Internal pipe distributors

Internal pipe distributors are frequently used for feed or reflux inlets for trayed columns or towers (fractionation or distillation columns). They are used to distribute the inlet stream to a particular point on a tray or uniformly across a tray. The distributor consists of one or more pipes, with or without branches, containing a series of holes, slots or spray nozzles. This procedure addresses the design of these distribution devices. 

Internal pipe distributors are also known as perforated spargers or perforated pipe distributors or headers. They can be designed for either liquid only or two phase flow. A pipe distributor may be considered as liquid service if the volume of vapor is no more than 5%. 

INTERNAL PIPE DISTRIBUTORS - FEED OPTIONS - ELEVATIONS... 

Reflux nozzles must be arranged to enter the tray with proper designed internal pipe to the tray downcomer or distributor. 

Figure 1335. Packed column and internals, (a) Example packed column with a variety of internals [Chen, Chem. Eng. 40, (5 Mar. 1984)]. (b) Packing support and redistributor assembly, (c) Trough-type liquid distributor, (d) Perforated pipe distributor, (e) Rosette redistributor for small towers. (0 Hold-down plate, particularly for low density packing.

The catalyst beds are mounted in a single reactor vessel because it is more economical than using multiple vessels. The spacing between beds is set at 1 m. The length-to-diameter aspect ratio of the vessel is 10. Because a multibed reactor must have internal piping, flow distributors, and bed supports, a multi-bed reactor vessel is more expensive than a simple vessel. We assume that each additional bed increases reactor capital cost by about 25%, as shown in Table 5.2. 

Slurry Reactors Slurry reactors are akin to fluidized beds except the fluidizing medium is a liquid. In some cases (e.g., for hydrogenation), a limited amount of hydrogen may be dissolved in the liquid feed. The solid material is maintained in a fluidized state by agitation, internal or external recycle of the liquid using pipe spargers or distributor plates with perforated holes at the bottom of the reactor. Most industrial processes with slurry reactors also use a gas in reactions such as chlorination, hydrogenation, and oxidation, so the discussion will be deferred to the multiphase reactor section of slurry reactors. 

The coal is crushed in a hammer mill, dried, and then screened to —16 + 80 mesh. About 500 lb. of coal are charged to a hopper, which is connected at the bottom to the pretreater by a screw feeder. The feed enters the pretreater about 6 inches above the distributor plate. Feed rates of up to 100 lb./hr. can be attained. A 3-in. diameter overflow pipe controls the bed height. The overflow collects in a receiver and is periodically dumped into drums. Fines from the bed were originally returned to the bed by an internal cyclone with a dipleg sealed in the bed, but tar tended to build up in the cyclone and caused the reactor pressure to increase. At present, a heated external cyclone with a collector pot is installed and operates much more smoothly. 

The normal direction of flow in such a bed is downward so that the resin acts as a packed bed without any relative movement of particles. The bed of resin can be supported by various means. The simplest is to fill the vessel to cover the lower dished end with coarse sand in which distributor manifold pipes are buried. This can create problems because the volume of liquid trapped in the voids of the sand can cause cross-contamination between cycles of operation. An internal false floor with distributor cups of plastic screwed into place on a grid pattern overcomes this problem. Such constraction is more expensive and has to be supported structurally to take the entire pressure thrust on the bed during flow. Some plants use an elaborate manifold of distributor pipes laid against the lower dished end which is itself filled with resin. 

In an HR system with internal heating large-diameter flow channels are located in the distributor or more usually in the mould plate itself (Figure 1.7a). In the channel axis there is normally a pipe with a cartridge heater. Because the external wall of the channel is cold, the outside layer of plastic freezes and forms an insulating layer. This gives a substantially lower electricity consumption (by some 50%), and there are no problems with heat insulation or thermal expansion of the distributor. The outside frozen layer of plastic functions at the same time as an excellent seal for the system. The HR temperature essentially has no bearing on the thermal balance of the mould. 

Large internal combustion engines are often started with air. This air is provided by a compressor—typically a conventionally lubricated reciprocating machine—and then piped to an air distributor on the engine. Explosions can be caused if combustible lubricant is present in the air. Therefore, noncombustible lubricants should be used. 

---