3 integration of asu in process of power generation final presentations/s2b … · linde...

Dr. Dimitri Goloubev, Dr. Alexander Alekseev

The Linde Group

3rd Oxyfuel Combustion Conference, Ponferrada, 10.09.2013

INTEGRATION OF ASU IN PROCESS OF POWER GENERATION

Linde Engineering

Linde AG Linde Engineering Division

Agenda

• Heat Integration between ASU and Oxyfuel Power PlantØWhat is meant by Heat Integration?

ØRealisation and Power Benefit

• Energy Management between ASU and Power Plant

ØWhat is meant by Energy Management?

ØEvaluation of different Concepts

ØSuitable Choice

• Discussion

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Heat Integration between ASU and Oxyfuel Power Plant

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

Ø 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 these losses

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

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• Optimisation is possible Ø 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

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

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

example picture

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Heat Integration between ASU and Oxyfuel Power PlantHeat 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 mechanical robustness

• Linde Technology (LNG Heat Exchangers)

The requirements for "Heat Integration"- heat exchanger are quite strict:

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

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

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Heat Integration between ASU and Oxyfuel Power PlantCase study, Results

specific Oxygen Demand: 420 Nm3/MWh @ 1.3 bar(a)

Oxygen Purity: 96.3 %

specific ASU Power: 0,118 MW/MW electrical gross output

Example Power Plant*: W = 400 MW (gross electrical output)

ASU power*: P = 47,2 MW

Heat Integration Gain: approx. 4.15 MW (gross electrical output)

Additional CAPEX: < 1000 Euro/kW

Usual energy evaluation: > 3000 Euro/kW

* No Heat Integration, atm. pressure 1.013 bar(a), rel. humidity 65%, amb. air temperature 291.1 K

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Energy Management between ASU and Power Plant MAIN IDEA

The main idea is• to liquefy the oxygen during the off- peak power phase (night time or sunny

day etc.) and store it in the LOX storage

• to supply the oxygen from the LOX storage during the peak power phase and to reduce the ASU load (the load of the ASU main air compressor)

Very Important• The overall energy efficiency for characteristic "day – night" cycle becomes

generally lower. There is no power saving from the thermodynamical point of view

• The idea here is, that the overall OPEX becomes lower too in case of certain difference in power prices (off-peak/peak power phases)

• CAPEX becomes higher due to additional hardware components required

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Energy Management between ASU and Power PlantSCENARIO UNDER CONSIDERATION

• Base load operation during the first yearsØ ASU design for normal flexibility range (80%-105% for the main air

compressor and rectification columns in the Coldbox)

• Scenario for energy management (future operation mode)Ø Oxygen consumption during the day time (16h) is always 100%

Ø Different energy tariffs for the night /day time and lower power output and respectively oxygen consumption in the night time (8h)

Ø It is possible, that he power plant will be operated at min load in the night time. Hereby the electricity feeding into the grid can be even penalised (but can be used for oxygen liquefaction)

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Energy Management between ASU and Power PlantDifferent concepts for energy management are possible

•Liquefaction of oxygen during the night and evaporation within the day time

Øsimple evaporation of liquid oxygen

Øevaporation of liquid oxygen in ASU

Øadvanced concept with cold compressor for evaporation of liquid oxygen in ASU

Øswapping the liquids in ASU (based on LINDE "VAROX" principle, widely used for steel mills since 1980s)

"Add-on" units are required

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Energy Management between ASU and Power PlantSimple Evaporation of Liquid Oxygen

Ø No "cold integration" àmuch energy is wasted

Ø Low efficiency of energy storage (only around 27%)

Ø High liquefaction capacities are required for "night" operation to reach significant reduction of ASU power consumption during the day

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Energy Management between ASU and Power PlantEvaporation of liquid oxygen in ASU

Ø The refrigeration in ASU is provided by LOX-Injection à "cold integration"

Ø Increased efficiency of energy storage (around 55%)

Ø The amount of LOX injected into ASU is limited by refrigeration demand

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Energy Management between ASU and Power PlantCold compressors for evaporation of liquid oxygen in ASU

Why cold compressors?The amount of LOX injected into ASU is limited by refrigeration demand

Øonly 10% of ASU power consumption can be saved during the day time (for optimised process design)

ØThe use of cold compressors leads to an additional heat input at low temperature level and allows to evaporate significantly higher amounts of LOX in the ASU

How to use cold compressors in the ASU?•Functional implementation of cold compressor into ASU process cycle

Øprofit not only by the heat input at low temperatures, but also by lower power demand with compression at low temperatures

•Adapt the process cycle and make use of cold compressor also in operation without LOX-Injection à CAPEX reduction

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Triple Column ASU Process Cycle WITHOUT Cold CompressorLOX-Injection Mode

Subc

oole

r

LP C

olum

n

MP

Col

umn

Heat Exchanger

GO

X

PGAN

HP

Col

umn

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Double Column ASU Process Cycle WITH Cold CompressorLOX-Injection Mode

Subc

oole

r

LP C

olum

n

HP

Col

umn

Heat Exchanger

GO

X

PG

AN

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Energy Management between ASU and Power PlantDouble Column ASU Process Cycle with Cold Compressor

• The cycle with Cold Compressor has around 1.5% lower "stand alone" -efficiency in normal operation case (without LOX-Injection), but however it is partially compensated by better Heat Integration with Power Plant

• Efficient "cold integration" due to direct influence on the rectification process

Ø operation of cold compressor at minimum load in normal operation case

Ø operation of cold compressor at maximum load in LOX-Injection case allows to shift the heat loads between both condensers leading to reduction of the outlet pressure of the main air compressor, what saves energy

• High efficiency of energy storage (around 65%)

• 20% of ASU power consumption can be saved during the day time

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Energy Management between ASU and Power PlantVarious oxygen production with swapping the liquids in ASU

• Liquids swapping in the ASU depending on Night/Day operation

• Storing the oxygen molecules (separation energy) in the night for day GOX production with reduced air consumption

• Additional costs due to LIN Tank (but no Hot Gas Expander and Liquefier)

GOX Product

AIR

LOX

Main Air Compressor

„COLD“ TurbinePGAN-Turbine for „cold production“(always in operation)

G

LIN

Cold Box ASU

LIN into ASU(Night)

LIN to tank(Day)

LOX into ASU(Day)

LOX to tank(Night)

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Energy Management between ASU and Power PlantVAROX with swapping the liquids in ASU

• Around 11-12% of ASU power consumption can be saved during the day time (16h) with 100% GOX production

• The amount of stored LOX in the night is limited due to ASU design made basically for normal operation

• The method allows to store the separation energy but not the energy of liquefacton. Therefore significant amount of LOX needs to be stored in the night and injected into the ASU during the day time to have an perceptible effect on power saving

• Energy storage efficiency is high (>90%)

0

20

40

60

80

100

120

0 20 40 60

Oxy

gen

prod

uctio

n, %

Opreation hours, h

Plant design

GOX

LOX to tank

LOX into ASU

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Energy Management between ASU and Power PlantCONCEPT COMPARISON, OPEX

Data for following scenario:

Ø ASU design for normal flexibility range (80%-105% for the main air compressor and rectification columns in the Coldbox)

Ø Power plant at 100% load during the day time (16h) and at minimal load during the night (8h)

70

80

90

100

110

120

130

0 2 4 6 8 10 12

Ove

rall

OPE

X fo

r ASU

, %

Power price factor (day/night)

Without EnergyManagement

LOX evaporation

LOX Injection

Cold compressor

Varox

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Energy Management between ASU and Power PlantCONCEPT COMPARISON

LOX evaporation LOX injection Cold Compressor Varox

ASU Power Consumption during the day time forproduction of 100% GOX(ASU design for 80%-105%)

83%* 90%* 81%* 89%*

LOX supply from storage during the day time for production of 100% GOX

20% 5,6% 9,5% 13,2%

Energy Storage Efficiency 27% 55% 65% >90%

ASU Process cycleOxygen LiquefierHot Gas ExpanderAdditional LIN storageCold Compressor

Triple columnYesNoNoNo

Triple columnYesYesNoNo

Double columnYesYesNoYes

Triple columnNoNoYesNo

Relaibility medium medium low high

* Numbers for power consumption during the highcost –power phase, not for overall OPEX!

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Energy Management between ASU and Power PlantSuitable choice

• The difference in oxygen consumption (day/night) is important for choosing the energy management concept

• VAROX concept can be very efficient in case of large day/night spread in oxygen consumption

• The concept with cold compressors is efficient in case of small day/night spread in oxygen consumption

• The presented concepts can be improved and the overall OPEX can be further reduced if the requirement for energy management is envisaged in the ASU design (multi compressor trains, adapted ASU coldbox design etc.)

Ø higher CAPEX!

• EFFECTIVE SOLUTIONS FOR ENERGY MANAGEMENT CAN BE REALISED

Ø IT IS ALL ABOUT THE COSTS AND RELAIBILITY

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Many thanksfor your attention

3 integration of asu in process of power generation final presentations/s2b … · linde...

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