safety report - chemical engineering - Engineering
I have asked each member of the process engineering team to assess potential safety issues that might pertain to one of the important unit operations in the i-pentane synthesis plant that we have been designing. Please send me an analysis of: Liquid Product Storage and Handling. What I need to know are the most important safety issues that you have identified for your unit operation, including the event itself that is of concern, what might cause that event and the magnitude of the consequences that would result. I recognize that there may be several events, so please concentrate on the ones that you consider to be the most important. Since there may be several different issues, please give me a detailed analysis of the types of event that you consider to be most critical for your assigned unit operation. This should include a description of each event, the general magnitude of its consequence and what you think might cause the event. I recognize that any single event might have more than one cause.If so, discuss briefly each of the causes that you have identified. It would also be helpful for you to estimate the approximate probability of each cause that you have identified. Let me know if you have identified any mitigation measures that you believe are adequate to reduce each safety hazard to an acceptably low level. Since I will have to pass your response to higher levels of management who do not have your technical expertise, please try to explain the mitigation method itself and why you think it will be effective. In addition to the major events you have identified, please also include (probably in a well-organized table) a listing of the other lesser events you have identified.Please include a very abbreviated version of the same topics (the event, the consequence itself and the magnitude of its importance, possible causes and a short description of the best mitigation you have identified). If you have identified an event with a serious consequence for which you cannot propose an acceptable mitigation, this might be a “show-stopper” for the project. So be sure to thoroughly analyze anything of that sort and make an appropriate recommendation.If you believe you can mitigate against all of the events you have considered, make an appropriate recommendation.If your mitigation method requires any new equipment or processes that were not part of the original process design, please make sure to report them. I hope you can give me a response in the next couple of weeks. Unit Operations Assigned:Liquid Product Storage and Handling- NOTE: the project report is attached.Process Engineering Team Subject: Preliminary Design Report We are pleased to inform you that the proposed addition to the plant in which we would convert n-pentane to iso-pentane and sell the iso-pentane as a 95\% purity product will give our plant enough revenue to justify continuing the development of the process. This has been discovered through the thorough economic analysis of the capital cost as well as the operating cost of the new additions needed for the plant. The return on investment is at about 30\% and the threshold to move forward should be about 15\%. Through the ASPEN simulations as well as the cost analysis, the threshold will easily be met. The goal of this project is to convert n-pentane to isopentane through a reaction and a catalyst that the R&D team had found. This process involves building a new section of the plant. The process we have come up with involves a reactor, a few distillation columns, a flash drum, and a bunch of compressors and heat exchangers. Hydrogen is also used to protect the catalyst from coking and must be at least at a 2:1 ratio to the feed stream. The feed stream being purchased contains a mixture of hydrocarbons including butanes, pentane, hexane, benzene, heptane, and trace amounts of components lighter than butane and heavier than heptane. We are able to purchase the feed at about 300 MM lb/yr. Similarly, the hydrogen being bought contains contaminants of methane and ethane. The purity of the product should be 95\% isopentane. The reaction used is an equilibrium reaction and has a side reaction which creates byproducts. The byproducts created from the reaction are methane, ethane, propane, and butane. As the process currently stands, there are two feed streams. The first feed stream is the feed that we are purchasing with pentanes and some other hydrocarbons. The other feed stream is the hydrogen feed. This stream is also being purchased and is used to prevent coking of the catalyst for the reaction to separate the isopentane from the n-pentane. The feed stream is coming in as a liquid at ambient temperature and pressure and the reaction needs to take place at 250 psia and 800°F. The feed stream is therefore sent to a vaporizer which brings vaporizes the stream so that it can mix with the hydrogen stream. Meanwhile, the hydrogen stream is sent to a compressor so its pressure is high enough to flow through the system. The two streams are then mixed and sent to a fired heater to get to the right temperature for the reaction. After the fired heater they are sent to the reactor and the reaction occurs. Next, coming out of the reactor, the stream must be cooled down using a heat exchanger and then a flash drum to get rid of excess light components. These light components are then sent back to the beginning of the process to be recycled to cut down on not only the cost of hydrogen, but also the loss of any isopentane. The heavier stuff comes out the bottom of the flash drum and is then sent to a series of distillation columns. The first distillation column separates anything lighter than isopentane off the top. The second distillation column separates anything heavier than n-pentane off the bottom. The bottom stream with the heavy components is then sent to another distillation column which recovers any lost isopentane and recycles it back into the system while the bottom is used for fuel for the fired heater. The final distillation column separates isopentane from n-pentane and isopentane is taken off the top as product while the npentane is recycled back into the process. Upstream: The process starts with two feed streams, one that contains the pentane and one that contains the hydrogen. The pentane stream is coming in from several choices of potential buyers that consist of petroleum refinery operations in the area and consist of industrial grade mixed pentanes that are contaminated by small amounts of lighter and heavier hydrocarbons. A low purity pentane feedstock was chosen as it is cheaper and the impurities did not affect the catalyst performance. This feed stream contains 4\% butane, 74\% n-pentane, 8\% isopentane, 6\% hexane, 2\% benzene, and 6\% heptane and larger. The amount that was chosen to purchase was 300 MMlb/year because any larger quantities would have to be purchased on the open market and would therefore cost more as we would have to outbid other buyers. As such, the maximum amount of pentane at the market price was chosen. However, because the plant will only be running for 90\% of the year, the 333.33 MMlb/year was used for the simulation to make up for it. This stream will also be coming in at atmospheric conditions which means 75°F and 16 psia and be initially stored in a tank for use. This stream is simply labeled as Feed on the flow diagram. From the tank, the stream is immediately taken to a pump that will bring the discharge pressure up to 280 psia. This, as a result, will bring the temperature of the stream to 77.78°F and require a power of 33.12 hp. This pump is used to bring the stream to an appropriate pressure to allow for flow throughout the entire system and accounts for all of the pressure drops throughout the plant. It was also brought up to a pressure that accounts for the pressure drops to the reactor as the reactor should be at a pressure of 250 psia. It is simply labeled as Pump with the exit stream labeled as HP-pent. Because this stream is still a liquid and will need to be mixed with the hydrogen stream which is a gas, the stream must be converted to the vapor phase using a vaporizer. The subsequent temperature that allowed for a molar vapor fraction of 1 was 339.59°F and accounted for a pressure drop to 270 psia and a heat duty of 9.97 MMBtu/hr. The vaporizer is labeled as Vap and the outlet stream is labeled as PentVap. The outlet stream combines with the hydrogen stream and two recycle streams. The other stream is the hydrogen stream which will be bought from Ajax Refining as their operations produce a byproduct stream of hydrogen. Because they are close by, the stream will be delivered by pipeline and then stored in tanks as well. This means that the stream will be at 75°F but will already be pressurized to 150 psia. As for the amount, the R&D team has determined the correct amount of hydrogen that is needed to protect the catalyst from coking. They determined that the ratio of hydrogen to pentane should not fall below 2 as some carbon deposition was detected during their runs. However, the runs were not long enough to observe any significant loss in reactivity or whether the catalyst would coke up entirely. Hence, a ratio of 2:1 was chosen which means a flow rate of 2.1 MMlb/year. Because this stream is produced from a catalytic reforming operation, there are some impurities which means a cheaper price but these impurities may cause a problem if removing the impurities is too expensive. This stream contains 80\% hydrogen. 15\% methane, and 5\% ethane. This stream is labeled as H2 on the flow diagram. This stream needs to be brought up to the same pressure as the pentane feed stream so an isentropic compressor, labeled Comp, was put in that will bring the discharge pressure to 270 psia. It has an isentropic efficiency of 0.7 and requires 16.54 hp. This also brings the outlet stream, labeled HP-H2, to a temperature of 203.2°F. After the compressor, the stream is brought to a mixer, labeled Mixer, that combines it with the pentane stream described previously and two recycle gas streams that are described in the recycle stream section. The combined stream, labeled HtrFeed, will have a temperature of 519.72°F. For the reactor, the R&D team has determined that the most promising runs in the reactor were a high pressure gas phase reaction at 800°F and 250 psia. Therefore a fired heater was put in place to bring the temperature to 800°F. A further pressure drop was accounted for meaning an outlet pressure of 255 psia. The resulting heat duty for this heater was 106.2 MMbtu/hr. This is labeled as the FiredHtr and goes to the reactor next. Initially, an equilibrium reactor, Rxr, was set up at 250 psia and a duty of 0 Btu/hr and used a 1:1 reaction of n-pentane to isopentane. From this, a mole fraction of isopentane was found and then, another reactor was made with a fraction conversion that allows for a mole fraction that is slightly lower than that of the equilibrium reactor. While only one reactor will be used in the actual plant, two are being used to simulate the reactor. The first, Rxr2 is for the 1:1 reaction of n-pentane to isopentane while the second, SideRxr, represents the side reaction. This first reactor has the same condition at 250 psia and a duty of 0 Btu/hr. This also means a mole fraction 0.0549 while the equilibrium mole fraction of 0.0609. As a result, a fraction conversion of 0.36 was chosen to allow for this lower value. This value can also not be too low as the fraction conversion plays a large part in the purity of the end stream. The inlet and outlet streams of this reactor are RxrFeed2 and Rxr2Prod respectively. While the R&D lab has determined that to prevent any carbonization of the catalyst, hydrogen must be incorporated into the feed. However, the catalyst produces side reactions as the hydrogen reacts with the pentane removing a methyl group. This reaction is as follows, C5H12 + H2 → C4H10 + CH4. In addition, the butane that is produced will perform the same reaction with C4H10 + H2 → C3H8 + CH4. This will then be repeated for the propane that is produced and then the ethane that is produced. These reactions are also irreversible and proceed at a slower rate to the main n-pentane to isopentane which means that a small amount is made. The R&D team determined through lab experiments that 2\% of the pentane entering the reactor is converted to the side products. These side all occur simultaneously and hence, the exact proportions are difficult to obtain. To counteract this, the leader of the R&D team said to model the side reactions as a single reaction with about the same ratios of byproducts that were determined in the lab. This single reaction is much either to model as one reactor than as several reactors. However, this reaction will have actual ratios of the byproducts that are different but should be approximately the same values. This new reaction is as follows, C5H12 + 1.3125 H2 → 0.3125 C4H10 + 0.5 C3H8 + 0.75 C2H6 + 0.75 CH4. This reaction occurs with the n-pentane and the isopentane produced from the main reaction. Hence, a fraction conversion of 0.01 was chosen for each of the 2 side reactions. The outlet stream of the reactor, SideRxrP, then goes to a series of heat exchangers in the downstream. Downstream: The next seven heat exchangers were all made using heat economy in mind which means that they are at other places in the process as well. Because this stream is coming out of the reactor at 800°F, it can be used to heat up other areas of the process. The first heat exchanger is one on the lights recycle stream and is talked about in the recycle section. It brings the temperature down to 533°F. The second is actually the vaporizer talked about previously in the upstream and brings the temperature down to 504°F. After that, there are the four reboilers on the distillation columns. The first is the stripper’s reboiler and brings the temperature down to 383°F. Then, the reboilers of Hvy-Pent, Hvy-Rec, and I-N-Pent bring the temperature of the stream down to 356°F, 355°F, and 223°F respectively. These distillation columns are talked about later in the downstream process. The last heat exchanger that uses heat economy is on the pentane recycle stream and brings the temperature down to 194°F. A pressure drop of 2 psia was used for each of the exchangers. These heat exchangers are, in order of being talked about, HX2, Vap, StprBoil, HvyBoil, RecBoil, PentBoil, and HX1. Then a condenser, labeled HX, is used to condense some of the stream to a liquid and therefore a temperature of 100°F and a pressure of 232 psia. However, this only results in a molar liquid fraction of 0.2934. Because heat economy was used in this stream, the required duty was only 56.23 MMBtu/hr. The outlet of this heat exchanger is HP-Prod. As stated previously, the heat exchanger outlet stream, HP-Prod, goes into the flash drum which is used to separate the vapor and liquid phase. The vapor stream is labeled Flashgas, which is talked about in the recycle stream section, and the liquid stream is labeled Flashliq. This is in place to separate all of the hydrogen and some of the methane from the rest of the stream as the hydrogen is basically impossible to condense to a liquid. The liquid coming out of the bottom of the drum is sent to the stripper column. This stripper column, labeled Stripper, is used to separate propane and everything else lighter from the rest of the stream. This works by having the stream enter the top of the stripper at which point the remaining gas from the stream is immediately separated from the stream by simply exiting the top of the column, labeled Lite. Because of this, there is not a condenser at the top of the column. The remaining material then travels down the column like a normal distillation column with a reboiler at the bottom. In this case, a kettle was used as the reboiler and the resulting duty was 39.88 MMBtu/hr. The number of stages used was 30 with a bottoms to feed ratio of 0.19 which resulted in a reflux ratio of 1.63. These values were chosen to remove most of the lights and to result in the desired purity of the end isopentane. The results of this stripper showed that the bottom stream, IPLiq, had lost all of the propane, ethane, methane, and hydrogen with the majority of the stream being made of isopentane and n-pentane. This bottoms stream then flows into a distillation column, labeled Hvy-Pent, which is being used to separate the heavies from the stream. This includes everything heavier than the npentane. The number of stages for this column was chosen to be 22 with a component recovery for the n-pentane of 0.99 and for the hexane of 0.01. This resulted in a reflux ratio of 0.913 and a distillate to feed ratio of 0.91. The inlet flow is coming in at the 12th tray from the top. The pressures for the condenser and reboiler were set to 43 and 45 psia respectively so that the temperature for the condenser was at 150°F. This allowed for cooling water to be used to its fullest as it comes in at 80°F and can leave at a max of 130°F. The duty required for the reboiler and the condenser were 8.67 and 14.85 MMBtu/hr. The duty generated in the reboiler was used to cool down the stream that exits the reactor. The bottom outlet stream, labeled Hvy, contains less than 1\% isopentane with the majority of the stream being made of heptane and then hexane. However, the stream contains about 5\% n-pentane so a new distillation column was put in place. This steam exits at 242°F, while the tops stream, labeled Pent, exits at 151°F and contains almost entirely n-pentane and isopentane as only about 1.3\% is made of the other components. The new distillation column that was made is labeled Hvy-Rec and is used to separate any remaining pentanes and then send them to combine with the top product of the Hvy-Pent distillation column. The bottoms are then serve as fuel gas for the fired heater. By using npentane and hexane recovery of 0.99 and 0.01 respectively, the resulting column has 18 stages, which meant a reflux ratio of 1.76, with the feed coming in at the 10th stage. The reboiler and condenser pressure were set to 36 and 38 psia so that cooling water could be used as the temperature would be 151°F. This would put the temperature of the stream out of the reboiler at 236°F. Similar to the other columns, the stream exiting the reactor was used as the heating source in the reboiler. The duty of the reboiler and condenser were 87 and 130 kBtu/hr respectively. The top stream, HvyRec1, combines with the top stream, Pent, of the previous column in amixer labeled PentMix. The exit stream Pent2 leaves at a temperature of 139°F and goes to the final column. This final distillation column is used to separate the n-pentane from the isopentane. The stream that is exiting this column at the top, labeled IPent leaves at 151°F and is the end product of the plant. By running the column with 80 stages with the stream entering at the 40th stage and component recoveries for the isopentane and n-pentane at 0.98 and 0.02 respectively, the desired minimum purity of 95\% was accomplished. The exact mole fraction was 0.957 with mole fractions of 0.025 amd 0.017 for butane and n-pentane respectively and then no lighter or heavier components. However, this meant there had to be a reflux ratio of 8.73 and then duties of 3.87 and 3.83 MMBtu/hr for the reboiler and condenser respectively. The reboiler and condenser were also run at 48 and 50 psia respectively to allow for the use of cooling water just like the previous 2 columns. In addition, just like the other columns, the reactor exit stream was used as the heating source for the reboiler. The amount being made is 29564 lb/hr. While the desired product has been achieved, there is still a lot of improvement that can be made to this column. The bottoms, RecPent, is then sent to be recycled back into the plant. Recycle Streams: The first stream that gets recycled is the stream coming off of the separator and has a temperature and pressure of 100°F and 232 psia. This stream is labeled Flashgas and it has a large amount of hydrogen in it. The hydrogen is being recycled back to the process so that it saves money on buying larger quantities of hydrogen in the beginning of the process. The other stream that is currently being recycled, labeled Lite, is the top stream of the first distillation column labeled Stripper. This distillation column is the one that is separating the components lighter than isopentane from everything else. While this mostly includes propane, ethane, and methane, there is still 4.44\% pentane and 6.78\% isopentane. This is a substantial amount of pentanes that can be sent back through the process to be recovered. This stream is exiting the column at 198°F and 232 psia. These two streams are then mixed together in a mixer labeled RecMixr which results in a stream that is at 198°F. This stream is then sent to a heat exchanger labeled HX2. This heater is in place to heat up the material in the recycle stream as it is going back into the Mixer at the beginning of the process. However, because this stream is so large and at a low temperature, the stream coming out of the mixer would be much lower. This would cause a lot more work for the fired heater. In addition, heat economy is used by having the reactor exit stream heat up this stream. The outlet stream, HT-Rec, is at 520°F, which results in a heat duty of 103 MMBtu/hr. The heated outlet stream then goes to an isentropic compressor, RecComp, which will then compress the stream to a discharge pressure of 270 psia so that the stream will be able to flow into the mixer at the beginning of the process. The compressor runs at an isentropic efficiency of 0.7 which results in a work of about 1971 hp. The outlet stream of the compressor leaves as 537°F due to being heated slightly by the compressor. This stream, HP-Rec goes to a splitter used to purge some of the gas. Coming out of this splitter, labeled purge, is two streams. One, the Ventgas stream, is a gas purge that lets out some of the gas to prevent build up of all the components being recycled throughout the system. The other, labeled RecGas is recycled back into the plant using the mixer from the upstream process. The split fraction of 0.005 was chosen as it was the lowest value that still allowed for the process to run without too much material building up in the process. In addition to this recycle process, there is a second stream that is being recycled back into the plant. This stream, RecPent, is coming off of the bottom of the last distillation column in the process. Because this stream is about 97.5\% n-pentane and 2.2\% isopentane, it is a good idea to recycle that before the reactor so that the n-pentane can be converted to isopentane and produce more desired product. This stream exits the column at 171°F and 50 psia so it must be pumped back into the plant meaning a pump was put in. This raises the pressure to 273 psia and also raises the temperature slightly to 173°F. A pump efficiency of 0.7 is assumed which results in a required power of 17.4 hp. The exit stream of the pump, RePent, is fed into a heat exchanger which is used to vaporize the material in the stream. This heat exchanger, labeled HX1, uses the stream exiting the reactor to heat up the material to 490°F. This means a heat duty of 8 MMBtu/hr. The pressure of the stream dropped to 270 psia as well. The exit stream of this heat exchanger, RecPent3 goes to the mixer in the upstream of the process. The ROI for this process was calculated to be 30.15\%. This was done by using Equation 1 below which factors in the revenue, costs, and some factors for inflation and equipment. These values can be found below in Table 1 with a breakdown of the capital and operating costs in Table 2. As the hurdle rate for this project was 15\%, this project should be continued. The product revenue was about $116M/yr and was found by selling the product stream at 29565 lb/hr for $0.50/lb. The pentane and hydrogen feed costs were $78M/yr and $1.9M/yr respectively. These were found by multiplied a cost of $0.26/lb and $0.92/lb, respectively, by the yearly amount used of 300 MMlb/yr and 2.1 MMlb/yr. From there, the utility cost was found by summing the operating costs of each component at $2657/hr and converting to the amount used in an operational year at about $21M/yr. This value includes any utilities used including heating steam, cooling water, and electricity. The calculations for the individual equipment can be found on the attached spreadsheet. The last number in the numerator is the overhead which covers any direct costs like labor, taxes, and repairs. For the sake of simplicity, this number was estimated to be 10\% of the capital cost making it about $700k. This capital cost is the total cost of all of the equipment being purchased. The exact calculations for the cost of each piece of equipment can be found on the attached spreadsheet. These values cost a total of about $7M. This value was then multiplied by Lang’s factor of 4.75 to account for things like piping, valves, and controls. This was then multiplied by a correction factor of 600/402 or 1.49 to account for inflation in Lang’s factor. Equation 1: ROI Calculation 𝑅𝑂𝐼 = 𝑃𝑟𝑜𝑑𝑢𝑐𝑡 𝑅𝑒𝑣𝑒𝑛𝑢𝑒 − 𝐹𝑒𝑒𝑑 𝐶𝑜𝑠𝑡 − 𝐻2 𝐶𝑜𝑠𝑡 − 𝑈𝑡𝑖𝑙𝑖𝑡𝑖𝑒𝑠 − 𝑂𝑣𝑒𝑟ℎ𝑒𝑎𝑑 𝐶𝑎𝑝𝑖𝑡𝑎𝑙 𝐶𝑜𝑠𝑡 ∗ 𝐿𝑎𝑛𝑔′ 𝑠 𝑓𝑎𝑐𝑡𝑜𝑟 ∗ 𝐶𝑜𝑟𝑟𝑒𝑐𝑡𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑜𝑟 Table 1: Return on Investment Summary Product Revenue ($/yr) Feed Cost ($/yr) H2 Cost ($/yr) Utility Cost ($/yr) Overhead ($/yr) Capital cost ($) Lang Factor Correction Factor ROI $116,544,442 $78,000,000 $1,932,000 $20,949,426 $700,033 $7,000,328 4.75 1.49 30.15\% Table 2: Capital and Operating Cost Breakdown HX HX1 HX2 VAP FIREDHTR COMP RECCOMP RXR STRIPPER HVY-PENT I-N-PENT HVY-REC STRIPPER reboiler HVY-PENT reboiler I-N-PENT reboiler HVY-REC reboiler HVY-PENT condenser I-N-PENT condenser HVY-REC condenser Total Capital cost ($) Utility Cost ($/hr) $45,471 $1,063 $7,215 ---$26,359 ---$10,885 ---$1,716 $871 $45,004 $3 $862,383 $318 $87,682 ---$1,579,062 ---$1,122,473 ---$3,125,517 ---$61,842 ---$3,609 ---$4,350 ---$3,508 ---$7,499 ---$1,796 $112 $1,716 $290 $2,240 $2 $7,000,328 $2,657 $20,949,426 The most important economic factors included values from the capital and operating cost along with the cost of hydrogen and product revenue. The first important factor was the hydrogen cost as that was not factored into the first cost estimate. In addition, the amount of hydrogen bought was able to be decreased from about 600MMlb/yr to 2.1 MMlb/yr which saves greatly on the cost. One of the largest factors that was changed was the product revenue as this was increased from about $12M to about $116M. This was done by making several changes seen in the following paragraphs. This increased the product flow rate from 1776 lb/hr to 29565 lb/hr. The largest factors for the capital cost are the three large distillation columns which cost from $1.1M to $3.1M. These were a lot higher than before because a lot more product is being made now than before. While these increases would have decreased the ROI value, the resulting positive changes in the product revenue far outweigh the negatives. The other large cost is the compressor on the recycle stream as this costs about $860k. Because the hydrogen feed was decreased so greatly, there was less that needed to be processed before the distillation columns which greatly lowered the capital costs of that equipment. The capital cost increased from the initial estimate of $2M to $7M. However, the largest change is easily the operating costs. First, the decrease in hydrogen also decreased the operating costs of the equipment before the distillation columns. This included the electricity cost of the compressors, the fired heater cost, and the cooling water cost for the heat exchanger after the reactor. The other important thing that was changed was the use of heat economy. This decreased the cost of the vaporizer, distillation column reboilers and condensers, recycle stream heat exchangers, and the heat exchanger after the reactor. All of these except for the reactor exit heat exchanger were decreased to a price of $0 due to the use of heat economy. This is discussed in the following paragraphs as well. These decreased the operating cost for that heat exchanger from $113k/hr to $1k/hr. All of these decreases changed the operating cost from over $1 billion to only $20M. That same heat exchanger still takes up the majority of the operating costs with the fired heater taking up the next largest. Some of the most important changes that were made to the process include adding a distillation column, Hvy-Rec on the HVY stream, correcting the input of hydrogen, fractional conversion of the reactor, and changes were made to the purge and ventgas stream. The top of the column is being used as a recycle stream to capture more iso-pentanes and the bottom of the column can be used for fuel in the fired heater. In previous simulations, the hydrogen input was at a 2:1 ratio with the feed input. This was never corrected for the amount of hydrogen that was being recycled into the system. Once the recycled hydrogen was taken into account, the input of hydrogen went from 600 MMlb/yr to only 2.1 MMlb/yr. This of course will drastically reduce the cost of hydrogen that we have to buy each year. As a result of there being much less hydrogen in the system, there needs to be much less gas being purged off at the end of the recycle stream. The amount being purged decreased from 0.03 to 0.005. This is an improvement because the less that we need to purge off, the less potential loss of product there is. In addition, the cost of the equipment went down because there was significantly less material in the streams as the majority of the streams before the distillation columns were made up of hydrogen. This also allowed for the fractional conversion in the reactor to be increased from 0.09 to 0.36. This greatly increased the product being made as well. However, with more pentanes being made the price of the distillation columns, condensers, and reboiler was greatly increased. The total capital cost increased by about $5 million due to the changes. The settings within the distillation columns were also changed slightly to ensure that the purity of the product remained on target. By making these changes, the rate of the product being made went from 1776 lb/hr to 29565 lb/hr. Another great change that was made was adding heat economy throughout the process. This means that some streams that needed to be heated were heated with the streams in the process that were already hot and vice versa. In this process there is a total of seven instances of heat economy being used. The first is the heat exchanger coming off of the recycled light key components named HX2. The second is the vaporizer at the beginning of the process that vaporizes the feed stream. The third use of heat economy was with the reboiler of the stripper distillation column. The fourth instance was with the HVY-PENT’s distillation column’s reboiler. The 5th use was with the I-N-PENT’s reboiler. The sixth use of heat economy was in the reboiler of the recycled HVY stream. The final use of heat economy was in the heat exchanger in the recycled pentane stream coming out of the bottom of the final distillation column. By implementing these changes, heating steam was not needed in any of these heat exchangers. In addition, the heat exchanger after the reactor had a temperature difference of about 100°F instead of the previous 740°F. This means that significantly less coolant is needed to cool down the stream. This brought the duty down from 1750 MMBtu/hr to 560 MMBtu/hr. In addition, the temperature of the outlet stream was set to 100°F instead of 60°F so that cooling water could be used instead of a coolant. This brought the operating cost down from $113,000 to $1000 an hour. All these heat economy changes brought the operating costs down from about $1 billion a year to about $20 million a year. For our future process, there are limited recommendations that are to be considered, that will slightly impact our economic evaluation. First, there is a 6537 lb/hr stream from the HVYREC distillation column, consisting of hexane and heptane. These heavy components would serve as a good fuel source for the fired heater. Therefore, the next step would be to factor in the lower heating value for these components and quantify the utility cost savings. Another option would be to determine the market value for this stream and decipher if its more beneficial to use as a fuel source or to sell for profit. Next, storage containment was not factored in our capital cost. We need to determine the total number of containers needed and the market pricing for each one. Then the total capital cost can be adjusted to account for these. Third, there are a total of eight heat exchangers in series, serving as heat economy and reactor cool-down. The pressure drop across each exchanger is currently 2 PSIA, which contributes to a total pressure drop of 18 PSIA. A compressor is recommended to supply enough driving force for the vapor flow to exchanger heat eight times. This would also have an impact on capital and utilities cost. The final recommendation is to sell off the VENTGAS. This is a 2164 lb/hr stream primarily consisting of butane and lighter components. There is currently no destination for the stream other than in the environment. This could pose a future EPA violation, that would ultimately fault the process. Therefore, its being recommended to find an outsource company that is willing to take the stream and refine on their own, to create ethane, propane, etc. This will save the company any environmental hazards, while creating another source of income. Bottom line, our process has a current ROI of 30.15\% which is above the expected 15\%. Therefore, the overall recommendation is to go forward with the project and evaluate the slight changes mentioned above, to finalize the process economics. Purchase answer to see full attachment
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