JP2007526976A - Generator with continuous combustion furnace for the purpose of generating steam - Google Patents

Abstract

The present invention comprises at least one combustor supplied with fuel and oxidant, an evaporation zone comprising an evaporative heat exchanger, a superheat zone comprising a superheat heat exchanger, a preheat zone comprising a preheat heat exchanger, and recovery A steam generator comprising at least two combustion furnaces (F1, F2) having a drum, each furnace comprising at least one evaporative heat exchanger (20).
According to the invention, each furnace comprises at least one evaporation furnace (20).

Description

[Field of the Invention]
The present invention relates to a heat generator for generating steam.

  More particularly, the present invention is more commonly referred to as a boiler, and in the presence of an oxidant, more particularly an oxidant having a high oxygen content, generally greater than 80%, fuel, particularly sulfur and nitrogen. The present invention relates to a steam generator that operates by burning a fuel containing the fuel.

  Such a generator can be used to drive a rotating machine such as a steam turbine of a thermal power plant, in particular, which generates hot steam called superheated steam having a temperature of about 560 ° C. There is a need. Another possible application of this generator is to generate steam at a refinery to meet the requirements of an oil conversion process. It is also possible to generate steam for crude oil extraction using such a generator.

[Background of the invention]
A steam generator that operates by burning fuel in the presence of air is already known, in particular from French Patent 2,528,540. This generator comprises a combustion furnace (or combustion chamber) provided with at least one combustor, and further comprises an evaporation zone comprising at least one evaporating heat exchanger called an evaporating screen or evaporator, and a superheat heat exchanger or Contain continuously, ie before and after, a superheat zone with a superheater, a preheat zone with a preheat exchanger or economizer (economiseur (France)), and a steam discharge zone and / or steam recirculation zone . There is also provided means for storing water in the vapor and liquid phases, called drums, which supply hot water to the evaporator and steam to the superheater.

  This type of generator is commonly referred to as two circuits, namely a water circuit, a first circuit comprising an evaporating zone, a superheated zone, a preheat zone heat exchanger and a drum, and a steam circuit, referred to as an oxidizer. A second purpose is to use steam obtained from the combustion of a fuel containing, and to transfer the thermal energy released by combustion to the various heat exchangers when this steam flows from the combustor to the steam discharge zone. Use with circuit.

  In practice, the steam obtained from the combustion heats the water, then evaporates it, and eventually heats the steam obtained by evaporation to various heat exchanges by convection and / or radiation. Hot steam that passes through the heat exchanger for transmission to the vessel. Furthermore, this steam is then sent to a combined treatment plant such as a dust collector before being discharged to the atmosphere through a stack (= chimney. Cheminee (France)) and then to a steam treatment unit. obtain.

  In the water circuit, water available at that location is pumped and injected into the economizer where it is preheated. This preheated water is then sent to the drum (in the case of a natural circulation generator), from which preheated water is fed to the evaporator or directly to the evaporator (in the case of a forced circulation generator) , Thereby evaporating most of the preheated water. This two-phase liquid water vapor mixture is then delivered to a drum where the liquid phase and the vapor phase are separated. The steam from the drum is fed to a superheater that can generate very hot steam.

  Thus, as is well known, combustion furnace evaporators have the highest energy requirements for steam to reach the highest heat level and to convert water into a two-phase fluid in the evaporator. In this evaporator, most of the water evaporates. Then, heat transfer of the steam energy to the superheater, i.e. transfer that also requires high temperature levels to obtain superheated steam, occurs in the superheat zone. Finally, when steam leaves the superheat zone, it uses its lowest temperature level steam to exchange its thermal energy with an economizer that preheats water. By making full use of the heat of the steam, all these heat exchange operations can maximize the efficiency of the generator.

  Operate this type of generator using an oxidizer with a high oxygen content, preferably above 80%, and further benefit from such combustion, especially by reducing the nitrogen ballast contained in this oxidizer It can also be a concern.

  In fact, when removing at least a portion of the nitrogen from the oxidant, the steam flow rate and the energy discharged by the combustion steam through the stack are reduced, thus increasing the thermal efficiency of such a steam generator. Therefore, fuel consumption is reduced for the same amount of heat transferred. As an example, heat loss in a stack of generators operating on air and exhausting steam at 250 ° C. is about 10% of the heat output supplied by the fuel, whereas as an oxidant under the same operating conditions When using pure oxygen, heat loss is reduced to 3%, which results in an increase in energy efficiency of about 7%. Similarly, the steam flow is reduced at least four times.

  Furthermore, emissions are greatly reduced when using combustion with oxygen. More specifically, the nitrogen oxides emissions (NOx) resulting from both the thermal dissociation of molecular nitrogen and the reaction of nitrogen contained in the fuel are reduced by a factor of 1 to 5 with the same combustor technology.

  Moreover, the treatment of the steam to remove sulfur oxides can be simplified in view of the increase in sulfur oxide concentration in the combustion steam. Thus, considerable savings can be realized with respect to the cost of sulfur oxide processing requirements.

  However, the steam generator design where combustion occurs between air and fuel cannot be applied to combustion in the presence of an oxidant with a high proportion of oxygen, ie, oxyfuel combustion.

  Actually, FIG. 1, which is a graph showing the temperature of steam (unit: ° C) on the abscissa and the combustion efficiency (unit%) on the ordinate, shows the relationship between air combustion (curve I) and oxyfuel combustion (curve II) Shows the difference in efficiency.

  To define the main features of a generator operating by oxyfuel combustion, it is first necessary to calculate the distribution of heat exchange in the various steam generation stages.

This will be demonstrated by an embodiment of a generator with 100 MW air delivering 124 tons / hour superheated steam at a temperature of 480 ° C. and a pressure of 80 bar. In this case, at a steam temperature of 250 ° C. at the outlet of the economizer, the output distribution obtained from the enthalpy table is as follows. That is,
-Evaporation of water in the evaporator 43.8%
-Steam overheating in superheater 18.8%
-Preheat water by economizer 27.6%
-Heat loss in discharge 9.8%
FIG. 1 gives a thermal efficiency of 90.2% for a steam temperature of 250 ° C. (point A) at the economizer outlet.

  By maintaining a steam temperature of 250 ° C. at the economizer outlet, FIG. 1 is obtained by oxyfuel combustion using an oxidant whose composition is about 95% oxygen, about 3% nitrogen, and about 2% argon. It shows that the temperature of the vapor at the outlet of the evaporator consuming 43.8% of the output delivered by the generator significantly exceeds 2000 ° C. (Line B).

  Such temperatures are detrimental for emissions such as nitrogen oxides (NOx). More specifically, there is an exponential dependence between NOx formation rate and steam temperature, demonstrating that the conversion of oxidant molecular nitrogen to NO from a steam temperature of about 1500 ° C increases very rapidly. Has been. Furthermore, the steam enters the superheater at temperatures above 2000 ° C., so that the tubes that generally form the superheater are exposed to very high steam temperatures. This solution creates a thermal resistance problem for the superheater tubes in which dry steam is already circulated.

  With regard to the formation of nitrogen oxides, it is proved by experience gained through extensive research by the applicant that it is preferable not to exceed a steam temperature of about 1300 ° C. at the outlet of the combustion furnace.

  FIG. 1 shows that the thermal efficiency corresponding to this temperature is about 80.9% (point C) in a combustion chamber operating under oxyfuel combustion, which is 43.8% (at a temperature of about 1200 ° C. required by the evaporator). This indicates that the efficiency exceeds the efficiency of point D).

  In the case of a normal boiler operating on air, the energy balance is about 30% of the heat energy for heating the water, about 40% for its evaporation, about 20% for overheating and about 10% for heat loss. It was also observed that it was absorbed. In the case of boilers operating by oxyfuel combustion, a steam temperature of about 1300 ° C at the outlet of the combustion chamber requires that about 80% of the energy be transferred to the combustion chamber, which causes steam superheating and water preheating. Not enough residual heat energy remains in the stage.

  The present invention overcomes the above drawbacks by means of a generator in which the steam temperature level enabling the realization of steam superheated to the required temperature is realized in a simple manner utilizing the techniques and materials normally used in boilers. The purpose is to do.

[Summary of Invention]
Accordingly, the present invention provides at least one combustor supplied with fuel and oxidant, an evaporation zone comprising an evaporative heat exchanger, a superheat zone comprising a superheat heat exchanger, and a preheat zone comprising a preheat heat exchanger, A steam generator comprising at least two combustion furnaces with a recovery drum, each furnace comprising at least one evaporative heat exchanger.

  Preferably, each furnace can be equipped with at least one superheat heat exchanger.

  Each furnace may also include at least one preheat heat exchanger.

  One of the furnaces may comprise at least one evaporative heat exchanger and the other furnace may comprise at least one superheat heat exchanger.

  One of the furnaces may comprise at least one evaporative heat exchanger, while the other furnace may comprise at least one superheat heat exchanger and at least one preheating heat exchanger.

  Alternatively, one of the furnaces may comprise at least one evaporation exchanger and at least one superheat heat exchanger, and the other furnace may comprise at least one superheat exchanger and at least one preheat heat exchanger. .

  The steam generator may comprise a purification chamber for steam from the combustion furnace.

  The steam purification compartment may be located upstream from the preheat zone.

  The steam purification chamber may include a humectant injection means.

  The steam purification chamber may include a reducing agent injection means.

  The steam purification compartment may comprise at least one evaporation zone.

  The hygroscopic agent injected into the steam purification chamber can be calcium or magnesium.

  The reducing agent injected into the steam purification chamber may be ureas or ammonia.

  The oxidant is a high oxygen content oxidant, while the fuel is a solid, liquid, or gaseous fuel such as heavy oil, petroleum residue, gas, oil coke, or coal.

  At least one furnace wall may consist of a shell (= outer shell, virole (France)) or a membrane (= membrane-like, membranee (France)) wall.

[Brief description of figure]
Other features and advantages of the present invention will become apparent upon reading the following description provided by way of non-limiting example with reference to the accompanying drawings.
FIG. 2 shows a generator according to an embodiment of the invention.
FIG. 3 shows a first variant of the invention.
FIG. 4 shows another variant of the invention.

[Detailed description]
With reference to FIG. 2, a steam generator 10, more commonly referred to as a boiler, includes two successive combustion furnaces F1 and F2 in which fuel burns in the presence of an oxidant. This fuel is a solid, liquid or gaseous fuel containing heavy oil, petroleum residue, gas, oil coke or coal, in particular containing sulfur and nitrogen, whereas the oxidant is preferably 80% Preference is given to gases or very pure oxygen having a very high oxygen content exceeding.

At least one combustor 12, which is supplied with fuel via line 14 and supplied with oxidant via line 16, is preferably arranged vertically above the main combustion furnace F 1 shown. The placement and quantity of the combustors is determined by those skilled in the art to achieve combustion with low emissions, while preventing the furnace wall 18 from coming into contact with the combustor flame. This combustion can also be performed by any other means such as a grate, fluidized bed, etc. Depending on the fuel injected, combustion is suitably performed using steam or an auxiliary fluid such as a gas or mixture such as CO ₂ or O _{2 in} particular, in order to recycle the steam that can be used for fuel evaporation. To optimize.

  The main combustion furnace F1 includes an evaporation zone V comprising at least one evaporation heat exchanger or evaporation screen 20 (referred to in the following description as an evaporator), which is preferably " It consists of the wall of the main furnace F1, which is a “membrane wall” type. As is well known, these membrane walls consist of tubes interconnected by welded fins to form a heat exchanger. The evaporator thus obtained is a high-temperature evaporator that evaporates at least part of the fluid circulating inside these tubes.

  The outlet 22 of this evaporation zone V and therefore of the main furnace F1 leads to the auxiliary combustion furnace F2, which is connected to the lower part and to the outlet 22 via the line 26 as defined above. Combustor 24, preferably fueled and supplied with oxidant via line 28, is preferably built vertically. Similarly, the placement and quantity of this combustor is determined by those skilled in the art to achieve combustion with low emissions, while preventing the secondary furnace F2 wall from coming into contact with the combustor flame.

  The sub-combustion furnace includes a high temperature superheat zone S1 with at least one superheat exchanger or superheater 30 (referred to as a high temperature superheater), which is the temperature of the fluid that is generally in the vapor phase passing therethrough. To raise. Therefore, the wall of the furnace consists of a preferably metal shell 32 protected from thermal radiation by an insulating material such as concrete, brick or fibrous material. A tube bundle 34 through which steam circulates is mounted along this insulating material. This superheater is a high temperature heat exchanger that superheats the fluid in the vapor phase passing through it.

  This high temperature superheat zone outlet 36 communicates at the top with a housing E which includes an additional superheat zone S2 (referred to as a low temperature superheat zone) and preferably a preheat zone P. The low temperature heating zone S2 includes at least one convective heat exchanger 38 (referred to as a low temperature superheater). The preheating zone P also includes at least one convective heat exchanger 40 (referred to as an economizer). These convective heat exchangers 38 and 40 consist of a bundle of tubes connected to a collector, as is known in the art.

  Thus, the steam generator includes two successive combustion furnaces, that is, a main combustion furnace F1, and a sub-combustion furnace F2 in series with the main combustion furnace. The main furnace F1 includes the combustor 12 and the evaporator 20, whereas the sub-furnace F2 includes the combustor 24 and the high temperature superheater 30, and then a casing E including the low temperature superheater 38 and the economizer 40 is provided. Continue.

  A preheating zone outlet 42 leads to a steam discharge zone F communicating with any known processing means or stack (not shown) at the bottom of the housing E.

  The economizer 40 includes a water inlet 44 and a preheated water outlet 46 that terminates via a conduit 48 into a fluid recovery means 50 such as a drum that is commonly used in this type of generator. The low temperature superheater 38 includes an inlet 52 for steam coming from the drum 50 via a conduit 54 and an outlet 56 for delivering this steam to the high temperature superheater 30. The hot superheater 30 is connected to any means utilizing such superheated steam, such as an inlet 58 for steam coming from the low temperature superheater 38, carried by line 60, and a turbine in a thermal power plant. And preferably an outlet 62 for superheated steam. Advantageously, the economizer and low temperature superheater can be provided with heat transfer enhancing devices such as fins if the vapor passing therethrough does not contain so much dust. The evaporator 20 is provided with an inlet 66 and an outlet 70, which is supplied with preheated water via a pipe 68 connecting the drum 50 to the inlet, and this outlet is two-phased by a pipe 72. A turbid liquid of water in the form (liquid steam) is delivered to the drum 50.

  Thus, during operation of the generator, water is fed into the economizer 40 via the inlet 44, which circulates through the economizer and on the other hand is preheated, which is then drummed 50 at the economizer outlet 46. Is collected in this drum by a pipe line 48 connecting the two. This hot water is then delivered from the drum 50 to the inlet 66 of the evaporator 20 via line 68 in order to at least partially convert it into a two-phase water turbid liquid at the outlet 70. The turbid liquid leaving the evaporator is sent via a line 72 to a drum 50 where it is separated into a gas phase and a liquid phase. The steam contained in the drum is then flowed through a superheater 38 that raises the temperature of the steam via line 54 to obtain dry steam at a first temperature level at outlet 56. Delivered to inlet 52. Dry steam is understood to be hot steam that exceeds the saturation temperature of water at the appropriate pressure. The inlet 58 of the hot superheater 30 receives steam from the cold superheater 38 via line 60, and this steam is in the form of superheated steam, i.e. at a high temperature above the temperature of the steam from the cold superheater 38. It flows through outlet 62.

  In order to achieve these different temperature rises and / or phase changes of the fluid circulating in the various heat exchangers, it is necessary to properly utilize the thermal energy generated by the combustion. Thus, part of the total amount of gas, liquid, or solid fuel (typically in the range between 20% and 80% of such total amount) and part of the total amount of high oxygen content oxidant (typically In the range between 20% and 80%) is injected into the combustor 12 of the main combustion furnace F1 via lines 14 and 16. In this way, the power distribution across at least two furnaces allows operation under relaxed operating conditions and higher generator flexibility. The steam generated by the combustion passes through the evaporation zone V and circulates in the evaporator tube to obtain a fluid in the form of two-phase liquid water vapor at the outlet 70 of the evaporator 20 and its heat. Exchange some energy.

  The steam is sent to the secondary furnace F2 at the outlet 22 of the main furnace F1, where the combustion of the total amount of fuel and oxidant is supplied to the fuel and oxidant via lines 26 and 28. By the combustor 24. Next, the temperature of the steam is increased, and further, the steam passes through the high temperature superheat zone S 1 including the high temperature superheater 30. The temperature of the steam circulating in the superheater tube is then increased, and the superheated steam is then released via line 64 and utilized by known means such as a turbine or any process. The steam leaving the high-temperature superheat zone S1 through the outlet 36 is sent to the low-temperature superheat zone S2 including the low-temperature superheater 38, where the steam receiving the temperature rise circulates. Alternatively, as described in more detail in connection with FIG. 3, before the steam enters the cold superheater 38, it is sent to a steam treatment area where a humectant is injected. The steam then passes through a preheating zone P where the water circulating in the economizer 40 is heated by heat exchange with the steam, while the steam is cooled to a suitable temperature, typically about 250 ° C. To do.

  This vapor is then discharged to the region F via the outlet 42 and further delivered to any suitable processing means or stack known in the art.

  As an example, the combustor 12 generates steam at a temperature of about 1300 ° C. at the outlet 22 of the furnace F1. Next, this steam flows into the auxiliary combustion furnace F2. This steam is raised in temperature by the combustor 24 and, after heat exchange in the furnace F2, reaches a temperature of about 1000 ° C. at the outlet 36 in region S1. The steam thus heated flows into the sub-superheat zone S2 by exchanging its thermal energy with the low temperature superheater 38, which exits this zone at a temperature of about 600 ° C. Then, it passes through the economizer 40 existing in the preheating zone P at a stretch, and is discharged to the region F through the outlet 42 at a temperature of about 250 ° C.

  In parallel, water is introduced into the economizer 40 at a temperature of about 150 ° C., which flows out at about 290 ° C. The preheated water then evaporates in part in the evaporator 20 after passing through the drum 50 and flows out at a temperature of about 305 ° C. before being sent to the drum 50. Steam exiting the drum at the same temperature is injected into the cold superheater 38, which raises its temperature to about 375 ° C at the outlet 56, which is sent from the cold superheater to the hot superheater 30, In addition, it exits this hot superheater at about 480 ° C.

  A number of combustion furnaces can be installed one after the other and in series with each other without departing from the scope of the present invention. Furthermore, an evaporation zone and / or a superheat zone comprising at least one heat exchanger, such as an evaporator and / or a superheater and / or an economizer, connected in series to a heat exchanger arranged after another combustion furnace And / or a preheating zone can be arranged in each combustion furnace.

  In the embodiment of FIG. 3 which shows a variant of FIG. 2 and therefore has the same reference numerals, a “membrane wall” type sub-combustion furnace F2 is used and a high temperature superheat zone is arranged in the main combustion furnace F1.

  Advantageously, in this variant, the entire generator is provided with a “membrane wall” type wall to make use of the thermal energy contained in the steam circulating from the main furnace F1 to the outlet 42.

  This generator includes a main combustion furnace F1 and a sub-combustion furnace F2 including a low-temperature superheat zone S2. This region leads to a preheating zone P that terminates with a steam discharge zone F. As described above, the “membrane wall” type main combustion furnace F1 includes the combustor 12 and the evaporation zone V including the evaporator 20 and the steam outlet 74, and this outlet is connected to the casing E1. It leads to the high temperature superheat zone S1 built in. This substantially vertical and elongated housing is also of the “membrane wall” type, which incorporates a conductive high temperature superheater 30 with a steam inlet 58 and a superheated steam outlet 62. The outlet 22 in the superheat zone is provided with the combustor 24 described in relation to FIG. The steam outlet 36 leads to a low temperature superheat zone S2 including a low temperature superheater 38 with a steam inlet 52 and a steam outlet 56, as described above, where the water supply inlet 44 and the preheated water outlet 46 are connected. The preheating area P including the provided economizer 40 is communicated with, and the preheating area is communicated with the steam discharge area F through the outlet 42.

  The low temperature superheat zone S2 and the preheat zone P preferably comprise “membrane wall” type walls. In this configuration, the intake of preheated water in the evaporator and the outflow of the two-phase fluid (liquid steam) can occur at different levels. In particular, there may be several preheated water inlets in the membrane wall and several two-phase fluid outlet openings in the drum.

  As an example, as shown in FIG. 3, the evaporator 20 includes a two-phase fluid (mainly connected to a drum 50 by a pipe 72, which is disposed in a preheating water inlet 66 and a preheating area outlet 42 in a main furnace F 1. Liquid vapor) outlet 70. Therefore, the combustion furnaces F1 and F2, the high-temperature superheat zone S1, the low-temperature superheat zone S2, and the preheat zone P, respectively, are evaporators distributed in the evaporation zones having the reference signs V, V1, V2, and V3 in the figure. Includes 20 parts. When only the furnaces F1 and F2 have a membrane wall, the two-phase fluid outlet 70 is disposed at the outlet of the sub-furnace F2, and as shown by the dotted line in the figure, Connected to drum 50 by line 72, leaving only the evaporation zones V, V1, and V2.

  In a variant in which all the walls are of the “membrane wall” type, the main furnace is composed of a combustor 12, an evaporation zone V including an evaporator 20, a high-temperature superheat zone S 1 including a high-temperature superheater 30, and a membrane of the casing E 1. In contrast to the evaporation zone V1 including the wall tube, the auxiliary furnace F2 includes the combustor 24, the low-temperature superheat zone S2 including the low-temperature superheater 38, the preheat zone P including the economizer 40, the membrane wall Evaporation zones V2 and V3 including tubes are provided.

  Thus, as described above in connection with FIG. 2, the combustor 12 of the main furnace F1 is supplied by a portion of the total amount of gas, liquid, or solid fuel and a portion of the total amount of high oxygen oxidant. The The steam in the furnace F1 passes through the evaporation zone V and preheated water circulates in the tubes of this heat exchanger so as to obtain a fluid in the form of a first two-phase liquid water vapor at the outlet of the evaporator 20. And exchange its thermal energy. The steam passes through the hot superheat zone S1 at the outlet 74 of the evaporation zone V, where the steam is obtained at the outlet of the hot superheater 30 to obtain steam at a first temperature level. The thermal energy is transferred to the superheater and on the other hand to the fluid circulating in the tube of the evaporation zone V1.

  The steam leaving the superheat zone S1 is sent to the sub-combustion furnace F2 through the outlet port 22, and the combustor 24 burns the residual amount of the total amount of fuel and oxidant in this furnace. Then, the temperature of the steam is increased, and the steam is discharged to the sub superheat zone S2 through the outlet 36, and the thermal energy is exchanged with the low temperature superheater 38. This steam also transfers some of its energy to the tube in the evaporation zone V2 as it passes through the secondary furnace and the hot superheat zone. The steam leaving the low-temperature superheat zone S2 passes through the preheat zone P, but in that zone, the temperature of water circulating in the economizer 40 is increased by heat exchange with the steam, and on the other hand, the steam is cooled to an appropriate temperature. Is done. Similarly, the vapor transfers its thermal energy to the membrane wall tube that forms the evaporation zone V3. This steam is then discharged into the region F via the outlet 42, which is delivered to any suitable processing means or stack known in the art.

  During operation, water flowing into the economizer 40 via the inlet 44 is heated by passing through the economizer and then delivered to the drum 50 via line 48. This hot water is then delivered from this drum to the inlet 66 of the evaporator 20 via line 68. The two-phase liquid steam fluid flowing out from the outlet 70 absorbs the heat of steam throughout the flow passing through the generator, that is, from the combustor 12 to the outlet 42, and enters the drum 50 via the pipe line 72. Sent out. In this drum, the two-phase fluid is separated between the vapor phase and the liquid phase, and the vapor is sent via pipe 54 to the inlet 52 of the low temperature superheater 38 where the temperature of this vapor is the first. Increased to 1 level. Steam is routed at this superheater outlet 56 via line 60 to the inlet 58 of the hot superheater 30 where the temperature of the steam is optional via the outlet 62 described above. It is raised again to a high level that exceeds the level of the low temperature superheater 38 before being discharged into the device.

  Of course, during all these operations, the combustors 12 and 24 are supplied with fuel as described in connection with FIG.

  Further, as an example, the temperature of the steam is about 1300 ° C. at the outlet of the evaporation zone V, about 500 ° C. at the outlet of the high temperature superheat zone S1, and about 1300 ° C. at the inlet of the low temperature superheat zone S2. About 350 ° C. and about 200 ° C. at the outlet 42 to the steam discharge zone F. The temperature of the fluid in the various heat exchangers is about 150 ° C at the inlet 44 of the economizer 40, about 165 ° C at the outlet 46 of this economizer, the outlet 70 of the evaporator and the inlet 52 of the low temperature superheater 38. About 304 ° C., about 360 ° C. at the outlet 56 of the superheater and the inlet 58 of the hot superheater 30, and about 480 ° C. at the outlet 62 of the hot superheater.

  FIG. 4 shows a variant of the embodiment of the invention according to FIG. 3, so that it has the same reference numerals.

  This modification is fundamentally different from FIG. 3 in that there is a housing E2 containing the steam purification chamber 76 and the medium-temperature superheat zone S3.

  In fact, Applicants have observed that combustion in the generator generally generates steam containing air pollutants such as sulfur oxides (SOx) and nitrogen oxides (NOx) that have a negative impact on the environment.

  Numerous methods are known for treating these contaminants, most of which are generally performed at low temperatures for steam exiting the preheat zone. However, in order to simplify the nitrogen oxide treatment or to prevent the sulfuric acid from condensing from the sulfur oxide, these contaminants are preferably treated at a high temperature of about 1000 ° C.

  Therefore, in the case of the modification of FIG. 4, a steam purification chamber 76 such as a desulfurization chamber is used for the steam generated by the combustor 24 so as to make use of the steam temperature at a high level in consideration of the operation of the sub-furnace. Arranged after the outlet 36.

  As already explained in connection with FIG. 3, the “membrane wall” type main furnace F <b> 1 includes a combustor 12, an evaporation zone V including an evaporator 20, a high temperature superheater 30 and a steam outlet 22. And a superheat zone S1. The outlet 22 in this superheated area leads to the auxiliary combustion furnace F2. The steam outlet 36 generated by the combustor 24 of the furnace F2 leads to the intermediate temperature superheat zone S3, and the intermediate temperature superheater 78 is connected to the outlet 56 of the low temperature superheater 38 by a line 82; And a steam outlet 84 connected to the inlet 58 of the high temperature superheater 30 by a pipe 86.

  The outlet in this region communicates with a purification chamber 76 which is a desulfurization chamber in the illustrated embodiment.

  The chamber is equipped with at least one humectant injector 88, which can quickly and uniformly disperse a humectant jet into the steam passing through the chamber. The injected hygroscopic agent may be calcium or magnesium, or any other type capable of reacting with sulfur oxides contained in the steam so as to limit the formation of sulfur oxides. The particle size and amount of the humectant injected is determined by those skilled in the art to achieve a desulfurization rate that complies with current regulations.

  Advantageously, this purification chamber will also serve to denitrify the vapor passing through this chamber by injecting a reducing agent such as urea or ammonia. The reducing agent is uniformly sprayed into the purification chamber by the same means as the hygroscopic agent injector 88.

  The number and arrangement of hygroscopic and / or reducing agent injectors will be determined by those skilled in the art so that the hygroscopic and / or reducing agent is properly sprayed into the purification chamber.

  The walls of this purification chamber advantageously consist of "membrane wall" type walls, which also serve to evaporate the water circulating in the evaporator by forming an evaporation zone V4.

  As already described in connection with FIG. 3, the outlet 90 of the purification chamber communicates with the preheating zone P leading to the steam processing zone F via the low temperature superheat zone S2 and the outlet 42.

  During operation, the steam generated by the main furnace F1 passes continuously through the main evaporation zone V and then passes through the hot superheat zone S1. The temperature of the steam is then raised by the combustor 24 at this superheated outlet. This steam then passes through the intermediate temperature superheat zone S3 and reaches the purification chamber 76, where it is desulfurized and / or denitrified by injection of a hygroscopic and / or reducing agent. The steam thus treated reaches the outlet 90, from which the steam flows into the low temperature superheat zone S2 and the preheat zone P before reaching the steam discharge zone F.

  In parallel, the water introduced into the economizer 40 is superheated by passing through the economizer, which is then delivered to the drum 50. Hot water present in the drum is delivered to the evaporator 20, and then the two-phase liquid steam fluid from the evaporator is delivered to the drum 50 via line 72. The steam present in the drum is sent to the low-temperature superheater 38, from which the steam is sent to the medium-temperature superheater 78 via the pipe line 82. The steam coming from this medium temperature superheater is then sent to the high temperature superheater via line 86 from which the steam exits via outlet 62 and line 64.

  The steam passing through the purification chamber 76 is preferably at a temperature in the range between 600 ° C. and 1100 ° C. so that the required desulfurization rate is obtained according to the residence time of the steam in the purification chamber. In this temperature range, it can be confirmed that the denitrification of the steam is possible if the small chamber is equipped with the reducing agent ejector described above.

  Furthermore, as already explained in connection with FIG. 3, the steam transfers its thermal energy to the tubes of the various evaporation zones V, V1, V2, V3 and V4.

  In an embodiment showing this variation, a 100 MW generator operating under oxyfuel combustion and delivering superheated steam to a temperature of about 480 ° C. at 124 tons / hour is considered. The fuel used consists of about 84% carbon, about 9% hydrogen, about 6% sulfur, and about 1% nitrogen in weight percent. The composition by volume of oxidant consists of about 95% oxygen, about 3% nitrogen, and about 2% argon. The fuel and oxidant flow rates are about 1.29 kg / sec and 4.24 kg / sec, respectively, in the main combustion furnace F1, while they are about 1.39 kg / sec and 4.56 kg / sec in the secondary combustion furnace F2. .

  Under these conditions, the temperature of water at the inlet of the economizer 40 is 150 ° C., and the temperature of hot water at the outlet of the economizer is about 180 ° C., whereas the temperature of the steam upstream from the preheating zone P Is about 450 ° C. and about 250 ° C. downstream from this region. The temperature of the two-phase liquid steam fluid is approximately 305 ° C. at the evaporator outlet 70 after passing through the evaporator 20. The temperature of the steam at the inlet of the low temperature superheater 38 is about 305 ° C. and the outlet thereof is 330 ° C., whereas the temperature of the steam upstream from the low temperature superheat zone S2 is about 750 ° C. It is about 450 ° C downstream. The temperature of the steam at the inlet 80 of the intermediate temperature superheater 78 is about 330 ° C., and the temperature at the outlet 84 is about 420 ° C., whereas the temperature of the steam upstream from the intermediate temperature superheat zone S3 is about 1300 ° C. The temperature is about 1000 ° C. downstream from this region and at the inlet of the purification chamber 76. The temperature of the steam at the inlet of the high-temperature superheater 30 is about 420 ° C. and the outlet 62 is about 480 ° C., whereas the temperature of the steam upstream from the high-temperature superheat zone S1 is about 1300 ° C. It is about 500 ° C. downstream from this superheat zone.

  The present invention is not limited to the examples of the embodiment described above, and the present invention includes all modifications.

  Advantageously, it may be considered to operate the main combustion furnace F1 with an excess of fuel relative to the oxidant under stoichiometric conditions so as to limit the emission of nitrogen oxides.

  Under such conditions, in order to achieve appropriate combustion efficiency, the sub-combustion furnace F2 can be operated with an excess of oxidant relative to the fuel under the stoichiometric conditions described above.

  Furthermore, considering the thermal energy available in the combustion furnace, it is possible to dispense with an economizer, and it may be advantageous to preheat water with an evaporator that receives water at a predetermined temperature at a predetermined location. . This water will be preheated at the beginning of the evaporator during circulation and then evaporated at the rest of the evaporator.

6 is a graph showing the efficiency difference between combustion with air (curve I) and oxyfuel combustion (curve II) in a conventional steam generator. It is a figure which shows the generator which concerns on one Embodiment of this invention. It is a figure which shows the 1st modification of this invention. It is a figure which shows another modification of this invention.

Claims (17)

  At least one combustor supplied with fuel and oxidant; an evaporation zone comprising an evaporative heat exchanger; a superheat zone comprising a superheat heat exchanger; a preheat zone comprising a preheat heat exchanger; and a recovery drum Steam generator comprising at least two continuous combustion furnaces (F1, F2), each furnace comprising at least one evaporative heat exchanger (20).   Steam generator according to claim 1, characterized in that each furnace comprises at least one superheat exchanger (30, 38, 78).   Steam generator according to any one of claims 1 and 2, characterized in that each furnace comprises at least one preheating heat exchanger (40).   One of the furnaces (F1) is provided with at least one evaporative heat exchanger (20), and the other furnace (F2) is provided with at least one superheat heat exchanger (30, 38, 78). The steam generator according to any one of claims 1 to 3.   One of the furnaces (F1) comprises at least one evaporative heat exchanger (20), and the other furnace (F2) also comprises at least one superheat exchanger (30, 38, 78) and at least one preheating heat. Steam generator according to any one of the preceding claims, characterized in that it comprises an exchanger (40).   One of the furnaces (F1) comprises at least one evaporative heat exchanger (20) and at least one superheat heat exchanger (30), and the other furnace (F2) also comprises at least one superheat heat exchanger ( 38. A steam generator according to any one of claims 1 to 4, characterized in that it comprises at least one preheating heat exchanger (40).   Steam generator according to any one of the preceding claims, characterized in that the steam generator comprises a steam purification chamber (76) for steam coming from the combustion furnace (F1, F2).   The steam generator according to claim 7, wherein the steam purification chamber (76) is arranged upstream from the preheating zone (P).   The steam generator according to any one of claims 7 and 8, wherein the steam purification chamber (76) is provided with a hygroscopic agent injection means (88).   The steam generator according to any one of claims 7 to 9, wherein the steam purification chamber (76) includes a reducing agent injection means.   The steam generator according to any one of claims 7 to 9, characterized in that the steam purification chamber (76) comprises at least one evaporation zone (V4).   The steam generator according to claim 9, wherein the hygroscopic agent is calcium or magnesium.   11. The steam generator according to claim 10, wherein the reducing agent is ureas or ammonias.   The steam generator according to claim 1, wherein the oxidant is an oxidant having a high oxygen content.   The steam generator according to claim 1, wherein the fuel is a solid, liquid, or gaseous fuel such as heavy oil, petroleum residue, gas, oil coke, or coal.   The steam generator according to any one of claims 1 to 6, characterized in that the wall of at least one furnace (F2) comprises a shell (32).   The steam generator according to any one of claims 1 to 6, wherein the wall of at least one of the furnaces (F1, F2) comprises a membrane wall.

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