Condensate Removal

Condensate Removal

Understanding stall

2

What is stall?

No movement of condensate = back-up in heater

Condensate Removal

3

This is pretty easy - what’s the problem?

We might not always know the pressures:

• Condensate backpressure?

• Full load pressure in the heat exchanger?

• Min. load pressure in the heat exchanger?

If an EXISTING installation is having problems due to stall – fit pressure gauges to diagnose the problem.

Condensate Removal

4

Symptoms and effects of stall?

Condensate Removal

5

Calculating stall in a heat exchanger

Use a stall chart

Quick and good enough for most practical purposes

Condensate Removal

6

The Stall Chart

It predicts:

• How the steam temperature varies with load

• How the secondary water temperature varies with load

Condensate Removal

7

The Stall Chart

Q = m.hfg = U.A.(Tsteam – Tprocess) = m.Cp.(Tout – Treturn)

Q

8

Steam temperature

Inlet temperature

Outlet temperature

100% 0%Percentage load

The classic stall chart

Stall Chart

9

Steam temperature

Inlet temperature

Outlet temperature

Backpressure

Add the backpressure line


Stall Chart

10

Steam temperature

Inlet temperature

Outlet temperature

atm Backpressure100oC

System stalls here


?%

Stall Chart

11

Steam temperature

Inlet temperature

Outlet temperature


Consider a minimum load – 20%

Steam temperature under backpressure line

Percentage load100% 0%20%

System will stall

SYSTEM STALLS

12

Steam temperature

Inlet temperature

Outlet temperature


Consider a minimum load – 80%

Steam temperature above backpressure line

Percentage load100% 0%80%

No stall

NO STALL

13

4 bar g

20o

C


1. What is steam temperature at no load?

Steam temperature = process temperature = 60oC

60o

C

Get other information

14

4 bar g

20o

C


1. What is steam pressure at no load?

0.199 bar absolute

60o

C

0.199 bar a


15

20o

C


2. What is steam pressure at stall?

Steam pressure = backpressure = 0.5 bar g

60o

C

152oC

0.5 bar g backpressure


16

20o

C


3. What is the stall percentage?

Read off bottom scale

60o

C

152oC

56%

112oC


17

20o

C


4. What is the sec. inlet temp. at stall?

Read off side scale

60o

C

152oC

56%

112oC

38o

C


18

Stall

A bigger exchanger will operate at a lower pressure for the same heating load.

5 bar g 1 bar g

50 kW 50 kW

Condensate Removal

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Full load

Steam temperature

Inlet temperature

Outlet temperature

50 kWQ = U A DT

Stall Chart

20

Full load

Steam temperature

Inlet temperature

Outlet temperature

50 kWQ = U A DT

Stall Chart

21

Specification Sheet Detail

Data: Foul condition

Heat To Be Exchanged: 7,939,000WSurface, Effective: 231m2

MTD Foul Condition: 49.4°C

Heat transfer coefficient, U: =7,939,000W231m2 x 49.4 °C

= 696 W/m2 °C

Data: Clean condition

Inlet temperature: 75.6°COutlet temperature: 79.0 °CHeat transfer coefficient. U: 1694W/m2 °C

MTD Clean condition: =7,939,000W231m2 x 1694W = 20.3 °C

SAT STEAM TEMP = 97.6 °C ?

PRESSURE = 0.93 bar absolute = Vacuum conditions!!!!

75.6°C+ 79°C 2Steam Temp (clean) = 97.6 °C= 20.3 °C +

Mean process temp.

22

If system is NEVER in stall

Use a float/thermostatic trap

(& no vacuum breaker)

If system is SOMETIMES in stall

Use a APT or pump trap combination

If system is ALWAYS in stall

Use a pump only

Selecting the correct trapping device

Condensate Removal

Condensate line sizing - discharge lines and pumped lines

24

Condensate discharge line sizing

Piping condensate from:

• a steam trap

25


• a pump trap


26


• a steam trap

• a pump trap

• a pump


27

Pumping

Trapping

Trapping & Pumping

Each condensate system is different . . .

. . . How?


28

When trapping,

Discharge line - sized on:

• Full load

100% load

Maximum flash steam

600 kg/h

5 bar g

1 bar g

Trapping

http://172.20.3.2/international/resources/cad/products/steam-traps/preview/ball-float-steam-traps.asp?drawing_id=675

Lifting pipe = 32 mm

600 kg/h

5 bar g

1 bar g

Falling pipe = 25 mm

30

When pumping, from vented systems,

Discharge line - sized on 4 x the pump capacity

(Based on average pump discharge is approximately 25% of total cycle time)

Maximum load 600 kg/h

Vent

Receiver

Motive steam pressure: 6 bar g

Back pressure: 1 bar g (10metres)

Mechanical pumps

http://172.20.3.2/international/resources/cad/products/condensate-pumps-and-energy-recovery/preview/mechanical-pumps-and-pump-traps.asp?drawing_id=979

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600 kg/h

6 barg

Mechanical pumps

Typical mechanical DN25 pump capacity chart

1150 kg/hMaximum Capacity

32

Condensate line sized on 4 x 1150 kg/h = 4,600 kg/h

When pumping, from vented systems,

Discharge line - sized on 4 x the pump capacity

(Based on average pump discharge is approximately 25% of total cycle time)

Maximum load 600 kg/h

Vent

Receiver

Motive steam pressure: 6 bar g

Back pressure: 1 bar g (10metres)

Mechanical pumps


33

4600 kg/h


34

When pumping, for electrical pumps,

Pump selected on:

• The specified condensate load

600 kg/h

15m backpressure

Electrical CRUs

35


Pump selected on:

• The specified output rate

Electrical CRUs

600 kg/h

17 metres delivery head

Pump selectionPump selection

15 metres backpressure

36


Pump selected on:

• The pump capacity at the PDH

Electrical CRUs

Pump capacity 1300 kg/hPump capacity 1300 kg/h

600 kg/h

15 metres backpressure

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1300 kg/h


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With a pump and trap, in a closed system

Discharge line sized on either 4 x pumping capacity or maximum process load, whichever is the greater.

5 Bar g

PumpMotive pressure: 6 bar g

TrapBack pressure: 1 bar g

Maximum Duty: 1,400 kg/hStall Condition: 800 kg/h

Pump and trap



39

800 kg/h 1150 kg/hMaximum Capacity

6 barg

Mechanical pumps


40

Condensate line sized on 4 x 1150 kg/h = 4,600 kg/h



5 Bar g

PumpMotive pressure: 6 bar g

TrapBack pressure: 1 bar g

Maximum Duty: 1,400 kg/hStall Condition: 800 kg/h

Pump and trap



4600 kg/h


Pumping condition

5 bar g

1 bar g

1400 kg/h


Full load condition

Trapping = 50 mm

Pumping = 40 mm

Pick larger pipe

Why bother to return condensate?• Pure water.

If thrown away, replaced with potable water + chemicals.• Hot water.

If thrown away, replaced with cold water + heat.• Disposal costs

Effluent charges can equal buying cost

Remember:• With higher operating pressures, more flash lost from vents

(a good case for using flash steam).• Higher feedwater temperature = less fuel.• More condensate returned = less blowdown.

Condensate Removal

Things to consider

• Mechanical or electrical pumps?

• Condensate pressures and loads

• Pump discharge pipe sizing

Condensate Removal

Electrical pumps?

• Electrical pumps have a higher capacity

• Electrical pumps usually require smaller discharge pipes

Mechanical pumps?

• Mechanical pumps need no electrics

• Mechanical pumps are safe in hazardous areas

• Mechanical pumps are versatile

Things to consider:

Mechanical or electrical pumps

Condensate Removal

Things to consider

Mechanical or electrical pumps?

Condensate pressures and loads

• System never stalls - Use steam trap

• System can sometimes stall - Use pump-trap, or pump and trap

• System always stalls - Use a pump only

Condensate Removal

Things to consider

Mechanical or electrical pumps?

Condensate pressures and loads

Pump discharge pipe sizing

Condensate Removal

Example 1

Condensate Removal

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Example 1:

Max. pressure 3 bar g (144oC)

Min. pressure 1 bar g at minimum load

Backpressure 0.5 bar g

5 m

Condensate Removal

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Stall?

5 m

Example 1:

?




Stall? No !

Min pressure >

Backpressure

Example 1: System never stalls: Use float trap




Stall? No !

Sec flow temp ( 90oC)

Sec return temp (full load) ( 40oC)

Full load

Plot these points on a stall Chart

Condensate Removal

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Percentage load100% 0%

Full pressure 3 bar g

Min. pressure 1 bar g


Min pressure >

Backpressure

Ts @ FULL load 144°C

Condensate Removal

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Min. load70% of full load


Min. pressure 1 bar g


Min. load Stall load

Required to size float trap

Required to size float trap

100% 0%

Full pressure 3 bar g Ts @ FULL load 144°C

Condensate Removal

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Summary:

1. Max. DP condition = 3 bar – 0.5 bar = 2.5 bar (400 kg/h)

2. Min. DP condition = 1 bar – 0.5 bar = 0.5 bar (280 kg/h)

5 m = 0.5 bar

DP

3 bar 1 bar




Stall? NO!

Sec flow temp ( 90oC)

Sec return temp (full load) ( 40oC)

Full load 400 kg/h

From the stall chart

Min load (70% x 400) = 280 kg/h


Size float trap

Condensate Removal

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Max DP 2.5 bar

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Full load

400 kg/h

Max DP 2.5 bar

DN 15 FT14-4.5

IS OK !

57

Min DP 0.5 bar

58

Min load

280 kg/h

Min DP 0.5 bar

DN 15 FT14-4.5

IS NOT OK !

59

Min load

280 kg/h

Min DP 0.5 bar

So a DN25 FT14-4.5TV trap must be used

60

Full load

400 kg/h

Rule of thumb?2 x

full load

Sizing the trap discharge pipe (Rising line)Size on the full load condition when the most flash is produced

Full load 400 kg/h

Full load pressure 3.0 bar g

Condensate backpressure 0.5 bar g

Using the condensate pipe sizing chart . . .

Condensate Removal

Trap discharge lines

3.0 bar g

0.5 bar g

400 kg/h

Trap discharge lines

3.0 bar g

0.5 bar g

400 kg/h

Rising line:

Pick next larger size:

DN25

The website calculator gives the same result

Condensate Removal

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5 m = 0.5 bar

3 bar 1 bar


Condensate and flash recovery

Result:

DN25 FT14-4.5

with DN25 pipe

Condensate and flash recovery

Example 2

68


Min. pressure - 0.3 bar g

Backpressure 0.5 bar g (5 m)

6 bar g

50m long 3 bends 2 valves

5m lift

Example 2:

Condensate Removal

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Stall ?

6 bar g


5m lift

Example 2:




Stall ?

??Min pressure

< Backpressure




Stall ? YES




Stall ? YES

Sec flow (90oC)

Sec return at full load (40oC)

Full load 400 kg/h

Minimum load 0 kg/h

Draw stall chart

Condensate Removal

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Tin 40°C

Tout 90°C


Ts @ MIN load 90°C


Example 2:


Backpressure <

Min pressure

40%

Stall load


Condensate Removal

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Tin 40°C

Tout 90°C

100% 0%

Ts @ MIN load 90°C


Example 2:


40%STALL load

Stall load


Condensate Removal

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Example 2: System sometimes stalls: Use pump-trap




Stall ? YES

Sec flow (90oC)


Full load = 400 kg/h


Stall load (40% of 400 kg/h) = 160 kg/h

300 mm

6 bar g

5m lift


Condensate Removal

Sizing

• the APT

• the discharge pipe

Enter all relevant data

Condensate Removal

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Installation Diagram

3 ELBOWS

2 VALVES

Stall = 159 kg/h

79

0

200

400

600

800

1000

1200

1400

1600

1800

2000

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

System Pressure (barg)

Co

nd

ensa

te L

oad

( k

g/h

r )

Process Pump Trap

Receiver Volume Required Is 0.68 Litres

Stall = 159 kg/h

80

Example 2: System sometimes stalls: Use pump-trap







From the APT software = 159 kg/h

??







From the APT software = 159 kg/h

Difference due to friction loss

300 mm

6 bar g

5m lift


Result:

APT14

with DN25 pipe

Condensate Removal

Example 3

Condensate Removal

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5 metre lift

3.8 Bar g

Steam pressure in heater – full load = 3.8 bar g (Ts=150°C)Secondary control temperature (Tc) = 60°CCondensing rate at full load = 1,400 kg/h

Lift = 5 metres (Tb = 112°C)Frictional loss – add 10% = 0.5 metres Use 0.5 bar for ΔP across trap = 5 metresTotal backpressure (metres) = 10.5 metresTotal backpressure (bar g) = 1.05 bar gPump motive pressure = 6 bar g

Example 3: Sizing steam trap and condensate lines for a pump trap combination

Condensate Removal



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Tin 40°C

Secondary temp (Tc)60°C


Ts @ MIN load 60°C

Full pressure 3.8 bar g

Example 3:


58%

Stall loadBackpressure 0.5 bar g

Backpressure >

Min pressure

Condensate Removal

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5 metre lift

3.8 Bar g

Steam pressure in heater – full load = 3.8 bar g (Ts=150°C)Secondary control temperature (Tc) = 60°CCondensing rate at full load = 1,400 kg/hStall load: 1400 kg/h x 58% = 812 kg/hLift = 5 metres (Tb = 112°C)Frictional loss – add 10% = 0.5 metres Use 0.5 bar for ΔP across trap = 5 metresTotal backpressure (metres) = 10.5 metresTotal backpressure (bar g) = 1.05 bar gPump motive pressure = 6 bar g


Condensate Removal



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812 kg/h

6 barg

Mechanical pumps


1150 kg/hMaximum Capacity

86

Full load 1,400 kg/h

Full load ΔP = 3.3 bar(3.8 – 0.5 bar)

Use ΔP = 0.5 bar across trap

Stall Conditions:4 x pump capacity = 4 x 1150 kg/h

Stall load: = 4,600 kg/h

Need a DN50 FT14HC-4.5

Sizing the steam trap in a pump-trap combination

87



3.8 Bar g

Pump

TrapMaximum Duty: 1,400 kg/hStall Condition: 812 kg/h

Back pressure: 0.5 bar g

Motive pressure: 6 barg

Sizing the condensate line in a pump-trap combination



3.8 bar g

0.5 bar g

1400 kg/h


Full load condition

4600 kg/h


Pumping condition

Trapping = 50 mm

Pumping = 40 mm

Pick larger pipe

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Summary:

• DN25 MFP Pump

• DN50 FT14HC-4.5 trap

• DN50 discharge pipe

5 metre lift

3.8 Bar g

Steam pressure in heater – full load = 3.8 bar g (Ts=150°C)Secondary control temperature (Tc) = 60°CCondensing rate at full load = 1,400 kg/hStall load: 1400 kg/h x 58% = 812 kg/hLift = 5 metres (Tb = 112°C)Frictional loss – add 10% = 0.5 metres Use 0.5 bar for ΔP across trap = 5 metresTotal backpressure (metres) = 10.5 metresTotal backpressure (bar g) = 1.05 bar gPump motive pressure = 6 bar g


Condensate Removal



Example 4

Condensate Removal

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40 m long

10 m lift

Example 4:


Min. pressure 0.5 bar g

Backpressure 3 bar g (30 metres)

Line pressure 2 bar g

Condensate Removal

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Stall:

40 m long

10 m lift


Example 4:

?




Stall: YES

Backpressure >

Max pressure




Stall: YES

Sec flow (90oC)


Full load 230 kg/h

Draw stall chart

Condensate Removal

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Tin

Tout 90°C



Example 4:

40°C

Example 4: System always stalls: Use pump only

Backpressure >

Max pressure

Backpressure 3 barg144oC

Condensate Removal

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Example 4: System always stalls: Use pump only

40 m long

10 m lift





Stall: YES

Full load 230 kg/h


Stall load (= full load) 230 kg/h

Permanent stall = pump only

Size PUMP on 230 kg/h and 30 m delivery head

Condensate Removal

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30 metre lift

Condensate Removal

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pp

230 kg/h

Minimum motive pressure required = 3.10bar g

Actual motive pressure = 4.0 bar g

750 kg/h

Condensate Removal

For a mechanical pump:

Size the discharge line on 4 x pump capacity:

4 x 750 kg/h = 3,000 kg/h

Condensate Removal

Using the condensate pipe sizing chart . . .

Sizing the pump discharge pipe

Size on 3,000 kg/h

Condensate Removal

3,000 kg/h

Rising line:

Pick DN 32 or DN40

Condensate Removal

Using the Engineering Support Centre . . .

Sizing the pump discharge pipe

Size on 3,000kg/h

And a pump delivery head of 4.0 bar g

Condensate Removal

Checking the friction loss and velocity

Condensate Removal

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A DN32 pipe passing 3,000kg/hA DN32 pipe passing 3,000kg/h will generate a friction loss of about 290 Pa/m

Total friction loss = 290 Pa/m x 50 m = 14,500Pa = 14.5 kPa

Condensate Removal

Summing up the DN32 pump discharge pipe

Size on 3,000 kg/h

DN32 pipe, 50 m in length

Friction loss 14.5 kPa = 0.145 bar

Pipe lift 10 m = 1 bar g

Condensate pressure = 2 bar g

Total backpressure = 3.145 bar g

The pump motive pressure must be higher than this for condensate to flow

Condensate Removal

Common condensate lines

Condensate Removal

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Falling

Condensate Removal

As long as each of the trap discharge lines has been sized using the condensate chart, the common line can be easily sized.

Falling

Condensate Removal

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DN15 DN20

DN ?

Falling

2 2Common line = 15 20 625 25

Condensate Removal

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Common condensate lines – Appendix 14.3.3

Condensate Removal

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2 2Common line = 20 25 1025 32

DN20 DN25

DN 32

Rising

Condensate Removal

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Common condensate lines – Appendix 14.3.3

Condensate Removal

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Condensate Return

Typical Condensate Return System - OPC

A typical OPC site will have HP, MP & LP steam mains.

It will also have separate HP, MP, and LP condensate return lines.

• Reduces condensate line size – Reduces specific volume of flash steam if condensate lines are pressurised.

• Eliminates risk of pressurising LP condensate system so de-rating the process (increased risk of stall)

• Reduces risk of water hammer in condensate lines.

We can cascade the condensate systems and utilise the flash steam generated…….

115

Why?

116

Typical Condensate Return System - OPC

To LP steam main (e.g. 4 bar g)

To MP steam main (e.g. 12 bar g)

Cascade Condensate Return:

To condensate water tank

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Example of condensate cascade on process

118

Typical issues on condensate return:

• Under sized condensate lines – no allowance for flash steam

• Thermal shock – mixing sub-cooled condensate with 2-phase condensate

• Water hammer – resulting from above two points

• Directly mixing condensate from HP steam line in to a L.P. condensate line.

• Using a lower pressure steam main as the condensate return from a HP steam line.

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Application showing possibility for thermal shock

2–phase condensate & flash steam at 0 bar g

Condensate cooled to 60°C

Single–phase condensate at =< 100°C

Next…..

Flash steam recovery

Condensate Removal

Business

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