High Temperature, High Pressure Black Liquor Gasification with Borate Autocausticizing

Transcription

1 High Temperature, High Pressure Black Liquor Gasification with Borate Autocausticizing Ingrid Nohlgren Ph.D. Chem Eng, Senior Research Engineer, Energy Technology Center, Piteå Scott Sinquefield Ph.D. Chem Eng, Senior Research Engineer, IPST at GT, Atlanta

2 Integration of BLG influences the kraft mill An increased causticization demand increased demand of lime increased capacity in the lime kiln increased demand of fuel Addition of borate in the gasifier has the potential to eliminate this increased causticization demand

3 Increased causticizing demand Sulfur is released to the gas in the gasifier Co-absorption of CO 2 in the quench Traces of Na and S Na, S H 2 S Na, S Na 2 CO 3, Na 2 S Na 2 CO 3, Na 2 S

4 Increased causticizing demand Formation of H 2 S gives formation of Na 2 CO 3 (which in the recovery boiler is Na 2 S). The causticizing demand increases with a factor 1.43 if all sulfur goes to the gas phase as H 2 S. In the Chemrec (HT, HP) gasifier is approx 55% of the sulfur estimated to be released to the gas phase. This corresponds to an increased causticizing demand with a factor 1.24.

5 Direct and Auto Causticization Addition of a chemical agent to the black liquor Reacts during combustion or gasification Forms a sodium salt and carbon is released as CO 2

6 Autocausticization the formed sodium salt is soluble in alkaline solutions, eg Na 3 BO 3 Autocausticization means self-causticization, i.e. The pulping alkali causticizes itself during combustion or gasifiction Direct causticization the formed sodium salt is insoluble in alkaline solutions, eg 4Na 2 O 5TiO 2 The causticization agent is added and subsequently removed, and added again...

7 LIME BURNING CaCO 3 Full Borate Autocausticization CaO CAUSTICIZATION NaOH Na2S, NaBO 2 Wood PULPING Na, S, B WASHING Pulp EVAPORATION LIME BURNING CaCO 3 Partial Borate Autocausticization CaO Wood NaOH PULPING Na2S, NaBO 2 CAUSTICIZATION Na S (aq) 2 Na CO (aq), 2 3 NaBO 2 (aq) NaOH Na, S, B WASHING Pulp EVAPORATION DISSOLUTION Na S (l) 2 Na BO (l) 3 3 BURNING GASIFICATION Na, S, B Na B O 5H O DISSOLUTION Na2S (l) Na2CO 3 (l) Na3BO 3 (l) BURNING GASIFICATION Na, S, B Na B O 5H O LIME BURNING CaCO 3 Full Titanate Direct Causticization CaO NaOH Na S 2 CAUSTICIZATION DISSOLUTION Na2S (aq) 4Na2O.5TiO2 Wood SOLID SEPARATION Na2S (aq) NaOH Na2O.3TiO 2 (s) PULPING BURNING GASIFICATION Na, S WASHING EVAPORATION Na, S Pulp Partial Titanate Direct Causticization LIME BURNING CaCO 3 CaO NaOH Na S 2 DISSOLUTION Na2S (aq) Na2CO 3 (aq) 4Na2O.5TiO2 Wood CAUSTICIZATION Na2 NaOH S (aq) Na CO (aq) SOLID SEPARATION Na2S (aq) Na CO (aq) NaOH Na O.3TiO (s) 2 2 PULPING BURNING GASIFICATION Na, S WASHING EVAPORATION Na, S Pulp Na O.3TiO (s) 2 2 Na O.3TiO (s) 2 2

8 Borate Autocausticization Partial autocausticization LIME BURNING CaCO 3 CaO Wood NaOH PULPING Na2S, NaBO 2 CAUSTICIZATION Na S (aq) 2 Na CO (aq), 2 3 NaBO 2 (aq) NaOH Na, S, B Pulp WASHING EVAPORATION In a gasifier (or a recovery boiler): DISSOLUTION Na2S (l) Na2CO 3 (l) Na3BO 3 (l) BURNING GASIFICATION Na, S, B Na B O 5H O NaBO 2 + Na 2 CO 3 Na 3 BO 3 + CO 2 In the smelt dissolver: Na 3 BO 3 + H 2 O 2 NaOH + NaBO 2 (aq)

9 Overall objective Experimentally test if borate autocausticization can be achieved during High Temperature, High Pressure Black Liquor Gasification

10 Experimental Primary gas + BLS Flow straightener Furnace Collector Secondary gas Quench gas Cyclone (3 μm cut off) Fine particle filter To FTIR, GC Atmospheric experiments, IPST, Atlanta, GA, USA Pressurized experiments, IPST, Atlanta, GA, USA

11 Experimental Sample Kraft BL + NaBO 2 4H 2 O Soda BL + NaBO 2 4H 2 O 25% autocausticization Expr conditions PEFR (14 expr runs) 5, 10, 15 bar 1000 C 0%, 5%, 10%, 15% CO 2 in N 2 Expr conditions LEFR (64 expr runs) 1 bar 900 C-1100 C 0% - 20% CO 2 in N 2 Analysis Char residue: Na, K, Ca, V, S, B, C, CO 3 Dissolving the char and analysing the formed solution for OH, CO3, S, B

12 Borate Autocausticization Aim: Determine the reduction of carbonate in gasification smelt due to reaction: Na + 2CO3 + NaBO 2 Na 3BO3 CO2 Two analytical possibilities: reduction of carbonate concentration in smelt hydroxide formation when dissolving the char

13 Borate Autocausticization - Analysis In a gasifier: NaBO 2 + Na 2 CO 3 Na 3 BO 3 + CO 2 In the smelt dissolver: Na 3 BO 3 + H 2 O 2 NaOH + NaBO 2 (aq) Hydroxide formation is based on both reactions above Reduction of carbonate concentration in the smelt on the first reaction

14 Temperature influence (LEFR) *10-4 g / g Ca CO Borate doped kraft liquor Kraft liquor Kraft liquor 5% CO 2 in N 2 Atm pressure Ca as tie component CO 3 2- based Temperature ( o C) Decreasing amount of carbonate in char with increasing temperature No clear influence of borate addition

15 CO 2 influence (LEFR) *10-4 g/ g Ca CO 3 2- based, Ca as tie component Borate doped kraft liquor Kraft liquor Kraft liquor 1000 C Atm pressure CO CO 2 (%) in N 2 Increasing amount of carbonate in char with increasing CO 2 No clear influence of borate addition

16 CO 2 influence (LEFR) OH - g / g Ca OH - based, Ca as tie component Borate doped kraft liquor Kraft liquor Kraft liquor 1000 C Atm pressure CO 2 (%) in N 2 Increasing amount of hydroxide in char with increasing CO 2 More hydroxide for the borate doped liquor

17 Fixed carbon conversion (LEFR) Kraft liquor and atm pressure 1000 C 5% CO 2 in N fixed carbon conversion Borate doped kraft liquor Kraft liquor fixed carbon conversion Borate doped kraft liquor Kraft liquor CO 2 (%) in N 2 Temperature ( o C) High degree of fixed carbon conversion (>99%) above 1000 C and with 5% CO 2 in the gas phase

18 Pressure influence (PEFR) 35 % Autocausticization Soda liquor (from carbonate analysis) Kraft liquor (from carbonate analysis) Soda liquor (from hydroxide analysis) Kraft liquor (from hydroxide analysis) 1000 C 5% CO 2 in N Pressure (bar) No strong influence of pressure on autocausticization More autocausticization for the soda liquor trends are the same but difference in absolute numbers between the analytical methods

19 Major findings Very small difference between doped and undoped liquors No strong evidence that the borate addition has achieved the desired effect (autocausticization) The different analytical methods (CO 3 2- and OH - ) give different absolute numbers but the trends are similar More autocausticization with the soda liquor than kraft liquor

20 Acknowledgement The group at IPST invaluable experimental support from Xiaoyan Zeng, Alan Ball, Christopher Young Dr. Kristiina Iisa s patience and willingness to work out a schedule for the utilization of the LEFR

21 Acknowledgement Financial support The Swedish BLG program STEM, MISTRA, SmurfitKappa Kraftliner, SCA, Södra, Sveaskog, Vattenfall, Länsstyrelsen, Chemrec Travel grant from IEA for the PEFR experiments Travel grant from The Swedish scientific council for the LEFR experiments