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A P P E N D I X

CDesign Projects

In this appendix, six design projects are presented. The projects are grouped in pairs, witheach pair of projects focused on a given process. The first project in each pair (Projects 1,3, and 5) deals with an existing facility in which a problem has arisen or in which achange of operating conditions is desired. These types of problems are typically encoun-tered in real operating plants and would be the type of project a young engineer mightencounter in his or her first year or two in the plant. These problems often are not com-pletely defined, and not all information is available. In addition, a solution to the problemis required in a fairly short period of time. This situation is not unheard of in the work-place and forces the engineer to make assumptions and analyze situations in which notall the operating variables are known. In analyzing these problems, the information inSection 4, Chapters 19–24, will be very useful. It is not recommended that these problemsbe given to students without some coverage of the material given in Section 4 of the text.

The second project in each pair (Projects 2, 4, and 6) is more like the typical “design”project that is covered in the senior capstone design course. Here, the student (or group ofstudents) should be familiar with the information given in Sections 1, 2, and 3 and theguidelines for written reports given in Chapter 29 (in this CD).

In the authors’ collective experience, the most worthwhile learning experience forthe student is obtained during an oral presentation in which the student (or group of stu-dents) presents the results to a group of faculty and then defends his or her solutions in a30–40-minute question-and-answer period. If this method of examination is chosen, theinformation in Chapter 29 (in this CD) on oral presentations will also be of use.

A note is made to any experienced engineer who may come upon these projects. It isrecognized that some of the information given in the flow diagrams reflects poor (andsometimes extremely poor) engineering judgment. In fact, parts of some of the flow dia-grams are almost caricatures of how the plant should be designed and operated. This isdone intentionally, with the hope that the student will be able to find these gross errorsand recommend improvements. The bottom line is that if, by doing these projects, thestudent can find errors and make improvements, then the transition from student to

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practicing engineer will have started, and we will have fulfilled our objective in writingthis text.

Additional design projects for a variety of processes, suitable for sophomorethrough senior classes, can be found at our Web site: http://www2.cemr.wvu.edu/~wwwche/publications/projects/index.html.

Finally, background information for this appendix was obtained from the followingsources:

1. Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed. (New York: John Wiley andSons, 1978).

2. McKetta, J. J., and W. A. Cunningham, eds., Encyclopedia of Chemical Processing andDesign (New York: Marcel Dekker, 1976).

3. Rase, H. F., Chemical Reactor Design for Process Plants, Vol. 2 (New York: John Wileyand Sons, 1977).

176 Appendix C Design Projects

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P R O J E C T

1Increasing the Production

of 3-Chloro-1-Propene (Allyl Chloride)

in Unit 600

C.1.1 BACKGROUND

You are currently employed by the TBWS Corp. at the Beaumont, Texas, plant, and youhave been assigned to the allyl chloride facility. A serious situation has developed at theplant, and you have been assigned to assist with troubleshooting the problems that havearisen.

Recently, our sister plant in Alabama was shut down by the EPA (EnvironmentalProtection Agency) for violations concerning sulfur dioxide emissions from a furnace inthe allyl chloride facility. Fortunately, the Beaumont facility had switched to natural gasas a fuel for its process in early 2000 and hence is currently in compliance with the EPAand Texas regulations. However, the loss of the Alabama plant, albeit for a short timeonly, has put considerable pressure on the Beaumont plant to fulfill contractual obliga-tions to our customers in Alabama for allyl chloride. Thus, part of your assignment is toadvise management concerning the increase in production of allyl chloride that can bemade at the Beaumont facility.

Another related issue that has been discussed by management is the long-term prof-itability of both allyl chloride facilities. Allyl chloride is used as a precursor in the produc-tion of allyl alcohol, glycerin, and a variety of other products used in the pharmaceuticalindustry. More efficient plants have been built recently by our competitors, and we arebeing squeezed slowly out of the market by these rival companies. We still maintain aloyal customer base due to our excellent technical and customer service departments andour aggressive sales staff. However, we have been losing an ever-increasing share of themarket since the mid-2000s. At present, the future looks bleak, and if the profitability andefficiency of our facilities do not increase in the near future, we may well be shut down inthe next year or two, when some of our long-term contracts come up for renewal. A sec-ond part of your assignment is to look into the overall profitability of the Beaumont allylchloride facility and determine whether any significant improvements in the overalleconomics can be made.

177


C.1.2 PROCESS DESCRIPTION OF THE BEAUMONT ALLYL CHLORIDE FACILITY

A process flow diagram (PFD) of the allyl chloride facility is provided in Figure C.1. Thisprocess (Unit 600) is the one to which you have been assigned.

Allyl chloride is produced by the thermal chlorination of propylene at elevated tem-peratures and relatively low pressures. Along with the main reaction, several side reac-tions also take place. These are shown below.

Main ReactionC3H6 + Cl2 → C3H5Cl + HCl ΔHreac,298K = −112 kJ/mol

allyl chloride

Side ReactionC3H6 + Cl2 → C3H5Cl + HCl ΔHreac,298K = −121 kJ/mol

2-chloropropene

Side ReactionC3H6 + 2Cl2 → C3H4Cl2 + 2HCl ΔHreac,298K = −222 kJ/mol

dichloropropene

Side ReactionC3H6 + 3Cl2 → 3C + 6HCl ΔHreac,298K = −306 kJ/mol

carbon


Propylene

1

poc

Air NG

FIC

E-601

cw

FIC

cw

LIC

2

Chlorine

TIC

3

4

5

H-601

R-601

P-601 A/B

E-602 E-603

3.58

5453.24

5113.04

2002.43

bfw

lps

H-601 R-601 J-601 E-601 P-601 A/B E-602 E-603Reactor Feed Fluidized-Bed Jet Mixer Dowtherm Dowtherm Waste-Heat CrudeAllyl

Heater Reactor Cooler Pumps Boiler Chloride Cooler

Crude AllylChloride

5112.77

502.09

Vent to Atmosphere

poc

AirTemperature, CPressure, bar

o

Figure C.1 Process Flow Diagram for the Production of Allyl Chloride (Reaction Section)


The propylene feed is heated in a furnace, fired by natural gas, and brought up to reactiontemperature (design conditions are given in Tables C.1 and C.2). The chlorine is mixed withthe hot propylene in a mixing nozzle and then fed to the reactor.

During the thermal chlorination process, a significant amount of carbon can be pro-duced, and it has a tendency to deposit on equipment that operates at temperaturesgreater than 400°C. For this reason, the reactor chosen for this process is a fluidized bedwith an inert solid, sand, on the reaction side. The sand provides a large surface area onwhich the carbon can deposit. It also acts as a scouring agent on the immersed heat trans-fer tubes in the reactor and prevents the buildup of carbon on the heat transfer surfaces.The carbon, which deposits preferentially on the sand, is removed by combustion in thesolids regeneration unit shown in Figure C.1. The regenerated sand is sent back to the

Appendix C Design Projects 179

Stream Number 1 2 3 4 5

Temperature (°C) 25 25 511 400 50

Pressure (bar) 11.7 6.44 2.77 11.34 2.09

Vapor fraction 1.0 1.0 1.0 0.0 1.0

Mass flowrate (tonne/h) 3.19 1.40 4.59 16.63 4.59

Molar flowrate (kmol/h)Propylene 75.89 — 58.08 — 58.08

Chlorine — 19.70 — — —

Allyl chloride — — 15.56 — 15.56

Dichloropropene — — 0.46 — 0.46

Dichloropropene — — 1.81 — 1.81

Hydrogen chloride — — 19.70 — 19.70

Carbon — — * — —

Dowtherm A — — — 4.62 kg/s —

Total mole flow (kmol/h) 75.89 19.70 95.61 4.62 kg/s 95.61

Equipment Fuel gas Cooling water bfw Steam(std m3/h) (kg/s) (kg/s) (kg/s)

H-601 131† — — —

E-601 — 14.5Tin = 30°C — —Tout = 40°C

E-602 — — 0.333 0.333(90°C) (sat. at 6 bar)

E-603 6.82— Tin = 30°C — —

Tout = 40°C

*Carbon is formed, but at a rate that does not affect the material balance.†Actual gas flowrate shown; heater efficiency is 90%.

Table C.1 Flow Summary Table for Unit 600: Crude Allyl Chloride Production Facility



J-601 Jet Mixer

Pressure Drop = 0.20 bar at design conditionsOperating Pressure = 3.24 bar (normal)

= 5.00 bar (maximum)

H-601 Reactor Feed Preheater

Process Side Conditions

Duty = 4000 MJ/h (normal)5400 MJ/h (maximum)

Operating Pressure = 3.58 bar (normal)= 4.50 bar (maxi-

mum)Operating Temperature = 545°C (maximum)

R-601 Fluidized-Bed Reactor

Operating Temperature = 511°C (normal)= 525°C (maximum)

Operating Pressure = 3.04 bar (normal)= 4.50 bar (maximum)

Dimensions

Square cross section 3.1 × 3.1 m, vessel height = 5 m

Fluidized-bed height = 1.5 mHeat transfer area = 23.0 m2

Normal duty = 2188 MJ/h

P-601 A/B Dowtherm A Circulation Pumps


mum)Operating Temperature = 350°C (normal)

= 400°C (maximum)ΔP (normal) = 1.55 bar (22.6 psi)ΔP (maximum) = 2.06 bar (30 psi)Power (motor) = 2.5 kWFlowrate = 0.0068 m3/s (normal)

E-601 Dowtherm A Cooler


mum)Operating Temperature = 400°C (maximum)Duty = 2188 MJ/h

Heat Transfer Area = 2.6 m2

Double-pipe heat exchanger with Dowthermin inner tube

E-602 Waste-Heat Boiler

Tube Side


Shell Side


Duty = 2850 MJ/h


E-603 Crude Allyl Chloride Cooler

Tube Side


Shell Side


Duty = 1025 MJ/h


Table C.2 Equipment Design Parameters (Unit 600)

reactor, thus maintaining a constant inventory of solids in the reactor. The heat producedin the reactor, by the exothermic chlorination reactions, is removed via the heat transfertubes through which is circulated a heat transfer medium. The heat transfer fluid is acommercially available coolant called Dowtherm A. Physical properties of this fluid areincluded in Table C.3 of this assignment.

The gases leaving the reactor contain unreacted propylene along with the reac-tion products, as given in the flow table in Table C.1. These hot gases are cooled ina waste-heat boiler and a trim cooler prior to being sent for further processing, inc-luding the refining of the allyl chloride and the separation and recycle of unusedpropylene.



C.1.3 SPECIFIC OBJECTIVES OF ASSIGNMENT

Your immediate supervisor, Ms. Jane Garcia, has taken you around the allyl chlo-ride facility and told you some of the details of the plant operation. These are sum-marized in Section C.1.4, Additional Background Information. She has confirmedthat the plant is currently operating at close to the design conditions given in Table C.1and that utility consumption is within a few percent of that shown in Table C.1. Inaddition, she also provided you with a set of battery limit conditions, Table C.4, forthe utilities, feeds, and products, which she has informed you are current and accurate.

Your assignment is to provide a written report to Ms. Garcia by two weeks fromnow. This report, at a minimum, should contain the following items:

1. A cover letter to your supervisor2. An executive summary covering the following major points:

• Findings on how much the throughput of Unit 600 can be increased in the shortterm (without the purchase of new equipment).

• Findings of any potential improvements that will increase the profitability of Unit600. You should provide an estimate of the impact of these changes (assume aninternal discount rate for such improvements to be 15% p.a. before tax, and all im-provements should be calculated using a five-year project life).

• The impact that the proposed changes in operations might have on the environ-ment and the health and safety of the plant personnel.

• Recommendations for immediate changes in plant operations and an estimatedtime schedule in which these changes might be implemented.

3. A list of assumptions made in carrying out your study4. An appendix giving details of all important calculations made in your study

The written report should follow the guidelines outlined in Chapter 29 (in this CD).

Properties of Dowtherm A:

Temperature Use Range Liquid 16°C – 400°C Gas 257°C – 400°C

Above 400°C Dowtherm A starts to decompose thermally.

Liquid Properties for 350°C–400°C

Thermal Conductivity 0.0943 W/m.K

Specific Heat Capacity 2630 J/kg K

Viscosity 1.4 × 10−4 kg/m s

Density 680 kg/m3

Vapor Pressure (400°C) 10.5 bar

Prandtl No. (Cpμ/k) 3.9

Table C.3 Properties of Dowtherm A: Heat Transfer Fluid



Conditions at which feed and utility streams are available and at which products and utilitystreams must be returned to the boundary of the process are known as the battery limit condi-tions. For Unit 600 the battery limit conditions that exist are listed below. The limiting condi-tions are given at the equipment and take into account the pressure loss in the associated supplyand return piping.

Utility Condition at Equipment

Cooling water 5 bar, 30°C

Cooling water return 4 bar, <45°C

Boiler feed water 6 bar, 90°C

High-pressure steam* 41 bar, saturated

Medium-pressure steam* 11 bar, saturated

Low-pressure steam* 6 bar, saturated

Natural gas 4 bar, 25°C

Feeds and Products Condition at Process Boundary

Propylene 25°C, saturated vapor

Chlorine 25°C, saturated vapor

Crude allyl chloride 50°C, >2.09 bar (Stream 5)

*Steam pressure at sources, such as waste-heat boilers, may exceed these values in order to overcomepressure losses in header piping.

Table C.4 Battery Limit Conditions for Feeds, Products, and Utilities (Unit 600)

C.1.4 ADDITIONAL BACKGROUND INFORMATION

A process flow diagram is provided in Figure C.1, and flow summary and equipmentsummary tables are given in Tables C.1 and C.2. This information is for the reaction sec-tion of Unit 600 only. The separation section is being studied by another group, and youshould not consider any changes for this section at this time. The separations section isshown in Figure C.3 and will be considered in Project 2. The data given in the tables andon the PFD reflect the current operating conditions and have been checked recently byyour operations department. Some additional information regarding the allyl chloride fa-cility has been provided by Ms. Garcia and is summarized below.

1. The temperature in the reactor should not exceed 525°C, because above this temper-ature, there is excessive coke production leading to operating problems in thedownstream units. It is further recommended that the reactor temperature be main-tained at close to 511°C during any changes in process operations.

2. All process exchangers using cooling water are designed to have a 5 psi (0.34 bar)pressure drop on the cooling water side for the design flow rate of cooling water.The velocity of cooling water at design conditions was set at 2 m/s, and long-termoperation at velocities above 3.5 m/s is not recommended due to increased erosion.

3. For the fluidized-bed reactor, you may assume that the pressure drop across the bedof sand remains essentially constant regardless of the flowrate.


4. The cyclone and regenerator were designed by the vendor of the equipment to beconsiderably oversized and are capable of handling any additional loads that mightbe required during this temporary change in operations.

5. The heat transfer coefficient between the fluidized bed and the immersed heat trans-fer coils (the outside coefficient) is known not to vary much with fluidizing gasflowrate and may be assumed constant regardless of gas throughput. The heat ex-changer in the fluidized bed may be reconfigured so that the three rows of tubes arepiped in parallel.

6. Flow of all process and utility streams may be considered to be fully developed tur-bulent flow. Thus the pressure drop through the equipment will be proportional tothe square of the velocity.

7. The conversion of propylene and chlorine in the fluidized bed will be virtually unaf-fected by changes in gas throughput. This is due to the long gas residence time inthe reactor. In fact, the reactor’s main purpose is to provide a large surface area forcoke deposition and to provide good heat transfer. In addition, small changes in op-erating pressure of the reactor will not affect the selectivity of the reaction.

8. The crude allyl chloride (Stream 5 in Figure C.1) must be delivered to the separa-tions section at a minimum pressure of 2.9 bar, and a maximum temperature of50°C.

9. A manufacturer’s pump curve for the circulating Dowtherm A pumps is providedfor your use and is given in Figure C.2 of this assignment.


Flow of Dowtherm A (gpm at 350°C)

0 20 40 60 80 100 120 140

Pre

ssur

e R

ise

acro

ss P

ump

(psi

)

0

5

10

15

20

25

30

35

P-601 A/B

Figure C.2 Pump Curve for P-601 A/B, Dowtherm A Circulation Pumps


10. A set of original design calculations outlining the design of the units is provided foryour information. Some units were built slightly differently from these designs.

11. The level of bfw in E-602 is set so that all of the heat transfer tubes are covered.

You have also taken a tour of the plant recently, and in addition to confirming some of thepoints above with the operators, you make the following observations:

1. The Dowtherm A recirculation pump (P-601 A) is making a high-pitched whiningnoise.

2. Steam is leaking from the safety relief valve placed on top of E-602.3. Some of the insulation on the pipe leading from the reactor R-601 to E-602 has come

loose and is hanging from the pipe.

C.1.5 PROCESS DESIGN CALCULATIONS

Fluidized-Bed Reactor, R-601

Heat generated in reactor = QR = 2188 MJ/hBed solids are 150 μm sand particles with density (ρs) of 2650 kg/m3

At conditions in the reactor, the process gas has the following properties:

�g = 2.15 kg/m3 and �g = 2.25 × 10−5 kg/m s

Using the correlation of Wen and Yu [1],

Rep,mf = [1135.7 − 0.0408 Ar]0.5 − 33.7

Therefore, Rep,mf = [1135.7 + 0.0408 × 372]0.5 − 33.7 = 0.2246

Total volumetric flow of gas at inlet conditions to the bed = Vgas = 0.5674 m3/s.Good heat transfer is needed, so the bed will be operated at 5 times umf, which puts it

into the bubbling bed regime. Free bed area (without heat transfer tubes ) = Vgas / 5umf = 0.5674/(510.0157) = 7.2 m2

Looking at the heat transfer area for the fluidized bed:

Heat transfer area required in bed = A0 Overall heat transfer coefficient = U0

Assume that the fluidized solids are well mixed and isothermal, and assume thatthe cooling medium enters the bed at 350°C and leaves at 400°C, which is the maximumoperating temperature for Dowtherm A.

�Tlm �(160 − 110)ln (160�110)

� 133.4°C

Rep,mf �umf dp�g

�g � umf �

(0.2246) (2.25 � 10−5)(2.15) (150 � 10−6)

� 0.0157 m�s

where Ar �d3

p(�s − �g)�gg�2

g�

(150 � 10−6)3 (9.81)(2650 − 2.15)(2.15)(2.25 � 10−5)2 � 372



Inside film heat transfer coefficient, hi, is calculated from the Seider-Tate equation:

Nu = 0.023 Re0.8 Pr 0.33 (�/�w)0.14

Assuming a velocity of 1.5 m/s inside a 3-in schedule-40 pipe (ID = 0.0779 m is assumed,OD = 0.0889 m), then

Outside film heat transfer coefficient ho = 267 W/m2K (from previous plant operatingdata), and fouling coefficient on inside = 2500 W/m2K.

do / di = 0.0889/0.0779 = 1.14

Ignoring the wall resistance, the overall transfer coefficient Uo is obtained from

Now assuming that the tubes are 10 ft long and 3 in in diameter (schedule-40), the heattransfer area per tube is

∴ number of tubes required NT = 22.2/0.8513 = 27 tubes.Using 3 layers of 9 tubes piped in series and placed in horizontal rows in the bed,

each row occupies the following csa of bed:

(9) (do) (L) = (9) (0.0889) (3.048) = 2.4 m2

∴ total csa for bed = 2.4 + 7.2 = 9.6 m2

Use a square bed with side dimensions = (9.6)0.5 = 3.1 m (10.2 ft).

�doL � (3.142) (0.0889) (10) (0.3048) � 0.8513 m2

A0 �QR

Uo�Tlm�

2188 � 106

(3600)(206)(133)� 22.2 m2

Uo �1

1267

�1.142500

�1.141750

� 206 W�m2K

hi � (1445) (0.0943)�(0.0779) � 1750 W�m2K

Nu � hid�k � 0.023 (567 � 103)0.8 (3.9)0.33 � 1445

Re � (0.0779) (1.5) (680)�(1.4 � 10−4) � 567 � 103


400°C

Q

350°C

T

510°CFluidized-Bed Solids

Dowtherm A


Check Velocity in Tubes

csa for flow of Dowtherm A in tubes = π di2/4 = (3.142)(0.0779)2/4 = 4.766 × 10−3 m2

flow of Dowtherm A = 6.797 × 10−3 m3/s∴ velocity of Dowtherm A in tubes = 6.797 × 10−3/4.766 × 10−3 = 1.43 m/s ⇒ assumption

is OK

Pressure Drop in Tubes

Re = 5.41 × 105 ∴ friction factor f = 0.0045 (with e/d = 0.0006)ΔP = 2fLeqρu2/d = (2) (0.0045) (680) (1.43)2 Leq/(0.0779) = 161 LeqNow Leq = equivalent length of pipe in three rows of heat transfer pipes in fluidized bed

= (27) (3.048) (1.5) = 123 m (take this as 1.5 times length of pipe to account for fit-tings)

∴ ΔP = (162) (123) = 0.20 bar

Set bed height (height of sand above distributor plate) = 1.5 m.This gives a gas residence time in the bed of (7.2) (1.5) (0.45)/0.5674 = 8.6 s. This

should be plenty of time because complete reaction should take only about 2–3 s.

ΔPbed = hbed ρsand (1 − ε)g = (1.5) (2650) (1 − 0.45) (9.81) = 0.214 bar

Assume 0.04 bar for distributor loss and 0.064 bar for cyclones to give the overall equip-ment pressure drop:

ΔPreactor = 0.214 + 0.04 + 0.016 = 0.27 bar

Design of fluidized bed is given in sketch below:

Side view of bed showing 3 rows of 9 tubes:


Overhead view of bed showing piping arrangement for one row; each row is piped inseries with the row below.


For exchanger E-601, ΔTlm = (360 − 320)/ ln (360/320) = 340°C and U = 850 W/m2 K(approximately equal resistances on both sides and small fouling resistances). Heat trans-fer area A is given by

Use a double-pipe heat exchanger because area is small. Considering the Dowtherm Acirculation loop shown in the following figure, the following information is given:

Cooling water flowrate = 2188 × 106/(3600) (4180) (10) = 14.5 kg/s Dowtherm flowrate = 2188 × 106/(3600) (2630) (50) = 4.62 kg/s Pressure drop across the exchanger = 0.34 bar for Dowtherm and cooling waterVelocity of cooling water through exchanger set at 2 m/s

A � 2188 � 106�(3600) (340) (850) � 2.1 m2


From R-601(400°C)

E-601 cw (30°C)

cwr (40°C)

FIC

To R-601(350°C)

P-601 A/B

Dowtherm A Cooling Loop

For pumps P-601 A/B, assume

0.34 bar (5 psi) pressure drop across exchanger on Dowtherm side 0.14 bar (2 psi) pressure drop for piping 0.85 bar (12.4 psi) pressure drop across the control valve 0.20 bar (2.9 psi) pressure drop across the reactor exchangerTotal loop pressure drop = 1.53 bar = 22.3 psiFlow of Dowtherm = 4.62/680 = 6.797 × 10−3 m3/s = 108 gpmPower required for pumping liquid = v̇ ΔP = (6.797 × 10−3) (1.53 × 105) = 1.04 kWAssuming an efficiency of 45%, the shaft power = 1.04/0.45 = 2.31 kW. Use a 2.5 kW pump plus a spare.

Considering the waste heat boiler, E-602, shown in the figure on the following page:

Zone I U = 90 W/m2 K (all resistance on gas side)Zone II U = 90 W/m2 K (all resistance on gas side)


Heat released as gas cools from 511°C to 200°C is 2850 MJ/h = 792 kW

ΔHbfw-steam = 2380 kJ/kg

Steam flowrate = 792/2380 = 0.333 kg/s (hL = 376.9, hL,sat= 675.5, hV,sat = 2756.9 kJ/kg)

For Zone I

For Zone II

Total Area A = AI + AII = 11.8 + 42.2 = 54 m2

Q � m Cp,gas�T � (4590) (1490) (200 − 50)�3600 � 0.285 MW

Cp,gas � 1490 J�kg.K

AIIQII�UII�Tlm � 693 � 103�(90)(182.4) � 42.2 m2

�Tlm �(239 − 160) − (511 − 160)

ln (239 − 160)(511 − 160)

� 182.4°C

AIQI�UI�TlmF � 99 � 103�(90)(93.6)(1.0) � 11.8 m2

�Tlm �(239 − 160) − (200 − 90)

ln (239 − 160)(200 − 90)

� 93.6°C

(TI − 200)�(510 − 200) � 99�792 ⇒ TI � 238.8°C

Q160°C, LiqVap � (0.333) (2756.9 − 675.5) � 693 kW

Q90160°C,Liq � (0.333) (675.5 − 376.9) � 99 kW


T

200°C

90°CQ

160°C

511°C

bfw (90°C)

To E-603(200°C)

From R-601(511°C)

6 bar steam (160°C)

Waste-Heat Boiler E-602

T


From the figure above, the following information is calculated:

C.1.6 REFERENCE

1. Wen, C. Y., and Y. H. Yu, “A Generalized Method for Predicting Minimum Fluidiza-tion Velocity,” AIChE J. 12, no. 610 (1966).

A � Q�U�TlmF � (0.285 � 106)�(90) (67.3) (0.95) � 49.5 m2

U � 90 W�m2 K

�Tlm � (160 − 20)�ln(160�20) � 67.3°C

mcw � (0.285 � 106)�(4180) (10) � 6.82 kg�s


Crude Allyl Chloride Cooler, E-603

From E-602 (200°C)

cw (300°C)

50°C

cwr (40°C)

200°C

T

40°C 50°C30°C

Q


P R O J E C T

2Design and Optimization of a New 20,000-Metric-

Tons-per-Year Facility to Produce Allyl Chloride

at La Nueva Cantina, Mexico

C.2.1 BACKGROUND

Recent developments at the Alabama plant have brought into question the stability of ourallyl chloride production capacity. It has been noted that the North American market forallyl chloride consumption will probably grow extensively in the next decade and thatadditional production capacity may be needed. In order to maintain our current marketshare and to remain competitive in this market, it may become necessary to build a newallyl chloride facility.

With this in mind, a new (grassroots) production facility to produce commercial-grade allyl chloride is being investigated. This facility would most likely be situated in LaNueva Cantina, Mexico, close to our petrochemical facility, which would be able to sup-ply propylene. The supply of chlorine from local manufacturers will also be plentiful.Your group has been given the task of doing a process estimate for this new facility.

C.2.2 ASSIGNMENT

Your assignment is to design and optimize a new grassroots 20,000 metric tons per yearallyl chloride facility. This facility will produce commercial-grade allyl chloride from thesynthesis reaction between propylene and chlorine. The front-end process is to use flu-idized-bed technology similar to that currently in use in Unit 600 at Beaumont, Texas (seeProject 1). This assignment concerns the design of a new plant, and, except for the flu-idized-bed reactor unit, the plant may be reconfigured in any way that you feel is appro-priate. For the fluidized-bed reactor, kinetic equations are not available, and therefore yourdesign should be similar to that of the Beaumont unit. With this in mind, the reactor tem-perature should be close to 511°C, and the ratio of propylene to chlorine into the reactorshould remain the same. Although the selectivity of the reaction will change with changes

190


in reactor pressure, you may assume for this preliminary design that the selectivity is unaf-fected by changes in pressure. Your final design should be the one that maximizes the netpresent value (NPV) of the project under the following economic constraints:

After-tax internal hurdle rate = 10%Depreciation = MACRS (6-year schedule; see Chapter 9)Taxation rate = 15%Labor costs to be based on U.S. equivalent wage rateConstruction period = 2 yearsProject plant life = 15 years after start-up

Additional process information and some hints regarding problem-solving strategy are givenbelow. You should plan to submit your written report in four weeks. The guidelines for writ-ten and oral reports given in Chapter 29 (in this CD) should be followed for this assignment.

C.2.3 PROBLEM-SOLVING METHODOLOGY

The optimization of a process as large and complicated as this one is not a trivial matter.To help you in this endeavor the following hints are given. (You may use all or none ofthem as you see fit.)

1. When initially running case studies using a process simulator, you should use anyshortcut methods for simulating distillation columns that are available. Avoid therigorous methods for this type of preliminary work. You should use the rigorous(tray-to-tray) methods at the end of your work for the optimized case.

2. Establish a base case from the information provided. This should include operatingcosts and capital investments for the process shown in Figures C.1, C.3, and C.4,using the new production rate of 20,000 metric tons/year. You should make surethat you have included all the equipment and costs.

3. See where the major capital investment and major variable operating costs lie, and usethis information to focus on where your optimization should begin.

Note: This is a multivariable optimization, and within the time frame given forsolving this problem, you can afford to concentrate on only a few variables. Identifythe key decision variables to be manipulated—that is, the variables that have thegreatest impact on the NPV.

4. Do not let the computer turn your mind to mush! Think about how changes in oper-ating variables and other things will affect the economics, and try to predict thedirection in which the NPV will change as each variable changes. You should beable to rationalize, at least qualitatively, why a certain change in a variable causesthe observed change in the NPV.

C.2.4 PROCESS INFORMATION

To help you in this task the following information has been included with this assignment:

1. A flowsheet and a process description for the existing separations section of Unit600 are included in Figures C.3 and C.4 and Tables C.5 and C.6.




C-602A C-602 B

E-616 E-617

E-613

E-611

E-606

E-604

45

Propylene Makeup

V-6072423

45�46

Temperature, Co

0.45 19.8

460.45

�620.50

�620.50

−350.45

Pressure, bar

cw cw

�

Figure C.4 Propylene Refrigeration Loop for Allyl Chloride Process (Unit 600)

E-604

-501.63

FIC

9

LIC

LIC

8

lps

E-606

E-605

V-601P-603 A/B

P-602 A/B

1

11

21

13

12

V-602

T-601

T-603

E-607

6

11

10

C-601 A C-601 BE-608 E-609

7

14

lps

E-604 V-601 T-601 E-605 E-606 V-602 P-602A/B P-603A/B E-607 T-602 V-603A/B C-601A/B E-608 E-609 T-603Allyl Allyl HCl HCl HCl HCl HCl Bottom HCl Reflux HCl HCl HCl C3 Recycle 1st-Stage C3 Rcyl. C3Condsr Phase Tower Reboiler Condsr Reflux Pumps Pumps Vapzr Absr Trap Compressr Cooler Condsr

refr

refr

PIC

15

LIC

LIC

P-605 A/B

1

7

14

V-604

T-602

E-611

P-604 A/B

E-610

V-603 A/B

Deionized Water

Crude AllylChloride

refr

5

Sep.

lps

cw cw

Tower

Figure C.3 Separations Section of Allyl Chloride Production Facility (Unit 600)


2. Product specifications are included in Table C.7.3. Note that the current process (Unit 600) is very energy intensive, because very cold

temperatures and expensive refrigeration are used throughout the process. Remem-ber that the existing Beaumont plant was designed more than 40 years ago, whenelectricity and energy were relatively cheap. The optimal process configuration fortoday’s conditions may be significantly different from that of the existing facility!


FIC

18

LIC

LIC

17

E-612

P-607 A/B

P-606 A/B

1

30

50

V-605

16

FIC

21

LIC

LIC

20

E-614

P-608 A/B

1

16

30

V-60619

22

E-610 E-611 V-604 P-604A/B P-605A/B T-604 E-612 E-613 V-605 P-606A/B P-607A/B T-605 E-614 E-615 V-606 P-608A/BC3 C3 C3 C3 Bottm C3 Reflux Chl-P Chl-P Chl-P Chl-P Chl-P Botm Chl-P Allyl Allyl Allyl Allyl AllylCondsr Reblr Reflux Pumps Pumps Tower Reblr Condsr Reflux Pumps Pumps Tower Reblr Condsr Reflux Reflux

E-613refr

T-604

T-605E-615 cw

Drum Drum Drum Pumps

Propylene Recycle

Chloropropene By-Product

Allyl Chloride Product

Mixed Chlorides

31.5 wt% HCl

By-Product

TBWS Designs - Allyl Chloride ProcessDrawn by Date

Checked by Date

Approved by Date

Drawing No. Revision 0

Temperature, CPressure, bar

o

lpslps

Figure C.3 Separations Section of Allyl Chloride Production Facility (Unit 600) (Continued)

Turton_CDAppC.qxd 5/11/12 12:19 AM 3

Stre

am N

umbe

r5

67

89

1011

1213

14

Tem

pera

ture

(°C

)50

−50

−50

46−5

7−5

625

1010

45

Pres

sure

(bar

)2.

091.

501.

501.

501.

401.

53.

01.

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319

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or fr

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00.

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00.

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0.0

0.0

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s fl

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onne

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4.59

0.27

4.32

1.45

0.19

3.14

1.48

2.17

2.44

2.44

Mol

ar f

low

rate

(km

ol/h

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opyl

ene

58.0

82.

7255

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0.55

3.65

57.5

30.

00.

057

.53

58.0

8

Ally

l chl

orid

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0.01

15.5

515

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0.0

0.01

0.0

0.01

0.0

0.0

Dic

hlor

opro

pene

0.46

0.0

0.46

0.46

0.0

0.0

0.0

0.0

0.0

0.0

Dic

hlor

opro

pene

1.81

0.0

1.81

1.81

0.0

0.0

0.0

0.0

0.0

0.0

Hyd

roge

n ch

lori

de

19.7

04.

1915

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1.03

19.6

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0.58

0.0

Wat

er0.

00.

00.

00.

00.

00.

082

.00

81.8

80.

120.

0

Tot

al m

olar

flow

rate

(km

ol/

h)95

.61

6.92

88.6

918

.38

4.68

77.2

382

.00

101.

0058

.23

58.0

8

Tabl

e C.

5Fl

ow S

umm

ary

Tabl

e fo

r Al

lyl P

rodu

ctio

n Pr

oces

s, F

igur

es C

.3 a

nd C

.4

Stre

am N

umbe

r15

1617

1819

2021

2223

24

Tem

pera

ture

(°C

)−4

059

6030

3010

655

55−4

645

Pres

sure

(bar

)1.

52.

01.

51.

41.

41.

51.

41.

40.

4519

.9

Vap

or fr

acti

on0.

00.

00.

00.

00.

00.

00.

00.

01.

00.

0

Mas

s fl

owra

te (t

onne

/h)

0.03

1.42

1.39

1.52

0.04

0.21

0.47

1.18

25.3

125

.31

Mol

ar f

low

rate

(km

ol/h

)Pr

opyl

ene

0.81

0.0

0.0

0.0

0.0

0.0

0.0

0.0

602.

560

2.5

Ally

l chl

orid

e0.

015

.54

15.5

20.

840.

020.

086.

1315

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0.0

0.0

Dic

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0.0

0.46

0.01

18.9

90.

450.

00.

00.

010.

00.

0

Dic

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opro

pene

0.0

1.81

1.81

0.0

0.0

1.80

0.0

0.01

0.0

0.0

Hyd

roge

n ch

lori

de

0.01

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

Wat

er0.

00.

00.

00.

00.

00.

00.

00.

00.

00.

0

Tot

al m

olar

flow

rate

(km

ol/

h)0.

8217

.81

17.3

819

.83

0.47

1.88

6.13

15.4

660

2.5

602.

5

194



Refer to the process flow diagram for Unit 600, Allyl Chloride Purification Process, Beaumont,Texas (Figure C.3).

Crude allyl chloride, Stream 5, from the reaction section of Unit 600 (Figure C.1) enters theallyl product cooler, E-604, at 50°C and 2.1 bar. This stream is cooled to −50°C using the circu-lating liquid propylene refrigerant. The two-phase mixture leaving E-604 is fed to V-601, wherethe liquid stream is taken off and is fed to the HCl column, T-601. The HCl column removes es-sentially all the HCl and propylene from the cooled crude allyl chloride feed as overhead prod-uct at approximately −57°C. This stream is mixed with the vapor coming from V-601 and is fedto E-607, where it is heated with low-pressure steam.

The bottoms product from T-601 contains essentially all the chlorinated hydrocarbon deriv-atives and a small amount of propylene. This stream is fed to T-603, where the remaining propy-lene is removed as the overhead product at approximately −40°C. The bottoms product from T-603 is fed to column T-604, where 95 mol% chloropropene is removed overhead at approxi-mately 30°C. The bottom product from T-604 is fed to the allyl tower, T-605, where 99.9% bymole pure allyl chloride is removed as overhead product at 55°C and sent to storage. The bot-toms product from T-605 contains 95 mol% 1,2, dichloropropene, and this stream is sent to stor-age after being cooled in an offsite heat exchanger (not shown on Figure C.3).

The stream leaving E-607 is fed to T-602, where it mixes with water at 20°C. The flow ofwater is controlled to give an aqueous solution of hydrochloric acid with 31.5 wt% HCl. Thisconcentration of acid is equivalent to a liquid density of 20° Baumé. The use of degrees Baumé isthe common method by which hydrochloric acid is specified. The vapor stream leaving T-602contains all the propylene and small amounts of water and HCl. This stream is sent to one of apair of acid traps, V-603 A and B, where the water and HCl are removed (by adsorption onto ac-tivated carbon). The vapor stream leaving the absorbers is pure propylene. This propylenestream is sent to a two-stage compressor, C-601 A and B, with intercooler E-408 and condenserE-409. The stream leaving the condenser is a liquid at 45°C and is recycled to the propylene stor-age tank for Unit 600.

Four of the exchangers in Unit 600 (E-604, E-606, E-611, and E-613) require heat to be re-moved from the process stream at temperatures less than 35°C. In order to do this, a refrigera-tion system is required. In Unit 600, this is achieved by circulating a stream of cold (−62°C)propylene through these exchangers. The refrigeration loop is shown in the second PFD for Unit600, Figure C.4. The refrigeration is achieved by taking a high-pressure (20 bar) stream of liquidpropylene (45°C) and flashing it down to low pressure (0.5 bar). Cooled liquid and vapor propy-lene streams (−62°C) are sent to the four process exchangers, where they provide the necessarycooling. The warmed propylene vapor (−46°C) is recycled back to the refrigeration loop com-pressors C-602 A&B, the intercooler E-616, and the condenser E-617. A makeup propylenestream is provided to account for minor system leaks.

Table C.6 Process Description of Unit 600



Product Specifications

Product Required Purity Battery Limit Condition

Allyl chloride > 99.9% by mole Liq, T < 55°C, P >1.5 barallyl chloride

By-Product Required Purity Battery Limit Condition

Mixed chlorides > 95% by mole Liq, T < 50°C, P >1.2 bar1,2-dichloropropene

Chloropropene > 95% by mole Liq, T < 50°C, P >1.2 barchloropropene

31.5 wt% hydrochloric 31.5 wt% hydrochloric Liq, T < 45°C, P >1.2 baracid acid ± 0.1 wt %

By-product and Waste Stream Selling Prices/Costs

By-Product Selling Price

Mixed chlorides $0.10 /kg*

Chloropropene $0.15 /kg*

31.5 wt% hydrochloric acid From Chemical Marketing Reporter (20° Baumé)

Waste Stream Cost of Disposal

Waste acid stream $0.40 /kg of HCl + hydrocarbons (cost of regenerating carbon) collected on carbon

*These are credits that we will receive from our petrochemical complex for supplyingthese chemicals, which must meet the specifications given above. We may alternativelypay to dispose of these chemicals at a cost of $0.25/kg. For this case, no specifications needto be met (i.e., these streams are now waste streams rather than by-products).

Table C.7 Product Specifications and By-Product Costs (Unit 600)


P R O J E C T

3Scale-Down of PhthalicAnhydride Production

at TBWS Unit 700

C.3.1 BACKGROUND

You have recently joined the TBWS Chemical Corporation. One of TBWS’s major busi-nesses has always been production of phthalic anhydride from naphthalene. Phthalic anhy-dride production is integrated as part of a large chemical plant, in which naphthalene isproduced and in which phthalic anhydride is immediately used to make polyester resins. Inrecent years, there have been some problems. Some end users have complained about thequality of the resins produced and have taken their business to other companies that pro-duce phthalic anhydride from o-xylene. Therefore, our plant, which had been designed toproduce 100,000 metric tons/year of phthalic anhydride from naphthalene, was scaled backto about 80,000 metric tons/year several years ago. We are now forced to scale down pro-duction once again due to the loss of another large customer. Marketing informs us thatwe may lose additional customers. Research is working on development of catalysts forthe o-xylene reaction, but their results are not expected for up to a year. There is an imme-diate need to determine how to scale down operation of our plant to 50% of current capac-ity (40,000 metric tons/year). We would like to accomplish this without a shutdown,because one is not scheduled for a few months. If 50% scale-down cannot be achieved with-out a shutdown, we need to know how much scale-down is possible immediately. Specifi-cally, you are to determine the maximum possible scale-down, up to 50%, under currentoperating conditions, and you are to define these operating conditions. Furthermore, youare to determine how the plant can be scaled down to 50% of current capacity, what operat-ing conditions are required, and what capital expenditures, if any, are needed. Any sugges-tions for plant improvements that can be made during shutdown are encouraged. Youmust clearly define the consequences of any changes that you recommend for this processand the consequences of these changes for other processes that might be affected. It shouldbe noted that one possible scenario is to operate the plant at design capacity for six monthsof the year and shut down the plant for the remaining six months. Although this solutionmight work, we are reluctant to lay off our operators for half the year and also to purchaseadditional storage in order to store enough phthalic anhydride to supply our customers forthe six months that the plant is down. You should not consider this option any further.

197



For your first assignment, you are to address the issues described above for the por-tion of the process before the switch condensers (see Figure C.5).

C.3.2 PHTHALIC ANHYDRIDE PRODUCTION

Unit 700 now produces about 80,000 metric tons/y of phthalic anhydride. The feeds areessentially pure naphthalene and excess air. These are pressurized, heated and vaporized(naphthalene), and reacted in a fluidized bed with a vanadium oxide on silica gel catalyst.The reactions are as follows:

naphthalene phthalic anhydride

maleic anhydride

naphthoquinone

Additionally, the complete and incomplete combustion reactions of naphthalene alsooccur. The large exothermic heat of reaction is removed by molten salt circulated throughcoils in the reactor. The molten salt is used to produce high-pressure steam. Total conver-sion of naphthalene is very close to 100%. The reaction products proceed to a set of

C10H8 �32

O2 → C10H6O2 � H2O

C10H8 � 6O2 → 2C4H2O3 � 2H2O � 2CO2

C10H8 �92

O2 → C8H4O3 � 2H2O � 2CO2

Naphthalene

P-701A/B

H-701

P-701A/B C-701 H-701 E-701 R-701 E-702 P-702A/B E-703 P-703A/BNaphthalene Feed Air Air Naphthalene Fluidized- Molten Molten bfw bfw

Feed Pumps Compressor Preheater Furnace Bed Reactor Salt Cooler Salt Pumps Preheater Pumps

1

poc

air f.g.

2

4

3

5

C-701

R-701

E-701

Air

6

FIC

7 8 FIC

18

3501.91

3501.10

2651.50

hps

9 10

E-702

E-703

hps

bfw

P-702A/B

P-703A/B

Figure C.5 Process Flow Diagram for the Production of Phthalic Anhy-dride from Naphthalene (Unit 700)


devices known as switch condensers. These are described in detail later. Design and oper-ation of these devices are provided under contract by CONDENSEX. They guarantee usthat their condensers can operate at any capacity and provide the same separation as incurrent operation, as long as the pressure and the composition of the condensable portionof Stream 10 remain constant. The net result of the switch condensers is that essentially allof the light gases and water leave as vapor, with small amounts of maleic and phthalicanhydrides, and that the remaining anhydrides and naphthoquinone leave as liquid. Theliquid pressure is then reduced to vacuum for distillation. The first column removesmaleic anhydride impurity overhead, and the second column removes the phthalic anhy-dride product overhead.

Organic waste is burned for its fuel value. The dirty air, Stream 11, must be treated.The anhydrides are scrubbed using water, which is then sent to the on-site wastewatertreatment facility.

C.3.3 OTHER INFORMATION

Other pertinent information is appended, including pump and compressor curves, FigureC.6 and Figure C.7; a flow summary table, Table C.8; and an equipment list, Table C.9.


To Air Treatment

FIC

14

LIC

LIC

15

LIC

FIC

16

LIC

Phthalic Anhydiride

17

cw

cw

hps

hps

E-704

E-705

E-706

E-707

T-701

T-702

P-706 A/B

P-704 A/B

P-705 A/B

V-701

V-702

Switch Maleic Maleic Maleic Maleic Maleic Phthalic Phthalic Phthalic Phthalic Phthalic Phthalic

SC-701 T-701 E-704 V-701 E-705 P-704A/B T-702 E-706 V-702 P-705A/B E-707 P-706A/B

Condensers Column Condenser Reflux Reboiler Reflux Column Condenser Reflux Reflux Reboiler Feed

TBWS Designs - Phthalic ProcessDrawn by Date

Checked by Date

Approved by Date


Heavies to Fuel

(by Vendor) Drum Pumps Drum Pumps Pumps

Maleic Anhydride

11

12

PIC

SC-701

13

1

33

1

86

0.30

Temperature, CPressure, bar

o

Figure C.5 (Continued)



Flow of Naphthalene (at 200 C), Mg/h

0 5 10 15

Pre

ssur

e R

ise

acr

oss

Pum

p, k

Pa

150

200

250

300

350

400

Flow of HiTec Molten Salt (at 350°C), Gg/h

0.0 0.5 1.0 1.5 2.0

Pre

ssur

e R

ise

acro

ss P

ump,

kP

a

0

50

100

150

200

250

P-701 A/B

P-702 A/B

o

Figure C.6 Pump Curves for P-701 A/B and P-702 A/B



Flow of Boiler Feed Water (at 90oC), Mg/h

0.0 50.0 100.0 150.0

Pre

ssur

e R

ise

acr

oss

Pum

p, k

Pa

2500

3000

3500

4000

4500

Flow of Air (at 25oC), Mg/h

0.0 50.0 100.0 150.0 200.0

Pre

ssur

e R

atio

acr

oss

Com

pres

sor,

Pou

t/P

in

1

2

3

4

Surge Line

P-703 A/B

C-701

2200 rpm

3500 rpm

Figure C.7 Pump and Compressor Curves for P-703 A/B and C-701


Stre

am N

umbe

r1

23

45

67

89

10

Tem

pera

ture

(°C

)20

025

200

164

400

240

263

263

360

160

Pres

sure

(bar

)0.

801.

013.

353.

10

2.85

2.85

2.75

2.25

2.00

1.70

Vap

or m

ole

frac

tion

0.0

1.0

0.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

Flow

rate

(ton

ne/

h)12

.82

144.

2512

.82

144.

2512

.82

144.

2515

7.07

157.

0715

7.07

157.

07

Flow

rate

(km

ol/h

)N

apht

hale

ne10

0.0

0.0

100.

00.

010

0.0

0.0

100.

010

0.0

0.0

0.0

Oxy

gen

0.0

1050

.00.

010

50.0

0.0

1050

.010

50.0

1050

. 046

9.0

469.

0

Phth

alic

anh

ydri

de

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

70.0

70.0

Mal

eic

anhy

dri

de

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0-

16.0

16.0

Nap

htho

quin

one

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

2.0

2.0

Car

bon

dio

xid

e0.

00.

00.

00.

00.

00.

00.

00.

030

6.0

306.

0

Car

bon

mon

oxid

e0.

00.

00.

00.

00.

00.

00.

00.

050

.050

.0

Nit

roge

n0.

039

50.0

0.0

3950

.00.

039

50.0

3950

.039

50.0

3950

.039

50.0

Wat

er0.

00.

00.

00.

00.

00.

00.

00.

023

8.0

238.

0

Tot

al (k

mol

/h)

100.

050

00.0

100.

050

00.0

100.

050

00.0

5100

.051

00.0

51

01.0

5101

.0

Tabl

e C.

8Fl

ow S

umm

ary

Tabl

e fo

r Cu

rren

t Op

erat

ion

of P

htha

lic A

nhyd

ride

Pro

duct

ion

Faci

lity,

Uni

t 70

0 (s

ee F

igur

e C.

5)

202


Tabl

e C.

8(C

onti

nued

)

Stre

am N

umbe

r11

1213

1415

1617

18

Tem

pera

ture

(°C

)13

113

113

114

124

119

024

135

0

Pres

sure

(bar

)1.

401.

400.

150.

110.

300.

050.

203.

00

Vap

or m

ole

frac

tion

1.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

Flow

rate

(ton

ne/

h)14

5.00

12.0

712

.07

1.61

10.4

710

.06

0.40

1624

.72

HiT

ec m

olte

n Fl

owra

te (

kmol

/h)

salt

Nap

htha

lene

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

Oxy

gen

469.

00.

00.

00.

00.

00.

00.

00.

0

Phth

alic

anh

ydri

de

0.7

69.0

69.0

0.69

69.0

68.0

0.69

0.0

Mal

eic

anhy

dri

de

0.8

15.0

15.0

15.0

0.01

50.

015

0.0

0.0

Nap

htho

quin

one

0.0

2.0

2.0

0.08

1.9

0.00

21.

910.

0

Car

bon

dio

xid

e30

6.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

Car

bon

mon

oxid

e50

.00.

00.

00.

00.

00.

00.

00.

0

Nit

roge

n39

50.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

Wat

er23

8.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

Tot

al k

mol

/h

5014

.086

.086

.016

.071

.068

.02.

6017

,660

203

(con

tinu

ed)


Cond

en.

Cond

en.

Cond

en.

cwr

cwr

hps

hps

tofr

omhp

s to

from

hps

tofr

omcw

to

from

cw t

ofr

ombf

w t

obf

w t

ofr

omSt

ream

Num

ber

E-70

1E-

701

E-70

7E-

707

E-70

5E-

705

E-70

6E-

706

E-70

4E-

704

E-70

3E-

702

E-70

2

Tem

pera

ture

(°

C)

254

254

254

254

254

254

3045

3045

9117

325

4

Pres

sure

(bar

)42

.442

.442

.442

.442

.442

.45.

164.

865.

164.

8642

.442

.442

.4

Vap

or m

ole

frac

tion

1.0

0.0

1.0

0.0

1.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

1.0

Tot

al to

nnes

/h

6.73

6.73

9.36

9.36

1.89

1.89

267.

8426

7.84

19.6

219

.62

104.

9810

4.98

104.

98

Tabl

e C.

8Fl

ow S

umm

ary

Tabl

e fo

r Cu

rren

t Op

erat

ion

of P

htha

lic A

nhyd

ride

Pro

duct

ion

Faci

lity,

Uni

t 70

0 (s

ee F

igur

e C.

5) (

Cont

inue

d)

204



Compressor (assume efficiency independent of flowrate)

C-701 centrifugal, 5670 kW, 80% efficient @ design flowrate and 3500 rpm; can operate at twodiscrete rpm values, as shown on compressor curve; surge line also shown on com-pressor curve

Pumps (assume efficiency independent of flowrate)

P-701 A/B centrifugal, 1.3 kW, 50% efficientP-702 A/B centrifugal, 54 kW, 70% efficientP-703 A/B centrifugal, 140 kW, 80% efficientP-704 A/B centrifugal, 0.5 kW, 40% efficientP-705 A/B centrifugal, 4.4 kW, 50% efficientP-706 A/B centrifugal, 0.8 kW, 40% efficient

Fired Heater (process fluid flows through a set of tubes with a natural gas or liquid fuel firedflame, providing the radiant and convective heat transfer necessary to heat thefluid to the desired temperature)

H-701 fired heater, Q = 9,350 MJ/hConsists of four identical banks of tubes—currently these are all in operation and areoperating in parallel—piping and valving exist to run any or all tube banks in any configuration (i.e., series, parallel, etc.)—there is a control system that maintains thetemperature of Stream 5 by measuring the temperature of Stream 5 and altering thenatural gas and air feed rate.

Heat Exchangers (all one pass on each side, unless otherwise noted; hi refers to tube side; tubewall resistance negligible, unless otherwise noted)

E-701 Uses high-pressure steam, steam in shell, Q = 11,370 MJ/hA = 695 m2, U = 112 W/m2°C, hi = 114 W/m2°C

E-702 Makes high-pressure steam, steam in shell, Q = 215,407 MJ/hA = 539 m2, U = 2,840 W/m2°C, hi = 3960 W/m2°Chps supplies Unit 700 needs, excess steam used in Unit 300

E-703 Preheats high-pressure bfw, bfw in shell, Q = 36,900 MJ/hA = 1519 m2, U = 57 W/m2°C, hi = 63 W/m2°C

E-704 Total condenser for T-701, condensing fluid in shellA = 5.52 m2, U = 600 W/m2°C, all resistance on water side

E-705 Reboiler for T-701A = 50 m2, U = 1400 W/m2°C, approximately equal resistances

E-706 Total condenser for T-702, condensing fluid in shellA = 51 m2, U = 600 W/m2°C, all resistance on water side

E-707 Reboiler for T-702A = 243 m2, U = 1400 W/m2°C, approximately equal resistances

Reactor

The reactor is a fluidized bed, which means that the bed temperature is essentially constant andequal to the exit temperature of the gas.

Table C.9 Equipment Summaries (Unit 700)



R-701 Fluidized bed with vanadium oxide catalyst coated on silica gelMolten salt circulated in tubes to remove heat of reactionHeat-exchange area = 15,850 m2 (parallel tube banks within reactor)U = 100 W/m2°C, all resistance on reactor sideHeat removal required = 2.154 × 105 MJ/hReactor pressure drop unaffected by flowrate

Molten Salt Loop

Molten salt is used to remove the heat generated in the reactor. It circulates in a closed loop andis thermally regenerated by making high-pressure steam in E-702. The properties of this moltensalt, known as HiTec, may be found in the 6th edition of Perry’s, pp. 9–77.

Switch Condenser

SC-701 There are three sets of condensers. Due to the low partial pressure of phthalic anhydridein the stream, it desublimates rather than condenses. Therefore, the process stream iscooled using a low-temperature oil in tubes to promote desublimation. Then after solidis loaded on the heat transfer surface, higher-temperature oil is circulated in the tubes tomelt the solid. There are three such devices, one operating in desublimation mode, oneoperating in melting mode, and one on standby. The net result is a liquid stream con-taining the condensables, and a vapor stream containing water and the noncondens-ables. These condensers are designed and maintained under contract by CONDENSEX.They indicate operation at any scale is possible as long as the pressure of Stream 10remains within 10% of current operating conditions, and as long as the relative composi-tion of the condensables remains approximately constant.

Distillation Columns (For both distillation columns, it may be assumed that weeping begins tooccur at 35% of flooding. Both use high-pressure steam and cooling waterat the maximum allowable temperature rise.)

T-701 Removes maleic anhydride impurity overheadReflux ratio = 0.2733 trays, 40% efficient, 12-in tray spacing, 2-in weirsDiameter = 0.84 m, active area = 75% of total areaQc = −1230 MJ/hQr = 3220 MJ/h

T-702 Removes phthalic anhydride product overheadReflux ratio = 2.4386 trays, 50% efficient, 18-in tray spacing, 0.75-in weirsDiameter = 4.2 m, active area = 75% of total areaQc = −16,810 MJ/hQr = 15,890 MJ/h

Vessels

V-701 Diameter = 0.50 m, Length = 1.50 m

V-702 Diameter = 1.25 m, Length = 3.75 m

Air Treatment

The organics in Stream 11 are removed in a scrubber, with 10,000 kg of water needed per kg oforganic, at the current operating conditions. If the organic content of Stream 11 becomes moreconcentrated, then the amount of water needed increases by 100 kg per 0.001 mass fraction oforganic. The water is sent to the on-site wastewater treatment facility.

Table C.9 Equipment Summaries (Unit 700) (Continued)


C.3.4 ASSIGNMENT

Your assignment is to provide recommendations as to how much immediate scale-downis possible and what, if any, modifications would be needed to scale down by 50%. Fornow, you are to consider only the portion of the process prior to the switch condensers.You should also recommend any other changes that you feel should be made to improveperformance in Unit 700. Because 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 ofthese alterations and/or modifications.

Specifically, you are to prepare the following by two weeks from now:

1. A written report detailing the maximum scale-down possible, how to achieve 50%scale-down, recommendations, and costs associated with scaling down productionin Unit 700.

2. A list of new equipment to be purchased, including size, cost, and materials of con-struction.

3. An analysis of any change in the annual operating cost created by your recom-mended modifications.

4. A legible, organized set of calculations justifying your recommendations, includingany assumptions made.

C.3.5 REPORT FORMAT

This report should be brief. Most of the report should be an executive summary, not toexceed five double-spaced, typed pages, that summarizes your diagnosis, recommenda-tions, and rationale. Figures and tables may be included (and do not count against thepage limit) in the executive summary. An appendix should be attached that includesitems such as the requested calculations. These calculations should be easy to follow. Ingeneral, the written report should follow the guidelines given in Chapter 29 (in this CD).



P R O J E C T

4The Design of a New

100,000-Metric-Tons-per- Year Phthalic Anhydride

Production Facility

C.4.1 BACKGROUND

The operation of Unit 700, our phthalic anhydride facility, has been successfully scaleddown by 50%. Over the long term, we are still considering changing to o-xylene as the rawmaterial. The catalysis and reaction engineering group has finished preliminary researchand is very optimistic about its new catalyst. They promise that it will be superior to otherversions of o-xylene to phthalic anhydride catalysts in that most side products are mini-mized. At this point we are uncertain as to whether Unit 700 will be retrofitted to accommo-date the new catalyst or whether we will build a new, grassroots facility at another site,nearer to an o-xylene producer.

In order for us to have enough information to make an informed decision, we needa preliminary process design for a grassroots facility to produce phthalic anhydride fromwhat may be assumed to be pure o-xylene. Your job is to prepare a preliminary designfor the new 100,000 metric tons/y phthalic anhydride from o-xylene plant, and it mustbe completed within the next month. You may assume that the o-xylene feed is availableat 100°C and 1.1 bar and that the required purity for phthalic and maleic anhydrideproducts is 99.9 wt% and 95.0 wt%, respectively.


Concentrated organic waste streams may be burned instead of natural gas only if a firedheater is included in the design. Dilute organic waste streams must be sent to a treatmentfacility, with the appropriate operating cost charged. The capital cost of this facility maybe assumed to be included in the grassroots cost of the new facility. Other pertinent infor-mation is given below and in Tables C.10, C.11, and C.12.

208



The catalysis and reaction engineering group has obtained the following kinetic information re-garding the o-xylene to phthalic anhydride reaction. The reactions are

o-xylene phthalic anhydride

maleic anhydride

In addition, the complete combustion reaction for each organic component occurs. The reactionnetwork is given below. As you can see, a major advantage of our catalyst is that CO formationis essentially eliminated and no heavy impurity is made.

maleic anhydride CO2

o-xylene phthalic anhydride CO2

CO2

The catalyst must operate between 300°C and 400°C, and at pressures between 1 atm and 3 atm.In this range, the kinetics are as follows. (Partial pressures in atmospheres, ri in kmol h−1 (kg cat-alyst) −1, k0 = 1 kmol h−1(kg catalyst)−1atm−2, R = 1.987 cal/K mole, and T is in K.)

The lower flammability limit of o-xylene in air is 1 mol%, and the upper flammability limit is 6 mol%. For safety reasons, it is necessary that process conditions not be within these limits. It isalso necessary that the o-xylene content of the reactor never exceed 10 mol%, because if that

r5 � k5pmapo2 ln

k5

k0� −

30,400RT

� 20.47

r4 � k4pxypo2 ln

k4

k0� −

27,900RT

� 19.23

r3 � k3pxypo2 ln

k3

k0� −

28,600RT

� 18.97

r2 � k2ppapo2 ln

k2

k0� −

31,000RT

� 20.86

r1 � k1pxypo2 ln

k1

k0� −

27,000RT

� 19.837

C8H10 �152

O2 → C4H2O3 � 4H2O � 4CO2

C8H10 � 3O2 → C8H4O3 � 3H2O

Table C.10 Information on Reaction Kinetics (Unit 700)

→→

→

→

→1 2

3

45



limit is exceeded, the catalyst no longer operates at the desired selectivity, and the reaction couldbecome oxygen starved, forming significant amounts of CO and other undesired by-products.

At this time, we are unsure as to whether a packed-bed reactor (shell-and-tube type, modeled asa plug flow reactor) or a fluidized-bed reactor (modeled as an isothermal plug flow reactor with10% feed gas bypass) is the better choice. Please address this in your preliminary design. For theshell-and-tube packed bed, the catalyst would be in the tubes. We do believe, however, thattube diameters exceeding 1 inch in a shell-and-tube configuration would not allow for rapidenough heat removal, causing significant hot spots and subsequent catalyst damage.

For a fluidized bed, the following data may be assumed:

Spherical catalyst particle, diameter range dp = 300–600μmCatalyst particle density �cat = 1600 kg/m3

Void fraction at minimum fluidization mf = 0.50Heat transfer coefficient from fluidized bed to tube wall h = 300 W/m2°CReactor should operate between 2umf (bubbling) and 50umf (turbulent)The reactor has a rectangular cross section (width of sides = w and v)Range of acceptable side ratios 0.2 < v/w < 5Maximum value of v or w = 8 mMaximum volume of bed displaced by tube banks is 40%The cost of the fluidized bed should be estimated as 5 times the cost of a vessel of thesame volume

For umf, use the correlation of Wen and Yu:

where ρg is the density of the gas in the fluidized bed (at average conditions) and �s is the solidcatalyst particle density (called �cat above).

For a shell-and-tube packed bed, the following data may be assumed:

Catalyst particle diameter dp = 3 mmCatalyst particle density �cat = 1600 kg/m3

Void fraction = 0.50Heat transfer coefficient from packed bed to tube wall h = 60 W/m2°CUse standard tube sheet layouts as for a heat exchangerShell diameter is a function of heat transfer characteristics and frictional losses

It is anticipated that a heat transfer fluid will be used in a closed loop to remove the highlyexothermic heat of reaction from either type of reactor. We anticipate that all surplus high-pressure steam made can be sold elsewhere in the plant. Because we have had many years of successful operation using the HiTec molten salt, we anticipate using it again for the newprocess. However, you should feel free to recommend an alternative if you can justify superiorperformance at the same cost, or equal performance at a lower cost.

Remf �dpumf �g

�� (33.7)2 �

0.0408d3p�g(�s − �g)g�2 �

0.5

− 33.7

Table C.10 Information on Reaction Kinetics (Unit 700) (Continued)



These are a complex set of three condensers. Because of the low partial pressure of phthalic an-hydride in the stream, it desublimates rather than condenses. Therefore, the process stream iscooled using a low-temperature oil in tubes to promote desublimation. Then, after solid isloaded on the heat transfer surface, gas flow to this condenser is stopped, and higher-tempera-ture oil is circulated in the tubes to melt the solid. There are three such devices, one operating in desublimation mode, one operating in melting mode, and one on standby. The net result is a liquid stream containing the condensables and a vapor stream containing somemaleic anhydride, some phthalic anhydride, and all of the noncondensables.

These condensers will once again be designed and maintained under contract by CONDENSEX. They indicate that operation at any scale is possible as long as the pressure of the feed to the condensers is between 1.70 and 2.00 bar. You may assume that all light gases areneither condensed nor dissolved and that 99% of the organics are desublimated and melted.Based on past experience, CONDENSEX suggests that we may estimate the capital cost of thesecondensers as 15% of all other capital costs for the new process, and that the annual operatingcost is 3 times the cost of an equivalent amount of cooling water needed to satisfy the coolingduty from the energy balance on the condenser unit modeled as a component separator.

The following cost of treating the waste (dirty) air stream leaving the switch condensersshould be used in your cost estimates:

where Vtot = the total volume of “dirty air” to be treated, m3, and xor = mole fraction of organicsin “dirty air” stream.

Air Treatment Cost � $10−4Vtot(0.5 � 1000xor)

Table C.11 Design of the Switch Condensers and Air Treatment Costs (Unit 700)

The following hints were developed for students using the CHEMCAD simulator. These shouldalso provide help to people using other simulator packages.

Use SRK (Soave-Redlich-Kwong) for the VLE and enthalpy options in the thermodynamicpackage for all the units in this process.

For heat exchangers with multiple zones, it is recommended that you simulate each zonewith a separate heat exchanger. For the switch condensers, use a component separator, and thencalculate the heat duty from the inlet and outlet streams.

When simulating a process using “fake” streams and equipment, it is imperative that theprocess flow diagram that you present not include any fake streams and equipment. It mustrepresent the actual process.

Table C.12 Simulator Hints (Unit 700)


C.4.3 ASSIGNMENT

Your assignment is to provide the following:

1. An optimized preliminary design of a plant to make phthalic anhydride from o-xylene using the new catalyst.

2. An economic evaluation giving the NPV (net present value), after tax, of the newproject. For your evaluation you should use the following economic information:• After-tax internal hurdle rate = 9%• Depreciation = MACRS (6-year schedule given in Chapter 9)• Marginal taxation rate of 35%• Construction period of 2 years• Project plant life = 10 years after start-up

Specifically, you are to prepare the following by . . . (four weeks from now):

1. A written report detailing your design and profitability evaluation of the newprocess

2. A clear, complete, labeled process flow diagram of your optimized process3. A clear stream flow table giving the T, P, total flowrate in kg/h and kmol/h, compo-

nent flowrate in kmol/h, and phase for each important process stream4. A list of new equipment to be purchased, including size, cost, and materials of con-

struction5. An evaluation of the after-tax NPV, and the discounted cash flow rate of return on

investment (DCFROR) for your recommended (optimized) process6. A legible, organized set of calculations justifying your recommendations, including

any assumptions made

C.4.4 REPORT FORMAT

This report should be in the standard design report format. It should include an abstract,results, discussion, conclusions, recommendations, and an appendix with calculations.The report format rules given in Chapter 29 (in this CD) should be followed.



P R O J E C T

5Problems

at the Cumene Production Facility,

Unit 800

C.5.1 BACKGROUND

Cumene (isopropyl benzene) is produced by reacting propylene with benzene. DuringWorld War II, cumene was used as an octane enhancer for piston engine aircraft fuel.Presently, most of the worldwide supply of cumene is used as a raw material for phenolproduction. Typically, cumene is produced at the same facility that manufactures phenol.

The plant at which you are employed currently manufactures cumene in Unit 800by a vapor-phase alkylation process that uses a phosphoric acid catalyst supported onkieselguhr. Plant capacity is on the order of 90,000 metric tons per year of 99 wt% puritycumene. Benzene and propylene feeds are brought in by tanker trucks and stored in tanksas a liquid.

C.5.2 CUMENE PRODUCTION REACTIONS

The reactions for cumene production from benzene and propylene are as follows:

propylene benzene cumene

propylene cumene p-diisopropyl benzene

C.5.3 PROCESS DESCRIPTION

The PFD for the cumene production process, Unit 800, is given in Figure C.8. Thereactants are fed from their respective storage tanks. After being pumped up to therequired pressure (dictated by catalyst operating conditions), the reactants are mixed,vaporized, and heated in the fired heater to the temperature required by the catalyst. Theshell-and-tube reactor converts the reactants to desired and undesired products as per the

C3H6 � C9H12 → C12H18

C3H6 � C6H6 → C9H12

213



above reactions. The exothermic heat of reaction is removed by producing high-pressure steam from boiler feed water in the reactor. The stream leaving the reactorenters the flash unit, which consists of a heat exchanger and a flash drum. The flash unitis used to separate the C3 impurities, which are used as fuel for a furnace in another on-site process. The liquid stream from the flash drum is sent to the first distillation col-umn, which separates benzene for recycle. The second distillation column purifiescumene from the p-diisopropyl benzene (p-DIPB) impurity. Currently, the waste p-DIPBis used as fuel for a furnace. The pressure of both distillation columns is determined bythe pressure in the flash drum; that is, there are no pressure-reduction valves down-stream of the flash drum.

C.5.4 RECENT PROBLEMS IN UNIT 800

Recently, Unit 800 has not been operating at standard conditions. We have recentlyswitched suppliers of propylene; however, our contract guarantees that the new propy-lene feed will be within specifications given in Table C.13.

Upon examining present operating conditions, we have made the followingobservations:

1. Production of cumene has dropped by about 8%, and the reflux in T-801 wasincreased by approximately 8% in order to maintain 99 wt% purity. The flows ofbenzene (Stream 5) and propylene (Stream 2) remained the same. Pressure in the

Benzene

V-801

P-801A/B

H-801

V-801 P-801A/B P-802A/B E-801 H-801 R-801 E-802 V-802Benzene Benzene Propylene Feed Reactor Reactor Reactor Phase

Feed Drum Feed Pumps Feed Pumps Vaporizer Feed Heater Effluent Cooler Separator

1

LIC

poc

air f.g.

3

24

5 6 6a

7

8

P-802A/B

FIC

PIC

LIC

R-801

bfw

hps

E-801 V-802

E-802

Propylene

cw

FIC

hps

9

Figure C.8 Process Flow Diagram for the Production of CumeneProcess (Unit 800)



storage tanks has not changed appreciably when measured at the same ambienttemperature.

2. The amount of fuel gas being produced has increased significantly and is estimatedto be 78% greater than before. Additionally, it has been observed that the pressurecontrol valve on the fuel gas line (Stream 9) coming from V-802 is now fully open,although previously it was controlling the flow.

3. The benzene recycle, Stream 11, has increased by about 5%, and the temperature ofStream 3 into P-801 has increased by about 3°C.

4. Production of steam in the reactor has fallen by about 6%.5. Catalyst in the reactor was changed six months ago, and previous operating history

(over last ten years) indicates that no significant drop in catalyst activity shouldhave occurred over this time period.

6. p-DIPB production, Stream 14, has dropped by about 20%.

We are very concerned about this loss in production because we can currently sell all thematerial we produce.

Another problem that has arisen lately is the malfunction of the feed pumps. Thisproblem arose during a very warm spell when the ambient temperature reached 110°F.A maintenance check showed that P-802 needed a new bearing, and this was taken careof, but P-801 seemed to be OK. The ambient temperature has now returned to a mild70°F, and both pumps seem to be working fine.

Fuel Gas

FIC

11

LIC

LIC

12

LIC

FIC

13

LIC

Cumene Product

14

cw

cw

hps

mps

E-803

E-804

E-805

E-806

T-801

T-802

P-804 A/B

P-803 A/B

P-805 A/B

V-803

V-804

Benzene Benzene Benzene Benzene Benzene Cumene Cumene Cumene Cumene Cumene Cumene

T-801 E-803 V-803 P-803A/B E-804 P-804A/B T-802 E-805 E-806 V-804 P-305A/B

Column Condenser Reflux Reflux Reboiler Pumps Column Condenser Reboiler Reflux Reflux

TBWS Designs - Cumene ProcessDrawn by Date

Checked by DateApproved by Date


DIPB

10

Drum Pumps Drum Pumps

1

27

37

1

Figure C.8 (Continued)



Currently, market conditions for cumene are very tight. We are in direct competi-tion with some local companies that have recently built cumene plants. It appears thatmanagement is very concerned about our competitiveness because other producers in thearea are beginning to undercut our prices. Management wants to find out whether anysignificant savings in operating costs can be found for Unit 800.


Other pertinent information is appended, including a flow table for the process streams atdesign conditions, that is, prior to the current operating problem, Table C.14; a utilitysummary table at design conditions, Table C.15; pump curves, Figures C.9 and C.10; a setof design calculations; and an equipment list, Table C.16.

C.5.6 ASSIGNMENT

Specifically, you are to prepare the following by . . . (two weeks from now):

1. A written report detailing your diagnosis of the operating problems with the plant,along with your recommendations for solving these problems

2. A list of new equipment to be purchased, if any, including size, cost, and materialsof construction

3. An analysis of any change in the annual operating cost created by your recom-mended modifications

4. A legible, organized set of calculations justifying your recommendations, includingany assumptions made

C.5.7 REPORT FORMAT

This report should be brief. Most of the report should be an executive summary, not to ex-ceed five double-spaced, typed pages, which summarizes your diagnosis, recommenda-tions, and rationale. Figures and tables may be included (do not count these against thepage limit) in the executive summary. An appendix should be attached that includesitems such as the requested calculations. These calculations should be easy to follow. Theguidelines given in Chapter 29 (in this CD) should be followed.

Raw Materials

Benzene >99.9 wt% purity

Propylene ≤ 5 wt% propane impurity

Product

Cumene >99 wt% purity

Table C.13 Specifications of Products and Raw Materials


Stre

am N

umbe

r1

23

45

66a

7

Tem

pera

ture

(°C

)25

2541

2844

4121

4.0

350

Pres

sure

(bar

)1.

0011

.66

1.01

31.5

031

.50

31.2

530

.95

30.7

5

Vap

or m

ole

frac

tion

00

00

0.0

0.0

1.0

1.0

Flow

rate

(ton

ne/

h)8.

194.

6416

.37

4.64

16.3

721

.01

21.0

121

.01

Flow

rate

s (k

mol

/h)

Ben

zene

105.

000.

020

5.27

0.0

205.

2720

5.27

205.

2720

5.27

Prop

ylen

e0.

010

5.00

2.89

105.

002.

8910

7.89

107.

8910

7.89

Prop

ane

0.0

5.27

2.79

5.27

2.79

8.06

8.06

8.06

Cum

ene

0.0

0.0

0.94

0.0

0.94

0.94

0.94

0.94

P-d

iisop

ropy

l ben

zene

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

Tot

al (k

mol

/h)

105.

0011

0.27

211.

8911

0.27

211.

8932

2.16

322.

1632

2.16

Tabl

e C.

14Fl

ow S

umm

ary

Tabl

e fo

r Cu

men

e Pr

oduc

tion

at

Desi

gn C

ondi

tion

s, U

nit

800

(Fig

ure

C.8)

217

Stre

am N

umbe

r8

910

1112

1314

Tem

pera

ture

(°C

)35

090

9057

179

178

222

Pres

sure

(bar

)30

.25

1.75

1.75

1.75

1.90

1.90

2.10

Vap

or m

ole

frac

tion

1.0

1.0

0.0

0.0

0.0

0.0

0.0

Flow

rate

(ton

ne/

h)21

.01

1.19

19.8

28.

1811

.64

11.0

80.

56

Flow

rate

s (k

mol

/h)

Ben

zene

108.

967.

8810

1.08

100.

270.

810.

810.

0

Prop

ylen

e8.

865.

972.

892.

890.

00.

00.

0

Prop

ane

8.06

5.27

2.79

2.79

0.0

0.0

0.0

Cum

ene

94.3

90.

7793

.62

0.94

92.6

891

.76

0.92

P-d

iisop

ropy

l ben

zene

2.79

0.0

2.79

0.0

2.79

0.03

2.76

Tot

al (k

mol

/h)

223.

0619

.89

203.

1710

6.89

96.2

892

.60

3.68


Stre

am N

ame

hps

to

Cond

ensa

te

mps

to

Cond

ensa

tehp

s to

Cond

ensa

teE-

801

from

E-8

01E-

804

from

E-8

04E-

806

from

E-8

06

Tem

pera

ture

(°C

)25

425

418

5.5

185.

525

425

4

Pres

sure

(bar

)42

.37

42.3

711

.35

11.3

542

.37

42.3

7

Flow

rate

(ton

ne/

h)7.

607.

603.

563.

563.

253.

25

Tabl

e C.

15Fl

ow S

umm

ary

Tabl

e fo

r U

tilit

y St

ream

s in

Uni

t 80

0

Stre

am N

ame

cw t

o cw

fro

m

cw t

ocw

fro

mcw

to

cw f

rom

E-

802

E-80

2E-

803

E-80

3E-

805

E-80

5

Tem

pera

ture

(°C

)30

4530

4530

45

Pres

sure

(bar

)5.

164.

965.

164.

965.

164.

96

Flow

rate

(ton

ne/

h)26

1.30

261.

3085

.88

85.8

887

.50

87.5

0

218



Flow of Benzene (at 41oC), l/s

0 1 2 3 4 5 6 7

Pre

ssur

e H

ead

acro

ss P

ump,

ft o

f Liq

uid

0

200

400

600

800

1000

1200

1400

1600

Flow of Benzene (at 41oC), l/s

0 1 2 3 4 5 6 7 8

NP

SH

R, f

t of L

iqui

d

0

1

2

3

4

5

6

7

8

9

10

Pump Curve

System Curve (Design Case)

P-801 A/B

P-801 A/B

Figure C.9 Pump, System, and NPSH Curves for P-801 A/B



Flow of Propylene (at 25oC), l/s

0.0 1.0 2.0 3.0

Pre

ssur

e H

ead

acro

ss P

ump,

ft o

f Liq

uid

-600

-400

-200

0

200

400

600

800

1000

1200

1400

1600

Flow of Propylene (at 25oC), l/s 0 1 2 3

NP

SH

R, f

t of L

iqui

d

0

1

2

3

4

5

6

7

8

9

10

Pump Curve

System Curve (Design Case)

Pump 802 A/B

P-802 A/B

Figure C.10 Pump, System, and NPSH Curves for P-802 A/B



Tanks (not shown on flowsheet)

TK-801 storage tank for benzeneThere are two tanks: one feeding Stream 1 and one in a filling mode.Each tank is 450 m3.

TK-802 storage tank for propyleneThere are two tanks: one feeding Stream 2 and one in a filling mode.Each tank is 450 m3.

Pumps (assume efficiency independent of flowrate)

P-801 centrifugal, 75% efficient, driver rated at 21.9 kW





Heat Exchangers (all one pass on each side, unless otherwise noted; hi refers to tube side; tubewall resistance negligible, unless otherwise noted)

E-801 uses high-pressure steam, steam in shell, Q = 12,800 MJ/hA = 20.8 m2 in two zonesDesubcooling zone: A = 13.5 m2, U = 600 W/m2°C, hi = 667 W/m2°CVaporizing zone: A = 7.3 m2, U = 1500 W/m2°C, equal resistances on both sides

E-802 condenser for flash unit, process stream in shell, 1-2 configurationQ = 16,400 MJ/h, A = 533 m2

E-803 total condenser for T-801, condensing fluid in shellA = 151 m2, U = 450 W/m2°C, all resistance on water side

E-804 reboiler for T-801A = 405 m2, U = 750 W/m2°C, approximately equal resistances

E-805 total condenser for T-802, condensing fluid in shellA = 24.0 m2, U = 450 W/m2°C, all resistance on water side

E-806 reboiler for T-802A = 64.0 m2, U = 750 W/m2°C, approximately equal resistances

Fired Heater

H-801 Q = 6380 MJ/h (heat actually added to fluid)Capacity 10,000 MJ/h of heat added to fluid70% efficiency

Reactor

R-801 shell-and-tube packed bed with phosphoric acid catalyst supported on kieselguhrBoiler feed water in shell to produce high-pressure steamReactor volume = 6.50 m3, heat exchange area = 342 m2

234 tubes, 3.0-in (7.62 cm) ID, 6 m longU = 65 W/m2°C, all resistance on reactor sideHeat removal required = 9840 MJ/h

Table C.16 Equipment Summary Table for Unit 800



Distillation Columns

T-801 removes benzene impurity overhead for recycleMedium-pressure steam used in reboilerCooling water used in condenser, returned at maximum allowable temperatureReflux ratio = 0.4427 trays, 50% efficient24-in tray spacing, 3-in weirsDiameter = 1.13 m, active area = 75% of total areaQc = −5390 MJ/hQr = 7100 MJ/h

T-802 removes cumene product overheadHigh-pressure steam used in reboilerCooling water used in condenser, returned at maximum allowable temperatureReflux ratio = 0.6337 trays, 50% efficient24-in tray spacing, 3-in weirsDiameter = 1.26 m, active area = 75% of total areaQc = −5490 MJ/hQr = 5520 MJ/h

Vessels

V-801 benzene feed drum 4.2 m length, 1.4 m diameter

V-802 flash drum 5.2 m height, 1 m diameter

V-803 T-801 reflux drum 4 m length, 1.6 m diameter

V-804 T-802 reflux drum 6.5 m length, 1.6 m diameter

Table C.16 Equipment Summary Table for Unit 800 (Continued)

C.5.8 PROCESS CALCULATIONS

Calculations for Fuel Gas Exit Line for V-802

Design flow of fuel gas = 1192 kg/hMolecular weight of fuel gas = 59.9Gas viscosity = 9.5 × 10−6 kg/m.sGas density = 1.18 (273) P/(293 + 90) (1.01) = 0.00876P kg/m3 (P in bar)Destination pressure (in burner in unit 900) = 1.25 barΔPline + ΔPvalve = 1.75 −1.25 = 0.50 barΔPvalve should be ≅ 0.30 bar and Δ Pline = 0.20 barLength of line (Stream 9A) ≅ 125 m (equivalent length including fittings)Average pressure in line, P = (1.45 + 1.25) / 2 = 1.35 barDensity of gas in line = 0.00876 P = 1.18 kg/m3

ΔPline = 2f ρu2Le/dpipe



Look at 3-in, 4-in, and 6-in schedule-40 pipe:

E-802 8A

V-802

9

PIC

9A To Burner in Unit 900

Set Pressure at 175 kPaDesign Temp. at 90°C Based on Cooling in E-802

LIC

10

T-801

dpipe (nominal) 3 in. 4 in. 6 in.

dpipe(inside) = di 0.0779 m 0.1022 m 0.1541 m

u = 4Q/πdi2 58.9 m/s 34.2 m/s 15.0 m/s

Re = uρdi/μ 5.69 × 105 4.34 × 105 2.88 × 105

e/di 0.00059 0.00045 0.0003

f (from friction factor diagram) 0.0046 0.0045 0.0042

0.603 bar 0.152 bar 0.018 bar�Pline �2f�u2 Leq

di

Choose 4-in schedule-40 pipe.

ΔPline = 0.152 bar and ΔPvalve = 0.50 � 0.152 = 0.348 bar



Calculations for P-801

Design Conditions (note that 1 kPa = 0.335 ft of water = 0.402 ft of benzene)LAL (low alarm level) = 5 ft from ground and pump center line is 2 ft from groundNOL (normal operating level) = 10 ft above ground level

NPSH Calculations (at LAL)Static head = 5 − 2 = 3 ft of benzene = hstat

Psupply = 1.01 bar = 40.7 ft of benzene = hsupply

ΔPfriction (in supply line) = 1 psi = 2.8 ft of benzene = hfriction

Vapor Pressure of Stream 3

T = 30°C P* = 54 kPaT = 40°C P* = 72 kPaT = 50°C P* = 94 kPa

Vapor Pressure of Stream 3 = 0.74 bar @ 41°C = 29.7 ft of benzene = hvp

NPSHavailable = hsupply + hstatic − hfriction − hvp = 40.7 + 3 − 2.8 − 29.7 = 11.2 ftNPSHrequired (from pump curve) = 6.1 ft @ 5.5 × 10−3 m3/s∴ cavitation should not be a problem

System Curve Calculations

Δ Pfriction (discharge) = 31.50 − 1.75 = 29.75 bar = 1196 ft of benzeneΔ Pfriction (suction) = 2.8 ft of benzeneΔ Pdischarge - tank = 1.75 − 1.01 = 0.74 bar = 30 ft of benzeneΔ Pstatic = 0 (E-801 entrance @ 10 ft above ground level = NOL)

Benzene Feed11

1

3

V-801

m = 16386 kg/h

pL = 832 kg/m3

P-801A/B Benzene Feed Pump

5 ft

2 ft

5 ft

5 ft

Benzene Recycle

LAH (Level Alarm High)

NOL (Normal Operating Level)

LAL (Level Alarm Low)

FIC

5

4

Propylene Feed

Valve for back pressure notcontrol (consider using turbine)

P = 3025 kPa to E-202

P = 175 k{aheld constant byPIC on fuel gasline



∴ Required head at design flow = 1199 + 30 + ΔPcv = 1230 ft of benzene + ΔPcv

From pump curve this gives us ΔPcv = 135 ft = 3.36 bar (this is high but OK)

Calculations for P-802

Design Conditions (note that 1 kPa = 0.335 ft of water = 0.666 ft of propylene)LAL (low alarm level) = 10 ft from ground and pump center line is 2 ft from groundNOL (normal operating level) = 20 ft from ground

NPSH Calculations (at LAL)

Static head = 10 − 2 = 8 ft of propylene = hstat

Psupply = Psat (@25°C) = 11.66 bar = 777 ft of propylene = hsupply

Δ Pfriction (in supply line) = 0.2 psi = 1 ft of propylene = hfriction (3-in schedule 40 pipeLe = 20 ft)

Vapor Pressure of Stream 2 = 11.66 bar = 777 ft of propylene = hvp

NPSHavailable = hsupply + hstatic − hfriction − hvp = 777 + 8 − 1 − 777 = 7 ft of propylene (@ propylene flowrate of 2.57 × 10−3 m 3/s)NPSHrequired (from pump curve) = 6 ft

∴ cavitation should not be a problem (put note on P&ID to increase LAL to 12 ft tobe safe)

System Curve Calculations

Δ Pfriction (discharge) = 31.50 − 1.75 = 29.75 bar = 1981 ft of propyleneΔ Pfriction (suction) = 1 ft of propyleneΔ Pdischarge-tank = 1.75 − 11.66 = −9.91 bar = −660 ft of propylene Δ Pstatic = −10 ft of propylene

∴ Required head at design flow = 1982 − 660 − 10 + ΔPcv = 1312 ft of propylene +ΔPcvFrom pump curve this gives us ΔPcv = 140 ft = 2.10 bar

Fresh Propylene Feed

LAH (Level Alarm High)

NOL (Normal Operating Level)

LAL (Level Alarm Low)

5 ft

10 ft

Propylene Feed Tankm = 4,651 kg/h

rL = 503 kg/m3

Valve for back pressure notcontrol (consider using turbine)

5 ft

22 ft

P-802A/B Propylene Feed Pumps

Benzene Feed

4

5

P = 3025 kPato E-202

P = 175 kPaheld constant byPIC on fuel gasline

FIC


C.6.1 BACKGROUND

In the opinion of our marketing research department, the demand for phenol-derivedplasticizers is on the rise. Therefore, we are investigating the possibility of a new, grass-roots phenol plant to handle the anticipated increase. Because phenol is made fromcumene, a grassroots cumene plant would also be necessary. Given your experience introubleshooting our existing cumene process, we would like you to study the economics ofa new cumene plant. Specifically, we would like a complete preliminary design of a grass-roots, 100,000 metric ton/y cumene process using benzene and propylene.

We have a new, proprietary catalyst, and the kinetics are included in Table C.17. Wewould also like you to consider the economics of our continuing to use propylene with5% propane impurity at $0.095/lb versus purer propylene feed. In preparing this prelimi-nary design, you should assume that all steam made can be used elsewhere in the plantwith the appropriate economic credit, that condensed steam can be returned as boilerfeed water for the appropriate credit, and that fuel gas can be burned for credit at its LHV(lower heating value). Additional information is given in Table C.18.

C.6.2 ASSIGNMENT

Your assignment is to provide the following:

1. An optimized preliminary design of a plant to make cumene from benzene andpropylene using the new catalyst

2. An economic evaluation of your optimized process, using the following information:• After-tax internal hurdle rate = 9% p.a.• Depreciation = MACRS (6-year schedule; see Chapter 9)• Marginal taxation rate = 35%

226

P R O J E C T

6Design of a New, 100,000-

Metric-Tons-per-Year Cumene Production Facility



• Construction period = 2 years• Project plant life = 10 years after start-up

Specifically, you are to prepare the following by . . . (four weeks from now):

1. A written report detailing your design and profitability evaluation of the new process2. A clear, complete, labeled process flow diagram of your optimized process includ-

ing all equipment and the location of all major control loops3. A clear stream flow table including T, P, total flowrate in kg/h and kmol/h, compo-

nent flowrate in kmol/h, and phase for each process stream4. A list of new equipment to be purchased, including size, cost, and materials of

construction5. An evaluation of the annual operating cost for the plant

The kinetics for the reactions are as follows:

C3H6 + C6H6 →k1 C9H12

propylene benzene cumene

C3H6 + C9H12 →k2 C12H18

propylene cumene p-diisopropyl benzene

where the units of the activation energy are kcal/mol, the units of concentration are mol/l, andthe temperature is in Kelvin.

For a shell-and-tube packed bed, the recommended configuration, the following data may beassumed:

Catalyst particle diameter dp = 3 mm

Catalyst particle density �cat = 1600 kg/m3

Void fraction = 0.50

Heat transfer coefficient from packed bed to tube wall h = 60 W/m2°C

Use standard tube sheet layouts as for a heat exchanger

If tube diameter is larger than in tube sheet layouts, assume that tube cross-sectional areais 1/3 of shell cross-sectional area

k2 � 2.9 � 106 exp� − 35.08RT �

r2 � k2cpcc mole�g cat sec

k1 � 3.5 � 104 exp� − 24.90RT �

r1 � k1cpcb mole�g cat sec

Table C.17 Reaction Kinetics for Cumene Reactions (Unit 800)



Cost of Manufacture

In order to estimate the cost of manufacture (not including depreciation), COMd, you should usethe following equation:

(8.2)

The current MACRS method for depreciation should be used in your calculations (see Chap-ter 9).

Hints for Process Simulator

The CHEMCAD process simulator was used to generate the flow table given in Project 5. Thehints given here are specifically directed to CHEMCAD users but should also be applicable forother process simulators.

Use SRK (Soave-Redlich-Kwong) thermodynamics package for VLE and enthalpy calcula-tions for all the equipment in the process.

For heat exchangers with multiple zones, it is recommended that you simulate each zonewith a separate heat exchanger. Actual equipment may include several zones, so costing shouldbe based on the actual equipment specifications.

For the reactor, you may use an isothermal reactor to estimate the volume of catalyst andheat-exchange area. For more accurate results, the temperature profile in the reactor should bemodeled by completing a differential heat and material balance on the reactor.

For the distillation columns, you should use the Shortcut method (SHOR) to get estimatesfor the rigorous distillation simulation (TOWR or SCDS). The Shortcut method may be useduntil an optimum case is near. It is then expected that everyone will obtain a final design usingrigorous simulation of the columns.

When simulating a process using “fake” streams and equipment, it is absolutely necessarythat the process flow diagram you present not include any “fake” streams and equipment. Itmust represent the actual process.

COMd � 0.180 FCI � 2.73 COL � 1.23 (CUT � CWT � CRM)

Table C.18 Additional Information (Unit 800)

6. An analysis of the after-tax NPV (10 years, 9%), and the discounted cash flow rate ofreturn on investment (DCFROR) for your recommended process

7. A legible, organized set of calculations justifying your recommendations, includingany assumptions made

C.6.3 REPORT FORMAT

This report should be in the standard design report format, consistent with the guidelinesgiven in Chapter 29 (in this CD). It should include an abstract, results, discussion, conclu-sions, recommendations, and an appendix with calculations.


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