Riser dimensions

The main goal of the CFB design is the determination of the reactor (riser) dimensions to firstly fulfil requirements of conversion (and thus of residence time) and secondly to achieve the heat exchange rate, if so required The recycle loop is of additional importance and its design can be based on correlations found in lito-ature (e.g. Smolders et al. [1]) and is not reported in this paper. 

Slope The slope of a stairway is the ratio of riser height to tread depth. The preferred slope for stairs is about 30-35 degrees from horizontal. Standards differ on actual values and slopes may fall between 20 and 50 degrees. Tread and riser dimensions should have dimensions that are easy to create using a tape or mle. Otherwise, it is difficult to lay them out or to buy them. Table 11-6 lists some combinations of tread and riser dimensions that result in slopes between 30 and 40 degrees. 

Stairs Standards specify various characteristics of stairs. Included are clear width, tread and riser dimensions, head room, distance between landings, and landing dimensions. There are also winder, spiral and curved stair specifications. There are other details about stairs including handrails, guardrails, stairs enclosures, and other features. 

Reaction M = model, E = Expt l References Riser dimensions... 

To construct a model which will give behavior similar to another bed, for example, a commercial bed, all of the dimensionless parameters listed in Eqs. (37) or (39) must have the same value for the two beds. The requirements of similar bed geometry is met by use of geometrically similar beds the ratio of all linear bed dimensions to a reference dimension such as the bed diameter must be the same for the model and the commercial bed. This includes the dimensions of the bed internals. The dimensions of elements external to the bed such as the particle return loop do not have to be matched as long as the return loop is designed to provide the proper external solids flow rate and size distribution and solid or gas flow fluctuations in the return loop do not influence the riser behavior (Rhodes and Laussman, 1992). 

Measurements of heat transfer in circulating fluidized beds require use of very small heat transfer probes, in order to reduce the interference to the flow field. The dimensions of the heat transfer surface may significantly affect the heat transfer coefficient at any radial position in the riser. All the treatment of circulating fluidized bed heat transfer described is based on a small dimension for the heat transfer surface. The heat transfer coefficient decreases asymptotically with an increase in the vertical dimension of the heat transfer surface [Bi et al., 1990]. It can be stated that the large dimensions of the heat transfer surface... 

Can be detected when the view makes it difficult to measure the deviation from a specific wall thickness. This may due to jarring of mold or insecure anchorage of cores Localized along the central plane of the wall. It is a network of filamentary veinlets in the direction of the nearest riser Appear as dark areas of irregular dimensions without distinct outline due to insufficient feeding of a section Appear as light areas of mottled type due to separation of alloy... 

Table 1 contains characteristic data and dimensions of the pilot plant. The reactor is manufactured with stainless steel and is insulated. The wann up is carried out with electrical preheating of all air streams and by combustion in both zones. The whole warm up lasts about 4 hours. An oil feeder was installed into the riser, which gives the possibility to change the temperature level of the system without varying other operation parameters. With this installation parameter studies can be carried out very easily. 

The split-cylinder IL airlift reactor (not shown in the figure) has a vertical flat partition which divides the column into two halves which act as the riser and downcomer sections. In these IL airlift reactors, as the gas holdup in the downcomer is smaller than that in the riser, the liquid will circulate through the riser and downcomer sections due to differences in the bulk densities of the liquid-gas mixtures in the two sections. The overall values of kLo for a well-designed IL airlift reactor of both the draft tube and split-cylinder types, are approximately equal to those of bubble columns of similar dimensions. 

TABLE 11-6 Some Acceptable Combinations of Stair Riser and Tread Dimensions... 

Modelling diffusion, reaction and deactivation in FCC catalysts becomes important as new trends in vacuum gas oil processing point to short catalyst/oil contact times (less than 1 sec) in industrial riser reactors. Under short contact times catalysts particles may experience diffusion limitations [6], and thus catalyst pore dimensions become very important in determining conversion and selectivity. FCC catalysts are made of several different components to produce the necessary activity and mechanical properties. As the accessibility of large molecules to the active sites within the catalyst might be constrained,... 

Aspen FCC (AFCC) is an open-equation, flowsheet-based model designed for both online and offline applications. The model is constructed from individual blocks that represent the separate pieces of equipment—riser, standpipe, slide valve, cyclone, transfer line, etc.—found in commercial FCC units. Each building block is generic and can be configured with dimensions corresponding to a given commercial unit (Table 5). 

To further evaluate the fluid-solid mixing characteristics taking place in the catalyst bed a fibre optic probe technique was used. The fibre optic probe was inserted from the side of the reactor through the basket where the probe contacts with catalyst particles. A schematic of the system is shown in Figure 1. It has to be noted that two models, cold and hot model, were constructed to apply the fibre optic technique (Kraemer, 1990). The cold model was made of plexiglass material and had the same internal dimensions as the hot model or the Riser Simulator Reactor made of inconel. 

Before conducting a repair on a corroded pipe, analysis must be done to determine whether a repair is sufficient to restore the strength of the riser. This can be evaluated using the codes provided in ASME B31G (1991). The standard used here is compliant for onshore pipelines where the equations are only functions of the corrosion dimensions and internal pressure. Nevertheless, it provides a basis for determining the required thickness of the composite laminate. 

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