CONVERTERS HAVING A FLANGED PRESSURE SHELL EXTENSION FOR HOUSING AN INTERNAL HEAT EXCHANGER

BACKGROUND

Field

[0001] Embodiments of the present invention relate to a method for revamping vertical converters which have a flanged pressure shell extension for housing an internal heat exchanger by replacing the pressure shell extension with a larger extension capable of housing two or more heat exchangers.

Description of the Related Art

[0002] Most legacy vertical quench converters with axial-flow beds have been modified over the years to a more efficient design with radial (including axial-radial) beds utilizing small, highly active catalyst for increased conversion and reduced pressure drop. Many of these retrofits also revised the process design from a 4-Bed Quench to a 3-Bed Quench-Intercooled design where-in direct quench between beds 2 and 3 is replaced with a more efficient indirect cooling step using a heat exchanger (intercooler). Due to severity of the service, internals for such modified converters are often replaced when a new catalyst charge is installed.

[0003] The competitiveness of the converter revamp market continues to drive the need for more efficient designs. Increasing the efficiency of the fundamental process design typically involves adding more process beds and associated cooling steps and/or replacing direct quench cooling steps with indirect cooling steps. For example, a 3-Bed Quench-Intercooled system can be upgraded to a 3-Bed Intercooled system using indirect cooling between beds 1 and 2 as well as beds 2 and 3. However, since the existing converter has a fixed volume, the improvement in performance from addition of the second intercooler is reduced by the lost catalyst volume taken up by the intercooler. In addition, the ability to add process beds and additional cooling steps is limited by the number of available nozzles on the existing converter pressure shell.

[0004] Legacy quench converters typically include an internal feed/effluent heat exchanger for bringing the main converter feed up to reaction temperature. The F/E exchanger is housed in a pressure shell extension (bonnet) attached via a flanged connection to the top pressure shell head of the main converter body (see Fig. 1 ). During a converter revamp, the F/E exchanger is often replaced with a new design which better fits the new loads, reduces pressure drop, or simply addresses maintenance issues with the existing exchanger. If the F/E exchanger is replaced, the new exchanger is designed to conform with the details and dimensions of the existing bonnet which is reused in the revamped converter. Reuse of the bonnet is a standard part of the converter revamp paradigm which seeks to minimize cost for a new converter system by reusing the old converter pressure shell.

Summary of the Invention

[0005] Briefly in accordance with aspects of the present technique, a method is provided for revamping a vertical converter with an internal heat exchanger housed in a flanged pressure shell extension by replacing the pressure shell extension with a larger extension capable of housing two or more heat exchangers.

Brief Description of the Drawings

[0006] The present invention will be described in detail with references to the accompanying figure wherein;

[0007] FIG. 1 depicts a schematic view of a of legacy vertical converter with 4- bed quench design according to the prior art;

[0008] FIG. 2 is a schematic diagram depicting the ammonia converter basket revamp 3 -bed intercooled design according to aspects of the present invention; [0009] FIG. 3 depicts a schematic view of ammonia converter basket revamp including a bonnet in accordance with aspects of the present invention

[0010] FIG. 4 depicts another embodiment of the ammonia converter basket revamp 3 -bed quench intercooled design, according to the aspects of the invention; and

[0011] FIG. 5 depicts another embodiment of the ammonia converter basket revamp 3-bed quench intercooled design with the bonnet, according to the aspects of the invention

Detailed Description

[0012] Embodiments of the present invention remove the shortcomings of the prior art by replacing the bonnet with a new and larger bonnet of sufficient size to house not only the F/E exchanger but also one or more intercoolers. The bonnet may be increased in length, increased in diameter (with an appropriate neck— down in diameter at the bottom flanged connection), or a combination of the both aspects.

[0013] The new and larger bonnet effectively increases the total volume available for the new converter system minimizing the loss in installed catalyst volume from using one or more intercoolers in the modified process design. In addition, one or more inlet nozzles can be included on the new bonnet allowing the number of process beds and associated cooling steps to be increased.

[0014] A simplified schematic of a previously proposed design for a 3-Bed Intercooled system is shown in Fig. 2. It may be noted that both intercoolers are located in the main converter basket shell.

[0015] The disclosed method has been applied as shown in Fig. 3 wherein the second intercooler has been relocated to the lower part of the bonnet allowing additional catalyst to be installed in the bed previously surrounding this inter cooler.

[0016] A simplified schematic of a 3 -Bed Quench Intercooled system is shown in Fig. 4 wherein the intercooler cooling bed 2 effluent sits in the middle of beds 1 and 2. The disclosed method has been applied as shown in Fig. 5 increasing the catalyst volume in both beds.

[0017] Although the increased bonnet size adds load to the top flanged connection on the main converter shell the entire converter basket and internals including the weight of the loaded catalyst charge already hangs from the top head flange, so a proportionally large increase in bonnet size is easily accommodated within the mechanical design margins on the flange.

[0018] The novel method disclosed according to the present invention has several advantages such as but not limited to Method allows more catalyst to be installed in a legacy quench converter revamp when using one or more intercoolers in the revamped process design providing for increased conversion to support greater energy savings and/or higher capacity.

[0019] The invention includes a method of revamping vertical converters having a bolt-on flanged pressure shell extension for housing an internal heat exchanger. The method comprises replacing an existing pressure shell extension with a larger pressure shell extension for housing a plurality of internal heat exchangers. The larger pressure shell extension may comprise one or more converter inlet nozzles and a converter outlet nozzle. Additionally, the larger pressure shell extension may have a substantially similar diameter as a diameter of an original pressure shell extension and greater length than the original pressure shell extension. Another alternative may include the larger pressure shell extension comprising an upper section of larger diameter than the original pressure shell extension and a lower flanged section of smaller diameter than the upper section to match with the existing main converter pressure shell flange. [0020] The invention also includes an existing feed-effluent exchanger or a replacement feed-effluent exchanger housed in the larger pressure shell extension. An additional alternative variation may also be inclusive of one or more inter-bed heat exchangers used for cooling reactant gases from a catalyst bed are housed in the larger pressure shell extension.

[0021] Various terms have been defined above. To the extent a term used in a claim is not defined above, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent. And if applicable, all patents, test procedures, and other documents cited in this application are fully incorporated by reference to the extent such disclosure is not inconsistent with this application and for all jurisdictions in which such incorporation is permitted.

[0022] While the foregoing is directed to certain illustrative embodiments, other and further embodiments of the invention can be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.