Patent Publication Number: US-2020298224-A1

Title: System and method for catalyst removal from mto effluent

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional patent application having Ser. No. 62/821,686 filed on Mar. 21, 2019 which is incorporated by reference herein. 
    
    
     FIELD 
     Embodiments of the present invention relate generally to catalyst removal and more particularly to the catalyst removal from MTO effluents. 
     BACKGROUND 
     Methanol to Olefins (MTO) is a preferred technology for olefins production in regions where there is availability of methanol for feed, or abundance of coal which can be converted to methanol via several processing steps. 
     Olefins are typically produced by converting a hydrocarbon feed at a high temperature to provide a hydrocarbon mixture containing various alkane, alkene, and alkyne hydrocarbons. The hydrocarbon mixture is then fractionated using a series of distillation columns, fractionation columns, compressors, and refrigeration systems to cool, condense, and separate the various hydrocarbon products. 
     Operating MTO plants have experienced difficulties due to catalyst fines contained in the reactor effluent. Since MTO reactor effluent contains a large quantity of water, a water quench tower is used to cool the reactor effluent and condense the water. The catalyst fines contained in the reactor effluent stream cannot easily be separated from quench water and as a result excessive fouling occurs in equipment with consequential high maintenance costs. 
     Hence, there is a need for an improved system and method for removing catalyst fines from MTO effluent stream. 
     SUMMARY 
     Briefly in accordance with aspects of the present technique, a method for catalyst removal from MTO effluent is provided. The method includes removing catalyst from ethanol to olefin effluent by contacting the methanol to olefin effluent with a wash oil to cool the effluent to obtain a cooled effluent, separating the catalyst fines from the cooled effluent in a separator or a column to obtain an essentially catalyst free effluent, directing the catalyst free effluent out from the separator or the column, slurrying the separated catalyst fines to obtain a slurry and directing the slurry to one or more filters to filter out the catalyst. 
     In accordance with another aspect of the present technique, a system for removing catalyst from MTO effluent is provided. The system includes a quench tower having an inlet for receiving MTO effluent, vapor liquid contacting elements disposed above the inlet for cooling the effluent and washing out fines, an outlet above the contacting elements for discharging the cooled effluent essentially free of catalyst fines, and a liquid hold up zone below the inlet for collecting a wash oil from the contacting elements; a recirculation loop for continuously recirculating the wash oil from the liquid hold up zone to the contacting elements; at least two filters alternatingly operable in filtration and backflushing modes; a filtration loop for circulating a slurry comprising catalyst fines and wash oil through a filtration mode filter and returning a filtrate to the quench tower; a backflushing loop for passing a compressed gas through the backflush mode filter for removal of catalyst fines from the slurry; and a catalyst accumulator for accumulating the catalyst fines obtained from the filters. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in greater detail with references to the accompanying figure wherein; 
         FIG. 1  is a process flow diagram depicting an embodiment of catalyst removal from methanol to olefin effluent with downstream oil/vapor separation vessel and associated filters; 
         FIG. 2  is a process flow diagram depicting catalyst removal from methanol to olefin effluent, in accordance with another embodiment; and 
         FIG. 3  is a process flow diagram depicting catalyst removal from methanol to olefin effluent, in accordance with another embodiment of the present technique. 
     
    
    
     DETAILED DESCRIPTION 
     The description of the embodiments and applications of the present invention is being done together with the accompanying drawings, which form a part hereof. The embodiments are described herein for illustrative purposes and are subject to many variations. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but are intended to cover the application or implementation without departing from the spirit or scope of the present invention. Further, it is to be understood that the phraseology and terminology employed herein are for the purpose of the description and should not be regarded as limiting. 
     The terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. 
     With reference to  FIG. 1  a schematic process flow diagram  100  of catalyst removal from MTO effluent is presented. An MTO effluent is introduced via line  102  to a quench fitting  104 , where it is mixed with a wash oil introduced via line  106  to obtain a cooled effluent  108  which is directed to a separator or a column  110  via line  108  through an inlet  109 . 
     The separator or column  110  may include separation elements such as contacting elements, packing material or trays (not shown) to separate the catalyst fines from the effluent. 
     In accordance with the aspects of the present technique, the separator or column  110  separates out the catalyst fines from the effluent, which is thereafter directed to an outlet  120  for discharging the cooled effluent essentially free of catalyst fines via line  122  for further processing, preferably to a water quench tower (not shown). The water quench tower is adapted to further cool the effluent and condense the water from the effluent. 
     The separated catalyst fines are directed out of the separator or the column  110  via line  124  in a slurried form which is circulated by a slurry circulating pump  128 . The slurry is circulated to one or more filters  140   a ,  140   b , via the pump  128  for filtering out the catalyst therefrom and thereafter returning a filtrate to the quench fitting  104 . 
     Backflush gaseous medium is provided via line  144  to pressurize and flush the collected catalyst fines into line  168 . The backflush medium which may be compressed gas that may be selected from an inert gas, air and/or fuel gas. One of the filters  140   a  or  140   b  is in filter mode, while the other is in backflush mode. For example, valves  148 ,  150 ,  152  and  154  are open and valves  156 ,  158 ,  160  and  162  are closed when filter  140   b  is filtering and filter  140   a  is being backflushed, as depicted in  FIG. 1 ; the valves are switched after the catalyst fines have accumulated in filter  140   b  and the filter  140   b  is ready for backflushing. The filtration is preferably continuous and should be at a rate that keeps the fines level from building to excessive levels in the wash oil, preferably no more than 0.5 weight percent fines, more preferably no more than 0.2 weight percent, and yet more preferably no more than 0.1 weight percent fines in the wash oil. 
     In accordance with aspects of the present technique, a catalyst accumulator  170  connected to the filters  140   a ,  140   b  via line  168  accumulates the catalyst fines from the filters  140   a ,  140   b . The catalyst fines and wash oil are removed from the system from the accumulator  170  via line  172  from the bottom of accumulator  170 , while the backflush gaseous medium is removed from the system from the accumulator  170  via line  174  from the top of accumulator  170 . 
     It may be noted that heat removal heat exchangers may also be present in line  166  for cooling the MTO effluent typically encompassing but limited to a steam generator  164  as depicted in  FIG. 1 . 
     Referring now to  FIG. 2 , another embodiment depicting a process flow  200  for separating catalyst fines from MTO effluent is depicted. The embodiment includes an oil quench tower  300 , the MTO effluent and the wash oil is supplied to the oil quench tower via lines  102  and  106  respectively. It may be noted that the entrained catalyst is washed from the MTO effluent by contact with the circulating wash oil. Overhead vapor from the tower  300  in line  122  is routed preferably to a water quench tower (not shown) at a typical temperature of 200-400° F. for recovery of MTO effluent. 
     The quench tower includes a vapor-liquid contacting zone  302  which can include conventional packing or trays that may be disposed above a liquid holdup zone  306 . MTO Effluent from line  102  is introduced below the contacting zone  302  through an inlet  303 . A recirculation loop  310  which includes a circulating pump  312 , heat removal heat exchangers  314 , typically encompassing but not limited to a steam generator  314 , and the line  316  is configured to introduce a continuous supply of wash oil to a liquid distributor  304  above the contacting zone  302 , In the contacting zone  302 , the catalyst fines in the effluent are washed into the oil, and the MTO effluent is cooled and separated. 
     It may be noted that the MTO effluent enters the quench tower  300  at a temperature of 800-1000′F and exits at a temperature from about 200-400° F. 
     A filtration loop  124  includes a slurry circulating pump  128 , filters  140   a ,  140   b  and the line  146  for returning filtrate to the oil quench tower  300 . Backflush gaseous medium is provided via line  144  to pressurize and flush the collected catalyst fines into line  168 . As previously noted with reference to  FIG. 1 , the backflush medius is a compressed gas medium that can be selected from an inert gas, air and fuel gas. One of the filters  140   a  or  140   b  is in filter mode, while the other is in backflush mode. For example, valves  148 ,  150 ,  152  and  154  are open and valves  156 ,  158 ,  160  and  162  are closed when filter  140   b  is filtering, that is in filter mode and filter  140   a  is being backflushed, that is in backflush mode, as depicted in  FIG. 2 ; the valves are switched after the fines have accumulated in filter  140   b  and the filter  140   b  is ready for backflushing. The filtration is preferably continuous and should be at a rate that keeps the fines level from building to excessive levels in the wash oil, preferably no more than 0.5 weight percent fines, more preferably no more than 0.2 weight percent, and yet more preferably no more than 0.1 weight percent fines in the wash oil. The catalyst fines obtained from the filters  140   a ,  140   b  is directed to the catalyst accumulator  170  via line  168 . The catalyst fines and wash oil are removed from the system from the accumulator  170  via line  172  from the bottom of accumulator  170 , while the backflush gaseous medium is removed from the system from the accumulator  170  via line  174  from the top of accumulator  170 . 
     Turning now to  FIG. 3 , an embodiment depicting a schematic process flow  400  of removing catalyst from methanol to olefin effluent is presented. An MTO effluent is introduced via line  102  to the quench fitting  104 , where it is mixed with the wash oil that is fed into the quench fitting via line  318 . The wash oil via line  106  may be directly fed to the quench fitting  104  or may be recirculated from the oil quench tower  300 . The MTO effluent mixed with oil is fed into the oil quench tower  300 . 
     As previously noted, the entrained catalyst is washed from the MTO effluent by contact with the circulating wash oil. Overhead vapor from the tower  300  in line  122  is routed most frequently to a water quench tower (not shown) at a typical temperature of 200-400° F. 
     According to the present embodiment, the quench tower  300  includes a vapor-liquid contacting zone  302  which can include conventional packing or trays, disposed above a separation zone  308 . The separation zone  308  is located at the bottom of the quench tower  300  and is adapted to separate vapors from liquids. MTO Effluent from line  108  is introduced below the contacting zone  302 . A recirculation loop  310  which includes the wash oil circulating pump  312 , heat removal heat exchangers  314 , typically encompassing but not limited to a steam generator  314 , and a line  316  to introduce a continuous supply of wash oil to a liquid distributor  304  above the contacting zone  302 . In the contacting zone  302 , the catalyst fines in the effluent are washed into the oil, and the MTO effluent is cooled. A slurry is obtained from the mixture of catalyst and wash oil, which settles at the bottom of the quench tower  300  and directed through an outlet  320  into a filtration loop  124 . 
     As previously noted, the MTO effluent enters the quench tower  300  at a temperature of 800-1000° F. and exits at a temperature from about 200-400° F. The filtration loop  124  includes a slurry circulating pump  128 , filters  140   a ,  140   b  and the line  320  for returning filtrate to the oil quench tower  300 . Backflush gaseous medium is provided via line  144  to pressurize and flush the collected catalyst fines into line  168 . As previously noted with reference to  FIG. 1 , the backflush medium is a compressed gas medium that can be selected from an inert gas, air and fuel gas. One of the filters  140   a  or  140   b  is in filter mode, while the other is in backflush mode. For example, valves  148 ,  150 ,  152  and  154  are open and valves  156 ,  158 ,  160  and  162  are closed when filter  140   b  is filtering, that is in filter mode, and filter  140   a  is being backflushed, that is in backflush mode, as depicted in  FIG. 3 ; the valves are switched after the fines have accumulated in filter  140   b  and the filter  140   b  is ready for backflushing. The filtration is preferably continuous and should be at a rate that keeps the fines level from building to excessive levels in the wash oil, preferably no more than 0.5 weight percent fines, more preferably no more than 0.2 weight percent, and yet more preferably no more than 0.1 weight percent fines in the wash oil. The catalyst fines obtained from the filters  140   a ,  140   b  is directed to the catalyst accumulator  170  via line  168 . The catalyst fines and wash oil are removed from the system from the accumulator  170  via line  172  from the bottom of accumulator  170 , while the backflush gaseous medium is removed from the system from the accumulator  170  via line  174  from the top of accumulator  170 . 
     In accordance with aspects of the present technique, a portion of the wash oil in the quench tower  300  may be recirculated to the quench fitting  104  via line  318 . Furthermore, the wash oil can also be supplied to the quench fitting continuously from a wash oil source via line  106  to maintain a steady amount of wash oil in the quench fitting. 
     Embodiments of the present invention have several advantages over the existing techniques, such as but not limited to ease of separation of catalyst fines and recovery, resulting in low maintenance cost of the equipment. 
     The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiment was chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated.