US20120234263A1

US20120234263A1 - Processes and systems for generating steam from multiple hot process streams

Info

Publication number: US20120234263A1
Application number: US13/051,191
Authority: US
Inventors: Mark Van Wees; Jason Lee Stahlman
Original assignee: UOP LLC
Current assignee: Honeywell UOP LLC
Priority date: 2011-03-18
Filing date: 2011-03-18
Publication date: 2012-09-20

Abstract

Embodiments of processes and an apparatus for generating steam are provided. The process comprises the steps of indirectly heating water in a first thermosyphon heat exchanger with a first hot stream to form a first stream of heated water comprising steam. The first stream of heated water is fluidly communicated to a first steam drum via natural circulation. Water is indirectly heated in a second thermosyphon heat exchanger with a second hot stream from the process unit to form a second stream of heated water comprising steam. The second stream of heated water is fluidly communicated to the first steam drum via natural circulation. Steam is recovered from the first steam drum.

Description

FIELD OF THE INVENTION

The present invention relates generally to processes and an apparatus for heat recovery in a process plant, and more particularly relates to processes and an apparatus for generating steam from multiple hot process streams from a process unit.

BACKGROUND OF THE INVENTION

Process plants, such as petroleum refineries, commonly generate steam using hot process streams from a process unit for recovering low value heat from hot process streams. Steam is generated by indirect heat exchange of a hot process stream with water in a kettle steam generator. A kettle steam generator typically comprises a cylindrical shell containing water, and a tube bundle that receives and circulates a single hot process stream inside the tube bundle. Heat is indirectly transferred from the hot process stream in the tube bundle to water in the shell to generate steam. The steam may then be recovered from the kettle steam generator.
Unfortunately, the economics of kettle steam generators often do not justify their installation. The expense of kettle steam generators is due in large part to the quantity of instrumentation required for each kettle steam generator. Piping, pumps, valves, vessels and other auxiliary systems also add cost to the installation. Each kettle steam generator is typically equipped with a boiler feed water inlet, a steam outlet, at least two drainage outlets for removing precipitates, and at least one steam vent for overpressure relief including all of the necessary piping and valving. Additionally, costs multiply for recovering heat from each additional hot process stream. This is because multiple kettle steam generators are often required for carrying multiple hot process streams since each kettle steam generator is typically configured with only one tube bundle that carries a single hot process stream and putting two or more tube bundles into a single kettle steam generator is difficult to package and cumbersome to install.
Accordingly, it is desirable to provide processes and an apparatus for generating steam from multiple hot process streams from a processing unit without the high cost associated with kettle steam generators. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings and this background of the invention.

SUMMARY OF THE INVENTION

Processes and an apparatus for generating steam are provided herein. In accordance with an exemplary embodiment, a process for generating steam comprises the steps of introducing a first hot stream to a first thermosyphon heat exchanger. Water is indirectly heated in the first thermosyphon heat exchanger with the first hot stream to form a first stream of heated water comprising steam. Water is thermosyphoned between a first steam drum and the first thermosyphon heat exchanger including fluidly communicating the first stream of heated water to the first steam drum via natural circulation. A second hot stream is introduced to a second thermosyphon heat exchanger. Water is indirectly heated in the second thermosyphon heat exchanger with the second hot stream to form a second stream of heated water comprising steam. Water is thermosyphoned between the first steam drum and the second thermosyphon heat exchanger including fluidly communicating the second stream of heated water to the first steam drum via natural circulation. Steam is recovered from the first steam drum.
In accordance with another exemplary embodiment, an apparatus for generating steam is provided. The apparatus comprises a first steam drum that is configured for providing water and receiving steam for recovery thereof, and a first thermosyphon heat exchanger. A first thermosyphoning water loop circuit is in fluid communication with the first steam drum and the first thermosyphon heat exchanger. The first thermosyphoning heat exchanger is configured for fluid communication with a first hot process line to receive a first hot stream from a process unit. The first thermosyphon heat exchanger is configured to indirectly heat water with the first hot stream to form a first stream of heated water comprising steam. The first thermosyphoning water loop circuit is cooperatively configured with the first thermosyphon heat exchanger for thermosyphoning water between the first steam drum and the first thermosyphon heat exchanger including fluidly communicating the first stream of heated water to the first stream drum via natural circulation. A second thermosyphon heat exchanger, and a second thermosyphoning water loop circuit that is in fluid communication with the first steam drum and the second thermosyphon heat exchanger. The second thermosyphoning heat exchanger is configured for fluid communication with a second hot process line to receive a second hot stream from the process unit. The second thermosyphon heat exchanger is configured to indirectly heat water with the second hot stream to form a second stream of heated water comprising steam. The second thermosyphoning water loop circuit is cooperatively configured with the second thermosyphon heat exchanger for thermosyphoning water between the first steam drum and the second thermosyphon heat exchanger including fluidly communicating the second stream of heated water to the first stream drum via natural circulation.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:

FIG. 1 schematically illustrates a system for generating steam in accordance with an exemplary embodiment; and

FIG. 2 schematically illustrates a lower portion of a thermosyphoning water loop circuit for generating steam in accordance with an exemplary embodiment.

DETAILED DESCRIPTION

The following Detailed Description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding Background of the Invention or the following Detailed Description.
Various embodiments contemplated herein relate to processes and an apparatus for generating steam from multiple hot process streams from a process unit. Each hot process stream is indirectly heat exchanged with a corresponding thermosyphoning water loop circuit that is in fluid communication with a steam drum. “Thermosyphoning” is herein understood to be a method of passive heat exchange based on natural circulation (e.g. natural convection) that circulates liquid in a fluid loop circuit without the use of mechanical pumps, and preferably without the use of valves (e.g. an open fluid loop circuit). Convective movement of the liquid starts when the liquid in the fluid loop circuit is heated, causing the liquid to expand (e.g. partial vaporization of the liquid) and become less dense, and thus more buoyant than the cooler liquid in the bottom of the fluid loop circuit. Convection moves the heated liquid upwards in the fluid loop circuit as the heated liquid is simultaneously replaced by the cooler liquid moving via gravity. Preferably, very little hydraulic resistance or pressure drop occurs across the fluid loop circuit to facilitate natural circulation of the liquid throughout the fluid loop circuit.
In particular, the thermosyphoning water loop circuits each include a thermosyphon heat exchanger that is external to the steam drum. Each of the thermosyphoning water loop circuits and the corresponding thermosyphon heat exchangers are cooperatively configured to thermosyphon (e.g. move via natural circulation) water from the steam drum to the thermosyphon heat exchanger that indirectly heats the water with the hot process stream to form heated water comprising steam. The heated water is passed back to the steam drum via natural circulation. Multiple thermosyphoning water loop circuits are preferably arranged separate from each other for indirect heat exchange with multiple hot process streams to feed a single steam drum to provide a steam product. Only one set of instrumentation is needed for the single steam drum and the thermosyphoning water loop circuits do not require the use of pumps and valves for moving water between the steam drum and the thermosyphon heat exchangers. Thus, steam is generated from multiple hot process streams from a processing unit without the high cost associated with multiple sets of instrumentation and other auxiliary components and systems, such as, for example, pumps and valves.
Referring to FIG. 1, a schematic depiction of a system 10 for generating steam in accordance with an exemplary embodiment is provided. The system 10 comprises a process unit 12. The process unit 12 may be a hydrocracking fractionation column for separating products in an effluent from a hydrocracking reactor, or any other process unit 12 that generates multiple hot streams suitable for generating steam. As illustrated, a hydrocracking effluent is fed to the process unit 12 via line 14. Side cut streams 16, 18, and 20 are stripped in corresponding stripper vessels 22, 24, and 26 to produce side hot product streams 28, 30, and 32, respectively, while a portion of each of the side cut streams 16, 18, and 20 is returned to the process unit 12. A bottom product 34 is removed from the bottom of the process unit 12. A portion of the bottom product 34 is reboiled in a reboiler 36 and return to the process unit 12, and the remaining portion of the bottom product 34 is passed along as a bottom hot product stream 38. An overhead stream 40 is removed from the top of the process unit 12 and condensed in a cooler 42 by heat exchange. A portion of the overhead stream 40 is recovered via line 44 and the remaining portion is returned to the process unit 12 via line 46.
As illustrated, the system 10 comprises first and second steam drums 48 and 50. The system 10, however, is not limited to two stream drums, and may alternatively have a single steam drum or more than two steam drums. The steam drums 48 and 50 each contain water 64 in the liquid phase. Referring also to FIG. 2, the first steam drum 48 is in fluid communication with a plurality of thermosyphoning water loop circuits 66, 68, 70, and 72. While four thermosyphoning water loop circuits are shown, it will be appreciated that less than four or more than four can be used. Preferably, the thermosyphoning water loop circuits 66, 68, 70, and 72 are each directly connected to the first steam drum 48 and are separate from each other such that each of the thermosyphoning water loop circuits 66, 68, 70, and 72 functions independently from the other thermosyphoning water loop circuits 66, 68, 70, and 72 using natural circulation without the use of pumps, shared piping, and/or valving. Alternatively, two or more of the thermosyphoning water loop circuits 66, 68, 70, and 72 may be in fluid communication with each other via a common feed header and/or common return line.
The thermosyphoning water loop circuits 66, 68, 70, and 72 have corresponding thermosyphon heat exchangers 74, 76, 78, and 80. Water 64 is passed from the first steam drum 48 to the thermosyphon heat exchangers 74, 76, 78, and 80 along drum outlet lines 71, 73, 75, and 77, and is heated and passed from the thermosyphon heat exchangers 74, 76, 78, and 80 back to the first steam drum 48 along heated water inlet lines 79, 81, 83, and 85. In an exemplary embodiment, the heat exchangers 74, 76, 78, and 80 are arranged underneath the first steam drum 48 just above the bottom of their respective thermosyphoning water loop circuit 66, 68, 70, and 72 to facilitate thermosyphoning or natural circulation of water 64 from the first steam drum 48 to the thermosyphon heat exchangers 74, 76, 78, and 80 via gravity.
Each of the thermosyphon heat exchangers 74, 76, 78, and 80 comprises a corresponding shell portion 82, 84, 86, and 88, and a corresponding tube portion 87, 89, 91, and 93. The tube portions 87, 89, 91, and 93 are configured in the corresponding shell portions 82, 84, 86, and 88 for indirect heat exchange with the shell portions 82, 84, 86, and 88. In an exemplary embodiment, the thermosyphoning water loop circuits 66, 68, 70, and 72 are in fluid communication with the shell portions 82, 84, 86, and 88, which have significantly larger flow areas than the tube portions 87, 89, 91, and 93, to preferably minimize or reduce the pressure drop of the thermosyphoning water loop circuits 66, 68, 70, and 72 across the thermosyphon heat exchangers 74, 76, 78, and 80.
The tube portions 87, 89, 91, and 93 are in fluid communication with the hot product streams 38, 32, 30, and 28, respectively. The tube portions 87, 89, 91, and 93 receive the corresponding hot product streams 38, 32, 30, and 28 and transfer heat from the hot product streams 38, 32, 30, and 28 to water 64 in the corresponding shell portions 82, 84, 86, and 88, producing heated water comprising steam and heated liquid water, and cooling the hot product streams 38, 32, 30, and 28 to produce cooled hot streams 90, 92, 94, and 96.
In an exemplary embodiment, the heated water generated in the thermosyphon heat exchangers 74, 76, 78, and 80 comprises steam at a temperature of about 175 to about 195° C. In another exemplary embodiment, about 1/10 to about 1/20, and more preferably about 1/15, by weight of the liquid water being fed to the thermosyphon heat exchangers 74, 76, 78, and 80 is converted to steam. In yet another exemplary embodiment, the cooled hot streams 90, 92, 94, and 96 are cooled to a temperature of about 190 to about 210° C.
As illustrated, the heated water including the steam is passed from the thermosyphon heat exchangers 74, 76, 78, and 82 to the first steam drum 48 along heated water inlet lines 79, 81, 83, and 85 via natural circulation. The heated water inlet lines 79, 81, 83, and 85 fluidly communicate with corresponding distributors 98, 99, 100, and 101 that terminate in the first steam drum 48. The distributors 98, 99, 100, and 101 direct the incoming heated liquid water and steam against a surface in the first steam drum 48 to facilitate separation of the steam from the heated liquid water that drains towards the bottom of the first steam drum 48.
The first steam drum 48 has an optional control valve 52 set for emitting steam through a steam outlet line 54 from a steam outlet 56 for recovery of the steam. A steam separator 53 is interposed between an interior volume of the first steam drum 48 and the steam outlet 56 to prevent liquid droplets from exiting with the steam. In an exemplary embodiment, the control valve 52 is set for emitting steam through the steam outlet line 54 at a relatively medium pressure of about 1300 kPa (gauge) or less, and more preferably of about 790 to about 1300 kPa (gauge). In another exemplary embodiment, the steam is emitted through the steam outlet line 54 at a temperature of about 175 to about 195° C.
The liquid water level in the first stream drum 48 may be monitored by a level indicator controller 55. The steam flow rate out of the first steam drum 48 through the steam outlet 56 and the water flow rate into the first steam drum 48 through a feed water line 57 may be monitored by a flow indicator. Based on the steam and water flow rates, a control valve 59 may regulate the flow rate of water into the first steam drum 48 through the feed water line 57.
In an exemplary embodiment, the second steam drum 50 is configured similar to the first steam drum 48. As illustrated, the second steam drum 50 is in fluid communication with a plurality of thermosyphoning water loop circuits 166, 168, 170, and 172. Preferably, the thermosyphoning water loop circuits 166, 168, 170, and 172 are directly connected to the second steam drum 50 and are each separate from each other such that each of the thermosyphoning water loop circuits 166, 168, 170, and 172 functions independently from the other thermosyphoning water loop circuits 166, 168, 170, and 172 using natural circulation without the use of pumps, shared piping, and/or valving. Alternatively, two or more of the thermosyphoning water loop circuits 166, 168, 170, and 172 may be in fluid communication with each other via a common feed header and/or common return line.
The thermosyphoning water loop circuits 166, 168, 170, and 172 have corresponding thermosyphon heat exchangers 180, 178, 176, and 174. Water 64 is passed from the second steam drum 50 to the thermosyphon heat exchangers 174, 176, 178, and 180 along drum outlet lines 171, 173, 175, and 177, respectively, and is heated and passed from the thermosyphon heat exchangers 174, 176, 178, and 180 back to the second steam drum 50 along heated water inlet lines 179, 181, 183, and 185, respectively. In an exemplary embodiment, the heat exchangers 174, 176, 178, and 180 are arranged underneath the second steam drum 50 just above the bottom of their respective thermosyphoning water loop circuit 172, 170, 168, and 166 to facilitate thermosyphoning or natural circulation of water 64 from the second steam drum 50 to the thermosyphon heat exchangers 174, 176, 178, and 180 via gravity.
Each of the thermosyphon heat exchangers 174, 176, 178, and 180 comprises a corresponding shell portion 182, 184, 186, and 188, and a corresponding tube portion 187, 189, 191, and 193. The tube portions 187, 189, 191, and 193 are configured in the corresponding shell portions 182, 184, 186, and 188 for indirect heat exchange with the shell portions 182, 184, 186, and 188. In an exemplary embodiment, the thermosyphoning water loop circuits 172, 170, 168, and 166 are in fluid communication with the shell portions 182, 184, 186, and 188, which have significantly larger flow areas than the tube portions 187, 189, 191, and 193, to preferably minimize or reduce the pressure drop of the thermosyphoning water loop circuits 172, 170, 168, and 166 across the thermosyphon heat exchangers 174, 176, 178, and 180.
The tube portions 187, 189, 191, and 193 are in fluid communication with the thermosyphon heat exchangers 74, 76, 78, and 84 of the first steam drum 48 to receive the cooled hot streams 90, 92, 94, and 96, respectively. The tube portions 187, 189, 191, and 193 receive the corresponding cooled hot streams 90, 92, 94, and 96 and transfer heat from the corresponding cooled hot streams 90, 92, 94, and 96 to water 64 in the corresponding shell portions 182, 184, 186, and 188, producing heated water comprising steam and heated liquid water, and cooling the cooled hot streams 90, 92, 94, and 96 to produce twice cooled hot streams 190, 192, 194, and 196. The twice cooled hot streams 190, 192, 194, and 196 may be passed along for subsequent processing and the like, or to a third steam drum arrangement for generating more steam.
In an exemplary embodiment, the heated water generated in the thermosyphon heat exchangers 174, 176, 178, and 180 comprises steam at a temperature of about 140 to about 160° C. In another exemplary embodiment, about 1/10 to about 1/20, and more preferably about 1/15, by weight of the liquid water being fed to the thermosyphon heat exchangers 174, 176, 178, and 180 is converted to steam. In yet another exemplary embodiment, the twice cooled hot streams 190, 192, 194, and 196 are cooled to a temperature of about 155 to about 175° C.
As illustrated, the heated water including the steam is passed from the thermosyphon heat exchangers 174, 176, 178, and 182 to the second steam drum 50 along heated water inlet lines 179, 181, 183, and 185 via natural circulation. The heated water inlet lines 179, 181, 183, and 185 fluidly communicate with corresponding distributors 198, 199, 200, and 201 that terminate in the second steam drum 50. The distributors 198, 199, 200, and 201 direct the incoming heated liquid water and steam against a surface in the second steam drum 50 to facilitate separation of the steam from the heated liquid water that drains towards the bottom of the second steam drum 50.
The second steam drum 50 has an optional control valve 152 set for emitting steam through a steam outlet line 154 from a steam outlet 156 for recovery of the steam. A steam separator 153 is interposed between an interior volume of the second steam drum 50 and the steam outlet 156 to prevent liquid droplets from exiting with the steam. In an exemplary embodiment, the control valve 152 is set for emitting steam through the steam outlet line 154 at a relatively low pressure of about 520 kPa (gauge) or less, and more preferably of about 260 to about 520 kPa (gauge). In another exemplary embodiment, the steam is emitted through the steam outlet line 154 at a temperature of about 140 to about 160° C.
The liquid water level in the second stream drum 50 may be monitored by a level indicator controller 155. The steam flow rate out of the second steam drum 50 through the steam outlet 156 and the water flow rate into the second steam drum 50 through a feed water line 157 may be monitored by a flow indicator. Based on the steam and water flow rates, a control valve 159 may regulate the flow rate of water into the second steam drum 50 through the feed water line 157.
Accordingly, processes and an apparatus for generating steam from multiple hot process streams from a process unit have been described. The various embodiments comprise indirectly heat exchanging each hot process stream with a corresponding thermosyphoning water loop circuit that is in fluid communication with a steam drum. The thermosyphoning water loop circuits each include a thermosyphon heat exchanger that is external to the steam drum. Each of the thermosyphoning water loop circuits and the corresponding thermosyphon heat exchangers are cooperatively configured to thermosyphon water from the steam drum to the corresponding thermosyphon heat exchanger that indirectly heats the water with the hot process stream to form heated water comprising steam. The heated water is passed back to the steam drum via natural circulation. Multiple thermosyphoning water loop circuits are arranged separate from each other for indirect heat exchange with multiple hot process streams to feed a single steam drum to provide a steam product. Only one set of instrumentation is needed for the single steam drum and the thermosyphoning water loop circuits do not require the use of pumps and valves for moving water between the steam drum and the thermosyphon heat exchangers. Thus, steam is generated from multiple hot process streams from a processing unit without the high cost associated with multiple sets of instrumentation and other auxiliary components and systems, such as, for example, pumps and valves.
While at least one exemplary embodiment has been presented in the foregoing Detailed Description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing Detailed Description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended Claims and their legal equivalents.

Claims

1. A process for generating steam comprising the steps of:

introducing a first hot stream to a first thermosyphon heat exchanger;

indirectly heating water in the first thermosyphon heat exchanger with the first hot stream to form a first stream of heated water comprising steam;

thermosyphoning water between a first steam drum and the first thermosyphon heat exchanger including fluidly communicating the first stream of heated water to the first steam drum via natural circulation;

introducing a second hot stream to a second thermosyphon heat exchanger;

indirectly heating water in the second thermosyphon heat exchanger with the second hot stream to form a second stream of heated water comprising steam;

thermosyphoning water between the first steam drum and the second thermosyphon heat exchanger including fluidly communicating the second stream of heated water to the first steam drum via natural circulation; and

recovering steam from the first steam drum.

2. The process according to claim 1, wherein the step of indirectly heating water in the first thermosyphon heat exchanger includes indirectly heating water with the first hot stream to form the first stream of heated water comprising steam that is at a temperature of about 175 to about 195° C., and the step of indirectly heating water in the second thermosyphon heat exchanger includes indirectly heating water with the second hot stream to form the second stream of heated water comprising steam at a temperature of about 175 to about 195° C.

3. The process according to claim 1, wherein the step of indirectly heating water in the first thermosyphon heat exchanger includes indirectly heating water with the first hot stream to form the first stream of heated water comprising steam that is at a pressure of about 790 to about 1300 kPa gauge.

4. The process according to claim 1, wherein the step of indirectly heating water in the first thermosyphon heat exchanger includes indirectly heating a first stream of liquid water with the first hot stream to form the first stream of heated water comprising steam such that from about 1/10 to about 1/20 by weight of the first stream of liquid water is converted to steam, and wherein the step of indirectly heating water in the second thermosyphon heat exchanger includes indirectly heating a second stream of liquid water with the second hot stream to form the second stream of heated water comprising steam such that from about 1/10 to about 1/20 by weight of the second stream of liquid water is converted to steam.

5. The process according to claim 1, wherein the first thermosyphon heat exchanger comprises a first shell portion and a first tube portion that is configured in the first shell portion for thermal exchange with the first shell portion, and wherein the step of introducing the first hot stream includes introducing the first hot stream to the first tube portion, and the step of indirectly heating water in the first thermosyphon heat exchanger includes fluidly communicating water through the first shell portion and fluidly communicating the first hot stream through the first tube portion to indirectly heat water and form the first stream of heated water.

6. The process according to claim 5, wherein the second thermosyphon heat exchanger comprises a second shell portion and a second tube portion that is configured in the second shell portion for thermal exchange with the second shell portion, and wherein the step of introducing the second hot stream includes introducing the second hot stream to the second tube portion, and the step of indirectly heating water and the second thermosyphon heat exchanger includes fluidly communicating water through the second shell portion and fluidly communicating the second hot stream through the second tube portion to indirectly heat water and form the second stream of heated water.

7. The process according to claim 1, wherein the step of thermosyphoning water between the first steam drum and the first thermosyphon heat exchanger includes fluidly communicating a first liquid water stream from the first steam drum to the first thermosyphon heat exchanger through a first drum water outlet line and fluidly communicating the first stream of heated water from the first thermosyphon heat exchanger to the first steam drum through a first heated water inlet line, and the step of thermosyphoning water between the first steam drum and the second thermosyphon heat exchanger includes fluidly communicating a second liquid water stream from the first steam drum to the second thermosyphon heat exchanger through a second drum water outlet line and fluidly communicating the second stream of heated water from the second thermosyphon heat exchanger to the first steam drum through a second heated water inlet line, and wherein each of the first and second drum water outlet lines and the first and second heated water inlet lines are separately and directly connected to the first steam drum.

8. The process according to claim 1, wherein the step of indirectly heating water in the first thermosyphon heat exchanger includes indirectly heating water with the first hot stream to form a first cooled hot stream, and the step of indirectly heating water in the second thermosyphon heat exchanger includes indirectly heating water with the second hot stream to form a second cooled hot stream, and wherein the process further comprises the steps of:

introducing the first cooled hot stream to a third thermosyphon heat exchanger;

indirectly heating water in the third thermosyphon heat exchanger with the first cooled hot stream to form a third stream of heated water comprising steam;

thermosyphoning water between a second steam drum and the third thermosyphon heat exchanger including fluidly communicating the third stream of heated water to the second steam drum via natural circulation;

introducing the second cooled hot stream to a fourth thermosyphon heat exchanger;

indirectly heating water in the fourth thermosyphon heat exchanger with the second cooled hot stream to form a fourth stream of heated water comprising steam;

thermosyphoning water between the second steam drum and the fourth thermosyphon heat exchanger including fluidly communicating the fourth stream of heated water to the second steam drum via natural circulation; and

recovering steam from the second steam drum.

9. The process according to claim 8, wherein the step of indirectly heating water in the third thermosyphon heat exchanger includes indirectly heating water with the first cooled hot stream to form the third stream of heated water comprising steam at a temperature of about 140 to about 160° C., and the step of indirectly heating water in the fourth thermosyphon heat exchanger includes indirectly heating water with the second cooled hot stream to form the fourth stream of heated water comprising steam at a temperature of about 140 to about 160° C.

10. The process according to claim 8, wherein the third thermosyphon heat exchanger comprises a third shell portion and a third tube portion that is configured in the third shell portion for thermal exchange with the third shell portion, and wherein the step of introducing the first cooled hot stream includes introducing the first cooled hot stream to the third tube portion, and the step of indirectly heating water in the third thermosyphon heat exchanger includes fluidly communicating water through the third shell portion and fluidly communicating the first cooled hot stream through the third tube portion to indirectly heat water and form the third stream of heated water.

11. The process according to claim 10, wherein the fourth thermosyphon heat exchanger comprises a fourth shell portion and a fourth tube portion that is configured in the fourth shell portion for thermal exchange with the fourth shell portion, and wherein the step of introducing the second cooled hot stream includes introducing the second cooled hot stream to the fourth tube portion, and the step of indirectly heating water in the fourth thermosyphon heat exchanger includes fluidly communicating water through the fourth shell portion and fluidly communicating the second cooled hot stream through the fourth tube portion to indirectly heat water and form the fourth stream of heated water.

12. The process according to claim 8, wherein the step of thermosyphoning water between the second steam drum and the third thermosyphon heat exchanger includes fluidly communicating a third liquid water stream from the second steam drum to the third thermosyphon heat exchanger through a third drum water outlet line and fluidly communicating the third stream of heated water from the third thermosyphon heat exchanger to the second steam drum through a third heated water inlet line, and the step of thermosyphoning water between the second steam drum and the fourth thermosyphon heat exchanger includes fluidly communicating a fourth liquid water stream from the second steam drum to the fourth thermosyphon heat exchanger through a fourth drum water outlet line and fluidly communicating the fourth stream of heated water from the fourth thermosyphon heat exchanger to the second steam drum through a fourth heated water inlet line, and wherein each of the third and fourth drum water outlet lines and the third and fourth heated water inlet lines are separately and directly connected to the second steam drum.

13. An apparatus for generating steam, the apparatus comprising:

a first steam drum configured for providing water and receiving steam for recovery thereof;

a first thermosyphon heat exchanger;

a first thermosyphoning water loop circuit that is in fluid communication with the first steam drum and the first thermosyphon heat exchanger, wherein the first thermosyphoning heat exchanger is configured for fluid communication with a first hot process line to receive a first hot stream from a process unit, and wherein the first thermosyphon heat exchanger is configured to indirectly heat water with the first hot stream to form a first stream of heated water comprising steam, and the first thermosyphoning water loop circuit is cooperatively configured with the first thermosyphon heat exchanger for thermosyphoning water between the first steam drum and the first thermosyphon heat exchanger including fluidly communicating the first stream of heated water to the first stream drum via natural circulation;

a second thermosyphon heat exchanger;

a second thermosyphoning water loop circuit that is in fluid communication with the first steam drum and the second thermosyphon heat exchanger, wherein the second thermosyphoning heat exchanger is configured for fluid communication with a second hot process line to receive a second hot stream from the process unit, and wherein the second thermosyphon heat exchanger is configured to indirectly heat water with the second hot stream to form a second stream of heated water comprising steam, and the second thermosyphoning water loop circuit is cooperatively configured with the second thermosyphon heat exchanger for thermosyphoning water between the first steam drum and the second thermosyphon heat exchanger including fluidly communicating the second stream of heated water to the first stream drum via natural circulation.

14. The apparatus according to claim 13, wherein the first and second thermosyphon heat exchangers are disposed underneath the first steam drum to facilitate thermosyphoning of water between the first steam drum and the first and second thermosyphon heat exchangers.

15. The apparatus according to claim 13, wherein the first thermosyphoning water loop circuit comprises a first drum outlet line and a first heated water inlet line, the first drum outlet line and the first heated water inlet line configured to fluidly communicate water from the first steam drum to the first thermosyphon heat exchanger and to fluidly communicate the first stream of heated water from the first thermosyphon heat exchanger to the first steam drum, respectively, and the second thermosyphoning water loop circuit comprises a second drum outlet line and a second heated water inlet line, the second drum outlet line and the second heated water inlet line configured to fluidly communicate water from the first steam drum to the second thermosyphon heat exchanger and to fluidly communicate the second stream of heated water from the second thermosyphon heat exchanger to the first steam drum, respectively, and wherein each of the first and second drum water outlet lines and the first and second heated water inlet lines are separately and directly connected to the first steam drum.

16. The apparatus according to claim 13, wherein the first thermosyphon heat exchanger comprises a first shell portion that is in fluid communication with the first thermosyphoning water loop circuit, and a first tube portion that is in fluid communication with the first hot process line and is configured in the first shell portion for thermal exchange with the first shell portion, and wherein the second thermosyphon heat exchanger comprises a second shell portion that is in fluid communication with the second thermosyphoning water loop circuit, and a second tube portion that is in fluid communication with the second hot process line and is configured in the second shell portion for thermal exchange with the second shell portion.

17. The apparatus according to claim 13, further comprising:

a second steam drum configured for providing water and receiving steam for recovery thereof;

a third thermosyphon heat exchanger;

a third thermosyphoning water loop circuit that is in fluid communication with the second steam drum and the third thermosyphon heat exchanger;

a first cooled hot stream line in fluid communication with the first and third thermosyphon heat exchangers to advance a first cooled hot stream from the first thermosyphon heat exchanger to the third thermosyphon heat exchanger, wherein the third thermosyphon heat exchanger is configured to indirectly heat water with the first cooled hot stream to form a third stream of heated water comprising steam, and the third thermosyphoning water loop circuit is cooperatively configured with the third thermosyphon heat exchanger for thermosyphoning water between the second steam drum and the third thermosyphon heat exchanger including fluidly communicating the third stream of heated water to the second stream drum via natural circulation;

a fourth thermosyphon heat exchanger;

a fourth thermosyphoning water loop circuit that is in fluid communication with the second steam drum and the fourth thermosyphon heat exchanger;

a second cooled hot stream line in fluid communication with the second and fourth thermosyphon heat exchangers to advance a second cooled hot stream from the second thermosyphon heat exchanger to the fourth thermosyphon heat exchanger, wherein the fourth thermosyphon heat exchanger is configured to indirectly heat water with the second cooled hot stream to form a fourth stream of heated water comprising steam, and the fourth thermosyphoning water loop circuit is cooperatively configured with the fourth thermosyphon heat exchanger for thermosyphoning water between the second steam drum and the fourth thermosyphon heat exchanger including fluidly communicating the fourth stream of heated water to the second stream drum via natural circulation.

18. The apparatus according to claim 17, wherein the third and fourth thermosyphon heat exchangers are disposed underneath the second steam drum to facilitate thermosyphoning of water between the second steam drum and the third and fourth thermosyphon heat exchangers.

19. The apparatus according to claim 17, wherein the third thermosyphoning water loop circuit comprises a third drum outlet line and a third heated water inlet line, the third drum outlet line and the third heated water inlet line configured to fluidly communicate water from the second steam drum to the third thermosyphon heat exchanger and to fluidly communicate the third stream of heated water from the third thermosyphon heat exchanger to the second steam drum, respectively, and the fourth thermosyphoning water loop circuit comprises a fourth drum outlet line and a fourth heated water inlet line, the fourth drum outlet line and the fourth heated water inlet line configured to fluidly communicate water from the second steam drum to the fourth thermosyphon heat exchanger and to fluidly communicate the fourth stream of heated water from the fourth thermosyphon heat exchanger to the second steam drum, respectively, and wherein each of the third and fourth drum water outlet lines and the third and fourth heated water inlet lines are separately and directly connected to the second steam drum.

20. The apparatus according to claim 17, wherein the third thermosyphon heat exchanger comprises a third shell portion that is in fluid communication with the third thermosyphoning water loop circuit, and a third tube portion that is in fluid communication with the first cooled hot stream line and is configured in the third shell portion for thermal exchange with the third shell portion, and wherein the fourth thermosyphon heat exchanger comprises a fourth shell portion that is in fluid communication with the fourth thermosyphoning water loop circuit, and a fourth tube portion that is in fluid communication with the second cooled hot stream line and is configured in the fourth shell portion for thermal exchange with the fourth shell portion.