FR2791055A1 - PROCESS AND UNIT FOR PRODUCING VINYL CHLORIDE THERMAL CRACKING OF 1,2-DICHLOROETHANE - Google Patents

Abstract

The invention concerns a method and a unit, both improved, for producing vinyl chloride (monomer: VCM) by thermal cracking of 1,2-dichloroethane (DCE). Said improved method is implemented with recovery of calories on the gaseous effluent (G) derived from cracking. The method is characterised in that said gaseous effluent (G) derived from cracking is transferred via at least a transfer line without decrease in its mass rate and said calories are recovered by at least a fluid cooler (L) circulating around the transfer line and around at least one of said transfer lines of said gaseous effluent derived from cracking, in a space provided between said transfer line(s) and a sleeve (11) arranged around the latter, said recovery of calories being carried out in conditions wherein the fluid cooler (L) remains liquid and wherein said gaseous effluent (G) remains substantially in gas form.

Description

The present invention relates to improved methods and units of

  production of vinyl chloride (monomer: VCM) by thermal cracking of

1,2-dichloroethane (DCE).

  Said cracking of DCE, to produce VCM, is a per se known method, implemented on several industrial sites. In the context of the present invention, the Applicant proposes to make an improvement to the

  level of recovery of calories on the gaseous effluent from cracking.

  In order to situate the context of the invention, it is proposed,

  afterwards, to give, at first, some general indications on said process of cracking of the DCE and, in a second stage, details on this subject, with reference to FIGS. 1 and 2 appended to the present text, figures which illustrate schematically, respectively, a low-pressure DCE cracking process (6 to 12 bar rms at the furnace outlet) and a high-pressure DCE cracking process (> 12 bar rms at the furnace exit) (processes performed without

  recovery of calories on the gaseous effluent directly from cracking).

  In said appended FIGS. 1 and 2 as well as in the other FIGS. 3 to 7 also appended and commented further in the present text (FIGS. 3 to 7 which illustrate the invention), referenced from I to 7 the seven successive steps. of the method and their associated device, specifying by an index the

  variant embodiment illustrated.

  Vinyl chloride monomer (VCM) is thus produced on a large scale by thermal cracking of 1,2-dichloroethane (DCE); the cracking process comprising the following steps: 1. pressurizing the liquid DCE (6-30 bar) by a pump; 2. preheating the liquid DCE; 3. vaporization of preheated liquid DCE; 4. overheating of vaporized DCE; 5. partial conversion of DCE (45-65%) to VCM according to the reaction: DCE -> VCM + HCI, by thermal cracking at temperatures between 400 and 500 ° C; 6. cooling and washing the cracked gas (containing VCM, HCI, DCE) by direct injection of a mixture of VCM + liquid DCE and / or by spraying with such a mixture. The washing of the cracked gas is intended to remove the particles and heavy products contained in said gas and thus minimize the fouling of downstream equipment. The temperature of the gas, at the end of this operation, is variable, depending on the operating pressure; 7. Complementary cooling of the washed gas (containing VCM, HCI, DCE) at a temperature, depending on the operating pressure. A fraction of the VCM + DCE condensed at this stage is used for the injection / watering of the previous step 6. The mixture HCI, VCM, DCE thus produced in the cracking section is then separated into its components (HCI, VCM and DCE) by multiple distillations with: recovery of the HCI, which can be used for the production of DCE by way of oxychlorination, - recovery of DCE (not cracked), for recycling as raw material,

- and recovery of the VCM product.

  The means or devices, most commonly used, to put

  the seven steps of the method listed above are explained below.

  Said means are referenced n, in the figures, with n which identifies step I to 7

  concerned and i the illustrated variant.

  Thus, step 2 of preheating the liquid DCE (pressurized by the pump 1) can it be implemented in three types of device a, b and c,

  referenced respectively 2a (see Figure 2), 2b (see Figure 1) and 2c (not shown).

  What is stated: 2. preheating the liquid DCE a - exchanger supplied with low pressure water vapor or other heat transfer fluid, b - exchanger heated by an intermediate stream in the cooling / distillation section, c - beam in the zone The convection oven of the cracking oven (heat recovery on flue gases), o30 Similarly, we have: 3. vaporization of the preheated liquid DCE a-reboiler kettle type fed with water vapor or other coolant, b-column of vaporization with reboiler (s) type kettle 3b 'or thermosiphon supplied (s) with water vapor or other coolant, c - bundle in the convection zone of the cracking furnace, d - independent furnace, 4. superheating of the vaporized DCE a - beam in the convection zone of the cracking furnace, b - beam in the direct heating zone ("radiation") of the cracking furnace, 5. partial conversion of the DCE to one or more tubular bundles placed in the zone of direct heating ("r adiation ") of the cracking furnace; the heat required for the reaction is provided by burners implanted either in the walls or in the hearth of the furnace; 6. cooling and washing of the cracked gas with mixing with direct injection of a VCM + liquid DCE stream into the furnace; hot effluent followed by a separation column, b-column of watering using a current VCM + DCE liquid, c - T of mixture combined with a column of watering, 7. cooling of the washed gas a - exchanger fed with a process stream (see 2b), b-water cooler,

c - refrigerant.

  The low temperature level of the washed gas does not allow at this stage (step 7) a considerable recovery of heat. Most of

  said heat is lost in the air and / or the cooling water.

  According to the prior art, the cracking of the DCE has therefore been implemented, as described above, without recovery of calories on the gaseous effluent directly from the cracking. However, it has also been recommended, according to said prior art, the intervention of two different types of device for recovering

such calories.

  Thus, in the patent CA-B-1,127,669, is it described the intervention of a tubular exchanger for cooling the cracked gas and the use of heat recovered in the process, for: - heating / evaporating directly the column bottoms of the distillation section, - heating a coolant to feed the reboilers of the distillation section, - generating water vapor to feed the reboilers of the distillation section,

  - preheat or vaporise the charge DCE.

  The preferred exchanger consists of a single tubular bundle, in the form of a coil, placed in a cylindrical container. The cracked gas circulates inside the tube, the refrigerant fluid outside said tube, inside said container. In the application EP-A-264 065, it is proposed to involve a heat exchanger of the above type, for the sole purpose of vaporizing the DCE load. Said exchanger is equipped with a charge balloon which ensures both a natural circulation through the shell of the exchanger and a separation of the mixture

  vapor / liquid from said exchanger.

  The devices recommended in these two documents of the prior art are not fully satisfactory. The volume of the cylindrical container required to house the coil-shaped beam is very important and limits the practical use of this type of exchanger. Indeed: - in the hypothesis of the intervention of a liquid as a refrigerant, the flow rate necessary to ensure a correct heat transfer side ferrule is about 20 times the flow circulating inside the beam: the required flow rate resulting is incompatible with available currents whose flow rates are either fixed by the process (liquid DCE to be preheated), or subjected to other constraints (heat transfer fluid). The use of the exchanger is therefore limited to the vaporization systems (vaporisation of DCE or steam generation) in which the heat transfer on the ferrule side is ensured either by the system's own turbulence (liquid in a state of boiling ) or by the installation of a recycling system (forced or natural circulation); - In the case of using the exchanger as a DCE vaporizer according to EP-A-264 065, the (natural) circulation through the exchanger is ensured by the charge balloon; However, said charge balloon only increases the volume of the assembly to give a residence time DCE on the order of 50 minutes. This high residence time causes a greater or lesser thermal degradation as a function of the operating temperature on the DCE side (between 150 and 250 ° C. depending on the operating pressure) and requires a high purge rate in order to keep the degraded product content at a minimum. acceptable level. In such a context of VCM production by DCE cracking,

  the Applicant proposes an original process - simpler than those mentioned hereinafter

  above - to recover calories from the gaseous effluent from cracking.

  According to its first object, the invention therefore relates to a method of producing VCM by thermal cracking of DCE, implemented with recovery of calories on the gaseous effluent from cracking. Characteristically, in the context of said process, said calories are recovered by at least one liquid refrigerant circulated around the transfer line of said gaseous effluent resulting from cracking, in a space provided between said line

  transfer and a folder arranged around it.

  It has been found, unexpectedly, that the installation of a single jacket, around the transfer line, at the exit of the cracking furnace (generally between said cracking furnace outlet and the injection cooling system / watering (quench)), makes it possible to constitute a "double tube" type exchanger whose characteristics are suitable for

  the use of a liquid refrigerant.

  The term tube used here does not imply any limitation as to the

  exact geometry of the transfer line and the shirt arranged around it

  this. Advantageously, said term tube, however, reads according to its connotation

  usual hollow cylinder (circular section).

  The inner tube is constituted by the transfer line which combines the effluent of one or more cracking beams. The passage section of said inner tube advantageously corresponds to the total passage section of the cracking beam (s) connected (s); which ensures a gas velocity

  sufficient to achieve proper heat transfer and minimize fouling.

  The outer tube is constituted by the jacket. Refrigerant

  liquid flows, co-current or counter-current, advantageously against

  current (of the gaseous effluent), in the annular space (if, actually two tubes intervene) formed by the transfer line and the jacket. The inside diameter of the liner is determined by the flow rate and the characteristics of the liner.

  refrigerant to optimize heat transfer.

  The jacketed length determines the available exchange surface and can be adapted according to the amount of heat to be discharged / recovered. It can be made in one or more segments connected in series, gas side. It can already be specified here, with reference to the device aspect of the invention, that - cracked gas side, the segments can be connected either by straight sections, or by bends; the use of flanges to connect the segments facilitating a possible mechanical cleaning of the transfer line; - refrigerant side, the segments can be connected in series or in parallel, either by standard pipe elements, or by elbows or

  return boxes adapted specifically to the dimensions of the shirt.

  The use of several segments also allows the use of different refrigerants or the use of the same type of refrigerant to

  different conditions (temperature, pressure, flow).

  The recovery of calories, implemented according to the invention in a simplissime way by means of a device simplissime, can be with any type of liquid refrigerant. It is generally used for the purpose of using said calories and advantageously in view of such use in the VCM production process. In such a perspective of recovering recovered calories, it is recommended to use refrigerants such as: - boiler feed water, - the liquid DCE charge, - a heat transfer fluid, for example pressurized water or a

  commercial fluid (mineral oil, synthetic oil, ...).

  One can, in fact, implement: - recovery / valuation of calories, "indirect", through a heat transfer fluid (see above). (The operating temperatures of the different heat consumers in a VCM production unit (liquid DCE preheater, distillation section reboilers, DCE charge vaporizer) range from 100 to 210 C for

  unit "low pressure" and 100 to 260 C for a unit "high pressure".

  The use of a commercial heat transfer fluid which can operate at low pressure (0-2 bar) and at temperatures of 150-350 C is suitable for cooling the cracked gas and then transferring the absorbed heat to users operating in a range. temperatures from 100 to 260 C, thus covering both "low pressure" and "high pressure" processes); - a "direct" recovery / recovery of calories via a process fluid (fluid from the VCM production process (the liquid DCE charge, for example) or fluid from another process, put into

  nearby (boiler feed water, for example)).

  It is ensured that, advantageously, the minimum temperature of the refrigerant is above the dew point temperature of the cracked gas; this, in order to avoid the concentration of solid particles, possibly present, in the

  (low) amount of condensed liquid.

  It is now proposed to describe, in general terms, the second

  object of the present invention, namely - the device associated with its first object -

  a VCM production unit by DCE cracking. Such a unit comprises: means for conditioning, in pressure and temperature, the liquid DCE feedstock; an oven for cracking said conditioned DCE; means for washing, cooling and condensing the gaseous effluent from said cracking furnace; said means and furnace being interconnected by suitable transfer lines of the treated charge; as well as means for recovering calories from the gaseous effluent resulting from said

cracking oven.

  Typically, said means for recovering said calories comprise: + a simple lining of the transfer line of the gaseous effluent from said cracking furnace; said liner advantageously constituting a "double tube" type exchanger; and means for putting into circulation, in the space thus arranged between said

  transfer line and the jacket arranged around, a liquid refrigerant.

  Advantageously, the transfer line (inner tube) has fins (longitudinal) on the outside, in order to improve the heat transfer on the refrigerant side. It has been seen above that the jacketed length of said transfer line can be made in one or more segments, arranged in various ways. Advantageously, the particular means which intervene, according to the invention, for the recovery of the calories on the gaseous effluent resulting from the cracking, are arranged in a circuit of recovery (thus) and distribution of said calories, integrated in the unit of production of VCM. In the context of this advantageous variant, said circuit can be arranged to distribute the calories recovered, at the level of the means for conditioning the liquid DCE feedstock. Said circuit also contains, according to a preferred variant, an auxiliary heat supply device (an oven for example) and / or a device

  heat removal schedule (a (aero) refrigerant, for example).

  The intervention of this type of device increases the flexibility of implementation of the method. The intervention of a furnace or any other equivalent means of heat input makes it possible to increase the capacity of the circuit beyond the quantity of heat recovered in the process and to possibly cover all the heat requirements of the heat. VCM production unit. It is also useful for

  facilitate / speed up start-up operations.

  The intervention of a (aero) refrigerant or other equivalent means of heat removal increases the flexibility of the system during

  startup, shutdown and decoking operations.

  Incidentally, it can be noted here that the calories recovered according to the invention can also be distributed through a circuit

adequate, in another unit.

  It is now proposed to describe the invention in its two aspects

  method and apparatus, with reference to the accompanying figures.

Said figures are diagrams.

  Figures 1 and 2 illustrate the technique of the prior art. Figure I illustrates a low pressure cracking process while Figure 2 illustrates a high pressure cracking process. Said Figures 1 and 2 have been commented

  in the introduction to this text.

  FIGS. 3A to 3D illustrate schematically, in a nonlimiting manner, different types of lining, which can be arranged according to

  the invention, around the transfer line of the effluent from cracking.

  Figure 4 generally illustrates the invention.

  FIGS. 5, 6 and 7 illustrate particular embodiments of the invention; FIG. 5 shows a modification according to the invention (with the intervention of a coolant as a coolant) of the technology of the prior art according to FIG. I (low-pressure technology), FIG. 6 shows another modification according to the invention (with the aid of the DCE feedstock as a refrigerant) of the technology of the prior art according to FIG. 1 (low-pressure technology). FIG. 7 shows a modification according to the invention (with the intervention of a coolant as a coolant) of the high pressure technology of the prior art (modification implemented in a different unit).

  of that shown in Figure 2).

  Said figures 5, 6 and 7 are commented, respectively, in the

  text of examples 1, 2 and 3 below.

  In all the appended figures, FIGS. 1 to 7, there is the same

logical at the reference level.

  With reference to FIGS. 3A to 3D and FIG.

following.

  Figure 3A schematically shows the basic apparatus that can be used, typically, in the context of the present invention. Around the transfer line of the gaseous effluent G from the transfer line cracking into a single rectilinear segment - a sleeve 1a (in a single rectilinear segment) was arranged. On the variant shown, it is intended to circulate the liquid refrigerant L against the current in the annular space, formed between said line

  transfer and said lining 1 la.

  Figures 3B to 3D show variants of such a device, more sophisticated. Circulations have always been planned - gaseous effluent G, refrigerant

L liquid - countercurrent.

  In Figs. 3A and 3B, reference numeral 20 represents expansion compensators. In FIGS. 3B and 3C, respectively, the jacketed length is in several segments: - connected by straight sections (sleeve Ib) - connected by elbows (sleeve I c). FIG. 3D shows an 8-segment heat exchanger (jacket I ld), which offers two passes to refrigerant L. FIG. 4 schematically shows the integration, for the purposes of the invention, of a recovery circuit and distribution system (circuit shown in bold) of heat, based on the use of a commercial heat transfer fluid in a unit

of VCM.

  The different "producers" and "consumers" are connected in series according to their respective operating temperatures but others

configurations are possible.

  FIG. 4 (as well as FIGS. 5 to 7) shows the references of the type n1, with n identifying one of the steps I to 7, as specified in the introduction to this text, and i one of its implementation variants

  in a particular device (i = a, b or c, generally).

  In addition, there are steps or means characteristic of the invention, namely: I. heating the heat transfer fluid in one or more of the following devices a. transfer line exchanger I 1 '. convection zone bundle of the cracking furnace 12. cooling of the heat transfer fluid to its initial temperature by giving up its heat in one or more of the following devices a. a reboiler for vaporizing part or all of the charge DCE b. DCE preheater charging c. one or more reboilers in the distillation section d. one or more exchangers heating other fluids (boiler feed water, heating water, ...) according to their presence near the VCM production unit 13. the circuit is completed by Il a. an expansion balloon b. a circulation pump 14. and advantageously comprises a. an independent oven allowing a contribution of heat in the event of a deficit b. a (aero) refrigerant to dissipate excess heat. The means 12d above (underlined) are not represented on the

figure 4.

  We now come to the description of three examples of implementation

of the invention.

  Example 1. Figure 5: Low Pressure Process - Heat Transfer Fluid as

  refrigerant - Heat transfer circuit grafted on an existing unit, according to Figure 1.

  The original unit (of FIG. 5) is identical to that represented in FIG. 1. It comprises, as already indicated with reference to FIG. 1, the following equipment: 2. Preheating the liquid DCE b. exchanger heated by an intermediate current in the cooling section 3. vaporization of the DCE O20 b. vaporization column with reboiler 3b 'type thermosiphon supplied with water vapor 4. superheat of vaporized DCE a. beam in the heat recovery zone on the fumes of the cracking furnace 5. partial conversion of the DCE a. two tubular bundles (Di = 154 mm) placed in the direct heating zone ("radiation") of the cracking furnace 6. cooling and washing of cracked gas c. Mixing T 6a combined with a watering column 6b 7. cooling the washed gas a. exchanger supplied with a process stream (see 2b) b. water coolant The main operating parameters are given below DCE charging flow rate 35 660 kg / h purge DCE 825 VCM steam column produced 12,550 DCE temperature preheater inlet 30 C DCE preheater output 110 DCE column output vaporization 195 cracked gas output oven 485 cracked gas quenching input T 485 pressure furnace output 10 bar eff. steam consumption: - reboil vaporising DCE 7240 kg / h residence time DCE: - the residence time (calculated) of the liquid DCE in the vaporisation system

  (column + reboiler + connecting pipe) is 10 minutes.

  Said original unit (according to FIG. 1) has been modified, as shown in FIG. 5, to incorporate a simple heat transport circuit comprising 1 lb. a transfer line exchanger 12a. a reboiler for vaporizing a portion of the charging DCE 13a. an expansion tank 13b. a circulating pump The heat transfer fluid passes through the exchanger I lb on the transfer line by cooling the cracked gas; the heat absorbed by the fluid is then used to vaporize a portion of the feed DCE in the additional reboiler 12a, thereby decreasing the heat exchanged in the (the duty of) reboiler 3b '

fed with steam.

  The transfer line exchanger is obtained by installing a jacket (Di = 255 mm) around the transfer line (C = 219 mm) in several segments over a total length of 70 m. The annular space is fed (in two passes) by 148 000 kg / h of coolant type "oil

  synthetic "at a temperature of 220 C.

  The regulation of the system remains simple and flexible - the DCE flow vaporized to the cracking furnace is regulated by the addition of water vapor to the existing reboiler 3b ',

  - the temperatures of the heat transport circuit are maintained by a by-pass

  pass on the extra reboiler 12a.

  For production conditions (charge flow, conversion) identical to those of origin, there is observed: a decrease in the temperature of the cracked gas of 185 C through the exchanger I lb on the transfer line; an increase in the temperature of the coolant of 22 C through this same exchanger I lb; a reduction in the steam consumption by the original reboiler 3b 'from 7240 to 3195 kg / h, ie a reduction of 4045 kg / h; - a residence time (calculated) of the liquid DCE in the vaporization system slightly increased (12 minutes compared to 10 minutes at the origin)

  due to the volume of the additional reboiler 12a and its connecting pipe.

  Example 2 Figure 6: Low pressure process - Process fluid as refrigerant (preheating and vaporization of the load DCE) - Heat transfer circuit grafted onto

  an existing unit, according to Figure 1.

  The original unit (of Figure 6) is identical to that shown in Figure 1. It functions as described above. The main operating parameters are given below: DCE charging rates 35 660 kg / h purge DCE 825 VCM vaporization column produced 12,550 DCE temperature preheater input 30 C DCE preheater output 110 DCE column output steam 195 cracked gas oven output 485 cracked gas quenching input T 485 pressure furnace output 10 bar eff. steam consumption: - reboiler vaporisation DCE 7240 kg / h residence time DCE: - the residence time (calculated) of the liquid DCE in the vaporisation system

  (column + reboiler + connecting pipe) is 10 minutes.

  Said original unit (according to FIG. 1) has been modified, as shown in FIG. 6, by the addition of a liquid DCE heating circuit, comprising: I lb. a transfer line exchanger 15a. a DCE circulation pump. The refrigerant is constituted by the addition of cold DCE and a flow of recycled DCE from the vaporization column 3b. The mixture passes through the transfer line exchanger Ib at a pressure slightly above the pressure of the vaporizer column 3b to maintain the fluid in the liquid state. Subsequently, the fluid is expanded at the inlet of the column 3b and a fraction of the DCE vaporizes under the effect of the relaxation. The heat absorbed by the DCE directly decreases the heat exchanged in

  (the duty of) reboiler 3b 'fed with steam.

  The exchanger l lb on transfer line is obtained by installing a jacket (Di = 255 mm) around the transfer line (C = 219 mm) in several segments over a total length of 70 m. The annular space is fed (in two passes) by 129 000 kg / h of liquid DCE at a pressure of 15

  bar eff; the temperature of the current at the inlet of the exchanger is 172 C.

  The regulation of the system remains simple: - the flow of DCE vaporized to the cracking furnace is regulated by the addition of water vapor to the existing reboiler 3b ', - the flow rate of recycled DCE remains fixed and its temperature does not require

no regulation.

  For production conditions (charge flow, conversion) identical to those of origin, we observe: a decrease in the temperature of the cracked gas of 185 C through the exchanger I lb on the transfer line, an increase of the temperature of the DCE of 37 C through this same exchanger 1 lb; after expansion at the entrance of column 3b, the temperature Jo30 falls to 195 ° C under the effect of the vaporization of a part of the DCE (approximately 10% - calculated value), - a reduction of the steam consumption by the reboiler of origin 3b 'from 7240 to 3195 kg / h is a reduction of 4045 kg / h, - a residence time (calculated) of the liquid DCE in the vaporization system slightly increase (12 minutes compared to 10 minutes to origin) due to the volume of the exchanger I lb on the transfer line and the connecting pipework. Example 3 Figure 7: High Pressure Process - Heat Transfer Fluid as

  Refrigerant - Heat transport circuit in a new unit.

  Said new unit is shown in FIG. 7 and comprises, on the DCE side, the following equipment: 2. preheating the liquid DCE a. exchanger fed with low pressure water vapor 3. vaporization of the DCE b. vaporization column with thermosiphon type reboiler supplied by coolant 4. superheat of vaporized DCE a. beam in the heat recovery zone on the fumes of the cracking furnace 5. partial conversion of the DCE a. a tubular bundle (Di = 162 mm) placed in the direct heating zone ("radiation") of the cracking furnace 1 l c. transfer line exchanger 6. cooling and washing of cracked gas c. T of mixture 6a combined with a watering column 6b 7. cooling of the washed gas b. water coolant The heat transfer circuit of the invention comprises the following equipment: 1 c. the exchanger on transfer line I 1 '. beam in the convection zone of the cracking furnace 14a. an independent oven allowing a possible heat input 1 2a. a reboiler for vaporizing the entire load DCE 14b. an air cooler for dissipating any excess heat 13a. an expansion tank 13b. A circulation pump The main operating parameters are the following flow rates DCE charging 55 500 kg / h purge DCE vaporization column 2100 VCM produced 18 550 temperature DCE inlet preheater 30 C DCE preheater output 145 DCE output column vaporization 250 DCE output beam convection 300 gas cracked furnace exit 485 cracked gas quench inlet 350 pressure outlet furnace 21 bar eff residence time DCE: - the residence time (calculated) of the liquid DCE in the vaporization system

  (column + reboiler + connecting pipe) is 10 minutes.

  The coolant is heated from 300 to 315 C in the exchanger 1 ic on transfer line by cooling the cracked gas, and then heated to 335 C in convection oven 11 '. The heat absorbed by the fluid is then used to vaporize the entire charge DCE in the reboiler 12a of the

vaporization column 3b.

  The exchanger 1Ic on transfer line is obtained by installing a jacket (Di = 255 mm) around the transfer line (C = 192 mm) in several segments over a total length of 100 m. The annular space is fed (in two passes) by 220 000 kg / h of oil-type heat transfer fluid

  synthetic "at a temperature of 300 C.

  In normal operation, the heat balance of the system is balanced by adjusting the temperature of the liquid DCE to the vaporization column 3b. The auxiliary oven 14a is out of service and the air cooler 14b is bypassed, in normal operation: their presence serves only to facilitate / accelerate the operations of

  starting and stopping the installation.

  Compared to a "conventional" unit operating at high pressure (unit as shown diagrammatically in FIG. 2), the following advantages are noted: the use of a heat-transfer circuit makes it possible to use a vaporization column 3b with reboiler 12a; degradation products (especially solids) can be purged from the system instead of crossing all the beams in convection and radiation as in the conventional system. The reduction in fouling allows a longer operating time and a higher cracking rate, - the energy gain (fuel consumption) compared to a conventional unit of the same VCM production capacity is approximately 4650 thermrnie / h. The gain directly attributable to the installation of the transfer line heat exchanger is 2300 thermal / h (calculated on the basis of the use of the booster oven instead of the heat exchanger), the rest comes from the heat transport system installation (higher cracking rate, better use of heat

available in convection zone).

  In order not to weigh down the following claims, reference was made to

  devices that exist according to different variants i by the unique reference n, in

place and place of different n ,.

Claims (12)

claims   1. Process for the production of vinyl chloride (monomer: VCM) by thermal cracking of 1,2-dichloroethane (DCE), carried out with recovery of calories on the gaseous effluent (G) resulting from cracking, characterized in that said calories are recovered by at least one liquid refrigerant (L) circulated around the transfer line of said gaseous effluent from cracking, in a space arranged between said transfer line and a jacket (II) arranged around of it.   2. Method according to claim 1, characterized in that said refrigerant   liquid (L) is circulated against the flow of the gaseous effluent (G).   3. Method according to one of claims I or 2, characterized in that said   Recovered calories are used in said VCM production process.   4. Method according to any one of claims I to 3, characterized in that   that said liquid refrigerant (L) is a coolant, in particular chosen from   pressurized water and a commercial oil-type heat transfer fluid.   5. Method according to any one of claims I to 3, characterized in that   said liquid refrigerant (L) is a process fluid, especially selected from   boiler feed water and liquid DCE feedstock.   6. Process according to any one of claims 3 to 5, characterized in that   that said recovered calories are used to heat and vaporize,   advantageously only in part, the liquid DCE feedstock.   7. Vinyl chloride production unit (monomer: VCM) by thermal cracking of 1,2-dichloroethane (DCE), comprising: - means for conditioning in pressure and temperature (1, 2, 3, 4) the load liquid DCE feed; - a cracking furnace (5) of said conditioned DCE; means (6, 7) for washing, cooling and condensing the gaseous effluent from said cracking furnace (5); said means (1, 2, 3, 4) and oven (5) being interconnected by suitable transfer lines of the treated charge; and means for recovering calories from the gaseous effluent from said cracking furnace (5); characterized in that said means for recovering said calories comprises: + a simple liner (1 1) of the transfer line of the gaseous effluent from said cracking furnace (5); said liner advantageously constituting a "double tube" type exchanger and means (13b, 15a) for circulating, in the space thus arranged between said transfer line and the jacket (I l) arranged around, a refrigerant liquid (L).   o 8. Unit according to claim 7, characterized in that said line of   jacketed transfer has fins.   9. Unit according to one of claims 7 or 8, characterized in that the   jacketed length of said transfer line is made in one or more segments.   1s Unit according to one of claims 7 to 9, characterized in that   said means for recovering said calories are arranged in a circuit for recovering and distributing calories, integrated in said unit of VCM production.   11. Unit according to claim 10, characterized in that said circuit is suitable for the distribution of recovered calories, at the level of the means (1, 2,   3, 4) for conditioning the liquid DCE feedstock.   12. Unit according to one of claims 10 or 11, characterized in that said   circuit encloses a heat supply device (14a) and / or a heat removal (14b).