Sulfuric Acid
An alternative outlet for sulfur to the production of merchant sulfur is sulfuric acid. This is particularly interesting in locations where there is significant production of phosphate fertilizers, such as Florida, where the Polk IGCC unit processes its acid gas to sulfuric acid rather than sulfur. Other examples can be found in ammonia plants, which have formed the core of complex fertilizer production sites in Portugal and China, for example.
Processing H2S to sulfuric acid differs from conventional acid plants (whether using sulfur or metallurgical off gases as feed) in that water is already present in the converter. This water reacts immediately with the S03 formed there and therefore demands a totally different approach to the recovery of liquid acid compared with a standard double absorption unit.
The H2S component of the acid gas is first combusted with excess oxygen to form S02 and water (see Figure 8-18). The excess is selected to produce a 02/S02 ratio in the hot gas of between 1.1 and 1.3. The hot combustion gases are cooled in a waste — heat boiler to a converter inlet temperature of 440°C. The S02 and oxygen react over a vanadium catalyst according to the reaction
S02+1/202<—>S03 (8-6)
and the water reacts with S03 as follows
S03 + H20<—>H2S04 (8-7)
The converter uses interbed quenching with cold air to control the temperature increase arising from these exothermic reactions. Depending on the feed gas quality, three or four catalyst beds are included.
Since the acid is already present in the gas phase leaving the converter, this is recovered by condensing at about 60°C. In a classic wet catalysis plant, the product is a 78% acid, below the 80-90% range that is critical for corrosion. The condensation is achieved by recycling this product acid to the condensation tower in a manner designed to minimize formation of acid aerosols. A candle filter is provided to remove any aerosols that are formed. If there is insufficient water in the gas leaving
|
Figure 8-18. Wet Catalysis Sulfuric Acid Plant (With permission: Lurgi) |
the converter, then make-up water is added to keep the acid strength at 78%—out of the corrosive range.
Advanced wet catalysis processes such as Concat (Lurgi) or WSA (Topspe) are able to produce 93-98% strength acid, even with very weak feed gases and excess water. Concat achieves this, for example, by using a two-stage condensation section, the first of which operates at 180-230°C so that a minimum of free water is present in the condensate, which is already about 93% H2S04.
REFERENCES
Air Liquide. Available at: www. airliquide. com.
Air Products. Company brochure, 2001.
Allam, R. J., Russek, S. L., Smith, A. R., Stein, V. E. “Cryogenics and Ceramic Membranes: Current and Future Technologies for Oxygen Supply in Gasification Systems.” Paper presented at IChemE Conference “Gasification for the Future”, Noordwijk, April 2000.
Allam, R. J., Foster, P. F., and Stein, V. E. “Improving Gasification Economics through ITM Oxygen Integration.” Paper presented at IChemE Conference “Gasification: The Clean Choice for Carbon Management”, Noordwijk, April 2002.
Armstrong, P. A., Stein, V. E., Bennet, D. L., and Foster, E. P. “Ceramic Membrane Development for Oxygen Supply to Gasification Applications.” Paper presented at Gasification Technologies Conference, San Francisco, October 2002.
Bajohr, S., Hoferer, J., Reimert, R., and Schaub, G. “Thermische und katalytische Umsetzung von Kohlenwasserstoffen in Rohgasen aus der Pyrolyse und aus der Vergasung von Bio — massen,” Paper presented at the DGMK Conference “Energetische Nutzung von Biomassen”, Velen, April 2002.
BASF. BASF Catalyst К 8-11. Technical leaflet. (Undated.)
Boerrigter, H., den Uil, H., and Calis, H.-P. “Green Diesel from Biomass via Fischer-Tropsch Synthesis: New Insights in Gas Cleaning and Process Design.” Paper presented at Pyrolysis and Gasification of Biomass and Waste Expert Meeting, Strasbourg, October 2002.
Butzert, H. E. “Ammonia/Methanol Plant Startup.” Chemical Engineering Progress 72 (Januaiy 1976):78-81.
Collodi, G. “Commercial Operation of ISAB Energy and Sarlux IGCC.” Paper presented at Gasification Technologies Conference, San Francisco, October 2001.
de Graaf, J. D., Zuideveld, P. L., van Dongen, F. G., and Holscher, H. “Shell Pernis Netherlands Refinery Residue Gasification Project.” Paper presented at IChemE Conference, “Gasification for the Future,” Noordwijk, April 2000.
Griinewald, G. “Selective Physical Absorption Using the Purisol Process.” Paper presented at 6th Continental Meeting of the European Chapter of the GPA, Bremen, 1989.
Gupta, R. “Emerging Technologies for the Production of Ultraclean IGCC Syngas,” Gasification Technologies Conference, San Francisco, 2001.
Higman, C. “Gasification of Heavy Residues.” Paper presented at IMP Gasification Seminar, Mexico City, 1994.
Hirtl, C. (Linde AG) Personal communication. September 2002.
Hofbauer, H. “Biomass CHP-Plant Giissing: A Success Story.” Paper presented at Pyrolysis and Gasification of Biomass and Waste Expert Meeting, Strasbourg, October 2002.
Knab, H., Neumann, G., and Nehb, W. “Operating Experience with Lurgi OxyClaus Technology.” Paper presented at Achema, Frankfurt, June 1994.
Kohl, A., and Nielson, R. Gas Purification. Boston: Gulf Publishing, 1997.
Korens, N., Simbeck, D. R., and Wilhelm, D. J. “Process Screening Analysis of Alternative Gas Treating and Sulfur Removal” SFA Pacific for U. S. Department of Energy, Mountain View, CA, December 2002.
Koss, U., Meyer, M., and Schlichting, H. “Zero Emissions IGCC with Rectisol Technology” Paper presented at Gasification Technologies Conference, San Francisco, October 2002.
Kriebel, M. “Gas Production” In Ullmann s Encyclopedia of Industrial Chemistry, 5th ed., vol. A12. Weinheim: VCH Verlagsgesellschaft, 1989, p. 265.
Kubek, D. J., Polla, E., and Wilcher, F. P. “Purification and Recovery Options for Gasification.” Paper presented at IChemE Conference, “Gasification Technology in Practice,” Milan, February 1997.
Kubek, D. J., Sharp, C. R., Kuper, D. E., DiDio, M., and Why sail, M. “Recent Selexol, PolySep, and PolyBed Operating Experience with Gasification of Power and Hydrogen. Paper presented at Gasification Technologies Conference, San Francisco, October 2002.
Lell, R. “New Technology for Sulfur Recovery from Tail Gases Based on the Sulfreen Process.” Paper presented at “Sulfur 93” Conference, Hamburg, April 1993.
Miller, G. Q., and Stoecker, J. “Selection of a Hydrogen Process.” Paper presented at NPRA Annual Meeting, San Francisco, 1989.
Morris, M., and Waldheim, L. “Update on Project ARBRE, UK.” Paper presented at IChemE Conference, “Gasification: The Clean Choice for Carbon Management” Noordwijk, The Netherlands, April 2002.
Muller, H. (2002) “Sulfuric Acid and Sulfur Trioxide.” In Ullmann s Encyclopedia of Industrial Chemistry. Weinheim: Wiley VCH, 2002.
Nagl, G. L. “Liquid Redox Enhances Claus Process.” Sulfur 274 (May-June 2001).
Nehb, W. “Sulfur.” In Ullmann s Encyclopedia of Industrial Chemistry, vol. A25. VCH, 1994.
Praxair. Available at: www. praxair. com.
Sharp, C. R. “Recent Selexol and Membrane/PSA Operating Experiences with Gasification for Power and Hydrogen.” Paper presented at Gasification Technologies Conference, San Francisco, October 2002.
Simbeck, D. “Industrial Perspective on Hot Gas Cleanup.” Paper presented at 5th International Symposium, “Gas Cleaning at High Temperatures,” Morgantown, 2001.
Smith, A. R., and Klosek, J. “A Review of Air Separation Technologies and Their Integration with Energy Conversion Processes.” Fuel 80 (2001): 115-134.
Stevens, D., Stern, L. H., and Nehb, W. (1996) “OxyClaus Technology for Sulfur Recovery.” Paper presented at Laurence Reid Gas Conditioning Conference, Norman, Oklahoma, March 1996.
Supp, E. How to Produce Methanol from Coal. Berlin: Springer, 1990.
U. S. Department of Energy. “Pinon Pine IGCC Power Project: A DoE Assessment.” DoE/ NETL report 2003/1183, December 2002.
Weiss, M.-M. “Selection of the Acid Gas Removal Process for IGCC Applications.” Paper presented at IChemE Conference, “Gasification Technology in Practice,” Milan, February 1997.
Zwiefelhofer, U., and Holtmann, H.-D. “Gas Expanders in Process Gas Purification.” Paper presented at VDI-GVC Conference, “Energy Recovery by Gas Expansion in Industrial Use,” Magdeburg, Germany, 1996.
Chapter 9