SA516371955B1 - Cooling Coil Design for Oxidation or Ammoxidation Reactors - Google Patents

Abstract

The cooling coils used in a commercial oxidation or ammoxidation reactors can be made more closely packed by providing the individual courses defining the cooling coil in a transverse arrangement rather than a linear alignment. Such cooling coils being part of a cooling coil assembly which comprise a support beam for each cooling coil, each support beam being arranged above its respective cooling coil, the cooling coil assembly further comprising cooling coil hangers arranged to suspend each cooling coil from its respective support beam. Fig. 9

Description

Cooling Coil Design for Oxidation or Ammoxidation Reactors Full Description Background The various processes and systems an atl acrylonitrile and methacrylonitrile are known. Conventional processes typically include extraction and purification of acrylonitrile 8006/methacrylonitrile produced by direct reaction of hydrocrion 07 purified from the propane comprising group; propylene or isobutylene ; ammonia and OXygen in the presence of a catalyst. For example, in the commercial manufacture of acrylonitrile, propylene reacts with ammonia and oxygen soba according to the following reaction scheme: CH2=CH-CH3 + NH3 + 3/2 02 — CH2=CH-CN + 3 00 0 carry out that process; which is commonly referred to as ammonia-oxygen ammoxidation ¢ in the gas phase ammoxidation at elevated temperature (eg; 3° sie to 4 80° (Age) in the presence of an ammonia-oxygen ammoxidation catalyst with a layer A suitable fluid bed Figure 1 shows a typical acrylonitrile reactor used to carry out this process 5 As shown herein Reactor 10 includes reactor shell 12 air grid 14" sprinkler feed sparger 16 (cooling coils 18 and cyclones 20). During normal operation, process air is charged into the reactor 10 through an air inlet 22 while a mixture of propylene and ammonia is charged ammonia in reactor 0 through a feed sprinkler 16. The flow rates of both are high AS Lay to fluidize a bed 0 24 of the dallas catalyst with ammonia and oxygen ammoxidation in the inner space of the reactor where the ammonia and oxygen treatment takes place catalytic

ammoxidation of propylene and ammonia to acrylonitrile .acrylonitrile The product gases produced by the reaction exit reactor 10 through the reactor effluent outlet 26. Before this occurs; they pass through cyclones 5 20; Which removes any ammonia and oxygen catalyst These gases can be captured to return to the catalyst bed 24 through through diplegs 25. The ammonia treatment is a highly exothermic process; Therefore a cooling coil assembly 18 is used to remove excess heat and thus keep the reaction temperature at an appropriate level. in that regard; Figure 2 schematically shows the design of a conventional cooling coil assembly 18 where 0 is used for that purpose. Figure 2 is a partial axial cross-sectional view of reactor 0. It shows one set of cooling coils in the cooling coil assembly of reactor 10; This set of cooling coils consists of three separate cooling coils; cooling coil 42; Cooling coil 44 and cooling coil 46. Cooling coil 42 includes an inlet Jane 48 to receive ele cooling and an outlet 50 to discharge this cooling water after heating and partial conversion to steam. similarly»; Refrigeration coil 44 includes inlet 52 and outlet 54; While the refrigerant coil 46 includes an inlet 56 and an outlet 8. As shown in Figure 2; The cooling coils 42 44 and 46 are each determined by a series of vertically oriented cooling coil turns 57; Each cycle consists of a pair of elongated cooling channels; Overlapping 60 where they are connected to each other at their bottoms by means of a non-rotating device 62. The sequential cooling coil cycles 57 are also connected together at their tops by means of devices 0 in a non-upper circular way 63 so that a continuous flow path is formed from the inlet to the outlet with each special cooling coil . Figure 3 is a top view of the refrigerant coil assembly 18 shown in Figure 2. As will be realized from Figures 2 and 3; The 42 44 and 46 refrigeration coils form a group of refrigeration coils where they are in common plane; any; Each of them is located in a common vertical plane. As can also be seen in Fig. 5 3 the refrigerant coil assembly 18 consists of several sets of refrigerant coils; where all set

of these refrigeration coils shall be equipped with a dale parallel to and (optionally) evenly spaced from; each other. Furthermore it; Lad can also be seen in Figure 3, although many of the coil assemblies in this coil assembly include three different coils; Other cooling coil assemblies include two or four cooling coils; While the two cooling coil groups contain only one api file.

Figure 4 is an extended top view taken on line 4-4 of Figure 2 showing more detail of the special structure of the cooling coil assembly 18 than Figures 2 and 3. particulary; Figure 4 is a schematic view in which only 63 coils are shown in rotation, not overhead

cooling.

0 As shown in Fig. of Refrigeration coil 61 has inlet 35; A supply line 64 connects an inlet 35 to the top of the first coil cycle (not shown) to the coil 61 and a series of topless-turn fittings 63 to connect successive coil turns to the coil together. As also shown in that figure; Each of these elements is » i.e.; All of the fittings are roundly no overhead 3 plus supply line 64 in a common level; any; They are all located in the same vertical plane

5 Subscriber 0. Further; from Figures 2 and 3; It will also be clear to Load that the remaining elements in this cooling file ie; Vertically oriented cooling conduits 60 that make up each cooling coil course 57 and rotary, bottom-linked fittings 62; It also lies in that common vertical plane. in the special form shown; Each equipment is supported in the form of a topless rotation 63 from the bottom by a deja support (TO) as it is received in the curve

The internal 0 specified by each device is not. Subsequently; The full weight of each refrigeration coil is supported including each of its component shal (ie 63 vertically oriented ducts 60 and bottomless revolving 62) as well as the entire contents of the Caley cooling (ie elo circulating cooling) by its support beam 70.

As can also be seen in Figure 4; A suitable walkway 74 shall be provided between each coil and another at a height that is at or near overhead turn fittings 63 to provide easy access and support to any maintenance personnel who may be needed for periodic inspection and/or repair of the coils. Figure 5 is another schematic view showing how to control the different cooling coils in the cooling coil assembly 18. In this respect; There is a common practice during operation of a conventional acrylonitrile reactor 10 to "peat" the coolant coils; ie, periodically stop dang that restart each coolant independently and in sequence. Most commercial ammonia catalysts result in sublimation of molybdenum which It naturally deposits as scale on the outer surfaces of the cooling coils over time.Since this molybdenum scale 0 negatively affects the efficiency of the cooling coil, it is necessary to flush these molybdenum scales occasionally AY to keep the coils working properly. Moderately; this is effected by periodically stopping and then restarting each cyt coil With this stop/restart procedure a non-insignificant mechanical shock is induced to the cooling coil due to the wide temperature fluctuations that the cooling coil experiences as a result of the shutdown and then restart 5 Such mechanical shock is in most cases sufficient to dislodge at least some of the molybdenum scales that may have deposited on the surfaces of the cooling coil and thus restore at least some of the heat transfer capacity of that coil. Gale is stable over extended periods of time. to supply cooling water to independent cooling coils; The structure shown in Figure 5 is used sparingly. As shown cds the inlet 35 of the cooling coil 61 is in fluid contact with head 0 of the process water inlet 80; the height of which is typically found below round rather than overhead fixtures 63. Similarly; The outlet 65 of the cooling coil 61 is in fluid contact with the process water outlet head 62; whose height is typically found above a turn-up not-upper-equipped 63. Moderately; The Jade water inlet header 80 and outlet header 82 take the form of large channels; cdl aia is oriented horizontally as it completely surrounds reactor 10. Periodic stop and restart for each 5 cooling coils independently moderately through special shut-off valve 84 linked

At the inlet, Cale 35 inlet, this cooling, where in most designs it is an opening valve-

A simple shut-off as opposed to a control valve capable of precise control of the fluid flow rate.

also notes; That the shut-off valve 84 be at least a valve in the cooling coil 61 between

Inlet header Jase process water 80 and outlet header Process water 82.

It means that; The refrigerant coil 61 is configured without any additional valve or OAT flow control device

In particular, without a flow control valve associated with the refrigerant coil outlet 65. This is because that valve

Additional operation is not necessary to achieve the required operation and control of the cooling coils in the manner described

above. in addition to"; Removing the Load outlet flow control valve eliminates the need for a valve

auxiliary safety Which could be otherwise necessary if the outlet 0 flow control valve is used.

Keeping the acrylonitrile reactor at or near its reaction temperature (All) is in OS of all

All parts of the reactor, in addition to from one area to another inside the reactor, is important for the efficiency of the reactor

good. Furthermore it; A good cooling coil design is important since the rate at which it can

Heat withdrawal from the reactor is often a rate-limiting step which determines the maximum power at which the acrylonitrile reactor can be operated. In addition, it can lead

Poor coil design and/or operation leads to excessive coil wear; Which requires a previous repair

premature This is considered very expensive.

US Patent No. 5,520,891 relates to; and European Patent No. 0,776,692 and patent

EP No. 1,563,900 design of the cooling coil inside reactors. EP No. 1,563,900 describes an alternate cooling coil design within a reactor where the cooling coils are vertical

Basically and not transversely from wall to wall.

Accordingly, there is a continuous need for improvements in the design and operation of the acrylonitrile reactor cooling coils

commercial; Not only to improve reactor efficiency; But also to reduce the erosion of the canal, which thus leads to

Reduce downtime and repair costs.

Examples of reactor coolant assemblies used in a chemical process include reactor and coolant assemblies discontinued by US Pat. 5,520,891; and European 0776692 and European 1563900. US 5520891 discloses a cross-flow fixed catalyst bed reactor. The flow in the reactor listed in US Patent 5520891 is horizontal (ie from side to side) through/through the reactor. The parts of the USP5520891 reactor closest to the feed inlet (where the reaction is most intense) have a greater density of the cooling tubes (i.e., the distances between the tubes are closer) compared to the density or distance between the cooling tubes near the discharge side of the reactor. In addition, the reactor in US Patent 5520891 is provided with a series of baffles perpendicular to the flow path in the reactor surrounding a line of parallel 0-cooler tubes. Finally, US Patent 5,520,891 reveals a reactor equipped with distribution and assembly openings inside the reactor that connect the cooling tubes. EP 0776692 discloses a fluid bed reactor for the production of halosilanes or orgastosilanes 5 M.. The reactor presented in EP 0776692 uses cooling coils 'backsliding' on a support column and where each tube with a JC 5 heat exchange element is seamless in a column Support. EP 5 1563900 also uses an alternate cooling coil scheme in the reactor where the cooling coils are vertical in nature and not the width of the wall-to-wall reactor. Nothing in this documentation discloses or suggests the unique features or solutions offered by the cooling assemblies described herein." General description of the invention Ga, for that invention; shal makes a set of improvements to the design and operation of the coil assembly | 0 109a00 used in an oxidation reactor or ammonia and oxygen treatment or ammoxidation reactor 0008000 typical “Ji” commercial acrylonitrile reactor. As a result; Not only improving reactor efficiency but; add to that; The useful life of the cooling coil assembly is extended. Accordingly »in one embodiment » that invention provides a cooling coil assembly for the removal of excess heat generated 5 by an oxidation reactor or dallas with ammonia and oxygen; The cooling coil assembly includes coils

multiple cooling; Each cooling coil includes multiple coil cycles connected to the fluid together in series until a cooling water path with cooling water inlet and outlet cays is specified Each cooling coil cycle defines a vertically oriented coil cycle level; Where each cooling coil extends from inside the reactor towards the periphery of the reactor along a special vertically oriented primary cooling coil level; Whereas, at least some of the cooling coil cycles are equipped in at least one cooling coil so that the coil cycle levels

Its cooling is transversal at the level of the primary cooling coil of this cooling coil. In addition” in the SU ¢ embodiment this invention provides a cooling coil assembly to remove excess heat generated by an oxidation reactor or dallas with ammonia and oxygen; The cooling coil assembly includes one or multiple cooling coils; Each refrigerant coil defines an ele refrigerant flow path to carry the refrigerant ele through;

0 cooling water inlet and cooling water outlet; Each cooling coil also includes a cooling water shut-off valve associated with its cooling water inlet; Each refrigerant coil is also devoid of a valve to control the slo flow of refrigerant that passes through its refrigerant water outlet; The lengths of at least some of the cooling water flow paths differ from one another. in that feature; The number of cooling coils is chosen to provide an average percentage of cooling water converted to vapor of about 9615 or less.

5 In addition» in a third form; This invention provides a cooling coil assembly to remove excess heat generated by Jolie oxidizing or treating with ammonia and oxygenation of it (has) The cooling coil assembly comprises one or multiple cooling coils; each cooling coil comprises multiple fluidized coil circuits connected together in series until a cooling water passage is specified having a cooling water inlet passing through the reactor wall and a capi water outlet where the cooling water inlet includes cooling coil inlet fittings connected

0 closely to the reactor wall and Jala thermal sleeve (ga) the cooling water inlet fittings, whereby the outer diameter of the thermal sleeve is smaller than the inner diameter of the cooling coil inlet fittings so that a thermal space is determined between them. In another embodiment this invention is presented Cooling coil assembly to remove excess heat generated by an oxidation reactor or treated with ammonia and oxygen; the cooling coil assembly includes cooling coils

5 multiple; Each coil includes a series of coil cycles, including a first cycle at the start of the coil

the chain and a final cycle at the end of the chain; The multiple refrigerant coil turns are connected to the fluid together until a cooling water passage is identified that has a cooling water inlet and a water outlet cay The cooling coil assembly also includes a coolant inlet header in fluid contact with the first cycle in each refrigerant and a coolant outlet header in fluid contact with The last cycle of each cays Each cooling coil also includes a cooling water outlet channel that connects the last cycle of this cooling coil to the cooling water outlet head; Where the height of the outlet head of the cooling coil is less than the height of the outlet conduit of the cooling coil of each cooling coil. BRIEF EXPLANATION OF DRAWINGS This invention may be more easily understood by referring to the following drawings therein: Figure 1 shows a conventional commercial acronitrile reactor for carrying out ammonia-oxygenation of 0 propylene and ammonia into acrylonitrile; Figure 2 is a schematic view showing the structure and design process of a conventional cooling coil used in a conventional commercial acronitrile reactor from Figure 1; Figure 3 is a top view of the conventional cooling coil design from Figure 2; Figure 4 is a top view similar to Figure 3 showing more detail of a conventional coil 5 design than Figure 2; Figures 5 is a schematic view similar to Figures 1 2 but as a single cooling coil 61 as well as its mode of operation; Figures 6 and 8 are schematic illustrations of a first feature of that invention whereby the cooling coils of a conventional commercial acronitrile reactor are more closely packed than in a conventional design; 0 FIGURE 7 is a top view similar to Figures 2 and 4 showing the top-only swivel fittings 63 of a refrigeration coil of the conventional design of those of JIC SY including the alignment of the top-down swivel fittings with each other; Figure 7 is taken on line 7-7 of Figure 5;

— 0 1 — FIG. 9 is a schematic illustration of a coil suspension element that can be used to suspend the coils from FIG. 6 9 8 from their support structure; Fig. 10 is a schematic illustration of another feature of that invention whereby a thermal sleeve is used to protect the joint between the inlet of the cooling coil and the reactor wall through which the inlet of the cooling coil passes; Figure 11 is a schematic illustration of another feature of that invention, whereby (sale) is placed

The outlet head to receive the cooling water and vapor from the cooling coils to a position where it is below the tops of those cooling coils. Detailed Description: In accordance with the first feature of that invention; A new equipment for cooling coils is being configured, allowing coils to be filled

0 cooling inside the reactor to be increased. As a result, the total surface area available by the cooling coil assembly as a whole can be effectively increased; Which in turn leads to a better total control over the operation of the cooling coil, at least in some cases »; An increase in the total reactor capacity. This feature is illustrated in Figure 6 where it is a schematic view similar to Figure 4; In it, the order of supply is clarified in the form of rotation, not the upper 63, with each cooling coil 61, and its arrangement in relation to

5 The catwalks 74 and the support beam 70 with the cooling coil assembly. See also Figure 7, which schematically shows the arrangement of winding turns in the traditional design of Figures 2-3; 4 and 5. By comparing it with Figure 8; Which is a schematic illustration similar to Figure 7 but showing the order of cooling coil cycles in the innovative design of Figure 6.

As shown in Fig. 6 the topless round fittings 63 are arranged on the refrigerant coil 61 in a compensating relationship with respect to each other instead of a common plane relationship as shown in Fig. 4 in the conventional design as shown in Fig. 4; Refrigerant coil 61 extends from within reactor 10 to the periphery of reactor 10 (ie, from R location to location 5) along vertically oriented plane 0. For simplicity’s sake, the vertically oriented plane is indicated—vertically

D oriented plane in this document is in the plane of the primary cooling coil of the cooling coil 61. As also shown in Fig. 4; Each of the main elements of the refrigeration coil 61 (ie, each of the vertically oriented cooling ducts 60 plus each of the bottomless swivel fittings 62 and the topless swivel fittings 63) are in common plane »; any; They are all aligned with the plane of the vertically oriented primary cooling coil, D, meaning that their centers and axes lie in that plane. This is also illustrated schematically in Figure 7, where it is shown that the cooling water channels 60 in addition to the fittings in a circular shape, not the bottom one 62, in the cooling coil cycles 57, are aligned with each other, meaning that their centers or axes are located in the plane of the primary cooling coil directed vertically joint 0. In addition till then; As can also be seen in Figure 4; 74 walking paths are also fitted between and parallel to those 0 basic elements. in a design modified for that feature of the invention; however; At least some of the coil turns 57 shall be fitted with at least one coil transverse to the plane of the vertically oriented primary coil in which the coil is situated; in full. mildly; At least each of the 57 Caley refrigeration coil cycles is equipped in this way; While some models have both cooling coil cycles in most or even 5 most or even both cooling coils are equipped this way. This design is illustrated more comprehensively in Figure 8; which shows that the cooling water channels 60 and the lower fittings 62 in each cooling coil cycle 57 of that design are each located in their respective cooling coil cycle ©; which is fitted with an angle Bala© with respect to the vertically oriented primary coil plane 0 in which the coil 61 is located; in full. The alpha acute angle can be any desired angle. In one feature the angle is between about 30° to about 60°; And in another aspect between ss 40°C to about 50°C. As can also be seen in Figure 6; The support beams 70 bearing the full weight of the cooling coils 1 and their contents are placed above the fittings in a U-turn 63 rather than under them in a U-turn as in the conventional design of Figures 2; 3; 4 and 5. in addition to; As described in

Figure 9; Suspension supporting elements suitable for the suspension of each equipment shall be fitted with a no-turn 63 of its associated support beam 70. A first advantage of a design modifying this feature of the invention is that the refrigerant coil turns 57 can be packed more closely than with a conventional design. This allows the effective surface area of the cooling coil assembly of this design to be increased relative to the conventional design; This in turn achieves greater cooling capacity and greater reactor temperature control compared to the conventional design. The coolant coil design described in this document provides more coolant cycles per meter of reactor diameter. in that feature; The coil design described herein is efficient to provide oa 40 to about 60 cooling coil cycles per meter of reactor diameter.” Ag is another characteristic; About 45 to about 55 0 cooling coil cycles per meter of reactor diameter. A second advantage of this crippled design is that the mechanical stress placed on the metallic elements that make up each cooling coil in that design as a result of shutdown and periodic restart can be better accommodated using that design compared to the conventional design. This is due to the fact that in the innovative design, the upper no-spinners 63 are suspended by 5 ce suspension elements and are additionally equipped transversely on the support beam 70. Accordingly; When the innovatively designed cooling coils expand and contract in response to temperature changes; Less pressure is transferred to these cooling coils than in other cases. This is because a large part of that expansion and contraction occurs transversely on these support beams; Also, because the suspension elements act as a crossbar, they absorb the volume changes and associated movements that occur between the cooling coils and these 0 support beams. Accordingly; As a result of this design modification it is not only possible to increase the cooling capacity provided by a cooling coil assembly without the auxiliary padding required to accommodate that assembly (namely in a number of tracks and support beams) but in addition it is also possible to remove; or at least significantly reduce to; 5 Refrigeration coil failure and associated maintenance costs that appear naturally due to mechanical stresses on the cooling coils as a result of shutdown

and periodic restart. as indicated; The design described in this document provides more files. Sag Spins more files with less frequency. According to a second feature of that invention; The cross-sectional areas of the flow paths within the different refrigerant coils of the innovative coil assembly shall be adjusted so that the amount of cooling water converted to steam in each refrigerant coil assembly has an average of about 9615 or less” in the coal aspect of about 10 to about 9015. Desirably ; Such cross-sectional areas shall be chosen so that the amount of cooling water converted to steam in each of the cooling coils in this cooling coil assembly varies from one to another le not more than 965; desirable le no more than 964 ; no more than 3 no more than 962 or no more than 961; Based on the total amount of cooling water passing through the cooling coils. As indicated [eal] the cooling coil assembly can include cooling coils where each cooling coil has different numbers of cooling coil cycles. For example, a coil assembly can include coils where most coils have multiple coil cycles (eg 6 coil cycles) and some coils have only one coil cycle. 5 Removing the coils affects production rates The different numbers of coil turns that can be removed in the coil cycle provide operational flexibility to maintain desired production rates. As can be seen in particular in Figure 2; Not all of the different refrigerant coils in a typical commercial Jolie acrylonitrile reactor have moderately the same number of refrigerant cycles as 7. As a result; Some of these refrigerants have longer flow paths while others have shorter flow paths. This feature can lead to erratic operation of the cooling coils; Because the retention time for cooling water within a longer flow path is naturally greater than the retention time for cooling water in a shorter flow path. as a result; More cooling water in a longer flow path is converted to steam than in a shorter passage. This naturally leads to higher flow velocities within the flow passages (Joh! particularly near its outlet ends. This, in turn, can cause excessive ISB as well as

to Jatt i.e. 0 precipitation and deposition of the minerals and other constituents in the cooling water at those locations. as ad] was indicated above; It is desirable in accordance with that feature of the invention that the amount of steam generated in each cooling coil assembly should have an average of about 91615 or less” in the characteristic of coil about to about B15 means that; It is desirable that the amount of cooling water converted to steam in each cooling coil assembly not exceed about 9615 in coal aspect about 10 to about 9615; from the water feed to this cooling coil assembly. Therefore, according to that feature of the invention; The cross-sectional area of the flow passages JS Cooling Coil is chosen so that; When all shut-off valves 84 are in the open position; The cooling water converted to steam in each pass 0 will be as close as possible to each other at dad where it is about 1615 or less” and in another aspect; about 10 to about 9615. In that aspect; The amount of steam generated is a calculated value. The most cost-effective way to design a commercial acrylonitrile reactor is to manufacture each refrigerant from piping of the same diameter and to control each refrigerant with the same shut-off valve 84; any; Each control valve is identical to the other valves. So; The method (Gla alla wl) selection 5 cross-sectional area of flow passages in each cooling coil to achieve the same water-to-vapor conversion is to place an appropriate flow restriction within each cooling coil; or at least within each refrigerant coil of an all flow passage as desirable at or near its inlet end, its outlet end, or both. The determination of the actual size of each flow obstruction or the relative cross-sectional areas of the flow passages if no flow obstructions are used can be easily carried out through conventional heat reduction calculations 0 by assuming the relative lengths of the different flow passages and therefore the different durations of time that the cooling water will encounter in those passageways. different. A third feature of that invention is illustrated in FIG. 10. In a conventional design such as that shown in FIG. oS the inlet line 64 of refrigerant coil 61 is welded directly to the reactor wall 36 of reactor 0. As noted above;. It is not uncommon to 'cycle' the refrigerant coils in a conventional acrylonitrile reactor 5 by shutdown and then [sale] cyclic operation of each refrigerant independently and in sequence.

when the cooling coil is turned off; Its temperature rapidly increases towards the normal operating temperature of the reactor—about 350°C to about 480°C. after that; When [ale] the cooling coil is actuated by contact with additional quantities of canal water its temperature drops to or near the boiling point of that cooling water almost instantly. This drop in temperature can cause significant thermal stress on the cooling coil [0] particularly when its inlet line 64 is welded to the reactor wall 36. Over that period the thermal stress can lead to mechanical failure at that location . la that is a feature of the invention.” This AS ad) is avoided by installing a thermal sleeve 6 at the location where the inlet line 64 of the cooling coil 61 is transverse to the wall of reactor 0 36 of reactor 10. As shown in the figure 10) The thermal sleeve 59, which connects with the inlet line of the cooling coil 64, is received at the inlet fitting of the cooling coil 33, which passes through and is welded to the wall of the reactor 36 of reactor 10. The outer diameter of the thermocouple 59 is slightly smaller than the inner diameter of the inlet fitting of the cooling coil 33 until a thermal space 75 is defined between it which is kept by spacer rings 77. The outlet flange 73 is not with the heat sleeve 59 welded 5 or otherwise permanently attached to the cooling coil fittings 33 and is therefore free to move, axially, with respect to the coil fitting By using this structure, any thermal stresses at the mechanical joint between the inlet line of the cooling coil 64 and the reactor wall 36 that could otherwise occur are mitigated by the large temperature changes that occur within the cooling coil 61 when it is turned off and back on by the expansion and contraction of the sleeve. 0 thermal 59. As a result, malfunctions are avoided a The mechanics of the cooling coil 61 at the location when it is largely transverse to the reactor wall 36 of reactor 10. According to another feature also of that invention; The cooling water outlet header which is provided to receive the cooling water and vapor exiting each cooling coil is repositioned to a location below the outlet line of each cooling coil and the outlet header. in one of the features; The refrigeration slo outlet is repositioned to a position 5 which is below the refrigeration coil cycle peaks of each refrigerant.

As shown in Figure 5; with traditional design; The head of the cooling water outlet 82 shall be placed above the cooling water outlet line 79 in addition to the fittings in a round shape No. 63; which determine the peaks of wll cycles 67' 69 and 71. As indicated above; The cooling coils of a conventional commercial acronitrile reactor are periodically shut down and then restarted to remove any molybdenum scale 5 scale that may be deposited on their outer surfaces. when the cooling coil is turned off; Any remaining cooling water inside evaporates quickly because the temperature inside the acrylonitrile reactor is very high. When this occurs due to the absence of an outlet valve connected to the outlet line 79, gravity causes the cooling water in the outlet header 82 to flow back to the stopped refrigerant coil through the outlet line of the refrigerant coil 79. This causes additional amounts of cooling water to continue evaporating 0 and thus turns to vapor inside the cooling coil. Cooling water moderately contains dissolved minerals as well as additional process chemicals. when the cooling coil is turned off; These metals and process chemicals tend to “sait” and deposit on the inner surfaces of canal coils, especially in rotary rather than bottom 2 installations. The amount of such deposits can be significant”; Especially if the cooling coil has been turned off for a long time; This allows significant additional amounts of cooling water to flow from the cooling water outlet header 82 back into and thus evaporate from this stopped cooling coil. by the time; This can cause the flow passage cross-sectional area within the capil coil) to be significantly reduced at these locations; This greatly increases the flow rate of the cooling water that passes through these locations. This in turn can lead to a large JST on the coils at those locations and thus 0 premature coil failure. According to that feature of the invention; This problem is avoided by repositioning the cooling water outlet head 84 to a height where it is below the outlet line 79. In a feature; The outlet head is positioned below the top of the last least cooling coil cycle; More desirable below the last cycle of the majority or even all of the cooling coils. In the coal attribute the header of the 5 output didd tops of all the cooling coil cycles in one coil is placed on (JAY) most desirable below

— 1 7 —

Peaks of all cooling coil cycles in all cooling coils. See Figure 11; which is illustrated schematically

those traits.

using that equipment; Backflow of additional amounts of cooling water from the outlet head is prevented

Cooling water 32 in essentially all-gravity stopped cooling coil; Inasmuch as the cooling water outlet line 79 is placed in one of the clad fittings in the form of an overhead swivel 63; also

far above the head of outlet 82 to enable gravity to move any significant amount of cooling water

Back inside the stopped cooling coil.

Although only simple examples of that invention are described above. It must be shown that can be made

Many modifications without deviating from the content and scope of that invention. All of those are to be included

0 the modifications within the scope of that invention; which is determined by the following safeguards.

Claims (1)

protection elements 1- A cooling coil assembly [18] to remove the heat generated by the Jolie cooling coil The cooling coil assembly includes “[10] ammoxidation with ammonia and oxygen dallas assembly [18] on multiple cooling coils; Each refrigeration coil includes refrigeration coil cycles manifold [57] connected by fluid to each other in series until a cooling water passage is specified 5 It has a cooling water inlet and a cooling water outlet; Each cooler cycle [ST] determines the coil cycle level dul vector) in which each cooling coil extends from inside the reactor [10] towards circumferential reactor [10] along the relevant vertically oriented precooler plane [0]; Where some of the cooling coil cycles are arranged in the cooling coil so that they are Their [Q] cooling coil course levels are shown at the 0 primary cooling coil levels of said cooling coil <[D] and It includes the cooling coil assembly [18] as well as the support beam [70]. For each cooling coil each support beam [70] is arranged over its cooling coil The cooling coil assembly [18] also includes coil holding elements Cooling is provided to suspend each cooling coil from its support beam [70]. 2. Cooling coil assembly [18] in accordance with claim 1; even it's happen Arranging all [ST] cooling coil cycles in one COI cooling coil so that they are levels Its [Q] cooling coil course is cross-sectional at the initial cooling coil 0 level [0] of said coil. 3- cooling coil assembly [18] 12 of protection element 1; Cua is done Arrange all refrigeration coil cycles [57] in all refrigeration coils so that the refrigeration coil cycle levels are Its cooling coil is transversal at the initial [Q] cooling coil course [0] of said cooling coil. 5 — 9 1 — 4— Gig [18] cooling coil assembly for claim 1; The cooling coils are generally parallel to each other. 5- Cooling coil assembly (a [18] cooling coil assembly for protection element 1; the cooling coils include from 40 to 60 cooling coil cycles per meter of reactor diameter [10]. 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