Economic pipe diameter

The fluid is available at a high pressure and eventually will be throttled to a low pressure, so the energy needed to overcome friction losses may come from the available pressure drop. 

The fluid is notj available at a high pressure, so a pump or compressor is needed to overcome the effects of fluid friction. 

The first is simple We select the smallest size of pipe which will carry the required flow with the available pressure drop. Example 6.5 is that case. 

If the effects of friction must be overcome by a pump or compressor, then the total annual costs of the pump pipeline system are the following  

Capital-cost charges for both line and pump 

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Economic Pipe Diameter, Laminar Flow Pipehnes for the transport of high-viscosity liquids are seldom designed purely on the basis of economics. More often, the size is dictated oy operability considerations such as available pressure drop, shear rate, or residence time distribution. Peters and Timmerhaus (ibid.. Chap. 10) provide an economic pipe diameter chart for laminar flow. For non-Newtouiau fluids, see SkeUand Non-Newtonian Flow and Heat Transfer, Chap. 7, Wiley, New York, 1967). 

The following analysis can be used to determine economic pipe diameters for the turbulent flow of Newtonian fluids. The working expression that can be used is ... 

The capital cost of a pipe run increases with diameter, whereas the pumping costs decrease with increasing diameter. The most economic pipe diameter will be the one which gives the lowest annual operating cost. Several authors have published formulae and nomographs for the estimation of the economic pipe diameter, Genereaux (1937), Peters and Timmerhaus (1968) (1991), Nolte (1978) and Capps (1995). Most apply to American practice and costs, but the method used by Peters and Timmerhaus has been modified to take account of UK prices (Anon, 1971). 

The formulae developed in this section are presented as an illustration of a simple optimisation problem in design, and to provide an estimate of economic pipe diameter that is based on UK costs and in SI units. The method used is essentially that first published by Genereaux (1937). 

Equation 5.13 is a general equation and can be used to estimate the economic pipe diameter for any particular situation. It can be set up on a spreadsheet and the effect of the various factors investigated. 

Equations 5.14 and 5.15 can be used to make an approximate estimate of the economic pipe diameter for normal pipe runs. For a more accurate estimate, or if the fluid or pipe run is unusual, the method used to develop equation 5.13 can be used, taking into account the special features of the particular pipe run. 

Nolte (1978) gives detailed methods for the selection of economic pipe diameters, taking into account all the factors involved. He gives equations for liquids, gases, steam and two-phase systems. He includes in his method an allowance for the pressure drop due to fittings and valves, which was neglected in the development of equation 5.12, and by most other authors. 

The use of equations 5.14 and 5.15 are illustrated in Examples 5.6 and 5.7, and the results compared with those obtained by other authors. Peters and Timmerhaus s formulae give larger values for the economic pipe diameters, which is probably due to their low value for the installation cost factor, F. 

Example 7-1 Economic Pipe Diameter. What is the most economical diameter for a pipeline that is required to transport crude oil with a viscosity of 30 cP and an SG of 0.95, at a rate of 1 million barrels per day using ANSI 1500 pipe, if the cost of energy is 50 per kWh (in 1980 ) Assume that the economical life of the pipeline is 40 years and that the pumps are 50% efficient. 

This value is compared with the result achieved by applying the economic pipe diameter formula for stainless steel from Ref. P1 (P-161) ... 

A graphical representation showing the meaning of an optimum economic pipe diameter is presented in Fig. 1-1. As shown in this figure, the pumping cost increases with decreased size of pipe diameter because of frictional effects, while the fixed charges for the pipeline become lower when smaller pipe diameters are used because of the reduced capital investment. The optimum economic diameter is located where the sum of the pumping costs and fixed costs for the pipeline becomes a minimum, since this represents the point of least total cost. In Fig. 1-1, this point is represented by E. 

Determination of optimum economic pipe diameter for constant mass-throughput rate. 

A classic example showing how added refinements can come into an analysis for optimum conditions is involved in the development of methods for determining optimum economic pipe diameter for transportation of fluids. The following analysis, dealing with economic pipe diameters, gives a detailed derivation to illustrate how simplified expressions for optimum conditions can be developed. Further discussion showing the effects of other variables on the sensitivity is also presented. 

FLUID DYNAMICS (OPTIMUM ECONOMIC PIPE DIAMETER)... 

The preceding analysis clearly neglects a number of factors that may have an influence on the optimum economic pipe diameter, such as cost of capital or return on investment, cost of pumping equipment, taxes, and the time value of money. If the preceding development of Eq. (39) for turbulent flow is refined to include the effects of taxes and the cost of capital (or return on investment) plus a more accurate expression for the frictional loss due to fittings and bends, the result is t... 

Prepare a plot of optimum economic pipe diameter versus the flow rate of fluid in the pipe under the following conditions ... 

For the conditions indicated in Prob. 7, prepare a log-log plot of fluid velocity in feet per second versus optimum economic pipe diameter in inches. The plot should cover a fluid-velocity range of 1 to 100 ft/s and a pipe-diameter range of 1 to 10 in. 

Derive Eq. (49) for the optimum economic pipe diameter and compare this to the equivalent expression presented as Eq. (5-90) in J. H. Peny and C. H. Chilton, ed., Chemical Engineers Handbook, 5th ed., p. 5-32, McGraw-Hill Book Company, New York, 1973. 

The derivation of equations for determining optimum economic pipe diameters is presented in Chap. 11 (Optimum Design and Design Strategy). The following simplified equations [Eqs. (45) and (47) from Chap. 11] can be used for making design estimates ... 

Nomograph for estimation of optimum economic pipe diameters with turbulent or viscous flow based on Eqs. (15) and (16). 

Economic Pipe Diameter, Turbulent Flow The economic optimum pipe diameter may be computed so that the last increment of investment reduces the operating cost enough to produce the required minimum return on investment. For long cross-country... 

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