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How much silicon is critical in SMR catalysts?

Feb-2025

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Ilya Sutyrin, OOO LINK, ilyasutyrin83@gmail.com

What maximum silicon content is allowed on the SMR catalyst carrier.

Feb-2025
Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

About this topic there are two approaches to be considered: Silicon in the feed of the SMR processing unit - This a more significant concern for refiners producing hydrogen from naphtha, which is normally straight run naphtha. Considering the deleterious effects of the silicon over the catalyst that is basically the same observed on hydrotreating units, the pre-treating section (normally CoMo catalyst bed) will be saturated by silicon raising the sulfur compounds concentration in the feed which will saturate the ZnO bed and then deactivating the steam reforming catalyst. The silicon limit will rely on the capacity of the CoMo catalyst to deal with this contaminant according to the desired operational life cycle of the processing unit which will determine the volume of the catalyst (CoMo) applied in the pretreatment bed. Typically, the silicon in the naphtha fed to the hydrogen processing unit is controlled below 1.0 ppmw. Silicon in the boiler feed water (BFW) - When the feed water has high silicon content, this can reach the gas phase and then deactivate the steam reforming catalyst and reduce the operational lifecycle. In this case, it is recommended that refiners follow recognized metrics like ASME which established limits to the silicon concentration in boiler feed water. For example, for a boiler operating under a 40 bar as maximum operating pressure the maximum silicon content in the boiler feed water is 40 ppmw according to ASME code. In the specialized literature its possible to found equilibrium curves detailing the expected silicon concentration in the vapor phase base on the operating pressure and silicon content in the BFW, for example for a boiler operating under 40 bar and with BFW containing 40 ppm of silicon is expected a silicon concentration in the feed around 0,025 ppmw. Normally, the boiler feed water in refineries has no more than 5 ppmw of silicon and this is not a great concern to SMR units. Refiners operating under higher silicon concentration in BFW should take actions (in the water treating section) to control the silicon content at least under the limit established by ASME code considering the characteristics of the processing unit.

Feb-2025