Design procedure

When designing GFRP pipes, in some cases, the designers would also specify a corrosion barrier (liner) layer. The thickness of the layer would then be added to the pipe s wall thickness as established based on the above-mentioned design methods. In less hostile environments, however, the designer may choose to include the corrosion barrier (or some portion thereof) in the structural calculations. In some cases, the pipe wall thickness is further increased to accommodate other design requirements, such as additional stiffness required for special loading conditions (e.g., in the presence of vacuum in a pipe). 

The following simple procedure can be use as the basis for the preliminary design of GFRP pipes. As an example, we consider the design of a 200 mm diameter pipe, subject to 5 MPa internal pressure, using a safety factor (FS) of 6. 

According to the basic mechanics of materials, the hoop stress/unit thickness of the pipe can be calculated by  

This would satisfy both the hoop and longitudinal strength. This pipe would have a total thickness of (12 x 0.015 + 6 X 0.043 ) = 0.438 or 11.125 mm (the data are selected from Vectorply.com). 

It should be noted that a more optimum lay-up could have been selected by selecting a biaxial roving woven fabric with biased amount of longitudinal to transfer fibers, so as to overcome the hoop and transverse stresses by approximately equal amounts. Such biased fabrics are commercially available from several vendors. 

The ratio of hpjh, is estimated (from table in Sec. 13-5) to be 6.5. Hence the heat-transfer coefficient for the packed-bed case is 

For this particular case the coefficient in the fluidized bed is six times that in the packed tube and thirty-seven times that in an empty tube. 

An important feature of the fiuidized-bed reactor is that it operates at a nearly constant temperature and hence is easy to control. There is no opportunity for hot spots to develop, as in the case of the fixed-bed unit. The fluidized bed does not possess the flexibility of the fixed bed for adding or removing heat. A diluent can be added to control the temperature level, but this may not be desirable for other reasons (requires separation after the reactor, lowers the rate of reaction, increases the size of the equipment). A heat-transfer fluid can be circulated through a jacket around the reactor, but if the reactor is large in diameter, the energy exchange by this method is limited.  

Another characteristic of the fluidized bed is the small size and density of catalyst particles necessary to maintain proper fluidization. The particles provide a much larger external surface per unit mass of catalyst than those, in a fixed-bed unit. This results in a higher rate of reaction (per unit mass) for a nonporous catalyst. Also, internal transport effects are negligible. 

From a practical standpoint catalyst loss due to carryover with the gas stream from the reactor and regenerator may be an important problem. Attrition of particles decreases their size to a point where they are no longer fluidized, but move with the gas stream. It has been customary to recover most 6f these catalyst fines by cyclone separators and electrical precipitation equipment placed in the effluent lines from reactor and regenerator. 

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On the other hand, this approach has a number of advantages. Many different design options can be considered at the same time. Also, the entire design procedure can be accommodated in a computer program capable of producing designs quickly and efficiently. 

Douglas, J. M., A Hierarchical Design Procedure for Process Synthesis, AlChEJ, 31 353, 1985. 

This design procedure is known as the pinch design method and can be summarized in five steps... 

Design procedures are developed with the intention of improving the safety of equipment. Tools used in this step are hazard and operability studies and quantitative risk analysis (ORA). The following scheme may be used ... 

Design Procedure. The packed height of the tower required to reduce the concentration of the solute in the gas stream from to acceptable residual level ofjy 2 may be calculated by combining point values of the mass transfer rate and a differential material balance for the absorbed component. Referring to a sHce dh of the absorber (Fig. 5),... 

Rapid Approximate Design Procedure for Curved Operating and Equilibrium Lines. If the operating or the equihbrium line is nonlinear, equation 56 is of Httie use because will assume a range of values over the tower. The substitution of effective average values for m and... 

The recommended design procedure uses the values of (E /and m from Figures 7 and 8 in equation 56 and yields a very good estimation of Alp despite the curvature of the operating and the equilibrium lines. This value differs from A/q obtained by equation 49 because of the /(I — y) term in the latter equation. A convenient approach for purposes of approximate design is to define a correction term AA/q which can be added to equation 55 ... 

To obviate the tedious graphical iategration, a simplified design procedure was developed on the basis of Colburn s analytical solution, equation 56. Substitution of the ratio presents no problem because this ratio stays fairly constant ia the tower at the low coaceatratioas for which Figure 12 is... 

Rapid Approximate Design Procedure. Several simplified approximations to the rigorous solutions have been developed over the years (57—60), but they aU. remain too compHcated for practical use. A simple method proposed in 1989 (61,62) uses a correction factor accounting for the effect of axial dispersion, which is defined as (57)... 

The recommended rapid design procedure consists of the following steps (/) The apparent is calculated using equation 56. (2) The extent of axial dispersion is estimated from Hterature correlations for each phase in terms of Pe numbers and transformed into values. (3) The correction... 

Simplified Design Procedure for Linear Equilibrium and Operating Lines. A straight operating line occurs when the concentrations are low such that and remain essentially constant. (The material balance is obtained from equation 35.) In cases where the... 

A general, approximate, short-cut design procedure for adiabatic bubble tray absorbers has not been developed, although work has been done in the field of nonisothermal and multicomponent hydrocarbon absorbers. An analytical expression which will predict the recovery of each component provided the stripping factor, ie, the group is known for each component on each tray of the column has been developed (102). This requires knowledge... 

Fluidized-bed design procedures requite an understanding of particle properties. The most important properties for fluidization are particle size distribution, particle density, and sphericity. 

Division 1. Below the creep range, design stresses are based on one-fourth of the tensile strength or two-thkds of the yield, or 0.2% proof stress. Design procedures are given for typical vessel components under both internal pressure and external pressure. No specific requkements are given for the assessment of fatigue and thermal stresses. 

The American Society of Mechanical Engineers (ASME) United Engineering Center 345 East 47th Street New York, NY 10017 The ASME Boiler and Pressure Vessel Code, under the cognisance of the ASME PoHcy Board, Codes, and Standards, considers the interdependence of design procedures, material selection, fabrication procedures, inspection, and test methods that affect the safety of boilers, pressure vessels, and nuclear-plant components, whose failures could endanger the operators or the pubHc (see Nuclearreactors). It does not cover other aspects of these topics that affect operation, maintenance, or nonha2ardous deterioration. 

The thermal design of cooling towers follows the same general procedures already presented. Integration of equation 35 is usually done numerically using the appropriate software, mass-transfer coefficients, saturation enthalpies, etc. In mechanical-draft towers the air and water dows are both suppHed by machines, and hence dow rates are fixed. Under these conditions the design procedure is straightforward. 

A hierarchical design procedure for process synthesis can be used in conjunction with a flow-sheeting program to analyze, evaluate, and optimize the options (60). The emphasis is on starting with the simplest possible models that will give answers to a particular question quickly so that the questions to be asked at the next decision level can be formulated. At each stage, it is necessary to ensure that the level of detail in the model is sufficient to give rehable information. 

Design considerations for air knives are discussed by Senecal (ibid.). Design procedures for extrusion dies when the flow is laminar. 

Tanks that could be subjected to vacuum should be provided with vacuum-breaking valves or be designed for vacuum (external pressure). The ASME Pressure Vessel Code contains design procedures. 

Design data for separation of the particular or similar mixture in a packea column are not available. Design procedures are better estabhshed for tray-type columns than for packed columns. This is particularly so with respect to separation efficiency since tray efficiency can be estimated more accurately than packed height equivalent to a theoretical stage (HETP). 

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