Abstract:
A quench column heater and a method for heating a circulating liquid in a gas-to-liquid heat exchanger and an indirect heat exchanger to produce a hot liquid stream for use for heat exchange in a selected process to supply heat to the process. One particularly useful application of the present invention is the revaporization of liquefied natural gas (LNG).

Description:
FIELD OF THE INVENTION 
   The present invention relates to a quench column heater and a method for heating a circulating liquid in a gas-to-liquid heat exchanger and an indirect heat exchanger to produce a hot liquid stream for use for heat exchange in a selected process to supply heat to the process. One particularly useful application of the present invention is the revaporization of liquefied natural gas (LNG). 
   BACKGROUND OF THE INVENTION 
   In many industrialized processes, heat is required at a temperature which is readily supplied by a circulating liquid, such as water. Such circulating streams require heating at a heat source to reheat the circulating liquid stream after it has given up heat in the area in which the heat was desired. 
   As indicated previously, one area wherein frequent applications of this type arise is in the revaporization of LNG. 
   In many remote areas of the world large natural gas deposits are found. These natural gas deposits, while constituting a valuable resource, have little value in the remote areas in which they are located. To utilize these resources effectively the natural gas must be moved to a commercial market area. This is frequently accomplished by liquefying the natural gas to produce LNG, which is then transported by ship or the like to a market place. Once the LNG arrives at the market place, the LNG must be revaporized for use as a fuel, for delivery to pipelines and the like. Other cryogenic fluids frequently require revaporization after transportation also, but by far the largest demand for processes of this type is for cryogenic natural gas revaporization. 
   The revaporization of the cryogenic natural gas requires the input of substantial quantities of heat. While seawater has been used in areas where seawater is readily available, certain disadvantages attend the use of seawater, not the least of which is lack of availability in some areas in which the LNG is to be revaporized. Other disadvantages relate to the corrosion of heat exchange surfaces by the seawater and the like. 
   In some instances, air has been used as a heat exchange medium to revaporize the cryogenic natural gas. One such process is shown in U.S. Ser. No. 11/133,762 entitled “Air Vaporizer” filed May 19, 2005 by Martin J. Rosetta, et al. This application is hereby incorporated in its entirety by reference. Other systems may also be used for the revaporization of the cryogenic liquid and include indirect heat exchangers such as shell and tube heat exchangers, direct fired heat exchangers in indirect heat exchange contact with the cryogenic gas as the like. In all such cases, substantial heat is required to revaporize the cryogenic natural gas. 
   In the air vaporization processes particularly, it would be desirable if a recirculating liquid stream could be used to heat the air prior to or during its passage through the revaporization vessels. Further it is desirable to heat the vaporized gas with a warm or hot liquid solution to raise it to a pipeline temperature after vaporization. 
   A continuing effort has been directed to the development of efficient equipment to provide a heated hot liquid stream in a recirculating loop for use in such processes. 
   SUMMARY OF THE INVENTION 
   According to the present invention, an effective heating and cooling system for use in a recirculating system comprises a quench column heater having a liquid inlet, a hot liquid outlet, a hot gas inlet and a cooled gas outlet and adapted to heat a liquid stream by heat exchange with a hot gas stream to produce a hot liquid stream and a cooled gas stream, the heater comprising: a heat exchanger including a passageway for the flow of an intermediate temperature liquid stream to produce a hot liquid stream and an intermediate temperature gas stream by indirect heat exchange contact with a passageway for the hot gas stream from the hot gas inlet to produce the hot liquid stream via the hot liquid outlet and the intermediate temperature gas stream; a quench column adapted to receive the liquid stream via the liquid inlet and pass the liquid stream into a quench column from a top of the quench column for recovery from a bottom of the quench column in gas-to-liquid contact with the intermediate temperature gas stream to produce an intermediate temperature liquid stream and a cooled gas stream for discharge via the cooled gas outlet; a collection zone to collect the intermediate temperature liquid from the quench column; and, a conduit in fluid communication with the collection zone and an intermediate temperature liquid inlet to the heat exchanger. 
   The invention further comprises a method for heating a liquid stream by a combination of gas-to-liquid contact in a quench heater and indirect heat exchange contact between the liquid stream and a hot gas stream, the method comprising: passing the liquid stream into a quench column for downward flow through the quench column in heat exchange direct contact with an intermediate temperature gas stream to produce a cool gas stream and an intermediate temperature liquid stream; passing the intermediate temperature liquid stream to an indirect heat exchange exchanger for heat exchange with the hot gas stream to produce a hot liquid stream and the intermediate temperature gas stream; recovering the hot liquid stream; and, discharging the cool gas stream. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of an embodiment of apparatus of the present invention; 
       FIG. 2  shows an alternate embodiment of the apparatus of the present invention; 
       FIG. 3  shows a further embodiment of the present invention; 
       FIG. 4  is a schematic diagram of an in-line heater useful to generate a hot gas for use in apparatus and method of the present invention; 
       FIG. 5  shows a turbine coupled to a fired heater for the production of hot gas; and, 
       FIG. 6  shows a turbine with a supplemental duct heater. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   In the discussion of the Figures, the same terms will be used throughout to refer to the same or similar components. 
   In  FIG. 1  a quench column heater  10  is shown. Heater  10  comprises a circulating liquid inlet  12 , a heated circulating liquid outlet  14 , a hot gas inlet  16  and a cooled exhaust gas outlet  18 . A vessel  20  contains a heat exchanger  22  in which an intermediate temperature liquid is passed via a line  44 , a pump  46  and a line  48  to an inlet to a heat exchanger  22  for heat exchange with hot gas passed to heat exchanger  22  via an inlet as shown by arrow  16 . A hot liquid stream is recovered through a heat exchanger outlet  52  via a line  14 . The resulting cooled exhaust gas is at an intermediate temperature and is recovered as shown by an arrow  24  and passed upwardly in vessel  20  through chimney trays  26  or other suitable equipment to pass the intermediate temperature gas through a liquid  40  having a liquid level  42  in a liquid collection zone  43  without direct liquid contact with the intermediate temperature gas. The intermediate temperature gas is passed upwardly as shown by arrow  28  into a quench packing column  30  through a bottom  34  of quench packing column  30  where it passes in direct heat exchange with downcoming liquid as shown by arrows  38 . The liquid is passed into quench packing column  30  via a plurality of sprays  36  or liquid distributors in a manner well known to those skilled in the art and a top  32  of quench packing column from inlet line  12 . The liquid passing through quench packing column  30  is in direct heat exchange contact with the intermediate temperature gas. The gas, after passing through quench packing column  30 , is discharged through a line  18  at a temperature which is typically about 20° F. above ambient. This temperature may vary substantially and may be from about IQ to about 50° F. above ambient. The gas stream may be below ambient in some instances and may be passed to further treatment if necessary for the removal of carbon oxides or other materials. 
   The downcoming liquid  40  is collected in a liquid collection zone  43  having a level  42  and withdrawn from liquid collection zone  43  by a line  44  as discussed previously. A pH monitor  56  is connected via a line  54  in fluid communication with the liquid  40  in liquid collection zone  43  to maintain the pH of the intermediate temperature liquid in collection zone  43 . This liquid is typically water, although other liquids could be used if desired. The pH is maintained typically in a range from about 6.0 to about 8.0. The pH tends to become increasingly acidic and is adjusted by the addition of an alkaline base material Such as sodium bicarbonate, soda ash, sodium hydroxide caustic, or the like. The alkaline material is added in response to signals from pH monitor  56  to a valve  62  via a connection shown as a broken line  58  through a treating chemicals line  60 , a valve  62  and a line  64 . While not shown, a filter may be positioned in the flow path, for instance in line  44 , of the liquid to remove particulates which may accumulate in the liquid as it recirculates. 
   In  FIG. 2 , an alternate embodiment of the invention is shown. The invention functions generally as described with respect to  FIG. 1  but in this embodiment the gas stream is passed through a heating zone  74 , through an outlet  70 , through a line  72  and back into a heating zone  68  via an inlet  76  to permit the positioning of an optional selective catalytic reduction unit  80  in vessel  20  as shown. Hot liquid is recovered from an outlet  78  from heat exchanger section  74 . Such units are well known to those skilled in the art and are used to reduce the NOx content of gaseous streams. 
   In  FIG. 3 , an alternate embodiment of the present invention is shown which is varied only in that the configuration of the vessel has been changed to position the heat exchanger coil  22  in a vertical position rather than in a horizontal position. Such variations are well within the scope of the preset invention. This embodiment may not require a pump in line  44 . 
   The hot gas stream can be supplied from a variety of sources. One such source is shown in  FIG. 4  wherein a fired combustion heater  82  is shown with the combustion heater being fired by a fuel from a line  84  and air from a line  86  to produce a hot exhaust gas  88 . 
   Similarly in  FIG. 5 , a hot gas stream is produced from a turbine system which comprises a compressor  90 , fed by an inlet air line  92  to produce a compressed air stream which is discharged via a line  94  to a combustion chamber  96  which supplies hot combustion gas to a turbine  102  via a line  100 . Gas is supplied to combustion chamber  96  via a line  98 . A hot exhaust gas is produced by turbine  102  and discharged via a line  164  as a hot exhaust gas stream. Typically compressor  90  and turbine  102  are operated on a common shaft  106  so that turbine  102  can drive compressor  90 . Such embodiments are typical but other embodiments can be used as desired and are effective to produce a stream of hot exhaust gas. The stream of hot exhaust gas in line  104  is passed to a fired combustion heater  82  fueled by fuel from a line  84  and air from a line  86  to produce a higher temperature in the exhaust gas than the gas temperature as recovered from turbine  102 . 
   In  FIG. 6  an alternate embodiment is shown wherein a duct burner  108  is shown fueled by a fuel line  110  and an air line  112  to produce a hot exhaust gas stream  88 . 
   In the practice of the method of the present invention, the liquid stream recovered as a cool liquid stream from the recirculating loop is first contacted with an intermediate temperature gas which is typically at a temperature from about 250 to about 350° F. as it enters quench column  30 . In quench column  30  by direct heat exchange with the liquid, efficient heat transfer is accomplished and the gas stream is cooled to a temperature as indicated to from about 10 to about 50° F. above ambient temperature. The intermediate temperature liquid  40  recovered in collection zone  43  is typically at a temperature from about 100 to about 150° F. as withdrawn and passed via line  44  to heat exchanger  22 . The hot liquid produced through line  14  is typically at a temperature from about 270 to about 300° F. The exhaust gas passed to the heat exchanger through line  16  is typically at a temperature from about 1000 to about 2200° F. 
   The quench column may be packed with any suitable packing material to facilitate intimate liquid contact with the rising intermediate temperature gas. Any suitable packing can be used in this column, as known to those skilled in the art. Some suitable materials are random packing (saddles, pall rings), structure packing, or the like. In some cases, the quench column internals can be designed with no structure to facilitate surface contact directly with the exhaust gas. 
   Very efficient heat exchange is accomplished in this quench column. To further heat the liquid, it is passed through a heat exchanger in indirect contact with the hot gas charged to the heat exchanger. As indicated previously, the hot gas may be an exhaust gas from a unit which produces a hot exhaust gas stream. 
   In the quench column the contact is referred to as gas-to-liquid contact and is very efficient for heat transfer. However, there are certain temperature limitations on this heat exchange operation because of the volatility of the heated fluid, which is typically water. The liquid is most readily heated to temperatures up to about 150° F. by direct heat exchange. Heating beyond these temperatures by gas-to-liquid contact will result in excessive loss of liquid by evaporation. Higher temperatures require the use of indirect heat exchange where the liquid is heated in a closed system heat exchanger to reach its desired outlet temperature. Typically such heat exchangers may be coiled tube exchangers, shell and tube heat exchangers and the like. By combining the use of a quench column heater with the indirect heater, a high temperature is readily achieved in the outlet liquid stream while preserving the efficiency of the contacting in the quench column. 
   As indicated previously, such liquid streams are readily used in circulating liquid loops to deliver heat to a desired operation. The revaporization of LNG is one operation which is readily accomplished using the hot liquid stream. The hot liquid stream can be used in shell and tube heat exchangers, coiled heat exchangers, air vaporization heat exchangers and the like to revaporize LNG. Of course, the hot liquid can also or alternatively be used to deliver heat for other processing requirements. While the invention has been discussed with reference to liquid generally the most frequently used and preferred liquid will be water. 
   Further while a recirculating loop has not been shown, it will be understood that the liquid recovered through line  14  may be passed to a heat exchange zone and retrieved via a line  12  after it has been cooled. Alternatively the liquid passed through line  12  may be from a different source and the liquid recovered through line  14  may be used for heating purposes without return to the quench column heater. Such variations are well within the scope of the present invention. 
   While the present invention has been described by reference to certain of its preferred embodiments, it is pointed out that the embodiments described are illustrative rather than limiting in nature and that many variations and modifications are possible within the scope of the present invention. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments.