Refinery planning & scheduling

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In this paper, we discussed on the important things that are to be taken care of while modelling planning and scheduling tools. One should not lose focus on the primary objectives of running these tools. The planning tool acts as a bible - it is the single most important tool from which directions are to be taken.

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Refinery planning & scheduling

  1. 1. Refinery Planning & Scheduling- Plan the Act. Act the Plan.By Sowmya Santhanam WIPRO TECHNOLOGIES
  2. 2. EXECUTIVE SUMMARYDue to the record high and fluctuating crude prices, refineries are under extreme pressure to cut downoperating costs. This has led to a great focus on the downstream supply chain management processes andtools, which when effectively used, result in significant benefits for the refinery. This paper talks about thebest practices that are followed while modelling the planning and scheduling tools. The planning tools areused with the single objective of maximising the margins from the refinery. The scheduling tools help inimplementing the plan on a day to day level.Currently, complete automation of scheduling tools has still not been achieved. This paper also talks aboutthe future improvements that refiners are looking forward to. This paper attempts to give some thoughtsand ideas that could be followed in developing general heuristics which are a step forward in the direction ofcomplete automation of scheduling tools.
  3. 3. TABLE OF CONTENTSIntroduction to the Refinery Supply Chain...................................................................4Refinery Planning and Scheduling in the Supply Chain................................................4Current Practices and Tool Modeling Basics.................................................................4 Planning Tool Modeling Basics.............................................................................................4 Need for a Scheduling Tool and Scheduling Tool Modeling Basics.......................................................5Scheduling in the Future.............................................................................................. 5 Crude Scheduling............................................................................................................6 Product Scheduling..........................................................................................................7Monitoring of Schedulers Performance........................................................................8Data Consistency across Models..................................................................................8Conclusion....................................................................................................................9Appendix...................................................................................................................... 9 About the Author...........................................................................................................9
  4. 4. Refinery Planning and Scheduling - Plan the Act. Act the Plan.Introduction to the Refinery Supply ChainSupply chain optimization is an important margin driver for a refinery. The Wikipedia Says...complexity, with which a refinery is built, provides the flexibility to optimizeoperations, thereby maximizing margins. Supply chain managers need to Supply Chain Optimization is theanalyze a very complex set of choices before taking decisions. Best in class application of processes and toolsSupply Chain Management (SCM) tools and practices will be required to give to ensure the optimal operation of aforward visibility to supply chain operations. manufacturing and distribution supply chain. This includes theThe principles necessary for an operationally effective and successful optimal placement of inventorydownstream supply chain, includes a requirement for integrated planning, within the supply chain, minimizinginformation flowing in all directions, efficient execution, and visibility to operating costs. This often involvesperformance across the organization. the application of mathematical m o d e l l i n g te c h n i q u e s u s i n gHence, one cannot underestimate the importance of an integrated computer software.architecture in the complete supply chain.Refinery Planning and Scheduling in the Supply ChainThe objective and scope of each tool in the supply chain should be well defined.Planning tools -> Plan the act! To maximize the margins from the refinery complexScheduling -> Act the plan!The manufacturing plants follow the guidelines as defined by the planning and scheduling tools, for optimized refineryoperations. A well-defined feedback mechanism should be part of the process, so as to analyze and identify any gaps in theplan, schedule, and operations and continually improve and tune the process.Current Practices and Tool Modeling BasicsPlanning Tool Modeling BasicsThe refinery planning tool is generally being used for different purposes like financial forecasting, feedstock valuation, cruderun and refinery unit optimization, stock forecasting, etc with the single objective of maximizing Gross Refining Margins(GRM).The planning tool serves as an important medium for aligning the midstream planning with the downstream marketing. Itcaptures the refinery as a whole; and the key is optimization of the various constraints with the single objective of marginmaximization. Hence, it is very important that we do not land up with local optima problems with this tool. Non-linearsolvers have an inherent problem of local optima, so all efforts should be made to keep all constraints in the tool as muchlinear as possible. The basic idea is to compromise on small inaccuracies caused because of linearization without losing anyfocus on the single main objective of the planning tool, i.e. maximizing GRM by optimization.4 | www.wipro.com WIPRO TECHNOLOGIES
  5. 5. Refinery Planning and Scheduling - Plan the Act. Act the Plan.Need for a Scheduling Tool and Scheduling Tool Modeling BasicsPlanning is typically done for a month, so we have a monthly average as the Linear Programming (LP) model output i.e.we have: ? crude blend to be fed to the crude distillers An average ? product mix, which is to be produced during the entire month An averageIn complex refineries, where different crudes are blended to produce a cocktail which is ultimately fed to the crude unit,the crude diet to the unit changes almost every day. It is generally difficult to implement this “average” schedule on aday-to-day basis, because of several issues like non-availability of crudes as planned during the LP model run, the tank-pump hardware constraints in the field, etc which are generally not configured in the LP in an effort to keep theconstraints linear.Hence, it is very important to have a scheduling tool, in which all the constraints are modeled in great detail, to check thefeasibility of plan implementation. The primary goal of a scheduling tool is to have a feasible schedule, meeting alltargets identified from plan. Once, all targets are met, the schedule is already optimal i.e. the schedule drives towardsmaximizing the GRM of the refinery.The process units behave in a highly non-linear fashion and many a product specification blend in a non-linear way. Theemphasis on the solution provided by the tool is on its practical implement ability, so the scheduling tool should providevery accurate results. Hence, we need to use Mixed Integer Nonlinear Programming (MINLP) solvers when solvingproblems of this type. Local optima problems, which are inherent problems with MINLP solvers, are no longer a concern,since optimization is not the primary objective. We are more bothered with the accuracy of the results for its day-to-dayimplementation; hence these complex solvers best suit refinery schedulers’ requirements.It is essential to have a high-fidelity scheduling tool forscheduling decisions that are accurate and enables the Tools today help us to move from a “findingscheduler to quickly respond to changing business scenarios a solution” scenario to an “analysis oflike emergency shutdown of a unit or purchase decision of a schedules” scenario i.e. with the availabilitydistress sale crude cargo. The scheduling team has to quickly of a good tool, schedulers will now spendact on such situations advising the traders the best possible more time on analyzing the various possiblesolution; else the refinery loses out on that opportunity. Not schedules and decide which one is the mostonly is it important to have a good tool, it is essential to have a effective in terms of maximizing GRM.good team of people working on these tools.Scheduling in the FutureThe current scheduling tools and processes have allowed the refinery planner and scheduler close the gap between LPplan and schedule to a fair extent. However, the preparation of the schedule is still largely person-dependent. Even witha fairly robust model and an experienced scheduler, it typically takes a couple of hours to prepare a months’ schedule fora complex refinery. The dream of the refiner is to move from a “person-dependent regime” to a “process dependentregime”. In other words, the idea is to have generic heuristics built into the tool so as to make it “intelligent” to handle all5 | www.wipro.com WIPRO TECHNOLOGIES
  6. 6. Refinery Planning and Scheduling - Plan the Act. Act the Plan.kinds of scenarios, so that the schedule will be the same irrespective of the person preparing the schedule. Thechallenge today for the tool developer is to have a “recursion” feature developed in the tool so that it has the capabilityto go back and forth in time to make the overall schedule feasible or find the “best schedule”.Crude SchedulingThe preparation of the crude blend itself has been automated in most tools to a large extent, however it is the receipt ofcrudes in various tanks that is present in the refinery is mostly manual. The receipt largely dictates the feasibility ofcrude blends from thereon. A “wrong” receipt could cause infeasibility even a couple of weeks forward in the schedule.The dilemma is to specify to the optimizer the time period it should go back and rework the schedule, just like ascheduler would, so as to make the blends over the entire horizon feasible.Typically, the following challenges are faced when developing a general heuristic: 1 Whether to make a blend or take receipt of the crude into tanks at any point in time? If there are multiple crudes present in the ship/ scheduled to be received through the 2 pipeline, which crude to be received first? If there is a problem with blend feasibility, then can some property be relaxed in the 3 crude blend window to make blend feasible? If multiple properties can be relaxed then the order of preference of relaxation? Incase of complete infeasibility, how many days’ schedule to be deleted and readjusted 4 so that we make the complete schedule feasible? Even with recursion features the challenge is to have a generic algorithm which will 5 decide how long should we go back in time and rework the blends inorder to make the schedule feasible. 6 Demurrage vs. blend quality6 | www.wipro.com WIPRO TECHNOLOGIES
  7. 7. Refinery Planning and Scheduling - Plan the Act. Act the Plan.It is also seen that, in a refinery which processes multiple crudes in a blend, the trick is to store crudes as diverse in quality aspossible in order to make blends feasible. This problem, by itself, is a mathematical challenge, as it is analogous to findingthe maximum distance between two points. However, it is possible to develop a practically implementable solution, if thescheduler is able to diversify categories of crudes to different tanks based on his experience.Such clues along with clear answers to above situations will help a scheduler develop general heuristics for the tool, whichwill lead to feasible blends in most cases. These procedures will help the scheduler a lot in running sensitivity cases, withsmall changes in crude cargo types, cargo arrival dates etc. The user still has to manually take receipt into the tanks and doone complete schedule to identify the problem areas, so that he can give the right kind of inputs to run the tool in “auto”mode while carrying out sensitivity analyses. We are going one step further in trying to avoid repetitive work for the crudeschedulerProduct Scheduling Primary unit throughputs, feedstock, product prices, The output crude production targets schedule Grade-wise disptatch schedule of products Product ScheduleThe output crude schedule is one of the primary inputs of the product scheduling tool. Apart from this, the primary unitthroughputs, the feedstock and product prices and production targets are inputs that are taken from the LP. The grade-wisedispatch schedule of products is taken from marketing. All these inputs are automated, with the help of a common databasewhich helps in data transfer between tools.7 | www.wipro.com WIPRO TECHNOLOGIES
  8. 8. Refinery Planning and Scheduling - Plan the Act. Act the Plan.Once all the required inputs are given, with just a click of a button, we should have the complete product schedule ready.The tool should provide a good analysis of the component production, component usage in each grade, component andproduct tanks usage, economic analysis, etc which helps the user analyze the solution. In case of infeasibilities, the toolshould be capable of providing clues to infeasibility breakers so that the scheduler is not lost in the vast amount of data thatis presented to him.These are typically decisions which vary with time. The challenge is to have a senior scheduler formulate a generic algorithmwhich would work in most of the situations. The goal is to have a full months’ schedule prepared by the tool without any userintervention in-between.All the above initiatives will help refinery planning and scheduling professionals to go one step ahead in automation ofscheduling tools. While we are still far from making the process completely automated, it is a step in the right direction.Monitoring of Schedulers PerformanceTo reap the full benefits of a tool implementation, the performance of the schedulers should also be monitored withquantifiable objectives. Some of the objectives for the product schedulers could be predicted grade-wise productionnumbers vs. actual, Quality Give Away in cents/bbl against a target, no of product/batch failures, etc. Similarly for the crudescheduler it could be the comparison of crude consumption as suggested by the LP model vs. actual consumed.These serve as important checks to continually make sure that the scheduler is completely in sync with the plan goals andobjectives, and working as per the schedule suggested by the tool.Data Consistency across ModelsThe data that is present in the planning and scheduling models should be accurate and tuned to represent the currentconditions of the plant. There should be a person/team of people who are given the responsibility of having consistent dataacross all models used in planning and scheduling. There should be a good business process for the model update. Changesin yields/quality in a plant for a small duration of time are generally not updated in the planning model, as it has greaterramifications including influencing decisions on crude valuations and buying. Hence, only consistent shifts in yields andqualities of streams are updated in the planning model with due explanation. However, these small changes could beupdated in the process models present in the scheduling tool to capture the variations in production that it might cause inthe immediate future.8 | www.wipro.com WIPRO TECHNOLOGIES
  9. 9. Refinery Planning and Scheduling - Plan the Act. Act the Plan.ConclusionIn this paper, we discussed on the important things that are to be taken care of while modelling planning and schedulingtools. One should not lose focus on the primary objectives of running these tools. The planning tool acts as a bible - it is thesingle most important tool from which directions are to be taken. The scheduling tool should primarily enact the plan, butwith all adjustments required because of the non-linear nature of refinery processes. With these thoughts, schedulersmove one step higher in scheduling automation. However, to make the tools more person independent, the seniorschedulers themselves have to identify general guidelines which work in their refinery in most situations. The effectivenessof a robust “recursion” feature is very essential for working towards this goal and more studies need to be done in thisdirection.AppendixAbout the AuthorSowmya Santhanam, Lead Consultant, Refining Practice of Wipro Technologies, is a Chemical Engineer with a degree inMathematics from BITS, Pilani. She has earlier worked with the Planning & Scheduling department of Reliance IndustriesLtd for over 6 yrs on various scheduling desks, and has implemented supply chain tools for the 1.2 kbpsd refinery.9 | www.wipro.com WIPRO TECHNOLOGIES
  10. 10. Refinery Planning and Scheduling - Plan the Act. Act the Plan.ABOUT WIPRO TECHNOLOGIESWipro is the first PCMM Level 5 and SEI CMMi Level 5 certified IT Services Company globally. Wipro provides comprehensive IT solutionsand services (including systems integration, IS outsourcing, package implementation, software application development andmaintenance) and Research & Development services (hardware and software design, development and implementation) to corporationsglobally.Wipros unique value proposition is further delivered through our pioneering Offshore Outsourcing Model and stringent QualityProcesses of SEI and Six Sigma.WIPRO IN ENERGY & UTILITIESThe Energy and Utility division of Wipro Technologies is one among the Top 10 IT solution providers to the E & U industry across the globe.The Energy & Utilities business unit has worked with over 75 top Energy and Utility companies across North America and Europe inregulated as well as deregulated markets providing solutions in areas such as Customer Care, Billing and Settlement, Work and AssetManagement and Grid Operations covering all industry sectors --- Electricity, Gas, Oil and Water.The cumulative experience of over 5,500 person years spans IT Consulting, Systems Integration, Business Process Outsourcing,Application Development and Application Management services.10 | www.wipro.com WIPRO TECHNOLOGIES

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