For safe firing of black liquor in recovery boilers
The Vaisala Polaris DD53 Digital Divert Control System is designed to verify black liquor solids concentration before firing, helping pulp mills safeguard recovery boiler operation. It conforms to the recommended practices from Black Liquor Recovery Boiler Advisory Committee (BLRBAC), The Finnish Recovery Boiler Committee (FRBC), and The Swedish-Norwegian Recovery Boiler Committee (SNRBC) to support safe and consistent operation.
The Vaisala Polaris DD53 system
- ensures that black liquor solids are fired into the furnace at the correct concentration
- enhances safety and usability with 2-out-of-3 refractometer logic, in addition to standard two-sensor operation
- maintains continuous measurement availability through coordinated monitoring and wash control, preventing all refractometers from being offline simultaneously due to washing.
- enables retrofit of existing PR-23-SD installations with a third sensor (PR53SD)
- supports compatibility with any combination of PR-23-SD and PR53SD sensors
Modern, digital divert control for safe black liquor firing.
Modern, fully digital system
BLRBAC compliance for safe firing of black liquor
Increased safety with 2-out-of-3 refractometers logic
Compatible with existing PR-23 + DTR installations
Industry-standard communication interfaces for direct connection to control systems and BMS
Error-free operation supported by digital signal transmission and microprocessor-based diagnostics
SIL-rated critical components and redundant power supplies
Easy to operate with clear multi-diagnostic messages
Designed for safe and efficient performance of pulp mills.
Polaris DD53 Digital Divert Control System
The system consists of two or three Vaisala Polaris™ PR53SD Process Refractometers, two or three Indigo520 indicating transmitters, and one DD53 digital divert control unit.
Together, these form a modern, fully digital divert control solution for black liquor concentration control and safe firing in recovery boilers.
Polaris DD53 digital divert unit
Digital divert control with SIL-rated critical components and redundant power supplies.
The Polaris DD53 is a completely microprocessor-controlled digital divert unit with a SIL-rated critical components and redundant power supplies. Digital signal transmission and microprocessor-implemented diagnostics ensure reliable, error-free operation of the divert function.
The DD53 provides industry-standard communication interfaces for direct connection to control systems, the Burner Management System (BMS) and factory safety automation. The divert unit includes an IP65 field enclosure and an optional remote Human Machine Interface (HMI) for convenient access from the control room.
Indigo520 indicating transmitters
Smart interface for diagnostics, wash control, and connectivity.
Indigo520 enables data logging, diagnostics, wash control, and configuration of connected sensors. It supports modern industrial cybersecurity practices, helping ensure secure data communication and system integrity in networked environments.
It offers versatile system connectivity with:
- Two selectable analog or digital inputs for process refractometers
- Four configurable analog outputs, for example to alarm relays
- Modbus TCP/IP digital communication for easy integration into mill control systems
Vaisala Polaris™ PR53SD Safe-Drive Process Refractometers
Inline black liquor solids measurement with Safe-Drive installation.
Vaisala Polaris PR53SD Process Refractometers are installed with a Safe-Drive SDI5 isolation valve that allows safe and easy insertion and retraction of the refractometer under full operating pressure, without having to valve off the black liquor piping or shut down the process.
The Safe-Drive SDI5 isolation valve includes a steam wash nozzle for integrating automatic prism cleaning with SWS100. The system also includes a Safe-Drive retractor tool to ensure safe refractometer insertion and retraction from pressurized black liquor lines. The operation is straightforward, with only a few clear steps needed to insert or remove the process refractometer while the process is running at full load.
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