The Recovery Optimization System developed by AAI utilizes the latest concepts in control strategy for Recovery Boiler Processes using the tools available in modern computer based control systems and instrumentation typical of a Recovery Boiler. By incorporating functionality which has traditionally been under manual control, and moving to a Liquor BTU based control strategy, the system improves Recovery Boiler throughput and efficiency, reduces carryover, reduces emissions, and stabilizes downstream processes.

A key component of the control strategy is BTU based liquor firing. As opposed to liquor volume or liquor solids flow to the boiler, BTU based firing uses the heat release of the liquor as the most representative value of long-term production rate. The advantage of this method is that heat release can be stabilized relative to production rates. This allows a stable and constant oxidation process to occur on the smelt bed. Once stability is achieved, carryover and emissions are reduced and the boiler can be pushed closer to maximum production rates.

Variations in heat release rate are controlled based on the amount of air being consumed in the furnace. The air consumed by burning liquor is continuously calculated and used to adjust liquor flow such that proper heat is maintained. Consumed air control provides the advantages of uniform burning, better oxygen control, and overall furnace stability. This optimization module functions with either oscillating liquor guns or stationary firing.

Consumed Air Firing (Btu) - The consumed air module adjusts liquor flow (within defined limits) for a given production rate setting in order to maintain constant heat release.

Throughput Firing - An additional method of operation that calculates and stabilizes Virgin Solids input to the recovery furnace.

Constant Liquor Flow Firing (GPM) - This method of operation is provided for emergency operation if the control system must be operated without the density or oxygen analyzers.

Enhanced User Interface Displays - The Recovery Optimization System includes a set of user interface displays which simplify operation of the recovery process. Through these displays, functionality such as automatic boiler heat-up and ramped load changing are provided for operations personnel through a single screen. The overview screen emulates the traditional operator panel board. Visual indication of process status is displayed using "analog meters" rather than engineering units. To see a sample display Click Here.

Production Rate Control and Ramping - The recovery process production rate is set via an operator adjustable setpoint. Generally this is established by the user, based upon liquor inventories, lab tests of liquor, and mill production targets.

Oxygen Trim - The oxygen trim controller compares measured oxygen to the requested setpoint. The error is used to trim secondary and/or tertiary air demand.

Liquor Flow Control - Measured liquor flow is corrected for solids content using the average value of two refractometer measurements.

Liquor Temperature Control - Temperature of Black Liquor flowing to the boiler is compared with an operator adjustable setpoint in the temperature controller. The output of this controller modulates the liquor heater to maintain proper droplet size of the liquor spray into the furnace as a function of load.

Primary Air Flow Control - Measured primary air flow is compared with demand in the air flow controller and the output is used to modulate the primary air damper.

Secondary Air Flow Control - Measured primary air flow is compared with demand in the air flow controller and the output is used to modulate the secondary air dampers.

Tertiary Air Flow Control - Measured primary air flow is compared with demand in the air flow controller and the output is used to modulate the tertiary air dampers.

Furnace Draft - A standard closed loop control strategy applies.

Primary Air Duct Pressure - A standard closed loop control strategy applies.

Drum Level Control - A standard closed loop control strategy applies.

Load Set Point Indexing - As the recovery process production rate changes, several setpoints should be modified to provide optimum control.

Inventory Control - Inventory control, when energized, provides a production rate setpoint to control either Black Liquor or Green Liquor inventory.

Blackout Detection - A fuzzy logic module alarms black out conditions.

Efficiency Calculation - Thermal efficiency is continually calculated and displayed using the TAPPI Recovery Boiler Test Procedure. This calculation can be used to determine the cost of steam by burning various fuels in the boiler. Additionally, daily boiler performance can be tracked.

(Optional) Tube Leak Detection - Recovery Boiler LeakTrac™ System can be included. LeakTrac is a state-of-the-art RB leak detection system developed co-jointly with Hecules Pulp and Paper Division (formerly BetzDearborn)

(Optional) DART - Enables a mill with throughput regulation limitations to precisely hit throughput maximum while realizing the benefits of consumed air optimization.

AAI furnishes guarantees of performance with installations of Recovery Boiler Optimization System based on a survey of existing Recovery Process operation. Guarantees typically involve measurable system and process parameters such as percentage of time on full automatic, BLS throughput, or percent Excess Oxygen. AAI is confident that installation of a Recovery Boiler Optimization System will result tangible benefit for the end user and is willing to back installations with a firm warranty.

Typical areas of process improvement include:

• Excess Oxygen will be Maintained Less Than or Equal to 1.5%, ±.15%
• Throughput will be maintained greater than a defined tDS/day
• Automatic Control will be Provided by the System 95% of the Time

AAI believes that competitive advantage can be gained by pulp and paper manufacturers through the proper application and use of today's computer and control equipment. This is proven everyday by AAI engineers that leverage their technical systems knowledge with process experience to provide clients with significant dollar savings through higher process throughputs and efficiencies. The AAI Recovery Boiler Optimization System is a specific example of this.

The Recovery Boiler Optimization System has been installed and is running at more than 16 locations across North America.