Exchanger Maintenance

Figure 1. Different histone chaperones in the key histone metabolic pathways Functions of histone chaperones range from the storage of newly synthesized histones in the cytoplasm, its transfer into the nucleus and in histone assembly into nucleosomes. Apart from diis die histone chaperones are also involved in histone exchange, maintenance of heterochromatin and in the regulation of chromatin structure during transcription. (See Colour Plate 10.)...

Particle deposition in the respiratory tract can initiate inflammatory responses. With repeated deposition, inflammation becomes chronic, and the site or sites of deposition beeome laden, not only with the particulates, but with several types of cells—fibroblasts, macrophages, leukocytes, and lymphocytes. These cells are normal constituents of the lung, an organ composed predominantly of connective tissue. Lung connective tissue forms the thin membrane that defines the functional alveolar-capillary unit. Inside this air sac and on the membrane are specialized eells required for gas exchange, maintenance, and repair (Fig. 3.6). 

The heat exchanger must be maintainable. It must allow mechanical or chemical cleaning if the heat transfer surface becomes fouled, and it must permit replacement of the tubes, gaskets, and any other components that may fail or deteriorate during the normal lifetime of the exchanger. Maintenance should be accomplished with minimum downtime and handling difficulties and labor cost. 

Resin Rinse. [Nalco] Ion exchange maintenance program. 

In exchanger maintenance either the complete unit is removed, cleaned and repaired, or only the tubebundle is removed for cleaning and repair — the shell is cleaned in place. If the complete unit is removed, all piping must be disconnected. If only the tubebun e is removed, only the channel nozzle piping need be disconnected. The piping designer can help maintenance in three ways ... 

The high costs of frequently repairing cryogenically cooled probes have prompted vendors to require or at least strongly suggest that their cooled probe customers purchase an annual probe plus heat exchanger maintenance contract for sums in excess of 25,000. 

Two such power modules are required for LEADIR-PS 200. The closed cycle gas turbine is very attractive, facilitating modular construction, module exchange maintenance and overhaul, and remote (unattended) operation. 

Traditionally maintenance parts are replaced on a time base. For example, an HPLC pump seal every 2 months, a detector s lamp every 3 months or so. This is not economical for the laboratory and not environmentally friendly because frequently a replacement of the parts would not yet be necessary. A better way is to exchange maintenance parts on a usage basis. The user can enter limits for the lamp, the solvent pumped through and the number... 

Fertilization of ponds to increase productivity is the next level of intensity with respect to fish culture, followed by provision of supplemental feeds. Supplemental feeds are those that provide some additional nutrition but caimot be depended upon to supply all the required nutrients. Provision of complete feeds, those that do provide all of the nutrients required by the fish, translates to another increase in intensity. Associated with one or more of the stages described might be the appHcation of techniques that lead to the maintenance of good water quaUty. Examples are continuous water exchange, mechanical aeration, and the use of various chemicals used to adjust such factors as pH, alkalinity, and hardness. 

The other space-saving approach is to use the Kobe (Kobe Steel) type of channel enclosure, which does not have all the external head bolts of typical TEMA Type B or Type C head enclosures. These exchangers require special tools to remove the tube bundles and trained maintenance personnel to do the work. These exchangers should never be located in stmctures because of the need to be able to access the channel from grade as it is difficult to remove the channel cover plate by using special equipment. 

Stacking heat exchangers so that the center line is higher than 5 m or more than three stacks high can be a problem for maintenance. If more exchangers are required, eg, four, then the exchangers must be stacked in two pair two bundles high, because the surface area exceeds that which can be fabricated into three bundles. 

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. 

Figure 12 shows the plan and elevation views of a process unit piping (9). A dmm is supported off the piperack. Heat exchangers are located far enough back from the support columns so that they are accessible and their shell covers can be removed. Pumps are located underneath the piperack, but sufficient room is provided for maintenance equipment to access the motors and to remove the pump if necessary. The motor is always oriented away from the process equipment and located on that side of the piperack. Instmment valve drops are shown supported from the columns. The instmment trays themselves mn on the outside of the support columns. Flat turns are only made from the outside position of the piperack. Nozzle-to-nozzle pipe mns are made whenever possible. Larger lines are located on the outside of the piperack. Connections to nozzles above the rack are made from the top... 

A flow diagram for the system is shown in Figure 5. Feed gas is dried, and ammonia and sulfur compounds are removed to prevent the irreversible buildup of insoluble salts in the system. Water and soHds formed by trace ammonia and sulfur compounds are removed in the solvent maintenance section (96). The pretreated carbon monoxide feed gas enters the absorber where it is selectively absorbed by a countercurrent flow of solvent to form a carbon monoxide complex with the active copper salt. The carbon monoxide-rich solution flows from the bottom of the absorber to a flash vessel where physically absorbed gas species such as hydrogen, nitrogen, and methane are removed. The solution is then sent to the stripper where the carbon monoxide is released from the complex by heating and pressure reduction to about 0.15 MPa (1.5 atm). The solvent is stripped of residual carbon monoxide, heat-exchanged with the stripper feed, and pumped to the top of the absorber to complete the cycle. 

Testing Upon completion of shop fabrication and also during maintenance operations it is desirable hydrostatically to test the shell side of tubular exchangers so that visual examination of tube ends can be made. Leaking tubes can be readily located and serviced. When leaks are determined without access to the tube ends, it is necessaiy to reroll or reweld all the tube-to-tube-sheet joints with possible damage to the satisfactoiy joints. 

The hairpin heat exchanger, unhke the removable bundle TEMA styles, is designed for bundle insertion and removal from the return end rather than the tubesheet end. This is accomplished by means of removable spht rings which shde into grooves machined around the outside of each tubesheet and lock the tubesheets to the external closure flanges. This provides a distinct advantage in maintenance since bundle removal... 

Tolling presents a special consideration that can make the training step easier. Typically a toller s technical staff, operators and mechanics are knowledgeable in the basic operations and tasks related to the toller s specialty. For example, experienced operators may know operations of the reactors, columns, exchangers, and packaging equipment quite well. The mechanical personnel may be very familiar with the required safe work practices, equipment cleaning procedures and maintenance tasks for standard vessels and piping. 

It is neeessary to understand the TDH and it s eomponents in order to make eorreet deeisions when parts of the system are changed, replaced, or modified (valves, heat exchangers, elbows, pipe diameter, probes, filters, strainers, ete.) It s neces.sary to know these TDH values at the moment of specifying the new pump, or to analyze a problem with an existing pump. In order to have proper pump operation with low maintenance over the long haul, the BF P of the pump must be approximately equal to the TDH of the system. 

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