C HEMENTATO R Source: Fluor
Gas to absorber 535 Mlb/h (240 m.t./h)
Gas to absorber
120°F (49°C)
FC
115°F (46°C)
535 Mlb/h 120°F (240 m.t./h) (49°C)
LC
TC
85 Mlb/h (39 m.t./h)
2,900 Mlb/h 70 MMBtu/h (1,320 m.t./h) (17.6 Gcal/h)
Water
LC
115°F (46°C)
TC
LC
2,900 Mlb/h 39 MMBtu/h (1,320 m.t./h) (9.8 Gcal/h) Refrigerant
Refrigerant
138°F (59°C)
LC 128°F (53°C) 143°F (62°C)
55 MMBtu/h (13.9 Gcal/h)
Water 35 Mlb/h (16 m.t./h)
FC 138°F (59°C)
LC
5,500 Mlb/h (2,500 m.t./h)
167°F (75°C) Makeup water
169°F (76°C)
Hot hydrogenated tail gas
620 Mlb/h (280 m.t./h)
Water 50 Mlb/h (23 m.t./h)
LC 154°F (68°C) 32 Mlb/h (15 m.t./h)
390°F (200°C)
86 MMBtu/h (21.7 Gcal/h)
157°F (69°C)
Hot hydrogenated tail gas
Makeup water 32 Mlb/h (15 m.t./h)
390°F (200°C)
LC FC
620 Mlb/h (280 m.t./h)
LC FC
167°F (75°C)
169°F (76°C)
1.400 Mlb/h (630 m.t./h)
1.400 Mlb/h (630 m.t./h)
Conventional design
Improved design
MMBtu = 1 million Btu Mlb/h = 1,000 lb/h m.t. = metric ton
New condenser design for Claus tail gas slashes refrigeration duty
L
ast month, at the AIChE Spring Meeting in Chicago, Henry Kister, director of Fractionation Technology at Fluor Corp. (Aliso Viejo, Calif.; www. fluor.com) presented a patent pending process (U.S. Patent Application WO/2011/016797) that promises to cut energy demand and capital costs for direct contacting condenser (DCC) units that would typically require refrigeration or cooling water in the pretreatment of Claus sulfur-laden tail gas. In a conventional process, tail gas from the Claus plant is hydrogenated to convert all the sulfur species to H2S. The tail gas is then cooled in a DCC (flowsheet, left) to prepare it for absorption in an amine-based H2S-removal unit. In many situations, DCC air coolers cannot sufficiently cool the H2Sremoval unit’s feedgas stream. And in arid regions, cooling water is usually not available for trim cooling, so expensive refrigeration must be used. Fluor’s new process (flowsheet, right), 12
developed and patented by Kister and Dick Nielson, vice president, of Process Technology at Fluor, splits the direct-contact tower’s packed bed into two direct-contact packed beds, and the pumparound circuit into two separate circuits. The bottom pumparound circuit is all air-cooled, while the top pumparound circuit is all refrigerant or water-cooled. The new DCC design transfers as much as 50% of trim cooling duty to the air cooler, says Kister, and results in a significant net reduction in capital costs. “You’re no longer stuck with two pinches,” says Kister. So, for each bed the temperature approach at the bottom can be larger (say 15°F or 8°C, compared to say 9°F or 5°C for the conventional process), which reduces required bed heights and renders the bed far less sensitive to liquid maldistribution and fouling, he explains. Meanwhile, the higher temperature approach in the bottom section readily
CheMiCaL engineering WWW.Che.CoM apriL 2011
permits using a low (say 5°F or 3°C) temperature approach between the process water and gas at the top of each bed. This low temperature approach at the top of the bottom bed brings the refrigeration savings, allowing more heat to be removed in the air-cooler pumparound loop. An evaluation of two recent large-scale Middle East projects indicated that this new design would result in about $13–20 million in power savings over a 20-year life of the plants and an additional $40–70 million in capital cost savings.
Ta heat exchangers Last month, Tantaline (Waltham, Mass.; www.tantaline.com) launched the irst fully welded plate-and-frame heat exchanger designed speciically for hot acids and corrosive materials. The tantalum-surface alloyed exchangers are said to have a heattransfer efficiency 5–7 times higher than shell-and-tube designs, which
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