FR2733304A3 - COOLING METHOD OF HOT RAW GAS LOADED WITH HARMFUL SUBSTANCES, AND ARRANGEMENT FOR IMPLEMENTING THE METHOD - Google Patents

Abstract

The arrangement comprises a raw gas cooler (3) mounted in the direction of flow of the raw gas stream (1) between an electrostatic precipitator (2) and a gas laser (6) which removes sulfur from the raw gas. The importance of the heat transmission surfaces of the raw gas cooler (3) is dimensioned as a function of the quantity and speed of the raw gas so that the raw gas which is directed in indirect counter-current with respect to the fluid of cooling presents in each zone of the raw gas cooler (3) a temperature located on or above the saturation curve of the SO3 / temperature diagram in deg.C which is defined by the temperature of the specific dew point. The formation of sulfuric acid aerosols can thus be avoided or the raw gas can be separated from the sulfuric acid aerosols.

Description

Process for cooling hot raw gas loaded with harmful substances,

  and arrangement for implementing the process The invention relates firstly to a process for cooling hot raw gas laden with harmful substances before a gas washer removing sulfur from the raw gas, in which the raw gas is brought to a lower temperature level during its passage through a cooling path by means of a cooling fluid which dissipates

the heat.

  On the other hand, the invention relates to an arrangement for implementing the method which comprises, in the direction of the flow of raw gas and before a gas washer which removes the sulfur from the raw gas, a raw gas cooler to which can be applied on the one hand the raw gas and on the other hand a cooling fluid which dissipates the heat. In the case of the combustion of fuels containing sulfur, there is generation, apart from sulfur dioxide (SO2),

  also sulfur trioxide (S03) in limited proportions.

  Sulfur trioxide condenses in a medium containing water vapor and when it passes below a temperature essentially dependent on the SO 3 concentration and the water vapor content to form sulfuric acid (H2SO4) (point temperature

dew).

  This process of condensation and sulfuric acid formation is on the whole complex. If a surface is offered to a gas containing sulfuric acid and whose temperature is located below the dew point, sulfuric acid is deposited on this surface. In addition, it has surprisingly been found that the supersaturation of SO3 decomposes not only by condensation and formation of H2SO4 on the cold surface, but also by condensation of sulfuric acid on condensation nuclei which are entrained in the raw gas. The sulfuric acid droplets that grow on and surround the partly very small condensation nuclei are also very small. Their mass represents as a rule

  general a multiple of the mass of the condensation nuclei.

  While SO2 can be separated in a high percentage in raw gas desulphurization plants (gas washers), the separation of SO3 or H2SO4 in gaseous form and in particular

  small aerosols of H2SO4 in practice pose big problems.

  In the case of a separation process that works by diffusion (gas washing), these aerosols are in fact much too large. Furthermore, and despite their growth by absorption of water vapor in a medium saturated with water vapor from a gas washer, they are

  too small for separation by significant inertia to take place.

  In any case, they are located below the limit conditions prevailing in a gas washer. This has the consequence that for a high SO3 load of a raw gas, the predominant percentage of

  the emission of sulfur is formed by aerosols of sulfuric acid.

  The emission of aerosols of sulfuric acid should not however be considered only from the aspect of the total emission of sulfur. In fact, the visual effect of waste gas effluents (stack clouds) charged with aerosols of sulfuric acid can be so pronounced that it is perceived by the public as unpleasant and therefore necessarily involves complaints. In addition, with effluents of waste gases laden with aerosols of sulfuric acid, account must be taken of the emission of small droplets of sulfuric acid for which sufficient neutralizing substances are not offered in the atmosphere. In the environment of chimneys through which a raw gas loaded with aerosols of sulfuric acid passes, it is not to be excluded either an immission of drops

  larger containing sulfuric acid.

  Based on the characteristics which have been indicated below

  above, the invention provides a method of cooling hot raw gas charged with harmful substances as well as an arrangement for implementing the method, by means of which it is possible, without a pronounced need for additional clean energy, to separate largely sulfur trioxide or sulfuric acid from the raw gas and power

  avoid the formation of aerosols of sulfuric acid.

  With regard to the process, this object is achieved by the fact that, depending on the degree of saturation of the raw gas with respect to water vapor and sulfur trioxide (S03), the raw gas is maintained in each longitudinal section. of the cooling path at an average temperature which is located on or above the saturation curve of the diagram S03 / temperature at C, which is defined by the

  specific dew point temperature.

  The essential point of the concept of the invention consists in cooling the raw gas "with care", in fact while it is passing through a cooling course and before it enters the gas washer. The raw gas is cooled in the course of

  cooling so that it retains in each section longitu-

  dinal of this course an average temperature which takes into account the specific dew point temperature determined by water vapor and sulfur trioxide while retaining realistic constructive dimensions in practice of the cooling course. The temperature of the raw gas therefore does not fall in any location below a temperature triggering the formation of aerosols after a certain time. This intentional adjustment of the temperature of the raw gas when it passes through the cooling path makes it possible on the one hand to reliably separate from the raw gas the S03 or the H2S04 and on the other hand to avoid the formation of aerosols of H2S04. At the same time and due to the low pressure losses, no additional clean energy is required, or only a small amount of this energy, and

  also obtains additional useful heat.

  The cooling of the raw gas can be carried out in accordance with a temperature curve situated above the saturation curve and falling permanently. However, it is also possible to envisage a process in which, when the saturation curve is reached or when it passes below for a short time, reheating the raw gas again by a determined quantity (sawtooth curve). This can be repeated several times if necessary during the cooling process. As regards the thermal energy intended for intermediate heating, it is possible to use part of the heat which has been previously derived and / or foreign energy. According to the invention, it is advantageous for the raw gas to be directed into the cooling path in order to be cooled in indirect counter current by supplying it with a cooling fluid such as water, which circulates in a closed circuit, which removes the heat of the raw gas and which transmits it either to a stream of purified gas largely free of sulfur dioxide or to a user device

  external useful heat, such as a remote heat pipe.

  As regards the device according to the invention, this is characterized in that the size of the heat transfer surfaces in the raw gas cooler is dimensioned in relation to the quantity and the speed of the raw gas so that the raw gas which is directed in indirect counter-current with respect to the cooling fluid circulating in a closed circuit, has in each zone of the raw gas cooler a temperature situated on or above the saturation curve of the diagram S03 / temperature in C which is

  defined by the specific dew point temperature.

  Therefore, the raw gas cooler is constructed so that the coolant, which behaves in the form of an accumulation mass and which circulates in a closed circuit, takes temperatures producing in the raw gas cooler

  surface temperatures that are not located anywhere

  below the expected dew point temperature of S03 / H2S04. This is obtained by providing for each contact between the raw gas and the cooling fluid (indirect contact) a temperature difference which is only limited. This makes it possible on the one hand to be certain of the necessary and desired transfer of heat between the raw gas and the cooling fluid, but on the other hand to avoid that limit temperature zones are produced by too pronounced cooling of the surfaces of the raw gas cooler, areas in which condensate seeds can form which cannot be separated in the various sections of a generator plant mounted downstream of the raw gas cooler (for example of desulfurization of raw gas or of reheating ), which thus remain in

  gas and can eventually reach the environment.

  As long as possible contact is obtained between the raw gas and the coolant with low relative temperatures in the various zones of the raw gas cooler by providing for the entry of the coolant into the raw gas cooler in the vicinity of the raw gas outlet from the raw gas cooler and the coolant outlet from the raw gas cooler near the raw gas inlet to this raw cooler

  raw gas. This produces a raw gas cooler against

  typical current through which the coolant flows and which can be fitted with tubes, pipes or plates on which

passes the raw gas.

  In this regard, an advantageous embodiment of the invention provides that the raw gas cooler is equipped with several coils arranged against each other, through which the coolant passes and around which the raw gas passes. These coils are subjected to the action of the coolant in the raw gas outlet area of the raw gas cooler. The coolant flows through the coil against the raw gas and leaves the raw gas cooler at the inlet of the raw gas into the latter. Therefore, gentle cooling of the raw gas is facilitated by the fact that in the cooling zone of the raw gas which is first crossed by the raw gas, this cooler is subjected to the action of the cooling fluid which

is already hot.

  An advantageous embodiment of a raw gas cooler provides that the latter consists of the assembly of several sections arranged one after the other in the direction of flow of the raw gas and each comprising bundles of tubes or U-shaped pipes. Thus, the raw gas cooler consists of several sections arranged one after the other in the direction of the flow of the raw gas and each comprising bundles of tubes or pipes in the form of U. In particular in the case of a constitution with pipes, these are formed from a solid synthetic material such as perfluralcoxide (PFA). Depending on the temperature of the raw gas to be cooled as well as the quantities of water vapor and sulfur trioxide which it contains, it is possible to obtain by an appropriate assembly of several sections a gentle cooling of the raw gas distributed O10 over several stages, without the raw gas temperature during the

  cooling process falls in the aerosol field at-

  below the saturation curve of the S03 / temperature diagram in C. The invention basically provides for an increase in the dimensions of the raw gas cooler. To reduce the pressure loss, large sections of current inlet are also advantageous. In this regard, it may be advantageous to integrate the raw gas cooler in the outlet zone of an electrostatic precipitator mounted upstream of the gas washer in the raw gas stream. Another field at least provided for the cooling of the raw gas and the separation of sulfuric acid can be connected directly to the fields arranged one after the other of the electrofilter and intended for the separation of fly ash, that is that is to say without an intermediate channel. This results in the elimination of a raw gas channel between the electrostatic precipitator and the raw gas cooler as well as the cover located on the side of the inlet and the current outlet of the raw gas cooler. The pressure loss of the raw gas (clean energy requirement) is significantly reduced by the simplification of the guide in the channel as well as by a reduction in the speed of passage of the raw gas cooler. The conditions of arrival of the current in

  the raw gas cooler are significantly improved.

  To take account of the variable load behavior of a plant burning sulfur-containing fuels, for example a generator plant, and the temperature differences in the resulting raw gas, it is advantageous for the inlet and return sections intended for the coolant and which are connected to the raw gas cooler are connected to each other by means of a mixing valve incorporated in the return section as well as by a bypass. The inlet and return sections can also be connected to a purified gas heater following the gas washer and to an external useful heat user device such as

than a heating pipe.

  In this regard, an advantageous embodiment of the invention provides that the raw gas cooler is coupled by the coolant circulating in closed circuit to a gas heater

  purified integrated into the raw gas stream after the gas scrubber.

  Regardless of whether the raw gas cooler is integrated between an electrostatic precipitator and a gas washer or directly in the electrostatic precipitator, heat is transferred from the raw gas cooler and through the gas washer to the purified gas heater mounted downstream of the gas washer in the

raw gas flow.

  By integrating a purified gas heater directly into the gas washer or in its outlet area, it is possible to reduce installation costs as in the case of integrating the raw gas cooler in a electrostatic precipitator, and improve the conditions for the flow of current into the purified gas heater and thus reduce the pressure loss. Optimal separation of the drops can be obtained by having a separator of

  drops upstream of the purified gas heater.

  As already indicated, it is also possible to couple the raw gas cooler by means of the cooling fluid which circulates in a closed circuit to a device.

  use of external useful heat such as a heating pipe.

  One can also imagine a coupling in parallel of the raw gas cooler with a purified gas heater as well as with an external useful heat utilization device by means of cooling circuits separated from each other. According to the invention, the bundles of tubes or pipes of the sections of the raw gas cooler can be mounted in series in the direction of flow of the raw gas. Thus, the coolant flows in the individual sections one after the other against the flow of the raw gas from the outlet zone of the

  raw gas cooler to its entry area.

  The invention also provides that a fluid which takes heat from a cooling fluid is sent into two successive heating stages, the first heating stage in the direction of the flow of the fluid being coupled to at least one section. of the raw gas cooler by a coolant circulating in a closed circuit, section which is subjected to the raw gas which has already been cooled, while the second heating stage is coupled by a coolant circulating in a closed circuit at least with the section which is subjected to the action of raw gas which has not yet been cooled. Thus, after the raw gas has cooled, part of the energy which has been collected can be used to pass the raw gas back through the cooler sufficiently above the dew point temperature of sulfuric acid to exclude also a passage below the dew point in the area of possible cold bridges in connection with the crude gas desulphurization installation (gas washer). The heating stages (sections) can be part of a purified gas heater integrated in the raw gas stream after a gas washer. The heat-capturing fluid then forms the purified gas. However, these stages can also be integrated into a heating pipe at

distance.

  So that in such a situation all the aerosols of sulfuric acid are vaporized, it is possible to connect at least the last section of the raw gas cooler in the direction of the flow of the raw gas, to the coolant circuit which mates the first section in the direction of

  the flow of raw gas to the second heating stage.

  The invention also provides a solution according to which the fluid which takes the heat from a cooling fluid is sent to a heat exchanger which is connected to two sections of the raw gas cooler which are mounted downstream of the first section in the direction of the flow of raw gas, while the outlet of the first section is thus connected to the inlet of the last section. This solution makes it possible to maintain the temperature of the raw gas in the cooler always above the saturation curve even when it contains a very high level of SO 3. According to another embodiment, the invention provides that the first sections mounted in series in the direction of flow of the raw gas are coupled by a cooling fluid circulating in closed circuit to a purified gas heater incorporated in the flow of purified gas at the rear of the gas washer, and the last sections in the direction of the flow of raw gas connected in series are coupled by a cooling fluid circulating in a closed circuit to an external useful heat user device. This solution also makes it possible to cool the raw gas in a way that protects it while allowing better separation of the SO 3 and a

  reduction of aerosol formation.

  Finally, a possible embodiment consists, in the case of a raw gas cooler comprising in the direction of the flow of raw gas three sections succeeding one another, to connect the inlet section of the front part from the coolant circuit at the inlet of the last section which is located in the front in the direction of the flow of raw gas, the outlet located in the rear of the last section in the inlet located in the front from the first section, the outlet at the rear of the first section at the inlet at the rear of the central section and the outlet at the front of the central section at the return section of the circuit. In this case, the separation of the SO 3 without the formation of aerosols takes place by a combination of heat recovery and

use of heat.

  The invention will now be explained in more detail below with the aid of the embodiments shown in the drawings in which: FIGS. 1 to 8 schematically represent various arrangements for cooling a hot raw gas loaded with harmful substances ; FIG. 9 is a view in longitudinal section of another embodiment of a raw gas cooler, and

  Figures 10 and 11 are two diagrams S03 / temperature in OC.

  In FIG. 1 is denoted in 1 a stream of raw gas coming from a fuel combustion installation containing sulfur

O10 which is not represented.

  The raw gas stream 1 is sent to an electrostatic precipitator 2 for dust separation, electrostatic precipitator from which the raw gas stream 1 enters at a temperature which is about 170 C in a raw gas cooler 3. The gas cooler gross 3 consists of two sections A, B arranged one after the other in the direction of flow and comprising bundles

  U-shaped pipes 4, 5 made of perfluralcoxide.

  In this raw gas cooler 3, the raw gas is cooled by a cooling fluid consisting of water, so that the raw gas from the cooler 3 leaves at a temperature of about 135 ° C and is sent to this temperature to a gas washer 6 (flue gas desulphurization installation) for the

separation of sulfur.

  A stream of raw gas 7 leaves the gas washer 6 at a temperature of about 550C. The raw gas stream 7 is directed to a purified gas heater 8 and brought to a temperature of about C therein by the water which has been heated in the raw gas cooler 3. The purified gas leaves at this temperature

  towards a chimney 9 and is released into the atmosphere by the chimney 9.

  The purified gas heater 8 comprises in the embodiment of FIG. 1 a bundle of U-shaped pipes 10 made of perfluralcoxide. The water which is used for cooling the raw gas circulates in a closed circuit 11 between the raw gas cooler 3 and the purified gas heater 8. To this end, a pump 13 driven by an electric motor 12 is incorporated in the circuit 11 . In addition,

  a balancing accumulator 14 is connected to circuit 11.

  In the raw gas outlet zone 15, the water coming from cooler 3 is directed at 78 into the pipe bundle 5 of section B located on the outlet side, and passes into the pipe bundles 4, 5 of the sections A, B connected in series, against the current with respect to the raw gas. The water outlet 17 is located in the inlet zone 16 of the raw gas into the cooler 3. This water is

  returned by the circuit 11 to the purified gas heater 8.

  The embodiment of FIG. 2 differs from that of FIG. 1 in that a mixing valve 19 is incorporated in the return section 18 of the circuit 11 between the raw gas cooler 3 and the purified gas heater 8, and that this mixing valve 19 is connected by means of a bypass 20 to the inlet path 21. This mixing valve 19 makes it possible to take account of a behavior under variable load of the installation which produces the raw gas. In the case of the embodiment of FIG. 3 and unlike the embodiments of FIGS. 1 and 2, the raw gas cooler 3 is integrated in the outlet zone 22 of the electrostatic precipitator 2. This arrangement can also be provided with 'a valve

  mixer 19 and a bypass 20 according to FIG. 2.

  In the case of the embodiment of FIG. 4, the purified gas heater 8 is connected to the outlet zone 23 of the gas washer 6. In this case also, the circuit 11 can be

  constituted as shown in Figure 1 or Figure 2.

  The embodiment of Figure 5 provides for the coupling of a raw gas cooler 3a which is formed in the direction of the flow of raw gas by three sections C, D, E mounted one after the other at the purified gas heater 8 in the raw gas stream 7 at the rear of the gas washer 6, cooler in which the inlet section 24 of the circuit 11a which is coupled to the outlet 36 of the bundle of pipes 10 of the gas heater purified 8 is connected to the inlet 25 of the pipe bundle 26 of the central section D. The outlet 27 of the pipe bundle 26 is connected in series to the inlet 28 of the pipe bundle 29 which is located at the front in the direction of flow of the raw gas. The outlet 30 of the pipe bundle 29 of the first section C which is located at the rear in the direction of the flow of the raw gas is connected to the inlet 31 of the pipe bundle 33 of the last section E which is located forward in the direction of the flow of raw gas. The outlet 32 of the pipe bundle 33 of the last section C which is located at the rear in the direction of the flow of the raw gas is coupled by the return section 34 to the inlet 35 of the pipe bundle 10 located at this place and forward in the direction of

the flow of purified gas 7.

  circuit 11a can be constituted in accordance with circuit 11 of

  Figure 1 or correspondingly to that of Figure 2.

  In Figure 6 is shown an embodiment in which a raw gas cooler 3b comprising four sections F, G, H, I of U-shaped pipe bundles is coupled by a circuit 11b to a purified gas heater 8 in the stream of raw gas 7 after the gas washer 6, and through another independent circuit 11c to a heat exchanger 41 which is also subjected to the action of a fluid which sends heat to a useful heat utilization device not shown. The fittings for the

  fluid with the heat exchanger 41 are designated at 42 and 43.

  It can be seen that the first two sections F, G of the raw gas cooler 3 in the direction of the flow of the raw gas are coupled to the purified gas heater 8 and that the two

  last sections H, I are connected to the heat exchanger 41.

  The two sections F, G or H, I of each circuit 11b, llc are connected in series, the inputs 46, 47 of the tube bundles 38, 40 located at the front in the direction of the flow of the raw gas being respectively connected to the inlet sections 44, 45 of the circuits llb, 11c, and the outlets 48, 49 which are located at the rear in the direction of the flow of the raw gas being connected to the sections of

  return 50, 51 of circuits 11b, lic.

  The circuits l1b, lic can be constituted in accordance with the

Figure 1 or Figure 2.

  FIG. 7 shows an arrangement which comprises a raw gas cooler 3c comprising three sections K, L, M with bundles of pipes 52, 53, 54 as well as a purified gas heater 8a comprising two sections N, O comprising bundles of pipes 55, 56 and arranged at the rear of the gas washer 6 in the direction of the stream of purified gas. The assembly is constituted in this case so that the second section O of the purified gas heater 8a in the direction of the flow of raw gas is coupled via a closed circuit lld to the first section K of the gas cooler o10 crude 3c in the direction of gas flow

  gross. In addition, the last section M is coupled to this circuit 11d.

  The first section N of the purified gas heater 8a in the direction of the flow of the purified gas is on the other hand connected by means of a closed circuit linked to the central section L of the

raw gas cooler 3c.

  In the case of the embodiment of FIG. 8, there is provided a raw gas cooler 3d which comprises three sections P, Q, R with bundles of pipes 57, 58, 59. The raw gas cooler 3d is coupled by the through a circuit 11f to the bundles of pipes 10 of the purified gas heater 8 at the rear of the gas washer 6. The inlet section 60 of the circuit 11f is connected to the inlet 61 of the bundle of pipes 59 which is located at the front in the direction of the flow of the raw gas. The outlet 62 of this bundle of pipes 59 is connected to the inlet 63 of the bundle of pipes 57 of the first section P in the direction of flow of the raw gas. The outlet 64 of the pipe bundle 57 is connected to the outlet 65 of the pipe bundle 58 of section Q which is located at the rear in the direction of the flow of the raw gas. The outlet 66 of the bundle of pipes 58 is

  connected to the return section 67 of the circuit 11f.

  Thanks to a circuit of this type, it is also possible according to FIG. 11 to maintain the temperature of the raw gas above the saturation curve 76 of the diagram S03 / temperature in OC, and this

  by a new heating in stages.

  Circuit 11f can be constituted like circuits 11 of

Figures 1 and 2.

  In the case of the embodiments of FIGS. 1 to 8, both the raw gas coolers 3-3d and the purified gas heaters 8, 8a are always provided with bundles of U-shaped pipes.

  4, 5, 10, 26, 29, 33, 37-40, 52-59 in perfluralcoxide (PFA).

  In Figure 9 is shown an embodiment in which a raw gas cooler 3e is equipped with several coils 68 arranged one against the other, letting through a cooling fluid and around which the raw gas passes. The coils 68 are located against each other in the plane of the drawing. In O10 this embodiment also, it is ensured that the inlet 69 of the cooling fluid into the raw gas cooler 3e is provided in the outlet area 70 of the raw gas stream 1 coming from the raw gas cooler 3e and that the outlet 71 of the cooling fluid coming from the raw gas cooler 3e is provided in the inlet area 72 of the raw gas stream 1 in the raw gas cooler 3e. The material of the coils 68 can be

a synthetic material.

  Naturally, it can be envisaged that a purified gas heater 8, 8a can also be formed in this way. In addition, it is possible to envisage a combination of heat exchangers comprising on the one hand bundles of U-shaped pipes and on the other

from the streamers.

  Figure 10 is a diagram on which is plotted on the abscissa 73 the SO 3 content of the raw gas in mg / Nm3 and on the ordinate 74 the temperature of the raw gas in OC. We can also see in the small field 75 located in the right corner the shape of the temperature curve as an example, the thermal energy required to heat the raw gas from 56 C to 850C being taken from a current raw gas, which at the start of gas cooling contains around 12% by volume

of H2O.

  This ensures gentle cooling and conserving the raw gas from about 170 C to about 135 C, that the temperature of the raw gas always remains above the saturation curve 76 (shown in dashed lines) defined by the specific dew point temperature, and does not fall into aerosol zone 77 located below. Thanks to the heat exchange, the water temperature rises from approximately 115 C to approximately 1500C and the temperature of the purified gas in the stream of purified gas 7 rises from approximately 560C to approximately 850C after the gas washer 6 These temperature points are indicated in I to VI in circles

in Figure 1.

  The same goes for the diagram in Figure 11.

  List of references 1 - Raw gas current 2 - Electrostatic precipitator 3 - 3a - 3b - 3c - 3d- 3rd raw gas cooler 4 - 5 - Pipe bundle 6 Gas washer 7 - Raw gas current 8 - 8a - Heater purified gas 9 - Chimney - 8, 8a pipe bundle 11 - 11la - 11b - 11c - 11d 11e - 11f Circuit 12 - Electric motor 13 - Pump 14 - balancing accumulator - Outlet area of 3, 3a-3e 16 - Entrance zone of 3, 3a-3e 17 - Exit of 4 18 - Return path of 11 19 - Mixing valve Bypass 21 - Arrival path of 11 22 - Exit zone of 2 23 Exit zone of 6 24 - Arrival route of 11a - Entrance of 26 26 - Pipe bundle of D 27 - Exit of 26 28 - Entrance of 29 29 - Bundle of pipes of C - Exit of 29 31 - Entrance of 33 32 - Exit of 33 33 Pipe bundle of E 34 - Return section of Ila - Inlet of 10 36 Outlet of 10 37 - Pipe bundle of F 38 - Pipe bundle of G 39 - Pipe bundle of H - Pipe bundle of I 41 - E heat changer 42 - Connection with 41 43 - Connection with 42 44 - Entry route of 11b - Entry route of lic 46 - Entry of 38 47 - Entry of 40 48 Exit of 37 49 - Exit of 39 - llb 51 return - 11c return path 52 - K 53 pipe bundle - L 54 pipe bundle - M pipe bundle - N 56 pipe bundle - O 57 pipe bundle - O pipe bundle P 58 - Pipe bundle of Q 59 - Pipe bundle of R - Entrance section of 11f 61 - Entrance of 59 62 Outlet of 59 63 - Entrance of 57 64 - Outlet of 57 - Inlet of 58 66 Outlet of 58 67 - Return section from 11f 68 - Serpentine 69 - Entrance from 68 - Exit area from 3e 71 - Exit from 68 72 - Entrance area from 3e 73 Abscisse 74 - Ordinate - Rectangular field 76 - Saturation curve 77 - Domain of aerosols 78 - Entry of 5 A - B Section of 3 C - D - E Section of 3a F - G- H - I Section of 3b K - L - M Section of 3c N - O Section of 8a P - Q - R Section I - Tem temperature between 2 and 3 II - Temperature between 3 and 6 III - Temperature between 6 and 8 IV - Temperature between 8 and 9 V - Temperature behind 3 VI - Temperature before 3

Claims (17)

  1. Method for cooling a hot raw gas charged with harmful substances before a gas washer (6) removing the sulfur from the raw gas, in which the raw gas is brought to a lower temperature level during its passage through a path cooling (3, 3a-3e) by means of a cooling fluid which dissipates heat, characterized in that, depending on the degree of saturation of the raw gas with respect to water vapor and sulfur trioxide ( S03), the raw gas is maintained in each longitudinal section of the cooling path (3, 3a-3e) at an average temperature, which is located on or above the saturation curve (76) of the S03 / temperature diagram in OC which is defined by the point temperature of specific dew.   2. Method according to claim 1, characterized in that the raw gas is cooled in indirect counter current with respect to the fluid   cooling system which circulates in a closed circuit (11, 11a-llf).   3. Arrangement for implementing the method according to claim 1 or 2, which comprises in the direction of the flow of raw gas (1) and before a gas washer (6) which removes sulfur from the raw gas, a cooler raw gas (3, 3a-3e) to which can be applied on the one hand the raw gas and on the other hand a cooling fluid which dissipates heat, characterized in that the size of the heat transmitting surfaces in the cooler of raw gas (3, 3a-3e) is dimensioned in relation to the quantity and speed of the raw gas in such a way that the raw gas, which is directed against an indirect current with respect to the cooling fluid circulating in a closed circuit (11 , 11a-1lf), present in each zone of the raw gas cooler (3, 3a- 3e) a temperature located on or above the saturation curve (76) of the diagram S03 / temperature in OC which is defined by the temperature specific dew point.   4. Arrangement according to claim 3, characterized in that the inlet (78, 47, 69) of the cooling fluid into the raw gas cooler (3, 3a-3e) is provided in the vicinity of the outlet zone (15 , 70) of raw gas from the raw gas cooler (3, 3a-3e) and the outlet (17, 48, 71) of the coolant from the raw gas cooler (3, 3a-3e) is provided in the vicinity of the raw gas inlet area (16, 72) in the raw gas cooler (3, 3a-3e).   5. Arrangement according to claim 3 or 4, characterized in that the raw gas cooler (3e) is equipped with several coils (68) arranged against each other, through which passes   the coolant and around which the raw gas passes.   6. Arrangement according to claim 3 or 4, characterized in that the raw gas cooler (3, 3a-3d) is constituted by the assembly of several sections (A, B; C, D, E; F, G, H, I; K, L, M; P, Q, R) arranged one after the other in the direction of the flow of the raw gas and each comprising bundles of U-shaped tubes or pipes (4 , 5; 23, 26, 33; 37, 38, 39, 40; 52, 53, 54; 57, 58, 59).   7. Arrangement according to any one of claims 3 to 6,   characterized in that the raw gas cooler (3, 3a-3e) is integrated in the outlet zone (22) of an electrostatic precipitator (2) mounted in   upstream of the gas washer (6) in the raw gas stream (1).   8. Arrangement according to any one of claims 3 to 7,   characterized in that the inlet and return sections (21, 18; 24, 34; 44, 50; 45, 51; 60, 67) intended for the coolant which are connected to the raw gas cooler (3, 3a -3e) are connected to each other by means of a mixing valve incorporated in the return section (18, 34, 50, 51, 67) as well as a bypass (20).   9. Arrangement according to any one of claims 3 to 8,   characterized in that the raw gas cooler (3, 3a-3d) is coupled by the coolant which circulates in the closed circuit (11, lia, 11b, 11d-llf) to a purified gas heater (8, 8a )   integrated into the raw gas stream (7) after the gas washer (6).   10. Arrangement according to any one of claims 3 to 8,   characterized in that the raw gas cooler (3) is coupled by the coolant which circulates in the closed circuit (11) to a purified gas heater (8) incorporated directly into the   gas washer (6) or at its outlet zone (23).   11. Arrangement according to any one of claims 3 to 8,   characterized in that the raw gas cooler (3b) is coupled by the coolant which circulates in the closed circuit   (11c) to an external useful heat user device (41).   12. Arrangement according to any one of claims 6 to 11,   characterized in that the bundles of tubes or pipes (4, 5) of the sections (A, B) of the raw gas cooler (3) are connected in series   O10 in the direction of flow of the raw gas.   13. Arrangement according to any one of claims 6 to 11,   characterized in that the fluid which takes the heat from a cooling fluid is sent in two successive heating stages (N. 0), the first heating stage (N) in the direction of the flow of the fluid being coupled to at least one section (L) of the raw gas cooler (3c) by a coolant circulating in the closed circuit (lHe), section which is subjected to the action of the already cooled raw gas, while the second heating stage (0) is coupled by a coolant circulating in the closed circuit (lld) at least with the section (K) which is subject   to the action of the raw gas which is not yet cooled.   14. Arrangement according to claim 13, characterized in that at least the last section (M) of the raw gas cooler (3c) in the direction of flow of the raw gas, is connected to the coolant circuit (lld) which couples the first section (K) in the direction of the flow of raw gas to the second heating stage (0)   15. Arrangement according to any one of claims 6 to 11,   characterized in that the fluid which takes the heat from a cooling fluid is sent to a heat exchanger (8) which is connected to two sections (D, E) of the raw gas cooler (3a) which are mounted in downstream of the first section (C) in the direction of flow of the raw gas, while the outlet (30) of the first   section (C) is connected to the entry (31) of the last section (E).   16. Arrangement according to any one of claims 6 to 11,   characterized in that the first sections (F, G) in the direction of the flow of raw gas, connected in series, are coupled by a cooling fluid which circulates in the closed circuit (11b) to a purified gas heater ( 8) incorporated in the purified gas stream (7) at the rear of the gas washer (6), and the last sections (H, I) in the direction of the flow of raw gas, connected in series, are coupled by a coolant circulating in the closed circuit (11c) to a user device for o10 external useful heat (41).   17. Arrangement according to any one of claims 6 to 11,   characterized in that in the case of a raw gas cooler (3d) comprising in the direction of flow of the raw gas three sections (P, Q, R) following one another, the inlet section (60 ) of the coolant circuit (11f) is connected to the inlet (61) of the last section (R) which is located forward in the direction of flow of the raw gas, the outlet (62) located at the rear of the last section (R) is connected to the inlet (63) located at the front of the first section (P), the outlet (64) located at the rear of the first section (P) is connected to the inlet (65) located at the rear of the central section (Q), and the outlet (66) located at the front of the section   central (Q) is connected to the return section (67) of the circuit (11f).