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Adriaan van Heiningen University of Maine IEA, August 21st, 2002 Pitea, Sweden

Integrated Sulfur Recovery and Causticization for Kraft Black Liquor Gasification. Adriaan van Heiningen University of Maine IEA, August 21st, 2002 Pitea, Sweden. Increased Causticizing Requirement.

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Adriaan van Heiningen University of Maine IEA, August 21st, 2002 Pitea, Sweden

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  1. Integrated Sulfur Recovery and Causticization for Kraft Black Liquor Gasification Adriaan van Heiningen University of Maine IEA, August 21st, 2002 Pitea, Sweden

  2. Increased Causticizing Requirement • H2S generation creates equal moles of Na2CO3, which in the recovery boiler is Na2S or ½(NaOH+NaHS), so a 30% sulfidity white liquor (Na2S/NaOH=0.43 mole/mole) and complete volatilization of the sulfur leads to 43% increased causticization requirement • Absorption in weak wash leads to co-absorption of CO2. At a selectivity factor of 10 moles H2S/mole CO2 this increases the causticization by another 60%

  3. Solution for Low T Gasification Direct Causticization with TiO2 Direct causticization reactions in gasifier: 3 TiO2 + Na2CO3 Na2O.3TiO2 + CO2 (1) 5 (Na2O.3TiO2) + 7 Na2CO3 3 (4Na2O.5TiO2) + 7 CO2 (2) Hydrolysis reaction in leacher: 3 (4Na2O.5TiO2) + 7 H2O  5 (Na2O.3TiO2) + 14 NaOH (5)

  4. Direct Causticization in the MTCI Steam Reformer

  5. Na2CO3 (and K2CO3) to be converted to titanates (Eutectic of Na2O.3TiO2 + 4Na2O.5TiO2 is 985 °C) 14 NaCl + 5(Na2O.3TiO2) + 7H2O  3(4Na2O.5TiO2) + 14 HCl Presence of steam and titanate reduces NaCl content Na2S + CO2 + H2O  Na2CO3 + H2S Volatilization of H2S is favored by high total P and low T Selection of Operating Conditions Criterium: Avoid formation of low melting point eutectic salt mixture (Na2CO3, Na2S, NaCl, K2CO3) and K decreases with increasing temperature

  6. Direct Causticization Process Conditions • K = equilibrium constant of H2S release from Na2S • td = time for 100% conversion of NT3 into N4T5 • tc = time for 100% conversion of organic carbon • P = total pressure Conclusions: 1. Minimum operating temperature of 675 °C 2. Pressurized gasification above 700 °C 3. At maximum temperature of 800 °C the solids residence time is reduced to 0.3 hours

  7. H2S Removal in KBL IGCC Various H2S scrubbing processes are possible: Absorption in weak wash. Na2CO3+ H2O + CO2 2 NaHCO3 (1) This increases lime requirements as can be inferred from: 2NaHCO3 + 2Ca(OH)2 2CaCO3 + 2NaOH + H2O (2) Na2CO3+ Ca(OH)2 CaCO3 + 2 NaOH (3) 2. Amine-based H2S absorption-stripping systems. Adds complexity of Claus plant for H2S to S conversion. Also recovered H2S still contains CO2

  8. Sulfur Capture By A Regenerative Calcium Based Process Sulfur Capture: H2S + CaO  CaS + H2O (1a) H2S + Na2CO3  CaS + CO2 + H2O (1b) CaS Conversion: CaS + NaOH  NaHS + Ca(OH)2 (2a) CaS + Na2CO3 + H2O  CaCO3 + NaHS + NaOH (2b) Calcination: Ca(OH)2  CaO + H2O(3a) CaCO3  CaO + CO2 (3b) Note that: Na2S + H2O  NaHS + NaOH

  9. Calcination and H2S RecaptureCaCO3CaO+CO2; Na2CO3+H2SNa2S+CO2+H2O

  10. Combining Calcium Based Sulfur Recovery with Gasification • Calcination in gasification gas of 1 or 20 atm. requires temperature above resp. 775 and 975 °C • Calcination of CaCO3 and avoiding H2S recapture by Na2CO3 are incompatible Conclusions:1. Desulphurization with CaO must be performed in separate reactor operating 100 °C above T of gasification reactor with TiO2 as bed material. 2. Desulphurization with CaCO3 or CaO may be combined with high T gasification

  11. Integrated Low T Gasification

  12. Integrated High T Gasification

  13. Process Integration Advantages Low T Process Version • Production of NaOH and sulfur rich liquors • Increased black liquor throughput • Increased carbon conversion • Increased tar conversion (also in CaS reactor!) • Elimination of lime cycle High T Process Version • Same causticizing requirement as conventional • Reduced capital cost • Simplest process

  14. Process Integration Technology Gaps Low T Process Version • Pulping benefits resulting from split sulfidity and polysulfide (with/without AQ) liquors (NCSU) • Direct causticization kinetics; Effect of low T, CO2 pressure and TiO2 particle size and source) • Pilot and PDU verification tests (MTCI and U of Utah) • Removal of NPEs from leached titanate product • Optimization of 4Na2O.5TiO2 leaching process • Desulphurization and tar cracking kinetics of CaO/CaS; Effect of Ca source and particle size, type of sulfur gas • System analysis (NCSU and VTT)

  15. Process Integration Technology Gaps High T Process Version • Desulphurization kinetics of CaO/CaCO3; Effect of T, Ca quality and particle size, P (IPST), type of sulfur gas, and mixtures with black liquor. • White liquor generation kinetics from CaS by Ca(OH)2 suspension and/or Na2CO3 solution; Effect of T, Ca quality and [NaOH] • Industrial validation (Weyerhaeuser) • System analysis (VTT)

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