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Chemical Process Design 1

by: Adriel Nader

Chemical Process Design 1 CHE 455

Adriel Nader
GPA 3.7

Joseph Shaeiwitz

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Joseph Shaeiwitz
Class Notes
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This 14 page Class Notes was uploaded by Adriel Nader on Saturday September 12, 2015. The Class Notes belongs to CHE 455 at West Virginia University taught by Joseph Shaeiwitz in Fall. Since its upload, it has received 16 views. For similar materials see /class/202700/che-455-west-virginia-university in Chemical Engineering at West Virginia University.

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Date Created: 09/12/15
ChE 455 Fall 2006 Major 1 Formalin Production Background You have recently joined a chemical company Among the chemicals that this company produces is methanol mostly for internal consumption A major use of internal methanol is to produce formalin which is a 37 wt solution of formaldehyde in water Formaldehyde and urea are used to make ureaformaldehyde resins that subsequently are used as adhesives and binders for particle board and plywood We recently have received a memorandum from a customer who buys our formalin indicating that there are periodic problems mostly in the summer with the formalin they are receiving from us They claim that the formalin contains unacceptably high amounts of formic acid relative to formaldehyde It seems that this alters the ureaformaldehyde resin properties such that the particle board and plywood subsequently manufactured does not have the appropriate tensile and load strength They are threatening legal action unless this problem is rectified immediately Form aldehyde Production Unit 800 produces formalin 37 wt formaldehyde in water from methanol using the silver catalyst process Figure 1 illustrates the current process Tables 1 and 2 are the stream tables and utility summary respectively Table 3 is a partial equipment summary Air is compressed and preheated fresh and recycled methanol is pumped and preheated and these two streams are mixed to provide reactor feed The feed mixture is about 39 mole methanol in air which is above the upper ammability limit for methanol For methanol UFL 36 mole LFL 6 mole In the reactor the following two reactions occur CH3OH 02 gt HCHOH20 mm 373 kcalmole 1 CH3OH gtHCHOH2 AHm 203 kcalmole 2 The reactor is a unique configuration in which the silver catalyst is in the form of a wire gauze suspended above a heat exchanger tube bank Because the net reaction is very exothermic the heat generated in the adiabatic reactor section must be removed quickly hence the close proximity of the heat exchanger tubes The heat exchanger resembles a pool boiler with a pool of water on the shell side If the temperature of the ef uent is too high the set point on a liquid level controller is adjusted The level controller feeds back to the boiler feed water inlet that increases the boiler feed water rate entering the heat exchanger to increase the water 0301 PABD lAB 5301 5802 R801 T801 Taoz E803 E804 EBOS vso1 PASUZAB PreoaAlB 5806 feed air mel anal methanol air formaldehyde lormaldehyde formaldehyde reactor tower owe tower pro uc1 pmduct compressor feed pump prehealer prehealer reactor absorber luwer ef uenl reboiler condenser re ux reflux pump cooler cooler drum pump deionized water of g as methanol quot1P5 formalin CW P803 NB to storage tank Figure 1 Unit 800 Formalin Production from Methanol Table 1 Stream Tables for Unit 800 Stream N0 Pres 733082 733082 257615 535421 Table 1 cont d Stream Tables for Unit 800 Stream N0 Pres Table 2 Utility Stream Flow Summary for Unit 800 E 801 E 802 E 803 E 804 mps hps cw mps 2063 kgh 4543 kgh 23500 kgh 18949 kgh E 805 E 806 R 801 cw cw bfw gt mps 775717 kgh 27957 kgh 3723 kgh Table 3 Partial Equipment Summary Heat 7 39 E801 E804 A405 m2 A373 m2 12 exchanger oating head carbon steel process stream in she 12 exchanger kettle reboiler stainless steel process stream in she Q4111MJh Q37755 MJh maximum pressure rating of 350 kPa maximum pressure rating of 250 kPa E802 E805 A 462 m2 A 269 m2 12 exchanger oating head carbon steel process stream in tubes 12 exchanger oating head stainless steel process stream in she Q 7675 MJh Q 32456 MJh maximum pressure rating of 350 kPa maximum pressure rating of 250 kPa E803 E806 A2816m2 A41m2 12 exchanger oating head carbon steel process stream in shell Q 98323 MJh maximum pressure rating of 350 kPa 12 exchanger oating head stainless steel process stream in tubes Q 1169 7 MJh maximum pressure rating of 400 kPa Reactors R801 Heat Exchanger Portion R801 Reactor Portion A 14044 In2 thin layers of silver wire gauze counter ow exchanger oating head carbon steel process stream in tubes Q 8928 MJh maximum pressure rating of 350 kPa suspended above heat exchanger tube bank Pumps and Compressors C801 P 801 AB carbon steel carbon steel power 658 MJh power h 70 efficient 80 efficient P 803 AB stainless steel power 152 MJh 75 efficient Towers T801 T802 carbon steel 10 m of packing 2 in ceramic Berl Saddles 20 theoretical stages 100 kPam pressure drop diameter 086 m packing factor 45 maximum pressure rating of 300 kPa carbon steel 31 sieve trays plus reboiler and partial condenser 70 efficient trays feed on tray 18 re ux ratio 3734 06096 In tray spacing 0091 m weirs column height 19 m diameter 25 m maximum pressure rating of 200 kPa vaporization rate to remove more heat The reactor ef uent enters an absorber in which most of the methanol and formaldehyde are absorbed into water with most of the remaining light gases purged into the offgas stream The methanol formaldehyde and water enter a distillation column in which the methanol overhead is recycled and the bottom product is a formaldehydewater mixture that contains S1 wt methanol as an inhibitor This mixture is cooled and sent to a storage tank which is sized at four days capacity This storage tank is essential since some of the downstream processes are batch The composition in the storage tank exceeds 37 wt formaldehyde so the appropriate amount of water is added when the downstream process draws from the storage tank This is not shown on the PFD Storage of formaldehydewater mixtures is tricky At high temperatures undesirable polymerization of formaldehyde is inhibited but formic acid formation is favored At low temperatures acid formation is inhibited but polymerization is favored There are stabilizers which inhibit polymerization but they are incompatible with resin formation Methanol at concentrations between 5 and 15 wt can also inhibit polymerizaton but no separation equipment for methanol currently exists on site and methanol above 1 wt also causes defective resin production With S1 wt methanol the storage tank contents must be maintained between 35 C and 45 C Observations You have toured the plant checked the log books spoken to engineers and operators and have gathered the following information The catalyst is replaced once per year and for about five days after startup a pressure relief valve in the reactor R801 releases During the same time period bfw consumption in R801 was not seen to increase beyond normal daytoday uctuations of il and the reactor outlet temperature was not seen to increase significantly Excess acidity occurs mainly in the summer All existing equipment is made of carbon steel One year ago an unscheduled emergency shut down was required to replace a control system between the tower T802 and the subsequent pump P803 NB Due to availability and time constraints 1quot schedule 40 pipe was used in place of 15quot schedule 40 pipe During hotweather periods the inlet temperature of cooling water has been observed to increase by as much as 5 C During these hot weather periods the pressure in the distillation column has been observed to increase slightly but operation over a long period of time shows no leakage or safety problems associated with this change in pressure Pump 803 MB is located a height of 5 m below the tower T802 exit There is a total of 30 equivalent meters of pipe elbows and valves in the line An inspection of the pressure relief valve on the reactor R801 indicates that it is rated at 1115 kPag ie it will open at or above that pressure Over long periods of time after catalyst replacement the pressure of mediumpressure steam leaving R801 is 1110 kPag During hot weather the volume of off gas leaving the absorber increases by 1 However the increase in formaldehyde is about 22 and the increase in water is about 3 Pump P803 NB constantly makes noise and each individual pump has been replaced within the last year Other Information Other pertinent information is appended including a memo from catalyst RampD an equipment list and utility and equipment costs Assignment Your assignment is to provide recommendations as to the causes of the periodic acid formation problem and ways to remedy the situation You should also recommend any other changes that you feel should be made to improve performance in Unit 800 Since our plant is due for annual shutdown in a few months we want specific recommendations as to what should be done at that time and the cost of these alterations and or modifications Specifically you are to prepare the following by 900 am Monday November 6 2006 1 a written report detailing your diagnosis recommended actions and costs associated with xing Unit 800 This should include a a diagnosis of all problems observed in Unit 800 b a methodology for maintaining the temperature entering the tank and in the tank between 35 C and 45 C all year c an incremental economic evaluation beforetax EAOC at an interest rate of 15 10 year lifetime of the required changes required d suggestions for any additional longterm modifications to the process that would provide a beforetax incremental DCFROR of 15 5 year lifetime e a PFD that illustrates anyall modifications recommended for the process 2 a list of new equipment to be purchased including size cost and materials of construction Deliverables Speci cally you are to prepare the following by 900 am Monday November 6 2006 1 Prepare a written report conforming to the guidelines detailing the information in items 1 2 and 3 above 2 Include a legible organized set of calculations justifying your recommendations including any assumptions made 3 Attach a signed copy of the attached confidentiality statement Report Format This report should be brief and should conform to the guidelines It should be bound in a folder that is not oversized relative to the number of pages in the report Figures and tables should be included as appropriate An appendix should be attached that includes items such as the requested calculations These calculations should be easy to follow The confidentiality statement should be the very last page of the report The written report is a very important part of the assignment Reports that do not conform to the guidelines will receive severe deductions and will have to be rewritten to receive credit Poorly written andor organized written reports may also require rewriting Be sure to follow the format outlined in the guidelines for written reports Oral Presentation You will be expected to present and defend your results some time between November 6 2006 and November 9 2006 Your presentation should be 1520 minutes followed by about a 30minute question and answer period Make certain that you prepare for this presentation since it is an important part of your assignment You should bring at least one hard copy of your slides to the presentation and hand it out before beginning the presentation Other Rules You may not discuss this major with anyone other than the instructors Discussion collaboration or any other interaction with anyone other than the instructors is prohibited Violators will be subject to the penalties and procedures outlined in the University Procedures for Handling Academic Dishonesty Cases begins on p 47 of 200507 Undergraduate Catalog Consulting is available from the instructors Chemcad consulting ie questions on how to use Chemcad not how to interpret results is unlimited and free but only from the instructors Each individual may receive ve free minutes of consulting from the instructors After ve minutes of consulting the rate is 25 points deducted for 15 minutes or any fraction of 15 minutes on a cumulative basis The initial 15minute period includes the 5 minutes of free consulting Late Reports Late reports are unacceptable The following severe penalties will apply 0 late report on due date before noon one letter grade 10 points 0 late report after noon on due date two letter grades 20 points 0 late report one day late three letter grades 30 points 0 each additional day late 10 additional points per day Appendix 1 Chemcad Hints Solutions of formaldehyde and water are very nonideal Individually the volatilities are from most volatile to least volatile formaldehyde methanol water However formaldehyde associates with water so that when this threecomponent mixture is distilled methanol is the light key and water is the heavy key The formaldehyde will follow the water The ESDK K value package in Chemcad simulates this appropriately Latent heat should be used for enthalpy calculations The expert system will recommend these choices When simulating an entire process we recommend using the shortcut distillation column within the process for the methanolwaterformaldehyde distillation SCDS should then be used as a separate item to simulate the column based on the results obtained from the shortcut column However due to the nonideality of the thermodynamics the actual column simulation using SCDS will probably require many more stages than predicted by the shortcut simulation possibly twice the number Calculations and Other Pertinent Information E 801 Q 4111 MJh process uid in shell mps condensing h 6000 WmzK desubcooling zone ATM 11655 C 0 500 WmzK U 1h 1h0391 4615 WmzK A 212 m2 boiling zone AT 1m 912 C ho 6000 WmzK U 1h 1h0391 3000 WmzK A 417 m2 superheating zone ATM 6068 C ho 50 WmzK U 1h 1h0391 496 WmzK A 3794 m2 AW 405 m2 Q n39M n4 19925 kJkg lps ow in Table 2 E 802 Q 7675 MJh ATM 6211 C process uid h 75 WmzK hps condensing ho 7500 WmzK U 1h 1h0391 7426 WmzK A 462 m2 mm QA Q1694 ldkg hps ow in Table 2 Appendix 2 187 150 958 4079 254 V T200 183 E 803 200 Q 98323 MJh ATM 10887 C T 40 100 cw h 1000 WmzK process stream ho 100 WmzK U 1h 1h0391 909 WmzK F 098 A 2816 m2 Q mm QCPAT Q41841dkgK10K cw ow in Table 2 30 E 804 Q 37755 MJh AT 1m 804 C n mps condensing h 7000 WmzK T 187 boiling process stream ho 7000 WmzK 106 6 U 1h 1h0391 3500 WmzK 39 A 373 m2 mm QA Q19901dkg mps ow in Table 2 Q E 805 Q 32456 MJh ATM 4024 C cw h 1200 WmzK condensing organic process stream ho 2500 WmzK T 40 U 101 1h0391 8333 WmzK A 269 m2 mm QCPAT Q41841dkgK10K 3 cw ow in Table 2 Q 755 E 806 Q 11697 MJh ATlm 238 C 1067 cw h 1000 WmzK T process stream ho 500 WmzK 40 U 1h 1h0391 3333 WmzK 35 A 41 m2 30 mm QCPAT Q41841dkgK10K cw ow in Table 2 Q R 801 heat exchanger Q 8928 MJh 923 adiabatic reaction temperature is 923 C ATlm 1791 C based on 187 C seen by process uid bfw to mps ho 7000 WmzK T 200 process stream h 100 WmzK 187 U 1h 1h0391 986 WmzK 90 A 14044 m2 mm QCPAT Q199241841dkgK187 90K mps ow in Table 2 T 801 use packed bed from Chemcad L 3000 kgh G 5750 kgh pL 925 kgm3 pG 115 kgm3 LGpgpL0395 0018 2 in ceramic Berl Saddles packing factor is 45 packing pressure drop is 1 kPam from ooding P Wankat Equilibrium Staged Separations Prentice Hall 1988 p 421 parameter at ooding 02 parameter at 75 ooding 01125 G 05551bft2s A 5750 kg3600 s0555 lbftzs22 lbkg 632 ft2 D 284 ft 086 m T 802 from Chemcad 22 ideal trays plus partial reboiler and partial condenser 716 overall column efficiency O Connell correlation 3 22 trays column is 19 m high with 18 in 06096 m tray spacing AP pghN 20000 Pa 725 kgm398 ms2hwer31 hm 0091 m m 36 in above feed L 21000 kgh G 21000 kgh p 750 kgm3 pG 1 kgm3 LGpgpL0395 000365 from ooding graph for 18 in tray spacing P Wankat Equilibrium Staged Separations Prentice Hall 1988 p 387 C5 029 u 793 fts um 181 ms 75 of ooding if 75 active area A G3600075pguact 429 m2 D 234 m below feed L 27000 kgh G 23000 kgh p 690 kgm3 pG 1 kgm3 LGpgpL0395 00447 from ooding graph for 18 in tray spacing P Wankat Equilibrium Staged Separations Prentice Hall 1988 p 387 C55 028 u 735 fts um 168 ms 75 of ooding if 75 active area A G3600075pguact 507 m2 D 254 m go with 25 m diameter no information available for P801 NB P802 NB C801 V801 prices methanol 029lb formalin 040lb


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