Encapsulation

The solution involved the design and implementation of an External Mixer Control System to support the encapsulation process. Key components and systems included:

• Cement Silo and Screw Feeds: For storing and transferring cement powders.
• External Mixer: For mixing dewatered sludge or sand with cement powders.
• Inactive Capping Grout Plant: For final capping of the waste containers.
• Bleed Water Recovery System: To manage excess water during the encapsulation process.
• Wash Down Skid: For cleaning the External Mixer.
• Ventilation Extract System: To maintain safe air quality and pressure conditions.
• Control System: Based on a Rockwell (Allen Bradley) CompactLogix PLC system, with Panelview Plus 7 HMIs for operator interaction.

The control system was designed to operate remotely, integrating various safety interlocks and emergency stop functions to ensure safe and efficient operations.

The Electrical, Control, and Instrumentation (EC&I) aspects of the External Mixer Control System are detailed and comprehensive. Here are the key points:

Electrical Aspects

1. Power Supply and Distribution:
   • The control system requires a 400V 3-phase, neutral, and earth supply at 50 Hz, rated at 100 Amps.
   • Various single-phase supplies are derived from the three-phase supply and balanced across the phases.
   • Internal control circuits are supplied from low-voltage DC supplies generated internally from the control panel supply.
2. Control Panels:
   • Local Control Panel: Houses all electrical power distribution and control system equipment, segregated into power and control sections.
   • Remote Control Panel: Located in the control room to minimise operator exposure, equipped with a colour HMI for operator interface.
3. Junction Boxes:
   • Various junction boxes (7 off) are used for local cable marshalling and distribution points for different components.
4. Motors and Drives:
   • Motors for the silo screw conveyor, hopper screw conveyor, wash down pump, external mixer, extract fan, bleed water recovery pump, and capping grout plant are controlled via variable speed drives (Allen Bradley PowerFlex 525) or direct online starters.

Control Aspects

1. PLC System:
   • The control system is based on a Rockwell (Allen Bradley) CompactLogix PLC, which controls all operations, interlocking, and event alarming related to the External Mixer equipment.
   • The PLC system includes main rack I/O and point I/O modules for various components.
2. Human Machine Interface (HMI):
   • Operator interfaces are provided via Rockwell (Allen Bradley) 15” Panelview Plus 7 HMIs located at both the remote and local control panels.
   • HMIs are configured to provide machine status displays, operational functions, and manual control for commissioning and maintenance activities.
3. Control System Network:
   • The network is based on EtherNet/IP technology, using Rockwell ‘Stratix 5700’ managed network switches.
   • The network facilitates communication between the PLC, HMIs, and other control system components.
4. Methods of Control:
   • Manual Control: Provides operations and control of individual plant items for recovery procedures.
   • Automatic Sequence Control: Automates operations with key points requiring operator confirmation.

Instrumentation Aspects

1. Sensors and Transmitters:
   • Various sensors and transmitters are used to monitor and control the system, including pressure switches, level indicators, flow transmitters, and differential pressure transmitters.
   • These instruments provide critical data for the control system to ensure safe and efficient operation.
2. Safety Interlocks:
   • Safety interlocks are implemented via standalone, hardwired safety relays, independent of the process control/PLC system.
   • Emergency stop buttons are positioned on control panels and field-mounted units, with dual-channel, series-connected inputs.
3. Pneumatic Control:
   • The local control panel contains pneumatic solenoids and pressure switches for actuating pneumatic outlet valves, such as silo aeration nozzles, hopper discharge valve, external mixer viewing screen wiper, and discharge valve.
4. CCTV and Audio Monitoring:
   • CCTV cameras and a microphone are installed to monitor the mixing operations visually and audibly, with signals sent to the control room for operator monitoring.

These EC&I aspects ensure that the External Mixer Control System operates safely, efficiently, and reliably, meeting the requirements for encapsulating Intermediate Level Waste at the Hinkley Point A site.