Omelchenko 1, D. A. Rychkov 1, V. V. Prytkov 1, D. E. Ukrantseva 1, A. G. Kasperovch 2 & M. V. Ovsyankn 2 1 OOO TyumenNIIgprogaz, Russa 2 OOO Gazprom pererabotka, Russa Abstract Modern software packages for smulaton of technologcal processng and transportaton of hydrocarbon streams are generally not well suted for use by non-traned professonals due to ther hgh functonal content, complexty and hgh cost of operaton. In response to engneerng communty needs, the authors developed ther Mcrosoft Excel based tools for modelng technologcal processes and performng stand-alone calculatons of component-fractonal composton, physcal and chemcal propertes, matter and component processng balances, as well as modelng thermal and hydraulc regmes of transport of hydrocarbon condensate streams n ol and gas felds. Model development and calculatons n the package are mplemented n the form of user-defned functons and functonal procedures (macro-procedures). The number crunchng procedures are programmed n CodeGear Delph and compled as a DLL lbrary. The functonalty of ths lbrary and macro-procedures n the Mcrosoft Excel envronment s acheved va add-on fles. The underlyng computatonal model s based on known thermodynamc laws and correlatons and the authors orgnal methods. In partcular, rectfcaton s smulated va a sgma-functon, whch generally characterzes the effcency of mass transfer. The proposed tools are not ntended to replace more sophstcated thermodynamc smulatons but rather provde suffcent functonalty and accuracy of calculatons together wth a short learnng curve to a broad range of professonals famlar wth the Mcrosoft Offce envronment. Keywords: smulaton of technologcal processng and transportaton of hydrocarbon streams, software packages for smulaton. ISSN (on-lne) WIT Transactons on Ecology and The Envronment, Vol 190, 2014 WIT Press do: /eq140782

2 846 Energy Producton and Management n the 21st Century, Vol. 2 1 Introducton Currently there s a large range of products for common technologcal and thermodynamc smulatons (technologcal modellng systems TMS). These nclude Aspen HYSYS (AspenTech), GIBBS (OOO Topenergobznes ) GazKondNeft (NTF Termogaz ) and others. All of these systems allow developng complex systems out of elementary parts and enable detaled technologcal calculatons. They nclude numerous computatonal methodologes whch must be specfed before the user proceeds wth calculatons. However, there s often a need to address multvarate balance problems wth smultaneous output and vsual dsplay of results for analyss that can be effectvely mplemented n Mcrosoft Excel. It s for ths purpose that a modellng methodology has been developed for feld preparaton and processng of hydrocarbons based on confgurable outputs and qualty streams of thermodynamc and statstcal selecton (dstrbuton) functons of the components (FSC). Based on ths methodology, the authors created computatonal models of refneres and other hydrocarbon processng facltes. 2 Concepts methodology A basc characterstc of hydrocarbon streams whch s consdered n the methodology s the component- fractonal composton (CFC) mass (percent) content of ndvdual components to pentanes nclusve and more narrow 10 degree (at bolng pont) fractons (pseudo- components). Each mass transfer unt (and even a large processng unt) s represented as a node of separaton (NS) wth one nput stream and two output (products) flows: easy (relatvely steam) flow and heavy (lqud) flow. Fg. 1 shows a technologcal example of a condensate stablzaton unt (CSU) n the data stream model of two NSs. The model development methodology s based on the representaton of a technologcal feld-preparaton scheme n the form of a set of nterrelated bnary splt nodes (ncludng recyclng) whch smulate mass transfer devces. Here detaled calculatons of mass transfer processes are replaced wth calculatons usng generalzed functons of component selecton whch characterze the effcency of NS. FSC s a (percentage-based) relaton of selecton coeffcents (SC) for components (fractons) of raw materals n the heavy output of the NS consdered. Thus the SC component (fracton) s calculated by the formula: where: L K L L G K 100% (1) n G L s the lqud selecton coeffcent for the -th element of CFC; G s n G s the content by the content by weght (or mass) of lqud separaton flow; weght (or mass) of nput (raw) flow n NS. WIT Transactons on Ecology and The Envronment, Vol 190, 2014 WIT Press ISSN (on-lne)

3 Energy Producton and Management n the 21st Century, Vol Gas relef Ol-gas mxture Wde lght-hydrocarbon fractons (WLHF) Stable condensate. Gas relef Ol-gas mxture К - 1 f(s,t 50 ) Е-1 f(p,t) Wde lght-hydrocarbon fractons (WLHF) Stable condensate Fgure 1: Converson of a technologcal scheme of CSU nto a stream model. FSC dfferent processes are shaped lke a s- shaped curve (see Fg. 2). The effcency of mass transfer of NS depends on the curve slope, whch n turn depends on technologcal parameters of a model element consdered. For example, for a stablzaton column the slope vares sgnfcantly dependng on the reflux rato and the number of theoretcal plates (see Fg. 3) When the temperature and pressure condtons of a technologcal apparatus change then the FSC of the correspondng NS move equdstantly wth a good degree of certanty along the temperature axs (see Fg. 4). To characterze ths change of FSC we use the temperature of a key Tb50 component whch s the bolng pont of a hypothetcal component unformly dstrbuted (50%) between the products of a node of separaton. Our model development experence suggests that the best way to get an equdstant mage WIT Transactons on Ecology and The Envronment, Vol 190, 2014 WIT Press ISSN (on-lne)

4 848 Energy Producton and Management n the 21st Century, Vol. 2 Fgure 2: Features selecton of components of dfferent technologcal elements. Fgure 3: Component selecton functons for the stablzaton column for a reflux rato of 1 and dfferent numbers of theoretcal plates. WIT Transactons on Ecology and The Envronment, Vol 190, 2014 WIT Press ISSN (on-lne)

5 Energy Producton and Management n the 21st Century, Vol Fgure 4: Change n the component selecton functons of the stablzaton column (10 theoretcal plates, reflux rato 1) wth the temperature. n the operatng condtons of a technologcal NS s the closest analytcal expresson that descrbes the shape of the FSC. Such s a sgmod functon: 100 K exp S Tb Tb (2) where: K s the selecton coeffcent of -th component n the lqud (heavy) product NS,%; S s the slope factor for an ndvdual component (fracton); Tb s the bolng pont of the -th component, C. Enterng ndvdual slope factors s logcal, snce FSC s not a smooth lne, but rather a mult-jont unt wth nodes placed at the ponts of components (fractons). From (2) we compute the slope factors: S ln 1/ 1- K / Tb Tb Evaluatng these factors for varous setups (for example, a dstllaton column, reflux ratos for varous and dfferent number of theoretcal plates) s an mportant task. Ths process forms a so-called unt passport. The formaton of a passport may be a result of the processng of expermental structures of output products (retrospectve calculatons) or may be done by usng the TMS for new modes (predctve calculatons). When the mass transfer characterstcs change then sgmod profle s modfed accordngly. Ths s acheved by usng varous (3) WIT Transactons on Ecology and The Envronment, Vol 190, 2014 WIT Press ISSN (on-lne)

6 850 Energy Producton and Management n the 21st Century, Vol. 2 methods of nterpolaton of array S of several varables responsble for the mode of operaton of the unt. For processng the expermental CFC dfferent smoothng algorthms can be used, whch are also ncorporated nto the methodology. Based on the above, the followng stages can be emphaszed when workng wth each node of separaton n the model: 1. Adaptaton usng retrospectve expermental data, specal research work, gettng a passport of NS; 2. Solvng the man problem of NS calculatons,.e. gettng the materal and component balance (MCB) for a specfed mode of NS. Let us dwell on the second stage. The problem of determnng FSC for a desred mode s reduced to the teratve search for sgmod slope factors that satsfy a gven specfcaton of one of the products of separaton. Ths can be physcal and chemcal propertes of the stream and qualty/yeld metrcs of products n mass terms. Ths methodology ncludes a number of calculatons used n specfcatons as parameters. One may also offer economc and other non-system ndcators, whch gves the potental to develop methodology. The calculaton tself s performed as follows. Frst, usng methods of multcrtera nterpolaton of slope factor data one fnds new sgmod slope factors specfc to a gven mass transfer mode. Then usng sngle parameter soluton technques (dchotomy or a combnaton of dchotomy and secant methods) a key parameter Tb50 s found. By usng the slope factors and Tb50 n each teraton one recovers FSC. The fnal soluton s found by satsfyng the accuracy requred for gven specfcatons of the NS. In some cases, one may need to perform a specfc task: the selecton of thermobarc separaton parameters (pressure and temperature) for a known value of ether of them n order to acheve a gven specfcaton. In such ( thermodynamc ) NSs the same methods are used but the estmated FSC are replaced by functons wth SC numercally equal to the coeffcents of thermodynamc equlbrum. As an equaton of state the well-known cubc equaton of Peng-Robnson s chosen. Ths method can be used for recovery of the raw stream of a separator based on a known composton of the lqud product and separaton condtons (pressure, temperature). 3 Software composton In the process of shapng ths methodology the followng nterconnected tools have been created for developng smulaton models: 1. Add-n fles for Mcrosoft Excel. They contan screen settng forms for macro-procedures, macro-procedures mplemented n language VBA; declaratve references to functons and functonals whose code resdes n a specally created DLL. There are also add-ns, whch offer user-defned functons mplemented n VBA (Vsual Basc for Applcaton). 2. A dynamc DLL lbrary mplemented n the programmng envronment CodeGear Ths lbrary mplements functons and functonals whose WIT Transactons on Ecology and The Envronment, Vol 190, 2014 WIT Press ISSN (on-lne)

7 Energy Producton and Management n the 21st Century, Vol declaratons (and ther lnk wth Excel) are found n add-n fles provded. A functon computes a sngle result. The noton of functonal assumes some processng, whch results n ranges of data, and even more massve calculatons on separately allocated sheets. A number of such complex functonals are used for adaptaton and adjustment of models. For example, these functonals model dfferental condensaton and balance of reservors. The practce of creatng functonals s currently expandng. They are mplemented drectly n VBA for processng of reports, texts unloadng of TMS, etc. 3. Xls program communcaton patterns and TMS. Such combned models provde more detaled calculatons of hydrocarbon processng plants and transmt results to an xls model for analyss. After performng the necessary analyss and correcton n the xls model through teratve exchange of data wth TMS one can solve the problem of recovery of raw materals wth a known composton of one of the products. It should be emphaszed that the methodology presented here does not rely on the conventonal approach for buldng models out of elementary consttuents. Models are set up usng forms, custom menu, and nteractve buttons. All settngs are n the form of a certan structure or worksheet n a Excel workbook, from whch the model gets parameters for nodes of separaton and all phases of the computatonal process. To understand the process of constructon of such models one needs good Mcrosoft Excel sklls, technologcal expertse, famlarty wth the contents of the toolkt. To facltate the process of famlarzaton wth the proposed technology, a number of documentaton packages, test models and gudelnes have been created. 4 Overvew of physcal and chemcal propertes of bult-n models and mathematcal algorthms 4.1 Physcal and chemcal propertes The basc concept of our methodology and most of the calculatons used are gven n [1]. In addton, the authors systematzed documentaton updates n the form of gudelnes for Gazprom pererabotka ( Gudelnes on the calculaton of the composton, propertes, modes of transport and processng of hydrocarbon streams balances condensate and ol and gas felds, MR , , 450). To start performng calculatons one needs to obtan nformaton on physcal and chemcal propertes of CFS n the rght format (data ranges for Mcrosoft Excel): molecular weght, bolng pont, calorc, crtcal parameters (pressure and temperature), acentrc factor, characterstc volume (separate array for calculatng the densty of the procedure COSTALD). These data can be taken from reference sources, obtaned expermentally or calculated usng the features bult nto the software. In partcular, there are functons for calculatng crtcal propertes (temperature and pressure), acentrc factor, calore and others for fractons. The known correlatons [2] are used for ths purpose. Models often WIT Transactons on Ecology and The Envronment, Vol 190, 2014 WIT Press ISSN (on-lne)

8 852 Energy Producton and Management n the 21st Century, Vol. 2 consder mxng of flows wth sgnfcantly dfferent propertes of fractonal composton. The authors have created a functonal for calculatng propertes of mxed flows wth dfferent mxng rules. To calculate the vapor lqud equlbrum, the authors have taken as a bass the cubc equaton of state (EOS) of Peng-Robnson [2 5]. It should be noted that n order to adapt varous algorthms to experment the authors have appled the most approprate calculaton of crtcal propertes of fractons usng ther orgnal solutons. Thus, beng based on the propertes of the CFS descrbed below, the software lbrary mplements the followng propertes of a hydrocarbon stream (ncludng the assgnment of thermobarc condtons): molecular weght, densty, calorfc value, vscosty, surface tenson, pour pont, cloud pont, octane, cetane number of propertes on the saturaton lne (ntal bolng pont, vapor pressure, dew pont temperature, pressure dew pont), gas and gas condensate rato and others. Note that for the densty of the lqud flow the Hanknson-Thompson (COSTALD) method was chosen [6]. The authors have modfed algorthms for saturaton lne propertes very extensvely. The past experence has shown that usng tradtonal methods (e.g., the Peng-Robnson EOS) frequently results n falures and the lack of relable results. The authors approached ths problem by usng approxmate nterpolaton technques for the mole fracton of the lqud phase to the specfed boundary phase transton (lnear and splne nterpolaton). These results are more stable and adequate, gvng greater confdence n the calculatons. 4.2 Models of expermental studes When determnng FSC n NS one may use as specfcatons for the desred flow both physcal and chemcal propertes and qualty ndcators derved by expermental methods. Accordngly, the authors have developed and mplemented computatonal models of the most common expermental studes. Among them are: dfferental condensaton, fractonal dstllaton by Engler, pressure of saturated vapor pressure, methods of degassng volatle lqud hydrocarbons. We have created and are now mprovng a model for the evaluaton of a gas condensate reservor. In ths model the materal balance calculaton s done by breakng down the reservor nto cells n whch the pressure vares n accordance wth the specfed bottom hole pressure. In addton, the model accounts for removal of the lqud phase at certan maxmum condensate saturaton. Almost all exstng models employ the algorthm for calculatng vapor lqud equlbra usng the cubc Peng Robnson equaton. Models are constantly beng mproved n accordance wth expermental data and current knowledge of the subject. 4.3 Mathematcal algorthms As descrbed above, n the search for solutons at varous FSC n both calculaton-drven models and n the case of adaptaton of expermental data, the authors use sngle-parameter and mult-parameter nterpolaton technques. Among them are methods of lnear nterpolaton, cubc splne nterpolaton, and WIT Transactons on Ecology and The Envronment, Vol 190, 2014 WIT Press ISSN (on-lne)

9 Energy Producton and Management n the 21st Century, Vol Shepard s mult-parametrc nterpolaton. To fnd solutons when obtanng FSC we use dchotomy and combnatons of dchotomy and secants. In some cases, models use Mcrosoft Excel solutons. In order to process the composton data and handle calculaton results, the authors ntroduce smoothng technques (the Gauss wndow, local polynomal approxmatons, smoothng of the sgmod). 5 Development The authors beleve that ther methodology for calculatng materal and component balances of hydrocarbon streams on the bass of FSC has broad prospects. On the one hand, t can be used by dfferent specalsts (engneers, project and research scentsts); on the other hand there s a real possblty of extendng the algorthms to other felds (for example, enterng the economc parameters of qualty) and related ndustres (petrochemcals). We are currently n the process of developng techncal documentaton (gudelnes, measurement technques, standard organzatons, etc) for ths methodology. The development of computatonal models of expermental studes s a separate promsng drecton, snce such studes are often tme-consumng and costly. The authors fnd further development of the algorthm for assessment calculaton of a gas condensate reservor very nterestng. Naturally, the authors do not clam ther model to be very accurate. However, f the adopted model shows a good correlaton wth experment and calculatons from more detaled models (e.g., Eclpse 300, Schlumberger), then ths multvarate assessment methodology wll be n demand. Therefore, the authors beleve that the proposed methodology has a good potental for future development. 6 Concluson Ths report sets out the man provsons of the orgnal methodology developed by authors for modelng technologcal processes, calculatons of composton, physcal and chemcal propertes, materal and component balances of processng and thermal hydraulc modes of transport of hydrocarbon streams of gas, condensate and ol felds. The prncples and means of the mplementaton n the publc envronment (Mcrosoft Excel spreadsheets) are also outlned. The proposed solutons allow a broad range of professonals (ncludng those who do not have access to modern technologcal modelng systems) to perform qute complex, mult-step and multple calculatons. The extensve functonalty and the user-frendly spreadsheet nterface provde opportuntes for the most dverse range of tasks, as well as applcaton of smlar tools n related felds. References [1] Kasperovch A.G., Magarl R.Z., Balance calculatons n the desgn and plannng of hydrocarbon processng gas condensate and ol and gas felds, [n Russan], Unversty Book House : Moscow, WIT Transactons on Ecology and The Envronment, Vol 190, 2014 WIT Press ISSN (on-lne)

10 854 Energy Producton and Management n the 21st Century, Vol. 2 [2] Bruslovsky A.I., Phase transformatons n the development of ol and gas felds, [n Russan], Publshng house Graal : Moscow, [3] Bruslovsky A.I., Nugaeva A.N., Theory and practce study propertes of natural hydrocarbon systems, [n Russan], ZAO Askonlne : Moscow, [4] Reed R., Prausnts J., Sherwood T., Propertes of gases and lquds, [n Russan], Chemstry : Lenngrad, [5] Ueyles S., Phase equlbra n chemcal engneerng, [n Russan], Mr : Moscow, [6] Hanknson R.W., Coker T.A., Thomson G.H., Get accurate LNG denstes wth COSTALD. Hydrocarbon Process: Unted States, 62, pp , WIT Transactons on Ecology and The Envronment, Vol 190, 2014 WIT Press ISSN (on-lne)