FR3011917A1 - METHOD AND INSTALLATION FOR HEAT RECOVERY ON WET FUMES - Google Patents

Abstract

A method of recovering heat from humid fumes having a temperature greater than 100 ° C., Comprising: a first step in which part of the sensible heat of the fumes is recovered by heat exchange (16) between a first fluid and the fumes, the first fluid being heated to a temperature at least equal to 100 ° C while the fumes are cooled to a temperature close to the condensing temperature (6) of the water vapor; a second step in which, by condensation of the steam of the fumes, a second cooling fluid recovers, at a relatively low temperature level 50 ° to 60 °, a quantity of heat corresponding to a part of the heat latent condensation of water; The heat of the fluid is raised by a heat pump at a higher level 55 ° to 70 ° and then a third step during which a third fluid, heated by the amount of heat recovered in the second step, is brought to a temperature level close to or above 75 ° C by heat exchange (16) with the first heated fluid.

Description

METHOD AND INSTALLATION FOR HEAT RECOVERY ON WET FUMES.

The invention relates to a method for recovering heat from humid fumes with a temperature greater than 100 ° C. The combustion fumes leaving a heat recovery boiler or an incineration furnace are generally cooled in one or more exchangers, evaporator, superheater and a main economizer.

The flue gas temperature at the outlet of the main economizer is usually between 160 and 220 ° C. This allows a significant recovery on part of the sensible heat contained in the fumes, before their treatment. Indeed, the smoke from a combustion are released into the atmosphere. Releases must, however, comply with regulatory thresholds (pollutant concentrations), which is why a fume treatment step is mandatory. After this treatment step, the fumes still contain a lot of energy because of their relatively high temperature, greater than 100 ° C, in particular of the order of 160 ° C. This temperature depends on the type of flue gas treatment (dry, semi-dry, semi-wet). The object of the invention is, above all, to provide a method which makes it possible to recover an even greater amount of energy in the combustion fumes, in particular after treatment, at a sufficiently high temperature level, in particular greater than 70.degree. C, to be compatible with the requirements of a heat user such as dryer, district heating network, heating plants or process equipment. According to the invention, the method for recovering heat on moist fumes whose temperature is greater than 100 ° C., is characterized in that it comprises: a first step during which part of the sensible heat of the fumes is recovered by heat exchange between a first fluid and the fumes, the first fluid being heated to a temperature of at least 100 ° C while the fumes are cooled to a temperature close to the condensation temperature of the water vapor , in particular 60 ° to 50 ° C, - a second step during which, by condensation of the steam of the fumes, a second fluid recovers, at a relatively low temperature level, a quantity of heat corresponding to a part latent heat of condensation of water, - and a third step during which a third fluid, warmed thanks to the amount of heat recovered during the second tape, 5 is increased to a level of neighboring temperature, or greater than 75 ° C, by heat exchange with the first fluid heated to a higher temperature. Advantageously, the third step comprises a first phase during which an intermediate fluid is heated by the amount of heat recovered during the second step and passes through the evaporator of a heat pump, while the third fluid passes through the condenser. the heat pump to be raised to a higher temperature level, and a second phase in which the third fluid exiting the condenser is heated by heat exchange with the first heated fluid. In the first step, the flue gases can be cooled to between 45 ° C and 55 ° C, while the first fluid, especially water, is heated to a temperature of at least 100 ° C. The intermediate fluid, heated by the amount of heat recovered in the second step, can be at a temperature level of between 25 and 50 ° C, and the third fluid is brought to a temperature level of between 60 ° C. C and 72 ° C, by the heat pump, then at a temperature level of at least 75 ° C by heat exchange with the first heated fluid. The invention also relates to an installation for the recovery of heat on humid fumes, for the implementation of the method defined above, this installation being characterized in that it comprises: an additional heat exchanger which makes it possible to recovering sensible heat contained in the fumes, transferred to a first heated fluid leaving the additional exchanger, 30 - followed by a condensation exchanger, which is traversed by the cooled fumes exiting the additional exchanger, and giving a second heated fluid, and an exchanger, in particular a "Platulaire®" water / water heat exchanger, located between the first heated fluid leaving the additional exchanger and a third fluid that has been heated using the heat recovered in the condensing heat exchanger. Preferably, the installation comprises, after the condensation exchanger, a single or two-stage heat pump which comprises an evaporator traversed by an intermediate fluid which recovers the heat of condensation in an exchanger, and a condenser crossed. by the third fluid. The additional exchanger may consist of a dry heat exchanger 5 fumes / water and a exchanger smokes / water with wet surface, placed in series. The first, second and third fluids are advantageously constituted by water or a suitable thermal fluid. The water outlet of the evaporator of the heat pump can be connected to a water / water cross exchanger so as to recover the heat on a loop of condensates of the condenser heat exchanger, while cooling the circuit of the heat exchangers. condensate sprayed in the upper part of the flue gas condenser. The condensation exchanger may consist of a trickle condenser or a vertical tube tube condenser. The plant is advantageously formed by the combination of several components: additional exchanger, trickle condenser, heat pump, and exchangers, in particular water / water, so that their interaction in the overall operation makes it possible to achieve objective with the highest possible performance, that is to recover almost 100% of the residual heat (sensible + latent) so as to transfer heat to a temperature adapted to a user, between 75 ° C. and 100 ° C. The installation may comprise an auxiliary loop connected in shunt between the input and the output of the additional exchanger, and valves 25 for putting this auxiliary loop into service when the heat requirements of users, in particular district heat networks, are reduced if not nonexistent. The installation may be provided to operate with, or partially with, or without the latent heat recovery recuperator. The invention consists, apart from the arrangements set out above, in a number of other arrangements of which it will be more explicitly question below about an embodiment described with reference to the accompanying drawing, but which is not limiting. In this drawing: FIG. 1 is a diagram of a heat recovery plant on wet fumes, according to the invention, and FIG. 2 is a diagram of a condenser variant for the installation. Referring to Fig. 1 of the drawing, it can be seen that wet fumes, shown diagrammatically by an arrow S, are admitted to the inlet, located in the upper part, of a heat exchange assembly, constituting an additional exchanger fumes water 1. The fumes S can be obtained from an oven, in particular for the incineration of sludge from sewage treatment plants or municipal and similar household waste or from a boiler that makes it possible to recover the heat released by the combustion and to transfer it to a heat transfer fluid, water or steam. Generally, the fumes pass through a first exchanger or main economizer (not shown) which allows a sensible heat recovery contained in the fumes, before their treatment to remove harmful components. The flue gas temperature at the outlet of the main economizer is usually between 160 and 220 ° C. At the outlet of this main economizer and the inlet of the additional exchanger 1, depending on the type of fuel, the water vapor content of the fumes is greater than 70 g / kg and can reach 300 g / kg. The process and the plant according to the invention are designed to recover a maximum of sensible and latent heat from the fumes, at a temperature level close to or greater than 75 ° C. that this amount of heat can be exploited in a user of the dryer type, or district heat network or other process thermal equipment such as digester, air heater, etc. In a first step, part of the sensible heat of the fumes S is recovered, in the additional exchanger 1, by heat exchange between a first fluid, usually a liquid, preferably water, and the fumes. The additional exchanger 1 consists of a dry exchanger smoke / water 1a and a exchanger smokes / water lb wet surface, placed in series. The flow of the fluids is carried out in a methodical, cross-flow manner: the first fluid, water in the example considered, enters through a pipe 2 in the lower part of the exchanger lb wet surface, and continues to the Dry exchanger from which it leaves by the pipe 3. The circulation of water is from the bottom upwards while the flow of fumes S is from top to bottom. The wet surface exchanger 1b is positioned below the dry heat exchanger 1a, to allow the flow and discharge of condensates in the lower part 4 of the assembly 1. The exchangers of the economizer 1 are advantageously consist of smooth tubes, or finned. The lower exchanger 1b, which allows a start of condensation of the fumes, is equipped with tubes protected against corrosion (example: Teflon-coated tubes). The water arrives via the pipe 2 at a relatively low temperature, for example about 42 ° C and exits through the pipe 3 at a temperature at least equal to 75 ° C, preferably of the order of 110 ° C. The fumes S, which exit in the lower part 4 of the additional exchanger 1, have been cooled to a temperature close to the condensing temperature of the steam, in particular 60 ° to 50 ° C. The fumes are directed, via a line 5, to a condenser 6, 10 to undergo a second heat recovery step, mainly latent heat, by condensation of the water vapor fumes. According to the example of FIG. 1, the condenser 6 consists of a flow exchange body 7, a mistletoe and a bleed 8 at the bottom. The flue gas flow direction is from bottom to top, and the fumes are removed, after treatment eliminating the harmful components, to the atmosphere via a chimney 9. The condensates 10 are collected, for the most part, partly 6, and are circulated in a recirculation loop 11 by a pump 12 to pass, as a hot fluid, a heat exchanger 13. The condensates constitute the second fluid which recovers a part of the latent heat condensation of water. The cooled condensates are dispersed in the upper part by a sprayer 14. The exchanger 13, designed to cool the recirculation loop 11 is advantageously constituted by a "cross-plate" water / water exchanger 25 installed on the recirculation loop 11 of the condensates, outside the condensing zone. The water flowing through the cooling circuit 15 of the exchanger 13 constitutes an intermediate fluid which recovers a quantity of heat corresponding to a part of the latent heat of condensation of the steam of the flue gases. This amount of heat is recovered at a relatively low temperature level. According to the example of FIG. 1, the condensates enter the exchanger 13 at a temperature of about 50 ° C and leave at a temperature of about 20 ° C. Water from circuit 15 enters exchanger 13 at a temperature of about 10 ° C to rise to a temperature of about 30 ° C to 40 °. During a third step, a third fluid, heated by the amount of heat recovered during the second step, is brought to a higher temperature level, close to or above 75 ° C, by heat exchange in a exchanger 16, in particular a water / water cross exchanger, with the first heated fluid exiting through the line 3 of the additional exchanger 1. Advantageously, the amount of heat recovered by the circuit 15 in the exchanger 13 is carried, in a first phase, at a higher temperature level, in particular between 60 ° and 70 ° C, by a heat pump 17, or abbreviated PAC, then in a second phase at a temperature level close to or greater than, 75 ° C through the exchanger 16. The cooling circuit 15 of the exchanger 13 is connected to the evaporator 17a of the heat pump. The condenser 17b of the heat pump is connected to the heat exchanger 16. The medium temperature hot water loop on which the condenser 17b is located comprises a pipe 18 which connects the hot outlet of the condenser 17b to the cold inlet of the condenser 17b. circuit of the exchanger 16, while the hot outlet of this exchanger is connected by a pipe 19 to 1 "input of a heat consumer 20, including a secondary cross exchanger for the transmission of heat to users U, such The heat pump 17 may be single-stage or two-stage depending on the temperature level of the output fluid, namely water in the example 20 considered. single-stage heat pump will obtain, at the outlet of the condenser 17b, a temperature of 63 to 65 ° C, while a two-stage pump will achieve a temperature of 70 to 72 ° C. At their evaporator , the industrial PACs are capable of withdrawing energy from a fluid (air or water) whose temperature is between 25 and 50 ° C. The recovered thermal energy is transferred to another fluid (water) at the condenser by raising the temperature. The coefficient of performance COP of the heat pump depends on the difference in temperature between the hot source and the cold source. The larger the gap, the lower the COP. The hot water arriving via the pipe 18 is heated in the exchanger 16 by the water of the pipe 3 leaving the additional exchanger 1, and whose temperature, according to the example, is about 110 ° vs. The water coming from the pipe 3 leaves the exchanger 16 via a pipe 21 at a temperature of the order of 75 ° C. in the example under consideration, which is also the temperature of the water in the pipe 19 to the outlet of the exchanger 16. The two lines 19 and 21 are connected downstream of the exchanger 16 and upstream of the exchanger 20, in a line 22. The water at 75 ° C of the pipe 22 is cooled in the exchanger 20 and exits through a pipe 23 at a temperature of the order of 42 ° C, while the fluid intended for users, flowing in the loop 24, enters the exchanger 20 at a temperature of the order at 40 ° C and comes out at a temperature above 70 ° C. The flow of water in the hot water loop at medium temperature of the condenser 17b is provided by a pump 25 located upstream of a three-way valve 26, an outlet of which is connected by a pipe 27 to the inlet of the condenser 17b, and another output is connected by a pipe 28 to the inlet pipe 2 of the economizer 1. According to the example, the temperature of the water in the pipes 27 and 28 is of the order of 42 ° C, while the temperature of the water in the pipe 18, at the outlet of the condenser 17b of the heat pump, may be between 63 and 70 ° C. For certain periods of the year, especially in summer, the heat requirements of U users, especially district heating networks, are reduced if not non-existent. Advantageously, an auxiliary loop 29 connected by three-way valves 30, 31 provided respectively on line 3 upstream of exchanger 16, and on line 2, for supplying hot fluid from line 3 with devices heating 32 internal to a plant, especially for the heating of digesters, atmospheric tarpaulins, return condensate. A pump 33 ensures the circulation of water in this auxiliary loop 29. According to the example shown, at the inlet of the loop, the water is at about 110 ° C and output at about 50 ° C. Depending on the circumstances, all or part of the flow of the pipe 3 can be derived in the auxiliary loop 29, and the heat pump 17 can be shut down or in reduced load when the needs of users U are non-existent.

The installation also includes isolation valves, bypass valves and circulation pumps that have not been shown in detail. It should be noted that, the more fuels from which fumes S have a high level of water and / or hydrogen H2, the higher the latent heat of condensation will be compared to the sensible heat of combustion fumes. In some extreme cases the latent heat is greater than the sensible heat, so it is necessary to bring external energy to ensure combustion. The operation of the installation results from the above explanations. The fumes S enter the head of the additional exchanger 1 at a temperature between 130 ° C and 170 ° C, in particular 145 ° C according to the example of FIG. 1. They leave in the lower part by the pipe 5 at a temperature close to the condensing temperature of the steam, of the order of 54 ° C in the example. During this first step, a portion of the sensible heat of the fumes is recovered by the water, constituting the first fluid, which enters the pipe 2 at a temperature of about 42 ° C and leaves via the pipe 3 at a temperature at least 75 ° C, and preferably 110 ° C. During the second step, in the condenser 6, the latent heat of condensation of the water vapor of the flue gases is recovered by the second fluid, essentially the water of the condensates, circulating in the exchanger 13. The condensates enter a temperature of about 50 ° C in the exchanger 13 and leave at a lower temperature, 20 ° C according to the example, to be dispersed by the sprayer 14 in the condenser 6. Part of the latent heat of The condensation is thus recovered and transferred to the intermediate fluid of the loop 15, passing through the evaporator 17a, which is brought to a temperature of about 10 ° C to 30 ° C. During the third step, in a first phase, the heat pump 17 makes it possible to raise the temperature of a third fluid, preferably water, passing through the condenser 17b at a level of about 63 ° C. 70 ° C. In a second phase, the exchanger 16 makes it possible to complete the rise in the temperature level to a value close to or greater than 75 ° C., for efficient exploitation of the quantity of heat recovered in users, such as dryers or district heating networks for which the hot fluid must have a temperature of at least 70 ° C. The water / water exchangers may consist of water / water "Platulaire0" exchangers which have extremely high performances, the nip (or temperature difference) between the available temperature and the fluid to be heated (water) being about 1 , 5 ° C. In addition, their cost is reduced. According to the invention, the particular combination of the various components of the installation makes it possible to achieve the fixed goal, that is to say the recovery of a maximum quantity of energy, in the form of sensible heat and latent heat in the fumes, and also to raise the temperature level of the fluid, in particular water, at which the recovered heat has been transmitted. Depending on the needs, the operation of the first recovery stage, namely only the additional exchanger 1, is possible, in particular in summer, which allows a flexibility in terms of thermal power and optimization of the electrical consumption, related in particular to the operation of the heat pump 17.

According to one variant, the condenser 6, instead of being composed of a trickle-shaped exchange body, can be produced in the form of a tubular condenser 6a (FIG 2), in which case the circulation of the fumes is carried out from above, by an inlet 5a, downwards, with an outlet 5b, in a bundle of parallel tubes 6b which bathe in the cooling water formed by the condensates, with inlet 11a at the top, and outlet 11b in lower part. The opposite is also possible: a bundle of vertical water tubes connected on both sides by a perforated plate with the fumes located outside the tubes The applications of the invention are numerous. The heat recovery plant may be provided in any type of combustion unit using a fuel whose latent heat is important, for example waste, sludge, raw wood, biogas, such as thermal power plants, energy recovery units of waste, biogas boilers, wood-burning boilers, or the like. Such an installation is particularly justified when the recovered energy can be supplied to a potential external user, for example an urban heat network, industrial drying units, industrial treatment processes, or to feed certain internal uses, for example reheating the combustion air, condensate heating, reheating during a treatment step of a process. The field of application is vast because it is possible to provide an installation according to the invention in all types of fuel combustion units whose PCS (higher fuel power) is high, since the recovered energy can be used (external users or internal uses).

Claims (12)

REVENDICATIONS1. Process for the recovery of heat on humid fumes the temperature of which is higher than 100 ° C., characterized in that it comprises: a first step during which part of the sensible heat of the fumes is recovered by heat exchange between a first fluid and the fumes, the first fluid being heated to a temperature at least equal to 100 ° C while the fumes are cooled to a temperature close to the condensation temperature of the water vapor, - a second step during whereby, by condensation of the steam of the flue gases, a second cooling fluid recovers, at a relatively low temperature level, a quantity of heat corresponding to a part of the latent heat of condensation of the water, - and a third step during which a third fluid, heated by the amount of heat recovered during the second step, is brought to a level of temperature close to or above 75 ° C by heat exchange with the first heated fluid at higher temperature. 2. Method according to claim 1, characterized in that the third step comprises a first phase during which an intermediate fluid is heated by the amount of heat recovered in the second step and passes through the evaporator (17a) of a heat pump (17), while the third fluid passes through the condenser (17b) of the heat pump to be raised to a higher temperature level, and a second phase during which the third fluid exiting the condenser is heated by heat exchange (16) with the first heated fluid. 3. Method according to claim 1 or 2, characterized in that, during the first step, the fumes are cooled to a temperature between 45 ° C and 55 ° C, while the first fluid, especially water, is heated to a temperature of at least 100 ° C. 4. Method according to claim 2, characterized in that the intermediate fluid, heated by the amount of heat recovered in the second step, is at a temperature level between 25 and 50 ° C, and that the third fluid is brought to a temperature level between 60 ° C and 72 ° C, by the heat pump, then to a temperature level of about 75 ° C or more by heat exchange with the first heated fluid. 5. Installation for carrying out a method according to claim 1, characterized in that it comprises: - an additional exchanger (1) which allows to recover the sensible heat contained in the fumes (S); - followed by a condenser heat exchanger (6, 6a), which is traversed by the cooled fumes exiting the additional heat exchanger, and outputting a second heated fluid, - and an exchanger (16) between the first heated fluid exiting of the additional exchanger (1) and a third fluid which has been heated by the heat recovered in the condensation exchanger. 6. Installation according to claim 5, characterized in that it comprises, after the condensation heat exchanger (6,6a), a single or two-stage heat pump (17) which comprises an evaporator (17a). traversed by an intermediate fluid which recovers the heat of condensation in an exchanger (13), and a condenser (17b) traversed by the third fluid. 7. Installation according to claim 5 or 6, characterized in that the additional exchanger (1) consists of a dry exchanger smoke / water (1a) and a exchanger smokes / water (1b) with a wet surface, placed serial. 8. Installation according to any one of claims 5 to 7, characterized in that the first, the second and the third fluid consist of water. 9. Installation according to all of claims 6 and 8, characterized in that the water outlet of the evaporator (17a) of the heat pump is connected to a water / water cross exchanger (13) so as to recovering the heat on a loop (11) of condensates of the condensing heat exchanger (6, 6a) while cooling the condensates sprayed in the upper part of the flue gas condenser. 10. Installation according to any one of claims 5 to 9, characterized in that the condensation exchanger is constituted by a runoff condenser (6) or a tubular condenser (6a) with vertical tubes. 11. Installation according to any one of claims 5 to 10, characterized in that it comprises an auxiliary loop (29) connected bypass between the inlet and the outlet of the additional exchanger, and valves to put into use. this auxiliary loop when the heat requirements of users (U), including urban heat networks, are reduced if not nonexistent. 12 Installation according to any one of claims 5 to 11, characterized in that it is intended to operate with, or partially with, or without the latent heat recovery recuperator10