oxygen production for oxyfuel power plants 02.ppt...

Linde Engineering

OXYGEN PRODUCTION for OXYFUEL POWER PLANTSStatus of Development

Dr. Dimitri GoloubevWorkshop on Oxyfuel-FBC Technology, 28.06.12

Linde Engineering

Linde AG Linde Engineering Division

Agenda

• Oxygen Requirements for Oxyfuel CombustionWhy new development for Air Separation Unit (ASU)?

• Development History and Current Status

• Heat Integration between ASU and Power Plant

• ASU Load Following Capability

• Discussion

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Oxygen Requirements for oxyfuel combustion

• Large amount (e.g. 280 t/h for Wel = 300 MW)

• Low purity (< 97%)

• Low pressure (nearly equal to atmospheric pressure)

• No demand for any significant quantity of other products (nitrogen, argon or liquid products)

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Why new development for ASU?

• Power consumption of ASU reduces the net power output

High efficiency is required!

• Large scale ASU means significant CAPEX

Capital cost should be minimized!

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Why new development for ASU?

Composition of atmospheric airPure oxygen product:

99,5% O2 and 0,5% Ar

(Argon has a big impact on the rectification process)

Separation of argon from oxygen is not required for "impure" oxygen product!

Saving potential is available

Low purity oxygen product:

95% O2, 2% N2 and 3% Ar (approx.)

(almost no impact, nearly the whole Argon remains in the oxygen product)

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“Classical” ASU Process with Double Column

Oxygen purity: 95%

G

1

AIR

1

Condenser

Main Air Compressor

Air Precooling

MS Adsorber

POWER

5.6 bar

UN2 to Evap. Cooler and for Adsorber regeneration

1.2 bar

Turbine

POWER

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Oxygen purity: 95%

McCabe-Thiele Diagram for the upper (low pressure) column

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DISADVANTAGES:

• High power consumption

Thermodynamical losses in the low pressure column lead to additional losses at the main air compressor

The process is not capable to realize the saving potential to a large extent

ADVANTAGES:

• Low capital cost

Small equipment dimensions due to high (usuall) air pressure

Reduced volume of main heat exchanger as a result of excessturbine refrigeration

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Single pressure Dual Reboiler ASU process

Oxygen purity: 95%

Subcooler

LP Colum

n

GO

X

PG

AN

Heat Exchanger

1

AIR

1

Condenser 1

Main Air Compressor

Air Precooling

MS Adsorber

~ 4.85 bar

1.2 bar

Condenser 2

HP C

olumn

Turbine

GPOWER

POWER

UN2 to Evap. Cooler and for Adsorber regeneration

2

2

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Single pressure Dual Reboiler ASU process

Oxygen purity: 95%

Subcooler

LP Colum

n

HP C

olumn

Nitr

ogen

in v

apou

r pha

se

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Dual Reboiler process

Efficiency improvement of the Dual Reboiler process:• Dual Reboiler process with the feed air stream under two different

pressures (MAC and BAC)

• Introduction of a third condenser into the process

Side condenser for evaporation of product oxygen only

• The use of advanced condenser types

Falling film condenser

Forced flow condenser

The power consumption of the OPEX opimised Dual Reboiler process isaround 13% lower compared to the "classical" Double Column process*

* compared assuming identical efficiency numbers for compressors

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Triple Column ASU process

Oxygen purity: 95%

LP Colum

n Part 1HP C

olumn 1

Side Condenser

AIR

Main Air Compressor

Air Precooling

MS Adsorber

POWER

LP Colum

n Part 2

Heat Exchanger

Subcooler

1.2 bar

GO

X

PG

AN

HP C

olumn 2

AIR

Main Air Compressor

Air Precooling

MS Adsorber

~ 4.8 bar

Booster Air Compressor

UN2 to Evap. Cooler

G

GAN for Adsorber regeneration

~ 3.1 bar

approx. 22% of the total ASU power

Low pressure column is devided into two partsMedium pressure column (MAC pressure)High pressure column (BAC pressure)

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Triple Column ASU Process

• The introduction of a third column into the Dual Reboiler process withfeed air stream under two pressures (MAC and BAC) lead to futherreduction of losses in the rectification part and allows the processoptimisation with quite low pressure at MAC outlet

• Slight advantage in power can be additionally reached with twoadsorber stations operating at different pressures as well as byprecooling of the air stream to the Booster Air Compressor

• The power consumption of ASU with this process cycle is around 20% lower than with "classical" double column process*

* compared assuming identical efficiency numbers for compressors

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Multi-column ASU process?

• The introduction of further condensers and rectification columns doesn't bringt any significant advantages and only increases the level of complexity

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Further Development of ASU process cyclesfor Oxyfuel Power Plants

The way

• Process Improvement (cost and complexity reduction)

• Improvements in "hardware" technology

• Heat Integration with Power Plant

Target

• To minimise the power consumption and capital cost

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Heat Integration between ASU and Oxyfuel Power Plant

• Thermodynamic losses in the air compressor of ASU are still very high

The isothermal compressor efficiency is around 75% (25% of consumed power is lost at compressor itself)

• The heat flow from the air compressor can be recovered at the power plant to reduce this exergy loss

• The heat recovering must be maximised with minimisation of the compressor power consumption

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• Optimisation is possible

adiabatic compression at lower pressures doesn't lead to significant power penalty due to saving the pressure loss in intercooler but allows to recover the heat at higher temperature level

The power penalty can be totally avoided with use of an axial compressor stage at lower pressures

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AIR

LP Air Stream to ASU, ~ 3.0 – 3.2 bar

Cold feed water T ~ 300 K

Warm feed water to power plantT > 400 K

Chilled H2O

H2OMP Air Stream to ASU,

~ 4.9 – 5.1 bar

first compressor section without intercooler

second compressor section

Axial compressor with radial stage for MP Air Stream can be used

example picture

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Heat Exchanger for "Heat Integration"

example picture for a small coil-wound HEX

Coil-Wound Heat Exchanger

• Efficient cross-flow counter-current

principle

• Air flow as a shell side stream

• Coiled tubes in layers for Feed-Water

• Compactness

• High mechanicall robustness

• Linde Technology (LNG Heat Exchangers)

The requirements for "Integration"- heat exhanger are quite hard:

Very large amount of Heat is to be transffered with small temeprature difference (MTD=10-15 K or even less)

Very small allowed pressure loss for the air stream (≤ 100 mbar)

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ASU process cycles for Oxyfuel Power Plants

Oxygen purity: 95% Oxygen pressure: 1.2 bar

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Load following capability of ASU for Oxyfuel Power Plants

• The requirements for load following capability for Oxyfuel Power Plants are higher than for conventional applications

• Tests with increased speed of load change were carried out to investigate the dynamic behavior of ASU:

To identify the highest speed of load change without big fluctuations in products purity

To find out the critical controllers and process parameters which restrict the maximal speed of load change

To collect the practical experience with an adjustment of parameters needed for high speed load change

• The tests were carried out at the existing Linde ASU with production capacity of 6000 Nm3/h of low pressure gaseous oxygen with a purity of 99.5% (double column process cycle with side condenser)

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Load change with 4% per minute (MAXMINMAXMIN)Process Air flow, GOX Product flow and GOX Product purity

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Load change with 4% per minute (MAXMINMAXMIN)„Liquids-Management" in the plant

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Load following capability of ASU for Oxyfuel Power Plants

• ASU load changes between 75 and 100% with a speed of 4% per minute and up to three load changes in a row were performed without appreciablechanges in oxygen product purity. The liquid levels in condensers could be held at required set point values

• The load changes with the speed of 8% per minute were successfully performed also without appreciable fluctuation of oxygen purity. The relevant parameters were taken over from the load change tests with 4% per minute without any further adjustments. The maximal deviation between the ramped set point and process value of oxygen product flow amounted to approx. 5%

• The results of experiments allowed the adaption of simulation models for ASU dynamic behavior prediction and gain confidence in offering the ASU that enables working with increased speed of load change

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Acknowledgement

To my colleagues for their actual and former contribution…

• Dr. Alexander Alekseev

• Dr. Dirk Schwenk

• Dr. Thomas Rathbone

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Many thanksfor your attention

oxygen production for oxyfuel power plants 02.ppt...

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