design of ammonia section in ammonia synthesis plant

1: Design of Ammonia Section in Ammonia Synthesis Plant Rashed Khalfan Al Kindi 200235986 Shabbeer Ali Yusuf 200337936 El-Hassan Mohammed 200337931 Ali Saleh Mohammed 200202794 Hamad Al Zaidi 200200655

3: Introduction Objectives Design of ammonia section in ammonia synthesis plant for a 30 ton/day production of ammonia Estimate the Cost Material and energy balance was done in GPI

4: Introduction Design of process units theoretically and using HYSYS software The units designed were reactor and heat exchanger

5: Special concerns related to the process was done corrective measures Safety and environmental impact of the project were analyzed Cost estimation was conducted using CAPCOST software

6: Process Flow Diagram

7: Reactor Design Assumptions The rate equation from HYSYS No catalyst, no void fraction No pressure drop Change in temperature

8: Derivation The design equation of PFR is X is the conversion V is the volume -rN2 is the rate of reaction of the limiting reagent, nitrogen FN2o is the input flow rate of the nitrogen

9: Derivation The rate of reaction kf and kb are the forward and backward rate constants PN2, PH2, PH3 are the partial pressures of nitrogen, hydrogen and ammonia

10: Derivation The partial pressure of component B where PBo is the intial partial pressure of component B b is the stoichiometric coefficient of the component B ?B is the ratio of flow rate of component B to that of flow rate of basis component.

11: Derivation So, for our reaction, Po is the total input pressure which in this case is

12: Derivation

13: Rate vs. Reactor Volume

14: Derivation Change in temperature through the reactor:

15: Behavior

16: Derivation Change in temperature through the reactor:

17: Derivation

18: Derivation Enter these equations to the polymath software to obtain the volume for 40% conversion

19: Results The volume of the reactor obtained from Polymath is 1.78 m3 Further HYSYS was used to obtain the volume of the reactor by setting the diameter to be 0.75 m. Thus the volume obtained was 0.998m3 for the highest conversion

20: Heat Exchanger Design Importance ? Heat integration Type of heat exchanger to be designed is countercurrent shell and tube The most important factor in a heat exchanger design is the heat transfer area (A)

21: Heat Exchanger Design Heat Exchanger design procedures: Inlet and outlet temperatures are: Flow rates: mc = mh =0.577 kg/s

22: Heat Exchanger Design 1- Find the physical properties: 2- Calculate the heat transfer rate (q) q = 148680.4 J/s

23: Heat Exchanger Design 3- also 4- Find (?T)LMTD (?T)LMTD = 216 oC 5- Find F

24: Heat Exchanger Design R = 0.92 and P = 0.25 ? F= 0.98

25: Heat Exchanger Design 6- Assume a value for U = 10 – 50 W/m2.C 7- The heat transfer area (A) is: A= 14.6 m2 8- choose initial values for L, Do and Di L = 2.3 m, Do = 0.04 m and Di = 0.036 m

26: Heat Exchanger Design Tube side 9- Calculate the area of one tube Atube = 0.37 m2 10- Calculate the number of tubes (Nt), Nt = 40 tubes 11- Find the fluid velocity uin = 9.14 m/s

27: Heat Exchanger Design 12- Find Reynolds number Re = 97063.2 ? turbulent flow 13- Find Nusselt number (Nu) Nu = 314.87 14- Calculate the pressure drop Np: number of tube passes (2) ?Pt =12.02 kPa

28: To find the tube side friction jf

29: Heat Exchanger Design Shell side 15- Choose the pitch type ? Triangular 16- Find the bundle diameter Db = 0.867 m 17- Find the shell diameter (Ds), Ds= Db + bundle diametrical clearance Ds= 0.92 m 18- Calculate the baffle spacing , lB = lB= 0.184 m

30: Heat Exchanger Design 19- Choose the tube pitch(pt), 1.25*Do, and the baffle cuts, 25% 20- Calculate the cross flow area As, As = 0.0121 m2 21-Calculate the mass velocity , Gs= 47.5 kg / s.m2 22- Calculate the equivalent diameter , de = 0.043 m

31: Heat Exchanger Design 23- Calculate the Reynolds number Re = 17607 24- Calculate the Nusselt number Nu = 1317.6 25- Calculate the pressure drop ?Ps = 128.7 kPa

32: To find shell side heat transfer factor, jh

33: To find shell side friction factor, jf

34: Heat Exchanger Design Overall heat transfer coefficient 26- Find the local heat transfer coefficient hin = 1054.5 W/m2.C and ho = 4255.3 W/m2.C 27- Calculate the overall heat transfer coefficient U: 28- Use Goal Seek Set U = 50 by changing L ? L = 2.35 m

35: Heat Exchanger Design Main Results:

36: Special Concerns Special concerns are out of normal operating conditions. Specific justification required else don’t use Normal conditions Pressure between 1 & 10 bar Temperatures between 40 °C & 260 °C

37: Concerns in Pressure Pressures up to 10 bars without much additional capital investment Higher pressures Thicker walls More expensive equipment In vacuum conditions Large equipment Special construction techniques Higher cost

38: Concerns in Temperature At high temperatures common construction materials like carbon steel lose their physical strength drastically high temperature - economic penalty more complicated processing equipment refractory-lined vessels exotic materials of construction

39: Operating Conditions

40: Reactor High Pressure of 196 bars Justification Thermodynamically Kinetically

41: Kinetic Justification Rate given by: Concentration becomes by: Substituting by partial pressure

42: Thermodynamic Justification @ constant temperature

43: Heat Exchanger Used Heat Integration If ?Tlm >100°C Else wastage of usable energy

44: Cost Estimation Profitability of the project The feasibility of any project proposal should pass the stage of preliminary cost estimation even before any further study can be done on the technical aspects Type of costs: - Capital - Operating 44

45: Capital Cost Cost of the plant ready for start-up Includes Design, and other engineering and construction supervision All items of equipment and their installation All piping, instrumentation and control systems Buildings and structures Auxiliary facilities, such as utilities, land and civil engineering work 45

46: Operating Cost Cost involved in the day to day operation of the plant. Includes Direct cost Raw Materials Utilities Operating Labor Fixed cost Insurance Local Taxes General Expenses Administration cost Distribution and selling cost 46

47: Equipments Compressors Heat Exchangers Reactors 47

48: Effect of Capacity on purchased cost Cb is the purchased cost of the equipment with base capacity Ab Ca is the purchased cost of the equipment with required capacity Aa n is the cost exponent 48

49: 49

50: Effect of time on purchased cost C is purchase cost I is the cost index 1 refers to base time when the cost is known 2 refers to time when cost is desired 50

51: 51

52: Bare Module cost estimation technique CBM is bare module equipment cost FBM is bare module cost factor CPo is the purchase cost for the base condition, i.e. atmospheric pressure and material of construction is carbon steel 52

53: Pressure factor - Fp C1, C2 and C3 are constants for each equipment type 53

54: Material FM 54

55: 55

56: Cost of manufacturing Total direct manufacturing costs (COM)= CRM + CWT + CUT + 1.33COL +0.3COM + 0.069FCI CRM is the cost of raw material CWT is the cost of waste treatment CUT is the cost of utilities COL is the cost of operating labor FCI is the fixed capital investment 56

57: CAPCOST 57

58: Results - Equipment cost 1- Compressor 58

59: Results, cont….. - Equipment cost 2- Heat Exchanger 59

60: Results, cont….. - Utility cost 60

61: Results, cont….. - Material cost 61

62: Results, cont….. The land cost is estimated to be $ 1,250,000 The operating labor cost is estimated to be $ 700,000 per year Total cost = $12,844,655 62

63: Results, cont….. The cost index for 2006 is 478.7

64: Safety and Environmental Impact The exposure limit for ammonia is 25 ppm for 8 hours exposure and 35 ppm for a 15 minutes exposure Noise low-noise let-down valves silencers Toxic hazard Explosion are not extremely dangerous

65: Conclusion Volume of the reactor 1.78 m3 (theoretical calculation) HYSYS value was 0.998 m3 Heat exchanger shell diameter of 1m and 60 tubes area of heat transfer 39.48 m2 with a length of 2.35 m. Total capital cost was $15,548,000

66: Thank you