Permit, column entry

Molecular sieve chromatography, useful for separating proteins of different sizes, operates as follows. The protein sample solution is placed in the top of a cylinder (or column) packed with molecular sieves, as shown at the left of Figure 6.28. The sieves consist of tiny balls (or beads) that contain small pores (or holes) of unifonn size. The size is small enough to permit the entry (or passage) of a small protein... 

When column diameter is restricted Examples include small columns, where the diameter needs to be at least 2 V2 to 3 ft to permit personnel entry an existing column used for a new service or a hydraulically underloaded section of a constant-diameter column. When the diameter in such columns is hydraulically oversized, it becomes attractive to minimize tray spacing, thus utilizing excess capacity to reduce column height or increase the number of trays. 

When satisfied that all is safe, the officer can issue a written permit for entry into the column. The permit should identify the joh site, indicate date and duration, and specify all safety requirements. A qualified supervisor should accept responsibility for policing these requirements. A copy of the permit should be available at the job site emd another in the control room. The permit should be valid for no longer than one shift, or at the most, one day. Extensive guidelines for the format of such permits are described elsewhere (416). 

Sticking a head in can be as hazardous as column entry (210), and must only be permitted when entry is permitted. 

When the entry in Column 15 of Table I ends with a "+", signifying that information about one or more rate or equilibrium constants associated with the ha If-reaction is given here, that information is contained in a table at the end of the entry. In all such tables individual compounds are identified by means of the code numbers that accompany them in Table I. A few values of equilibrium constants obtained by spectrophotometric or other non-electrochemica1 techniques are included to permit comparison with the accompanying electrochemical results. 

An alternative approach is to use a splitless injection system. If the valve in Fig. 1 is closed, then all the sample passes into the column and there is no split ipso facto, the device is a splitless injector. When used in the splitless mode, however, it is usual to employ a somewhat wider capillary column, which will allow the penetration of a small-diameter injection syringe and thus permit on-column injection. Under these circumstances, there can be no differential sampling of the form described. This procedure, however, introduces other injection problems that can affect both resolution and quantitative accuracy that need to be addressed (See the entries Retention Gap Injection Method and Solute Focusing Injector Method). 

In a moving bed column the flow of liquid is up through the bed of carbon, while the carbon advances periodically down through the column.9 This permits frequent removal of small amounts of spent carbon from the bottom of the column and corresponding additions of fresh carbon to the top. The withdrawal of spent carbon is controlled by a valve below the cone-shaped bottom. The fresh carbon should be immersed in water or in the liquid being treated to facilitate its entry at the top of the column.9... 

Any electrical equipment connected to the column should be locked out and any radiation sources should be removed or shielded. The mere removal of fuses is unsatisfactory, as fiises can easily be (inadvertently) replaced. Ignition sources should be removed from the vicinity of the column. Any exceptions (e.g., electric lighting equipment) should be carefully examined and clearly stated on the entry permit. 

The total mass of the system is m, /> is the total mass flux (mass flow per unit area) relative to the system boundaiy at any point, and S is the cross-sectional area normal to flow at that same location. The summations extend over all mass entry and exit locations in the system. The mass flux at any point is equal to pv, where /> is the mass density and u is the vdoci relative to the boundary at flitt point. Equation (2.2-1) can be applied equally well to a countercurrent gas absorption column or to a lake with in and output streams such as rain l, evapmation, streams flowing to or fnmi the lake, deposition of sediment on the lake bottom, or dissolution of minerals from the sides and bottom of the lak. The steady-slate version of Eq. (2.2-1) dmidt 0) is of use in chemical process analyas because H permits calcularion of various flow rates once some have been specified. 

We have reviewed the work authorized by this permit and the information contained here-in. Written instructions and safety procedures have been received and are understood. Entry cannot be approved if any squares are marked in the "No" column. This permit is not valid unless all appropriate items are completed. 

Both bed limiters and hold-down plates should be of sectional construction to permit entry into the column through a manhole. These plates must fit closely to the column wall to prevent passage of individual packing pieces. The free space through these plates must be high enough not to restrict the capacity of the tower packing. 

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