Reforming unit feed – sulfur injection, water injection, chlorine injection

Water and chlorine injection are primarily determined by the water content in the reaction system; this water content is generally kept between 15-30 ppm. If the water level in the system becomes too high, it is necessary to reduce or stop water injection, and the amount of chlorine injected must be increased to prevent loss of chlorine from the system. Sulfur injection is primarily based on the expected sulfur content in the reformate; the sulfur content in the reforming feedstock is generally kept between 0.25–0.45 ppm. A low sulfur content can lead to phenomena such as coking in the furnace tubes

Why does coking occur in the furnace tubes when the sulfur content is low?

Continuous reforming generally does not involve water injection; there are three sources of water in the system. I. Water in the feed ； II. Water produced by reduction ； Catalyst entrained in the third regeneration section

Coking caused by too low sulfur levels occurs in low-pressure continuous reforming units, and it has happened on several units in China; the first instance was at Shanghai Petrochemical, but it wasn’t given much attention. Later, coking on the unit walls and the formation of iron-cap carbon also occurred intermittently at several other plants within Sinopec. Sulfur will passivate the inner wall of the furnace tubes, forming a protective film of ferrous sulfide; this occurs especially in newly built plants or during the renovation of existing plants, where there are new pipelines, equipment, and particularly furnace tubes in the reaction areas. In the early days of catalytic reforming, non-platinum catalysts were used; such catalysts contained metals like chromium, and these metals are important components in the materials chosen for hydrogen-handling equipment. The highest temperatures in the reforming reaction occur in the furnace tubes, rather than within the reactor itself; therefore, the furnace tubes are the most likely locations for coking to occur on the reactor walls. A small amount of coking can be carried into the reactor along with the reactants, leading to coking on the reactor walls as well

The device is generally not filled with water, as the water content in the system is controlled at around 15 to 25 PPM; it is rare for the water content to be low. Chlorine addition is determined by calculating the amount of chlorinating agent required based on the chlorine content in the raw catalyst analyzed daily, together with the catalyst circulation rate. When the reformation feed is within the range of 0.25 to 0.5 ppm, no sulfur injection is required; if it falls below this level, sulfur must be added to bring it up to that standard. During the startup phase, sulfur injection is necessary to prevent coking reactions between the pipes and internal components at high temperatures, which could otherwise cause damage to these components.