API RP 932-B pdf free download
API RP 932-B pdf free download.Design, Materials, Fabrication, Operation, and Inspection Guidelines for Corrosion Control in Hydroprocessing Reactor Effluent Air Cooler (REAC) Systems.
4.1.3 Surveys dealt with flow distribution through air cooler banks, inlet and outlet piping designs, determining and monitoring adequate wash water injection rates, material selection, flow velocities through tubes and piping, etc.
4.1.4 The survey results highlight industry-wide experience with corrosion in the reactor effluent system of hydroprocessing units. From the earliest studies to the most recent, corrosion continues to cause unscheduled unit outages, and in some instances, catastrophic events involving major fires and explosions. Although early studies proposed guidelines for operating, monitoring, and inspecting effluent systems, significant corrosion and leaks in these systems were still being reported on a regular basis at industry forums. Industry experience- sharing sessions, as well as the first and second editions of this recommended practice, have helped to reduce the frequency of these failures.
4.2 Typical Hydroprocessing Units
4.2.1 Hydroprocessing units use hydrogen at elevated temperatures and pressures along with a suitable catalyst to improve the quality of the feedstock. Common to all units is the production of H2S and NH3 from the reaction of hydrogen with sulfur and nitrogen present in the hydrocarbon feed.
4.2.2 Hydrotreating processes remove heteroatoms, such as sulfur and nitrogen, from the feedstock. The removal of sulfur can be necessary for either processing in downstream units where the sulfur can contaminate the catalyst or for product quality reasons. Feedstocks to the units can vary from light naphtha to heavy vacuum residuum. Generally, the “heavier” feedstocks require the most severe operation (i.e. higher temperature and pressure) and contain higher concentrations of sulfur and nitrogen that produce the highest concentrations of H2S and NH3. Several other reactions can also occur, including the conversion of any chlorides in the feed to HCI. The formation of H2S, NH3, and HCI are of primary importance to fouling and corrosion in the reactor effluent system. Generally, these three reactants will interact to form NH4CI and NH4HS, but in units with minimal nitrogen in the feed, highly corrosive HCI may form. Figure 1 shows a typical process flow diagram.
4.2.3 Hydrocracking is a process whereby low-value hydrocarbon feedstocks are cracked or broken down into higher-value hydrocarbons. Typically, this takes heavy hydrocarbons and creates lighter hydrocarbons, such as cracking coker distillate, to make gasoline. Figure 2 shows a typical process flow diagram.
4.2.4 Hydrocracking and hydrotreating units have similar process characteristics, especially in the front-end processing, as illustrated in Figure 1 and Figure 2. The feed is preheated through a series of exchangers and a furnace to temperatures of -700 °F (370 °C). Hydrogen is injected into the feed upstream of the reactor. The hydrogen and feedstock enter the reactor, where the catalyst promotes the reaction of hydrogen with sulfur and nitrogen to produce H2S and NH3. The reactor effluent is a mixture that includes H2S, NH3, hydrogen, hydrocarbons, and possibly HCI and H20. Again, these reactants will generally interact to form NH4CI and NH4HS salts unless minimal nitrogen is present in the feed. Downstream of the reactor, the effluent is cooled through a series of shell-and-tube heat exchangers.
4.2.5 Downstream of the heat exchangers, the effluent is separated into hydrogen-rich vapor, water, and hydrocarbons. Units can have several different design schemes (described more fully in 4.3).
4.2.6 Continuous injection of wash water into the reactor effluent stream is commonly used to prevent fouling by NH4HS and NH4CI salts, typically upstream of the REAC or shell-and-tube heat exchanger. For some hydroprocessing units (primarily low-severity naphtha hydrotreaters), good feed quality does not result in salt deposition, and therefore, the use of wash water is not required. Other units may produce a low volume of salts that may only require intermittent wash water.API RP 932-B pdf download.
