Patent Abstract:
A process for treating sulfur at elevated pressures by which the sulfur may be separated from a process gas in a separation vessel, sent to one or more transfer vessels, and the transfer vessel(s) vented to depressurize the sulfur to near atmospheric pressure. The sulfur may subsequently be transferred to ambient storage or other desirable use. The sulfur exiting the separation vessel may also be transferred to an intermediate vessel. The rate of transfer of the sulfur throughout the process may be controlled by controlling the pressure differentials between the various vessels.

Full Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Patent Application No. 60/474,842 filed Jun. 2, 2003, incorporated herein by reference for all purposes. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND 
     Natural gas, as it comes from the ground, may contain impurities. One impurity that is often found in natural gas is sulfur, particularly sulfur in the form of H 2 S. It may be desirable to remove the sulfur from a natural gas stream because, for example, it may prematurely corrode pipelines and it also may act as a poison to catalysts in downstream processes. One method of removing sulfur from a natural gas process is the Claus Process. The Claus Process generally consists of several steps: (1) oxidizing a portion of the H 2 S to form some elemental sulfur and some SO 2  and (2) reacting some of the remaining H 2 S and SO 2  to form elemental sulfur and water. The sulfur produced in the Claus Process is generally produced at near atmospheric pressure (e.g., less than about 15 psig). 
     Another method of removing sulfur from a gas stream is through the direct partial oxidation of the H 2 S to produce water and elemental sulfur. Generally, in this partial oxidation process, a stream containing up to about 3% H 2 S is partially oxidized over a catalyst to produce, inter alia, elemental sulfur at elevated pressures (e.g., greater than about 15 psig). See generally, U.S. Pat. Nos. 5,271,907 and 6,099,819, incorporated herein by reference. The methods of processing sulfur at near atmospheric pressure may not work properly when handling elemental sulfur at elevated pressures. Additionally, other high pressure treatment processes may be capital intensive, may require many moveable parts, which may require frequent maintenance and/or possibly expose workers and operators to high pressure sulfur. Thus, there is a need for a process for processing sulfur at elevated pressures which alleviates or eliminates one or more of these concerns. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic drawing of a system for treating sulfur in accordance with embodiments of the present invention. 
         FIG. 2  is a schematic drawing of a second system for treating sulfur in accordance with embodiments of the present invention. 
         FIG. 3  is a schematic drawing of a third system for treating sulfur in accordance with embodiments of the present invention. 
     
    
    
     SUMMARY 
     Disclosed herein is a process for treating sulfur at elevated pressures wherein the sulfur may be separated from the process gas, sent to a transfer vessel, and the transfer vessel is vented to depressurize the sulfur to near atmospheric pressure. The sulfur may then be transferred to ambient storage or any other desirable use. 
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , there is shown a system comprising a product separator  100 , a pressurized sulfur storage vessel  110 , a sulfur transfer vessel  120 , and valves V 1 , V 2 , V 3 , V 4 , V 5 , V 6 , and V 7 . In operation, sulfur and process gas (e.g., H 2 O and/or H 2 ) at elevated pressure (e.g., above about 15 psig) flow continuously or semi-continuously into process separator  100  through inlet line  190 . Most of the process gas exits separator  100  through gas outlet  200 . Likewise, most of the sulfur exits separator  100  through sulfur outlet  210 , through valve V 1  and into sulfur storage vessel  110 . 
     At steady state, the pressure of storage vessel  110  is maintained equal to the pressure of separator  100  (e.g., about 70 psig) less the hydrostatic head of the sulfur as it rises through elevation A before entering storage vessel  110 . In some embodiments the pressure of storage vessel  110  may be about 65 psig. Elevation A may be adjusted as desired to provide the desired pressure drop between vessels  100  and  110 . In some embodiments, elevation A may be about 7.7 feet. Pressurized gas may be injected or released through gas lines  230  and  220  respectively so as to maintain the desired pressure in storage vessel  110 . For example, an automatic or manual level control sensors  280  and  290  may be introduced into vessel  100 . If the level of sulfur in separator  100  increases above a desired level, as indicated by level sensor  280 , valve V 2  may be opened and gas released to decrease the pressure in vessel  110 , thereby increasing the flow rate of sulfur from the separator through sulfur line  210 . Likewise, if the level of sulfur in separator  100  decreases below a desired level, as indicated by level sensor  290 , valve V 3  may be opened and gas injected so as to increase the pressure in vessel  110 , thereby decreasing the flow rate of sulfur from the separator through sulfur line  210 . Similarly, if the operating pressure in separator  100  changes, as indicated by pressure sensor  300  it may be necessary to increase or decrease the pressure in vessel  110  correspondingly. 
     As the level of sulfur in storage vessel  110  reaches a desired level, as indicated, e.g., by level sensor  310 , the pressure in transfer vessel  120  may be increased (automatically by a control device or manually) to just below that of storage vessel  110 . For example, if storage vessel  110  is at 100 psig, transfer vessel  120  may be brought to, e.g., 50 psig (via, e.g., high pressure gas line  260 ) and valve V 4  opened to allow sulfur to flow from storage vessel  110  to transfer vessel  120 . Additionally, vessel  120  may be vented through, e.g., valve V 5  as vessel  120  is filled. Valve V 4  can be closed when the sulfur level in vessel  110  reaches a desired lower level (e.g., its minimum safe operating level). This closure of valve V 4  can occur manually or via an automated device that closes V 4  in response to a signal from a level indicator  320  in vessel  110 . Once the sulfur has been transferred from vessel  110  into transfer vessel  120  and valve V 4  has been closed, the pressure in vessel  120  may be reduced to near atmospheric pressure (e.g., through gas release line  250 ) and the sulfur transferred to atmospheric or near atmospheric storage (e.g., 0 to about 5 psig) through sulfur removal line  270 . Once the sulfur level in vessel  120  reaches its desired lower level, valve V 7  may be closed and vessel  120  may then be repressurized to receive sulfur from storage vessel  110 , and the sequence may be repeated. The closure and repressurization may be manual or automatic via a control device. In some embodiments, sulfur production may be about 10 tons/day. 
     In some embodiments, either or both of vessels  110  and  120  may have a diameter of about 4 feet and a height of about 20 feet. 
     Referring now to  FIG. 2 , there is shown a separator  400 , a sulfur transfer vessel  410 , and valves V 21 , V 22 , V 23 , and V 24 . In operation, sulfur and process gas (e.g., H 2 O and/or H 2 ) at elevated pressure (e.g., above about 15 psig) flow continuously or semi-continuously into process separator  400  through inlet line  490 . Most of the process gas exits separator  400  through gas outlet  500 . Likewise, most of the sulfur exits separator  400  through sulfur outlet  510 , through valve V 21  and into sulfur storage vessel  410 . 
     In operation, when the sulfur level of separator  400  reaches the desired level, valve  21  may be opened to allow sulfur to flow from separator  400  to vessel  410 . During transfer of sulfur from separator  400  to vessel  410 , it is desirable to keep the pressure of vessel  410  just below that of separator  400 . Pressurized gas may be injected or released through gas lines  530  and  520  respectively so as to maintain the desired pressure in storage vessel  410 . So long as the pressure of vessel  410  is less than the pressure of separator  400  less the hydrostatic head of the sulfur in transfer line  510 , sulfur will flow from separator  400  to vessel  410 . For example, automatic or manual level control sensors  580  and  590  maybe introduced into vessel  400 . If the level of sulfur in separator  400  increases above a desired level, as indicated by level sensor  580 , valve V 22  may be opened and gas released to decrease the pressure in vessel  410 , thereby increasing the flow rate of sulfur from the separator through sulfur line  510 . Likewise, if the level of sulfur in separator  400  decreases below a desired level, as indicated by level sensor  590 , valve V 23  may be opened and gas injected so as to increase the pressure in vessel  410 , thereby decreasing the flow rate of sulfur from the separator through sulfur line  510 . Similarly, if the operating pressure in separator  400  changes, as indicated by pressure sensor  600  it may be necessary to increase or decrease the pressure in vessel  410  correspondingly. 
     As the level of sulfur in vessel  410  reaches a desired level, valve V 21  may be closed and the pressurized sulfur in vessel  410  vented through gas release line  520  to the desired pressure (e.g., atmospheric) and the sulfur transferred to atmospheric or near atmospheric storage (e.g., 0 to about 5 psig) through sulfur removal line  640 . Once the sulfur level in vessel  410  reaches its desired lower level, valve V 24  may be closed and vessel  410  may then be repressurized to receive sulfur from separator  400 , and the sequence may be repeated. The closure and repressurization may be manual or automatic via a control device. 
     Referring now to  FIG. 3 , there is shown an embodiment in which two transfer vessels may be operated alternately in parallel. There is shown separator  700 , first transfer vessel  710 , second transfer vessel  720 , and valves V 31 , V 32 , V 33 , V 34 , V 35 , V 36 , V 37 , and V 38 . In short, one vessel is filled with sulfur from separator  700 , the valve between the filled vessel and the separator is closed, and the sulfur in the filled vessel is vented to the desired pressure (i.e., atmospheric or near atmospheric). Once the pressure of the sulfur is reduced as desired, the sulfur can be transferred to its destination (e.g., storage or a process). For the purpose of this disclosure, vessel  720  will be filled first, however, the order of the steps may be changed such that another vessel is filled first. Additionally, in some embodiments, it may be desirable to allow sulfur to transfer to both vessels simultaneously. p In operation, sulfur and process gas are injected into separator  700 , sulfur exits separator  700  trough sulfur outlet  810  and gas exits through gas outlet  800 . Valves V 38  is open and the pressure of vessel  720  may be just below that of the separator  700  less the hydrostatic head of the sulfur flowing from the separator  700  to vessel  720 . The flow of sulfur flowing from separator  700  to vessel  720  may be controlled by controlling the pressure in vessel  720  by injecting or venting gas through valves V 35  or V 37  respectively. To increase the rate of sulfur transfer, gas may be vented. Conversely, to decrease the rate of sulfur transfer, high pressure gas may be injected. Once the amount of sulfur in vessel  720  reaches its desired upper level, valve V 38  is closed, valve V 31  is opened, and the high pressure sulfur in vessel  720  is vented until the sulfur reaches its desired pressure. The sulfur may then be transferred to storage or any other desirable use. While the sulfur in vessel  720  is brought to atmospheric pressure, vessel  710  may be filled with sulfur from separator  700 , and the same process repeated. 
     The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. For example, the embodiments of  FIG. 1  and/or  FIG. 3  may be modified to include 3 or more vessels. It is intended that the following claims be interpreted to embrace all such variations and modifications.

Technology Classification (CPC): 2