Design guidelines for urea hydrolysers for ammonia demand of the SCR DENOX project in coal-fired power plants

Abstract

Ammonia is highly volatile and will present substantial environmental and operation hazards when leaking into the air. However, ammonia is the most common reactant in the DENOX project to eliminate NO_x in the flue gas. The storage and transportation of liquid ammonia has always been a dilemma of the power plant. Urea is a perfect substitute source for ammonia in the plant. Urea hydrolysis technology can easily convert urea into ammonia with low expense. Presently, there is still no self-depended mature urea hydrolysis technology for the DENOX project in China; therefore, this paper proposes several guidelines to design the urea hydrolyser by theoretical analysis. Based on theoretical analysis, a simulation model is built to simulate the chemical reaction in the urea hydrolyser and is validated by the operational data of the commercial hydrolyser revealed in the literature. This paper endeavors to propose suggestions and guidelines to develop domestically urea hydrolysers in China.

Keywords

urea / hydrolyser / ammonia / selective catalytic reduction (SCR)

References

[1] Chao G T Y. Urea its Properties and Manufacture. West Covina: Chao’s Institute, 1967

[2] Mu G W. Nitrogen Process Design Handbook. Beijing: Chemical Industry Press, 1988

[3] Bhattacharya S, Peters H J, Fisher J, Spencer H W III. Urea to ammonia (U2A^TM) systems: Operation and process chemistry. 2003, http://www.ecctech.com/pdfs/2003%20MEGA%20U2A.pdf

[4] Sahu J N, Patwardhan A V, Meikap B C. Response surface modeling and optimization for production of ammonia from urea in a batch reactor. Asia-Pacific Journal of Chemical Engineering, 2009, 4(4): 462–470

[5] Kawazuishi K, Prausnitz J M. Correlation of vapor-liquid equilibria for the system ammonia-carbon dioxide-water. Industrial & Engineering Chemistry Research, 1987, 26(7): 1482–1485

[6] Goppert U, Maurer G. VLE in aqueous solution of ammonia and carbon dioxide at temperature between 333 and 393 K and pressure up to 7 MPa. Fluid Phase Equilibria, 1988, 41(1,2): 153–185

[7] Wei S A, Zhang H J. Calculation of H₂O-NH₃-CO₂ vapor-liquid equilibria at high concentration conditions. Chemical Industry and Engineering., 2004, 12(1): 134–136

[8] Spencer H W III, Peters H J, Hankins W. Design considerations for generating ammonia from urea for NO_x control with SCRs. 2008, http://www.ecctech.com/pdfs/Paper%200835%20AWMA%202007%20-Spencer,%20Peters,%20Hankins.pdf

[9] Brooks B, Jessup W A, Macarthur B W, Sheats W B. Process and apparatusfor quantitatively converting urea to ammonia on demand. <patent>US Patent No. US7008603B2</patent>, 2006

[10] Macarthur B W, Jessup W A, Brooks B. Method for removing contaminants in urea hydrolysis reactor. European Patent No. <patent>EP1 322 553B1</patent>, 2005

[11] Cooper H B H, Spencer H W. Methods for the production of ammonia from urea and/or biuret, and uses for NO_x and/or particulate matter removal. US Patent No. US6730280B2, 2004

[12] Lagana V. Process for ammonia production through urea hydrolysis. US Patent No. <patent>US5985224</patent>, 1999

[13] Sahu J N, Gangadharan P, Patwardhan A V, Meikap B C. Catalytic hydrolysis of urea with fly ash for generation of ammonia in a batch reactor for flue gas conditioning and NO_x reduction. Industrial & Engineering Chemistry Research, 2009, 48(2): 727–734

[14] Sahu J N, Patwardhan A V, Meikap B C. Equilibrium and kinetic studies of in situ generation of ammonia from urea in a batch reactor for flue gas conditioning of thermal power plants. Industrial & Engineering Chemistry Research, 2009, 48(5): 2705–2712

[15] Sahu J N, Mahalik K K, Patwardhan A V, Meikap B C. Equilibrium studies on hydrolysis of urea in a semi-batch reactor for production of ammonia to reduce hazardous pollutants from flue gases. Journal of Hazardous Materials, 2009, 164(2,3): 659–664

[16] Mahalik K, Sahu J N, Patwardhan A V, Meikap B C. Kinetic studies on hydrolysis of urea in a semi-batch reactor at atmospheric pressure for safe use of ammonia in a power plant for flue gas conditioning. Journal of Hazardous Materials, 2010, 175(1–3): 629–637

[17] Sahu J N, Chava V S R K, Hussain S, Patwardhan A V, Meikap B C. Optimization of ammonia production from urea in continuous process using ASPEN Plus and computational fluid dynamics study of the reactor used for hydrolysis process. Journal of Industrial and Engineering Chemistry, 2010, 16(4): 577–586

[18] Mahalik K, Sahu J N, Patwardhan A V, Meikap B C. Statistical modelling and optimization of hydrolysis of urea to generate ammonia for flue gas conditioning. Journal of Hazardous Materials, 2010, 182(1–3): 603–610

[19] Aoki H, Fujiwara T, Morozumi Y, Miura T. Measurement of urea thermal decomposition reaction rate for NO selective non-catalytic reduction. In: Proceedings of 5th International Conference on Technologies and Combustion for a Clean Environment. Lisbon, Portugal, 1999, 115–118

[20] Liu Y. Optimum operation of urea hydrolization. Chemical Fertilizer Design, 2000, 38(4): 30–34 (in Chinese)

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg