Pitch stepped

Conventional feeder screws have full-face flights welded to a centre shaft or tube. Uniform pitch screws are sometimes used in simple feeding applications. In order to secure differential intake of product along the axis of a screw, a range of techniques can be adopted, either individually or in combination where appropriate. Typical constructional features are (see Fig. 4.5) stepped pitch variable pitch stepped or taper centre tube or shaft variable screw diameter part ribbon or shaftless construction. (Occasionally the construction is stepped on the outside diameter.)... 

Roimding to the next larger, even number of pitches, the chain length equals 146 pitches. Step 9 Calculate the Final Center Distance... 

When the recycle soot in the feedstock is too viscous to be pumped at temperatures below 93°C, the water—carbon slurry is first contacted with naphtha carbon—naphtha agglomerates are removed from the water slurry and mixed with additional naphtha. The resultant carbon—naphtha mixture is combined with the hot gasification feedstock which may be as viscous as deasphalter pitch. The feedstock carbon—naphtha mixture is heated and flashed, and then fed to a naphtha stripper where naphtha is recovered for recycle to the carbon—water separation step. The carbon remains dispersed in the hot feedstock leaving the bottom of the naphtha stripper column and is recycled to the gasification reactor. 

The coal tar first is processed through a tar-distillation step where ca the first 20 wt % of distillate, ie, chemical oil, is removed. The chemical oil, which contains practically all the naphthalene present in the tar, is reserved for further processing, and the remainder of the tar is distilled further to remove additional creosote oil fractions until a coal-tar pitch of desirable consistency and properties is obtained. 

Fig. 10. Mass flow screw feeder designs, (a) Combined tapered shaft and variable pitch screw feeder where A represents a conical shaft and constant pitch (feed section) B, constant shaft and increasing pitch (feed section) and C, constant shaft and constant pitch (conveying section), (b) Stepped shaft screw feeder where A represents a stepped diameter shaft and constant pitch (feed section) and B, constant shaft and constant pitch (conveying section).

The first step in CTO distillation is depitching. A relatively small distillation column is used as a pitch stripper. The vapor from the pitch stripper is fed directiy into the rosin column, where rosin and fatty acids are separated. Rosin is taken from the bottoms of the column and fatty acids as a sidestream near the top. Palmitic acid and light neutrals are removed in the rosin column as heads. The operation is designed to minimize holdup and product decomposition. Care is taken to prevent carryover of some of the heavier neutrals, such as the sterols, from the depitcher to the rosin column (24). 

If the stock is to receive a second impregnation, it must be rebaked. In the past, stock containing raw impregnating pitch could be graphitized directly. However, the air polluting effect caused by this practice has made rebaking a necessary preliminary step to graphitization in order to achieve effective environmental control. 

Graphitization. Graphitization is an electrical heat treatment of the product to ca 3000°C. The purpose of this step is to cause the carbon atoms in the petroleum coke filler and pitch coke binder to orient into the graphite lattice configuration. This ordering process produces graphite with intermetaHic properties that make it useful in many appHcations. 

More than 95% of current carbon fiber production for advanced composite appHcations is based on the thermal conversion of polyacrylonitrile (PAN) or pitch precursors to carbon or graphite fibers. Generally, the conversion of PAN or pitch precursor to carbon fiber involves similar process steps fiber formation, ie, spinning, stabilization to thermoset the fiber, carbonization—graphitization, surface treatment, and sizing. Schematic process flow diagrams are shown in Eigure 4. However, specific process details differ. 

Air-Flow Control Process operating reqmrements and weather conditions are considered in determining the method of controlling air flow. The most common methods include simple on-off control, on-off step control (in the case of multiple-driver units), two-speed-motor control, variable-speed drivers, controllable fan pitch, manually or automatically adjustable louvers, and air recirculation. 

From Figure 8-144 or by calculation determine the plate area required for the holes on the pitch selected. Several selections may be tried to be used with the tray layout. These should be checked to agree with the assumed per cent hole area of Step 3. 

Decide plate layout details calming zones, unperforated areas. Check hole pitch, if unsatisfactory return to step 6 (Section 11.13.11). 

To determined if the ash removal steps could be simplified, experiments were performed on hydrogenated coals. Hydrogenation experiments were conducted at 400°C in tetralin and the pitch isolated from the insoluble mineral matter and... 

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