TRANSIENT FLOW ANALYSIS OF FAST VALVE CLOSURE IN SHORT PIPELINES

Abstract: The present paper presents an analysis of transient pressure behavior in short pipelines for tanker's loading at a marine terminal. The analysis was focused on the interaction of several dynamic components that are present in the line, such as check, flow control and block valves, pump and pipe elasticity. The purpose of the analysis is to maximize flow rate through the line thereby minimizing tankers dockage time, without exceeding the allowable pressure limits. A commercial software was employed in the calculations that were able to reveal the complex interaction of the dynamic components present.

ANALYSIS OF THE ENERGY CONSUMPTION BY CHANGING THE PUMP ARRANGEMENT

Abstract: In the present work an optimization study was conducted with the objective of providing pipeline operators with a simple, spreadsheet-based computational tool to help decrease the electrical energy consumption associated with a particular transport operation. The methodology proposed encompasses the construction of a database of information on the pipeline regarding pumping power consumption, for all possible pumping arrangements and flow rate ranges considered viable for the pipeline. This database is fed to a spreadsheet programmed to calculate the minimum pumping cost for a particular operation. This calculation takes into account, the volume of product to be transported, start and finish times, fluid properties, and the possibility of the existence of a low and a high electricity tariff based on geographical location and time of the day. The methodology was applied to the ORBEL II pipeline in Brazil, and two case studies were conducted. Significant cost savings were obtained by the use of the methodology developed.

COMPORTAMENTO DE PULSOS DE PRESSÃO EM TRECHOS DE DIÂMETRO REDUZIDO DE DUTOS DE TERMINAIS MARÍTIMOS

Abstract: In a shipping terminal, the pipeline in the pier usually has a diameter smaller than the main pipeline diameter. This diameter reduction amplifies the effects caused by hydraulic transients. It was noticed during simulations that check valves placed in the pier may introduce some error in the maximum pressure when it was modeled in a conventional fashion. The dynamic check valve model had been added to a commercial pipeline simulation software and the results was compared with a similar model using the method of characteristics. Considering a real state shipping terminal case, it was proved even a pipeline that works with low pressure and smooth elevation profile needs a detailed valve modeling to prevent the calculation of unreal pressure values in the region with diameter reduction.

ANÁLISE DE TRANSIENTES DEVIDO A FECHAMENTO RÁPIDO DE VÁLVULAS EM DUTOS CURTOS

Resumo: Ao acionar uma válvula de segurança em um duto curto com alta vazão são provocados pulsos de pressão no duto, gerando o fenômeno conhecido como Golpe de Aríete. Em decorrência, a sobrepressão resultante pode vir a ultrapassar a máxima pressão de operação da tubulação, causando sua falha mecânica. O presente trabalho tem como objetivo identificar as variáveis envolvidas neste fenômeno e determinar a importância de cada uma para o caso de um duto real.

DETERMINAÇÃO DE VOLUMES EM OPERAÇÃO DE DRENAGEM DE OLEODUTOS

Resumo: Nas operações de manutenção de oleodutos ou de seus equipamentos muitas vezes torna-se necessário o esvaziamento total ou parcial do duto. O planejamento desta operação requer o conhecimento prévio dos volumes drenados nos pontos de manutenção para definição mais precisa dos recursos necessários à remoção do produto.Com este objetivo foi desenvolvido uma ferramenta capaz de determinar os volumes drenados apenas com as informações contidas no perfil de elevação do duto, geralmente importado do GIS. Isto é possível se considerarmos o oleoduto em repouso onde somente as forças de corpo agem no fluido.O presente trabalho apresenta uma planilha para determinação de volumes drenados que permite estabelecer a sequência ideal de drenagem considerando os locais possíveis de isolamento. Para validação do cálculo é realizada uma comparação dos resultados obtidos com uma ferramenta comercial de simulação de oleodutos e com um caso real de operação de drenagem.

SIMULATION OF HORIZONTAL PIPE TWO-PHASE SLUG FLOWS USING THE TWO-FLUID MODEL

Abstract: Slug flow occurs in many engineering applications mainly in the transport of hydrocarbon fluids in pipelines. The intermittency of slug flow causes severe unsteady loading on the pipelines carrying the fluids, this gives rise to problems in design. Therefore, it is important to be able to predict the onset and development of slug flow as well as slug characteristics. The present work consists in the simulation of two-phase flow in slug flow through horizontal pipes using the two-fluid model in its transient and one-dimensional form. The advantage of this model is that the flow field is allowed to develop naturally from any given initial conditions as part of the transient calculation; the slug evolve automatically as a product of the computed flow development. Simulations are then carried out for a large number of flow conditions that lead a slug flow.

ESTUDO DO COMPORTAMENTO DE SISTEMAS DE ALÍVIO EM DUTOS DE TERMINAIS MARÍTIMOS

Abstract: In order to reduce operational costs, maritime terminals work with high flows transferring product between ships and in shore tanks. To protect the pipeline from any hydraulic transient, relief systems are commonly installed in strategic positions. During the project stage, computational simulation is widely used as auxiliary tool to determine the kind of valve and the place where the relief system must be installed. The present work points out the importance of the kind of valve chosen and its location along the pipeline, and shows that these factors affect directly the surge pressure produced by the valve closure. Besides, it compares a conventional spring-loaded relief valve behavior to a rupture disc one, making use of commercial program tools and employing a model based on the method of the characteristics.

MODELAGEM DINÂMICA DE VÁLVULAS DE RETENÇÃO EM TERMINAIS MARÍTIMOS

Resumo: A transferência de óleo e derivados entre terminais marítimos e navios é realizada por oleodutos que são formados basicamente por uma estação de bombeamento, dutos de transporte, tanques de envio e recebimento do produto e demais acessórios, como válvulas de controle, bloqueio e retenção. Como nos procedimentos de carga e descarga de navios é comum que a coordenação da operação seja compartilhada tanto pela equipe de terra como pelo pessoal do navio, existe a possibilidade de que uma válvula numa extremidade do duto seja fechada com as bombas, na outra extremidade, ainda operando, gerando o fenômeno conhecido como golpe de aríete. Assim, quando uma válvula na extremidade é indevidamente fechada com as bombas ainda operando, espera-se observar uma onda de sobre-pressão se deslocando em sentido contrário ao escoamento e sendo gradativamente reduzida, até atingir a pressão de descarga da bomba. Porém, a existência de uma válvula de retenção na descarga da bomba pode mudar significativamente este comportamento, podendo gerar pressões superiores às normalmente esperadas neste ponto. O presente trabalho utiliza um programa comercial de simulação de escoamentos em dutos para caracterizar a existência deste fenômeno através de uma modelagem dinâmica das válvulas de retenção. É estudada a influência do diâmetro, do comprimento do duto e do tipo da válvula de retenção na elevação de pressão durante o transiente de fechamento indevido de uma válvula de bloqueio. É demonstrado também que o tempo de fechamento da válvula de retenção, em relação à velocidade de propagação da onda de pressão, interfere de forma acentuada no perfil de máximas pressões geradas no transiente.

ANÁLISE DE TRANSIENTES EM LINHAS PARA ALTO-FORNO

Abstract: Blow processes for blast-furnaces lines are characterized by air flowing at high rates and temperatures, in ducts of large diameter and relatively small length. The improper closing of valves along of the line, blocking the flow, can lead to undesired phenomena, such as the appearance of a surge situation, which can damage the components of the blast-furnace system. The objective of the present work consists of analyzing numerically the flow and temperature field of a blow process for a blast-furnace in an iron and steel industry. The velocity, pressure and temperature fields are obtained through the solution of the conservation equations of mass, linear momentum and energy, using the finite difference method. The presence of several typical components in a blast-furnace system, such as axial compressors, anti-surge systems, block valves and regenerators, are considered. The effect on the turbo-blower and the performance of the protection systems are evaluated due to the transient operations provoked by the closing of valves in the pipeline, the coupling of different regenerators to the flow line and the interruption of the blast-furnace operation.

ANALYSIS OF THE TRANSIENT COOLDOWN OF SUB-SEA PIPELINES

Abstract: A precise analysis of the transient cooldown of subsea pipelines is crucial for offshore flow assurance, to avoid, for example, hydrate formation or wax deposition. Flow assurance in transportation lines, where column separation can occur due to large temperature drop coupled with large pressure drop, must also be addressed. Usually, pipeline thermal insulation is designed for steady state conditions. However, during shutdowns, the temperature drop experienced by the stagnant fluid is more pronounced, eventually reaching some critical temperature level, that can lead to flow line blockage and flow re-start problems. Thus, the determination of the temperature and pressure distributions along the pipeline under transient conditions is important to maintain the line operating safely. To determine the transient heat transfer in pipelines, the fluid flow conservation equations coupled with the heat conduction equation applied to the pipeline wall were numerically solved. The heat loss from the pipeline was determined by solving the transient heat conduction equation for the pipewall layers, utilizing a simple one-dimensional model in the radial direction. The coupled system was solved numerically employing the finite difference method. Transient analyses were performed for two scenarios. In the first one, the cooldown process of oil in a subsea pipeline was evaluated, with the effect of variable thermal properties on the temperature profile being investigated. The dependence of the temperature on the thermal conductivity and specific heat capacity was analyzed. In the second scenario, gas flows inside the pipeline, and the effect of temperature variation on a stagnant fluid is presented. Tests for different values of thermal diffusivity corresponding to new and old thermal insulations were performed.

Optimizing Energy in Orbel II Oil Pipeline

Abstract: Energy is the main expend of an operating pipeline, representing its major operational cost. Optimizing it represents decreasing energy losses that are possible to act on. This article presents a study of the process and economic effects of substituting traditional pressure control valves by medium voltage frequency variable drives in ORBEL II oil pipeline. Three driving configurations were chosen and its implantation costs detailed. Pipeline flow simulation software was used to study the process effects of the driving configurations application and to calculate the amount of energy spent using control valves and using velocity variable control systems. The difference was the energy savings, quantified in money according with the supplying energy contracts data and operational data. Finally, an investment analysis is done, regarding the energy savings and an estimative of overall implantation costs of drives.

UM MODELO PARA ANÁLISE DE ESCOAMENTO TRANSIENTE TÉRMICO EM GASODUTOS E SEUS COMPONENTES

Abstract: An innovative and useful computational code to simulate gas flow in pipeline networks was developed. The model is able to simulate compressible, thermal and transient flow. The program has, besides the pipes, the main components present in gas pipelines such as valves, compressors, heat exchanges, pipe junctions, etc. The mathematical model is based on the conservation principles of mass, momentum and energy, combined with the constitutive equations of each component. The solution of the conservation equations was handled by the finite volume method. A simple and efficient method is employed to solve directly the algebraic system. Several test cases were investigated in loops with different types of bifurcation and several combinations of supply and delivery positions. It was also analyzed the transient regime during the opening of relief valves installed along the pipeline. The results were compared with data available in the literature showing an excellent agreement.

ANÁLISE DAS VARIÁVEIS RELACIONADAS AO PROJETO DE OPERAÇÃO DE OLEODUTOS COM COLUNA CHEIA

Abstract: The objective of the current study is to analyze the variables related to operation of oil pipelines, avoiding column separation, through theoretical analysis and computational simulations, using commercial software. The positive and negative points of view of this modus operandi will also be considered. The operation of a pipeline avoiding column separation (whose original concept was to allow separation) may lead to changes in the relief systems or even require the replacement of pipe sections. Even in stopped pressurized pipes, one may observe variations in the pressure profile, due to temperature variation, mainly for heated pipes which, after a few hours, will cool and contract, turning the maintenance of pressure above the pumped product’s vapor pressure not possible. Another interesting point is that the selection of P-I-D parameters of the control valve controller located at the pipe extremity interferes in its set point that may lead to over-dimensioned and conflicting values.

PROCEDIMENTO PARA SIMULAÇÃO TERMOHIDRÁULICA DO PLANO DIRETOR DE DUTOS DE SÃO PAULO

Abstract: A significant part of the São Paulo’s pipeline network is located in the metropolitan region of the capital. The Pipeline Director Plan of São Paulo considers network modifications that include the shutdown of existent pipelines, the installation of new pipes and the relocation of others in new or existent routes in order to improve the standards of operation, maintenance and safety. Because the physical modifications also involve alterations of the logistic of products, the viability of these changes must be confirmed by computational simulation. The São Paulo pipeline network is the most complex of Brazil, involving the transport of fuel oil derivatives and natural gas. Thereby, it was necessary to set a standard methodology that allows that the thermohydraulic simulation can be done in the short period of time available. In the present paper is made a general description of each pipeline/system and is also presented the basic information necessary to perform the simulation. Here are discussed the premises adopted and the operation sceneries for both the steady and unsteady states. Based on this information, for each pipeline/system are developed computational models to be used in two commercial pipeline simulation programs, commonly used by the industry. The simulation results attempt to show if the logistic programmed can be completed and if the pipeline system operates safety in all the sceneries. Additional information, as the hydraulic head gradient, charts of maximum and minimum pressures and volumetric flow are also given. When operational problems are detected due to limitations of the system, different alternative solutions are given in order to assure the programmed logistic.

GAS PIPELINES OPTIMIZATION ROUTINE

Abstract: The growth of Natural Gas in Brazil is due mostly because it’s a cleaner and more versatile energy source than oil. This growth demands new technology development both in the production and in the transportation of natural gas. In the transportation field, an important question is the consumed power at compression stations throughout the gas pipes. These compressors’ operational costs represent such an high percentage of the total costs that even small enhancements may cause a substantially high cutback on the cost of the operation. Thus, a greater power consumption leads to a lower profit margin and an even larger pollutant emission. The operation of a gas pipe or a network of gas pipes is based on the maintenance of a certain gas inventory in the system that allows the supply of current and future demands. The compression stations are operated in order to keep this inventory. However, due to the system's complexity, the selected operational points for the compression stations are experimentally-based and are usually not optimal values. The purpose of this work is to develop an optimization routine using accessible computational tools, capable of calculating flow parameters and to minimize the total consumed power at compression stations of gas pipes. Parameters like diameter, length, elevation profile, equipment and arbitrated operational conditions are inserted in an MICROSOFT EXCEL™ spreadsheet and serve as input for a MATLAB™ routine that calculates pressure and flow profiles at steady state, as well as consumed power and gas at the stations. This routine allows proper treatment of complex gas pipes networks or those with several intermediate sample points and compression stations. From this calculated initial condition, the developed optimization routine, using minimization functions available at MATLAB™, defines the ideal discharge pressures that represent a new valid operational condition, whose power and fuel consumptions are minimized, decreasing operational costs and pollutant emissions. The optimal solutions of three cases are presented, including an actual section of GASBOL (Brazil-Bolivia gas pipe), evidencing the usefulness and flexibility of the developed methodology.

PROCEDIMENTO OPERACIONAL PARA REDUÇÃO DO CONSUMO DE ENERGIA EM OLEODUTOS

Abstract: The study’s objective establishes a procedure to avail the energy consumption used in the oil pipeline pumping stations and define the most economic operational modes that can optimize the energy usage, reducing the costs, and raising the enterprise’s competitive. It’s notorious that energy cost applied in pump station plants and terminals represents a high contribution of the hydrocarbon products transfer price. The power monitoring and the calculation of the specific energy consumption are necessary for a high effiency transport system.The security conditions also must be considered due the study nature. To accomplish this objective a spreadsheet was developed to simulate the pipeline operational conditions in the steady state, taking in account the several paths or alignments between terminal and refineries, the pumps arrangement, the change of product. The spreadsheet calculates the power required to each pipeline condition and respective volume rates that are associated with the energy prices to result the specific energy cost of the product being transported. With this information and the pipeline diary program which lists the volumes transported, it’s possible to determine the operational plan that would result the minor total cost. This methodology was applied in the OSVAT, a Brazilian crude oil pipeline, for all possible pump arrangements, with the volume rates allowable for each alignment. A considerable cost reduction was observed depending on selected pump arrangement; a new solution was tested using an economical study.

UMA ALTERNATIVA PARA A SIMULAÇÃO NUMÉRICA DE ESCOAMENTO TÉRMICO TRANSIENTE DE GÁS EM REDES DE DUTOS

Resumo: Foi desenvolvido no presente trabalho, um novo e prático código computacional para simular escoamentos transientes de gás em redes de dutos, na presença de vários tipos de componentes, como válvulas, compressores, trocadores de calor, bifurcações, etc. O modelo matemático é baseado nos princípios de conservação de massa, quantidade de movimento linear e energia, além das equações constitutivas para os diversos componentes. A solução das equações de conservação foi tratada utilizando o método das diferenças finitas. Diversos casos testes foram analisados utilizando circuitos com diferentes tipos de bifurcações e várias combinações de pontos de recebimento e entrega, localizados ao longo das linhas dos gasodutos. Os resultados dos testes foram comparados com dados disponíveis na literatura apresentando excelente concordância.

SIMULAÇÃO NUMÉRICA DE ESCOAMENTO INCOMPRESSÍVEL AO LONGO DE UMA VÁLVULA DE ALÍVIO DE PRESSÃO

Resumo: Dos vários modais de transporte de fluidos, tanto líquidos como gasosos, os dutos se destacam pelo baixo custo e pela segurança operacional. Dentre os itens cruciais no projeto de uma linha de transporte para operar com segurança encontram-se as válvulas de alívio, sendo o coeficiente de descarga essencial para a seleção destas. Este coeficiente depende das características do escoamento: separação, acumulação e recirculação, as quais dependem do projeto da válvula e dos valores das condições de contorno impostas. Dessa maneira, no presente trabalho, uma predição numérica do escoamento ao longo de uma válvula de alívio de pressão é realizada, utilizando um modelo estático, sendo o escoamento considerado axi-simétrico. O escoamento turbulento e incompressível foi modelado através de dois modelos. A distribuição da pressão e a força resultante no disco da válvula são comparadas com dados experimentais e numéricos disponíveis na literatura, apresentando concordância razoável. O coeficiente de descarga é determinado como uma função de diferentes aberturas da válvula.

A NUMERICAL MODEL ABOUT THE DYNAMIC BEHAVIOR OF A PRESSURE RELIEF VALVE

Abstract: Pressure relief valve is one of the most important devices used on the security of pipelines, since it is responsible to guarantee the integrity of the installations. Generally, the response and behavior of a relief valve during its transient is unknown by users, who employ simplified and static analysis to design the pipeline, further, the information provided by manufactures is limited. In this work, a numerical dynamic model of a spring load pressure relief valve was developed using the principles of conservation of mass and momentum in combination with solid dynamics equation. The valve discharge coefficient was numerically determined by employing a simplified twodimensional model with FLUENT. The dynamic characteristics of the valve were examined with regard to the pressure set point, disc lift and spring parameters, during the transient discharge flow.

ESTUDO TERMOHIDRÁULICO PARA AMPLIAÇÃO DE CAPACIDADE DE OLEODUTOS

Abstract: This paper intent to assist the development of a oil pipeline expansion study. It will show that each pipeline has it's own solution, because it has several variables of technical, economical and environmental order, as well as several ones of political nature.

ANALYSIS OF THE DISCHARGE COEFFICIENT OF A SPRING LOADED PRESSURE RELIEF VALVES DURING ITS DYNAMIC BEHAVIOR

Abstract: Direct acting spring loaded pressure relief valve is one of the most important devices to ensure security to pipeline oil transport. However, relief valves’ manufactures generally only provide information on valve characteristics under full opening stage, which is obtained under steady state regime, therefore, valve and flow’s transient behavior are neglected. Understanding the transient behavior of relief valves is crucial because critical conditions may be attained, damaging the pipeline. In order to overcome this lack of information, a direct acting spring loaded pressure relief valve’s computational model was developed. A simplified two dimension model was built based on the valve geometrical and constructive characteristics. Further, a dynamic equation, which defines the valve disc position, was implemented. From the solution of the transient form of the conservation equations, the velocity and pressure distributions were obtained, allowing the determination of the discharge coefficient versus valve opening under its transient state. Comparisons with one-dimensional integral approach model were performed to evaluate the model.

CRITERIA AND PROCEDURES TO OBTAIN THE MAXIMUM OPERACIONAL PRESSURE PROFILE IN PIPELINES

Abstract: This study analyses the most reliable criteria and procedures used for thermal-hydraulic simulations to acquire the maximum pipeline pressure and the influence of different configurations on the pipeline project. The maximum pressure profile of a pipeline must obey certain criteria and procedures to ensure the operational safety, obeying the standard ASME B31.4. To obtain the maximum pressure curve, a computer model of the pipeline is created and the pressure along its length is simulated. The simulation calculates the steady state of each product transported by the pipeline and the transient of possible operational failures. The pressure control valve (PCV), installed at the downstream of pumps or at the upstream of the receiving terminal can alter the maximum pressure results if they are active during the transient state. The controller's PID of a PCV can also affect the results. If the PCV fails, the fail safe mode (open, close or remain at the same position) also have to be considered. The interlocks also change the maximum pressure results when considered. The interlocks can be local (linked directly to a pressure gauge near a pump, for example) or remote (for instance, a satellite connection that stops the pump when the receiving end block valve closes). The remote interlock should only be consider if the communication of the remote system if reliable. This paper presents the requirements to obtain the Maximum Allowed Operating Pressure (MAOP) and studies the criteria and procedures to obtain the Maximum Operating Pressure (MOP) and the Maximum Transient Pressure (MTP).

DEFINING INDICATORS TO MOTORIZE BLOCK VALVES AIMING TO REDUCE POTENCIAL LEAKAGE APPLIED TO OSBRA PIPELINE

Abstract: The discussion about motorizing block valves is a constant point being brought up when it is intended to control or reduce the amount of liquid leaking in the event of a pipe rupture. During the pipeline's project stage the installation of blocking valves along the pipeline must be taken into consideration to meet the operation and maintenance requirements as well as to reduce the potential amounts of volume being leaked. In existing pipelines, the main concern is the definition of which valves are candidates to be motorized. In both situations criteria should be established to define this choice. A math algorithm was developed to define the potential leakage due to gravity along the pipeline profile where the influence of a valve over another is verified, as well as the contribution of the check valves existing in the pipeline. The present work defines a parameter based on the extension protected by the valve and the reduction of the potential leakage. This parameter is then fed to a worksheet where the efficiency indicators are calculated to each valve eligible to be motorized. It also takes into consideration factors relative to the valve location, such as the environmental sensitivity, risk assessment, social diagnosis and device's proximity to contingency resources. Finally, after considering all the above aspects, it's possible to come up with a final classification, recommending specific valves to be priorized on an eventual process of motorization adequacies. This methodology was applied, experimentally on a pipe segment of TRANSPETRO's São Paulo-Brasilia pipeline – OSBRA , where it proved to be an important technological and management tool.

PIPELINE OPERATORS TRAINING AND CERTIFICATION USING THERMOHYDRAULIC SIMULATORS

Abstract: The continuous pipeline operators training and certification of the Transpetro's Pipeline National Operations Control Center (CNCO) is an essential task aiming the efficiency and safety of the oil and derivatives transport operations through the Brazilian pipeline network. For this objective, a hydraulic simulator is considered an excellent tool that allows the creation of different operational scenarios for training the pipeline hydraulic behavior as well as for testing the operator's responses to normal and abnormal real time operational conditions. The hydraulic simulator is developed based on a pipeline simulation software that supplies the hydraulic responses normally acquired from the pipeline remote units in the field. The pipeline simulation software has a communication interface system that sends and receives data to the SCADA supervisory system database. Using the SCADA graphical interface to create and to customize human machine interfaces (HMI) from which the operator/instructor has total control of the pipeline/system and instrumentation by sending commands. Therefore, it is possible to have realistic training outside of the real production systems, while acquiring experience during training hours with the operation of a real pipeline. A pilot Project was initiated at Transpetro – CNCO targeting to evaluate the hydraulic simulators advantages in pipeline operators training and certification programs. The first part of the project was the development of three simulators for different pipelines. The excellent results permitted the project expansion for a total of twenty different pipelines, being implemented in training programs for pipelines presently operated by CNCO as well as for the new ones that are being migrated. The main objective of this paper is to present an overview of the implementation process and the development of a training environment through a pipe simulation environment using commercial software. This paper also presents their potential as a pipeline operators training and certification tool. Additionally, it mentions important points gained during our experience in this project.

GAS ALLOCATION PLANS BASED ON FAILURES SCENARIOS – PETROBRAS – GAS& POWER SECTOR

Abstract: The purpose of this paper is to present gas allocation plans developed for Petrobras Gas & Power Sector, considering failure to supply scenarios that could occur along gas supply network. Those scenarios, as well as the associated contingency plans, were identified and validated by an experienced team, composed by engineers and operators from different PETROBRAS sectors. The key issue of concern was the anticipation of possible undesired scenarios that could imply on contract shortfalls, the evaluation of possible maneuvers, taking into account best gas delivery allocation. Different softwares were used for the simulation of best gas supply allocation and for the verification of delivery pressure and conditions for final consumers. The ability of being capable of dealing with undesired or crisis scenarios, based on suitable anticipation levels, is, nowadays, a highly valuable attribute to be presented by competitive corporations, for best crisis management and prompt recovery response. Those plans are being used by Gas & Power Gas operation Control Centre and as an input for reliability modeling of gas supply chain.

BRAZILIAN GAS NETWORK COMPUTATIONAL MODEL FOR RELIABILITY ANALISYS

Abstract: This paper presents a discussion of the alternatives and strategies used in the thermo-hydraulic simulation of the Brazilian gas pipeline network. It analyses the advantages and disadvantages of each approach and the option used in order to meet the demands of the overall reliability analysis developed by the Gas Reliability Management Sector of PETROBRAS.

TRANSIENT SIMULATION OF NATURAL GAS CITYGATES STATIONS

Abstract: The demand of natural gas in the Brazilian energy market is increasing very fast over the few years and it was necessary to enhance the operational performance and safety of the gas distribution. The perfect operation of the natural gas citygate stations is essential to guarantee the delivery of natural gas for the end users like local distribution companies, thermoelectric power plants and large industrial customers within the contracted marketing conditions. These stations receive natural gas directly from high pressure pipelines and reduce the pressure using regulation valves that provoke a temperature reduction due the Joule-Thompson (JT) behavior, typical of natural gases. This temperature loss is compensated by forcing part of the gas flow through water/glycol bath heaters that use natural gas as fuel in the heating process. Usually the downstream gas temperature condition is controlled above a minimal set point while modifying the three-way valve position that regulates hot and cold streams flows. A numerical tool has been developed to simulate the dynamic process inside the natural gas citygate station, and proved to be a reliable tool to analyze the transient performance of the main equipments (filter, three way valve, heater, JT valve, relief valves) when submitted to abnormal conditions or changes in capacity. The methodology developed is able to handle a variety of citygate design.

OPASC PIPELINE OPTIMIZATION USING DRA

Abstract: The objective of this paper is evaluate the use of DRA for increase flow and optimize energy consumption under certain conditions, using as model the OPASC pipeline. The OPASC is batch pipeline located in the southern region of Brazil, used mainly for the transport of diesel, gasoline, ethanol and LPG. The pipeline is dependent on the seasonality of both the production and the demands of the sector. It usually presents an increase in demand in the summer and a decrease in the winter. This situation accounts for two of the pipeline major problems. During the peak season, the pipeline is operating on its maximum capacity, but still cannot supply with the market needs, causing an income loss. During the low season, the average flow causes the pipeline to operate using PCVs to control its flow and the pumps to operate at low efficiency points, causing unnecessary energy consumptions. The OPASC 10” is 197 km pipeline, from the REPAR refinery to the Tejaí terminal, with a delivery at the Guaramirim base, with receive most products at a smaller flow rate. The pipeline works with small batches, from 2 to 6 thousand cubic meters. The DRA was only applied on the gasoline and diesel batches, which are the most transported products. The DRA field test occurred on July 2010, and was sponsored by several sector of both Petrobras e Transpetro, such as: the Presidente Getúlio Vargas Refinery (REPAR), the Guaramirim Terminal (TEMIRIM), The Itajaí Terminal (TEJAÍ) e o National Operational Control Center (CNCO), located at Transpetro headquarters in Rio de Janeiro. Several batch plans and DRA concentrations were tested during the course of the test. This paper proposes the use of DRA to increase pipeline flow and to change operating conditions to optimize energy consumption. This works was based on a worldwide action supported by TRANSPETRO and involved several sectors of the company. The result gathered from both the field test and the hydraulic simulations support and verified the assumption made.

EXPERIMENTAL AND NUMERIC ANALYSIS OF SPRING-LOADED PRESSURE RELIEF VALE

Abstract: The majority of oil and refined-product pipelines in Brazil have their protection systems design based on pressure relief valves. Thus, the proper design and operation of these valves is essential to ensure the safety of pipelines and loading/unloading terminals during any abnormal operation conditions that generate overpressures. These valves work by relieving the internal pressure in case it exceeds a set value. In simple terms, the spring-type pressure relief valve has a disk which is pressed by a spring against the inlet nozzle of the valve. When the pressure rises, the force generated on the surface of the disc increases and, depending on the pressure relief valve set point, the force due to pressure overcomes the force exerted by the spring, causing the disk to rise and discharge the fluid through the outlet nozzle to the relief line, reducing the pressure level within the pipeline. Using this principle, the relief valve ensures that the pipeline is not subjected to high transient pressures, which could, otherwise, lead to pipeline or equipment rupture and possible product leakage. Despite its importance, the models commercially available to simulate the transient behavior of pressure relief valves do not present a satisfactory performance. The present paper presents an experimental study aimed at determining the dynamic behavior of a commercial spring-type relief valve. The valve was installed in a pipe loop where the flow was established. The valve and the loop were instrumented with pressure and flow transducers. The transient motion of the valve disc was measured with a fast-response displacement transducer. The transient in the flow loop was generated by the controlled closing of a block valve positioned downstream of the relief valve. The recorded transient data for disc position, upstream and downstream pressures, and discharge flow rates were compared with results predicted by different models for relief valve dynamic behavior implemented in a commercial pipeline flow simulation software.

CHOICE OF OIL BLEND TO IMPROVE PIPELINE TRANSPORT

Abstract: In Brazilian oil pipelines, the number of different oils transported is enormous and keeps on growing. The number of heavier crude oil is increasing worldwide, as well as in Brazil, and both the pipeline companies and the refineries are trying to adapt their system to this new reality. The standard procedure for oil pipelines is trying to transport the lightest possible oil blend, so as to increase flow and reduce operating costs. While this method works, it requires companies to buy lighter oil, what can be significantly more expensive. This paper intent to show that, depending on the pipeline and on the blend physical properties, using a heavier and more viscous blend can cause the flow to be higher or the specific energy needed to be equal or higher than a lighter blend. This phenomenon is explained using the Reynolds number and the different flow regimes. Using a hydraulic pipeline simulator, a theoretical pipeline and varying the blend transported within the pipeline, it will be shown that for higher viscosities there can be a higher flow then the original blend transported on the selected pipeline. A second theoretical pipeline will show a pipeline configuration where the desire effect does not happens. Afterward, the results can be used to change the standard procedure for oil pipeline transport that is used today.

USE OF VARIABLE FREQUENCY DRIVE TO REDUCE ENERGY CONSUMPTION ON A MATURE OIL PIPELINE

Abstract: Reducing energy consumption has been an ever increasing concern for the oil industry, and the world in general. As energy costs keeps getting higher, any percentage of reduction can become a great economy in the operating costs. This paper analyses a mature oil pipeline. This pipeline has a 24 inches diameter, 360 kilometers, three pumping stations and a single product. All the stations have pressure control valves and pressure relief valves. The first pumping station has four main pumps, arranged in parallel, and the PCV are active during normal operation. All four pumps have slightly different curves from one another. This makes for an interesting analysis, since using a Variable Frequency Drives on one pump can, and will have different results from another. Since the pumps are in a parallel setting, a hydraulic study of the change of frequency must be a priority. This paper will focus on two main subjects: the technical study of using Variable Frequency Drives in one or more pumps at the first pumping station, without changing the operating flow but reducing the energy consumption of the station and an economic analysis to verify if the investment of installing one or more Variable Frequency Drives on the pumps is cost effective. The paper will show that even in mature pipelines, the use of Variable Frequency Drives is an effective and proven method for reducing the energy consumption without having to worry about changing the operating conditions of the pipeline.

AVALIAÇÃO DOS CONTROLADORES DAS ESTAÇÕES DE ENTREGA DE GÁS NATURAL ATRAVÉS DE SIMULADOR

Abstract: This paper presents the methodology applied in the research and development of a dynamic simulator for modeling the thermodynamic process in natural gas pressure reduction and delivery stations, also known as citygates. The simulator reproduces the real transient behavior of the main local equipments: three way control valves, pressure reduction valves, gas heaters, including the automation and control logic. A great focus is given in the numeric transient model of the indirect fired water bath heaters and the downstream station (delivery) temperature regulation using a PID controller that commands the three way valves. The citygate station process simulator was submitted for trials: (1) Validation of the equations of state and applied equipment formulation due direct comparison with commercial simulators; (2) Modeling an existent citygate station based on operational conditions that are defined at station design; (3) Operational simulation of a real citygate station using comparison with instrumentation data from supervisory system (SCADA). The study of the real citygate station shows the simulation of normal operational events and equipment fail scenarios like a sudden gas heaters pilot flame shut off. It will be discussed in the paper the simulator results obtained with the actual and modified temperature control and the impact on delivery temperature and fuel consumption produced by changing the automation logic and their parameters.

Alternativas para Redução de Custos Energéticos Operacionais em Oleodutos

This paper intends to give a brief overview of some cost reduction alternatives in oil pipelines, to optimize the pipeline operation. Four different alternatives are presented, based on previous studies made on existing pipelines, to demonstrate the response obtained with these solutions. Pipeline operation, especially on mature ones, tends to have a high operational cost, be by tradition, the aging of the installation, change of operational characteristics – such as nominal flow, product, or even flow direction – for which the pipeline wasn’t originally designed. The alternatives showed allow for an increase survival time of the pipeline, without resorting to major changes, such as replacement of pipes or adding pumping stations to the system. The alternative studied varies from no implementation cost to high installation cost or operational cost increase, depending on the system and the alternative chosen. From changing the pump arrays during operation or changing the products viscosity with different blends, that represent virtually no cost to the pipeline operation, to the use of VFDs, with a high installation cost or DRA, which increase the operational cost.

SIMULATION AND PLANNING OF PIPELINE EMPTYING OPERATIONS

ABSTRACT: Thepipeline pigging operation for emptying purposes is a common practice in the petroleum and gas transport industry. The emptying operation is employed for removal of the pipeline liquid products and substitution for an inert gas like nitrogen. This operation is necessary before pipeline maintenance or hydrostatic test procedures. The emptying operation applied for oil pipelines usually demands large volumes of nitrogen because of the pressure difference that is necessary to maintain the pig in a velocity that guarantee an efficient and safe operation. The nitrogen that is originally stored inside cryogenic vessels in liquid phase is pumped and vaporized to be injected into the pig launcher, after heating the gas. The gas injection and expansion inside the pipeline propel the pig, delivering the product that was in the pipeline at the receiver station. It is common to cut the nitrogen injection in a certain instant of the operation, before the pig reaches its destination. From then on, the expansion of the gasis able to finish the operation alone.

DYNAMIC BEHAVIOR OF SPRING-LOADED PRESSURE RELIEF VALVE: NUMERICAL AND EXPERIMENTAL ANALYSIS

The majority of oil and refined-product pipelines in Brazil have their protection system designs based on spring-type pressure relief valves. Thus, the proper design and operation of these valves is essential to ensure the safety of transport pipelines and loading/unloading terminals during any abnormal operation conditions that generate a surge pressure. In simple terms, these valves have a disk which is pressed by a spring against the inlet nozzle of the valve. When the pressure rises, the force generated on the surface of the disc increases and, depending on the pressure relief valve set point, the force due to pressure overcomes the force exerted by the spring, causing the disk to rise and discharge the fluid through the outlet nozzle to the relief line, reducing the pressure level within the pipeline. Despite its importance, most commercial applications do not present a specific model to simulate the transient behavior of pressure relief valves. This paper presents an experimental study aimed at determining the dynamic behavior of a commercial spring-type relief valve. The valve was installed in a pipe loop instrumented with pressure and flow transducers. The transient motion of the valve disc was measured with a fast-response displacement transducer. The transient in the flow loop was generated by the controlled closing of a block valve positioned downstream of the relief valve. The recorded transient data for disc position, upstream and downstream pressures, and discharge flow rates were used to compute the discharge coefficient as a function of opening fraction and the opening fraction as a function of time. Simulation models based on a spring-mass damped system were developed and implemented in a PID-actuator-control valve system. The systems were implemented in a commercial pipeline simulation program modeling the experimental loop employed in the tests. The numerical and experimental data of the block valve closure transient were compared displaying good agreement. Simulations results employing a generic relief valve model frequently used in simulations were also obtained revealing problems associated with this approach.

THERMAL-HYDRAULIC SIMULATION AS AN EVALUATION TOOL FOR THE CONTINGENCY RESPONSE STRUCTURE

The Transpetro Gas Pipeline System, the largest of the country, with more than 7.3 thousand kilometers, 129 delivery stations, 414 SDVs and several compressing stations, moves over 77.3 million cubic meters of natural gas. Highly linked with Brazil’s energy grid, during the dry period of the year a large part of the transported gas is used to generate around 6.4 gigawatts to power the country. It operates as an integrated mesh of pipelines running throughout the country, much like an energy grid system, but with the gas being stored in the pipelines. The gas pipeline operation is a continuous one, without interruption, and as such depends heavily on the maintenance of its contingency response structure, to solve any problem at the field so there are no deliveries impacts. Due to the company’s constant search for optimization, especially in regards to its operation and maintenance sector, a revision of the contingency response structure was studied to reduce costs linked to the activity. To this end, a study of the pipeline system requirement was commissioned. A part of this study was the evaluation of the system survival time (in regards to its deliveries commitment) in the case of incidental scenarios, focus mainly on inadequate Shut Down Valve (SDV) activation. This study was implemented simulating a normal system scenario and closing the system SDVs. The study evaluated the impact each valve had on the system and its deliveries, classifying each of them according to the system survival time, without human interference. The study result was used to determine in which region of the pipeline system a quicker intervention could be needed outside office hours.

TECHNICAL AND ECONOMICS STUDY FOR THE EXPANSION OF THE GASMIG PIPELINE

PUC-Rio/SIMDUT and GASMIG developed a technical and economic study for the expansion of the pipeline São Brás do Suaçuí (SBS) – Belo Oriente (BO), through thermo hydraulic simulations and economic calculations. The objective was to analyze and propose possibilities to increase the transport capacity of the pipeline for specific demands scheduled for 2015, 2017 and 2022, doing economic and technical comparisons of different possibilities. To make sure that the optimal economic solution for the problem is found, the methodology was developed dividing the problem in two steps, called preliminary and detailed. The first one was designed to analyze a bigger number of different solutions, filtering a big number of very different solutions to some winner cases and was applied only to the 2022 scenario. The second one (detailed) is then applied to the winner cases of the preliminary step. Two cases were chosen to be studied in details, with real budgets and with the analysis of the possibilities to meet the demands of the intermediary scenarios (2015 and 2017). The economics was checked and the best solution was selected. After this preliminary stage, two cases were chosen to be studied in details, with real budgets and with the analysis of the possibilities to meet the demands of the intermediary scenarios (2015 and 2017). It was used a commercial pipeline simulator software to perform this analysis. A numerical model developed to represent actual situation was tuned with real operational conditions. For each case, the model was upgraded with the alternatives selected for each year and a precise thermo hydraulic solution was obtained. The economics were checked and the best solution was found.

PROJETO DE ENGENHARIA DE SISTEMA PARA TESTES DINÂMICOS DE VÁLVULAS DE ALÍVIO EM DUTOS

Among the several transportation methods available, pipeline stands out due to its low cost and operational security. Changes in operating conditions generate undesirable effects such as sudden pressure rise to critical levels that can compromise the integrity of the pipeline. In this context, the relief valve has the function of maintaining the operating pressure within the specified range of design in order to ensure safety. The behaviors of the valve, i.e., the response time, and the behavior of the discharge due to opening, are key for proper definition of maximum resultant pressure values. This dynamic behavior is not currently established in standards and rarely available even by the manufacturer. The purpose of the present work is to develop a testing and certification system of pressure relief valves on an existing pipeline loop, by determining their static and dynamic behaviors in experimental installations 1:1 scale. Through this procedure, the characteristics of the relief valves will be better known, which will increase the reliability of future designs and operational safety checks of existing facilities.

CONDITIONING TRANPETRO GAS PIPELINE NETWORK TO THE BAÍA DE GUANABARA LNG TERMINAL NEW REGASIFICATION PROFILE

Petrobras Transporte S.A. – TRANSPETRO’s Gas Pipeline System, composed by 7.3 thousand kilometers, 135 delivery stations and 21 compressor stations, has a very seasonally dependent operation. Highly linked with the Brazilian energy grid, during the dry season of the year a large part of the 77.3 million cubic meters of natural gas daily transportation are used to generate around 6.4 gigawatts to power the country. Additionally, the ever increasing number of power plants and distribution companies around the country demand more and more gas to be offered to supply the system. Among the different sources of natural gas available, the LNG is the most flexible for such seasonal operation. In order to support this current demand and to attend future demands, the regasification ability of Baía de Guanabara LNG Terminal was increased in December 2012, by changing the regasification vessel that supplies the southeast portion of the gas pipeline network, from 14 to 20 million cubic meters per day. To prepare to receive the new ship, some tests were performed to determine the operational limits on system survival time without LNG supply during vessel exchange. This assessment involved two different issues. The ship change operation occurred during a period of high consumption, when the LNG terminal was needed to sustain the network inventory. A long period without this supply, caused by the exchange of LNG vessel, would affect the deliveries. On the other hand, the new ship’s commissioning curve would introduce a large amount of natural gas into the system during a short period of time, demanding that the deliveries absorbed such volume. Four planning scenarios were assessed based on some expected pipeline supply and delivery conditions. The work was important as a reference for future changes on operating supply units of TRANSPETRO gas pipeline system, showing the importance of pipeline simulation both as a planning tool for pipeline logistic problems and as operational support.

Deployment of a Gas Pipeline City-Gate Simulation Tool for Training Purposes

The appliance of Real Time Simulation (RTS) systems for gas pipelines is essential for supervisory and control rooms, providing safer and more efficient operations and complementing Supervisory, Control and Data Acquisition System (SCADA) functionalities. Another common usage of these softwares is for training purposes in order to simulate critical variations on system parameters or failure scenarios of the involved equipment, based on up-to-date operational conditions. Since the implementation of its RTS system for gas pipelines, the Natural Gas National Operational Control Center (CNCO/Gas) of Petrobras Transporte S.A. - TRANSPETRO has been facing the need of developing a more specific tool to simulate gas city-gate and their processes in details. Based on that, an initiative was launched and a tool called SimPE was developed with the additional intention of integrating it to the existent RTS system that simulates the thermo-hydraulic behavior of gas pipeline networks. This article presents a brief description of this RTS, including: real time monitoring module, predictive module, look-ahead module and trainer module. The development of the SimPE is described in four phases: (1) modeling an existent city-gate based on its equipment and historical operational conditions (prototype); (2) development of a new communication interface between SimPE and RTS to share the station process variables; (3) programming of city-gate failure scenarios through SimPE and verification of their impact on the gas pipeline during an RTS trainer session; (4) upgrade the simulator, creating three additional models aiming to cover the maximum possible number of different characteristics among the city-gates operated by TRANSPETRO. The simulator SimPE, sponsored and owned by TRANSPETRO, has been already validated and is able to reproduce real transient behavior of the gas city-gates’ main equipment, such as: filtering systems, shut-down valves (SDV’s), pressure control valves (PCV’s) and their failure mode, flow metering systems and gas heaters, including their automation and programmable logic control. It is also discussed in the present work the development and integration of these different simulation tools (RTS and SimPE) with SCADA through a shared data platform that connects all three softwares using Modbus-RTU protocol and giving the trainee a reproduction of city-gates real operation with the highest possible fidelity. Finally, the whole work has been conceived and carried out in order to support and to improve CNCO/Gás’ training and certification processes.

PIPELINE THERMO-HYDRAULIC SIMULATOR APPLIED TO DELIVERY POINTS’ GAS QUALITY DETERMINATION PROCESS

Determining the gas quality of natural gas delivery points is not only compulsory for transmission pipeline companies, in order to comply with the national regulatory agency (ANP) ordinances, but also mandatory from the business perspective, for both the transmission fee and the commodity price depend on the energy delivered, in terms of Higher Heating Value (HHV). So, the energy or HHV is calculated through the analysis of the flowing gas by devices known chromatographs, for each delivery point or city-gate. However, since not every point has a field-installed gas chromatograph, the pipeline operator needs to link actually calculated HHVs to the city-gates that have no local analysis. These calculated HHVs are obtained from devices installed in other stations such as hubs or receipt, delivery and interconnection points. Taking into account all the regulatory, commercial and financial issues, and in order to perform these links precisely, TRANSPETRO has decided to use a pipeline thermo-hydraulic simulator. The technique consists of considering significant variables of the pipeline, namely the volume balance, receipt and intermediate pressure values and the pipeline inventory, to achieve the most accurate results on linking HHVs to delivery points. This methodology represents a noticeable improvement if compared to the previous one, which only considered the volume balance. In spite of that, there is still some room for improvement, since the current simulation considers a steady state, and it is known that the flow, pressure and inventory changes may influence the final result. Therefore, the future challenge is to evolve from steady state to transient state simulation, which must come along with an increased reliability of the field automation to succeed.

VALIDATION OF THERMO-HYDRAULIC SIMULATION MODEL FOR OIL PIPELINE TRANSPORTING HEATED FLUIDS

The study of operations and security conditions at the transport of oil and derivatives in pipelines is strongly leaned on thermo-hydraulic computational simulations. Due to characteristics of oil production or derivatives refining, they can be presented with temperatures above the environment. However, in other situations, typically in the marine fuel case, it is necessary the fluid to be heated, and with its viscosity reduced, be easily transported. When the goal is defining operational conditions, it is desirable to check the impact of the temperature, mostly, in the transport rate. On the other hand, when the aim is the operational security, the minimum and maximum temperatures of the process are the subject. The minimum temperature may be due to fluidity point, which, if reached, may cause a pipeline blockage. The maximum temperature is limited by the temperature of the pipeline’s mechanical design. The pipeline simulation process used in the temperature computation involves physical and mathematical modeling that introduces simplifications. However, these formulations are established in the literature and the uncertainties introduced in the results are known. On the other hand, to complete the formulation, it is needed information about the thermophysical properties (thermal conductivity and specific heat) of the material (fluid, pipeline, thermal isolation, and ground) and about the environment temperature. Since the uncertainties on these data can be high, this paper carries out a sensibility analysis applied to real pipelines, in order to define which parameters should be acquired with higher precision. In addition to these variables, the correlations used for the calculation of the internal heat transfer coefficient present great impact on the results. For heavy crude oil and fuel oil, the flow may happen in the laminar band with high Prandtl numbers, producing situations where there is a high thermal development length, reducing the reliability of the correlations. Some correlations found in the literature are used in this study to determine which one produces the best results. With the stage set, a computer simulation of a real pipeline transporting heated fluids was conducted, using the history of process variables as input data and the key variables identified in the study of sensitivity were adjusted to reproduce, as faithfully as possible, the temperature variation along the pipeline.

IS VELOCITY FLOW A LIMIT TO INCREASE CAPACITY? A STUDY CASE

There are several possibilities to guarantee reliable and safe liquid transport (mostly fuel) between two points. When the solution applicable is based on pipeline transport, two scenarios may be applicable: a green field new pipeline or capacity expansion of a brown filed pipeline. Literatures show that pipeline velocities normally vary between 1.0 and 2.0 m/s. This range of line velocity generally yields the most economical solution corresponding to the lowest combined CAPEX and OPEX in Brazil. When considering using an existing pipeline with as build diameter and wall thicknesses based on the original design condition and flow capacity the modification and operation cost and operation limits at a different flow rate must be evaluated and compared against building a new pipeline. Industrial standards and specifications normally do not restrict specify the suitable velocity limits to be used in pipeline design and operation. Researches and codes provide some recommendations on maximum allowable line velocity based on erosion and static electricity problems in pipeline transport of liquid. Some other considerations associated with higher line velocity in pipeline design and operation include, e.g. surge pressure created during transient conditions, and the conflicts between lower NPSHa and higher NPSHr at higher flow rates, etc. In addition to these technical issues that need to be taken into consideration, the focus should be on the increase of OPEX due to energy/fuel consumption increase and CAPEX increase for new pump stations or pump additions. This paper presents a case of capacity increase where the flow velocity will reach 3.6 m/s. Even considering the higher cost of higher energy consumption the project still remains economical.

ECONOMIC AND OPERATIONAL EVALUATION OF THE USE OF DRAG REDUCING AGENTS IN A PIPELINE

The use of drag reduction agents (DRA) can be a decisive factor in determining the technical and economic feasibility of new pipelines projects, meeting the demands not foreseen and seasonality accommodation without large investments in infrastructure. Knowing the friction reduction mechanism and its impact on the operating procedure of existing products is essential in order to have the guarantee of the benefit for your application. Most of the works published report field experiences obtained from its application, seeking to determine the influence that internal and external factors have on the polymer. Knowing these effects is essential for better application performance. However, few authors have sought to identify the best way to operate an existing pipeline with DRA, with either an increase in capacity or an energy reduction. Operationally, the use of drag reducing agents may decrease the currently used arrangement of pumps, or even the complete shutdown of a pumping station. In this context, the use of drag reducers may be a suitable solution for decreasing power consumption in fluid transport pipelines of petroleum and derivatives. This paper presents a case study of the application of drag reducing agents in a Brazilian high-energy pipeline. It features five intermediate pumping stations and three withdrawal points along its nearly one thousand kilometer stretch. With the aid of a computer simulation software, it is proposed a methodology to evaluate the best application condition, minimizing pump costs, polymer volume and meeting the scheduled demand of the month. This methodology first sought to validate the computational model of the pipeline. It was made a historical survey and inserted into the simulator, in order to reproduce faithfully a monthly operation. A sensitivity analysis is performed to determine which pump stations are most relevant. It was established an initial concentration of polymer to be injected in the sending refinery, aiming the reduction of arrangement or total shutdown of the subsequent station and keeping volume delivered on all points. The other bases remain working according to the operation of the month. This procedure is then repeated for the other bases, resulting in a combined and continuous injection, minimizing the operating costs. An economic evaluation is finally performed to quantify the benefits of this application. A reduction in energy consumption of 49% was noticed, and considering the costs with DRA, the monthly movement had a 35% drop in the total costs of operation.

METHODOLOGY FOR CAPACITY CALCULATION APPLIED TO THE BRAZILIAN NATURAL GAS PIPELINE NETWORK

The Brazilian law number 11909 from 2009, commonly known as Gas Law, improved the regulatory rules related to free access to the infrastructure of natural gas transportation and imbued the National Oil & Gas Agency (ANP - Agência Nacional de Petróleo, Gás Natural e Biocombustíveis) the attribution to set standards and criteria to determine the capacity of transport gas pipelines. Despite the legal framework establishing several definitions for transport, booked, available and idle capacity, no technical procedures to calculate those capacities were defined. International experience shows that several different methodologies were used accordingly with the specifics characteristics of legislation and gas pipeline infrastructure on each country. In the Brazilian case, the legislator concerns in establishing the several definitions of capacity were focused on optimizing the transport infrastructure and promoting free access to it. This access must occur by a transport service contract, using firstly the available capacity (firm and extraordinary transport service contract) until it is fully used. In this way, a correlation can be identified between optimized technical values, linked to the gas flow on the pipelines, and commercial values, defined by contracts. With this focus, there is no meaning on declaring a single and static capacity for a pipeline as a whole and, in fact, the important values are the capacities for every delivery point were the gas would effectively be available for booking. With this in mind, ANP developed a two-year project in partnership with PUC-Rio/SIMDUT that raised the main characteristics of all the transport gas pipelines, defined the minimum requirement for a thermal hydraulic flow simulator, standardized the capacity reports for the transport companies, created and documented models for all national gas pipeline to use thermal hydraulic flow simulation and defined the methodology to calculate capacity. This methodology follows a step-by-step system where initially the maximum transport capacity is calculated for each delivery point, without violating any technical or contractual condition of the pipeline network. To insure operational flexibility, the methodology subtracts from this calculated number the value related to an Operational Margin, specific to each pipeline or network. The resulting capacity is the commercial capacity. The available capacity is the difference between commercial capacity and booked capacity for each delivery point. Using mutually excluding available capacities as access criteria assures the methodology consistency. This must be applied to all delivery points and is linked to the physical and contractual configuration of the pipeline or network. Any modification implies recalculating the capacities and publishing the new values. The methodology was applied to the national gas network, using historical delivery values, and the results were registered in standardized tables, validating the feasibility of the project. Complementary projects will be developed to incorporate each transport company definition of operational margin and to prepare the future transport contracts be in accordance with the methodology.

THE DEVELOPMENT OF A COMPUTATIONAL TOOL FOR GEORREFERENCED CLASS LOCATION ASSESSMENTS

The Class Location concept is adopted by most gas pipeline standards as a way to mitigate risk of third party damage in densely populated areas. These standards define a straightforward process to determine the Class Location, as well as the Maximum Allowable Operating Pressure (MAOP) based on the population living close the pipeline. While this process is well established, there are several challenges faced by pipeline operators when implementing it. These challenges include: (a) locating and classifying buildings close to the pipeline, (b) counting the number of buildings making use of the sliding mile concept and (c) correlating the geographic position of the identified Class Location segments with the pipeline characteristics such as diameter, wall thickness, material and pressure test level. This paper presents a method to perform Class Location Change assessments along pipelines using computational tool aided by georeferenced map imagery and counting algorithms. The tool also provides a framework where right-of-way inspection teams are able to locate and classify buildings near the pipeline. A building-based sliding mile have been implemented to appropriately count building and identify the current Location Class. Post-processing algorithms evaluate possible MAOP restrictions, such as pipe replacement and hydrotest. This methodology have proved to be effective by completing Class Location Assessments in 6500 km of gas pipelines.