Return Headers

All process traps should have a Strainer in the trap inlet line. An outlet shutoff valve should be provided to permit isolation of the trap for maintenance without having to drain the equipment or shutdown the condensate return header. The trap, strainer, and valves should be arranged to allow access for operation, maintenance, testing, and inspection. Modular hook-ups are recommended. 

Traps should be installed below the equipment being drained. If this is not possible, a lift fitting or water seal should be provided at the low point. Discharge lines should be kept short to minimize freezeup damage. Traps should be installed to be self draining. Bucket traps must be protected from freezing and must be protected against loss of prime as a result of sudden or frequent drops in steam pressure. 

Condensate return lines are more important today because significant amounts of energy can be conserved by collecting condensate and returning it for recycle. Condensate return lines must be adequate to avoid problems as a result of  

Improperly sized condensate return headers result in overpressurization of the return system, venting of excessive amount of vapor, vapor binding of condensate pumps, faulty steam trap operation, and water hammer. The following factors should be considered  

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Specimen Location Main cooling water return header... 

Steel pipe in a cooling water return header contained numerous deep pits on internal surfaces one pit penetrated the pipe wall (Fig. 5.8). Pits range in size from pinpoint depressions to y2-in. (1.3-cm) pockets. Some pits are filled... 

Water hammer can also occur in steam mains, condensate return lines, and heat exchange equipment where steam entrapment can take place (Fig. I). A coil constructed and installed as shown here, except with just a steam trap at the outlet, permits steam from the control valve to be directed through the center tube(s) first. Steam then gets into the return header before the top and bottom tubes are filled with steam. Consequently, these top and bottom tubes are fed with steam from both ends. Waves of condensate are moved toward each other from both ends, and steam can be trapped between the waves. 

A 450 psig steam system discharges 9,425 lbs,/hr of condensate through traps into a return condensate line. The return header is to discharge into a flash tank held at 90... 

Pipes buried in the structural slab. These are connected to delivery and return headers, and glycol circulated. This is heated by waste heat from the refrigeration plant. Steel pipe should not be used under the floor unless protected against corrosion. Air vent pipes to allow a current of ambient air through the ground under the base slab. This is not very suitable in cold climates. 

The 35 ft of elevation (about 15 psi of head pressure) that the water had to gain to climb to valve B. Of course, this 15 psi of head loss was regained when the water flowed back down to the cooling-water return header. 

The tube-side fluid now flows into the floating head, which acts as a return header for the tubes. The tube-side flow makes a 180° turn and flows back through the top hah of the floating-head tubesheet. The floating head is firmiy attached to the floating-head tubesheet. But why is it that one end of the tubes must be left free to float The reason is thermal expansion—or, more precisely, the differential rate of thermal expansion between the tubes and the shell. 

THE PRESSURE DROP (psi/lOOft.) OF THE STEAM CONDENSATE MIXTURE IN THE RETURN HEADER. 

Return headers are available with minimum center-to-center distances of the tubes from 1-1/2 o 2 diameters, depending on the tube size and... 

For a given working pressure the cost of a tube varies approximately as the square of the diameter. Return headers, being geometrically similar, vary in weight and cost approximately as the cube of the diameter. For a given total surface, smaller tubes are obviously cheaper. On the other hand, the pressure drop per unit length varies as the inverse of the diameters, 1/T>. To use smaller diameter tubes and have a reasonable pressure drop, it is usually necessary to have some passes in parallel. 

Figure A modern "screw lock" return header.

The results show that six rows of finned tubes can do the work of 18 rows of bare tubes. Finned tubes are more expensive than bare tubes, but other costs must also be considered such as additional steel structure, refractories and return headers. 

Cooling water lines are generally below grade and should run right under the aligned channel nozzles of all coolers. The cooling water return header is usually adjacent to the cooling water line. 

The storm-water sewer should be designed to collect the maximum surface drainage. This is to include the rainfall in one hour, wash water not of a contaminated nature and cooling water when not returned in return headers to the cooling water facilities. 

Take steam off the top of the steam header put condensate into the top of the condensate return header. 

Chilled water supply involves a closed circuit. The water flows through a supply header, the users, and a return header to a storage/pump tank. Demineralized water is a typical source. It is added occasionally to replace water lost from the system or deliberately purged to remove contaminants such as process fluids and corrosion products. Storage tank construction is simple. The pressure is essentially atmospheric and the temperature is low. Since water is more corrosive when aerated, the tank may be blanketed, and plain carbon steel construction should be avoided. Lined steel and FRP are acceptable materials of construction. 

A similar problem sometimes occurs when heating with high pressure steam. In these cases there is not enough pressure differential between the steam supply header and the condensate return header to allow the steam condensate pressure to be properly controlled. This problem usually occurs when the process boiling temperature is lower than the saturated steam temperature at a pressure equal to that of the condensate return header. 

A steam-generation system is designed to safely return cooled condensate to the boiler. A device called a steam trap is used to collect and transfer this material. Low points in the steam system are used to capture cooled condensate before it can damage the piping or equipment. Water can expand to many times its original volume when vaporized, so the condensate return header is a... 

Heat exchangers Hot-water return header Blow-down... 

Having determined that hydrocarbons are entering the cooling water return header, one will want to find which exchanger is the culprit. Open the V4-in. vent on top of the channel head (refer to Fig. 16-2). Then, without immersing the probe in the flowing water, check for combustibles with a gas test meter. 

An example of process cooling water and potable water layout is shown in Exhibit 13-21. As with most piping layouts, the lines are run in the most direa route possible to each of the water users (shown shaded in the exhibit). The locations where the cooling and hot water lines enter and leave the unit are usually set by the client or by the location of any existing supply and return headers. In this case, the west battery limit has been seleaed. Both lines run at the same elevation, as shown in Exhibit 13-22. When branch lines must cross over supply headers, they should return to the elevation of the higher branch line, unless the distance is so short that it would be impractical to do so. 

Parallel cooling water and hot water return headers must be kept a minimum of 12 in (300 mm) from the outside of the pipe diameters. Running these two headers too close together may affect the temperature... 

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