Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With regeneration – reclamation – reuse – recycling or...
Patent
1997-08-12
1998-10-13
Silverman, Stanley S.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With regeneration, reclamation, reuse, recycling or...
162 3011, 162 62, 422185, 422236, D21C 1112
Patent
active
058207295
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a device for dissolving smelt chemicals from recovery boilers, a so-called soda smelt dissolver, and also to a process for dissolving such chemicals using the device according to the invention, with the principal advantage of the device and the process being that plugging and coating of the device are prevented as a result of the deposition of pirssonite being decreased.
STATE OF THE ART
When concentrated spent liquor, so-called black liquor, from cellulose production is combusted in recovery boilers, smelt chemicals are obtained which are tapped off from the recovery boiler and down into a so-called soda smelt dissolver. This soda smelt dissolver consists of a tank which is preferably elongate, and which is equipped with devices for supplying smelt chemicals and liquid for dissolving the chemicals, which liquid is normally in the form of so-called weak liquor, which is a dilute aqueous alkaline solution which comes from the lime treatment. Normally, the temperature of the smelt is in the region of 800.degree. C. and that of the weak liquor is 70.degree.-80.degree. C. The temperature of the solution in the soda smelt dissolver is approximately 95.degree. C. The soda smelt dissolver is provided with stirring devices and with spraying devices for adding the smelt so that the latter, which is at a high temperature, does not produce too violent a reaction when it meets the surface of the liquid, which is at a substantially lower temperature. For tapping it, the tank is provided with two outlet pipes which are placed at a distance from each other.
However, one of the pipes can alternately be used as an inlet pipe for weak liquor while the other is used as an outlet pipe for the solution, so-called green liquor.
TECHNICAL PROBLEM
A continually recurring problem associated with soda smelt dissolvers is that pipes and valves have a tendency to become plugged with solid matter and that the stirrers also become coated with such matter. This solid matter principally consists of pirssonite, which is a chemical combination of sodium carbonate and calcium carbonate. While the sodium carbonate derives in the main from the chemical smelt, the calcium carbonate arrives in the soda smelt dissolver together with the weak liquor. Deposition of this double salt depends partly on the concentration and partly on the temperature of the solution. The higher the concentration of alkali and the lower the temperature of the solution, the more pirssonite is deposited. This problem is described, for example, by W. J. Frederick Jr. and Rajeev Krishnan and also Russell J. Ayers, in the article Pirssonite Deposits in Green Liquor Processing in the journal Chemical Recovery 1989, pp. 151-156. The need to decrease, or completely eliminate, this deposition problem in soda smelt dissolvers has therefore existed for a long time.
SOLUTION
In accordance with the present invention, therefore, the abovementioned problem has been solved and a device for dissolving smelt chemicals from recovery boilers, a so-called soda smelt dissolver, has been produced, which device includes devices for supplying smelt chemicals and dissolving liquid and also outlets for the resulting solution, which device is characterized in that it consists of at least two separate dissolving tanks, which are connected to each other near the bottom to allow free flow of liquid between them, and of devices for the separate supply to each tank of dissolving liquid and smelt chemicals in dependence on the measured and established chemical concentration in the solution in each of the tanks, wherein the outlets from the tanks can be separately shut off and regulated.
According to the invention, the device for supplying dissolving liquid includes a separate conduit from which branches pass to the different tanks by way of an adjustment valve.
According to the invention, it is expedient for each tank to be provided with an outlet pump which can be regulated separately.
According to the invention, the devices for measuring the
REFERENCES:
Lavigne, John R., "Instrumentation . . . Paper Industry", Miller Freeman Publications, pp. 120-125, 1979.
Frederick, W.J., "Pirssonite . . . Processing", Tappi Journal vol. 73, No. 2, pp. 135-140, Feb. 1990.
Tappi Journal, vol. 73, No. 2, Feb. 1990, W.J. Frederick, Jr., et al, "Pirssonite deposits in green liquor processing", pp. 135-140.
Ericsson Tommy
Jansson Sven-Erik
Fasth Rolf
Kvaerner Pulping AB
Nguyen Dean T.
Silverman Stanley S.
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