Polypropylene Production Plant

HATA

Polypropylene Production Plant

May 2, 2006

Submitted By:

Donald Scott

Jason Hixson

Michael Hickey

Stephanie Wilson

Abstract

This paper documents the technical, environmental, and economic feasibility study of a four stage chemical plant designed to convert methane to propylene with some profitable byproducts. This project was contracted to Henry Advanced Technical Associates (HATA): specifically to teams Alpha-Creative, and One-Tops. Each team handled two of the four stages designed. The four stages of the plant are as follows:

Section 100-converts methane to syngas (Alpha-Creative)

Section 200-converts syngas to methanol (Alpha-Creative)

Section 300-converts methanol to dimethyl ether (One-Tops)

Section 400-converts dimethyl ether to propylene (One-Tops)

In the year 2000, the world demand for propylene was 53.5 million tons, with growth rates averaging 5% per year. “According to Chemical Market Associates Inc.’s global propylene consulting team, world propylene prices are expected to continue to exhibit a cyclical “up-and-down” pattern in the future, due to fluctuations in energy prices and fluctuations in the supply/demand balance for propylene. The global propylene market supply/demand balance is expected to be relatively tight in 2004-2006 (causing upward movement in prices). Beyond 2006, the cyclical pattern is expected to continue.” [1] Based on this and other economic research conducted by HATA, the goal for production of propylene via this plant was set at 10 tonne/hr, or approximately 84,000 tonne/yr. A simple cost analysis estimated the profitability of a plant design to produce propylene via the process mentioned above at $24.5 million. This analysis was done only considering the required reactants and products. Further analysis proved the profitability of the plant based on a more extensive economic analysis. At the conclusion of the design process that implemented pinch technology, individually designed equipment, and professional CAPCOST software; the projected return on investment is estimated at 144 million by year 12 with a return on investment of approximately 2 years. All process flow diagrams, flow summaries, equipment summaries, and economic analysis are presented in the following sections of this report.

Introduction

The HATA Propylene Production Plant was designed in an effort to produce 10 tonne propylene per hour and receive a return of investment in three years. The design was divided into four sections, with each section representing a major process of the plant. The section numbered 100 corresponds to the first process, the production of syngas. Section 200 converts the syngas from section 100 to methanol. Section 300 converts the methanol from section 200 to dimethyl ether. Section 400 converts the dimethyl ether from section 300 to propylene product. The design of each section was completed separately, allowing special consideration to be given to the specifics of each process. The four section designs were then reconsidered as one plant design, allowing many processes from separate sections to be combined. The results of the design processes for each of the sections are presented below. Included in each are: a Process Flow Diagram; flowsheets; material and energy balance tables with temperatures, pressures, phases, mass and molar flowrates, and component mole flowrates; equipment summaries; and manufacturing cost summaries itemized by piece of equipment. The final economic analysis of the HATA Propylene Production Plant may be found at the end of these section results.

Equipment Design

The equipment used for each process was designed to meet the requirements of production. The major equipment that was considered for design includes compressors, distillation columns, heat exchangers, turbines, reactors, and separation units.

Compressors:

The primary focus of compressor design is an understanding of the power requirements for the equipment. The power needed for the equipment was estimated using Equation 1, and assuming a γ of 1.31 and a η of .75.

Reactors:

The size of the reactor is determined by volumetric flowrate of the reactant feed, along with the resonance time necessary for the reaction to take place. Each reactor was assumed to have a resonance time of approximately 1 minute, allowing the volume of the reactor to be found using Equation 2.

Separation Vessels:

The separation units were sized similar to that of the reactors, with the only exception being a very small resonance time during which the separation takes place. The primary means of separation were filters, and pressure swing adsorption units. Equation 2 is used again to determine the required volume for the vessel.

Heat Exchangers:

The primary method to determine the best placement for heat exchangers was found by using Pinch Technology5. This method of analysis enables the most efficient use of available heat to reduce operating expenses. An example of the pinch analysis can be seen in Figure 1 below. With the help of the pinch analysis the correct hot and cold streams can be combined for use in a heat exchanger. The pinch analysis gives the amount of available heat that a stream can supply, which then used with Equation 3 to provide the exiting temperature of the hot stream. A negative value for a particular section indicates a pinch point, which requires and additional heat source to supply the additional energy. The heat exchanger will be sized according to the area of heat transfer required, and the amount of heat that needs to be transferred. The heat transfer area can be found using Equation 4. This same methodology was used for the condenser design, with the unknown being the required mass flow rate of the cooling water.

Figure 1: Pinch Analysis for Section 300.

Distillation Column:

The data necessary for designing a distillation column for separating propane and propylene was not available. However, research showed that industry practice used a column under high pressure and about 150 stages. Assuming a tray spacing of .1 m the height was estimated at 15 m and a diameter of 2 m seemed reasonable.

Storage Tanks:

The size of the storage tanks was assumed to be the amount produced in a 24 hr period assuming that the product was to be shipped out on a continual basis. The amounts calculated are listed in Table 402.

Blowers:

The blowers were estimated by calculating the volumetric flow rate in m3/s which was done by dividing the hourly flow rate in the flow summary by 3600.

Cyclones:

The volume of the cyclones was estimated by using the volumetric flow rate of the liquid portion of the stream in one minute and using Equation 2.

Feed Heater:

The feed heater is a fired heater with a load of 1090 MJ/hr which was determined by Equation 6.

Plant Section 100-Syngas Production

Section 100 represents the start of the propylene production process. The primary function of section 100 is to reform the natural gas feed into a more useful mixture of carbon monoxide, carbon dioxide, and hydrogen. The process flow diagram (PFD) for this section can be seen in Figure 101. The flow rate of the natural gas is associated with what is required to meet the production demands of 10 tonne of propylene per hour. The process begins with a natural gas feed, Stream 101, which must be filtered with a desulferizer. Stream 103 is then mixed with a steam feed, Stream 105, with a steam to methane ratio of 2.5 to 1. Additional reactant is also fed from Stream 209 to salvage un-reacted syn gas that is present in section 200. These three streams are combined in M-101, to form the reactant feed, Stream 106. Stream 106 then proceeds through a compressor which raises the pressure from 1 to 5 atm. This is done to reduce the required volume of the reactor. Stream 107 then proceeds through two heat exchangers where it is heated by the reactor effluent, Stream 115, which raises the temperature to 800 °C. Stream 109 is then brought through a steam-methane reformer which converts the mixture into carbon monoxide, carbon dioxide, and hydrogen. The extent of conversion is assumed 92% according to the first reaction, and 4% according to second, with 4% remaining un-reacted.

CH4 + H20 → CO + 3 H2

CH4 + 2 H20 → CO2 + 4 H2

Two additional streams are shown entering the reformer which are necessary during the startup procedure and involve the combustion of methane. The reaction products exit the reactor as Stream 115, which is a combination of CO, CO2, CH4, and H2, and is generally referred to as syn gas. This mixture is then used to transfer heat to the entering reactant feed and continues to condenser E-104, which is used to condense the excess water that is present in the syn gas. The water exits the process in Stream 119, and proceeds to wastewater treatment. The sny gas mixture exits the condenser as Stream 119, where it is then separated into Stream 120 and 121. Stream 120 is a bypass stream and contains 60% of the original syn gas, with all the required hydrogen to meet the demands of Section 200. This is done to reduce the amount of separation that is needed for the pressure swing adsorption system (PSA). Stream 121 is fed through the PSA which has the capability to separate hydrogen from organic gases. The hydrogen that is separated exits as Stream 127, is compressed to 100 atm and is fed to a storage tank through Stream 128. The CO, CO2, and CH4 exits the PSA through Stream 126 where it is recombined with the bypass stream to form Stream 129. Stream 129 is the supply for the methanol synthesis in section 200 of the plant design, and contains all the necessary reactants to fulfill production demands. The process flow summary for this section can be seen below in Table 101.

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Figure 101: Process Flow Diagram for Section 100

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Table 101: Flow Summary for the Production of Hydrogen and Syn Gas from Natural Gas
Stream Number / 101 / 102 / 103 / 104 / 105 / 106 / 107 / 108 / 109 / 110
Temperature (°C) / 30.0 / 30.0 / 30.0 / 210.0 / 210.0 / 170.0 / 170.0 / 590.0 / 800.0 / 30.0
Pressure (MPa) / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 5.0 / 5.0 / 5.0 / 1.0
Vapor Fraction / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0
Mass Flow (tonne/h) / 15.4 / 15.4 / 15.4 / 53.9 / 53.9 / 71.9 / 71.9 / 71.9 / 71.9
Molar Flow (kmol/h) / 960.4 / 960.4 / 960.4 / 2996.5 / 2996.5 / 4393.4 / 4393.4 / 4393.4 / 4393.4
Vol. Flow (m3/h) / 23880 / 23880 / 23880 / 118764 / 118764 / 159706 / 31941 / 62224 / 77366
Component Mole Flow (kmol/h)
Hydrogen / 0.0 / 0.0 / 0.0 / 0.0 / 0.0 / 351.8 / 351.8 / 351.8 / 351.8
Methane / 960.4 / 960.4 / 960.4 / 0.0 / 0.0 / 998.8 / 998.8 / 998.8 / 998.8
Carbon Monoxide / 0.0 / 0.0 / 0.0 / 0.0 / 0.0 / 44.2 / 44.2 / 44.2 / 44.2
Carbon Dioxide / 0.0 / 0.0 / 0.0 / 0.0 / 0.0 / 2.0 / 2.0 / 2.0 / 2.0
Water / 0.0 / 0.0 / 0.0 / 2996.5 / 2996.5 / 2996.5 / 2996.5 / 2996.5 / 2996.5
Methanol / 0.0 / 0.0 / 0.0 / 0.0 / 0.0 / 0.0 / 0.0 / 0.0 / 0.0
Mole Fraction
Hydrogen / 0.00 / 0.00 / 0.00 / 0.00 / 0.00 / 0.08 / 0.08 / 0.08 / 0.08
Methane / 1.00 / 1.00 / 1.00 / 0.00 / 0.00 / 0.23 / 0.23 / 0.23 / 0.23
Carbon Monoxide / 0.00 / 0.00 / 0.00 / 0.00 / 0.00 / 0.01 / 0.01 / 0.01 / 0.01
Carbon Dioxide / 0.00 / 0.00 / 0.00 / 0.00 / 0.00 / 0.00 / 0.00 / 0.00 / 0.00
Water / 0.00 / 0.00 / 0.00 / 1.00 / 1.00 / 0.68 / 0.68 / 0.68 / 0.68
Methanol / 0.00 / 0.00 / 0.00 / 0.00 / 0.00 / 0.00 / 0.00 / 0.00 / 0.00
Details / NG Feed / NG Feed / NG Feed / Steam Feed / Steam Feed / Feed Mixture / Feed Mixture / Feed Mixture / Feed Mixture / Fuel
Table 101 (cont.): Flow Summary for the Production of Hydrogen and Syn Gas from Natural Gas
Temperature (°C) / 300.0 / 90.0 / 250.0 / 150.0 / 800.0 / 650.0 / 412.0 / 392.0 / 90.0 / 90.0
Pressure (MPa) / 1.0 / 1.0 / 1.0 / 1.0 / 5.0 / 5.0 / 5.0 / 5.0 / 5.0 / 5.0
Vapor Fraction / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0
Mass Flow (tonne/h) / 0.0 / 0.0 / 0.0 / 0.0 / 71.5 / 70.3 / 70.3 / 34.0 / 36.3 / 34.0
Molar Flow (kmol/h) / 6206.2 / 6162.1 / 6163.1 / 4146.3 / 2015.7 / 4146.3
Vol. Flow (m3/h) / 109289 / 93342 / 69284 / 45251 / 36 / 24701
Component Mole Flow (kmol/h)
Hydrogen / 3156.3 / 3156.3 / 3156.3 / 3156.3 / 0.0 / 3156.3
Methane / 40.0 / 40.0 / 40.0 / 40.0 / 0.0 / 40.0
Carbon Monoxide / 933.5 / 889.3 / 889.3 / 889.3 / 0.0 / 889.3
Carbon Dioxide / 40.4 / 40.4 / 40.4 / 40.4 / 0.0 / 40.4
Water / 2036.1 / 2036.1 / 2036.1 / 20.4 / 2015.7 / 20.4
Methanol / 0.0 / 0.0 / 1.0 / 0.0 / 0.0 / 0.0
Mole Fraction
Hydrogen / 0.51 / 0.51 / 0.51 / 0.76 / 0.00 / 0.76
Methane / 0.01 / 0.01 / 0.01 / 0.01 / 0.00 / 0.01
Carbon Monoxide / 0.15 / 0.14 / 0.14 / 0.21 / 0.00 / 0.21
Carbon Dioxide / 0.01 / 0.01 / 0.01 / 0.01 / 0.00 / 0.01
Water / 0.33 / 0.33 / 0.33 / 0.00 / 1.00 / 0.00
Methanol / 0.00 / 0.00 / 0.00 / 0.00 / 0.00 / 0.00
Details / Air Feed / Air Feed / Exhaust Gas / Exhaust Gas / Syn Gas / Syn Gas / Syn Gas / Syn Gas / Water / Syn Gas
Table 101 (cont.): Flow Summary for the Production of Hydrogen and Syn Gas from Natural Gas
Temperature (°C) / 90.0 / 90.0 / 90.0 / 90.0 / 90.0 / 90.0 / 90.0 / 90.0 / 90.0 / 90.0
Pressure (atm) / 5.0 / 5.0 / 5.0 / 5.0 / 5.0 / 5.0 / 5.0 / 680.0 / 5.0 / 5.0
Vapor Fraction / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0 / 1.0
Mass Flow (tonne/h) / 8.2 / 6.6 / 1.5 / 1.5 / 20.4 / 27.0
Molar Flow (kmol/h) / 995.1 / 237.6 / 757.5 / 757.5 / 2487.8 / 2725.4
Vol. Flow (m3/h) / 5928 / 1415 / 4513 / 33 / 14821 / 16236
Component Mole Flow (kmol/h)
Hydrogen / 757.5 / 0.0 / 757.5 / 757.5 / 1893.8 / 1893.8
Methane / 9.6 / 9.6 / 0.0 / 0.0 / 24.0 / 33.6
Carbon Monoxide / 213.4 / 213.4 / 0.0 / 0.0 / 533.6 / 747.0
Carbon Dioxide / 9.7 / 9.7 / 0.0 / 0.0 / 24.2 / 33.9
Water / 4.9 / 4.9 / 0.0 / 0.0 / 12.2 / 17.1
Methanol / 0.0 / 0.0 / 0.0 / 0.0 / 0.0 / 0.0
Mole Fraction
Hydrogen / 0.76 / 0.00 / 1.00 / 1.00 / 0.76 / 0.69
Methane / 0.01 / 0.04 / 0.00 / 0.00 / 0.01 / 0.01
Carbon Monoxide / 0.21 / 0.90 / 0.00 / 0.00 / 0.21 / 0.27
Carbon Dioxide / 0.01 / 0.04 / 0.00 / 0.00 / 0.01 / 0.01
Water / 0.00 / 0.02 / 0.00 / 0.00 / 0.00 / 0.01
Methanol / 0.00 / 0.00 / 0.00 / 0.00 / 0.00 / 0.00
Details / PSA Feed / PSA / PSA / PSA / PSA / Syn Gas / H2 / H2 / Syn Gas Bypass / 200 Feed

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