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  3. Simulation of air fans of hydrogen unit of Imam Khomeini Oil Refining Company (RA) Shazand using Aspen B-jac software

Simulation of air fans of hydrogen unit of Imam Khomeini Oil Refining Company (RA) Shazand using Aspen B-jac software

Number of pages: 115 File Format: word File Code: 31856
Year: 2011 University Degree: Master's degree Category: Chemical - Petrochemical Engineering
Tags/Keywords: air flow - Aspen B-jac software - Fan freezing - Hydrogen unit - Neural network - Oil refining company - Refinery streams - Simulation of air fans
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  • Summary of Simulation of air fans of hydrogen unit of Imam Khomeini Oil Refining Company (RA) Shazand using Aspen B-jac software

    To obtain a master's degree in chemical engineering

    Abstract

    Fans freezing in operational units, including the hydrogen unit of Imam Khomeini Shazand Refinery in the cold seasons of the year is one of the important problems in this refinery. In order to provide a suitable solution to this problem, we must have a suitable estimate of the fan outlet temperature. The neural network method is a very powerful computational tool for modeling phenomena. In this research, a three-layer forward neural network [1] has been used in order to predict the temperature of the output fluid from the air fans of the hydrogen unit of Imam Khomeini Shazand Refinery. The results showed that the average relative error [2] for this method was equal to 7.2% for experimental data and 6.5% for training data. In this project, the fan is also simulated using Aspen B-jac software, and a suitable solution is provided to prevent the pipes from freezing.

    Introduction

    During the last 20 to 30 years, both for domestic and industrial uses, the use of air as a cooling fluid and alternative to water has increased. Currently, air-cooled heat exchangers (air-cooled) are an important part of the industrial heat transfer technology. These types of exchangers are widely used to cool liquids and condense vapors, for example, in refinery streams and vapors coming out from the top of distillation columns.

    1-1 - Advantages and disadvantages of cooling with air

    1-1-1- Advantages

    The most basic advantage of air as a cooling fluid Its availability. In addition, in its use, compared to systems that are cooled with water, there is no need for piping and pumping systems related to the feeding of cooling water, and there is no problem with removing sediment and worrying about harmful chemical and thermal effects on the environment. The air is clean and chemically inactive and there is no need for pre-treatment or chemical process to prevent the growth of bacteria and fungi and the formation of sediment, if these things are needed for water. Usually, the formation of sediment or corrosion on the air side of the exchanger is low, although this is also related to the location of the exchanger. As a result, air-cooled heat exchangers require less repair and maintenance by technical people compared to water-cooled systems. The last point is that due to the relatively simple structure and the absence of an auxiliary cooling fluid purification unit, air-cooled heat exchangers have a lower initial cost compared to water coolers. It has low density and low specific heat. Heat transfer coefficients with simple tubes (without fins) at air velocities that are economically possible (10 m/s) are smaller than 100.k) W/(m2) and improving the heat transfer coefficients by means of finned tubes is necessary even to achieve moderate values ??of thermal efficiency. As a result, air fans compared to similar water-cooled exchangers

    they are bigger and need wider support structures and more land and space for installation. Because of this large size, air-cooled heat exchangers cannot be used everywhere like water coolers. For example, it is difficult to mount them on top of distillation towers to condense the steam exiting from the top of the tower.

    In some places, the air temperature is high and as a result the temperature difference In order to cool the fluid passing through the pipes, it is necessary to use very large areas of the heat exchanger surfaces. This often happens when, depending on the location, the water supply is also problematic.

    The last point that should be noted is that the air-cooled heat exchangers in which the air is moved by the propeller may be noisy and therefore a form of environmental pollution. (sound pollution).

    2-1- The structure of air-cooled heat exchangers

    In air-cooled heat exchangers, the fluid to be cooled flows inside the tubes of the finned tube bundle, while the air passes through the outer surface of the tubes as a cross flow. The air flow may be created by the natural passage of air in the air duct or tower or by the forced passage of air by means of propeller and electric motor. Multiple flow configurations along with many types of blades are used in these heat exchangers.

    1-3- Arranging the bunch of pipes and creating air flow

    1-3-1- Passing air in the form of blowing (forced) and suction (induction)

    In a diagram, it shows how A bundle of tubes can be cooled by blowing or suction air flow. In the blowing flow mode, the nearby air is drawn into the propeller (fan) and the propeller increases the air pressure by a small amount that is enough to overcome the hydraulic resistance of the flow passing over the pipe handle (equivalent to a few millimeters of water). In the suction flow mode, the impeller slightly reduces the air pressure, which is enough to draw air from the tube handle. In the latter case, the air that enters the propeller is hotter than the temperature of the surrounding air, and therefore its density is lower than the density of the ambient air.

    The stack of tubes usually includes a small number of rows of tubes that are placed inside a rectangular frame and can be placed vertically, horizontally, or in an inclined position as shown in Figure 1-1. The most common form is to be in a horizontal position.

    The relative advantages of the air flow in the form of suction and blowing are as follows:

    Advantages of the flow in the form of blowing

    A- As a result of the colder inlet air temperature to the propeller and greater air density, less electrical power is needed to create a specific mass rate, in addition, the propeller can be smaller and therefore has a lower initial cost.

    b- Compared to the suction flow state, the propeller is in a cool air flow, and the need for insulation or cooling of the propeller motor and bearings is reduced or eliminated.

    c- When the process fluid leaks from the pipes and assuming that the leaking fluid is carried by the air current, the probability of contamination of the propeller or engine is less

    D- When the pipe handle is positioned horizontally, the propeller is close to the ground and it is easier to access it for maintenance operations.

    In figures 2-1 and 3-1, suction and blowing fans are shown.

    In this arrangement, the pipes are located in the blower part of the fan, that is, the fan is located under the set of pipes.

    (Images are available in the main file)

    In the blower type, the pipes are placed in the upper part of the fan. In this way, due to the heating of the incoming air at the top of the pipes, the air is naturally sucked upwards. Therefore, the power consumption of the fan will be less. On the other hand, in this type of converters, fan parts are easily available for repair. In addition, these types of converters are more compatible in cold regions. However, this system, contrary to the mentioned advantages, also has disadvantages, including the lack of proper distribution of air between the pipes and the possibility of hot air returning due to the low speed of the air exiting the pipes. At the same time, due to the fact that the pipes are exposed to sunlight, rain and hail, the rate of depreciation increases. 

    Advantages of suction flow

    A- The distribution of flow is more uniform.

    B- The propeller protects the pipe handle from the accumulation of snow or heavy rain.

    C- The recirculation and passage of hot air inside the pipe handle is prevented.

    The main disadvantage of blowing flow arrangement is non-uniform flow distribution. The main disadvantages of the suction flow arrangement are the larger free space required to ensure uniform airflow distribution, higher noise levels, risk of impeller or motor damage due to process fluid leaks, and impeller operation at hotter temperatures.

  • Contents & References of Simulation of air fans of hydrogen unit of Imam Khomeini Oil Refining Company (RA) Shazand using Aspen B-jac software

    List:

    Introduction 2

    1-1 - Advantages and Disadvantages of Air Cooling 2

    1-1-1-Advantages 2

    1-1-2- Disadvantages 3

    2-1- The structure of air-cooling heat-cooling with air cooled 3

    1-3- pipeline arrangement and airflow 4

    1-3-1- air passing air as a blower (mandatory) and suction (induction) 4

    1-4- air pass Natural 8

    1-5- Pipe bundle structure and flow configurations 9

    1-5-1- Pipe bundle structure 9

    1-5-2- Flow configuration 11

    1-5-3- Fin tube structure 12

    1-5-4- Fined pipes 16

    1-6- Types of blades 16

    1-7- Applications of air fans 19

    1-7-1- Applications Industrial 19 1-8 - Basic equations of heat transfer 20 1-9 Air fan components 22 1-10 Vertical air fans 23 1-11 Tube bundles and various coil components 26

    1-12- Fan and air drive 29

    1-13- Problems of air cooling converters 31

    2-1- Review of past works 34

    3-1- Introduction of hydrogen unit 38 3-2- Process chemistry 38 3-3 Description of unit operation 40 3-4 Simulation using Aspen B-jac software 44 3-5 Simulation steps with software 56

    3-6- Simulation using neural network algorithm 59

    3-7- Network concept 59

    3-8- Artificial neural network 60

    3-9- Mathematical model of artificial neural network                                                  

    3-9-1- Multilayer perceptron 63

    3-10- Network training by error backpropagation method 65

    3-11- Error backpropagation algorithm 66

    3-12- Problem simulation process 71

    13-3-Simulation 73 4-1 Aspen B-jac software results 85 4-2 Neural network algorithm results 92 Sources and references 96

    Abstract 102

    Source:

    [1]- Paikert, P. (1983) Air cooled heat exchangers, in Heat Exchangers Design Handbook, Hemisphere Publishing, New York, Chap 3.8.

    Petrochemical Industry Information Society  [2]

    [3]- Chu, C.C (1985) Studies of the plumes above air cooled heat exchangers operating under natural convection, Ph. D. University of Birmingham.

    [4]- Sadic Kakac- Hongtan Liu, Chapter 11, translated by Dr. Sepehr Sanyaat, Karma exchangers

    [5]- Engineering Science Data Unit (ESDU) (1986) High-fin staggered tube banks: Heat transfer and pressure drop for turbulent single phase gas flow, ESDU International  Ltd., London.

    [6]- www.amercool.com, Basic of Air cooled Heat Exchanger

     

    [7] Keyes W.M., London A.L., Terjeh, Training and Research Center of Iran Radiator Company, 1371. Design of heat-compression exchangers. Iran Radiator Special Joint Stock Company.

     

    C.J. Meyer*, D.G. Kroger: Air-Cooled Heat Exchanger Inlet Flow Losses. Thermal Engineering (2001).

    [9]- G.J. Kosten, K.I. Morgan, J.M. Burns, P.L. Curlett, Operating and Performance Testing of the World's Largest Air-cooled Condenser, American Power Conference, Chicago, 1981.

    - H.B. Goldschagg, Lessons Learned from the World's Largest Forced Draft Direct Air-cooled Condenser, EPRI meeting, Washington, 1993. [11]- M.A. Mohandes, T.V. Jones, C.M.B. Russell, Pressure loss mechanisms in resistances inclined to an air flow with application to fin tubes, First National Heat Transfer Conference, Leeds, 1984.

    [12]- F.K. Moore and J.R. Ristorcelli, Turbulent flow and pressure losses behind oblique high-drag heat exchangers. Int. J. Heat Mass Transfer 22 (1979), pp. 1175–1186.

    [13]- F.K. Moore, Flow Fields and Pressure Losses of V-bundles with Finite Resistance, ASME Paper 79-WA/HT-4, 1979.

    [14]- J.C.B. Kotze, M.O. Bellstedt, D.G. Kroger, Pressure drop and heat transfer characteristics of inclined finned tube heat exchanger bundles, Proc. Eighth Int. Heat transfer Conf., San Francisco, 1986.

    [15]- D.J. Van Aarde and D.G. Kroger, Flow losses through an array of A-frame heat exchangers. Heat Transfer Engng. 14 1 (1993), pp. 43-51.

    [16]- K. Duvenhage, D. G. Kroger*: The influence of wind on the performance of forced draft air-cooled heat exchangers. University of Stellenbosch (1996).

    [17]- D.G. Kroger, Fan performance in air-cooled steam condensers. Heat Rec. System CHP 14 (1994) 391-399.

    [18]- C.G. Du Toit and D.G. Kroger, Modeling of the recirculation in mechanical draft heat exchangers. South African Inst. of Mech. Engrs. R & DJ 9 (1993), pp. 2-8.

    [19]- K. Duvenhage and D.G. Kroger, Plume recirculation in mechanical-draft air-cooled heat exchangers. Heat Transfer Eng. 16 4 (1995), pp. 42-49.

    [20]- A.Y.

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