7/24/2019 Revamp of Ammonia Plants http://slidepdf.com/reader/full/revamp-of-ammonia-plants 1/5 From our investigation of HK40 material, it was confirmed that the macrostructure of the metal is the most significant factor affecting the creep-rupture properties. Therefore, the macrostructure of the speci- men should b e inspected and recor ded for discussion of the creep-rupture properties of heat-resisting alloy castings. Our destructive investigation of catalyst tubes used for long periods of time reveals that the maximum wall thickness of the catalyst tubes for steam reformers should be limited to reduce creep damage due to ther- mal stresses. Controlling the macrostructure of individual cast tubes and of weld metals can contribute to prolonging the catalyst tube life, even if the material and the wall thickness are kept the same. In order to prevent too great an increase in the wall thickness, modified HK40 material, such as IN519, Hika, or BST alloys, should be used for the catalyst tubes of steam reformers. LITERATURE CITED 1. 2. 3. 4. 5 6. 7. 8. National Research Institute for Metals,” “NRIM Creep Data Sheet, No. 16” (1974). National Research Institute for Metals, “NRIM Creep Data Sheet, No. 16A” (1980). Kawai, T., K. Takemura, T. Shibasaki, and T. Mohri, “Effect of Macrostructure on Catalyst Tube Damage and Creep Rupture Properties of HK40”, AIChE, Ammonia Plnnt Safety, 22, 119 (1979). Ohta, S., “Report of the 123 Committee on Heat-Resisting Metals and Alloys, Japan Society for the Promotion of Sci- ence,” Vol. 18, 383 (1977). Kawai, T., K. Takemura, T. Shibasaki, and T. Mohri, private report, “Catalyst Tube No. 3” Topsae-Chiyoda Steam Re- former Symposium, July (1977). INCO Europe Limited, Inco Databooks, “IN-519 Cast Chromium-Nickel-Niobium Heat-Resi sting Steel ” (1976). Sasaki, R., H. Hataya, and Y Fukui, Institute ofMechanicaZ Engineer Vol. 13, 169.1 (1973). Zaghloul, M. B. E. Doctoral Thesis, Tokyo Inst. ofTech. (1976). Takao Kawai, is assistant principal e ngineer at the combustion engineering department of Chiyoda Chemical Engineering Construction Co., Ltd., and is responsibl e for the devel opment of a furnace for high temperature services. He holds a B.S. and M.E. degr ee from the Tokyo Institute of Technol. O Y. Katsuaki Takemura, is assistaut principal eng ine er at material and welding technology department, and earne d his B.E. and M.E. degree in metallur- gical engineering at the Tohoku University, Sen- dai. Current responsibilities include material evaluation and development of welding technol- ogy. Toshikazu Shimbasaki is the material and welding technology department engineer. His work in- volves materials engineering at elevated tempera- ture services, welding technology and failure analysis. He holds a B.E. and M.E. degree in met- allurgical engineering from the Tohoku Univc: sity, Sendai. Takaaki Mohri, is heater engineer at the combus- tion engineering department, and is engaged in the development of a furnace for high tempera ture services. He holds a B.S.M.E. degree from the col- lege of Science and Technology, Nihon Univer- sity. Revamp of Ammonia Plants A reduction of the steam/carbon ratio below the traditional level can result in a considerably higher energy efficiency. Anders Nielsen, John B. Hansen, Jens Houken, and Erik A. Gam, Haldor Topsoe NS Lyngby, Denmark. The rapid escalation of the costs of hydrocarbons during the last decade has brought about increasing interest in re- vamping ammonia plants for energy savings. Today’s costs of natural gas and projected prices may justify investments in the range of several millions of U.S. dollars. In connection with the production of synthesis gas in plants based on steam reforming, an appreciable improve- ment of the efficiency can be achieved by decreasing the overall energy loss due to the large amounts of excess pro- cess steam usually consumed. The present paper deals with various aspects ofthe mod- ification of existing ammonia plants to operate at a steam/- carbon ratio appreciably below the usual level of 3.7-4.0. ISSN 0278-4513-82-6329-0186-$2.00. he American Institute of Chemical Engineers, 1982. REFERENCE PLANT In order to describe the changes of the operating condi- tions brought about by a substantial decrease ofthe steaml- carbon ratio, and in order to determine the potential en- ergy savings, a typical ammonia plant designed by Haldor Topsoe JS at the end of the sixties has been taken as a starting point. It may be expedient to mention the process sequence. Desulfurization of the hydrocarbon feed stock is carried out using hot zinc oxide at about 400°C (750°F).If necessa- ry-due to the pre sence of refractory sulfur compounds-a hydrogenation step is inserted upstream of the zinc-oxide vessels. Reforming of the hydrocarbons at about 34 bar (480 psig) takes place in two steps, primary reforming in a 186 July, 1982 Plant/Operotions Progress Vol. 1, No. 3)
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