Liquor flow devices

At the bottom of this zone, the outlet device is located. The most digester input variables are the wood chips flow ood,m, the liquor flow (pngour,m and the heat supply Qheatmg and the most important output variables are the Kappa number x which is a measure for the amount of lignin in the wood chips and the yield % which is a measure of the amount of wood recovered in comparison to the amount fed to the digester. 

Crystals suspended in liquors emerging from crystallizers are normally passed to solid-liquid separation devices such as gravity settlers or thickeners that may subsequently feed filters to remove yet more liquid prior to drying. Here the transport processes of particle motion and the flow of fluids through porous media are important in determining equipment size, the operation of which may be intensified by application of a centrifugal force. 

Crystallizers are made more flexible by the introduction of selective removal devices that alter the residence time distributions of materials flowing from the crystallizer. Three removal functions—clear-liquor advance, classified-fines removal, and classified-product removal— and their idealized removal devices will be used here to illustrate how design and operating variables can be manipulated to alter crystal size distributions. Idealized representations of the three classification devices are illustrated in Fig. 17. 

Clear-liquor advance from what is called a double draw-off crystallizer is simply the removal of mother liquor without simultaneous removal of crystals. The primary action in classified-fines removal is preferential withdrawal from the crystallizer of crystals of a size below some specified value this may be coupled with the dissolution of the crystals removed as fines and the return of the resulting solution to the crystallizer. Classified-product removal is carried out to remove preferentially those crystals of a size larger than some specified value. In the following discussion, the effects of each of these selective removal functions on crystal size distributions will be described in terms of the population density function n. Only the ideal solid-liquid classification devices will be examined. It is convenient in the analyses to define flow rates in terms of clear liquor. Necessarily, then, the population density function is defined on a clear-liquor basis. 

Reactor designs based upon a rotating inner cylinder in turbulent flow have been well described in the literature [35-37] and a wide variety of devices has been used for metal removal from chemical process liquors [32,37] and hydrometallurgical process streams [38-40]. Despite the drawbacks associated with a rotating drive assembly and associated electrical power brushes, RCE reactors have exploited the following key characteristics [37] ... 

Oxidizer Configuration. Several types of oxidizers have been employed (Thompson and Nicklin, 1964). The simplest and most commonly used is a vertical tank containing an air distribution device at the bottom. The liquid and air flow concurrently upward, and the sulfur froth is removed by overflowing a weir at the top of the vessel. The liquor, which is essentially sulfur free, is withdrawn at a point located below the top of the oxidizer. 

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