A chemical recovery boilers is described in which the primary air system is reconfigured to provide aggressive charbed control and improved combustion in the lower furnace. The fewest number of primary air ports are used on two opposing walls to generate powerful air jets that penetrate across the boiler providing physical and thermal stability to the charbed while increasing the heat release and combustion stability in the lower furnace, increasing reduction efficiency, and lowering carryover and emissions. Various embodiments are described including operating strategies and multi-level black liquor injection.

A chemical recovery boilers is described in which the primary air system is reconfigured to provide aggressive charbed control and improved combustion in the lower furnace. The fewest number of primary air ports are used on two opposing walls to generate powerful air jets that penetrate across the boiler providing physical and thermal stability to the charbed while increasing the heat release and combustion stability in the lower furnace, increasing reduction efficiency, and lowering carryover and emissions. Various embodiments are described including operating strategies and multi-level black liquor injection.

The invention discloses a process for treating black liquor comprising pyrolysing black liquor in a fluidized bed reactor to obtain solid particles and pyrolysed black liquor gas, heating the solid mass, returning the heated solid mass to the fluidized bed reactor for use in the pyrolysis reaction; condensing the pyrolysed black liquor gas to obtain a condensate and recover heat and a residual gas released during condensation for heating the solid mass to a predetermined temperature for that is required for the pyrolysis.

The invention discloses a process for treating black liquor comprising pyrolysing black liquor in a fluidized bed reactor to obtain solid particles and pyrolysed black liquor gas, heating the solid mass, returning the heated solid mass to the fluidized bed reactor for use in the pyrolysis reaction; condensing the pyrolysed black liquor gas to obtain a condensate and recover heat and a residual gas released during condensation for heating the solid mass to a predetermined temperature for that is required for the pyrolysis.

A method and system to determine one or more proportional particle group shares in flue gas of a recovery boiler (110) based on optical information gained from a flue gas sample. A processor (202) is used to read (301) a digital frame comprising the area under consideration, which represents at least a part of the surface of a sampler (120) kept in the flue gas flow of a recovery boiler. Particle group areas matching a color characteristic of the particle group comprised in the flue gas is determined (302) from the area under consideration. The joint area of the identified particle group areas is determined (304), and the share of the joint area from the total area is determined (305) as the proportional particle group share of the particle group.

A method and system to determine one or more proportional particle group shares in flue gas of a recovery boiler (110) based on optical information gained from a flue gas sample. A processor (202) is used to read (301) a digital frame comprising the area under consideration, which represents at least a part of the surface of a sampler (120) kept in the flue gas flow of a recovery boiler. Particle group areas matching a color characteristic of the particle group comprised in the flue gas is determined (302) from the area under consideration. The joint area of the identified particle group areas is determined (304), and the share of the joint area from the total area is determined (305) as the proportional particle group share of the particle group.

A method to be used in conjunction with a single-stage or multi-stage process for leaching ash originating from the recovery boiler of a pulp mill, particularly when the ash contains a significant amount of carbonate, wherein calcium compounds, such as calcium oxide (CaO) or calcium hydroxide (Ca(OH).sub.2), are employed as additives in one or more leaching stages, a liquid fraction formed in the leaching process is utilized outside the main chemical recovery cycle, such as a substitute for purchased sodium hydroxide in the bleaching line of the pulp mill, and a solids fraction may be mixed with a black-liquor stream of the mill or subjected to further processing to separate calcium compounds for recycle.

A method to be used in conjunction with a single-stage or multi-stage process for leaching ash originating from the recovery boiler of a pulp mill, particularly when the ash contains a significant amount of carbonate, wherein calcium compounds, such as calcium oxide (CaO) or calcium hydroxide (Ca(OH).sub.2), are employed as additives in one or more leaching stages, a liquid fraction formed in the leaching process is utilized outside the main chemical recovery cycle, such as a substitute for purchased sodium hydroxide in the bleaching line of the pulp mill, and a solids fraction may be mixed with a black-liquor stream of the mill or subjected to further processing to separate calcium compounds for recycle.

A feedstock includes feedstock paper and non-paper material. The feedstock paper includes lignin and cellulose. A method includes cooking the feedstock in cooking liquor to dissolve at least a portion of the lignin from the feedstock paper and to at least partially dissolve the non-paper material in the cooking liquor, thereby yielding a cooked pulp. The method further includes washing the cooked pulp to yield washed pulp and spent cooking liquor, regenerating the spent cooking liquor to yield regenerated cooking liquor, and bleaching the washed pulp.

The present invention relates to a heat recovery system 10, 11, 12 for recovering heat from flue gas generated by combustion at a biomass plant installation. The heat recovery system 10, 11, 12 comprises a flue gas cooler 200 configured to receive flue gas 201 from a combustion and transfer heat from the flue gas 201 to feed water in a heat recovery fluid circuit101. The feed water in the heat recovery fluid circuit101 is taken from and returned to a feed water main system. The feed water main system could be provided with a feed water tank 100to which a heat recovery circuit inlet 112 and a heat recovery circuit outlet are connected. Further, the heat recovery system comprises a waste heat accumulator 300 configured to receive feed water, heated by flue gas 201 in a flue gas cooler 200, and cool by flashing the received feed water in order to generate flash steam, and the heat recovery system 10, 11, 12 comprises a control arrangement 533. Further, the present invention also relates to a method performed by the control arrangement for use in recovering heat from flue gas generated by combustion at a bio plant installation.