Chemistry of pulp and paper making . on this principle is so constructed that thesteam from the liquid evaporated in the first section, or effect,is used to boil that in the second effect, this being kept underenough lower pressure so that active ebullition takes place. Thesteam from the second effect in turn boils the liquor in the thirdeffect and so on through the system which may consist of threeto five effects. The only necessity for heat from outside sourcesis therefore in the first effect in which the liquor is raised fromthe entering temperature to the temperature of ebullition at thepr
Chemistry of pulp and paper making . on this principle is so constructed that thesteam from the liquid evaporated in the first section, or effect,is used to boil that in the second effect, this being kept underenough lower pressure so that active ebullition takes place. Thesteam from the second effect in turn boils the liquor in the thirdeffect and so on through the system which may consist of threeto five effects. The only necessity for heat from outside sourcesis therefore in the first effect in which the liquor is raised fromthe entering temperature to the temperature of ebullition at thepressure in this effect. The pressure in the first effect variesgreatly in different mills and with different types of apparatus. One of the evaporators most frequently used in soda pulpmills is the Yaryan in which the liquor passes back and forththrough the tubes and finally is discharged against baffle platesin a separating chamber. The tubes are 3 ins. in diameter 1 Beveridge: Paper Makers Pocket Book, p. 106. RECOVERY OF SODA 129. NiL Fig. 17. YARYAN EvaporatorCourtesy of Mr. Chas. Ordway I30 THE SODA PROCESS and 12 ft. long and as five tubes form a unit the liquor travels60 ft. before it is discharged. From this chamber the steampasses into the shell of the next effect while the liquor goes tothe tubes. The vacuum is maintained by means of a con-denser and pump and the strong black liquor is removed from
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