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CFD Analysis of Chemical
A typical chemical process plant involves fluid flow devices such as pipes and valves. Fluid transport equipment such as pumps, compressors are employed for moving fluid from one unit operation to another. Drying equipment such as fluidized beds,
Computational fluid dynamics (CFD) methods can be applied to examine different equipment designs, or compare performance under different operating conditions. Studies to examine the influence of various parameters on flow behavior and hence performance can be conducted using CFD methods. It also allows for various concepts to be examined in a virtual setting, without actually building a physical model. Equipment at its full-scale can be analyzed, thus scale-up related issues can be eliminated. These methods provide an inside look into the function and operation of process equipment and provide valuable information to equipment manufacturers, plant managers, production managers, process engineers and research and development staff.
At a chemical process plant CFD can be applied for diagnosis, analysis and troubleshooting; it can be applied for prototyping and performance evaluation of process equipment as shown in Figure 1.
Computational fluid dynamics (CFD) methods are based on first principles of mass, momentum and energy conservation. CFD methods involve the solution of conservation equations for mass, momentum and energy at thousands of locations within the flow domain. The details of these methods are described in references [2-3]. The computed solution provides flow variables such as velocity, pressure, temperature, density, concentration, etc. at thousands of locations within the domain.
CFD Applications in the Chemical Processing Industry
CFD applications to a number of unit operations and processes in the chemical process industries, oil and gas industry are described in references [4-11]. In general CFD methods are applied to understand the overall flow and heat transfer behavior. A typical study is aimed at comparing and evaluating designs or concepts. What- if studies are performed to examine the influence of various parameters on flow behavior and hence performance. Unlike experimental methods, CFD provides full- field data. The impact of CFD on chemical process equipment is summarized in Table I.
Table I: Impact of CFD on Various Processes in the Chemical Processing Industries
CFD for Separators
In the following study, CFD is applied to improve the performance of an electrostatic precipitator (ESP). The effect of distributor plate arrangement on flow uniformity in the diffuser section of an ESP is examined. The original design employs a grid-type distributor plate as shown in Figure 2a. As depicted in Figure 2b, the flow entering the diffuser is not uniformly distributed and continues as a jet in the core of the diffuser section. The effect of a grid employing splitter plates is examined. This configuration is shown in Figure 3a. The velocity field in the ESP, as depicted in Figure 3b is more uniform but the recirculation region is not entirely eliminated.
CFD for Dryers
Drying equipment is usually large and expensive. As a result, efficiency is an important factor that influences production and operation cost. In this section the benefits derived from CFD study of a spray dryer are discussed.
CFD is used to analyze the performance of an industrial spray dryer in advance of making major structural changes to the dryer. The risk of lost profit during changeover (especially if the improvement did not materialize) is minimized. CFD is applied to examine configuration changes and thus minimize risk and avoid unnecessary downtime during testing. The velocity distribution depicted in Figure 4 shows skewed flow. This is a result of uneven pressure distribution in the air dispersing head. CFD models are applied to determine optimum equipment configuration and process settings. CFD results can provide the necessary confidence that the proposed modifications will work before capital equipment is ordered and field-testing scheduled.
CFD for Heat Generation and Heat Transfer Equipment
Heat transfer and power generation equipment is employed throughout a chemical processing plant. Failure of this equipment can lead to downtime and significant loss of revenue. Hence, it is essential for this equipment to perform as reliably as possible. Inefficiencies associated with heat transfer equipment directly influence production cost. Small increments in improved efficiency can result in significant reduction of operating cost and increased revenues. CFD techniques can provide an insight into the function of these devices and can help identify areas for improvement.
CFD methods are applied to eliminate tube- failure in a gas- fired boiler. The boiler is depicted in Figure 5a; the burner as shown in Figure 5b consists of a fuel lance. The oxidant is introduced through the annular space and passes through a set of swirl- vanes. The swirl imparted by the vanes stabilizes the flame. The temperature plot in Figure 5c depicts the high temperature region in the convective section of the furnace chamber. This is the region where boiler tubes are most likely to fail. The velocity field in Figure 5d depicts a low velocity region near the outer surface of the radiant section. However, the temperatures in this region are acceptable. Design changes to induce a more uniform temperature field in the convective section of the furnace were explored using CFD methods.
Additional applications of CFD to processes and process equipment are described in references [4-11].
Unit operations in chemical process industries handle large amounts of fluid, as a result, small increments in efficiency lead to large increments in product cost savings, CFD solutions can help accomplish this. The number of processes that can be improved with the aid of CFD techniques are many. Chemical process industries are now beginning to accept this technology; however, it is yet to be fully integrated. The potential for process improvements using CFD solutions is yet to be realized.
1) Perry, R.H., Green. D., Chemical engineers handbook, Mc Graw Hill, 1984.
2) Patankar, S.V., Numerical heat transfer and fluid flow, Hemisphere, 1983.
3) Anderson, D.A., Tannehill, J.C., Pletcher, R.H., Computational fluid mechanics and heat transfer, Mc Graw Hill, 1984.
4) C.J. Matice., T.J. Fry., E.M. Luther., Computer flow modeling for pump performance, Appliance engineer, January 2001.
5) H.S. Pordal., C.J. Matice, T.J. Fry., Computational fluid dynamics: a key analytical tool, Hydrocarbon processing, August 2001.
6) H.S. Pordal., C.J. Matice, T.J. Fry., Using CFD models to simulate multiphase flow, Chemical processing, November 2001.
7) C.J. Matice., High speed filling of plastic containers. SME, November 1997.
8) H.S. Pordal., SES review of liquid-liquid mixing, mixing equipment and ultrasonic emulsification, SES report March 2001.
9) H.S. Pordal., SES review of mixing for scale-up and scale-down, SES report November 2001.
10) T.J. Fry., CFD aids in the development of novel spray drying technology, Powders and bulk magazine, 2001.
11) C.J. Matice., H.S. Pordal., Design of venturi mixers, Flow control magazine, November 2001.