Steam Trap Calculation Sheet - 02 [PDF]

Zitiervorschau

Pipe Identification

Steam Temperature o

Test

C 174.5

Steam Latent Heat

Pipe Length

kJ/kg 2038

m 275

Outside Air Temperature o

C 5

Outer Material Surface Temp o

C 25

Outer Diameter of Steam Pipe

Insulation Material Thickness

Outer Material Thickness

Wind Speed

Insulation Thermal Conductivity

Wind Speed Coefficient

mm 216.3

mm 50

mm 0.5

m/s 2

kJ/mhoC 0.1827

1.7

Wind Speed Coefficient

D1

D2

D3

1.7

mm 216.3

mm 316.3

mm 317.3

Gs-Ta o

C 20

Convective HTC

Thermal Resistance

10

mhoC/kJ 0.331270793952

Heat Dissipation Generated Steam kJ/m.h 511.6660

kg/h 69.04

Gs : Surface Temperature of outer Material (degC) Ta : Outside air Temperature (degC) Gs - Ta 20 40 60 80 100

Wind Speed (m/s) 1 2 3 4 5

as 10 10.5 11.5 12.3 13.3

Coeffficient 1.5 1.7 1.85 2 2.2

Pipe Identification

Steam Temperature o

Test Test

F 100 250

Process Fluid Temperature o

F 50 50

Steam Latent Heat

Pipe Length

Heat Transfer Factor

Insulation Efficiency

btu/lb 857 880

ft 200 100

Btu/sq ft/oC/hr 3.1 2.44

-

0 0.75

Lineal Feet of Pipe Line per Condensate Load sq ft of surface mm 0.355 0.191

lb/hr 101.9 72.6

1. BACKGROUND PT South Pacific Viscose (SPV) / Owner plans to make a new Closing Loops of Utility Streams Facilities. Current situation in some processing area, water effluent from utility or untreated stream are being discharged into storm drains, which potentially contaminates the storm water with chemicals and solid matters. By applying closing loops of utility stream systems, the water from utility streams will be collected and might either be reused by feeding back to Water Treatment Plant or being discharged after the contaminants being separated.

Among the utility streams that are being discharged into storm drains are steam trap condensates. These steam trap condensates need to be collected in some pits, and then will be sent to WTM cooling water tank. The condensate flowrates need to be determined before advancing to the design of the facility for steam traps condensate collection and transfer. Initially, the flowrates already being calculated using steam trap capacity approach. The aproach is to determine the flowrate from steam traps capacity based on vendor data. There are several brand of steam traps, the brand which has the highest capacity will be used as the basis for flowrate determination of every steam traps. Then 10% of the steam traps total capacity is assumed to be the condensate load of this closing loop system. Below are the tabulation of the calculation based on this approach:

Table 1. Steam Trap Condensate Disharge

Steam Trap Size

Steam Trap Capacity

(Inch) 1/2 3/4 1

(kg/h) 410 680 1250

Condensate Load Per Steam Trap (10% of Steam Trap Capacity) (kg/h) 41.0 68.0 125.0

In order to validate that this approach can cover the actual formed condensate rate discharged by the steam traps, the different method of calculations which use heat loss approach need to be conducted. The calculations are presented in the following sections.

2. REFERENCE - Steam Trap, Yoshitake - How to Trap: Steam Tracer Lines, Armstrong International - Calculating Condensate Load for Steam Tracer Lines, Velan Steam Traps

3. STEAM TRACER CONDENSATE FLOWRATE ESTIMATION USING HEAT LOSS APPROACH This approach estimates the flowrate of the condensate, based on actual heat loss of the steam inside the steam tracer. The formula for this approach is as follows:

Q=(𝐿⨯𝑈⨯𝑇⨯𝐸)/(𝑆⨯𝐻) Where: Q = Condensate Load in lb/hr L = Length of Product pipe between tracer line traps (ft) U = Heat Transfer Factor (Btu/sq ft/oF/hr) ΔT = Temperature differential in oF E = 1 minus efficiency of the insulation S = Linear feet of pipe line per sq ft of surface H = latent heat of steam in btu/lb

The heat transfer factor (U), can be obtained from graph below:

Figure 1. Heat Transfer Factor

The linear pipe length per sq ft of pipe can be obtained from standard dimension of pipe below: Table 2. Standard Pipe Dimensions for Sch40 Pipe

Condensate flowrate of one point of the steam traps will be calculated using this approach: a. Heat Transfer Factor (U) Estimation Pipe Size Steam Pressure Steam Temperature Process Fluid Temperature Temperature Difference Heat Transfer Factor (U) (from the graph)

: : : : : : : : :

10" 10 145.0 184.1 363.4 40 104.0 259.4 2.8

bar(g) psig o C o F o C o F o F Btu/sq ft/oF/hr

b. Condensate Load Calculation Pipelength Heat Transfer Factor Temperature Difference Insulation Efficiency (Note 1) E factor Linear Pipe Length per sq ft pipe Latent Heat of the Steam

Q

=

= =

328.1

x

: : : : : : : : : 2.8 0.381

100 328.1 2.8 259.4 0.75 0.25 0.381 477.6 859.1 x x

m ft Btu/sq ft/oF/hr o F (One minus insulation efficiency) ft kcal/kg Btu/lb

259.4 859.1

x

0.3

181.983 lb/hr 82.55 kg/hr

The same calculation method is done for other size.

Pipe Size Steam Trap Size Steam Pressure Steam Temperature Process Fluid Temperature Temperature Difference Heat Transfer Factor (U) (from the graph) Pipelength Heat Transfer Factor Temperature Difference Insulation Efficiency (Note 1) E factor Linear Pipe Length per sq ft pipe Latent Heat of the Steam

Condensate Load

Sample Case 1

Sample Case 2

Sample Case 3

: : bar(g) : psig : o C: o F: o C: o F: o F: [Btu/sq ft/oF/hr] :

4" Pipe 4" 1/2" 10 145.0 184.1 363.4 40 104.0 259.4 3

6" Pipe 6" 3/4" 10 145.0 184.1 363.4 40 104.0 259.4 2.85

10" Pipe 10" 1" 10 145.0 184.1 363.4 40 104.0 259.4 2.8

m: ft : Btu/sq ft/oF/hr : o F: : : ft : kcal/kg : Btu/lb :

100 328.1 3 259.4 0.75 0.25 0.948 477.6 859.1

100 328.1 2.85 259.4 0.75 0.25 0.629 477.6 859.1

100 328.1 2.8 259.4 0.75 0.25 0.381 477.6 859.1

lb/hr : kg/hr

78.4 35.5

112.2 50.9

182.0 82.5

Note: 1. Engineering practice for insulation efficiency is 90% for newly installed insulation. But for old insulation, the efficiency may drop to below 80%.

4. STEAM PIPE CONDENSATE FLOWRATE ESTIMATION USING HEAT LOSS APPROACH This approach estimates the flowrate of the condensate, based on actual heat loss of the steam inside the steam pipe. The calculation will utilize the heat loss of the steam to the outside air. The condensate flowrate is obtained by dividing the heat loss with the steam latent heat. The heat loss can be estimated by following formula

Q=(𝑇_𝑠−𝑇_𝐴)/𝑅 Where: Q = Amount of heat loss per 1 m pipe (kJ/m.h) Ts = Steam temperature (oC) Ta = Outside air temperature (oC) R = Thermal resistance (m.h.oC/kJ) The thermal resistance is calculated by following formula:

R=1/2π(1/𝜆 ln⁡〖𝐷 _2/𝐷_1 +2/(𝐷_3 ℎ) 〗 ) Where: λ = Thermal conductivity of insulating material (kJ/m.h.oC) D1 = Outer diameter of steam pipe (mm) D2 = Outer diameter of insulating material (mm) D3 = Outer diameter of outer material (mm) h = Coefficient of convective & radiative heat transfer between outer material and outside air Coefficient of convective and radiative heat transfer (h) can be obtained from following table: Tsur - Ta

20

40

60

80

100

h

10

10.5

11.5

12.3

13.3

Tsur = Surface temperature of outer material (oC) Ta = Outside air temperature (oC) In case of outdoor aplication with wind, the heat transfer coefficient (h) should be multiplied by following coefficient: Wind Speed (m/s) Coefficient

1 1.5

2 1.7

3 1.85

4 2

The calculation for one point of steam trap condensate from steam pipe: a. Coefficient of Convective and Radiative Heat transfer determination o Steam Temperature : 184.1 C o Outer material temperature : 35 C o Outside air temperature : 27.1 C Wind speed : 2.75 m/s

5 2.2

(saturated T for 10 bar steam) (assumption) (design basis) (design basis)

heat transfer coefficient correction factor corrected heat transfer coeff.

: : :

10 1.85 18.5

(based on table above) (based on table above, for 2.75 m/s wind speed)

b. Thermal Resistance Calculation Outer diameter of steam pipe Insulation thickness Outer diameter of insulation Outer material thickness Outer diameter of outer material Thermal conductivity of insulation

: : : : : :

323.8 50 423.8 0.5 424.8 0.223

mm (12") mm mm mm mm kJ/m.h.oC (rockwool insulation @ steam temperature)

Thermal resistance : 1 R = 2π =

0.192

x

(

1 0.223

m.h.oC/kJ

x

ln

423.8 323.8

+

424.8

2 x

18.5

)

c. Heat loss calculation Thermal resistance Steam Temperature Outside air temperature Pipelength Heat loss per 1 m pipe : 184.1 Q = =

: : : :

0.192

0.192 184.1 27.1 100

m.h.oC/kJ o C o C m

2

(note 1)

27.1

817.19

kJ/m.h

817.19 x 163437.48

100 kJ/h

Total Heat Loss : Q

= =

d. Condensate load calculation Heat Loss Steam Latent Heat Condensate Load

x

: :

163437.5 1999.7

kJ/h kJ/kg

:

81.7

kg/h

The same calculation method is done for other size: Sample Case 1

Sample Case 2

Sample Case 3

4" Pipe 1/2" 184.1 35 27.1 2.75

8" Pipe 3/4" 184.1 35 27.1 2.75

12" Pipe 1" 184.1 35 27.1 2.75

(based on table) : (based on table) : :

10 1.85 18.5

10 1.85 18.5

10 1.85 18.5

Outer diameter of steam pipe Insulation thickness Outer diameter of insulation Outer material thickness Outer diameter of outer material Thermal conductivity of insulation

mm : mm : mm : mm : mm : kJ/m.h.oC :

114.3 50 214.3 0.5 215.3 0.223

219.1 50 319.1 0.5 320.1 0.223

323.8 50 423.8 0.5 424.8 0.223

Thermal Resistance

m.h.oC/kJ :

0.449

0.268

0.192

m : kJ/m.h : : kJ/.h :

100 349.9 2.0 69983.7

100 585.0 2.0 116994.9

100 817.2 2.0 163437.5

kJ/kg : kg/h :

1999.7 35.0

1999.7 58.5

1999.7 81.7

Steam Trap Size Steam Temperature Outer material temperature Outside air temperature Wind speed heat transfer coefficient correction factor corrected heat transfer coeff.

Pipelength Heat Loss per 1 m pipe Safety Factor (note 1) Total Heat Loss Steam Latent Heat Condensate Load

: o C: o C: o C: m/s :

Note: 1. Engineering practice safety factor for steam header condensate calculation is 2 (two).

5. CALCULATION RESULT COMPARISON Previously, the calculation have been done for one sample point of each steam trap size. The summary of the result is tabulated below: Table 3. Comparison of calculated condensate rate from steam trap between heat loss method and initial method

Steam Trap Size (Inch) 1/2 3/4 1

Steam Trap Capacity (kg/h) (kg/h) 410 680 1250

10% of Steam Trap Steam Tracing Heat Loss Capacity (kg/h) Sample Case Condensate Rate (kg/h) (kg/h) 41.0 1 35.5 68.0 2 50.9 125.0 3 82.5

Steam Pipe Heat Loss Sample Case Condensate Rate (kg/h) 1 35.0 2 58.5 3 81.7

6. CONCLUSION According to the comparison table above, the calculated condensate rate based on heat loss method from both steam pipe and steam trace are still less than 10% steam trap capacity (initial method). Therefore, it can be concluded that the initial method of 10% steam trap capacity is feasible to cover the actual formed condensate that will be collected in the close loop system.