04-10-2012, 12:58 PM
Production of Ethylene Oxide
Ethylene oxide is a chemical used to make ethylene glycol (the primary ingredient in antifreeze). It is also used to make poly(ethylene oxide), and both the low molecular weight and high molecular weight polymers have many applications including as detergent additives. Because ethylene oxide is so reactive, it has many other uses as a reactant.
This project addresses the design of a new facility to produce 50,000 metric tons/yr of chemical grade ethylene oxide.
Process Description
The process concept diagram is shown in Figure 1. Ethylene feed, Stream 1, (via pipeline from a neighboring plant) is mixed with recycled ethylene, Stream 9, and then heated. This stream is mixed with compressed, dried (drying step not shown), and heated air, Stream 2, and then fed to the reactor as Stream 3. The reactions that take place are given below and consist of the catalytic oxidation of ethylene to produce ethylene oxide. In addition to the desired reaction, combustion reactions for both ethylene and ethylene oxide occur, and these are undesirable.
Specific Objectives of this Project
The main objective of this project is to optimize the feed section of the ethylene oxide process. In order to do this, you will need to establish the flows and temperatures of all streams (Streams 1 –9) in Figure 1. You should use the Chemcad process simulator to do this task using the SRK thermodynamics package.
Once flows and temperatures are set, you should complete each of the following mini-projects that relate ChE 310, 311, and 320.
Thermodynamics (ChE 320) Mini-Project
In Figure 1, only one air compressor is shown. Since the reactor operates at 26 bar pressure, several stages of compression, with inter-cooling, may be necessary. The purpose of this mini-project is to find the optimum compressor arrangement for the design air flowrate. The efficiency of each compression stage may be assumed to be 75%. The costs for heat exchangers, compressors, and utilities are all given in the Appendix to this problem statement. For the sake of this mini-project, you may assume that the pressure drops for all inter cooling heat exchangers are 3 psi, and the pressure drops between equipment are 1 psi. The pressure drop through the steam heater, E-701, may be assumed to be 3 psi and the pressure drop from E-701 to R-701 may be assumed to be 5 psi. As described in the Fluids section, a drier/filter must be placed upstream of the first compressor and the pressure drop across it may be assumed to be 3 psi.
Fluid Flow (ChE310) Mini-Project
You are required to find the optimum pipe sizes and make the pressure drop calculations for the air handling system that includes all piping, pipe fittings, the air filter, and all heat exchangers between the air filter and the reactor inlet. Specifically, you should assume the following:
• The air feed should be taken from the environment (14.7 psi and 20C) and compressed via a series of compressors (see the section on Thermodynamics).
• Before compression, the air must flow through a drier/filter to remove any residual moisture and particulates. The drier/filter is standard equipment, and the vendors recommend that at the design flow a pressure drop of 3 psi be used.
• The air should pass through the shell side of any heat exchanger used to heat or cool it.
• For any heat exchanger for which a detailed design is not performed (see the Heat Transfer section), a pressure drop of 3 psi should be used, for the air-side. For any heat exchanger for which a detailed design is required, the pressure drop must be calculated from the information in the detailed design.
• For each piece of equipment in the feed air line (compressors, heat exchangers, drier/filter), isolation gate valves and a bypass line should be provided to allow for use in the event of unscheduled maintenance. The sketch below illustrates this arrangement.
Heat Transfer (ChE 311) Mini-Project
You should perform a detailed design of the first inter-cooler heat exchanger (after the first compressor). You should assume that cooling water is available at the conditions specified in the appendix of this problem statement. For this heat exchanger design, you should report the following information:
• Diameter of shell
• Number of tube and shell passes
• Number of tubes per pass
• Tube pitch and arrangement (triangular/square/..)
• Number of shell-side baffles and their arrangement (spacing, pitch, type)
• Diameter, thickness, and length of tubes
• Calculation of both shell- and tube-side film heat transfer coefficients.
• Calculation of overall heat transfer coefficient (you may assume that there is no fouling on either side of the exchanger).
Ethylene oxide is a chemical used to make ethylene glycol (the primary ingredient in antifreeze). It is also used to make poly(ethylene oxide), and both the low molecular weight and high molecular weight polymers have many applications including as detergent additives. Because ethylene oxide is so reactive, it has many other uses as a reactant.
This project addresses the design of a new facility to produce 50,000 metric tons/yr of chemical grade ethylene oxide.
Process Description
The process concept diagram is shown in Figure 1. Ethylene feed, Stream 1, (via pipeline from a neighboring plant) is mixed with recycled ethylene, Stream 9, and then heated. This stream is mixed with compressed, dried (drying step not shown), and heated air, Stream 2, and then fed to the reactor as Stream 3. The reactions that take place are given below and consist of the catalytic oxidation of ethylene to produce ethylene oxide. In addition to the desired reaction, combustion reactions for both ethylene and ethylene oxide occur, and these are undesirable.
Specific Objectives of this Project
The main objective of this project is to optimize the feed section of the ethylene oxide process. In order to do this, you will need to establish the flows and temperatures of all streams (Streams 1 –9) in Figure 1. You should use the Chemcad process simulator to do this task using the SRK thermodynamics package.
Once flows and temperatures are set, you should complete each of the following mini-projects that relate ChE 310, 311, and 320.
Thermodynamics (ChE 320) Mini-Project
In Figure 1, only one air compressor is shown. Since the reactor operates at 26 bar pressure, several stages of compression, with inter-cooling, may be necessary. The purpose of this mini-project is to find the optimum compressor arrangement for the design air flowrate. The efficiency of each compression stage may be assumed to be 75%. The costs for heat exchangers, compressors, and utilities are all given in the Appendix to this problem statement. For the sake of this mini-project, you may assume that the pressure drops for all inter cooling heat exchangers are 3 psi, and the pressure drops between equipment are 1 psi. The pressure drop through the steam heater, E-701, may be assumed to be 3 psi and the pressure drop from E-701 to R-701 may be assumed to be 5 psi. As described in the Fluids section, a drier/filter must be placed upstream of the first compressor and the pressure drop across it may be assumed to be 3 psi.
Fluid Flow (ChE310) Mini-Project
You are required to find the optimum pipe sizes and make the pressure drop calculations for the air handling system that includes all piping, pipe fittings, the air filter, and all heat exchangers between the air filter and the reactor inlet. Specifically, you should assume the following:
• The air feed should be taken from the environment (14.7 psi and 20C) and compressed via a series of compressors (see the section on Thermodynamics).
• Before compression, the air must flow through a drier/filter to remove any residual moisture and particulates. The drier/filter is standard equipment, and the vendors recommend that at the design flow a pressure drop of 3 psi be used.
• The air should pass through the shell side of any heat exchanger used to heat or cool it.
• For any heat exchanger for which a detailed design is not performed (see the Heat Transfer section), a pressure drop of 3 psi should be used, for the air-side. For any heat exchanger for which a detailed design is required, the pressure drop must be calculated from the information in the detailed design.
• For each piece of equipment in the feed air line (compressors, heat exchangers, drier/filter), isolation gate valves and a bypass line should be provided to allow for use in the event of unscheduled maintenance. The sketch below illustrates this arrangement.
Heat Transfer (ChE 311) Mini-Project
You should perform a detailed design of the first inter-cooler heat exchanger (after the first compressor). You should assume that cooling water is available at the conditions specified in the appendix of this problem statement. For this heat exchanger design, you should report the following information:
• Diameter of shell
• Number of tube and shell passes
• Number of tubes per pass
• Tube pitch and arrangement (triangular/square/..)
• Number of shell-side baffles and their arrangement (spacing, pitch, type)
• Diameter, thickness, and length of tubes
• Calculation of both shell- and tube-side film heat transfer coefficients.
• Calculation of overall heat transfer coefficient (you may assume that there is no fouling on either side of the exchanger).