Energy efficiency in industrial steam production and …okolje.arso.gov.si/ippc/uploads/File/Energy_efficiency...1 EU-Twinning Project SL04/EN/01 Integrated Pollution Prevention and

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EU-Twinning Project SL04/EN/01Integrated Pollution Prevention and Control (IPPC)

Dries Maes, STEVITO, Mol

Ljubljana, 13 -15 March 2006

Mission 6.2: Energy Efficiency

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Energy efficiency in industrial steam production and distribution

Workshop Energy-efficiency 13-15 March 2006, Ljubljana

Dries MaesFlemish Institute for Technological ResearchBelgium





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Structure1) Working with steam ? 2) To Determine the cost of steam3) Different points and ideas to save

energy in a steam system

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Working with steam in the industry ?Different heat transport fluids are available - Water

- no transition to steam allowed- temperatures are not too high : ± 150°C

- Thermal oil- specific composition of the oil for long lifetime - higher boiling temperatures so higher operating temperatures.

- Steam- Specific use of latent energy in the fluid- High heat transfer gives smaller heat exchangers

• Water : 4.000 W/m²C• Oil : 1.500 W/m²C• Steam : > 10.000 W/m²C

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Working with steam in the industry ?Boiling point of water at

different pressures

0

50

100

150

200

250

300

0 10 20 30 40

Absolute Pressure [Bar]

Boiling point [°C]

Distribution of the energy content in steam between the sensible and latent heat

0

500

1000

1500

2000

2500

3000

0 5 10 15 20 25 30 35 40

Absolute Pressure [Bar]

Enth

alpy

[kJ/

kg]

Sensible heat

Latent heat

Total energy content





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The right pressure..• Benefits of higher pressure :

– The steam has a higher temperature– The volume is smaller, the distribution pipes are smaller. – It is possible to distribute at high pressure and to relax steam prior to

application. The steam thus becomes dryer and reliability is higher.– a more stable boiling process in the boiler.– ...

• Benefits of lower pressure : – There is less loss of energy at boiler level and in the distribution– The amount of remaining energy in the condensate is relatively small.– Leakage losses in the pipe system are lower. – ...

!! Working with steam also has implications for safety, reliability, costs, lifespan of the equipment... !!!

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The cost of steam ? Different factors :• CF Fuel • CW Water supply• CBFW Feed water treatment (includes softening, clarification..)• CP Feedwater pumping power• CA Combustion air fan• CR Sewer charges for boiler blowdown• CD Ash disposal costs• CE Environmental emissions management and control cost

(includes additives)• CM Maintenance materials and labour

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The cost of steam• Fuel costs are normally by large the most important costs :

– CG = 1.1 x CF

• What does this cost mean ?– average cost– no effect of different pressure levels– no effect of marginal consumption– no effects of regulation or intermediate electricity production– ....





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Average versus marginal costs of steamAverage cost = Total operating cost / Total Steam

= CO/SMarginal cost = Marginal production cost /

Marginal quantity of Steam Consumption = ∆CO/∆S

Very different approach, but more correct for the evaluation of energy saving measures

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The cost of steam : via marginal costs, example

Boiler 2

Cap. 18 ton/h

Eff. 83%

Boiler 1

25 ton/h

84%

Cap.

Eff. 82%

Boiler 4

Cap. 19,5 ton/h

Eff. 83%

Boiler 3

Cap. 19,5 ton/h

Eff.

Boiler 5

Cap. 19,5 ton/h

Eff. 81%

50 Barg Users

Boiler 6

Cap. 19,5 ton/h

Eff. 73%

Boiler 7

Cap. 65 ton/h

Eff. 83%

Deaerator

Flash recuperator

116,2 ton/h

74,3 ton/h

1 Barg Users

0,4 ton/h

PRV Turbines 2 & 3 Turbine 1

Fresh water makeup

Blowdown

Condensate recuperation

PRV

PRV

10 Barg Users7,5 ton/h

25 Barg Users

8,3 ton/h





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The cost of steam : via marginal costs, example• Marginal cost is highly

variable• Picture differs for every

steam pressure level• cost shows influences of

varying efficiencies, turbines, pressure-reducing valves,...

Marginal cost for steam production

€ 0

€ 5

€ 10

€ 15

€ 20

€ 25

€ 30

€ 35

0 20 40 60 80 100[ton/h]

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Different ways to save energy in a steam system• Use economisers to pre-heat feedwater• Install an air pre-heater• Prevent scale deposits on heat transfer surfaces. Ensure deposits are regularly removed on

the waterside of boilers• Minimize boiler blowdown• Recoverable heat from boiler blowdown• Minimise boiler short cycling losses• Consider installing high-pressure boilers with backpressure turbine generators for the

production of electricity or for rotating installations• Implement a control and repair programme for steam traps• Install insulation on steam pipe and condensate return pipes• Installation of removable insulating pads on valves and fittings• Collect condensate and return it to the boiler for re-use• Re-use of flash steam• Use of flash steam on the premises or through recovery of condensate at low pressure• .....

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1) Implement a control and repair programme for steam traps

• Steam systems without regular inspection often have defect steam traps

• Without inspection, after 3 to 5 years, 30% of all steamtraps needs repair or replacement

• Normally, a distribution system should have less then 5% of defective steam traps.

• Critical traps :– High pressure steam traps– Traps connected to expensive or critical equipment.





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Function of steam traps• prevent the

steam to pass.• evacuate the

condensate(once all the energy hasbeen used)

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Different operation modes for steam traps

The steam trap cannot be reached and was therefore not tested. Not testedNT

This line of out of order. Out of orderOO

This steam trap can no longer deal with the flow of condensate. To be replaced with a trap of the right size.

SubmergedSB

The steam trap is closed. No condensate can flow through it. To be replaced

FixedFX

The cycle of this thermo-dynamic steam trap is too fast. Must be repaired or replaced.

Fast cycleFC

Steam leaks from this steam trap. It needs to be repaired or replaced.LeaksLK

Steam is escaping from this steam trap, with maximum steam losses. Needs to be replaced.

Steam escapingESWorks as it shouldAll rightOK

DefinitionDescription





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Related costs of escaping steam• Amount of escaping steam can be

huge.• Defective trap represents large losses• Example :

– leakage– standard application– operating pressure difference : 15 bar– losses : 16.650 € per year

• If not simply leaking, but full Blow-through : 66.570 € per year

• These costs easily justify a control programme for steam traps.

Yearly steam losses in function of operating pressure

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20000

40000

60000

80000

100000

120000

0 5 10 15 20[bar]

[Ton/year]

10





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2) High pressure boilers and turbines to producelow-pressure steam

• The intervention is large. Economic yield can be equallylarge.

• This is applicable if :– continuous steam supply is necessary– or continuously steam is being reduced in pressure by PRV’s

• Alliance with electricity providers is often possible.

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Pressure-Enthalpy Diagram for Water and SteamBased on the IAPWS-95 Formulation for General and Scientific Use

1

10

100

1000

10000

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5Enthalpy, kJ/kg

Pres

sure

, bar

Copyright © 1998 ChemicaLogic Corporation.Drawn with SteamTab V3.0.

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2 3 Steam is used at this point.





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Pressure-Enthalpy Diagram for Water and SteamBased on the IAPWS-95 Formulation for General and Scientific Use

1

10

100

1000

10000

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5Enthalpy, kJ/kg

Pres

sure

, bar

Copyright © 1998 ChemicaLogic Corporation.Drawn with SteamTab V3.0.

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4 Steam is used at this point.

Steam is prepared at

higher pressure(100 bar)

Expansion of the steam over a turbine to

produce electricity

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Example• Situation : Boiler needs to be replaced : - 25 tonnes/h of steam - at 15 barg- efficiency 74 %- 6,500 hours per year operating timeOptions :1) Replace by equivalent boiler of better quality2) Replace by high-pressure boiler and back-pressure

turbine





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Examplea) Yearly operating cost of the old boiler:

= 2.051.836 €/year

b) Operating cost of the new boiler (new boiler equivalent with the old one, option 1)

= 1.898.041 €/year

1000 x 0.74€/GJ 3,8 t/h x 25 x kJ/kg 2459h/year x 6500

1000 x 0.80€/GJ 3,8 t/h x 25 x kJ/kg 2459h/year x 6500

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Examplec) High pressure boiler, yearly operating cost (option 2)

= 2.070.555 €/year

Steam is overheated to 330°C to make energy available for the turbine

d) Amount of electricity generated by the turbine

= 7.022 MWh/year

Annual gain is equivalent to 351.106 €/year

This compensates largely for the higher operating cost

1000 x 0.80€/GJ 3,8 t/h x 25 x kJ/kg 335) - (3017.5h/year x 6500

0.97 t/h 25 x kJ/kg 150.9h/year x 6500





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Practically• Turbines can be interesting when :

– high operation load during the year– large use of lower pressure steam– energy prices have an important role

(collaboration with electricityproviders can be interesting)

– not the first measure to be taken, butcan be considered when high energyefficiency has been achieved byother measures.

50 Barg Users

Boiler 7

Cap. 65 ton/h

Eff. 83%

116,2 ton/h

1 Barg Users

0,4 ton/h

Turbine 1

10 Barg Users

7,5 ton/h

25 Barg Users

8,3 ton/h

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3) Minimising Blowdown and recuperation of Blowdown energy

• Blowdown :– necessary discharge of boiler water to

• reduce concentration of salts in the boiler water• remove suspended particles in the boiler water

– Blowdown percentages depend largely on the quality of fresh water preparation.





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Bottom blowdown

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Deconcentration blowdown





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Minimising Blowdown ? • TDS (Total dissolved salts) concentration needs to be

controlled. • Example : initial blowdown rate is 8%• Boiler :

– 25 bar – 5,500 hours a year. – 25 tonnes of steam per hour – boiler efficiency 82%– Gas : 5 €/GJ– Freshwater 1,3 €/ton– Discharging 0,1 €/ton

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Minimising Blowdown ? • Automatic blowdown control reduces blowdown

rate from 8% to 6%. • 8% -> 2,08 t/h• 6% -> 1,5 t/h• Gains :

• Water savings : 4,451 €/year

• Total : 15,172 €.

€/year107211000.000x 0.82

€/GJ 5 x kJ/kg 553.1h x 5500l/h x 578=





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Recuperation of energy from Blowdown

94873661451642110%

7585894914133378%

5694423683102526%

3792942462071684%

190147123103842%

95746152421%

50 barg20 barg10 barg5 barg2 barg% of boiler supply

Operating pressure of the boilerBlowdown rate

Recovered energy from blowdown losses, in MJ/h [1]

[1] These quantities have been determined based on a boiler supply of 10 tonnes/h, an average temperatureof the boiler water = 20°C, and a recovery efficiency of 88%.

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Solubility of oxygen in water in function of the temperature

0

2

4

6

8

10

12

14

16

0 10 20 30 40 50 60 70 80 90 100

Water temperature (oC)

Solu

bilit

y of

oxy

gen

(ppm

)





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0,2 bar105°C

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Conclusions• Much more interventions are possible• Raising energy prices make several interventions

economically interesting• Good set-up of priorities necessary among

different interventions (economic yield of interventions may interact)

• Definitively a good idea to look into any existingsteam system.





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Thank you Dries Maes

VITO, Flemish Institute for Technological ResearchBoeretang 2002400 MolBelgium+32/14/[email protected]

Documents

Energy efficiency in industrial steam production and …okolje.arso.gov.si/ippc/uploads/File/Energy_efficiency...1 EU-Twinning Project SL04/EN/01 Integrated Pollution Prevention and