Dimethyl Sulfide (DMS)
In ethane steam crackers, Dimethyl Sulfide (DMS) is injected continuously into the furnace section (hot section) to inhibit coke formation and to control the creation of CO. The rate of DMS injection is determined by the feed rate of the charge gas/liquid and its native sulfur content. The lower the sulfur content of the feedstock, the higher the injection rate of the DMS. Some steam crackers utilize Dimethyl Disulfide (DMDS) for sulfur injection in place of DMS.
How It Works
After furnace tubes are de-coked, charge gas is re-introduced to the furnace and DMS or DMDS is injected at up to double the normal rate to passivate the furnace tubes. Passivation is accomplished by the decomposition of the sulfur chemical in the presence of hydrogen to form H2S. This H2S reacts with iron on the furnace tube walls, creating a layer of iron sulfide that dramatically reduces the rate of coke formation inside the tubes. After the initial passivation step is complete, the DMS/DMDS injection rate is reduced to maintain a partial pressure of H2S in the furnace adequate to preserve the iron sulfide layer.
There are two basic methodologies for injection. Sites that use DMS usually require only one injection point in the charge gas as DMS will readily disperse throughout the furnace system. Customers utilizing DMDS typically have injection points at each furnace section to ensure equal distribution to the furnace tubes. This method usually requires multiple measurement devices and atomization quills.
Chemical trailers for DMS are capable of handling pressures up to 100 psi, enabling the pressured transfer of DMS from the delivery trailer to the tank via a control valve and flow meter combination. Tank trucks unloading into this type of scenario must have a tank capable of handling the extra pressure associated with the transfer. Delivery can also be made via a pumping system, but this is less than an ideal situation.
ChevronPhillips Chemical Co. (CP Chem) is the only producer of DMDS in North America, making CP Chem the only domestic manufacturer of both DMS and DMDS. Reactor Resources, LLC is the sole distributor of thiochemicals for CP Chem in the US, Canada, and Mexico.
Contact Reactor Resources to discuss the optimum methodology and sulfur chemistry for your application.