Refincor Ammonium Chloride References

5F8.8-01: HYDROCRACKER AND HDS UNIT:

D. R. Clarida discussed increasing problems with corrosion of HDS effluent exchangers over the past 18 months, seemingly related to ammonium chloride. He speculated as to whether this was due to not doing an adequate job of removing chlorides on the crude units because of poorer quality crudes being changed, or whether more ammonia is being produced on the HDS units. The exchangers are midway down the effluent train, and two are 304 stainless steel and the rest carbon steel.

92C5.7-11: HYDRODESULFURIZATION UNIT:

George Moller (Consultant) experienced cracking in a hydrotreater desulfurizer prefractionator feed/bottoms exchanger. Feed is on the shellside, enters at ~280øF, and leaves at ~450øF. Bottoms on the tubeside enter at ~460øF and leave at ~290øF. The carbon steel life was relatively short at 1 to 1-1/2 yrs. AL6XN was available off the shelf; they had 2 years' successful service under similar conditions on a different unit. The AL6XN failed in the hottest section at 400ø to 450øF in 2 to 8 months with transgranular cracking. They blamed it on ammonium chloride cracking. The only difference was perhaps the Cl in the recycle gas was higher on the unit where they had the problems. AL6XN will crack in a boiling magnesium chloride solution test, but not in boiling NaCl or boiling NH4Cl solutions. However, AL6XN does crack in NH4Cl in an autoclave at 440øF. He would advise against the use of AL6XN in the future since you can't always plan on the chloride content.

93F5.6-01: HYDROCRACKER AND HDS UNIT:

Jon Dobis (BP) - They had a failure in a second stage reactor effluent air cooler in a hydrocracker. The cooler was carbon steel and about 20 years old. The bottom row of tubes corroded out. They had lost trays in the recycle splitter tower which caused the first stage stripper to operate at 10 to 25øF lower in temperature. As a result, they carried a small amount of water into second stage. They knew they had ammonium chloride in the second stage but it was normally dry enough not to have problems. The water carryover allowed corrosion to begin. During the upset operation, they determined corrosion rates were 75 to 100 mpy. They also had deposits on outlet header and piping. These deposits gave a pH <1 when dissolved in water.

93F5.7-02: HYDRODESULFURIZATION UNIT:

Joerg Gutzeit (Consultant) commented that amine hydrochlorides can be like ammonium chloride. They don't need water to cause corrosion but the salts are hygroscopic and can draw water from the environment. There is some data that shows corrosion rates as a function of humidity for ammonium chloride. At about 20 to 40% humidity, which is a relatively dry system, corrosion rates were in the 50 to 60 mpy range.

93F5.7-05: HYDRODESULFURIZATION UNIT:

Jim Edmondson (Betz) would draw a distinction between ammonia and amine chlorides. Many of the amine chlorides will be molten. Their data show that these salts are much more aggressive in the absence of water than solid salts like ammonium chloride. They will be presenting a paper at CORROSION/94 on vapor pressure relationships for amine salts.

85F8.8-01: HYDROCRACKER AND HDS UNIT:

D. R. Clarida discussed increasing problems with corrosion of HDS effluent exchangers over the past 18 months, seemingly related to ammonium chloride. He speculated as to whether this was due to not doing an adequate job of removing chlorides on the crude units because of poorer quality crudes being changed, or whether more ammonia is being produced on the HDS units. The exchangers are midway down the effluent train, and two are 304 stainless steel and the rest carbon steel.

 

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