Coal gasification and CO 2 capture

Transcription

1 Coal gasification and CO 2 capture an overview of some process options and their consequences (Evert Wesker) Some on the context Zooming in on Coal Gasification Pre combustion capture (after gasification) Post combustion capture (after powdered coal fired boiler) Final remarks / food for thought

2 World energy consumption ~ 520 ExaJoule / year = ~ 16 x Watt 2

3 More than 80% of the energy is (still ) based on fossil fuels (Statistics from 2008; total 520 EJ/year) OPEC + Russia: ~60% of the total world conventional oil production Coal: Security of supply plays in the background 3

4 The possible global climate perspective To what do we owe this good fortune? Nobody knows for sure. However: Business as usual could mean pushing one s luck. roller coaster Stable! 4

5 Some more numbers Coal reserves: (numbers from BP statistical review of world energy) Bituminous coal & anthracite Sub-bituminous coal & lignite ~500 Gton (~2500 Gbbl oil equivalent) ~400 Gton ( at least, but probably more ) World power production (2008) Total power production Power from fossil fuels Power from coal 73 EJ/year 48 EJ/year 30 EJ/year (about 40% of the total) Worldwide CO 2 emissions (2008) Total (excluding land change) Coal Power from coal 32 Gton/year 13 Gton/year 8 Gton/year!» Coal & coal based power will (still) be with us for quite some decades, so if we want to do something about these CO 2 emissions we will have to look into CCS... 5

6 CO 2 capture, the various routes 6

7 Why? Zooming in on Coal Gasification Turning coal into a gaseous product enables combined cycle line-ups with a high efficiency (currently ~47%, possible future» 50%) High pressure process enables high pressure removal of CO 2 (after a shift step) This is part of this lecture. Sulphur ends up as H 2 S (and as elemental sulphur after Claus) instead of SO 2 which has to be removed as e.g. CaSO 4. No Ca(OH) 2 with its energy requirement (CaCO 3» CaO costs 3.8 MJ/kg CO 2 ) is needed. The combined production of power and Hydrogen ( poly-generation ) is a distinct possibility. For the Shell process Dry feeding of the coal (no water evaporation losses) leads to a higher cold gas efficiency. (Often >80% of the initial heating value is retained) The design (membrane wall, burners) is highly robust. 7

8 SCGP process line-up 8

9 Flows in a CC plant IGCC: HP steam SGC BFW to Syngas Island HP steam HPST MP steam (to reheat) MP/LPST Flue gas MP steam LP steam To HRSG Fuel gas Air HRSG GT BFW 9

10 IGCC CCS pre combustion Options 10

11 Flows in a CC plant (IGCC & precom-ccs) HP steam SGC & Shift IP steam to Shift BFW to Syngas Island HP steam HPST MP steam (to reheat) MP/LPST Flue gas MP steam LP steam To HRSG Fuel gas Air HRSG GT BFW 11

12 CO 2 from syngas / pre-combustion LHV [MJ/kg CO 2 ] Fuel O 2 Steam Gasification (LHV loss) Heat generated Steam Shift (LHV loss) Heat generated CO 2 power out η = 30 35% H 2 to power or heat & power CO 2 removal

13 Physical solvents: a pressure swing process 13

14 Waterfall diagram for SCGP + shift + selexol Efficiency IGCC, %LHV st drop ~5.5%p (sour shift) nd drop ~1.5%p (Selexol) 42 3 rd drop ~2.5%p (CO 2 compression) No capture Shift CO 2 AGR CO 2 compress TIT reduction 14

15 The consequences of gas turbine development (η without CCS) Efficiency IGCC [%LHV] E class (Buggenum) F class - base case G class H class (TIT=1425 C) H+ class (TIT=1525 C) ASU 50% integration High efficiency ASU Hot Gas CleanUp USC with reheat@620 C are also leading to higher efficiencies for SCGP power + CO 2 capture

16 IGCC + 90% CCS tomorrow A promise for the future: 4.5-5% LHV efficiency improvement potential for Future IGCC + CCS Based on application of new technologies under development this widens the efficiency gap with post combustion CCS solutions Efficiency IGCC, %L LHV New technology New technology New technology CO 2 compression Next Gen GT 16

17 Another option is still a powdered coal fired power plant. This implies post combustion CO 2 capture. 17

18 18

19 Post combustion: An amine based temperature swing process 19

20 20

21 21

22 Pre versus Post Observations from pre-combustion : The biggest losses are in the shift step (~5.5%!!) In the CO 2 removal step little can be gained (loss ~1.5%) The difference between pre and post is relatively small in case the employment of a conventional shift step: %» 36.8% for amine state of the art solvent %» 36.4% for selexol after shift However: We are looking at a moving target. Gas turbine efficiencies go up (good for pre ) Shift process improvements will be pursued (good for pre ) Solvents will be improved (good for post ) Further ultra supercritical boiler development (good for post ) And finally: There are other options under development (However: quite often not yet commercially operational) 22

23 CO 2 capture with chilled ammonia. However, there are still quite some open questions 23

24 24

25 A final reminder: These examples were by no means an exhaustive and complete list 25

26 A last word (and food for thought) Imagine: CCS for MW ( 10 EJ/year) Coal based power Efficiency power plants on coal (+CCS): 40%» Ergo: ~2.3 Gton CO 2 /year A density for CO 2 when injected (~200 bar, ~30 C) of ~ 900 kg/m 3 implies: ~2.3 Gton CO 2 /year» 43 million barrel per day To put it in perspective: The present conventional oil production is about ~73 million barrel per day. (1 barrel = 160 litre). So: For CCS, equivalent to about 5% of the current world energy consumption in this case an infrastructure (pipelines, injection wells, etc.) of the size of an order of magnitude of half of the oil production infrastructure is required. This is big stuff (if we decide to go for it) 26