Method and apparatus for burning odor gas

A pulp mill comprising:

• an apparatus for burning primary fuel, the apparatus comprising:
• a furnace limited by at least a wall, the furnace having a primary process zone, a tertiary process zone, and a secondary process zone arranged in between the primary process zone and the tertiary process zone,
• a combustion gas heater comprising a secondary furnace configured to burn tertiary fuel to produce primary combustion gas,
• a primary pipeline for conveying primary combustion gas from the combustion gas heater to the primary process zone,
• a first pipeline for conveying primary fuel to the primary process zone,
• a tertiary pipeline for conveying tertiary combustion gas to the secondary process zone, and
• a quaternary pipeline for conveying quaternary combustion gas to the tertiary process zone,
• wherein the combustion gas heater is configured to form primary combustion gas having a temperature of at least 450° C. and the combustion gas heater comprises a compressor or a fan configured to drive primary combustion gas to the furnace;
• and
• at least one of:
• (i) an evaporator area to which at least one evaporator has been arranged,
• (ii) a digester area to which at least one digester has been arranged, and
• (iii) a stripper, and
• a collector configured to collect strong odorous gas, such as stripper off gas from the stripper and/or concentrated non-condensable odorous gas from the evaporator area and/or the digester area,
• wherein the first pipeline extends from the apparatus to the collector.

A method for burning primary fuel, wherein the primary fuel comprises at least a first compound containing nitrogen and a second compound comprising sulfur, the method comprising:

• producing primary combustion gas having an oxygen content from 7 vol % to 19 vol % by burning a tertiary fuel,
• feeding the primary fuel and the primary combustion gas to a primary process zone of a furnace,
• feeding tertiary combustion gas to a secondary process zone of the furnace,
• letting at least one of the primary fuel, the primary combustion gas, or their reaction products move from the primary process zone via the secondary process zone to a tertiary process zone of the furnace,
• feeding quaternary combustion gas comprising oxygen to the tertiary process zone of the furnace,
• producing such primary combustion gas that has a temperature of at least 450° C.,
• delivering the primary combustion gas to the primary process zone by means of a compressor or a fan, and
• controlling an amount of the quaternary combustion gas in such a way that an air-fuel equivalence ratio at the tertiary process zone is more than 1.1.