High power generation from recovery boilers: What are the limits?

Sep 5, 2017

Increasing power generation from recovery boilers has become a boiler design emphasis in the last 5 to 10 years. This trend comes from industry desire to increase efficiency and reduce cost, and also from the legislative authorities' desire to reduce Green House Gas emissions and their role in climate change.

A recovery boiler currently under design for the first next-generation bioproduct mill, Äänekoski, uses high power features. The system is scheduled to come on line in late 2017. The energy efficiency of modern recovery boilers, such as Äänekoski, can be improved by introducing the following high power features to the boiler:

  • higher black liquor dry solids,
  • air preheating,
  • a fully pressurized feedwater tank,
  • feedwater preheating,
  • heat recovery from vent gases,
  • heat recovery from flue gases in a flue gas cooler, and
  • higher main steam parameters.

High power features in recovery boilers

High power features in recovery boilers

Ash composition, especially potassium and chlorine contents, have a significant impact on recovery boiler design through corrosion and fouling phenomena. Ash composition can be controlled by using an ash treatment system such as ash leaching or crystallizer. Having low potassium and chlorine contents decreases the need for expensive stainless-steel material in superheaters, but at the same time valuable sodium losses are higher. In other words, it is an optimization between investment and operation costs and the optimum solution must be determined case by case.

Learn more about recovery boiler high power generation and ash treatment

A Valmet white paper, available HERE, presents the current possibilities to increase recovery boiler power generation, with Äänekoski as an example. A review of the technical and financial impact of various alternatives to improve power generation and their associated returns on investment is also reviewed.

Download and read the white paper and give your Valmet representative a call to discuss improving power generation.