Lincoln Fernando Lautenschlager Moro

A PLANNING MODEL FOR REFINERY DIESEL PRODUCTION

The main objective of this paper is to develop a nonlinear planning model for refinery production. The model is able to represent a general refinery topology and allows the implementation of nonlinear process models as well as blending relations. A real-world application is developed for the planning of diesel production in the RPBC refinery in Cubatao (SP). The resulting optimization model is solved with the generalized reduced gradient method. The optimization results were compared to the current situation, where no computer algorithm is used and the stream allocation is made based on experience, with the aid of manual calculations. Considering the market limitations for each kind of diesel oil usually supplied by the refinery, the optimization algorithm was able to define a new point of operation, increasing the production of more valuable oil, while satisfying all specification limits. This new operating point represents an increase in profitability of about US

Planning and scheduling for petroleum refineries using mathematical programming

6,000,000 per year.

Constrained multivariable control of fluid catalytic cracking converters

The objective of this paper is the development and solution of nonlinear and mixed-integer (MIP) optimization models for real-world planning and scheduling problems in petroleum refineries. Firstly, we present a nonlinear planning model that represents a general refinery topology and allows implementation of nonlinear process models as well as blending relations. The optimization model is able to define new operating points, thus increasing the production of the more valuable products and simultaneously satisfying all specification constraints. The second part addresses scheduling problems in oil refineries, which are formulated as MIP optimization models and rely on both continuous and discrete time representations. Three practical applications closely related to the current refinery scenario are presented. The first one addresses the problem of crude oil inventory management of a refinery that receives several types of crude oil delivered exclusively by a single oil pipeline. Subsequently, two optimization models intended to define the optimal production policy, inventory control and distribution are proposed and solved for the fuel oil and asphalt plant. Finally, the planning model of Moro et al. (1998) is extended in order to sequence decisions at the scheduling level in the liquefied petroleum gas (LPG) area for maximization of the production of petrochemical-grade propane and product delivery.

Process technology in the petroleum refining industry: current situation and future trends

Abstract This paper concerns the development of a multivariable controller for the FCC Kellog Orthoflow F reactor/regenerator unit. A nonlinear dynamic model, based on the model of Kurihara, is used as a reference for the design of the control algorithm. This model is compared with the plant data, for open loop changes on the air flow and the regenerated catalyst valve opening. The adopted control algorithm incorporates both the regulatory and optimization functions. The regulatory layer is based on the usual DMC algorithm, while the optimization layer solves a linear programming problem, based on the DMC formulation, to perform steady-state economic optimizations. The calculated variables of the LP are the setpoints to the regulatory layer. The proposed control structure is simulated for a particular set of manipulated and controlled variables of the Kellog FCC converter and the results indicate good potential for the application to the real system.

A planning model for petroleum refineries

Abstract This paper analyzes the technology of process and production optimization in the petroleum refining industry. There is, virtually, no refiner nowadays that does not use advanced process engineering tools to improve business results. The degree of maturity of those tools varies greatly, and there are still many unsolved problems. For instance, advanced process control is considered a mature technology, while the automatic generation of a scheduling of refinery operations is considered a goal to be achieved only in mid-term. The current state of these technologies as well as the current needs of the industry and the expected future trends are presented.

A mixed-integer model predictive control formulation for linear systems

The main objective of this paper is to develop a nonlinear planning model for refinery production. The model described here represents a general petroleum refinery and its framework allows the implementation of nonlinear process models as well as blending relations. This model assumes the existence of several processing units, producing a variety of intermediate streams, with different properties, that can be blended to constitute the desired kinds of products. Two real-world applications are developed, one for the planning of diesel production in the RPBC refinery in Cubatao (SP) and the other for the general production planning in the REVAP refinery in S. Jose dos Campos (SP). In both cases, different market scenarios were analyzed using the planning optimization and the results were compared with the current situation, in which there is no extensive use of planning decision support tools. Results revealed that there is a very large potential of profitability embedded in the planning activity, reaching several millions of dollars per year.

A mixed integer model for LPG scheduling

Abstract Since their inception in the early 1980s industrial model predictive controllers (MPC) rely on continuous quadratic programming (QP) formulations to derive their optimal solutions. More recent advances in mixed-integer programming (MIP) algorithms show that MIP formulations have the potential of being advantageously applied to the MPC problem. In this paper, we present an MIP formulation that can overcome difficulties faced in the practical implementation of MPCs. In particular, it is possible to set explicit priorities for inputs and outputs, define minimum moves to overcome hysteresis, and deal with digital or integer inputs. The proposed formulation is applied to simulated process systems and the results compared with those achieved by a traditional continuous MPC. The solutions of the resulting mixed-integer quadratic programming (MIQP) problems are derived by a computer implementation of the Outer Approximation method (OA) also developed as part of this work.

PETROBRAS Experience Implementing Real Time Optimization

This work addresses the problem of LPG production and inventory management of a real world refinery. The problem concerns decisions related to LPG and LPG byproduct production strategies and decisions related to the selection of storage facilities that are used to receive these products and to feed the product pipeline. We develop a general framework for the modeling of similar scheduling problems. The result is a mixed integer optimization model with non-uniform time slots that can generate a short-term schedule for refinery LPG management. This schedule, spanning a horizon of approximately one-week, takes into account volume constraints as well as operational rules.

Optimization in the Petroleum Refining ndustry – I The Virtual Refinery

Abstract PETROBRAS has defined Real Time Optimization (RTO) as a “High Sustainability” technology for downstream operations, due to its high economic return. Since 2001, RTO tools are being tested within the Company, either using in-house process simulators or, sometimes, using available commercial ones. This paper presents an overview of the PETROBRAS experiences on RTO, showing applications on Distillation and Fluidized Catalytic Cracking (FCC) units. Alternatives based on Sequential-modular simulators, along with reduced models (Kriging models and neural nets), as well as Equation-oriented based simulators / optimizers have been explored. The project scopes vary from covering only the Reactor / Regenerator section of a FCC unit up to a whole Crude distillation unit, including the preheat train, all distillation towers and the heat and material integration. Some of these RTO applications have been running close loop for almost 6 months, with proved expressive economical benefits. Based on the knowledge acquired during all these years, some of the future development needs for the improvement of RTO technology will be presented and discussed, as a guide for future research projects.

Closed-loop model re-identification of processes under MPC with zone control

Abstract As a result of the recent world economy slowdown many investment plans for refinery capacity expansions were postponed, and the optimization of existing process units, that had lost priority in relation to the design of new ones, came again to prominence. We cannot be sure if this priority will change in the near future but it seems sure that petroleum companies must be prepared to cope with a very uncertain scenario. This means that the abilities and the corresponding tools need to be well adapted to optimization and design activities, and the transition from one to the other has to be as quick and smooth as possible. The tools used for both activities, e.g. process simulators, are usually diverse and the same applies to the teams in charge of optimization and design. The present work tries to point out the main improvements that will have to be performed in the process engineering tools so that they may be better adapted to the this scenario. The main improvement we point out is the so called “virtual refinery”, which is basically a rigorous dynamic model incorporating every piece of equipment in the plant. This model would be kept running continually in order to mimic the actual behavior of the plant and would be periodically upgraded to include new equipment and different operating modes. This model would then be able to represent the process in a comprehensive and detailed way and could supply the models used in simpler and narrowly oriented tools. In order to make this vision come true several problems demand further investigation and development, and some of them are described.