Abstract:
The disclosure provided herein describes processes for rapidly quenching an over-temperature hydroprocessing reaction utilizing a pressurized quenching agent that is rapidly released into the hydroprocessing reactor. Optimally, the quenching agent blocks acidic catalytic sites of the hydroprocessing catalyst to competitively inhibit exothermic reaction rate. Exemplary quench agents include ammonia or a chemical that is converted to ammonia under hydroprocessing conditions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Non-Provisional application that claims the benefit under 35 USC §119(e) of U.S. Provisional Application Ser. No. 62/098,804 filed Dec. 31, 2014, titled “Ammoniated Quenching of a Hydroprocessing Reaction”, which is hereby incorporated by reference in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    None. 
       BACKGROUND 
       [0003]    Hydroprocessing reactions are highly exothermic, especially hydrocracking reactions. In a petroleum refinery, temperatures generated during operation of hydroprocessing reactors are managed by (1) inlet temperature to the reactor, (2) continuous flow of fluids through the reactor to remove the heat generated, and in many cases, (3) introduction of quench gas or oil into specially designed “quench zones” inside the reactor. Hydrocrackers also generally include emergency quench that can be introduced at the reactor inlet, if necessary. The quenches can be warm, cold or a combination, but typically comprise fluids that are relatively cool, recycled and hydrogen-rich. 
         [0004]    Under certain conditions, it is possible to lose control of the temperatures in the reactor, resulting in very high temperatures. If the temperatures are rising radically, this loss of control is usually referred to as a “temperature excursion.” If the temperatures rise rapidly or are very high already, exothermic hydrocracking/hydrodemethylation reactions can begin to dominate, even in a hydrotreating reactor. The rapidly rising temperatures are referred to as a “hydrocracking runaway.” Such an event cannot be stopped by normal quenching. The acidic hydroprocessing catalyst enhances the runaway reactions. The crossover from a controllable excursion to an uncontrolled runaway generally occurs between 800 and 850° F., although it can be lower in a hydrocracking reactor. 
         [0005]    There are only limited options to stop runaway hydroprocessing reactions and regain control. The runaway reaction is supported by the presence of concentrated reactants (e.g., hydrogen and oil), temperature, and the catalyst in the reactor. Conventional emergency protocol involves rapid elimination of the hydrogen by rapid pressure reduction (or de-pressuring) of the unit. De-pressuring dumps the hydrogen at a high rate to the refinery flare, in addition to stopping the input of fired heat and, usually, feedstock to the reactor. This is sufficient to stop the runaway event, but can result in massive flaring, which may violate emissions regulations. Reluctance to de-pressurize in a timely manner during a runaway hydroprocessing reaction has resulted in equipment failures and fatalities. 
         [0006]    Accordingly, a need exists for better systems and methods for controlling potentially dangerous temperature excursions and runaway hydroprocessing reactions in a petroleum refinery setting. 
       BRIEF SUMMARY OF THE DISCLOSURE 
       [0007]    A process for quenching a catalytic hydroprocessing reaction, comprising: a) contacting a feedstock derived from at least one of petroleum or biomass with a hydroprocessing catalyst comprising at least on acidic catalytic active site in a reaction zone at a temperature and pressure that facilitates hydroprocessing reactions, wherein the contacting converts the feedstock to a reactor effluent comprising a liquid hydrocarbon fuel or a blending component thereof; b) detecting a temperature condition in the reaction zone; c) dispensing a quenching agent from a pressurized vessel to the reaction zone when the temperature condition exceeds a first predetermined threshold temperature, wherein the quenching agent binds to and blocks at least one active site of the hydroprocessing catalyst. 
         [0008]    In certain embodiments, the first predetermined threshold temperature is at least 473° C. (820° F.), at least 476° C. (825° F.), at least 479° C. (830° F.), at least 482° C. (835° F.), at least 484° C. (840° F.), at least 487° C. (845° F.), or even at least 490° C. (850° F.). 
         [0009]    Certain embodiments also include a step for stopping a flow of water that mixes with the reactor effluent when the temperature condition in the reaction zone exceeds a second predetermined threshold temperature that exceeds the first predetermined threshold temperature, thereby increasing recycling of the quenching agent to the reaction zone via a recycling pathway. 
         [0010]    In certain embodiments, the first predetermined threshold temperature is at least 473° C. (820° F.), at least 476° C. (825° F.), at least 479° C. (830° F.), at least 482° C. (835° F.), at least 484° C. (840° F.), at least 487° C. (845° F.), or even at least 490° C. (850° F.). 
         [0011]    In certain embodiments, the quenching agent is added to the hydroprocessing reaction zone via one or more conduits that transport at least one of a recycle gas, a treat gas, and quench gas under nominal hydroprocessing conditions when the temperature condition is less than the first predetermined threshold temperature. In certain embodiments, the quenching agent is added to the feedstock at a location upstream from the reaction zone of the hydroprocessing reactor. Optionally, the quenching agent is added to a pretreating reactor located upstream from the hydroprocessing reactor, where the pretreating reactor contains one or more catalysts for de-aromatization, de-metallization, hydrodesulfurization, hydrodenitrogenation, Optionally, the hydroprocessing catalyst in the hydroprocessing reactor is a hydrocracking catalyst. 
         [0012]    In certain embodiments, the quenching agent is selected from the list consisting of ammonia, a chemical compound that is converted to ammonia at hydroprocessing temperatures and pressures and combinations thereof. In certain embodiments, the pressurized vessel stores the quenching agent at a pressure in a range from 100 to 4000 psig. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    A more complete understanding of the present invention and benefits thereof may be acquired by referring to the follow description taken in conjunction with the accompanying drawings in which: 
           [0014]      FIG. 1  depicts a schematic of an embodiment comprising a rapid ammoniated quenching system on a hydroprocessing reactor. 
           [0015]      FIG. 2  depicts a schematic of an embodiment comprising a ammoniated quenching system on a single-stage hydrocracker. 
       
    
    
       [0016]    The invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings. The drawings may not be to scale. It should be understood that the drawings and their accompanying detailed descriptions are not intended to limit the scope of the invention to the particular forms disclosed. Rather, the intention is to cover all modifications, equivalents and alternatives encompassed by the spirit and scope of the claims. 
       DETAILED DESCRIPTION 
       [0017]    The disclosure provided herein describes processes and systems for rapidly quenching an over-temperature hydroprocessing reaction in a commercial refinery setting. In its most basic form, the inventive process and system rapidly adds a quenching agent to at least one of: the recycle gas, treat gas, or the quench gas. The inventive processes and systems are optimally employed during an over-temperature excursion as a first course of action that is a less drastic alternative than de-pressurization of the hydroprocessing reactor by rapid venting to the atmosphere or to the flare system of a refinery. 
         [0018]    Certain embodiments of the rapid quenching system and processes disclosed herein additionally include a mechanism for preventing the removal of the quenching agent by the effluent wash water from the system, thereby allowing the added quenching agent to recycle in the treat gas and enhance the quenching effect. This is primarily intended for use in situations where dangerous loss of temperature control is imminent and the systems and processes are intended to be utilized as a temporary measure to reduce system temperatures back to a safe level while other measures are being taken, such as (but not limited to) decreasing charge heater temperature, reducing feedstock feed rate, etc. 
         [0019]    In extreme circumstances, rapid quenching of the hydroprocessing reaction can optionally be combined with depressurization of the reactor as an added safety measure in events where equipment damage is imminent or a serious safety hazard is present. 
         [0020]    In certain embodiments, rapid quenching of the hydroprocessing reaction can additionally be used as a safety measure after an emergency over-temperature event. In such instances, the hydroprocessing reactor remains hot and the system must be re-pressurized to a certain extent to enable circulation of recycle gas and also to enable cooling via adding a quenching agent to the makeup or circulating gas. 
         [0021]    Hydroprocessing in a refinery setting is conventional in nature and will not be outlined herein beyond the detail required to understand the inventive systems and processes. Certain embodiments of the inventive process and system comprise storing sufficient quenching agent (e.g., ammonia or other ammonia-generating compound) in a pressurized vessel that is rapidly-discharged when needed to quench an over-temperature condition in the hydroprocessing reactor. Various injection points for the quench are feasible while still enabling the system to work effectively. Design details can vary significantly, depending on the specific hydroprocessing units utilized in a given embodiment, but universally result in rapid addition of quenching agent to the system. In one embodiment, pressurized ammonia (or other compound that generates ammonia under hydroprocessing conditions) is injected into a conduit that carries the treat gas and the resulting mixture is injected directly into the hydroprocessing reactor. 
         [0022]    Hydrocracking and hydrodemethylation reactions tend to occur at acidic sites on hydroprocessing catalysts. While not wishing to be bound by theory, ammonia is believed to interact directly with these acidic sites on the catalyst to rapidly, yet reversibly, decrease hydroprocessing reaction rate. This interaction may involve competitive inhibition, or alternatively, reversible deactivation of the acidic active sites to slow the reaction rate. 
         [0023]    The catalyst utilized for the invention may be any catalyst capable of facilitating hydroprocessing reactions. This includes, but is not limited to, any catalyst currently known to be useful for hydrotreating, hydrocracking, or catalyst mixtures comprising more than one of these catalysts. Such catalysts are conventional in nature and thus will not be recited here. The quenching agent may react with all catalysts, or only a portion of the catalysts present in the catalyst mixture. 
         [0024]      FIG. 1  depicts a more detailed schematic representation of one embodiment of the current disclosure comprising rapid quenching in a hydroprocessing reactor system. At least a portion of a feedstock  101  that may be derived from petroleum, biomass, or mixtures of these is first heated by feed/effluent heat exchanger  105 . The feedstock is then conveyed to charge heater  110 , which further heats the feedstock, then conveys the heated feedstock to a hydrotreating reactor  120  that is maintained at a temperature that generally ranges from 290° C. to 427° C. (550° F. to 800° F.). The hydrotreating reactor  120  contains a hydrotreating catalyst  130  that contacts the mixture comprising feedstock and hydrogen in the reactor  120  and facilitates conversion to a reactor effluent  135  comprising a mixture of hydrocarbons, hydrogen sulfide, unreacted hydrogen and other light gases and reaction products. The details of these reactions are conventional in nature and will not be discussed further. 
         [0025]    Further referring to  FIG. 1 , the reactor effluent  135  is at least partially cooled as it is conveyed through feed/effluent heat exchanger  105 , then is conveyed to hot high pressure separator  140  to separate treated liquid components  143  from gaseous components  147  that generally include unreacted hydrogen, light hydrocarbons (C 1 -C 4 ) and H 2 S. Note that the hot high pressure separator  140  is not required for all types of hydroprocessing systems and processes. The gaseous components  147  are diluted by addition of wash water  150  with the quantity of wash water added controlled by water inlet valve  152 . The gaseous components mixed with wash water are then cooled by air cooler  155  before entering cold high pressure separator  160 . A sour water outlet  163  removes separated liquid sour water from the cold high pressure separator  160 , while a second outlet removes separated recycle gas  167  predominantly comprising hydrogen and light hydrocarbons (C 1 -C 4 ) from the cold high pressure separator  160 . A third outlet  161  from the cold high pressure separator  160  removes liquid hydrocarbons that can be further converted into a transportation fuel or a component thereof. 
         [0026]    The separated recycle gas  167  is compressed in a recycle compressor  170  to form a treat gas  173  that may be returned to the hydrotreating reactor  120  in any of several ways. Referring to  FIG. 1 , a variable first portion of the treat gas is directed via conduit  171  to be added to the feedstock  101  at a point located upstream from the charge heater  110 . Optionally, the first portion of treat gas  173  is added to the feedstock  101  at a point that is located upstream from feed/effluent heat exchanger  105 . A variable second portion of the treat gas  173  is added directly to the hydrotreating reactor  120  through one or more inlets ( 175 ,  176 ) to mix with the feedstock  101  and provide a source of hydrogen for hydrotreating and temperature control by quenching. 
         [0027]    Again referring to the embodiment depicted in  FIG. 1 , in the event of over-temperature event within the reaction zone of the hydrotreating reactor  120 , or an elevated runaway temperature condition that necessitates emergency intervention to slow the rate of exothermic reactions taking place in the hydrotreating reactor  120 , a pressurized quenching agent  180  is released from quench vessel  185  by the operation of valve  191 . Optimally, valve  191  is capable of opening rapidly to release the pressurized quenching agent  180  to mix with the treat gas  173  at a point that is immediately upstream from where the treat gas  173  enters the hydrotreating reactor  120  via inlets  175  and  176 . The mixture of quenching agent  180  and treat gas  173  may then be conveyed into the hydrotreating reactor  120  via the inlets  175 ,  176 , and/or conveyed via conduit  171  to mix with the feedstock at a point located upstream from the charge heater  110 . In certain embodiments, the threshold hydrotreating reactor temperature at which valve  191  is opened may be, for example, 473° C. (820° F.), 476° C. (825° F.), 479° C. (830° F.), 482° C. (835° F.), 484° C. (840° F.), 487° C. (845° F.), or even 490° C. (850° F.). 
         [0028]    In certain embodiments, the system also includes one or more valves that when opened, stops the flow of water that washes the reactor effluent, thereby increasing recycling of the quenching agent to the reaction zone of the hydroprocessing reactor. Again referring to the embodiment depicted in  FIG. 1 , valve  197  can be closed to prevent the addition of wash water  150  to the system. 
         [0029]    Optionally, the valves that control entry of quenching agent or wash water may be automated to by operated (i.e. opened and closed) remotely by signals from control panel  195 .  FIG. 1  depicts control panel  195  operably connected to remotely control the operation of valve  191  and valve  152  via an electrical signal. In certain embodiments, each valve may comprise motorized or hydraulic components adapted to operate the valve in response to an electric signal input, and operation of each valve may be controlled independently from the other valves by the control panel. Further, the control panel  195  may be electrically interfaced with, and operable to receive electrical signal input from one or more temperature sensors located on or within the hydrotreating reactor. In the embodiment depicted in  FIG. 1 , control panel  195  comprises a programmable computing device and is further operable to respond to input from temperature sensor  196 . When the control panel  195  detects a temperature via electrical signal input from the temperature sensor  196  that exceeds a predetermined first threshold temperature, control panel  195  sends a signal to open valves  191  and/or  152 , thereby rapidly quenching the over-temperature condition via the mechanisms described previously. In certain embodiments, this first pre-determined threshold temperature may be, for example, 473° C. (820° F.), 476° C. (825° F.), 479° C. (830° F.), 482° C. (835° F.), 484° C. (840° F.), 487° C. (845° F.), or even 490° C. (850° F.). In certain embodiments, the control panel  195  detects a temperature via signal input from the temperature sensor  196  that exceeds a second predetermined threshold temperature that is greater than the first predetermined threshold temperature. In response, control panel  195  sends a signal to open valves  191 ,  152 , or both to rapidly quench the over-temperature condition via the mechanisms described previously. 
         [0030]      FIG. 2  depicts a more detailed schematic representation of an alternative embodiment of the inventive system and process integrated with a system for single-stage hydrocracking of a hydrocarbon feedstock. Conventional hydrocracking reactors are typically maintained at a temperature in the range from 448° C. to 476° C. (775° F. to 825° F.). The upper end of this range is higher than the temperatures typically utilized for hydrotreating reactors. Therefore, the threshold temperature at which the emergency quenching system described herein would be utilized would typically be higher when incorporated into a hydrocracking reactor system. 
         [0031]    At least a portion of a feedstock  201  that may be derived from petroleum, biomass, or mixtures of these is first heated by feed/effluent heat exchanger  205 . The feedstock  201  is then conveyed to a charge heater  210 , which further heats the feedstock  201  and conveys it to a pretreating reactor  215 . The pre-treating reactor  215  contains one or more pretreating catalysts  216  that are useful for removing metals, complex aromatics (e.g, asphaltenes), as well as sulfur and nitrogen from the feedstock  201 . In general, pretreating of the feedstock  201  in such a manner prior to contacting the feedstock with a hydrocracking catalyst prevents premature deactivation of the hydrocracking catalyst. Referring again to  FIG. 2 , pretreated feedstock  218  leaves the pretreating reactor  215  and is conveyed to a hydrocracking reactor  220 , which facilitates mixing of the pretreated feedstock  218  with hydrogen and a hydrocracking catalyst  230  to facilitate conversion of the pretreated feedstock  218  to a hydrocracking reactor effluent  235  comprising a mixture of hydrocarbons and unreacted hydrogen. The details of these hydrocracking reactions are conventional in nature and will not be discussed further. 
         [0032]    Further referring to  FIG. 2 , the hydrocracking reactor effluent  235  is at least partially cooled as it is conveyed through feed/effluent heat exchanger  205 , then is conveyed to hot high pressure separator  240  to separate treated liquid components  243  from gaseous components  247  that generally include unreacted hydrogen, light hydrocarbons (C 1 -C 4 ) and H 2 S. Note that the hot high pressure separator  240  is not required for all embodiments. The gaseous components  247  are cooled by treat gas preheat exchanger diluted by addition of wash water  250 , with the quantity of wash water added controlled by water inlet valve  252 . The gaseous components  247  mixed with wash water  250  are then cooled by air cooler  255  before entering cold high pressure separator  260 . A sour water outlet  263  removes separated liquid sour water from the cold high pressure separator  260 , while a second outlet removes separated recycle gas  267  predominantly comprising hydrogen and light hydrocarbons (C 1 -C 4 ) from the cold high pressure separator  260 . A third outlet  261  from the cold high pressure separator  260  removes the liquid hydrocarbons. 
         [0033]    The separated recycle gas  267  is compressed in a recycle compressor  270  to form a treat gas  273  that may be returned to the hydrocracking reactor  220  in any of several ways. Referring to  FIG. 2 , a variable first portion of the treat gas  273  is directed via conduit  271  to be added to the feedstock  201  at a point  272  located upstream from the charge heater  210 . In the embodiment depicted in  FIG. 2 , the variable first portion within conduit  271  is added to the feedstock  201  at a point that is located upstream from feed/effluent heat exchanger  205 . A variable second portion of the treat gas  273  is added directly to the hydrocracking reactor  220  through one or more inlets  274 ,  275  and  276  and/or inlet  277  located just upstream from the hydrocracking reactor  220  to mix with the pretreated feedstock  218  and provide a source of hydrogen for hydrocracking and normal quenching for temperature control. A variable third portion of treat gas  273  may be added to the pre-treat reactor  215  via one or more inlets ( 278 ,  279 ) to provide a source of hydrogen for the de-metallization, de-aromatization, and hydrotreating reactions taking place there and for normal quenching for temperature control. 
         [0034]    Again referring to the embodiment depicted in  FIG. 2 , in the event of over-temperature excursion within the hydrocracking reactor  220 , or an elevated runaway temperature condition that necessitates emergency intervention to slow the rate of exothermic reactions taking place in the hydrocracking reactor  220 , a pressurized quenching agent  280  is released from quench vessel  285  by the operation of valve  291 . Optimally, valve  291  is capable of opening rapidly to release the pressurized quenching agent  280  to mix with the treat gas  273  at a point that is immediately upstream from the one or more inlets where the treat gas  273  enters the hydrocracking reactor  220  and/or pretreating reactor  215 . In the embodiment depicted in  FIG. 2 , the mixture of quenching agent  280  and treat gas  273  may then be 1) conveyed into the hydrocracking reactor  220  via the inlets  274 ,  275 , and  276 , 2) conveyed into the pretreating reactor via inlets  278 ,  279  and/or 3) conveyed via conduit  271  to mix with the feedstock at a point  272  located upstream from the charge heater  210 . 
         [0035]    In certain embodiments, the system also includes one or more valves that when opened, stop the addition of water to the system, thereby increasing recycling of the quenching agent to the reaction zone of the hydroprocessing reactor and amplifying the quenching effect. Again referring to the embodiment depicted in  FIG. 2 , valve  252  can be closed to prevent the addition of wash water  250  to the system. 
         [0036]    Optionally, the valves that control entry of quenching agent or wash water may be automated to be operated (i.e. opened and closed) remotely by control panel  295 .  FIG. 2  depicts control panel  295  operably connected to remotely control the operation of valve  291  and valve  252  via an electrical signal. In certain embodiments, each valve may comprise motorized or hydraulic components adapted to operate the valve in response to an electric signal input, and operation of each valve may be controlled independently from the other valves by the control panel. Further, the control panel  295  may be electrically interfaced with, and operable to receive electrical signal input from one or more temperature sensors located on or within the hydrotreating reactor. In the embodiment depicted in  FIG. 2 , a temperature sensor  296  provides electrical signal input to control panel  295 . When the control panel  295  detects a temperature electrical signal input from temperature sensor  296  that exceeds a predetermined threshold temperature, control panel  295  sends an electrical signal to open valves  291  and/or  252 , thereby rapidly quenching the over-temperature condition via the mechanisms described previously. In certain embodiments, the predetermined threshold temperature within the hydrocracking reactor that necessitates intervention according to the inventive processes and systems described herein may be, for example, 476° C. (825° F.), 479° C. (830° F.), 482° C. (835° F.), 484° C. (840° F.), 487° C. (845° F.), or even 490° C. (850° F.). 
         [0037]    The inventive systems and processes disclosed herein are not envisioned to completely replace emergency de-pressurization of a hydroprocessing reaction as an option for responding to extreme temperature spikes and excursions above normal operating temperature. However, the inventive systems and processes disclosed herein do provide a more environmentally-acceptable alternative response to a hydroprocessing over-temperature event; A response that increases the quenching effectiveness, thereby preventing the need for more drastic depressurization of the system. Such depressurization events may violate emission regulations and should be avoided if at all possible. 
         [0038]    Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. Thus, the scope of the invention disclosed herein is specifically intended to be as broad as is legally defined by the claims and any variations and equivalents that are encompassed by the scope of the claims.