A process for the preparation of small aromatic compounds from black liquor comprising: providing black liquor that derives from alkaline treatment of wood chips; subjecting the black liquor to a pyrolysis treatment to yield a pyrolysed black liquor gas and a solid mass comprising char and salts in a first reactor, wherein the salts substantially derive from the treatment of black liquor; contacting at least part of the pyrolysed black liquor gas with a catalyst in a second reactor, which is different from the first reactor to provide a conversion treatment to yield a conversion product; and recovering small aromatic compounds from the conversion product.

The spent liquor (SL) of a thermomechanical pulping (TMP) process introduces a high load to the wastewater system of this process. To reduce this load, fly ash from a biomass boiler is used and the application of fly ash improves the performance of biological process. Three different alternatives are introduced to apply fly ash to treat spent liquor.

The spent liquor (SL) of a thermomechanical pulping (TMP) process introduces a high load to the wastewater system of this process. To reduce this load, fly ash from a biomass boiler is used and the application of fly ash improves the performance of biological process. Three different alternatives are introduced to apply fly ash to treat spent liquor.

A process for the preparation of small aromatic compounds from black liquor comprising: providing black liquor that derives from alkaline treatment of wood chips; subjecting the black liquor to a pyrolysis treatment to yield a pyrolysed black liquor gas and a solid mass comprising char and salts in a first reactor, wherein the salts substantially derive from the treatment of black liquor; contacting at least part of the pyrolysed black liquor gas with a catalyst in a second reactor, which is different from the first reactor to provide a conversion treatment to yield a conversion product; and recovering small aromatic compounds from the conversion product.

A method for removing ammonia (NH.sub.3) from a gas produced in a pulp mill (100). The method comprises producing raw non-condensable gas comprising ammonia (NH.sub.3) in the pulp mill (100) and transferring at least some of the raw non-condensable gas to a scrubber (200) containing aqueous scrubbing solution (130, 140). The method comprises adding a compound capable of decreasing a pH of the scrubbing solution to the scmbbing solution (130, 140) and in the scrubber (200), contacting the raw non-condensable gas with the scmbbing solution (130, 140), to react the ammonia (NH.sub.3) of the raw non-condensable gas with the scmbbing solution to produce clean non-condensable gas and ammonium (NH.sub.4.sup.+). A pulp mill comprising equipment for performing the method.

A method of recovering wood pulping chemicals from black liquor produced in a wood pulping process where the process entails burning the black liquor in a recovery boiler to form ash containing high levels of carbonate as well as sodium, potassium and chloride. The ash is dissolved to form a dissolved ash solution that is directed to a first stage crystallization unit that concentrates the dissolved ash solution and which results in the precipitation of sodium sulfate and sodium carbonate. Thereafter the concentrated dissolved ash solution is directed to a second stage crystallization unit which adiabatically cools the concentrated dissolved ash solution to form a glaserite slurry and a purge stream that is rich in chloride. In order to reduce the tendency of sodium carbonate and burkeite to crystallize in the second stage crystallization unit and to encourage pure glaserite to crystalize in the crystallizer, the method entails mixing a sulfate source, such as sodium sulfate or sulfuric acid, to the concentrated dissolved ash solution upstream of the crystallizer.

The present invention relates to a process for treating ash recovered from a recovery boiler. The process is designed to recover valuable pulping chemicals, such as potassium, sodium, carbonate, and sulfate. In the course of treating the ash, a chloride-rich purge stream is produced and includes sulfate, carbonate, potassium, and sodium that can be beneficially used in a wood pulping process. To segregate the chloride from the beneficial chemicals, the chloride-rich purge stream is directed into an anion segregation unit such as a nanofiltration or ion exchange unit. This effectively separates or removes the chloride from the purge stream and enables the beneficial chemicals to be recycled and used in the wood pulping process.