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Project: LPG Fractionation & Separation Unit Automation

1. Process Overview

This project provides a complete automation solution for the refinery’s new LPG Fractionation & Separation Unit. This unit processes liquefied gas streams from other refining units to produce high-purity, specification-compliant products.

The core process involves the collection and fractional distillation of the feed to separate its components into the following final products:

  • Light Gases (for Refinery Fuel Gas)

  • Propane (C3)

  • Butane (C4)

  • Pentane (C5)

2. VFD (Variable Frequency Drive) Integration & Application

A key element of this project is the integration of Variable Frequency Drives (VFDs) to enhance process control, ensure asset protection, and optimize energy consumption. VFDs will be applied to all major rotating equipment.

Power ratings will be finalized during detailed engineering, with typical applications and ratings as follows:

  • Process Feed & Transfer Pumps:

    • Application: VFDs will be used on the main LPG feed pumps and the product transfer pumps (Propane, Butane, Pentane).

    • Benefits: Allows for precise flow control to stabilize the unit, adapting to feed composition changes and reducing reliance on control valves.

    • Typical Power Rating: Low Voltage (400V) drives in the 75kW to 220kW range.

  • Column Reflux Pumps:

    • Application: VFDs will be installed on the reflux pumps for the de-ethanizer, de-propanizer, and de-butanizer columns.

    • Benefits: Provides fine-tune control of the column’s internal liquid-vapor traffic, which is critical for achieving high-purity product specifications and minimizing energy use in the reboilers.

    • Typical Power Rating: Low Voltage (400V) drives in the 45kW to 132kW range.

  • Condenser Air-Cooler Fans:

    • Application: VFDs will control the large fin-fan motors used in the overhead condensers.

    • Benefits: Allows for precise temperature control of the column overheads, optimizing condensation and separation efficiency while saving significant electrical energy.

    • Typical Power Rating: Low Voltage (400V) drives in the 30kW to 75kW range.

3. Control System Architecture

The control system is a high-performance, distributed solution based on the Siemens SIMATIC S7-1500 platform, providing a mix of high-power CPUs for core processes and smaller CPUs for package/utility integration.

  • Core Process Controllers (4x): CPU 1517-3 PN/DP

    • These high-performance CPUs will manage the main fractionation columns and critical process loops, ensuring maximum reliability and processing speed.

  • Package/Utility Controllers (9x): CPU 1513-1 PN

    • These controllers will be used for decentralized control, managing auxiliary systems, package units (e.g., utility skids), and serving as a high-speed interface for field I/O.

  • Serial Communications (9x): CM PTP RS422/485

    • These modules will be used to integrate third-party systems via serial protocols (e.g., Modbus RTU), providing a data interface for gas chromatographs, VFDs, and other skid-mounted packages.

4. Project I/O Bill of Materials

The system I/O will be composed of the following SIMATIC S7-1500 modules:

  • Digital Input (29x): DI 32x24VDC

  • Digital Output (29x): DQ 32x24VDC

  • Analog Input (32x): AI 8xU/I/RTD/TC (Multi-function modules for universal signal-type inputs)

  • Analog Output (22x): AQ 8xU/I HS (High-speed analog output modules for precise control valve operation)