APPARATUS AND PROCESS FOR PRODUCING A SUPERHEATED STEAM

Description

FIELD

The field is related to an apparatus and a process for producing a steam stream. Particularly, the field relates to an apparatus and a process for producing a superheated steam stream.

BACKGROUND

The organic chemical hydride process for hydrogenating aromatic compounds such as toluene has recently been developed for the purposes of storing and transporting hydrogen in the form of organic hydrides. In this process, hydrogen is converted into an organic hydride at the site of hydrogen production and transported in the form of the organic hydride. The organic hydride is separated into hydrogen and the aromatic compound at a plant or a hydrogen station located near a city or other user of hydrogen by dehydrogenating the organic hydride. The aromatic compound produced from this dehydrogenation process is transported back to the production site of hydrogen to be hydrogenated by hydrogen once again.

The dehydrogenation reaction that is used for producing hydrogen from an organic hydride in the organic chemical hydride process is an endothermic reaction. A large amount of heat is required to generate hydrogen from methylcyclohexane. The reaction heat required for this dehydrogenation reaction may be typically obtained from the combustion of fossil fuel. A significant amount of heat can be wasted in the process.

Steam is one of the prominent components in refinery operations. Steam can be used as a heat source for heating various process streams. Steam can also be used as a heat carrier for transferring heat from various process streams to be used elsewhere. Further, the steam generated from these processes may have limitations which may affect its utility in downstream operations. Such limitations include insufficient steam temperature, low flow rate or intermittent supply. These limitations may affect the utility and supply of the steam for downstream operations.

To balance out such limitations, steam supply may be augmented by feeding steam to boilers. However, this exercise may be costly or lead to energy loss to fuel the boilers to maintain their operation at some minimum steam rate even when steam demand is down.

Therefore, there is a need for a solution to provide steam for peak demand.

SUMMARY

An apparatus and a process for producing a superheated steam stream is disclosed. The apparatus comprises a primary heater comprising a radiant section and a convection section. The primary heater comprises a convective heat transfer conduit in communication with a source of water and passing through the convection section to provide a steam stream. The apparatus further comprises a secondary heater. The secondary heater comprises a radiant section and a secondary heat transfer conduit in communication with the convective heat transfer conduit of the primary heater. The secondary heat transfer conduit passes through the radiant section of the secondary heater to provide a superheated steam stream. The apparatus of the present disclosure may be used to provide primary heating of a process fluid and produce the steam from the excess heat which may result from the primary heating of the process fluid. The steam is further heated in the secondary heater during fluctuation of heat duty of the primary heater. The secondary heater is integrated with the primary heater to produce a superheated steam or increase the degree of superheat of a superheated steam. Thus, the apparatus may reduce heat loss and provide superheated steam to meet the steam demand in a downstream unit. Further, a process for producing superheated steam is disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic diagram of an apparatus and a process for producing a superheated steam in accordance with an embodiment of the present disclosure.

FIG. 2 illustrates a schematic diagram of an apparatus and a process for producing a superheated steam in accordance with another embodiment of the present disclosure

DETAILED DESCRIPTION

The present disclosure provides an apparatus and a process for producing a superheated steam stream. In some processes the steam generation is integrated as a secondary service there during a normal operation to heat up a process fluid and recover the rest of the heat to produce steam. However, at times the unit capacity is modulated. Then, the process must be operated at a lower feed or in some instances the heater duty is turned down for the primary heating of the process fluid. In these scenarios, steam generation is reduced. For the turned down heater duty, the flow rate and the temperature of the steam produced is decreased and the steam may not be suitably used for a downstream supply as it may not meet the steam specifications required for the supply. This may pose challenges for downstream consumers of steam.

The present disclosure provides an apparatus and a process with heat integration for producing a superheated steam stream. The present disclosure provides a dedicated steam heater integrated with a primary heater to further heat and provide additional steam that meets the temperature and flow rate requirements. Though at a lower flow rate, the steam generated in the primary heater may be routed to the steam heater wherein the degree of superheat of steam will be increased. The superheated steam produced from the steam heater may be mixed with a water stream which increases the quantity of steam produced. This way, steam quantity required for the unit while the primary service duty is modulated can be maintained.

Referring to the FIG. 1, an apparatus and a process 101 is disclosed for producing a superheated steam stream. The apparatus 101 comprises a primary heater 103 and a secondary heater 130 for producing the superheated steam stream. In an exemplary embodiment, the primary heater 103 is a fired heater.

Fired heaters are common process units in chemical plants and refineries which heat process streams to reaction temperatures. The fired heaters have a radiant section having one or more burners configured to combust fuel to provide heat to process fluid in radiant tubes extending through the radiant section. The process streams may be heated to supply heat for promoting endothermic reactions of hydrocarbons in the process fluid.

A convection section of the fired heater is located adjacent to the radiant section, usually above, and receives hot flue gases from the radiant section. The convection section is typically used for steam generation in a way to improve overall heater efficiency by transferring heat to water or other fluids in convection tubes extending through the convection section. The heat input of the heaters in the radiant section is necessary to provide process heating.

In an embodiment, the fired heater 103 comprises a radiant section 110, a convection section 120, and a stack 125. As shown in FIG. 1, a process fluid stream in line 102 may be primarily heated in the radiant section 110. While the process fluid stream in line 102 is not necessarily limited to a particular desired reaction, the apparatus 101 is particularly advantageous for heating process fluid for reforming, dehydrogenation, isomerization, disproportionation, transalkylation, and dehydration reactions. Dehydration reactions involve conversion of alcohols to hydrocarbon fuels. The process fluid stream in line 102 may be passed to the radiant section 110 through an inlet 11 in the wall of the radiant section 110.

The radiant section may include one or more burners 114 which receive oxygen and a fuel, such as fuel gas and/or fuel oil, ignite the combustion of the fuel, and produce heat and flue gas (as well as a flame). The heat in the radiant section is used to heat the process fluid stream in line 102. The process fluid stream may be contained in one or more radiant heat transfer conduits 116 passing through the radiant section 110. As shown in the FIG. 1, one radiant heat transfer conduit 116 is shown for simplicity but, there may be a plurality of radiant heat transfer conduit 116 in the radiant section 110. The radiant heat transfer conduit 116 is typically a tube or coil in which the process fluid is contained and moves from the inlet to the outlet.

The radiant section 110 may comprise a horizontal or a vertical radiant heat transfer conduit 116. The radiant heat transfer conduit 116 is located along the walls in the radiant section 110 and receive radiant heat direct from the burners 114. The radiant section 110 comprises refractory lining. This is also called the firebox.

The radiant section 110 may comprise a first radiant manifold 111 and a second radiant manifold 112 both in communication with the radiant heat transfer conduit 116. The process fluid stream in line 102 may be passed to the radiant section 110, through the first radiant manifold 111 and into the radiant heat transfer conduit 116 and other radiant heat transfer conduits not visible in the FIG. 1 behind conduit 116. In the radiant section 110, the process fluid stream is heated and delivered to the second radiant manifold 112. A heated process fluid is delivered from the second radiant manifold 112 and discharged through an outlet 21 of the radiant section 110.

The burners 114 may be selected from duct burners and the surface burners. Duct burners are usually used in combined cycle and they can work either with fresh air or exhaust gas. Duct burners are generally provided in several rows depending of the thermal power required and the general duct arrangement. Duct burners typically attempt to achieve uniform heat generation by attempting to improve the uniformity of airflow across the duct burner, and by including multiple fuel runners across the duct. Surface burners may be free convection burners which provide oxygen-containing gas such as air through a passageway that directs air in proximity to injected fuel gas to generate a flame. Although the duct burners and the surface burners are designed for fuel gas, both duct and surface burners that can burn liquid fuel are contemplated as well. Supply of the fuel gas to the burners 114 may be regulated based on the exit temperature of the heated process fluid exiting the radiant section 110 and the firing rate may be determined by the level of heat transfer or the temperature of the heated process fluid desired.

In an exemplary embodiment, the burners 114 may be surface burners located at the bottom of the radiant section 110. Although two burners 114 are shown, there may be more or less than two burners in the radiant section 110. Further, there are typically one or more burners located on the wall of the radiant section 110 in the FIG. 1 not visible behind the burners 114.

In an aspect, the radiant heat transfer conduit 116 may comprise a multi-pass coil conduit which include bends or turns to increases the residence time of the process fluid within the radiant section 110. For example, the multi-pass coil conduit may be a U coil, arbor coil, I, Double I, W coil, twin U, serpentine, helical or other such configurations.

Typically, a large amount of heat is produced in the radiant section 110 through the burners 114. The amount of heat generated may exceed the heat needed to generate steam. The convection section 120 provides a recovery of the excess heat from the radiant section 110 which may otherwise be lost. The convection section 120 may be disposed adjacent to the radiant section 110, so that the hot flue gas from the radiant section 110 is received in the convection section 120. For example, the convection section 120 may be above or laterally beside the radiant section 110.

Although not shown, the radiant section 110 may be tapered at the top. The radiant section 110 may have sloped roof section which defines a transition section between the radiant section 110 and the convection section 120. The radiant section 110 may comprise a roof section having inwardly sloping walls.

In accordance with the present disclosure, the convection section 120 may comprise one or more convective heat transfer conduits 124. It is contemplated that a plurality of parallel convection conduits 124 may be utilized. Alternatively, another suitable configuration of the convective heat transfer conduit 124 may be used. In order to reduce any pressure drop, the convection conduit(s) 124 may comprise a straight conduit that contains no bends. However, the convective heat transfer conduit 124 may comprise bend and designs other than a straight conduit.

The convection section 120 may provide a secondary heat recovery after the radiant section 110. The flue gas from the radiant section 110 moves upwardly while carrying a significant amount of heat. This heat may be recovered from the radiant section flue gas in the convection section by producing steam. A water stream may be passed to the convection section which is converted to steam after absorbing the heat from the rising flue gas of the radiant section 110.

In an aspect, the convective heat transfer conduit 124 may provide a plurality of services in addition to the steam heating or superheating. In an exemplary embodiment, the convective heat transfer conduit 124 may comprise a first convective heat transfer conduit 124a, a second convective heat transfer conduit 124b, a third convective heat transfer conduit 124c, and a fourth convective heat transfer conduit 124d. In an embodiment, the first convective heat transfer conduit 124a may be used for preheating water destined for steam production also known as an economizer. The second convective heat transfer conduit 124b, and the third convective heat transfer conduit 124c may be used for steam heating. The fourth convective heat transfer conduit 124d may be used for steam superheating. Although four convective heat transfer conduits 124 are shown in FIG. 1, the convection section 120 may comprise more or less than four convective heat transfer conduits 124. Further, the convective heat transfer conduit 124 may comprise a fifth convective heat transfer conduit 124e for heating a process fluid stream in line 108.

In an aspect, the convection section 120 may comprise a first convection manifold 121 in upstream communication with the convective heat transfer conduit 124a and a first convection collector 123 in downstream communication with the convective heat transfer conduit 124a. The first convection manifold 121 may be configured to receive a water stream. The first convection manifold 121 may be in downstream communication with a water stream such as a boiler feed water (BFW) stream in line 104. The water stream in line 104 may be passed to the convection section 120 from an inlet 13 and into the first convective heat transfer conduit 124a through the first convection manifold 121. In the convection section 120, the water stream is heated and a first heated stream that may comprise steam with heated water is delivered through the first convection collector 123. A first heated stream that may comprise a steam stream with heated water is delivered from the first convection collector 123 and through an outlet 14 of the convection section 120. The first heated stream is taken in line 106 from the first convective heat transfer conduits 124a from the outlet 14. The first heated stream in line 106 may be combined with a second heated stream that may comprise steam in line 156 to provide a combined heated stream in line 107. The combined heated stream in line 107 may be passed to a steam disengaging drum 153 to separate steam from the liquid water. A steam stream is taken in line 122 and a water stream is taken in line 154 from the steam disengaging drum 153. The water stream in line 154 may be fed to the third convective heat transfer conduit 124c from a third inlet 18 of the third convection manifold 141. The third convective heat transfer conduit 124c heats the liquid water stream to produce steam. A third heated stream that may comprise steam with heated water is taken in line 155 from the third convective heat transfer conduit 124c from an outlet 17 of a third convection collector 142. In an embodiment, the third heated stream in line 155 may be further heated in the convection section 120. The third heated stream in line 155 may be fed to the second convective heat transfer conduit 124b from an inlet 15 of a second convection manifold 143. After heating in the second convective heat transfer conduit 124b the second heated stream is discharged from an outlet 16 of the second convection collector 144. The second heated stream in line 156 is combined with the first heated stream in line 106 and transported in line 107 to the steam disengaging drum 153.

Referring back to the steam disengaging drum 153, the steam stream in line 122 may be further heated in the convection section 120. The steam stream in line 122 may be heated or superheated in the convection section 120 to produce a heated or superheated steam stream. The steam stream in line 122 may be fed to the fourth convective heat transfer conduit 124d of the convection section 120 from an inlet 31 of a fourth convection manifold 145. After heating, a heated steam stream is produced which may be taken in line 126 from an outlet 41 of the fourth convection collector 146.

In accordance with the present disclosure, the relative sequence and location of conduits the second convective heat transfer conduit 124b, third convective heat transfer conduit 124c and fourth convective heat transfer conduit 124d can be interchanged depending on the heat recovery integration requirements. The heat recovery integration requirements may be dependent on the pressure and temperature conditions of steam required by the process unit.

The convection section 120 removes heat from the rising flue gas to heat the water stream in the convective heat transfer conduits 124a-e and significantly reduces the temperature of the flue gas exiting the stack 125. By the time the flue gas exits the stack, most of the heat should be recovered in the convection section 120 and the temperature of the flue gas is much reduced.

In process turn down conditions when a lower amount of process fluid is heated in the radiant section 110 or the amount of fuel burned in the radiant section 110 is reduced, the flue gas from the radiant section 110 may not provide sufficient heat to produce steam at a required flow rate and temperature compared to a scenario of normal operation. The secondary heater 130 is provided to further heat or superheat the steam to a higher degree from the primary heater to produce a superheated steam or increase the degree of superheat of the superheated steam.

In an embodiment, the primary heater 103 may be configured as an enhanced efficiency heater 103. For an enhanced efficiency heater 103, a provision may be provided for primary heating the process fluid stream in the convection section 120 of the primary heater 103. In such embodiment, the water stream in line 104 may be parallelly heated in the convection conduits 124a along with primary heating of the process fluid stream.

In an embodiment, the process fluid stream in line 108 may be heated in the convection section 120. The process fluid stream in line 108 may be fed to the fifth convective heat transfer conduit 124e from an inlet 52 of the fifth convection manifold 147. After heating, a heated process fluid stream may be taken in line 109 from an outlet 54 of the second convection collector 148. In an aspect, the process fluid stream in line 102 may be passed to the fifth convective heat transfer conduit 124e for preheating it before heating in the radiant heat transfer conduit 116. In that case, line 102 may be in downstream communication with line 109. Alternatively, a second process fluid stream in line 108 may be heated in the fifth convective heat transfer conduit 124e of the convection section 120.

The heated steam stream is discharged from the convection section 120 in line 126 through the outlet 41 of the fourth convection collector 146. In an aspect, the heated steam stream in line 126 may be a superheated steam. The heated steam stream in line 126 may be split into a primary steam stream in line 127 and a secondary steam stream in line 128. A valve 12 may be provided on the primary steam line 127 and a valve 22 may be provided on the secondary steam line 128 for controlling their respective flow rates and proportions. An entirety or a portion of the heated steam stream in line 126 may be taken in the secondary steam line 128 by controlling the valves 12 and 22.

As shown in FIG. 1, the secondary steam stream in line 128 is supplied to the secondary heater 130. The secondary steam stream in line 128 is passed into the secondary heater 130 from an inlet 61. The secondary heater 130 may be selected from a fired heater or an electric heater. In an exemplary embodiment, the secondary heater 130 is a fired heater comprising a radiant section 131.

The radiant section 131 may include one or more burners 132 which receive oxygen and a fuel stream, such as fuel gas and/or fuel oil, ignite combustion of the fuel and produce heat and flue gas from a flame. The heat in the radiant section 131 is used to further heat the secondary steam stream in line 128 to produce a superheated steam or it may increase the degree of superheat of the superheated steam in line 128. The superheated steam in the secondary steam line 128 may be heated to a higher temperature in the radiant section 131 to increase its degree of superheat. The secondary steam stream may be contained in one or more secondary heat transfer conduits 134 passing through the radiant section 131. As shown in the FIG. 1, one secondary heat transfer conduit 134 is shown but, there is typically a plurality of secondary heat transfer conduits 134 not visible behind the secondary heat transfer conduit shown in the radiant section 131. The secondary heat transfer conduit 134 is typically a tube or coil in which the secondary steam stream is contained and moves from the inlet to the outlet.

The radiant section 131 may comprise a horizontal or vertical secondary heat transfer conduit 134. The secondary heat transfer conduit 134 may be located along the walls in the radiant section 131 and receive radiant heat direct from the burners 132. Alternatively, the secondary heat transfer conduit 134 may be located at the center of the radiant section 131 with burners on either side of the secondary heat transfer conduit 134. The radiant section 131 comprises refractory lining.

The radiant section 131 may comprise a secondary radiant manifold 133 and a secondary radiant collector 135 both in communication with the secondary heat transfer conduit 134. The secondary steam stream in line 128 may be passed to the radiant section 131 and into the secondary heat transfer conduit 134 through the first radiant manifold 133. In the radiant section 131, the secondary steam stream is heated and delivered through the secondary radiant collector 135. A further heated and superheated steam stream is delivered from the second radiant collector 135 and through an outlet 71 of the radiant section 131.

The burners 132 may be selected from duct burners and the surface burners. Supply of the fuel gas to the burners 132 may be regulated based on the exit temperature of the superheated steam exiting the radiant section 131 and the firing rate may be determined by the level of heat or temperature of the superheated steam desired.

In an exemplary embodiment, the burners 132 may be surface burners located at the bottom of the radiant section 131. Although two burners 132 are shown, there may be more or less than two burners in the radiant section 131. Further, there may be one or more burners located on the wall of the radiant section 131.

In an aspect, the secondary heat transfer conduit 134 may comprise a multi-pass coil conduit which includes bends or turns to increase the residence time of the steam stream within the radiant section 131. For example, the multi-pass coil conduit may be a U coil, arbor coil, I, Double I, W coil, twin U, serpentine, helical or other such configurations.

Although not shown, the radiant section 131 may be tapered at the top. The radiant section 131 may have sloped roof section which defines a transition section between the radiant section 131 and a stack (not shown). The radiant section 131 may comprise a roof section having inward sloping walls.

The flue gas from the radiant section 131 may comprise recoverable amount of heat. The present disclosure provides recovering the heat of the flue gas from the radiant section 131 to further heat the steam. In an embodiment, the apparatus 101 may comprise a flue gas conduit 144 in upstream communication with primary heater 103 and in downstream communication with the secondary heater 130. In an exemplary embodiment, the flue gas conduit 144 may be in upstream communication with the convection section 120 of the primary heater 103 and in downstream communication with the radiant section 131 of the secondary heater 130. The flue gas may leave the radiant section 131 from a flue gas outlet 51 of the secondary heater 130. The flue gas conduit 144 may supply the flue gas from the radiant section 131 of the secondary heater 130 to the convection section 120 from a flue gas inlet 53 of the primary heater 103. The flue gas from the radiant section 131 that enters the convection section 120 may provide additional heat to the water streams in the convection conduits 124. This way overall heat recovery is increased and steam can be made even from the flue gases generated from fuel fired in the secondary heater 130 to increase degree of steam superheating.

In an embodiment, the secondary heater 130 may comprise an electric heater. For an electric heater, the burners 132 may be replaced with an electrically heated source for supplying the heat to the secondary steam stream.

The superheated steam or a superheated steam with a higher degree of superheat than the secondary steam stream in line 128 is discharged from the secondary radiant section 131 in line 136. The superheated steam stream in line 136 may have a lower flow rate than the normal supply to the downstream unit. In an aspect, a water stream may be added into the superheated steam stream in line 136 to increase its flow rate. In an embodiment, the superheated steam stream in line 136 may be passed to a pressure reducing device 137 such as an expansion valve. A boiler feed water stream in line 138 may also be passed into the pressure reducing device 137 for mixing with the superheated steam stream. A valve 42 may be provided on the line 138 to regulate the supply of boiler feed water stream into the pressure reducing device 137.

In the pressure reducing device 137, the superheated steam stream in line 136 is mixed with the boiler feed water stream in line 138 to provide a desuperheated steam stream. A desuperheated steam stream is discharged from the pressure reducing device 137 in line 139. In accordance with the present disclosure, a desuperheated steam stream is a superheated steam stream but has a lower temperature than the superheated steam stream. The desuperheated steam stream in line 139 has lower temperature than the superheated steam stream in line 136. However, the desuperheated steam stream in line 139 has a higher flow rate than the superheated steam stream in line 136 due to the vaporization of the added boiler feed water.

In an aspect, the primary steam stream in line 127 may be combined with the desuperheated steam stream in line 139. In an embodiment, the primary steam stream in line 127 may be passed to a pressure reducing device 140 such as a valve. A boiler feed water stream in line 129 may also be passed into the pressure reducing device 140 for mixing with the primary steam stream in line 127. A valve 32 may be provided on the line 129 to regulate the supply of boiler feed water stream into the pressure reducing device 140. A mixed steam stream may be discharged in line 142 from the pressure reducing device 140. The mixed stream in line 142 may be reduced to below critical temperature, so as to not be superheated.

The mixed steam stream in line 142 may be combined with the desuperheated steam stream in line 139. In an alternate embodiment, the primary steam stream in line 127 may be combined directly with the desuperheated steam stream in line 139.

In an exemplary embodiment, the desuperheated steam stream in line 139 and the mixed steam stream in line 142 may be passed to a steam header 150. The steam header 150 may comprise a pipe for receiving one or more steam streams before supplying them to the downstream unit. In an aspect, product steam stream may be taken in one or more product line 152 from the steam header 150 which may be supplied to the one or more downstream units.

FIG. 2 shows another embodiment of the apparatus and the process 201 for producing a superheated steam stream. Elements in FIG. 2 with the same configuration as in FIG. 1 will have the same reference numeral as in FIG. 1. Elements in FIG. 2 which have a different configuration as the corresponding element in FIG. 1 will have the same reference numeral but designated with a prime symbol (′). The configuration and operation of the embodiment of FIG. 2 is similar to FIG. 1 with the following exceptions.

In the embodiment as shown in FIG. 2, the primary steam stream in line 127 is combined with the superheated steam stream in line 136 to produce a combined steam stream in line 146. The combined steam stream in line 146 is passed to the pressure reducing device 137 such as an expansion valve. The boiler feed water stream in line 138 is passed into the pressure reducing device 137 for mixing with the combined steam stream. A desuperheated steam stream is discharged from the pressure reducing device 137 in line 139′. The desuperheated steam stream in line 139′ is passed to the steam header 150 to produce product steam stream which may be taken in one or more product line 152. Rest of the process is same as described in FIG. 1.

Example

An experimental study was conducted to demonstrate the integration of the secondary heater with the primary heater to produce a superheated steam or increase the degree of superheat of a superheated steam. Details of the study are provided in the Table below:

As evident from the study, the net quantity of steam to header can be maintained even when the primary heater generates lower steam, as the secondary heater increases the degree of superheat of steam as shown in the Table above. The desuperheating water is added downstream of secondary heater to increase overall steam quantity. The study demonstrated that if there is a need then overall steam quantity to header can be increased by the integration of the secondary heater with the primary heater to produce a superheated steam or increase the degree of superheat of a superheated steam.

Specific Embodiments

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.

A first embodiment of the present disclosure is an apparatus for producing a superheated steam, the apparatus comprising a primary heater comprising a radiant section and a convection section, a convective heat transfer conduit in communication with a source of water and passing through the convection section to provide a steam stream; and a secondary heater, comprising a radiant section and a secondary heat transfer conduit in communication with the convective heat transfer conduit, the secondary heat transfer conduit passing through the radiant section of the secondary heater to provide a superheated steam stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising a pressure reducing device in communication with the secondary heat transfer conduit to receive the superheated steam stream and a water stream to provide a reduced pressure desuperheated steam stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the primary heater and the secondary heater are arranged in series such that all or a portion of the steam stream from the primary heater is passed through the secondary heater. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein valving is provided to direct flow in the convective heat transfer conduit around the secondary heat transfer conduit. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising a flue gas conduit configured to deliver a flue gas stream from the radiant section of the secondary heater to the convection section of the primary heater and transfer heat to the steam stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising a first pressure reducing device in communication with the convective heat transfer conduit to receive the steam stream and a water stream to provide a reduced pressure steam stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising a steam header in communication with the reduced pressure steam stream and the desuperheated steam stream, the header configured to provide a product steam at a higher flow rate than the reduced pressure steam stream or the desuperheated steam stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the secondary heater is a fired heater or an electric heater. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the convective heat transfer conduit comprises one or more coils. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the radiant section of the primary heater comprises a multi-pass coil conduit. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the convection section of the primary heater comprises a plurality of parallel convective heat transfer conduit in communication with a plurality of water stream and configured to produce a plurality of steam stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph, wherein the secondary heater comprises a plurality of secondary heat transfer conduit in communication with the plurality of parallel convective heat transfer conduit and configured to produce a plurality of superheated steam stream.

A second embodiment of the present disclosure is an apparatus for producing a superheated steam, the apparatus comprising a primary heater comprising a radiant section and a convection section, a convective heat transfer conduit in communication with a source of water and passing through the convection section to provide a steam stream; a secondary heater, comprising a radiant section and a secondary heat transfer conduit in communication with the convective heat transfer conduit, the secondary heat transfer conduit passing through the radiant section of the secondary heater to provide a superheated steam stream; and a flue gas conduit configured to deliver a flue gas stream from the radiant section of the secondary heater to the convection section of the primary heater and transfer heat to the convective heat transfer conduit. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising a pressure reducing device in communication with the secondary heat transfer conduit to receive the superheated steam stream and a water stream to provide a reduced pressure desuperheated steam stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising a first pressure reducing device in communication with the convective heat transfer conduit to receive the steam stream and a water stream to provide a reduced pressure steam stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising a steam header in communication with the reduced pressure steam stream and the desuperheated steam stream, the header configured to provide a product steam at a higher flow rate than the reduced pressure steam stream or the desuperheated steam stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph, wherein the secondary heater is a fired heater or an electric heater.

A third embodiment of the present disclosure is a process of producing a superheated steam, comprising heating a water stream in a convection section of a primary heater to produce a steam stream; passing the steam stream to a secondary heater; heating the steam stream in the secondary heater to produce a superheated steam stream; and adding water to the steam stream downstream of the secondary heater to desuperheat the steam stream but increase the steam flow rate. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph further comprising passing a flue gas stream from the secondary heater to the convection section of the primary heater to heat the steam stream. An embodiment of the present disclosure is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph further comprising passing the superheated steam stream and a water stream through a pressure reducing device to provide a reduced pressure desuperheated steam stream.

Without further elaboration, it is believed that using the preceding description that one skilled in the art can utilize the present disclosure to its fullest extent and easily ascertain the essential characteristics of this disclosure, without departing from the spirit and scope thereof, to make various changes and modifications of the disclosure 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.

In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.