Abstract:
An apparatus and process is disclosed for the cooling of a reactor effluent gas stream. The apparatus includes a contact cooling system with a discharge drum providing a second wash zone. Each wash zone has a packed bed, or other type of mechanical system for contacting the gas stream with the cooling liquid. The liquid in the first stage will remove heavy components, allowing for a cleaner second stage that can be reduced in size.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is related to contact coolers. In particular, the invention is related to contact cooling equipment for use with the cooling of process streams from hydrocarbon processing units. 
       BACKGROUND 
       [0002]    Light olefins, such as ethylene and propylene, are important commercial precursors for a number of products. Most notably the manufacture of polyethylene and propylene, but also as contributing precursors for products such as cumene. 
         [0003]    The production of light olefins is generally through cracking of petroleum streams, such as catalytic or steam cracking of a naphtha stream. Light olefins can also be generated by other hydrocarbon processes. The production of light olefins produces by-products from the processes, and the light olefins product streams need to be of a high purity for producing high quality plastic products. 
         [0004]    The processing of hydrocarbons generally goes through several stages. The processing steps can be expensive, so reducing cost to improve the economics is important for the production of these products. There is a continuous need for searching for new equipment designs and process to lower the cost of production. 
       SUMMARY 
       [0005]    The present invention is an apparatus for contact cooling comprising a vessel having a gas inlet, a gas outlet, a wash oil inlet, and a wash oil outlet; a first packed bed disposed within the vessel at a position above the gas inlet and below the wash oil inlet; a discharge drum, having a discharge drum gas inlet in fluid communication with the vessel gas outlet, a discharge drum gas outlet, a drum wash oil inlet and a drum wash oil outlet; a second packed bed disposed within the discharge drum at a position above the drum gas inlet and below the drum wash oil inlet; and a demister pad disposed within the discharge drum above the second packed bed and below the discharge drum outlet. 
         [0006]    A second form of the invention is an apparatus for contact cooling comprising a vessel having a gas inlet, a gas outlet, a wash oil inlet, and a wash oil outlet; a first packed bed disposed within the vessel at a position above the gas inlet and below the wash oil inlet; a plurality of disk and donut trays disposed above the gas inlet and below the first packed bed within the vessel; a compressor having an inlet in fluid communication with the vessel gas outlet, and an outlet; a discharge drum, having a discharge drum gas inlet in fluid communication with the compressor outlet, a discharge drum gas outlet, a drum wash oil inlet and a drum wash oil outlet; a second packed bed disposed within the discharge drum at a position above the drum gas inlet and below the drum wash oil inlet; a plurality of disk and donut trays disposed above the gas inlet and below the first packed bed within the vessel; and a demister pad disposed within the discharge drum above the second packed bed and below the discharge drum outlet. 
         [0007]    An aspect of the invention is a process for cooling a reactor effluent stream comprising passing a reactor effluent gas to a contact cooling vessel; passing a wash oil to the contact cooling vessel, to intermingle with the reactor effluent gas and generate a cooled effluent gas; passing the cooled effluent gas to a discharge drum; passing a second wash oil to the discharge drum to intermingle with the cooled effluent gas to generate a washed and cooled gas. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph further comprising passing the washed and cooled gas through a demister to generate a cooled gas with droplets removed. 
         [0008]    Other objects, advantages and applications of the present invention will become apparent to those skilled in the art from the following detailed description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0009]    FIGURE is a diagram of the present invention showing the contact cooler and discharge drum. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    The processing of hydrocarbons generally goes through several stages. After a process stream containing a desired product, such as light olefins, is generated, the process stream needs to be purified and cooled. The cooling process can be combined with a wash process to remove impurities, as well as cooling the process stream. Cooling the process stream reduces thermal reactions that can occur should the process stream be maintained at a high temperature. In particular, the production of olefins, such as C3 or C4 olefins, from the direct dehydrogenation of a paraffin stream needs to be cooled, washed and compressed before further processing. 
         [0011]    Contact coolers can also be used to remove heavy by-products from a reactor effluent stream in a light olefin generation process. A traditional design recirculates a washing oil, or heavy hydrocarbon stream, collected at the bottoms of a contact cooling vessel, and passed back to the top of the contact cooling vessel. This limits the ability to remove heavies from the reactor effluent stream, which can result in heavies being carried to downstream processing equipment and fouling that downstream equipment. A current design circulates the wash oil, but has a drag stream removing a portion of the circulating oil, and a fresh stream of new oil added to the circulation. This does not, however, prevent all heavies from being removed from the process stream, and therefore allows for some carryover of heavies. Typically, the fresh stream and drag stream have flow rates about 0.5 to 1% of the mass flow of the circulating stream. Important equipment to protect includes downstream compressors, heat exchangers and adsorbent beds. 
         [0012]    The present invention provides for a contact cooler with a discharge drum providing for a cleaner wash oil to remove residual heavies that can be carried over from the contact cooler. An effluent gas from a reactor is cooled in a contact cooler, and then compressed and further cooled during compression. Wash oil carried over is condensed and collected in a discharge drum. The discharge drum includes a second wash oil that circulates and is spread over a packing section in the discharge drum to further wash the effluent gas. This is a cleaner wash oil, and further removes heavies that have not been removed in the contact cooler, leading to an effluent gas with improved purity. The compressed effluent gas occupies a smaller volume, therefore leading to a discharge drum having a smaller diameter than the contact cooler and the axial length is increase to provide for a packing section. 
         [0013]    The present invention is an apparatus for contact cooling, as shown in the FIGURE. The apparatus includes a vessel  10  having a gas inlet  12 , a gas outlet  14 , a wash oil inlet  16  and a wash oil outlet  18 . The apparatus further includes a first packed bed  20  disposed within the vessel  10  at a position above the gas inlet  12  and below the wash oil inlet  16 . The apparatus further includes a discharge drum  30  having a discharge drum gas inlet  32 , a discharge drum gas outlet  34 , a drum wash oil inlet  36  and a drum wash oil outlet  38 . The discharge drum gas inlet  32  is in fluid communication with the gas outlet  14 . The discharge drum  30  includes a second packed bed  40  disposed at a position below the drum wash oil inlet  36  and above the drum gas inlet  32 . A demister pad  50  is positioned within the discharge drum  30  at a position above the drum wash oil inlet  36  and below the drum gas outlet  34 . 
         [0014]    The apparatus can further include a compressor  60  for compressing the effluent gas leaving the contact cooler vessel  10 . The compressor  60  has an inlet in fluid communication with the vessel outlet  14  and an outlet in fluid communication with the discharge drum inlet  32 . The compressed effluent gas can be further cooled upon leaving the compressor, and the apparatus can have a gas cooler  70  having an inlet in fluid communication with the compressor outlet, and an outlet in fluid communication with the discharge drum inlet  32 . The gas cooler  70  can be a heat exchanger that uses air and a fan for cooling with the effluent gas passing through pipes, or conduits. In an alternative the gas cooler can be a heat exchanger that uses a cooling fluid such as water. 
         [0015]    In one embodiment, the apparatus can further include a plurality of disk and donut trays  80  disposed within the vessel  10 . The disk and donut trays  80  are disposed above the gas inlet  12  in the vessel  10  and below the first packed bed  20 , to provide a direct contact for initial washing out of the heavies from the effluent gas. 
         [0016]    The apparatus further can include a first wash oil recycle system  100  having an inlet  102  in fluid communication with the wash oil outlet  18 , and an outlet  104  in fluid communication with the wash oil inlet  16 . The first wash oil recycle system  100  includes a first heat exchanger  110  in thermal communication with the first wash oil to cool the wash oil. The first wash oil recycle system  100  further includes a pump  112  for circulating the first wash oil. The first wash oil recycle system  100  can include a filter system for filtering particles accumulated in the first wash oil. In addition, the first wash oil recycle system  100  can include a drain for drawing off some of the wash oil as heavies and other contaminants accumulate. 
         [0017]    The apparatus can further include a second wash oil recycle system  120  for circulating and cooling the second wash oil stream associated with the discharge drum  30 . The second wash oil recycle system  120  has an inlet in fluid communication with the drum wash oil outlet  39 , and an outlet in fluid communication with the drum wash oil inlet  36 . The second wash oil recycle system  120  can include a second heat exchanger  130  for cooling the second wash oil stream. The apparatus can further include a fresh wash oil inlet  136  to provide for the addition of clean wash oil. 
         [0018]    The apparatus can further include a conduit  44  having a conduit inlet in fluid communication with the drum wash oil outlet  38 , and an outlet in fluid communication with the wash oil inlet  16 . This provides for passing a portion of the relatively clean wash oil in the second wash oil recycle system  120  to the first wash oil recycle system  100 , thus providing for a cascading system with fresh, clean wash oil added to the second wash oil recycle system  120  and then passing a portion to the first wash oil recycle system  100 , and drawing off a portion of the first wash oil stream as it accumulates heavies. 
         [0019]    An embodiment of the invention is a process for cooling an effluent gas from a reactor system. The process includes passing a reactor effluent gas to a contact cooling vessel. In particular, the effluent gas is a hydrocarbon rich gas with light and heavy hydrocarbon components, and the contact cooler will wash out the heavy hydrocarbon components. A wash oil is passed to the contact cooling vessel to intermingle with the reactor effluent gas to generate a cooled effluent gas. The effluent gas is contacted over a packed bed to produce a large surface area for the gas and liquid contact. The effluent gas can be contacted through a plurality of disk and donut trays to perform an initial contact between the effluent gas and a cascading wash oil prior to the contact in the packed bed. 
         [0020]    The cooled effluent gas is compressed and cooled in a compression unit to condense residual wash oil and to further cool the gas. The compressed and cooled gas is passed through a heat exchanger to further cool the compressed gas and to further condense any residual wash oil carried out of the contact cooling vessel. 
         [0021]    The compressed and cooled gas is passed to a discharge drum for separation of liquid droplets from the gas. In the discharge drum, a second wash oil is passed to the discharge drum to contact the compressed and cooled gas in a second packed bed, to generate a washed and cooled effluent gas. The second wash oil is a relatively clean wash oil to further remove any heavies not removed in the contact cooling vessel. The cooled and washed gas can further be passed through a demister pad to remove any droplets suspended in the gas. 
         [0022]    The process can further include collecting the wash oil in the bottom of the contact cooling vessel, filtering the wash oil, and cooling the wash oil to generate a cooled wash oil. The cooled wash oil is passed to the contact cooling vessel to continue the process of cooling the effluent gas. 
       SPECIFIC EMBODIMENTS 
       [0023]    While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims. 
         [0024]    A first embodiment of the invention is an apparatus for contact cooling comprising a vessel having a gas inlet, a gas outlet, a wash oil inlet, and a wash oil outlet; a first packed bed disposed within the vessel at a position above the gas inlet and below the wash oil inlet; a discharge drum, having a discharge drum gas inlet in fluid communication with the vessel gas outlet, a discharge drum gas outlet, a drum wash oil inlet and a drum wash oil outlet; a second packed bed disposed within the discharge drum at a position above the drum gas inlet and below the drum wash oil inlet; and a demister pad disposed within the discharge drum above the second packed bed and below the discharge drum outlet. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising a compressor having an inlet in fluid communication with the vessel gas outlet and an outlet in fluid communication with the discharge drum inlet. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising a gas cooler having an inlet in fluid communication with the compressor outlet, and an outlet in fluid communication with the discharge drum inlet. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising a plurality of disk and donut trays disposed above the gas inlet and below the first packed bed within the vessel. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising a first wash oil recycle system having an inlet in fluid communication with the wash oil outlet and an outlet in fluid communication with the wash oil inlet. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further including a first heat exchanger in the first wash oil recycle system for cooling the wash oil. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising a second wash oil recycle system having an inlet in fluid communication with the drum wash oil outlet, and an outlet in fluid communication with the drum wash oil inlet. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further including a second heat exchanger in the second wash oil recycle system for cooling the wash oil. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising a fresh wash oil inlet in fluid communication with the drum wash oil inlet. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising a conduit having a conduit inlet in fluid communication with the drum wash oil outlet, and an outlet in fluid communication with the wash oil inlet. 
         [0025]    A second embodiment of the invention is an apparatus for contact cooling comprising a vessel having a gas inlet, a gas outlet, a wash oil inlet, and a wash oil outlet; a first packed bed disposed within the vessel at a position above the gas inlet and below the wash oil inlet; a plurality of disk and donut trays disposed above the gas inlet and below the first packed bed within the vessel; a compressor having an inlet in fluid communication with the vessel gas outlet, and an outlet; a discharge drum, having a discharge drum gas inlet in fluid communication with the compressor outlet, a discharge drum gas outlet, a drum wash oil inlet and a drum wash oil outlet; a second packed bed disposed within the discharge drum at a position above the drum gas inlet and below the drum wash oil inlet; a plurality of disk and donut trays disposed above the gas inlet and below the first packed bed within the vessel; and a demister pad disposed within the discharge drum above the second packed bed and below the discharge drum outlet. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising a conduit disposed between the compressor outlet and the discharge drum inlet for carrying gas; and a cooling unit in thermal communication with the conduit. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising a first wash oil recycle system having an inlet in fluid communication with the wash oil outlet and an outlet in fluid communication with the wash oil inlet. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising a second wash oil recycle system having an inlet in fluid communication with the drum wash oil outlet, and in outlet in fluid communication with the drum wash oil inlet. 
         [0026]    A third embodiment of the invention is a process for cooling a reactor effluent stream comprising passing a reactor effluent gas to a contact cooling vessel; passing a wash oil to the contact cooling vessel, to intermingle with the reactor effluent gas and generate a cooled effluent gas; passing the cooled effluent gas to a discharge drum; passing a second wash oil to the discharge drum to intermingle with the cooled effluent gas to generate a washed and cooled gas. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph further comprising passing the washed and cooled gas through a demister to generate a cooled gas with droplets removed. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph wherein the reactor effluent gas first contacts the wash oil through an oil cascade over disk and donut trays, and then contacts the wash oil through a packed bed. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph further comprising passing the cooled effluent gas to a compressor to generate a compressed gas; passing the compressed gas through a heat exchanger to generate a cooled, compressed gas; and then passing the cooled compressed gas to the discharge drum. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph further comprising collecting the wash oil from the vessel; filtering the wash oil to generate a filtered wash oil; cooling the filtered wash oil to generate a cooled wash oil; and passing the cooled wash oil to the vessel. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph further comprising collecting the second wash oil; cooling the second wash oil to generate a cooled second wash oil; and passing the cooled second wash oil to the discharge drum. 
         [0027]    Without further elaboration, it is believed that using the preceding description that one skilled in the art can utilize the present invention to its fullest extent and easily ascertain the essential characteristics of this invention, without departing from the spirit and scope thereof, to make various changes and modifications of the invention and to adapt it to various usages and conditions. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limiting the remainder of the disclosure in any way whatsoever, and that it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.