Reboiler piping requirement

Lines interconnecting exchangers with other process equipment can run just above the required headroom or about on the same level as the yard piping. Reboiler line elevations are determined by the draw-off and return line nozzles on the tower. Symmetrical reboiler piping arrangements — between the tower draw-off and reboiler inlet nozzles and between reboiler outlets and return... 

Valves are rarely included in reboiler piping — except, for example, when a standby reboiler is provided or when two or three reboilers are used and operated on an extremely wide heat capacity range. Some companies require line blinds at the tower nozzles for blanking off during shutdown, turn-around and maintenance. 

Used for small duties, clean process, and only infrequent cleaning required. Vaporization is usually less than 30%, but less than 15% if the fractionator pressure is below 50psig. The viscosity of the reboiler feed should be less than 0.5 cp. Put a butterfly valve in the reboiler inlet piping. This type is used in nearly 100% of chemical plant thermosyphon applications (70% of petrochemical). 

A centrifugal pump is required to circulate a liquid of density 800 kg/m2 and viscosity 0.5 x 10 3 Ns/m" from the reboiler of a distillation column through a vaporisor at the rate of 0.004 m3/s, and to introduce the superheated vapour above the vapour space in the reboiler which contains a 0.07 m depth of liquid. If smooth-bore 25 mm diameter pipe is to be used, the pressure of vapour in the reboiler is 1 kN/m2 and the Net Positive Suction Head required by the pump is 2 m of liquid, what is the minimum height required between the liquid level in the reboiler and the pump ... 

When alloy piping or large bore piping is required, the associated equipment is located together as much as possible to keep the pipe runs short, preferably nozzle-to-nozzle by avoiding the piperack. Items such as elevated overhead condensers are located near the source and destination. Similarly, theonosyphon reboilers need to be placed adjacent to the column they reboil. Where gravity flow is required, these lines must be kept short and sloped. Space allocation for future additions must also be considered. 

Estimation of column costs for preliminary process evaluations requires consideration not only of the basic type of internals but also of their effect on overall system cost. For a distillation system, for example, the overall system can include the vessel (column), attendant structures, supports, and foundations auxiliaries such as reboiler, condenser, feed neater, and control instruments and connecting piping. The choice of internals influences all these costs, but other factors influence them as well. A complete optimization of the system requires a full-process simulation model that can cover all pertinent variables influencing economics. 

Low investments are required for these external modifications to adjust the piping network to remove the inefficiencies and to install a new reboiler at the bottom of the LD side stripper. External modifications were considered first. This is because of the low investment that is required by these modifications. The throughput through the modified column could be increased by 39%. There are two options concerning the use of a reboiler or a combination of live steam and a reboiler at the KE side stripper. A trade-off exists between these two options where the use of a reboiler only is more beneficial with respect to the savings in the energy costs while the use of the combination of reboiler and steam save 16% in the furnace duty. 

The heating mediums of steam or a hot process stream always connect to the tube side of horizontal reboilers. The inlet piping should have a control valve — with block valves and a bypass globe valve, if required. This should be arranged near the reboiler s tube side inlet. 

Vapor disentrainment is not required in a sump or draw pan used exclusively to feed a thermosiphon reboiler, because the reboiler can handle some vapor bubbles in its liquid supply. It is important to size the reboiler sump for self-venting flow otherwise vapor pockets may choke the reboiler sump. Figure 4.5 can be applied to determine the maximum allowable velocity through the reboiler sump. The pipe diameter on the y axis of the diagram is considered... 

Restricting heat input to the reboiler This can be achieved by adding a restriction orifice or a short length of narrow-bore pipe in the heat input line to the reboiler, or a valve limiter to the heat input control valve. Alternatively, a pressure controller can be installed in the heat input line (in addition to the normal heat input controller). Restricting heat input is most effective when heat input failure sets column relief requirement. Two cases have been reported (60,414) where adding such a restriction orifice drastically reduced column relief requirements. Precautions are required to assure that the restriction orifice is not removed or resized in the future without resizing the relief device. Further discussion is in Sec. 9.4. 

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