Designing C4/C5 Olefins & Alcohols from Wet Natural Gas, Papers of Chemistry

Download Designing C4/C5 Olefins & Alcohols from Wet Natural Gas and more Papers Chemistry in PDF only on Docsity! Olefin and Alcohol Production from Wet Natural Gas Holdings Background Recently, a “wet” natural gas supply was acquired near a small pilot scale production and research facility. This existing facility became very profitable through the production of small quantities of specialty chemicals. This new raw material supply is very intriguing because it can be used as a feed stock to the existing plant itself or as salable products via the design of new units. The main goal is to design a plant for the production of C4 and C5 olefins and alcohols from the feedstock of wet natural gas. The composition of the natural gas is as follows: Component Volume % Methane 78.00 Ethane 4.75 Propane 6.50 Isobutane 1.60 n-Butane 3.45 Isopentane 4.75 CO2, N2, He 0.95 The yearly feed of this supply is approximately 5000 metric tons per year. The designed process consists of four steps: 1. Separation of C4 and C5 alkanes from the wet natural gas. Also, included is a column design for the cryogenic separation of propane from the methane and ethane. This propane may either be sold if the market is favorable, or returned to the well with the methane and ethane. 2. Dehydrogenation of the C4 and C5 alkanes to mono-olefins. 3. Hydration of the C4 and C5 mono-olefins to alcohols. 2 The block flow diagram (Figure 1) shows how the natural gas plant will be built around the already existing, Semi-Works, plant. The overall plant design consists of three sections: cryogenic separation of the C4 and C5 hydrocarbons from the lighter hydrocarbons in the “wet” natural gas, production of mono-olefins from these hydrocarbons, and hydration of these olefins to alcohols. This plant is not only to be designed to produce marketable products, but also to supply the Semi-Works plant with a small supply of heavy hydrocarbons, olefins, and alcohols. These processes are very distinct and are more easily handled separately. The titles of the three processes are Cryogenics Separation, Olefins, and Alcohols. The uniqueness of this design is the time element used. In the Olefin and Alcohol units, the same equipment is used to produce three different products. The plant is set up to make one product for a certain period of time and then new raw materials are added to make different products over the course of a year. 5 tower, T-102, where the C5 is separated from the C4’s. The distillate, Stream 17, from this tower is sent to a third column, T-104. Here the iC4 is separated from the nC4. The C5, iC4, and nC4 streams (Stream 18, Stream 19, and Stream 20) are then sent to holding tanks. From here, theses higher hydrocarbons are sent to the Semi-Works plant or to the olefin unit for further processing. The refrigeration loop for the system (Figure 3) compresses and expands ethylene for cryogenic cooling. The ethylene is compressed to 100 bar in C-102. Heat exchanger, E-104, cools the stream from 167°C to 45°C. E-105 cools Stream 28 further to 10°C with refrigerated water. The pressure is then released to 4 bar. By releasing the pressure, the ethylene cools to -76.2°C. The flash vessel, V-102, separates the liquid and vapor of Stream 21. The liquid is used in the condenser of T-101. Stream 23 is vaporized at a temperature of -75°C. Stream 24 is mixed with the vapor stream from flash vessel, V- 102. Stream 25, the combined stream at -75.7°C and 4 bar, is used as the coolant in heat exchanger, E-103. Stream 26, -49.6° and 3.7 bar, is sent back to compressor, C-102. [There are a few extra pieces of equipment on the PFD (Figure 2). Compressor, C-101, and distillation tower, T-103, are only to be used when the sale of propane is desirable. Propane is typically sold at a pressure of 20 bar. Therefore the system needs to be run at a higher pressure. Therefore, the process needs to be adjusted for the increase of pressure throughout the system. When selling propane, T-103 is needed to separate the lower carbons, methane, ethane, and propane. With the addition of T-103, the cryogenic loop needs to be adjusted for the low temperature of the heat exchanger, E- 110.] 6 Necessary Information and Simulation Hints When optimizing the separation towers, the number of stages, sequencing of columns, and operating pressure need to be varied in order to minimize the EAOC. The major cost of the cryogenic plant is the refrigeration loop (Figure 3). The electricity cost of the compressor is high due to the large amount of refrigerant needed to cool the feed from 10°C to -63°C. Using two heat exchangers, one with cooling water and one with refrigerated water, reduced the utility costs. The significant savings can also be obtained by optimizing the refrigeration loop. The use of different refrigerants in a temperature cascade should be considered. Equipment Description E-101 Cooler E-102 Cooler E-103 Cooler (Cryogenic loop) E-104 Cryogenic loop cooler (CW) E-105 Cryogenic loop cooler (RW) E-106 C1, C2, C3 condenser (Cryogenic loop) E-107 C4, C5 reboiler E-108 C4’s condenser E-109 C5 reboiler E-110 C1, C2 condenser E-111 C3 reboiler E-112 i-C4 condenser E-113 n-C4 reboiler 7 P-101 Pump P-102 C1, C2, C3 reflux pump P-103 C4’s reflux pump P-104 C1, C2 reflux pump P-105 i-C4 reflux pump C-101 Optional compressor if propane is desired for sale C-102 Cryogenic loop compressor V-101 Flash vessel V-102 Cryogenic loop flash vessel T-101 C1-C5 distillation tower T-102 C4, C5 distillation tower T-103 C1, C2, C3 distillation tower T-104 C4’s distillation tower 10 Stream 25 26 27 28 29 Temp. (°C) -75.7 -49.6 166.9 45.0 10.0 Press. (bar) 4.0 3.7 100.0 100.0 100.0 Vapor Fraction 1.0 1.0 1.0 1.0 1.0 Total Flow (kg/h) 2358.40 2358.40 2358.40 2358.40 2358.40 Total Flow (kmol/h) 84.01 84.01 84.01 84.01 84.01 Component Flows (kmol/h) Methane -- -- -- -- -- Ethane -- -- -- -- -- Propane -- -- -- -- -- I-Butane -- -- -- -- -- I-Pentane -- -- -- -- -- N-Butane -- -- -- -- -- Nitrogen -- -- -- -- -- Carbon Dioxide -- -- -- -- -- Helium -- -- -- -- -- Ethylene 84.01 84.01 84.01 84.01 84.01 ** Very small traces Units shown in | __! are required E-109 LPS if C, is a required product. i-C, Figure 2: Unit 100 -- Initial Separation  E-103 V-102 E-106 Condenser of T-101 C-102 RW CW E-105 v E-104 Xy- 1] Figure 3: Unit 100 -- Refrigeration Cycle 15 Secondly, since the dehydrogenation reaction is endothermic, heat must be supplied to the reaction to maintain an isothermal process. The majority of the heat of reaction is added to the process during regeneration – reheat step from several sources. These include: 1. Combustion of coke deposited during the dehydrogenation step. 2. Sensible heat from the hot regeneration air stream. 3. Reduction of the catalyst following the regeneration. N-butane and isobutane only require two distillation columns, while isopentane requires three. This means that a third tower must be used when processing the isopentane (Figure 6-8). Equipment Description E-201 Reactor inlet heater R-201 A/C Reactor E-202 Reactor effluent cooler C-201 Compressor E-203 Pre-flash cooler E-204 Pre-flash cooler V-201 Flash E-205 Heater (only used in the production of 1-Butene) T-201 Hydrogen distillation tower E-206 Condenser E-207 Reboiler V-202 Reflux drum 16 P-201 Reflux pump T-202 Distillation tower E-208 Condenser E-209 Reboiler P-202 Reflux pump T-203 Distillation tower E-210 Condenser E-211 Reboiler P-203 Reflux pump Recycle Point Recycle Point Figure 4: Unit 200 -- Base Case R-201 A/C E-206 V-201 H, V-202 / Waste | ( Q o> Recycle for { { P-201 I-Butene E-205 T-201 E-208 E-202 4 1-Butene Q o> 4 P-202 E-207 T-202 Recycle for C-201 E-203 _E-204 2-Methy]-1-Butene E-210 4 E-209 Recycle for 1-Butene P-203 T-203 2-Methyl- 1-Butene I-Butene E-211 **T-103 is only required far ?_mathwl1_hntene 20 In this case, the single-pass fractional conversion is raised to 93 percent, which is the value obtained from the patent example after which the operating conditions were modeled (1). The new production schedule is as follows: t-butanol --58 days, sec-butanol -- 103 days, and 2-methyl-1-butanol -- 189 days. Reference 1. Giles, J.H., J.H. Stultz, and S.W. Jones, “Process for Hydration of Olefins to Produce Alcohols,” U.S. Patent #4,182,920, 1980. Equipment Description TK-301 Mixing tank P-301 Pump TK-302 Mixing Tank E-301 Cooler R-301 Packed Bed Reactor A-301 Anion Exchange Bed E-302 Heater V-301 Flash Vessel E-303 Cooler E-304 Heater V-302 Flash Vessel V-303 Flash Vessel T-301 Alcohol Purification Tower P-302 Reflux Pump E-305 Condenser E-306 Reboiler Acetone a Acetone & Water Feed V-303 Alcohol Figure 9: Unit 300 -- Alcohol Production