Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Agitating to form larger particles
Patent
1995-05-03
1996-09-03
Theisen, Mary Lynn
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Agitating to form larger particles
23313P, B29B 908
Patent
active
055520995
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for pelletising particles of an alkali metal ferrite.
Wood may be mechanically or chemically pulped. The chemical pulping processes normally employed are the sulphate, sulphite and soda pulping processes. The economics of these processes rely heavily on the recovery of chemicals employed in them.
In the sulphate process wood chips are digested in a solution of sodium hydroxide, sodium sulphide and possibly some sodium carbonate. In the sulphite process wood chips are cooked in the presence of sulphur dioxide and a bisulphite or a sulphite. In the soda process the wood chips are cooked in the presence of a solution of sodium hydroxide and possibly some sodium carbonate. The wood pulp is separated from the liquor. The liquor from the sulphate process and the soda process is normally referred to as black liquor. The present invention is concerned with the recovery of sodium hydroxide from black liquors derived from the soda process.
The specification of Australian Patent No. 486122 describes a method of recovering sodium hydroxide from black liquor which involves the following process steps: a precipitate of ferric oxide; and repeating steps 3 and 4.
The specification of Australian Patent No. 519156 describes a process for recovering sodium hydroxide from black liquor which differs from the process described in Patent No. 486122 by the inclusion of a cold washing step. Sodium ferrite is washed in cold water to remove sodium chloride, sodium sulphate and other soluble impurities. The specification of Australian Patent No. 519156 also describes the use of a fluidised bed in the burning step.
The specification of Australian Patent No. 552973 describes a process similar to the process described in Australian Patent No. 519156 with the exception that it includes the step of agglomerating fines of ferric oxide and fines of sodium ferrite with black liquor before or during burning in a fluidised bed. The fines of ferric oxide are derived from the ferric oxide precipitated when sodium ferrite is added to warm water.
Normally flue gas from a fluidised bed furnace used for recovering sodium hydroxide from black liquor is laden with a dust which is typically pure sodium ferrite. It is desirable that the dust be collected, agglomerated and returned to the furnace. An aqueous binder such as black liquor differs from other agglomerating processes because the dust can chemically react exothermically with the binder and depending on the conditions, prevent agglomeration. The size and strength of the pellets produced by agglomeration of the dust also determines their subsequent utility as suitable bed material.
An object of the invention is to provide a process that is capable of agglomerating particles of sodium ferrite under plant conditions.
Accordingly, the present invention provides a process for pelletising particles of alkali metal ferrite with an aqueous binder, the process comprising: particle size range; binder into a microgranulator; microgranulator to produce microgranules of alkali metal ferrite; pan temperature to produce pellets of alkali metal ferrite wherein the pan temperature is controlled by cooling either or both the particles of alkali metal ferrite or aqueous binder prior to measuring them into the microgranulator.
Preferably the particles are ground to a size having an even distribution about a mean in a range from 25 to 50 micron and more preferably 25 to 30 micron. Particles ground to this size provide pellets of optimum strength and size.
The pellet size required preferably lies in the range from 0.5 to 3 mm. If the proportion of bed material less than 0.5 mm in size increases beyond about 20%, the fluidised bed cannot be successfully operated. The finer material is prone to stick and leads to defluidisation of the bed. The fluid bed will also not accommodate more than approximately 20% oversize material as this leads to segregation and defluidisation.
The acqueous binder may be a black liquor in which case it preferably has a solids concentration in a rang
REFERENCES:
patent: 4251475 (1981-02-01), Varrasso
patent: 5460765 (1995-10-01), Derdall et al.
Derwent On-Line Abstracts, Accession No. 80-19389C, Class E31, JP,A, 55015960 (Mitsui Shipbuilding Eng.) 4 Feb. 1980 (Apr. 2, 1980).
Derwent Abstracts, Accession No. 85-272336, Class V02, JP,A, 60183030 (Fuji Pauldal KK) Sep. 18, 1985 (Sep. 18, 1985).
Maddern Kenneth N.
Scott-Young Robert E.
Scukovic Jack
Wunder Heiko
Amcor Limited
Theisen Mary Lynn
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