Column repair

The location of exchangers is the key to maintenance. Usually the back head is kept at a distance of about three meters from the piperack support columns. Access equipment must be able to get in and remove the sheU cover and flange head. Access area must also be provided to handle and remove the sheU cover usually located under the piperack. The tube-pulling or rodding-out area must be kept clear to allow access to the channel end. This space should be at least equal to the tube length and about two meters from the tube sheet location. Tube removal space should be allowed for but is not mandatory if grade-mounted heat exchangers are used and mobile maintenance equipment employed to pick up the entire unit and transfer it to the repair shop. 

Example 1 Calculation of FUG Method A large hutane-pentane splitter is to he shut down for repairs. Some of its feed will he diverted temporarily to an avadahle smaller column, which has only 11 trays plus a partial rehoiler. The feed enters on the middle tray. Past experience on similar feeds indicates that the 11 trays plus the rehoiler are roughly equivalent to 10 equilih-rium stages and that the column has a maximum top-vapor capacity of 1.75 times the feed rate on a mole basis. The column will operate at a condenser pressure of 827.4 kPa (120 psia). The feed will he at its huhhle point (q = 1.0) at the feed-tray conditions and has the following composition on the basis of... 

Compared to syringe type or reciprocating pumps, pneumatic amplifier pumps are very cheap. They tend to be rather difficult to dismantle for repairs, and some types are very noisy in operation. Because they do not provide a constant flow of mobile phase, they are not used much in analytical hplc. They can, however, operate at high pressures and flow rates and so are used mainly for packing columns, where high pressures are needed and variations in the flow rate through the column do not matter. 

When no peaks are observed upon injection of a sample, it is common to blame the column but there are other factors that could cause this. Is the sample actually getting into the column The syringe needle may become clogged with parts of the septum or insoluble material from the sample. Loose plungers can permit the sample to be blown back by the pressure of the carrier gas. The syringe is a precision device and should be handled with care. Those with burred or bent needles, or bent plungers should be repaired before use. 

Finally, other proposals include the introduction of an amine into the eluent so that, unlike in bonded phases, preparation of the amino phase takes place in situ. This competes advantageously in terms of degradation of the column, since with this procedure columns may be immediately repaired by recoating and therefore losses in performance are minimized and even avoided. 

Both cationic and anionic silica columns need occasionally to be repaired. If you have the same packing material as the column, make a paste of it with mobile phase and paste it on to the column head. If the same packing is unavailable, use cyanopropyl packing for small repairs. If necessary, these columns can be washed with water, then with 20% DMSO/MeOH, with water, and, finally, reequilibrated with buffer. 

Table V gives the return p( 70, tb, tT) for 1970-71 which would result from continuing to operate the old plant. There are of course 15 entries, one for each possible combination of construction date and repair date. The net profit p0( 70 — fr) for each overhaul date is given in the left margin the technological bonus Pb(tb), in the top margin. An entry in row tr and column tb, which is simply the sum of the value at the left of the row with that at the top of the column, is the actual profit p( 70, fb, t,) to be gained from the decision not to repair or build in 1970. The blank entries represent impossible combinations—plants repaired before they are built. The asterisks will be explained later.

Let us consider now all possible dates of construction and previous overhaul. The two-stage returns (ib, tr) from a decision repair" in 1968 followed by an optimal decision in 1970 are given in Table X, which is constructed in much the same way as Table VI. The only difference is that at the head of each construction year column has been added the corresponding return /i(fb, 68), from an optimal decision in 1970. These num-... 

The skirt diameter is equal to the diameter of the column, and its height varies from 2 to 12 ft (0.61 to 3.66 m). The height of the skirt is determine by maintenance requirements. Maintenance workers need space to repair the bottom section of a colinnn. Columns could also be supported on a stracture. Assume that the skirt height for the absorber, Lai, in Figure 5.4.2, is 2.0 m (6.56 ft). 

Column entry fields for dates, times, and events (e.g., initial installation and calibration, updates, column changes, errors, repairs, performance tests, quality control checks, cleaning, and maintenance, plus fields for the name and signature of the technician making the entry). 

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