FR2467834A1 - SIMULTANEOUS PROCESS FOR CONVERSION AND METHANATION - Google Patents

Abstract

The invention relates to a simultaneous conversion and methanation process. The invention improves methods of producing a natural gas substitute containing methane from a primary synthesis gas containing hydrogen and carbon monoxide in an H2 / CO molar ratio of less than 3 per heating the synthesis gas, adding water to the synthesis gas, then diluting this gas with a stream of diluent 14 to produce a reaction mixture and reacting the latter by passing over a catalyst in several reaction zones 20, 30, 40, 50, 60, the improvement consisting in adding water to the diluent stream 14 so as to improve the vapor recovery efficiency of the process and to control the process with greater flexibility. Production of a natural gas substitute.

Description

The present invention relates to a method of

  production of a natural gas substitute.

  The invention further relates to a process for producing a natural gas substitute containing methane from a primary mixture of synthesis gas containing hydrogen and carbon monoxide in a ratio

molar H2 / CO less than 3.

  The invention also relates to a process for producing a natural gas substitute from a gaseous stream containing hydrogen and carbon monoxide in an H 2 / CO molar ratio of less than 3, wherein a stream of diluent is mixed with the synthesis gas to form a reaction mixture for

  reaction in several reaction zones.

  The invention also relates to a process for producing a natural gas substitute containing methane from a primary synthesis gas containing hydrogen and carbon monoxide in a molar ratio of H 2 / CO of less than 3, which is mixed with a gaseous diluent to produce a reaction mixture for reaction in a plurality of reaction zones so as to improve the process water vapor recovery efficiency and increase the process flexibility of the process;

  the addition of process water to the diluent stream.

  In recent years, considerable effort has been devoted to developing processes for producing a natural gas substitute from fuels such as various grades of coal, heavy residual oils, and the like. The processing of coal has been of particular interest, and one path has been the conversion of coal into synthetic raw gas in slag gasification apparatus, etc. One such process is described in U.S. Patent No. 4,071,329. Using such containers, a relatively high content carbon dioxide synthesis gas with a relatively low water content is produced. Conventional methanation processes such as those described in U.S. Patent Nos. 3,854,895, 3,890,113 and 3,922,148 have been found to be less advantageous.

  for the production of methane from such charges.

  It has been found advantageous to carry out the conversion reaction, that is CO + H2Q> H2 + Co2 and the methanation reaction, that is to say

CO + 3H2 ---> CH4 + H20

  at the same time in the same reactor, when charges of this type were used. Certain processes in which this simultaneous conduct of conversion and methanation is practiced are described in U.S. Patent Nos. 3,938,968, 3,958,956, 4,017,274 and 4,133,825. patents are cited as

  references in this memo.

  U.S. Patent No. 3,938,968, supra, discloses the use of a high temperature reaction zone in which a simultaneous conversion and methanation reaction is conducted by passing over a remarkable catalyst defined in columns 3. and 4 of this patent. This process does not practice the recycling of the product in the load and it is implemented at high

  temperatures (from 4921C at the inlet to 87-10C at the exit).

  The aforementioned U.S. Patent No. 3,958,956 discloses a method in which a closed loop system is used to charge water into the synthesis gas treated as a feedstock in the process. The illustrated process clearly does not use recycle stream

  of the product and involves an isothermal zone of methanation.

  U.S. Patent No. 4,017,274 discloses a process for methanation of purified raw gases containing more than 3 mole percent carbon monoxide and having a methane concentration of less than 25 mole percent. In the process in question, water or water vapor is added to the feed introduced into the zone of simultaneous conversion and methanation reactions and a steam reforming catalyst is used in the zone. simultaneous reactions of conversion and methanation. This

  The process clearly does not use product recycling.

  U.S. Patent No. 4,133,825 relates to a process in which a portion of the product from a conversion and methanation simultaneous reaction zone is recycled as a diluent to the synthesis gas feed admitted to a zone. simultaneous conversion and methanation. In the process in question,

  water is added to the synthesis gas charge.

  Considering the processes described, it is clear that a continuing effort is currently focused on improving processes for converting carbon monoxide to methane for use as a substitute for natural gas. It has now been discovered that refinement is accomplished in processes in which the water required for simultaneous conversion and methainiation reactions is added to the diluent or recycle stream mixed with the synthesis gas prior to introduction of the resulting mixture into the reaction mixture. a reaction zone. The recycle or diluent streams each constitute a portion of the product stream exiting a simultaneous conversion and methanation reactor and are cooled prior to being used as a recycle stream or diluent stream. The product streams leaving the zones of simultaneous reactions of

  conversion and methanation are at a relative temperature-

  high temperature and create a large temperature difference in the heat exchangers used to cool these

  currents and to generate water vapor. Cooling

  This is done at a temperature chosen so that when water is injected into the liquid state, which vaporizes while entering the stream, sufficient cooling is produced to bring the current used as the cooling current to the desired temperature. recycling or as a diluent stream. The single figure of the appended drawing schematically illustrates a form of implementation of the method of the

24678.34

  present invention. In this figure, a desulphurized synthesis gas is introduced into the circuit via a feed inlet duct 10, a heat exchanger 11 and a duct 12 which causes the feed to enter the intake of several reactors 20, 30, 40, 50 and 60 for the simultaneous conduct of conversion and methanation. A portion of the charge passing through line 12 arrives via line 18 into line 17 and thus enters the conversion and methanation reactor 20. The feedstock is mixed with a recycle stream arriving via line 14 to form a reaction mixture of suitable composition for use as a feed stream fed to reaction zone 20. The reaction mixture is fed to reactor 20 at a temperature of 50.degree. temperature of about 260 to about 3430C, the composition of the feed being adjusted to provide a temperature rise across the reactor of from about 137 to about 302WC. Although representative ranges have been indicated, temperatures down to 2321C at the inlet and reaching

  816WC in the product stream discharged through a conduit 21.

  The product stream discharged through the conduit 21 passes into a heat exchanger 22 and is mixed with the incoming water via a pipe 29. The cooling in the heat exchanger 22 is sufficient to give a current which, by addition of water flowing through line 29 is cooled to a desired temperature as it flows through line 21 'to mix with a portion of the charge flowing from line 12 to reactor 30 as it passes through a pipe 28, a valve 13 and a pipe 23. The gas feed arriving via line 28 and the diluent of the product stream arriving via line 21 'are mixed and the mixture is introduced via line 23 into reactor 30. The inlet and outlet temperatures of the reactor 30 are substantially the same as those of the reactor 20, the product leaving the reactor 30 being introduced via a pipe 31 into a heat exchanger 32, then into a pipe 31 'after The diluent of the product stream flowing in the pipe 31 'is introduced into the mixture with a portion of the gaseous feed introduced into the reactor 40 via a pipe 38, a valve 13 and a pipe 13. a pipe 33. The inlet and outlet temperatures in the reactor 40 are substantially the same as in the reactors 20 and 30, the gaseous product being discharged from the reactor 40 via a pipe 41 and introduced into a heat exchanger 42, the current is cooled and introduced into a pipe 41 'in which it is mixed with water charged by a pipe 44. The resulting mixture will mix with a pipe 41' with a current

  gaseous charge coming from line 12 via

  The inlet and outlet temperatures in the reactor 50 are substantially the same as the temperatures in the reactors of a line 48 and a valve 13 for producing a reaction mixture in a line 43 which opens into the reactor 50. 20, 30 and 40, the gaseous product leaving the reactor 50 being collected by a pipe 51 and introduced into a heat exchanger 52 where it is cooled, then sent into a pipe 51 'where it mixes with an additional amount of the charge gas passing through a pipe 58 and a valve 13 to form a reaction mixture in a pipe 53 introducing the charge into the reactor 60. The reaction product leaving the reactor 60 is introduced via a pipe 61 into a heat exchanger 62 where it is cooled, then flows through a pipe 61 'which divides the stream into a portion passing through a pipe 621 and a portion passing through a pipe 67. The water whose presence is The heat exchangers 22, 32, 42, 52 and 62 are provided in a pipe 24, the flow being adjusted in the desired manner by valves 25 for producing high temperature steam. The high temperature vapor is recovered by a pipe 26 and conveyed to its use station in the process or at another point. The water flowing through lines 29, 35 and 44 is supplied by a pipe 34 preferably from a source of condensate or a similar source, the flow being effected by the lines 21 ', 31' and 41 'being controlled by valves 29',

'and 44'.

  The portion of the gaseous product passing through the pipe 62 'is at a temperature chosen so that an additional quantity of water injected through a pipe 63 and a valve 64 is vaporized before the compression of the recycled stream 62' in a compressor 70. In the reactor 20. A separating tank 65 comprising a water discharge line 66 is incorporated in the line 62 'so as to prevent the passage of water in the liquid state in the compressor 70. compressing the recycled gas stream and discharging at a high pressure through line 71 into a heat exchanger 72 where the recycled stream is heated. The heated recycled stream then passes into line 73 and is mixed with water vapor introduced through line 15 and valve 16 to

  produce a mixture that flows through a pipe 14.

  The other portion of the gaseous product exiting the reactor 60 arrives via a line 67 into a heat exchanger 68 where appreciable amounts of water are condensed and discharged through a line 69, the resulting gaseous stream entering through a line 67 'into a carbon dioxide removal vessel 80, in which substantial quantities of carbon dioxide are discharged through a pipe 81, the resulting gas passing through a pipe 82 in which it is divided into two portions, the first being introduced by a 84 and by a heat exchanger 85 in a methanation purification reactor 90 o the carbon monoxide content of the gas stream is reduced by formation of additional amounts of methane. The gaseous product leaving the reactor 90 is collected via a pipe 91 and mixed with the other portion of the stream coming from the pipe 82 via a pipe 83, the resulting mixture being introduced through a pipe 92 into a second purification reactor 100. methanation in which additional amounts of carbon monoxide are converted to methane so as to further reduce the carbon monoxide content of the gas stream. The flow

2467834 1

  gaseous product leaving the reactor 100 is collected by a pipe 101, introduced into the heat exchanger 11 and discharged into a product line, to another

  treatment, etc., by a conduit 102.

  It is observed in the implementation of the process of the present invention that a certain latitude in the amount of water added to each of the streams used as diluent with the gaseous feedstock entering the reactors 20, 40 and 50 is possible, whereas water is added to each of these currents by an independent circuit. On the other hand, when water is added to the mixture constituting the gaseous feedstock, the composition of said mixture is constant for all the reactors, the quantity of water added being determined by the added amount of gaseous feedstock. In addition, the amount of water added to the recycled stream also leaves some latitude, since this amount does not depend on any other stream, but is simply determined by the amount of water that the current passing through line 14 must contain. It has further been found that the addition of water upstream of the compressor 70 results in an improvement in the efficiency of the process. The addition of water via a pipe 64 has the effect that a colder current flows to the compressor 70 and reduces the necessary power of the latter. The use of steam in the recycle circuit is also desirable with respect to the current flowing in the reactor 20, i.e. the first

  simultaneous conversion and methanation reactor.

  Another advantage of the process of the present invention is the production of high pressure water vapor. A significant expense related to processes for converting carbon monoxide to methane is the cost of

  Heat exchangers that are needed. Thanks to the

  According to the present invention, the product streams having the highest temperature are used to produce high pressure water vapor, cooling from lower temperatures to the reaction temperature being carried out at least in part.

2467834 3

  by the vaporization of the water in the liquid state rather than by means of heat exchange, that is to say that the differential temperature in the heat exchangers 22, 32, 42, 52 and 62 is optimized since cooling is from a high temperature stream to a temperature higher than that used in the next reactor. In other words, the final cooling is carried out by the vaporization of water coming from the pipes 29, 35 and 44. This results in the possibility of using less powerful heat exchangers, because with a greater difference of temperature, the effective area of the heat exchangers is greatly reduced. In addition, the total heat dissipation in the heat exchanger is reduced by the injection of water in the liquid state, which further reduces the useful surface area of the heat exchanger. Consequently, a noticeable improvement is achieved in the more profitable production of a

high quality water vapor. -

  It should be noted that there is no addition of water to the stream 51 ', since it is not desirable to add water to this stream since the reactor does not work. under the same conditions as the reactors 20, 30, 40 and 50. In particular, the reactor 60

  is used to trigger the purification reactions, that is,

  that is, the reactor 60 is used to initiate the reduction of the amount of carbon monoxide in the feed and, therefore, the reactor 60 operates at an inlet temperature of about 260 to about 3430C, but a generally lower exit temperature than reactors 20, 30, 40 and 50. Higher temperatures may exist in product line 61 depending on the amount of carbon monoxide available for reaction in reactor 60 or in a reactor similar. In any case, the process steam passing from the pipe 61 into the heat exchanger 62 does not require cooling at a low temperature, since it is either recycled or intended for the subsequent treatment of formation of the

  product stream containing methane.

EXAMPLE

  A computer simulation of the conduct of the process of the invention was performed and the temperatures, pressures and compositions of the streams were determined according to the indications given in the following table.

  indicated in the single figure of the accompanying drawing.

T A B 1. E A U

  No. of the current Temperature (C) Absolute pressure (MPa) Composition (moles / h) H 2 O (moles) H 2 H 2 (moles CH 4 (moles) CO (moles) CC 2 C H n m N 2

  73 12 18 17 21 29 28 23 31 35 38 33 41 44

  3.95 (mole%) (mole%) (mole%) (mole%)

329,234

2.62 2.62

4067 6699

42.8 1.0

3.2 28.5

21.7 6.9

0.4 60.3

31.4 2.4

0.3

0.5 0.6

  Current No. Temperature (C) Absolute Pressure (MPa) Composition (moles / h) H20 (mole%) H2 (mole%) CH4 (mole%) C2 (mole%) CO2 (mole%) CnHM (mole%) N2 ( moles%) N2 N (moles%)

  48 43 51 58 53 61 62 '63 71 67 69 67' 82 101

  2, 62 28, 6.9, 3 2.4 2.37 37.6, 1 16.5 11.4 23.9 2.32 36.6 7.5 21, 1 1, 8 32.5 2 , 62 28.5 6.9, 3 2.4 2.28 34.6 8.6, 4, 0, 9 0.3 Traces - 0.3 Traces

0.6 0.5 0.5 0.6 0.5

  2, 24 36.7 3.6 24.0 0.5 34, 7 2, 16 36, 7 3.6 24.0 0.5 34, 7 3.15

0.5 0.5

  2.69 42.8 3.2 21.7 0.4 31.4 2, 16 36.7 3.6 24.0 0.5 34, 7

0, 5 0, 5

  2.27 32.0 3.8, 8 0.5 37.3 1.95 6.1 11.4 77, 6 1.5 1.7 1.88, 2 2.9 84.4 Traces 0, 7 3.15 2.62 2.62 28.5 6.9, 3 2.4 0, 3 0, 6 2.58 36.8 7.1 21.3 1, 7 32.6 2.62 39, 3 7.9 17.0 12.1 23.1 0, 1 0.5 3.15 2.62 2.54 37.6 9.9 16.6 11.4 24.0 Traces 0.5 2.50 36 7 7.2 21.3 1, 7 32.6 0.5 28, 6.9, 3 2.4 0, 3 0.6 3.15 0.5 2.45 37.6, 0 16, 5 11.4 24.0 Traces 0.5 2.41 36.6 7, 4 21.2 1, 7 32.6 0.5 28, 5 6.9, 3 2.4 0, 3 0.6 o

0.6 1, 7 1.8

  It should be noted that the process of the present invention makes it possible to obtain simply the same

  reaction conditions in reactors 30, 40 and 50.

  This is very advantageous because it can thus optimize the life and efficiency of the catalyst. A slightly higher inlet temperature is used in reactor 20 because it is advantageous that the temperature at the inlet of vessel 20 be slightly higher as a precaution against high potential.

  nickel-carbonyl formation. Nickel formation

  carbonyl is not as likely in reactors 30, 40 and 50, and so admission temperatures are

lower.

  In summary, it should be noted that the improvement according to the present invention makes it possible to improve the high-temperature steam production yield from the product streams coming from the zones of simultaneous conversion and methanation reactions and that the Addition of water to the recycle stream or diluent stream during processing gives the process greater flexibility. By practicing the present invention, there is practically no addition of water to the gaseous feed stream because all of the process water is added to the recycled stream or dilution stream. The term "recycle" as used herein refers to the recycle of a portion of the product stream from reactor 60 back to reactor 20 as a diluent in contrast to the use of product streams from various products.

  reactors as diluent in the next reactor.

  It goes without saying that the present invention has been described for explanatory purposes, but in no way limiting, and that many modifications can be made without

get out of his frame.

Claims (6)

REVENDICMAIONS   1. Improved process for producing a substitute   a natural gas containing methane from a synthesis primary gas containing hydrogen and carbon monoxide in an H 2 / CO molar ratio of less than 3, comprising the steps of: (a) heating and add water to the synthesis gas; (b) dividing the synthesis gas into at least two portions;   (c) mixing a cooled stream of recycle gas   clage (14) from the gaseous product of a simultaneous conversion and methanation reaction with a first portion (12) of the synthesis gas to form a first mixture; (d) subjecting the first mixture to simultaneous conversion and methanation reactions by passage over a catalyst in a first reaction zone to form a first gaseous product; (e) cooling the first gaseous product; (f) mixing a second portion of the synthesis gas with at least a portion of the cooled first gaseous product as a dilution stream to form a second mixture; (g) subjecting the second mixture to simultaneous conversion and methanation reactions by passage over a catalyst in a second reaction zone to form a second gaseous product; and (h) recycling at least a portion of the cooled gaseous product from the last conversion and methanation reaction zone to the mixture formed with the first portion of the synthesis gas, characterized in that the improvement comprises (i) add essentially no water to the synthesis gas (10); and (j) adding water (29) in the liquid state to   minus a portion of the dilution streams after cooling   in order to further cool the currents of   dilution by vaporization of said water in the liquid state.   2. Improvement according to claim 1, characterized in that the water in the liquid state is added to the recycle stream in the first reaction zone after cooling (22) of said recycle stream to cover part of the process requirements and to further cool the recycle stream by vaporization of the water in the liquid state. 3. Improvement according to claim 1, characterized in that the process comprises more than two zones   simultaneous reactions of conversion and methanation.   4. Improvement according to claim 3, characterized in that there is no addition of water to the dilution stream introduced into the last reaction zone.   simultaneous conversion and methanation.   5. Improvement according to claim 4, characterized in that the process comprises five zones (20, 30, 50, 60) of simultaneous conversion and methanation reactions. 6. Improvement according to Claim 5, characterized in that the composition of the mixture of the primary synthesis gas and the diluent charged to the second, third and fourth reaction zones (30, 40, 50) is substantially the same.