Until recently even the thought of disposal of any NCG in the recovery boiler was frowned upon by many companies; A. H. Lundberg Associates, Inc. has had over ten years of experience with this process. With the increase in size of dilute NCG systems and the need for a simple, efficient, safe and inexpensive location for destruction, the recovery boiler is now being given more consideration. The Black Liquor Recovery Boiler Advisory Committee has developed a set of guidelines and recommendations to follow when burning the gases in the recovery boiler. The A. H. Lundberg Associates, Inc. system design is in strict accordance with the recommendations and includes many additional safeguards.

All three types of NCG have been successfully disposed of in the recovery boiler, though it is most suited for dilute NCG. When burning strong NCG or stripper off gas (SOG), an auxiliary fuel burner is used to insure combustion. The SOG may also be liquefied and mixed with the liquor to be burned. Introduction of the dilute NCG into the boiler may be either at the secondary or tertiary air level.

When burning the dilute NCG with the secondary air the gas is injected into the secondary air duct requiring the duct to be stainless steel. When burning the gases in the tertiary air, a separate NCG header and air injection ports are provided. In all cases when burning the dilute NCG, it is preheated to minimize concern over entrained liquid entering the boiler. The degree of preheat is dictated by the boiler requirements.

The NCG piping design is such as to make it almost impossible for water to enter the boiler with the NCG. A fail safe design using rupture discs and piping elevation changes protect the system from a slug of water entering the recovery boiler.