Project Scope

Design, engineering, supply, and commissioning of a closed-loop agitator motor control system featuring VFD (Variable Frequency Drive) and PLC (Programmable Logic Controller) integration.

Background

We implemented a control system to manage the agitator motor for a chemical reactor for an industrial customer. This system is designed for the precise mixing of two compatible liquids with a viscosity of up to 520 centipoises (cP), with the objective of achieving complete homogeneity within a 12-minute timeframe. The project implemented a closed-loop control system that seamlessly integrated a VFD and a PLC.

The customer requested both local and remote control capabilities for managing the agitator mixer’s operations. This dual-control functionality facilitated day-to-day operations and ensured adjustments could be made from a centralized control room, enhancing operational efficiency and control.

An all-in-one panel was delivered, housing both the VFD and PLC, integrating seamlessly into the existing Distributed Control System (DCS). This integration was a critical step in streamlining the control and monitoring of the agitator mixer.

System Description

The system consisted of a 15 kW VFD, an 1800 RPM agitator motor, and a PLC-based control system, designed to ensure both efficiency and safety during operations. Its primary objective was to safeguard personnel and prevent overheating incidents. PTC (Positive Temperature Coefficient) sensors were integrated into the PLC, providing real-time indicators of overheating status. This ensured the agitator motor’s safe operation in potentially hazardous environments while maintaining precise control over its speed and operation.

To facilitate remote control, a dedicated control interface was established in the control room. The control panel interfaced with the existing DCS onsite, establishing a comprehensive closed-loop control system that optimized operational safety and efficiency. This integrated system addressed critical safety concerns, offered real-time oversight, and enhanced overall control of the agitator motor in industrial processes involving chemical mixing.

Implementation Approach

The design and manufacturing specification followed:

Key Components:

• VFD (Variable Frequency Drive): 15 kW, Mitsubishi Electric A800 Series
• PLC (Programmable Logic Controller): Mitsubishi Electric IQR Series
• Motor: 1800 RPM agitator motor
• MPCB (Motor Protection Circuit Breakers): Schneider Electric
• Communication Protocol: Modbus TCP/IP
• Cooling System: Forced air cooling, with an option for a panel climate control unit if ambient temperatures exceeded 32°C
• Line Filter: Mitsubishi Electric
• Safety Sensors: PTC sensors for overheating status

Design and Manufacturing Standards:

• The design and manufacturing followed the PIP (Process Industry Practices) standard, conforming to ELSMC20 standard.

Cable Management:

• Cable entry was configured at the bottom of the enclosure.

Integration with DCS:

• Communication between the DCS and the new control panel was established using Modbus TCP/IP. Power supply from the local control panel was provided via a transmitting junction box.
• Integration of the agitator motor speed sensor with the DCS enabled real-time monitoring and control.
• An oil level indication system with an accompanying buzzer was set up to provide feedback on the motor’s oil levels.

Safety Measures:

• PTC sensors were integrated into the PLC panel to indicate overheating status.
• Explosion-proof components were implemented to enhance safety.

Project Outcomes

• The incorporation of local and remote control functionalities, integration with the existing DCS, and the implementation of safety measures such as explosion-proof components and overheat sensors significantly improved the efficiency and safety of the chemical mixing process.
• The closed-loop control system facilitated precise monitoring and control, contributing to seamless and optimized operations.