DESIGN CALCULATION FOR THE CONSTRUCTION OF A STEAM BOILER - Main.pdf

Instruments and Materials Instruments 

2 Pressure gauges



1 Drain Valve



1 Pressure safety Valve



1 Feed check valve



1 Pressure relief valve



1 Water gauge



Name Plate



Ring heaters



1 Thermostat



Insulation/Lagging



Mains control switch



Flexible Wire

Materials 

Boiler Feed Water (distilled water)



Stainless steel sheet



Circular weight



Aluminium Spring



1 Steam Hose



1 Water Hose

DESIGN CALCULATION FOR THE CONSTRUCTION OF A STEAM BOILER The method that will be used for the designing and constructing of the electric steam boiler is the Direct Coding Method. A) Generating the Power needed to produce steam at the desired Mass Flowrate Basis: 300cl/s

Density of steam;

From Steam Tables, The Specific Enthalpies of saturated steam and water are given in the table below; T (K)

Hsteam (kJ/Kg)

T1= 417.15

H1= 2738.1

T= 418.15

Hsteam= ?

T2= 419.15

H2= 2740.6

By interpolation; Saturated Steam at 145°C

Hwater (kJ/Kg) H1= 606.3 Hwater= ? H2= 614.9

Saturated Water at 145°C

Where; = 24.3Kg/hr cp,water(30°C) = 4.179 J/Kg.K cp,water(145°C) = 4.30 J/Kg.K cp,avg =(cp,water(30°C) + cp,water(145°C))/2 = 4.24 J/Kg.K

B) Generating saturated steam at 145oC From steam tables; At 145oC (418.15K) The pressure exerted by saturated steam at 145oC is given as follows; T (K)

P (kpa)

T1= 417.15

P1= 404.20

T= 418.15

P= ?

T2= 419.15

P2= 427.09

Using the method of interpolation,

Operating pressure P = 415.65kpa C) Calculating the internal thickness under normal operating pressure The steam boiler to be designed is cylindrical.

The Boiler is to be designed to operate for 5(five) hours

Therefore; taking into consideration that the water level in the boiler is 80% Then;

Taking the radius, r of the cylinder to be = 23cm = 9.1in

Under the ASME BPV code (section VIII D.1 Part UG-27) The minimum thickness, t, of a pressure vessel that is cylindrical is given as;

Where t = minimum required thickness of shell P = internal design pressure R = inside radius of the shell course when consideration E = Joint efficiency for, or the efficiency of, appropriate joint in cylindrical or spherical shells or the efficiency of ligaments between openings. For welded vessels, the efficiency in UW-12 (of ASME BPV code section VIII D.1) S = max. allowable stress value (from UG-23) Operating pressure, P = 415.65kpa (60.29psi) The max. allowable stress value, S, for carbon and low alloy steel at temp between 20 and 650oF for grade SA-515 70 = 17500psi The steam boiler is fabricated by welding; therefore, the efficiency of the welded joint is gotten from section VIII D. 1 Part UW-12j E = 0.85, efficiency of spot- examined joints of shell R = 23cm = 9.1in

Assuming a corroded condition, a corrosion allowance, C.A factor is used The C.A factor is 0.079in based on ASME BPV code (for non-severe corrosion)

D) Determining the design pressure The design pressure is the pressure used in the design of the vessel. The design pressure is gotten by making the operating pressure higher by either 30psi or 10%; whichever is higher.

Thus, the design pressure is taken to be 90.29psi E) Determining the minimum thickness under the design pressure

Under non-severe corroded conditions,

Determining MAWP for 0.134in,

Determining MAWP for 0.116in,

F) Determining the thickness of the head There are two (2) formulae that can be used based on their constraints; i.

From the ASME BPV code (sec. VIII D. 1) (Circular Flat Heads)

This formula shall be applied under the following conditions; a. When d does not exceed 24 in. b. th/d is not less than 0.05 nor greater than 0.25 i.e.

c. Head thickness, th is not less than the shell thickness. Therefore; P = Design pressure, psi E = Joint efficiency. d = inside diameter of shell, in S = maximum allowable stress value of material, psi t = minimum thickness of head, exclusive of Corrosion Allowance, in th = actual thickness of head.

P = 90.29 psi S = 17500 psi E = 0.85 d = 18.2

Checking the Limitation of the formula;

Therefore, this formula cannot be used due to the contradiction between the result and the boundary conditions. ii.

Using the second formula which states;

Where, Cmin = 0.20 Where tr = required thickness of seamless shell under pressure.

ts = actual thickness of shell. tr = 0.24 in ts = 0.134 in

Conditions for applying this formula include; 

If a value of

less than 1 is used in calculation, t, the shell thickness ts shall be

maintained along the distance inwardly from the inside face of the head equal to at least

.

Testing; Since, 1.79 is not less than 1 therefore, is satisfactory

Due to the large amount of power needed to produce 300cl/s of saturated steam at 145°C, the production rate of the saturated steam has to be reduced so as to make the project attainable on a laboratory scale. The modeled laboratory scale electric steam boiler’s production rate is taken to be a quarter of the original basis of 300cl/s. A) Generating the Power needed to produce steam at the desired Mass Flowrate New Basis:

= 75cl/s

Density of steam;

From Steam Tables, The Specific Enthalpies of saturated steam and water are given in the table below; T (K)

Hsteam (kJ/Kg)

Hwater (kJ/Kg)

T1= 417.15

H1= 2738.1

H1= 606.3

T= 418.15

Hsteam= ?

Hwater= ?

T2= 419.15

H2= 2740.6

H2= 614.9

By interpolation; Saturated Steam at 145°C(418.15K)

Saturated Water at 145°C

Where; = 6.075Kg/hr cp,water(30°C) = 4.179 J/Kg.K cp,water(145°C) = 4.30 J/Kg.K cp,avg =(cp,water(30°C) + cp,water(145°C))/2 = 4.24 J/Kg.K

B) Generating saturated steam at 145oC From steam tables; At 145oC (418.15K) The pressure exerted by saturated steam at 145oC is given as follows; T (K)

P (kpa)

T1= 417.15

P1= 404.20

T= 418.15

P= ?

T2= 419.15

P2= 427.09

Using the method of interpolation,

Operating pressure P = 415.65kpa

C) Calculating the internal thickness under normal operating pressure The steam boiler to be designed is cylindrical.

The Boiler is to be designed to operate for a maximum time of 5(five) hours

Therefore; taking into consideration that the water level in the boiler is 75% Then;

Taking the radius, r of the cylinder to be = 14.71cm = 5.79in

Under the ASME BPV code (section VIII D.1 Part UG-27) The minimum thickness, t, of a pressure vessel that is cylindrical is given as;

Where t = minimum required thickness of shell P = internal design pressure R = inside radius of the shell course when consideration E = Joint efficiency for, or the efficiency of, appropriate joint in cylindrical or spherical shells or the efficiency of ligaments between openings. For welded vessels, the efficiency in UW-12 (of ASME BPV code section VIII D.1) S = max. allowable stress value (from UG-23) Operating pressure, P = 415.65kpa (60.29psi) The max. allowable stress value, S, for carbon and low alloy steel at temp between 20 and 650oF for grade SA-515 70 = 17500psi The steam boiler is fabricated by welding; therefore, the efficiency of the welded joint is gotten from section VIII D. 1 Part UW-12j E = 0.85, efficiency of spot- examined joints of shell R = 14.71cm = 5.79in

Assuming a corroded condition, a corrosion allowance, C.A factor is used The C.A factor is 0.079in based on ASME BPV code (for non-severe corrosion)

D) Determining the design pressure The design pressure is the pressure used in the design of the vessel. The design pressure is gotten by making the operating pressure higher by either 30psi or 10%; whichever is higher.

Thus, the design pressure is taken to be 90.29psi E) Determining the minimum thickness under the design pressure

Under non-severe corroded conditions,

Determining MAWP for 0.1117in,

Determining MAWP for 0.1025in,

F) Determining the thickness of the head There are two (2) formulae that can be used based on their constraints; i.

From the ASME BPV code (sec. VIII D. 1) (Circular Flat Heads)

This formula shall be applied under the following conditions; a. When d does not exceed 24 in. b. th/d is not less than 0.05 nor greater than 0.25 i.e.

c. Head thickness, th is not less than the shell thickness. Therefore;

P = Design pressure, psi E = Joint efficiency. d = inside diameter of shell, in S = maximum allowable stress value of material, psi t = minimum thickness of head, exclusive of Corrosion Allowance, in th = actual thickness of head. P = 90.29 psi S = 17500 psi E = 0.85 d = 11.58in

Checking the Limitation of the formula;

Therefore, this formula cannot be used due to the contradiction between the result and the boundary conditions.

ii.

Using the second formula which states;

Where, Cmin = 0.20 Where tr = required thickness of seamless shell under pressure. ts = actual thickness of shell. tr = 0.24 in ts = 0.1117 in

Conditions for applying this formula include; 

If a value of

less than 1 is used in calculation, t, the shell thickness ts shall be

maintained along the distance inwardly from the inside face of the head equal to at least

.

Testing; Since, 2.15 is not less than 1 therefore,

is satisfactory

G) Calibration of the Spring for the Exit of Stream of steam The Operating pressure that will be exerted by the saturated steam at 145°C is 415.65 kPa.

Assuming an opening diameter of 2cm;

Cross Sectional Area (CSA) of the exit stream =

Therefore, the spring has to be pulled to a force of 816.13N enclosed in a circular area that has a diameter of 5cm so that the force exerted by the saturated steam can counter balance the force acting on the spring.