Chemical Recovery Boiler Performance Efficiency

We discussed improvement of multi-fuel boilers in an earlier post. Similarly, pulp and paper manufacturers often wrestle with chemical recovery boilers because of the complexity of the combustion process. This complexity is largely driven by the variability in the “fuel” (black liquor) and often by swings in production rate.
The variation in the BTU content of the incoming black liquor can cause difficulty in meeting the emissions restrictions, can lead to fouling of the boiler, may impact boiler efficiency, and can limit liquor throughput. Safety is also a major concern around a recovery boiler process.
Bob Sabin, a consultant in Emerson’s Industrial Energy Solutions organization described the challenge as maximizing liquor throughput while minimizing the fouling of the upper boiler and maintaining optimal unit thermal efficiency. This can be done if the boiler combustion controls are configured to compensate for liquor BTU changes.
The process Bob and the team follow with pulp and paper manufacturers typically begins with an analysis where they measure the mills operating performance and compare it with world class performance. Some benchmarks include: maintaining excess oxygen at 1.5% to maximize unit efficiency, maximizing liquor throughput to either permit or steaming limits, minimize fouling to require one water wash per year, and running the recovery boiler in fully automatic mode more than 95% of the time.
Through this benchmarking process deficiencies and mechanical design limits can be identified and corrected. The economic benefits of process improvements can also be calculated.
Next a detailed field audit of valves, instrumentation, wiring, and control system performance is performed to find areas requiring attention.
With this assessment completed a complete cost estimate and return on investment calculation and justification can be developed to improve the performance of the recovery boiler. The expertise of the team has been packaged into a SmartProcess Recovery boiler solution which encompasses design, installation, commissioning, start-up, and operations personnel training.
Pulp and paper manufacturers typically experience project payback in three to six months through increased liquor throughput, better thermal efficiency, water wash reductions, and reduced variability in green liquor reduction.

Posted Tuesday, June 13th, 2006 under Energy, Pulp & Paper.


  1. himanish chakravarty says:

    myself D.G.M.(rec). facing problem in controlling carryover in boiler.

  2. Bob Sabin says:

    Many things contribute to carryover in a Recovery Boiler, but the work that Emerson does in optimizing Recovery Boiler combustion control has had positive effects on carryover. This has been accomplished by firing these units under a constant liquor Btu strategy that stabilizes combustion in the lower furnace and allows a reduction in flue gas volume and velocity. In addition, providing precise control of the boiler during times of load change prevents cases of large fouling in a short period of time due to imbalances in available liquor Btu and air supply.

  3. zulfiqar ali cheema says:

    At 33% Firing What will be the impact on combustion of black liquor and quality of the smelt?

  4. I understand that 33 % liquor firing is getting near the point that you must be more concerned about maintaining the reaction and less about the quality. With an optimized control strategy such as SmartProcess, we would able to a better job than typical because we would still be able to determine the liquor BTUs, and if there was sufficient control of the air, we would maintain the highest efficiency and lower furnace temperatures, which would translate to better smelt quality.

  5. kamlakar dubey says:

    What will be effects of RAA in recovery boiler combustion ,indirect heater effects7 what will effects of low RAA in RECOVERY BOILER.

  6. We have not specifically done trials to test affects of varying RAA, but would not expect to have this significantly impact combustion performance in the Recovery Boiler. Our control approach compensates for variations in liquor Btu per volume in real-time, combustion performance should be stable.

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