Q & A > Question Details
The Delayed Coker Unit (DCU) and the FCC GasCon Dry Gas is treated in an Amine Unit (with MDEA), in order to eliminate H2S, prior to injection into the refinery fuel gas system. However, operational problems have been experienced at the Amine Unit, due to MDEA degradation and the presence of heat stable salts (HSS), among other factors.
We know that HSS formation is due to an irreversible reaction between some contaminants (strong acids anions such as formate, acetate, thiosulfate, thiocyanate and chloride) and the amines molecules. Furthermore, we know that the DCU Gas contains anions such as acetate, formate and cyanide.
However, we have no available information about the contaminant concentration in the DCU Gas or FCC GasCon Dry Gas.
Do you have any information related to a typical contaminant concentration (e.g. strong acids anions) for a DCU and/or FCC GasCon Dry Gas? Moreover, any additional information would be appreciated (E.g. What kind of process do you think would be appropriate for reducing contaminants concentration? We have heard that a water wash stage previous the amine treating could be useful).
21/07/2011 A: Sudhakara Babu Marpudi, Dangote Oil Refinery Company, m_sudhakarababu@yahoo.com
To handle the Amine degradation caused by Heat stable salts, HSS filteration units are available in the market. One such unit is supplied by M/s Amipure. Other suppliers are also available for HSS removal from Amine.
27/07/2009 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
HSS concentration in amine should be maintained below 1%. This can be accomplished by removal using a small ion exchange unit on a lean amine slipstream. This is well proven to maintain HSS at levels below 1%. In conjunction, care should also be taken to ensure other impurities are not introduced into the amine unit also or are allowed to build up. Liquid hydrocarbon carryover from FCC and/ or DCU can also adversely effect amine unit performance and often result in foaming and amine unit instability. High efficiency SepraSol LG coalescer can prevent liquid HC entry into amine unit if it is occurring. As well as removing free H/C, SepraSol LG coalescers also remove some HSS precursors. PhaseSep Liquid liquid coalescer is also now commercially proven to remove liquid H/c's from rich amine. Particulate matter (mainly corrosion products) in amine system loop can also stabilise foam and suspended solids foul lean/rich HX, contactores and regenerator towers. Total Suspended Solids (TSS) should be maintained at <5 ppmw and preferably ~1ppmw. 10um absolute rated filters (beta ration>5000) can achieve TSS levels in this range. Water wash can help to remove some water soluable HSS precursors and combined with high efficiency filters and coalescers can reduce amine contamination issues and ensure stable amine plant operation. We would recommend a site audit to determine the optimum approach in each case as each refinery unit layout and needs are different. Pall Corp offers such a consulting service as a part of our Amine Reliability Program.
26/07/2009 A: Egbert van Hoorn, Hocon B V, Egbertvh@hotmail.com
The treatment of DCU gas but also FCC gas often creates problems in refineries with HSS or HSAS. The most important reason is that this gas contains HCN. These gasses do NOT contain acids such as acetate formate. The HCN present in the gas reacts to form HSCN and HCOOH in your amine solution.

HCN + FeS <== > HSCN +Fe
HCN + 2 H2O <==> HCOOH + NH3

Other acids present in your amine solution may come from oxygen being present in the FCC gas.
The formed acids in your amine solution can cause problems like corrosion in the regenerator or not enough amine present to absorb all H2S.
There is very little typical information available about the concentration of HCN or oxygen in these gasses. A lot depends on the operating conditions of the DCU and the FCC.
HCN can be removed from these gasses with a water wash column, possibly in combination with a scavenger or amonium polysulphide.
A water wash will require a multiple tray column.
In a lot of cases it is therefore more economical to remove or neutralise the acids from the amine solution.
This can be in several ways and would be a it long to explain here.