WO2016036517A1

WO2016036517A1 - Temperature control for ammoxidation reactor

Info

Publication number: WO2016036517A1
Application number: PCT/US2015/046046
Authority: WO
Inventors: Timothy Robert Mcdonel; Jay Robert COUCH; David Rudolph Wagner; Paul Trigg Wachtendorf; Thomas George TRAVERS
Original assignee: Ineos Europe Ag
Priority date: 2014-09-02
Filing date: 2015-08-20
Publication date: 2016-03-10
Also published as: RU2696436C2; CN104190331B; RU2017109910A; SA517381016B1; CN104190331A; RU2017109910A3

Abstract

Control of a reaction temperature occurring inside an ammoxidation reactor is achieved by controlling a flowrate of superheated steam allowed to bypass superheat cooling coils of the cooling system of the reactor in response to a measured reaction temperature. In another aspect, control of the reaction temperature is achieved by controlling a pressure inside a steam drum used to supply the superheated steam used for cooling purposes.

Description

TEMPERATURE CONTROL FOR AMMOXIDATION REACTOR

[001] A process and apparatus is provided for temperature control of an ammoxidation reactor.

More specifically, the process includes measuring a temperature in the ammoxidation reactor and adjusting a flow rate of superheated steam to superheat coils in the ammoxidation reactor.

BACKGROUND

[002] In the commercial manufacture of acrylonitrile, propylene, ammonia and oxygen are reacted together according to the following reaction scheme:

CH₂=CH-CH₃ + NH₃ + 3/2 0₂→ CH₂=CH-CN + 3 H₂0

This process, which is commonly referred to as ammoxidation, is carried out in the gas phase at elevated temperature (e.g. , 350° to 480° C) in the presence of a suitable fluid bed ammoxidation catalyst.

[003] Fig. 1 illustrates a typical acrylonitrile reactor used to carry out this process. As shown, reactor 10 includes reactor shell 12, air grid 14, feed sparger 16, a cooling system generally indicted at 18 including saturated cooling coils 17 and superheat cooling coils 19, and cyclones 20. While Fig. 1 shows saturated cooling coils 17 and superheat cooling coils 19 being located on one side of reactor 10 and cyclones 20 being located on the other side, it will be understood that in actual practice these structures are positioned uniformly throughout the reactor. During normal operation, process air is charged into reactor 10 through air inlet 22, while a mixture of propylene obtained from propylene supply line 13 and ammonia obtained from ammonia supply line 15 is charged into reactor 10 through feed sparger 16. The flow rates of both are high enough to fluidize a bed 44 of ammoxidation catalyst in the reactor interior, where the catalytic ammoxidation of the propylene and ammonia to acrylonitrile occurs.

[004] Product gases produced by the reaction exit reactor 10 through reactor effluent outlet 26.

Before doing so, they pass through cyclones 20, which remove any ammoxidation catalyst these gases may have entrained for return to catalyst bed 44 through diplegs 25. Ammoxidation is highly exothermic, and so cooling system 18 is used to withdraw excess heat and thereby keep the reaction temperature at an appropriate level. [005] As further illustrated in Fig. 1, in addition to saturated cooling coils 17 and superheat cooling coils 19, cooling system 18 also includes steam drum 24, recirculating pump 26, shut-off valve 28 and steam control valve 30. The lower portion of steam drum 24 is filled with saturated liquid cooling water maintained at an elevated pressure and elevated temperature such as about 255° C at about 4.2 mPaG. The upper portion of steam drum 24 is filled with saturated steam in equilibrium with this liquid cooling water. As is well understood in the art, water exists as a liquid at these elevated temperatures because it is also under greater than one atmosphere of pressure.

[006] The primary way cooling system 18 removes heat from the interior of reactor 10 is by the recirculation of liquid cooling water from the lower portion of steam drum 24 through cooling coils 17. For this purpose, recirculation pump 26 is arranged to pump liquid cooling water from the bottom of steam drum 24 through shut-off valve 28 and then through cooling coil 17. In cooling coil 17, some liquid vaporizes to steam and cooling water and steam produced is returned to steam drum 24. Since the saturated cooling water fed to cooling coil 17 is composed of 100% liquid water, cooling coil 17 is typically referred to as a "saturated" cooling coil.

[007] In actual practice, the flowrate of cooling water through saturated cooling coil 17 is selected so that a predetermined proportion of this cooling water, typically about 15% for example, is converted to steam. Accordingly, as shown in Fig. 1, the heated cooling water produced in saturated cooling coil 17 is returned to an upper portion of steam drum 24, so that the vaporous fraction of this cooling water stream can remain in the upper portion of the steam drum while the liquid portion of this cooling water stream can fall to the lower portion of the steam drum for mixing with the liquid cooling water already there. The steam drum 24 may include make-up water conduit 54.

[008] In many designs, shut-off valve 28 is a simple on-off valve as opposed to a control valve capable of fine control of fluid flowrate. This is because other means are typically used for fine control of the reaction temperature inside the acrylonitrile reactor, and so a more complicated and expensive control valve is unnecessary. Also it is not desirable to convert to much of the liquid water into vapor inside the cooling coil as this can result in negative consequences such as erosion of the inside of the cooling coil pipe or scaling. ] Each individual shut-off valve 28 on each individual coil is the only valve controlling whether or not cooling water flows through a particular saturated cooling coil 17. That is to say, saturated cooling coil 17 is constructed without any additional valve or other flow control device for controlling the flow of cooling water through saturated cooling coil 17. This is because such an additional valve is unnecessary to achieve the desired operation and control of the cooling coils in the manner described here. In addition, eliminating a valve on the outlet also eliminates the need for a safety valve, which would otherwise be necessary if such an outlet valve were used. Thus, the total flow through all of the cooling coils in service (that is for the saturated cooling coil 17 which have their valve open) is set by a discharge flow rate from pump 26. ] In addition to saturated cooling coils 17, cooling system 18 also uses superheat cooling coils 19 for removing heat from the interior of acrylonitrile reactor 10. Superheat cooling coils 19 differ from saturated cooling coils 17 in that superheat cooling coils 19 are connected by means of steam inlet header 32 to an upper portion of steam drum 24 so that the feed to these cooling coils is superheated steam rather than saturated steam. The steam entering superheat cooling coil 19 is at a saturation temperature corresponding to the steam drum pressure. The steam drum pressure increases as it flows through superheat cooling coil 19 and thus becomes superheated. Accordingly, cooling coils 19 are typically referred to as "superheat cooling coils." ] An important function of superheat cooling coils 19 is to raise the temperature of steam produced in coils 19 so as to provide superheated steam for driving the steam turbines used in other parts of the acrylonitrile plant as liquid droplets in wet steam may damage turbine internals. For this purpose, the superheated steam passing out of superheat cooling coils 19 is typically discharged through steam outlet header 34 to steam supply conduit 35 for transfer directly to these steam turbines. [012] Although the temperature of the superheated steam being fed to these steam turbines is not critical, nonetheless it is still desirable to maintain this temperature within certain relatively broad limits for maintaining smooth overall operation of the acrylonitrile plant. For example, in most commercial acrylonitrile plants, it is desirable to maintain the temperature of the superheated steam being fed to these steam turbines within a temperature range of about 300 to about 400 ° C.

[013] Common practice in many acrylonitrile plants includes connecting steam inlet header 32 and steam outlet header 34 with bypass line 33 so that the temperature of the steam passing into steam supply conduit 35 can be controlled by adjusting the amount of steam supplied to this conduit directly from steam drum 24. Because the temperature of the steam in steam drum 24 is necessarily lower than the temperature of the superheated steam passing out of superheat cooling coil 19, increasing the flowrate of steam passing through bypass line 33 necessarily lowers the temperature of the steam reaching steam supply conduit 35. So, it is also customary in most commercial acrylonitrile plants also to include steam control valve 30 in bypass passageway 33, whose operation is controlled by controller 39 in response to the measured temperature Ti of the steam in steam supply conduit 35. Control valve 30 is then operated to maintain the measured temperature Ti of the steam in steam supply conduit 35 at a constant temperature somewhere between about 340 to 385 ° C.

[014] In order to keep an acrylonitrile reactor operating in peak condition, it is desirable to maintain its operating temperature within a temperature range of about 200 to about 240 °C, in another aspect, about 215 to about 230 ° C, when modern molybdenum based ammoxidation catalysts are used. In this aspect, it is more desirable to maintain the reactor temperature as close as possible to a single control point temperature rather than to allow the operating temperature to drift up and down within a range of temperatures. Although control of reaction temperature can be carried out by adding to or subtracting from the number of cooling coils in active service, this approach does not provide precise temperature control. Rather, the addition and subtraction of cooling coils alone does not necessarily achieve the precise reactor operating temperature.

[015] Accordingly, precise temperature control of acrylonitrile reactor 10 is commonly done by increasing and decreasing the flowrate of propylene supplied to the acrylonitrile reactor in response to the measured temperature T_R of the ammoxidation reaction occurring inside the reactor. For this purpose, as illustrated in Fig. 1, propylene control valve 37 in propylene supply line 13 and controller 41 are provided to control the flow of propylene into acrylonitrile reactor 10 in response to the measured ammoxidation reaction temperature, T_R. Thus, a certain number of cooling coils are put into service to provide reactor temperature control within a desired temperature range, and a propylene feed rate is adjusted up or down to achieve a more precise temperature adjustment.

[016] Although this approach works well in terms of enabling precise control of ammoxidation reaction temperature, it does require that the flowrate of propylene as well as flow rates of the ammonia and air co-reactants being fed to the reactor also be adjusted in the same way in order to maintain fixed molar ratios between these ingredients. In addition, decreasing the flowrate of propylene fed to the reactor inherently reduces the capacity of the reactor to produce product acrylonitrile.

[017] Accordingly, it would be desirable to provide another means for precisely controlling the temperature of the ammoxidation reaction while maintaining a constant desired propylene feed rate and constant desired acrylonitrile production.

SUMMARY

[018] A process for controlling temperature of an ammoxidation reactor includes providing superheated steam to superheat cooling coils disposed in the ammoxidation reactor; measuring a temperature in the ammoxidation reactor; and adjusting a flow rate of superheated steam to the superheat cooling coils to provide an increase or decrease in the temperature in the ammoxidation reactor. [019] A process for controlling temperature of a reaction occurring inside an ammoxidation reactor includes removing a first portion of excess heat from the ammoxidation reactor by indirect heat exchange between hot gases produced by the ammoxidation reaction and saturated steam passing through saturated cooling coils, removing a second portion of excess heat being removed from the ammoxidation reactor by indirect heat exchange between the hot gases produced by the ammoxidation reaction and superheated steam passing through superheat cooling coils, measuring a temperature in the ammoxidation reactor; and adjusting a flow rate of superheated steam to the superheat cooling coils to provide an increase or decrease in the temperature in the ammoxidation reactor.

[020] A cooling system for an ammoxidation reactor includes superheat cooling coils and

saturated cooling coils disposed in the ammoxidation reactor, the superheat cooling coils configured to receive superheated steam from a steam drum and the saturated cooling coils configured to receive saturated steam from the steam drum; a bypass valve configured to allow superheated steam to bypass the reactor; a reactor temperature sensor: and a controller configured to receive a signal from the reactor temperature sensor and control operation of the bypass valve.

BRIEF DESCRIPTION OF THE DRAWINGS

[021] This invention may be more readily understood by reference to the following drawings wherein:

[022] Fig. 1 is a schematic view illustrating a conventional way for accomplishing fine control of the reaction temperature occurring inside a commercial acrylonitrile reactor in which the flow of propylene to the reactor is controlled in response to measured reaction temperature;

[023] Fig. 2 is a schematic view similar to Fig. 1 illustrating one aspect for accomplishing fine control of the reaction temperature occurring inside a commercial acrylonitrile reactor in which the flowrate of superheated steam passing through the superheat cooling coils of the acrylonitrile reactor is adjusted in response to the measured ammoxidation reaction temperature, T_R; and

[024] Fig. 3 is a schematic view similar to Figs. 1 and 2 illustrating another aspect for

accomplishing fine control of the reaction temperature occurring inside a commercial acrylonitrile reactor in which the pressure inside the steam drum is adjusted in response to the measured ammoxidation reaction temperature, T_R.

[025] Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various aspects. Also, common but well-understood elements that are useful or necessary in a commercially feasible aspect are often not depicted in order to facilitate a less obstructed view of these various aspects.

DETAILED DESCRIPTION

[026] In accordance with a first aspect, fine control of the reaction temperature occurring inside an ammoxidation reactor is accomplished by adjusting the flowrate of steam passing through the superheat cooling coils of the reactor in response to the measured

ammoxidation reaction temperature, T_R.

[027] This aspect is illustrated in Fig. 2, which is a schematic view similar to Fig. 1, except that it shows that the operation of steam control valve 30 in bypass 33 being controlled primarily in response to the measured ammoxidation reaction temperature, T_R.

[028] As explained above, at least some of the excess heat generated by the ammoxidation reaction occurring inside acrylonitrile reactor 10 is removed from the reactor during normal operation by indirect heat exchange between the superheated steam passing through superheat cooling coils 19 and the hot gases inside the reactor. Accordingly, it will be appreciated that increased flowrate of superheated steam passing through superheat cooling coils 19 will result in a decrease in ammoxidation reaction temperature,

T_R.

[029] Accordingly, one aspect takes advantage of this phenomenon by adjusting steam control valve 30 to control the flowrate of steam through bypass 33 in response to the measured ammoxidation reaction temperature, T_R. Because of the resistance to flow inside superheat cooling coil 19, the pressure of the steam in steam outlet header 34 is necessarily lower than the pressure of the steam in steam drum 24. Accordingly, opening steam control valve 30 inherently increases the flowrate of saturated steam though bypass 33 which, in turn, inherently decreases the flowrate of superheated steam through superheated cooling coil 19. This, in turn decreases the amount of heat removed from inside reactor 10, which in turn causes a corresponding increase in the ammoxidation reaction temperature, T_R. In the same way, closing steam valve 30 inherently decreases the flowrate of saturated steam through bypass 33 which, in turn, inherently increases the flowrate of superheated steam through superheat cooling coils 19. This, in turn, results in an increase in the amount of heat removed from inside reactor 10 and hence causes a corresponding decrease in the ammoxidation reaction temperature, T_R.

[030] Thus, by controlling steam control valve 30 to adjust the flowrate of saturated steam

through bypass 33 in response to the measured ammoxidation reaction temperature, T_R, it is possible to achieve fine control of the amount of heat withdrawn from the acrylonitrile reactor and hence the temperature of the ammoxidation reaction occurring inside this reactor in response to this measured ammoxidation reaction temperature.

[031] As indicated above, to insure good operation of the steam turbines in an acrylonitrile plant, it is customary practice to maintain the temperature of the superheated product steam being fed to these steam turbines at a constant temperature somewhere within the broad temperature range of about 300 to about 400 °C. Steam fed to the steam turbines of a typical acrylonitrile plant is not critical in the sense that these turbines can accept a fairly wide variation in this temperature and still operate properly. Therefore, allowing the temperature Ti of the steam in steam supply conduit 35 to vary somewhat does not lead to any adverse effect on these steam turbines or their operation.

[032] On the other hand, if the temperature of the superheated product steam fed to the steam turbines departs from its target by too great an amount, then the operation of these turbines could be adversely affected. Therefore, to prevent this from occurring, controller 39 is also programmed to insure that the measured temperature Ti of the steam in steam supply conduit 35 is maintained within an acceptable range such as, for example, about 300 to 400 °C. That is to say, this controller is programmed to adjust the operation of steam control valve 30 in response to the measured ammoxidation reaction temperature, T_R, with the constraint that should the measured temperature Ti of the steam in steam supply conduit 35 exceed maximum limit, e.g., about 400 °C, or decreases below its minimum limit, e.g., about 300 ° C. Upon exceeding limits, the control paradigm of steam control valve 30 changes so that that the measured temperature Ti of the steam in steam supply conduit 35 is brought back to within its acceptable limits before control of steam control valve 30 is returned to being based on the measured ammoxidation reaction temperature, TR. In practice for example, this can be

accomplished by adding or removing a coil 17.

[033] Accordingly, it can be seen that it is possible in accordance with this first aspect of the invention to achieve fine control of the ammoxidation reaction temperature, TR, by simple adjustment of steam control valve 30 only, without changing the flowrates of the propylene and other reactants fed to the system. This not only stabilizes reactor operation but also enables the acrylonitrile reactor 10 to operate continuously at maximum capacity, which is not possible with most earlier techniques for fine temperature control. In this aspect, the process is effective for maintaining a reactor temperature of about 200 to about 400 ° C, in another aspect, about 220 to about 380 ° C, in another aspect, about 250 to about 350 ° C, and in another aspect, about 275 to about 325 ° C.

[034] In another aspect, the process is effective for minimizing temperature variations in the reactor. In this aspect, temperature control provided by saturated cooling coils is effective for maintaining a reactor temperature within about 10 °C of a desired reactor temperature, and in another aspect, within about 5 °C. In a related aspect, temperature control provided by superheat cooling coils is effective for maintaining a reactor temperature within about 5 °C of a desired reactor temperature, and in another aspect, within about 1 °C

[035] Another advantage of this aspect is that no additional equipment is needed to adopt this technology. In this regard, additional "hard" equipment be added such an additional auxiliary steam drum, additional control valves, and the like are not needed. Equipment needed to implement the process e.g., the temperature sensors for sensing temperatures T_R and T_1; steam control valve 30 and controller 39 for controlling steam valve 30 are already present. The only physical modification the plant which is needed to adopt this technology is to electronically connect the temperature sensor sensing temperature T_R with controller 39 for controlling steam control valve 30 and to reprogram this controller to control steam valve 30 in the manner indicated above.

[036] An additional feature and advantage of this aspect of the process is that the temperature of the acrylonitrile reactor is controlled without using a control valve to directly control the flowrate of superheated cooling water flow through the saturated cooling coils and also without using a control valve to directly control the flowrate of steam flowing through the superheat cooling coils. In this context, "without using a control valve to directly control the flowrate" of a fluid flowing through a particular line or conduit will be understood to mean that a control valve is not mounted in that particular line or conduit, or in another line or conduit which feeds or receives fluid only from that line or conduit. It does not include situations in which another control valve is mounted in a different line or conduit, even though operation of this other control valve may have some impact on the fluid flowing through that particular line or conduit. So, for example, the flowrate of steam through superheat cooling coils 19 is controlled without using steam control valve 30 to directly control this flowrate, within the meaning of this disclosure, because steam control valve 30 is not mounted in superheat cooling coil 30 or the two lines which feed and withdraw steam from this superheat cooling coil, i.e., steam inlet header 32 and steam outlet header 34. In one aspect, superheat coil 19 represents multiple individual superheat coils, while bypass line 33 and control valve 30 are a single line and valve. Hence, a single bypass line and/or control valve can be used without the need for additional valves for each individual superheat coil.

[037] Thus it will be appreciated that this aspect of the process not only provides a simple yet elegant way of achieving fine control of the ammoxidation reaction temperature, T_R, without relying on changes in propylene flow rate but also achieves this fine control with requiring any additional hard equipment for this purpose. In this aspect, the flowrate of propylene to the ammoxidation reactor is effective for providing a ratio of air to propylene of about 9 to about 9.5 and a ratio of ammonia to propylene of about 1 to about 1.5.

[038] In accordance with a second aspect of this invention, fine control of the reaction

temperature occurring inside a commercial acrylonitrile reactor is accomplished by adjusting the pressure inside steam drum 24 in response to the measured ammoxidation reaction temperature, T_R.

[039] This aspect is illustrated in Fig. 3, which is a schematic view similar to Figs. 1 and 2, except that it shows that the operation of steam control valve 30 in bypass 33 being controlled primarily in response to the measured pressure Pi in steam drum 24.

[040] As indicated above, steam drum 24 is a closed vessel which contains both superheated liquid cooling water and superheated saturated steam in equilibrium with one another at elevated temperature and pressure. As well understood in the art, this means that if the pressure inside steam drum 24 is raised, the temperature of its contents will undergo a corresponding increase in temperature, and conversely.

[041] In another aspect, this phenomenon is taken advantage of by providing steam outlet

control valve 38 downstream of steam supply conduit 35 and using this control valve to adjust the flowrate of steam passing through steam supply conduit 35 in response to the measured ammoxidation reaction temperature, T_R. Decreasing the flowrate of superheated steam passing through steam supply conduit 35 causes a corresponding increase in the pressure of the superheated steam in this steam supply conduit, which pressure increase is also realized in steam drum 24, as the two are directly connected to one another. This pressure increase in steam drum 24 then causes a corresponding increase in the temperature of both the superheated liquid cooling water and the superheated saturated steam in this steam drum. As a result, the cooling duty provided by both of these cooling fluids decreases because they begin their indirect heat exchange with the hot reaction gases inside reactor 10 at higher temperature. As a result, the temperature inside reactor 10 increases, because less heat is withdrawn by cooling system 18.

[042] In the same way, adjusting steam outlet control valve 38 to increase the flowrate of

superheated steam passing through steam supply conduit 35 ultimately achieves a corresponding decrease in the temperature inside reactor 10.

[043] It will therefore be appreciated that fine control of the temperature of ammoxidation reaction occurring inside acrylonitrile reactor 10 can also be easily accomplished in accordance with the second feature of this invention by adjusting the pressure of the contents of steam drum 24 in response to the measured ammoxidation reaction temperature, T_R. If so, steam control valve 30 can be operated in a conventional manner such as described above in connection with Fig. 1, i.e., by adjusting this control valve in response to the measured temperature T_\ of the superheated steam in steam supply conduit 35 to achieve a constant predetermined temperature such as 650° F (343° C). In addition, for safety reasons and to insure good operation, it is also desirable to monitor the pressure Pi in steam drum 24 and to program controller 43 controlling steam outlet control valve 38 to insure that this pressure does not vary outside predetermined limits.

[044] In one aspect, a total available superheat coil area per reactor cross sectional area (ft 2 fr 2) is about 1 to about 7, in another aspect, about 2 to about 6, and in another aspect, about 3 to about 5. The superheat coil area (ft ) per heat removed by the superheat coils (Kcal) per metric ton of acrylonitrile produced is about 275,000 to about 475,000, in another aspect, about 300,000 to about 400,000, and in another aspect, 325,000 to about 375,000.

[045] In another aspect, a total available saturated coil area per reactor cross sectional area

(ft 2 /ft 2 ) is about 8 to about 18, in another aspect, about 8 to about 15, and in another aspect, about 10 to about 13. The saturated coil area (ft ) per heat removed by the saturated coils (Kcal) per metric ton of acrylonitrile produced is about 2,375,000 to about 2,900,000, in another aspect, about 2,400,000 to about 2,800,000, and in another aspect, about 2,500,00 to about 2,700,000.

[046] Although only a few embodiments of this invention have been described above, it should be apparent that many modifications can be made without departing from the spirit and scope of this invention. All such modifications are intended to be included within the scope of this invention, which is to be limited only by the following claims.

Claims

What is Claimed Is:

1. A process for controlling temperature of an ammoxidation reactor, the process comprising:

providing superheated steam to superheat cooling coils disposed in the ammoxidation reactor;

measuring a temperature in the ammoxidation reactor; and

adjusting a flow rate and/or pressure of superheated steam to the superheat cooling coils to provide an increase or decrease in the temperature in the ammoxidation reactor.

2. The process of claim 1 wherein an amount of the superheated steam provided to the superheat coils is controlled with a bypass valve.

3. The process of claim 2 wherein the bypass valve is configured to increase or decrease an amount and/or pressure of superheated steam provided to superheat coils entering the ammoxidation reactor.

4. The process of claim 1 wherein superheat steam from the superheat coils exiting the ammoxidation reactor is conveyed to a stream turbine.

5. The process of claim 4 wherein steam conveyed to the steam turbine has a temperature of about 300 °C to about 400 °C.

6. The process of claim 1 wherein the process is effective for maintaining a reactor temperature of about 200 °C to about 400 °C.

7. The process of claim 1 wherein the reactor temperature is controlled without substantially changing the flowrate of propylene being fed to the ammoxidation reactor.

8. The process of claim 7 wherein the flowrate of propylene to the ammoxidation reactor is effective for providing a ratio of air to propylene of about 9 to about 9.5 and a ratio of ammonia to propylene of about 1 to about 1.5.

9. The process of claim 1 wherein the process includes providing saturated cooling coils disposed in the ammoxidation reactor and providing saturated steam to the saturated cooling coils.

10. The process of claim 9 wherein both the saturated steam charged into the saturated cooling coils and the superheated steam charged into the superheat cooling coils are derived from a common steam drum in which the saturated steam and superheated steam are present in equilibrium with one another.

11. The process of claim 10 wherein a pressure inside the steam drum is increased or decreased in response to the measured ammoxidation reaction temperature.

12. The process of claim 1, wherein the superheat cooling coils are effective for providing temperature control within about 5 °C of a desired reaction temperature.

13. The process of claim 9, wherein the saturated cooling coils are effective for providing temperature control within about 10 °C of a desired reaction temperature.

14. The process of claim 1, wherein a total available superheat coil area per reactor cross sectional area (ft 2 /ft 2 ) is about 1 to about 7.

15. The process of claim 14, wherein the superheat coil area (ft ) per heat removed by the superheat coils (Kcal) per metric ton of acrylonitrile produced is about 275,000 to about 475,000.

16. The process of claim 9, wherein a total available saturated coil area per reactor

2 2

cross sectional area (ftVfr) is about 8 to about 18.

17. The process of claim 16, wherein the saturated coil area (ft ) per heat removed by the saturated coils (Kcal) per metric ton of acrylonitrile produced is about 2,375,000 to about 2,900,000.

18. A process for controlling temperature of a reaction occurring inside an ammoxidation reactor, the process comprising:

removing a portion of excess heat being removed from the ammoxidation reactor by indirect heat exchange between the hot gases produced by the ammoxidation reaction and superheated steam passing through superheat cooling coils;

measuring a temperature in the ammoxidation reactor; and

19. The process of claim 18 wherein an amount and/or pressure of the superheated steam provided to the superheat coils is controlled with a bypass valve.

20. The process of claim 19 wherein the bypass valve is configured to increase or decrease an amount and/or pressure of superheated steam provided to superheat coils entering the ammoxidation reactor.

21. The process of claim 18 wherein superheat steam from the superheat coils exiting the ammoxidation reactor is conveyed to a stream turbine.

22. The process of claim 21 wherein steam conveyed to the steam turbine has a temperature of about 300 °C to about 400 °C.

23. The process of claim 18 wherein the process is effective for maintaining a reactor temperature of about 200 °C to about 400 °C.

24. The process of claim 18 wherein the reactor temperature is controlled without changing a flowrate of propylene being fed to the acrylonitrile reactor.

25. The process of claim 24 wherein the flowrate of propylene to the ammoxidation reactor is effective for providing a ratio of air to propylene of about 9 to about 9.5 and a ratio of ammonia to propylene of about 1 to about 1.5.

26. The process of claim 18 wherein a portion of excess heat from the ammoxidation reactor is removed by indirect heat exchange between hot gases produced by the ammoxidation reaction and saturated steam passing through saturated cooling coils;

27. The process of claim 26 wherein both the saturated steam charged into the saturated cooling coils and the superheated steam charged into the superheat cooling coils are derived from a common steam drum in which the saturated steam and superheated steam are present in equilibrium with one another.

28. The process of claim 27 wherein a pressure inside the steam drum is increased or decreased in response to the measured ammoxidation reaction temperature.

29. The process of claim 18, wherein the superheat cooling coils are effective for providing temperature control within about 5 °C of a desired reaction temperature.

30. The process of claim 18, wherein the saturated cooling coils are effective for providing temperature control within about 10 °C of a desired reaction temperature.

31. The process of claim 18, wherein a total available superheat coil area per reactor cross sectional area (ft 2 /ft 2 ) is about 1 to about 7.

32. The process of claim 31, wherein the superheat coil area (ft ) per heat removed by the superheat coils (Kcal) per metric ton of acrylonitrile produced is about 275,000 to about 475,000.

33. The process of claim 26, wherein a total available saturated coil area per reactor

2 2

cross sectional area (ftVfr) is about 8 to about 18.

34. The process of claim 33, wherein the saturated coil area (ft ) per heat removed by the saturated coils (Kcal) per metric ton of acrylonitrile produced is about 2,375,000 to about 2,900,000.

35. A cooling system for an ammoxidation reactor comprising:

superheat cooling coils disposed in the ammoxidation reactor, the superheat cooling coils configured to receive superheated steam from a steam drum;

a bypass valve configured to allow superheated steam to bypass the reactor;

a reactor temperature sensor; and

a controller configured to receive a signal from the reactor temperature sensor and control operation of the bypass valve.

36. The cooling system of claim 35 further comprising saturated cooling coils disposed in the ammoxidation reactor, the saturated cooling coils configured to receive saturated steam from the steam drum.

37. The cooling system of claim 36 wherein the same steam drum is used as a source for saturated steam and superheated steam.

38. The cooling system of claim 35 further comprising a turbine steam supply conduit.

39. The cooling system of claim 38 further comprising a turbine steam supply conduit temperature sensor.

40. The cooling system of claim 39 wherein the turbine steam supply conduit temperature sensor is configured to provide a signal to the controller and control operation of the bypass valve.

41. The cooling system of claim 35 wherein a total available superheat coil area per reactor cross sectional area (ft 2 /ft 2 ) is about 1 to about 7.

42. The cooling system of claim 36 wherein a total available saturated coil area per

2 2

reactor cross sectional area (ftVfr) is about 8 to about 18.