Trainer A.R.KANADE [email protected] Standard Steam Circuit - Energy Balance BoilerProcessPlant PowerPRDS PlantUnit Flue gases Blow down HP steamPRS

Trainer [email protected]

Standard Steam Circuit - Energy Balance

Boiler ProcessPlant Plant

Power PRDS Plant Unit

Fluegases

Blowdown

HP steam PRS unit

Condensate

losses

losses

Fuel100%

15%

5%

80%

3%

55% to process

20%

2%

Trainer [email protected] Selection of Working Pressure

• What is the right pressure for given processObjective should be process temp.Heating water to 850C can be achieved using steam at any pressure above atmospheric.

• Would you use steam at - (a) 2 barg.sat.

Or (b) at 7 barg.sat. Or (c) superheated at 2barg.2000C?

• For indirect heating, latent heat released will be -(a) 517.6 Kcal/Kg.(b) 489.9 Kcal/Kg. 5.3% more consumption(c) 517.6 Kcal/Kg. At a very slow rate

Trainer [email protected] Selection of Working Pressure -

contd.

For indirect heat transfer process -

The right choice is ‘the lowest possible’.Rule of thumb - Pressure giving T(steam) + 350C

For Direct heat transfer process -

It does not matter so long as you ensure thorough mixing of steam with the product.


This will have the following advantages:

Smaller bore steam mains needed and therefore less heat (energy) loss due to the smaller surface area.

Lower capital cost of steam mains, both materials such as pipes, flanges and support work and labour.

Lower capital cost of insulation (lagging).

Dryer steam at the point of usage because of the drying effect of pressure reduction taking place near the equipment.

The boiler can be operated at the higher pressure corresponding to its optimum operating condition, thereby operating more efficiently.

The thermal storage capacity of the boiler is increased, helping it to cope more efficiently with fluctuating loads, and a reduced risk of priming and carryover

How much reduction in thermal storage capacity of a 10.5 barg rated boileroperated at 7 barg.?

Distribute at High Pressure


On the basis of:

Fluid Velocity Pressure Drop

How Do We Pipe Size?

SpiraxCustomer


Pipe Sizing

Greater Cost Greater Heat Loss Greater Volume of Condensate

Formed

Lower Pressure to Steam Users, or Not Enough Volume of Steam Water Hammer and Erosion


Methods of Steam-pipe Sizing

Velocity Method

For saturated steam system

Ideally suited for Process use

Pressure Drop Method

For superheated steam

Ideally suited for Power Plants & Co-gen units


Methods of Steam-pipe Sizing - contd.

Factors governing the method to be used -

Steam Pressure and Temperature

Size of distribution network

Longer lengths

Larger pipe sizes

Criticality of pressure drop & th.stresses

Mostly for Power plants and HP cogen


Methods of Steam-pipe Sizing

Rules of thumb to be followed -

Maximum velocity 15 m/s for LP wet steam(flash steam)

25 m/s for sat.steam long lengths

30 m/s for sat.steam short tappings

40 m/s for superheated steam

Normal Pressure Drop Less than 10% inlet pressure

Less than 1 Kg/cm2 for given length of piping.

Equivalent length of piping - Add 10% for fittings in the line.

Trainer [email protected] Pipeline Capacities at Specific Velocities

PressureVelocity kg/hbar m/s 15mm 20mm 25mm 40mm 50mm 80mm

100mm 150mm

1.0 15 8 17 29 65 112 260 470 1020

25 12 26 48 100 193 445 730 1660

40 19 39 71 172 311 640 1150 2500

4.0 15 19 42 70 156 281 635 1166 2460

25 30 63 115 270 450 1080 1980 4225

40 49 116 197 456 796 1825 3120 7050

10.0 15 41 95 155 372 626 1485 2495 5860

25 66 145 257 562 990 2205 3825 8995

40 104 216 408 910 1635 3800 6230 14390


Steam-pipe Sizing Examples

Size the line to carry -

(a) 300 kgs/hr.steam at 1 barg to FWT 150 m.away

(b) 1100 kgs/hr.steam at 10 barg to a drier 300m.away

(c) Superheated steam 2TPH at 15 barg.300C to turbine at a distance of 50 m.


Waterhammer - a phenomenon

Steam has low density but high velocity

WP 10 barg Density 5.5 Kg/m3 Velocity 25m/s

Condensate has high density but low velocity

WP 10 barg Density 909 Kg/m3 Velocity 3m/s

Impact or Momentum = Mass X VelocityCondensate having 160 times mass density travelling

at 10 times it’s normal velocity will exert

1600 times greater impact.


WaterhammerSAGGING MAIN

Slug of water from condensate

Vibration and noise caused by

waterhammer

Condensate


What is water-hammer?

Water-hammer is the hammer like impact due to fluid flow in a pipeline.

This can happen in any line carrying two-phase flowSteam lines with lot of condensed steam not properly drainedCondensate lines with flashing of condensate in the line.

The effect would be - Severe mechanical vibrations Heavy leakages from joints Ruptured pipelines


Ineffective, and Proper Drain Points

Steam

Steam

Condensate

PocketSteam trap

Correct

Incorrect

25/30mm

Cross-Section

Cross-Section


Steam Line Reducers

Steam

Steam

Condensate

Correct

Incorrect


Branch Connections

CorrectIncorrect

Steam Steam

Condensate


Shut off Valve

Trap Set

Main

Drop Leg

Trainer [email protected] Warm Up Loads/Running Loads(kg)

per 50m of Steam Main

SteamPressureBar g 50 65 80 100 125 150 200 250 300 350 400 450 500 600

99.59.3

15.111.3

19.714.1

28.116.5

38.120.6

49.424.5

7431.5

10539

13946.5

16451.5

21660

27264

32072

43688

109.99.8

15.711.9

20.414.6

29.216.9

39.621.3

51.325

7733

10941

14449

17154

22462

28267

33275

46390

1210.410.9

16.513.0

21.615.7

30.717.7

41.722.5

54.126

81.136

11545

15253

18059

23667

29873

35081

48897

MAINS SIZE-mm

Figures in italics represent running loads

Ambient temperature 200C, insulation efficiency 80%


Calculation of Pipe Expansion

Expansion ( ) = L x )

Where: L = Length of pipe between anchors (m) C = Expansion coefficient

0

0

t

t o

x (mm

= Temperature difference

Trainer [email protected] Recommended Support Spacing

for Steel Pipes

Nom. PipeSize mm.Steel/Copper

Interval of Horizontal runmetres

Interval of Vertical run metres

Bore O/D Mild Steel Copper Mild Steel Copper

1215

1518

--2.0

1.01.2

--2.4

1.21.4

2025

2228

2.42.7

1.41.7

3.03.0

1.72.0

3240

3542

2.73.0

1.72.0

3.03.6

2.02.4

5065

5467

3.43.7

2.02.0

4.14.4

2.42.4

80100

76108

3.74.1

2.42.7

4.44.9

2.93.2

125150

133159

4.44.8

3.03.4

5.35.7

3.64.1

200250

194267

5.15.8

----

6.05.9

----


Twin Pipe Support Bracket

Rollers for Steel Pipework

Chair & Roller Chair Roller & Saddle


Air Venting

Steam Main

Thermodynamic Steam Trapwith optional Blowdown andfor ease of maintenance a universal coupling

Air

Balanced Pressure Air Vent


Heat Emission from Bare PipesTemp. diff. Steam to Air

Pipe Size

15mm 20mm 25m 32mm 40mm 50mm 65mm 80mm 100mm 150mmo C W/m

56 54 65 79 103 108 132 155 188 233 324

67 68 82 100 122 136 168 198 236 296 410

78 83 100 122 149 166 203 241 298 360 500

89 99 120 146 179 205 246 289 346 434 601

100 116 140 169 208 234 285 337 400 501 696

111 134 164 198 241 271 334 392 469 598 816

125 159 191 233 285 321 394 464 555 698 969

139 184 224 272 333 373 458 540 622 815 1133

153 210 255 312 382 429 528 623 747 939 1305

167 241 292 357 437 489 602 713 838 1093 1492

180 274 329 408 494 556 676 808 959 1190 1660

194 309 372 461 566 634 758 909 1080 1303 1852


Calculation of Heat Transfer

Q = U. A. t

Where Q =heat transfer rate (W)

U =overall heat transfer coefficient (W/m2K)

A =mean surface area (m2)

t =temperature difference (K)


THERMAL INSULATION

TO REDUCE HEAT LOSS

TO PROTECT FROM DAMAGE/BURNS

TO PROVIDE WEATHER PROOFING


DESIRED PROPERTIES

THERMAL

–TEMP.RESISTANCE–LOW CONDUCTIVITY

MECHANICAL

–SHOCK RESISTANCE–POROSITY FOR AIR BINDING

CHEMICAL

–INERT ACTIVITY


INSULATION MATERIALS

MINERAL WOOL (IS-3677)

- Most commonly used

GLASS WOOL

- Specified as alternative

CALCIUM SILICATE OR MAGNESIA

- Use as Refractory

ASBESTOS

- Used for small lines


INSULATION MATERIALS

• WIRENETTING

- TO KEEP INSULATION IN PLACE

• SURFACE COVERING

- TO PROTECT INSUL. FROM DAMAGE

- GI/AL SHEET OF 22/24g THK.

- CEMENT PLASTER

- THERMOSETTING COMPOUND

Trainer [email protected] INSULATION

APPLICATION METHODSWIREBRUSHING HOT SURFACES

PREPARATION OF INSULATION MATTRESSES OF CORRECT DENSITY

(USUALLY 120 OR 150 Kg/M3)

WRAPPING WITH WIRENETTING

(USUALLY 24g GI WIRENET USED)

BINDING THE LINEAR JOINTS


APPLICATION (contd.)

SURFACE COVERING WITH METAL

(USUALLY AL.CLADDING WITH 22g OR 24g SHEET)

JOINT PREPERATION WITH OVERLAP TO AVOID WATER SEEPAGE.

MAKING BOXES FOR FITTINGS SUCH AS VALVES AND FLANGES.

MITER CUT SHAPES FOR BENDS.


INSULATION STANDARD

CURRENTLY IS-7413 IS APPLICABLE

SPECIFIES METHODS OF

–MATERIAL SELECTION–APPLICATION OF INSULATION MATERIALS–MEASUREMENTS OF FINISHED SURFACES.


HEAT LOSS FROM UNINSULATED SURFACES

INTERNAL TEMP. HEAT LOSS

IN DEG.C IN KCAL/HR.M2

• 291

• 894

200 3065

• 6690

400 12115

Trainer [email protected] HEAT LOSS FROM INSULATED

SURFACES

244320370455400

170220255310420300

122150190244338200

7395135100

364750

100thk80thk65thk50thk40thk25thkTemp

Temp.in deg.C Thk. In mm. and Heat Loss in Kcal/hr/sq.mtr.

Trainer [email protected] ECONOMIC THICKNESS OF

INSULATION

80805050400

80655040300

80505040200

65504025150

50402525100

2525252550

FlatsDia >150Dia > 50Dia < 50TEMP.

Documents

Trainer A.R.KANADE [email protected] Standard Steam Circuit - Energy Balance BoilerProcessPlant PowerPRDS PlantUnit Flue gases Blow down HP steamPRS