Sinclair 3HDS Reaction & Separation System PDF

# #3 Hydrogen Desulfurization (HDS) Unit ## Overview The purpose of the #3 Hydrogen Desulfurization (HDS) Unit is to produce distillate product. This unit uses a blend of light distillate, medium distillate, light cycle oil, light coker gas oil, and mixed gas oils from various locations in the ref...

# #3 Hydrogen Desulfurization (HDS) Unit ## Overview The purpose of the #3 Hydrogen Desulfurization (HDS) Unit is to produce distillate product. This unit uses a blend of light distillate, medium distillate, light cycle oil, light coker gas oil, and mixed gas oils from various locations in the refinery. The primary objective of the #3 HDS Reaction and Separation System is to convert contaminants in the blended feed, such as sulfur and nitrogen, into compounds that are easily separated from the product. This is accomplished using a process called catalytic hydrotreating, which involves reacting the feed stream with hydrogen in the presence of a catalyst at high temperatures and pressures. Through this process, sulfur is converted into hydrogen sulfide, and nitrogen is converted into ammonia. In addition, olefins and aromatics contained in the feed are saturated with hydrogen. Hydrogen and sour gases are separated from the reactor effluent and treated in the Absorption System. Reactor effluent is sent to the Stripping System for further separation in order to meet product specifications. ## #3 HDS Unit Operation The #3 HDS Unit is designed to reduce the sulfur and nitrogen content of the refinery diesel pool using a process called catalytic hydrotreating. The diesel product will have an improved cetane index, odor, and stability. The normal #3 HDS feedstock is a blend of light distillate from tankage, medium distillate from tankage, and light cycle oil (LCO) from 9TK-404 and the LCO header. Each individual feed stock stream is routed to the unit on flow control. Depending on unit needs, mixed gas oil from the gas oil header, and light coker gas oil (LCGO) from the Coker Unit can also be blended into the feedstock on flow control. The #3 HDS Unit has an operating mode that produces “railroad diesel,” which is a diesel product that contains more sulfur than normal. The light distillate, medium distillate, and LCO feed lines are each provided with a bypass line that feeds directly to the #3 HDS Stripping System. If needed, some or all of the feedstock can bypass the HDS reactors and be sold as a product with a higher sulfur content. ## #3 HDS Feed Preheating In the Feed Preheating Subsystem, #3 HDS feed is prepared by blending varying amounts of light distillate, medium distillate, light cycle oil, and mixed gas oils, depending on unit requirements. The feed is filtered, combined with hydrogen, and preheated through a series of six heat exchangers to the appropriate reaction temperature. Reactor effluent is simultaneously cooled so it can be condensed and separated in downstream equipment. ### Feed Preheating Subsystem - **1:** #3 HDS feed flows through the Charge Filter (13PV-2316). > Purpose: > 13PV-2316 removes debris from the feed stream to protect downstream equipment. - **2:** #3 HDS feed is sent to the Charge Surge Drum (13PV-2310). > Purpose: > 13PV-2310 provides the necessary surge capacity to maintain a constant flow of feed to downstream equipment and minimize pulsating flow. This prolongs the reactor catalyst life and prevents downstream spikes in pressure. - **3:** Fuel gas from the Fuel Gas KO Drum (13PV-2311) is used as a pressuring gas to help maintain a pressure head in the surge drum. > Purpose: > Hydrocarbon vapors can be vented from the drum to the flare header on pressure control. > > During startup, #3 HDS feed can bypass the exchangers, on flow control, through FV-501. This is used for heater control. - **4:** #3 HDS feed is pumped by the Reactor Charge Pump South/North (13P-101/102) from 13PV-2310 to the Feed/Effluent Exchanger (13EX-2331). - **5:** #3 HDS feed can be routed through an automatic recirculation valve (ARV) and recirculated back to the Charge Surge Drum. > Purpose: > ARVs are used to ensure a minimum flow to the Reactor Charge Pump by recirculating feed back to 13PV-2310. This is done to avoid damage to the pump caused by overheating or cavitation. - **6:** Sour water is removed from the boot of the surge drum and sent to the SWS Collection Drum (14PV-2402). > Purpose: > The separated water is removed from the #3 HDS feedstock and treated downstream. - **7:** The #3 HDS feed is combined with a hydrogen stream that consists of both make-up hydrogen and recycle hydrogen from the #1/#2 Distillate Hydrogen Compressor East/West (13C-101/102) in the Compression 1 & 2 System. > Purpose: > Hydrogen is added to provide a hydrogen-rich feed to the reactor section. Make-up hydrogen is supplied to replace hydrogen consumed in the reactor. - **8:** Hydrogen bleeds from the #4 HDS and the Hydrocracker Units are routed to the recycle hydrogen stream. A portion of this stream is sent to the Effluent Cold Separator (13PV-2318). > Purpose: > A portion of the make-up hydrogen stream is routed to the #1 HDS hydrogen header. - **9:** A portion of the recycle hydrogen stream is used as a quench line in the Distillate HDS Reactors West/East (13PV-2301/2302). - **10:** The combined hydrocarbon and hydrogen feed enters the tube side of the Feed/Effluent Exchangers (13EX-2331/30/29/28/26/27). The mixed feed is heated by the #3 HDS Reactor effluent flowing through the shell side of the exchangers. The flow rate is controlled to maintain the level in the Charge Surge Drum (13PV-2310). > Purpose: > 13EX-2331/30/29/28/26/27 are six heat exchangers, arranged in series, that are used to preheat the reactor feed before it is sent to the Reactor Charge Heater (13HT-101). Preheating the feed helps to reduce the load on the fired heater and increases the heater efficiency. - **11:** Hot reactor effluent from the Distillate HDS Reactor East (13PV-2302) is routed through the shell side of the Feed/Effluent Exchangers. It is cooled by reactor feed flowing through the tube side of the exchangers. > Purpose: > The six heat exchangers begin cooling the hot reactor effluent so it can later be condensed and separated. - **12:** Preheated reactor feed exits the subsystem and flows to the Reactor Charge Heater. - **13:** Cooled reactor effluent is sent to the Hot Separator (13PV-2317) for liquid/gas separation. ## Heating and Reaction The Heating and Reaction Subsystem converts sulfur and nitrogen contaminants in the #3 HDS feed into compounds that can easily be removed downstream. This is accomplished through a process called catalytic hydrotreating, which involves reacting the feed stream with hydrogen in the presence of a catalyst at high temperatures and pressures. A fired heater, two multibed reactors in series, and interstage quench lines are used to optimize reactor conditions. ### Heating and Reaction Subsystem - **1:** Preheated #3 HDS feed, consisting of hydrogen and a blend of light distillate, medium distillate, light cycle oil (LCO), and mixed gas oils, splits into two streams and enters the convection section of the Reactor Charge Heater (13HT-101). > Purpose: > HDS reactions are favored by an increase in temperature. The Reactor Charge Heater is a fuel fired furnace that heats the reactor feed stream to the temperature necessary for the hydrotreating reactions to proceed. The feed is split to provide the proper flow through each pass. In the convection section of the heater, heat is transferred to the feed stream from the hot flue gas rising through the heater stack. - **2:** #3 HDS Reactor feed is further heated in the radiant section of 13HT-101. > Purpose: > In the radiant section of the heater, heat is transferred to the feed stream by direct radiation on the fired heater tubes from the burner flame. - **3:** Fuel gas from the Fuel Gas KO Drum (13PV-2311) flows to the three burners on the Reactor Charge Heater. The flow rate of fuel gas is controlled to maintain the desired heater outlet temperature. > Purpose: > Combustion of fuel gas provides the heat necessary to raise the HDS feed temperature - **4:** Pilot gas from the natural gas header is provided to the pilot burners of 13HT-101 on pressure control. > Purpose: > The pilot flame is a subsidiary flame used to ignite the main burner. Pilots are used to avoid the hazards of directly lighting the main flame. - **5:** Heated HDS feed is sent to the top of the Distillate HDS Reactor West (13PV-2301). The hydrogen-rich feed flows through two beds of cobalt-molybdenum catalyst. Within the reactor, several reactions occur, including desulfurization, denitrification, olefin saturation, and aromatic saturation. As the feed travels down the reactor, hydrogen breaks the carbon-sulfur and carbon-nitrogen bonds and saturates the remaining hydrocarbon chains. As a result, sulfur contained in the feed is converted to hydrogen sulfide (H2S), nitrogen is converted to ammonia (NH3), and olefins and aromatics are saturated with hydrogen. > Purpose: > Specifications for distillate product produced in the #3 HDS are regulated by federal and state standards. 13PV-2301 converts contaminants in the feed into compounds that can easily be removed downstream to meet product specifications. - **6:** Hydrogen from the #1 /#2 Distillate Hydrogen Compressor East/West (13C-101/102) in the Compression 1 & 2 System is added to the west reactor feed stream and the stream between 13PV-2301 and 13PV-2302. > Purpose: > All of the hydrotreating reactions are exothermic and therefore produce heat. Hydrogen is used as a quench stream to cool the reactor feed for temperature control. The hydrogen quench flow rate is controlled to maintain the desired temperature between reactors. Limiting the temperature rise in the reactors is essential for reducing the formation of coke. Reducing the formation of coke helps prolong the life of the reactor catalyst. - **7:** Reactor effluent flows to the Distillate HDS Reactor East (13PV-2302), where hydrotreating reactions continue. > Purpose: > The #3 HDS Unit contains two reactors installed in series, which enables it to process a higher volume of feedstock than the #1 and #2 HDS Units, which contain one reactor each. Utilizing two reactors provides the surface area needed to handle a higher volume of feedstock, and thus, a larger sulfur load, while maintaining target product specifications. It also prolongs the life of the catalyst, reducing the need for frequent shutdowns, catalyst replacement, and maintenance. - **8:** Hot reactor effluent exits 13PV-2302 and flows to the Feed/Effluent Exchanger (13EX-2326) to be cooled prior to separation and product recovery. This stream contains distillate product, hydrogen, and sour gas (H2S and NH3). ## Effluent Separation In the Effluent Separation Subsystem, reactor effluent is cooled, condensed, and separated. Liquids and gases are separated in two stages - a high temperature separator and a low temperature separator - with condensers in between. This maximizes the separation of hydrogen/sour gas from the liquid distillate product. ### Effluent Separation Subsystem - **1:** Cooled reactor effluent from the Feed/Effluent Exchanger (13EX-2331) enters the subsystem. This stream consists of distillate product, hydrogen sulfide (H2S), ammonia (NH3), and hydrogen. - **2:** Reactor effluent enters the Hot Separator (13PV-2317). > Purpose: > 13PV-2317 is a vertical separation vessel that supplies the space and residence time for the cooled reactor effluent stream to separate into two phases - vapor and liquid due to difference in densities. - **3:** Hot separator liquid, containing distillate product and some light hydrocarbons, exits the bottom of 13PV-2317 and flows to the Stripper Feed/Bottoms Exchanger (13EX-2332) on level control. > Purpose: > Liquid recovered from the Hot Separator must be stripped of volatile light ends before it can be sold as product. - **4:** Wash water from the Water Wash Injection Pump East/West (13J-104/105) in the #3 HDS Stripping System is injected into the Hot Separator effluent gas line. > Purpose: > Wash water is used to prevent the buildup of ammonia salt deposits on downstream equipment, which can cause corrosion. - **5:** Hot separator effluent gas, which consists mainly of hydrogen and sour gas (H2S, and NH3), flows through the tubes of the Effluent Condenser (13EX-2341). 13EX-2341 is an air cooler that uses ambient air to cool the process stream. > Purpose: > The Effluent Separation Subsystem separates liquids and gases from the reactor effluent in two stages. After the high temperature separator, the effluent gas is condensed back to a liquid before flowing to the Effluent Cold Separator (13PV-2318) for further separation. - **6:** Hot separator effluent gas flows through the shell side of the Effluent Condenser (13EX-2336). It is cooled by cooling water flowing through the tube side of the exchanger. - **7:** Condensed effluent gas flows from 13EX-2336 to the Effluent Cold Separator. > Purpose: > 13PV-2318 is a horizontal separation vessel that supplies the space and residence time for the condensed effluent gas to separate into three phases - non-condensable gas, hydrocarbon liquid, and sour water - due to difference in densities. - **8:** Cold separator liquid, consisting of distillate product and some light hydrocarbons, exits the bottom of 13PV-2318 and flows to 13EX-2332 in the #3 HDS Stripping System on level control. - **9:** Sour water is removed from the boot of the cold separator and sent to the SWS Collection Drum (14PV-2402) on level control. > Purpose: > The separated water is removed from the hydrocarbon liquid and treated downstream. - **10:** Non-condensable gases, mainly hydrogen, H2S, and NH3, exit the top of Effluent Cold Separator (13PV-2318) and flow to the #3 HDS Absorber (13PV-2306) for sour gas removal. - **11:** During a total unit upset, the Emergency Shut Down (ESD) valve XV-141 is opened, which will quickly depressure the entire unit. - **12:** Hydrogen from the HP Separators (21PV-2636/2637) in the Hydrocracker Unit is let down to a lower pressure and routed to 13PV-2318.