The black liquor recovery boiler presents problems of operation and safety that far exceed those of the conventional power boiler or other forms of combustion equipment that can be used for the thermal oxidation of waste streams. The recovery boiler is primarily a chemical recovery process unit in which organic materials in the black liquor are burned while the oxidized sulfur compounds of sodium and potassium are reduced and drained as molten smelt from the furnace bottom. At the same time, the heat released is used for generation of steam for power and process.This document is intended to address concerns of the industry relating to safe thermal oxidation of waste streams in recovery boilers. “Waste streams” for this document are produced in the pulping process. The major waste stream is noncondensible gases (NCG), which are gases that contain reduced sulfur compounds from the digester and evaporator operations and are a source of odor.
The following list is representative of the pulping process waste streams that are addressed:
- Dilute Noncondensible Gas (DNCG)
- Concentrated Noncondensible Gas (CNCG)
- Stripper Off Gas (SOG)
- Chip Bin Noncondensible Gas (CBNCG)
- Dissolving Tank Vent Gas (DTVG)
- Soap
- Methanol
- Turpentine
- Tall Oil
- Spent Acid
- Secondary Sludge
