Gasoline Blend Control, Optimization and Planning System in Mexican Refineries

Introduction

PEMEX Refinacion, Mexico awarded two lump-sum contracts in 1994 to ABB Industrial Systems, Inc., Houston for the engineering and implementation of an integrated advanced online blend control, optimization, and planning systems for its Cadereyta and Tula refineries. The detailed engineering for the blender is done by two local Mexican engineering companies, namely, CONIP Consultores y Contratistas for Cadereyta refinery and GMD for Tula refinery. ABB has implemented the identical state-of-the-art advanced online blend control, optimization, and planning systems in both PEMEX refineries.

This blog presents details of the ABB implemented blend control systems from its features and system architecture points of view.

Blender design

The design of blender in both PEMEX refineries has the following characteristics:

  • Tank-to-tank in-line blending, using blending components from component storage. Most of the stock tanks in both refineries are closed during blending keeping their qualities constant during blending. However, few stock tanks are live or running during blending with considerable variation in their qualities
  • The blending control system design allows for the use of up to 16 simultaneous blend components (expandable); it also handles the use of oxygenates such as MTBE and TAME, and additives -TEL, Aniline, and detergent.
  • Stock qualities (RON, MON, %Ar, %Olef, RVP) are measured by one online NIR using multiple stream sampling systems. Each stream is sampled once every two minutes. Distillation points for the stock tanks are input from laboratory values.
  • Blend product qualities are measured online by three analyzers, namely, NIR multi-property analyzer (RVP, RON, MON, %Ar, %Olef), multi-point chromatography distillation analyzer, and an RVP analyzer.
  • Configured up to 8 grades (expandable) of unleaded gasoline, both leaded and unleaded, with multiple quality specs (RON, MON, RDOI, RVP, Distillation point).
  • The maximum blender flow rate is 12,000 Bls/hr. The blender hardware architecture consists of a blender manifold for up to 16 components; the legs for each component include mass flow meters, control valves, strainers with pressure switches across it, pumps with computer-controlled recycles, and block valves.

NIR-type multi-property online analyzer for RON, MON, RVP, and distillation, mounted in an analyzer shelter system, which integrates together with the analyzers, the sampling system, and the prototype fuel system used by the Octane comparators. Compared with conventional analyzers, CC-96-124 the latest generation of Near Infra-Red (NIR) multi-property analyzers promise equal performance and more properties at a fraction of the operating and maintenance costs.

Control hierarchy levels

ABB’s blend control, optimization, and planning system consists of the following three distinct control levels:

  1. Regulatory Blend Control (RBC) – First level of blend control strategy resides in Fisher DCS ProVox and controls the amount of each component in the final product tank automatically. Although this level of computer does not give any guarantees to blend the product to specifications as it does not use any analyzer feedback, it does relieve the operator from monitoring the process continuously.
  2. Advanced Online Blend Control and Optimization (ABC) – The second level of the blend control strategy is a scheme that is implemented in the HP-9000/715 computer and is linked to Fisher ProVox executing the first level of control. This control uses the analyzers feedback, corrects the recipe frequently, and guarantees the final product on specifications. This is a very complex technology and the refineries achieve considerable economic benefits because of continuous optimization and feedback.
  3. Offline Optimization and Planning System (OOPS) – Third level of the blend control strategy is offline optimization of a blend recipe taking into account the refining process as expected in advance. This is done on an HP X-terminal by the refinery planner and then he downloads the optimized recipe to the online blend control (ABC) system for further online control and optimization and is finally executed in Fisher ProVox by RBC. The planner typically may plan many recipes at one time depending upon the refinery’s operational characteristics.
Hierarchy of ABB Blend Control System

Figure 1. Hierarchy of ABB Blend Control System

Technology set

ABB Integrated Blend Control, Optimization, and Planning System is based on ABB or any third party vendor DCS for Regulatory Blend Control (RBC) and UNIX HP work-station for advanced on-line and off-line blend control, optimization, and planning system. It uses the technology set shown in Table 2.

Components of ABB blend control system technology set

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