Vaisala K-PATENTS® Digital Divert Control System DD-23

for recovery boiler safety

Vaisala K-PATENTS DD-23 system includes two K-Patents SAFE-DRIVE Refractometer PR-23-SD sensors in the main black liquor line, and two Indicating transmitters and a Divert control unit in an integrated panel. Remote monitoring, and event data logging is via Ethernet.

Vaisala K-PATENTS SAFE-DRIVE Process refractometer sensors are installed with SAFE-DRIVE Isolation valve that allows for safe and easy insertion and retraction of the refractometers under full operating pressure without having to valve off the liquor piping or having to shut down the process. The SAFE-DRIVE Isolation valve contains a steam wash system for automatic prism cleaning. The system contains a SAFE-DRIVE Retractor tool SDR-23 for safe sensor insertion and retraction.

Each refractometer is a completely independent measurement system. Each system sends a separate mA output signal, which can be used by a control system or a DCS.
The DD-23 system is completely microprocessor controlled. The digital signal transmission and microprocessor implemented diagnostics ensure error free operation.

Learn more How DD-23 is built to conform to the BRLBAC recommendations (pdf)


  • Completely digital system from the sensors to the transmitters. The system is completely microprocessor controlled and all analog circuitry has been eliminat-ed.
  • Digital signal transmission and microprocessor implemented diagnostics ensure error free operation.
  • The system eliminates false alarms, because it reacts only when the level of sol-ids truly falls below the safe limit. By using K-Patents DD-23, costly process dis-turbances resulting from unwarranted divert actions can be avoided.
  • Easy to operate and clear multi-diagnostic messages.
  • K-Patents SAFE-DRIVE® isolation and retractor allow for safe and easy insertion and removal of the refractometer sensor under full process pressure. Easy-to-place and self-retaining design. Triple sealing by two lip seals and an O-ring.
  • SAFE-DRIVE® retractor protects the user from accidental spills during retraction and insertion.
  • Accidental opening or closing of the isolation ball valve is prevented.
  • The retractable prism wash nozzle can be safely removed for a service check.
  • Remote monitoring using a standard web browser: Data of real-time measurement, divert condition, measurement values, diagnostic messages and event log records remotely available to control room via Ethernet connection.
  • Alarms and contact functions: Warning and alarm relays for low solids and refractome-ter difference. Relays for instrument and system status. Header wash switch. Contact inputs for external divert switch and hard-wired divert reset