It is used to lift dry gas. What are its advantages and disadvantages compared with lifting steam?

There are many such discussions on this forum, you can search for them. I summarized everyone’s discussion: The purpose of using dry gas as the lifting medium in the catalytic riser is 1. The molecular weight of dry gas is small, about 18, which is equivalent to the molecular weight of water vapor. After the same amount of medium is injected, the flow rate in the riser reactor is basically unchanged, so dry gas has a good expansion and lifting effect, and is used as a substitute for lifting steam. 2. Dry gas injection can reduce the aging and thermal collapse of high-temperature catalysts caused by steam, reduce the hydrothermal deactivation of the catalyst caused by water vapor, effectively protect the acidic center of the catalyst, improve its selectivity, and help ensure the activity of the catalyst. ； Since the light hydrocarbons in the catalytic dry gas can passivate the heavy metals on the catalyst, reduce the hydrogen content in the dry gas, improve product distribution and reduce catalyst loss, etc., they can improve the reaction selectivity, help protect the activity and selectivity of the catalyst, and make the reaction proceed in the desired direction. ； From the perspective of reaction chemical balance, dry gas injection increases the dry gas partial pressure under the reaction conditions of the reactor, which is conducive to the reaction proceeding in the direction of inhibiting the generation of dry gas, thereby further reducing the process and coke yield and increasing the yield of the target product gasoline. In fact, dry gas pre-boost has limited impact on product distribution! Although there is industrial test data supporting the fact that dry gas pre-boost technology can reduce dry gas and coke yields, this is conditional. Ashland Company pointed out that the condition for dry gas pre-boost to reduce coking is that hydrogen can be activated at 704 degrees. ； When the carbon content of the regenerant is less than 0.15%, passivation is completed within one second. Global Petroleum Corporation of the United States believes that in a device with a regeneration agent of 716 degrees and heavy metals of 3000PPM, the dry gas pre-boosting process is more effective. 3. Due to the low specific heat capacity of dry gas, less heat is brought to the fractionation tower, which is beneficial to reducing the load of the overhead condenser. 4. It can save steam, reduce energy consumption, and reduce the discharge of sulfur-containing sewage. 5. Dry gas pre-lifting is not to save steam. It is not entirely correct to prevent thermal collapse of the catalyst. Its main function is that the dry gas is the first to react with the high-temperature and high-activity regenerated catalyst from the lifting tube and the regeneration inclined tube. First, the catalytic dry gas contains a large amount of hydrogen. According to expert research, the hydrogen in the dry gas has a passivation effect on nickel and other metals adsorbed on the catalyst. Second, the hydrocarbons in the dry gas react on the highly active molecular sieve of the catalyst, which can reduce the dry gas yield and increase the liquid recovery. 6. When designing, dry gas and steam are generally used together, and considering the accident status, pre-lift steam must also be retained. The distribution of the two quantities can be adjusted accordingly according to the actual conditions of the respective devices. Some analysts also believe that the use of dry gas pre-lift increases the load on the air compressor and stabilizing system, which is not economical in terms of energy consumption. Therefore, many companies have this system but do not use it. Things to note: When the air compressor is shut down, the dry gas pre-lift valve must be closed immediately and replaced with steam pre-lift.