FR3014540A1 - SOLID FUEL BOILER AND CONDENSATION - Google Patents

Abstract

Solid fuel boiler equipped with a furnace (1) comprising at least two separate primary and secondary air supplies (C1, C2). The air supply (5) is equipped with a mass and heat exchanger of air (6) for humidifying the combustion air and enhancing the water vapor content of the fumes, and a superheater (65) in downstream of the mass and heat exchanger of air (6) and before the entry of the humidified air into the hearth (1), to raise the temperature of the humid air and to desaturate it.

Description

Field of the Invention The present invention relates to a solid fuel boiler equipped with a furnace comprising at least two distinct primary and secondary air supplies.

STATE OF THE ART There are boilers with mass and heat exchangers making it possible to raise the dew point of the products of combustion to improve their performance, patent FR 71 12770. These boilers raise the dew point of the fumes by using an oxidizing air warmed and saturated with water vapor. The combustion efficiency is improved by the possibility of condensing the steam of the flue gases at higher temperatures than conventional condensing boilers. These boilers are usually boilers with liquid or gaseous fuels, because this process is difficult to apply to solid fuel boilers. In fact, boilers for solid fuels such as wood or coal, for example, are made of steel boiler parts of very large dimensions which can not be made of stainless steel for economic reasons, and which therefore fear corrosion. that would produce moist air from the mass and heat exchanger. A final part is the condenser recovery exchanger intended to cause the condensation of water vapor combustion fumes, to supply energy to a circuit for heating. Similarly, these boilers have a fireplace that includes large refractory masses. These refractories are generally masonry elements and do not support projections of droplets of liquid water such that the mass and heat exchanger inevitably dispenses with the production of its hot air and saturated with water vapor, or those resulting from condensation on the walls of pipes carrying this hot air. On the other hand, the stoves of solid fuel boilers must have at least two independent air supplies: primary air supply passing through the bottom of the combustion grate, secondary air supply which is brought into the hearth by holes generally made through the refractory.

A supply of hot and saturated primary air directly under the cold fuel below the grid would result in wetting it by condensation effect, the wood so wet would gorge with water by capillary action which would make it difficult to ignite.

The proportion of primary air and secondary air obeys precise rules according to the oxygen requirements of each of these circuits, but it turns out that the quantity of water vapor contained in the saturated humid air which the heat exchanger and thermal changes permanently the volumes of oxidant gas and the pressure drops of the supply circuits. Therefore it is not possible to properly adjust the combustion, or the ratio of primary air / secondary air due to the perpetual variations in oxidant moisture. These variations in oxidant moisture are inevitable due to adaptations of the mass and heat exchanger to the different power and temperature regimes during the operation of the boiler. For these reasons there are no solid fuel boilers with condensation. Object of the invention The object of the present invention is to develop a solid fuel and condensation boiler. DESCRIPTION AND ADVANTAGES OF THE INVENTION For this purpose, the subject of the invention is a boiler with solid fuels, characterized in that the air supply is equipped with a mass and heat exchanger for humidifying the combustion air and raising the water vapor content of the flue gases, and a superheater downstream of the mass and heat exchanger and before the entry of humidified air into the firebox, to raise the temperature of the humid air and to desaturate it.

The mass and heat exchanger combined with a superheater associated with the fireplace allow for a solid fuel and condensation boiler to enjoy all the advantages of the condensation effect applied to a boiler.

According to another characteristic of the invention, the superheater is supplied with energy from the furnace or from the heating water produced by the boiler or from the steam produced by the boiler. The superheater is in particular a device consisting of a heat exchanger combined with a heat pipe or a thermosiphon, a heat exchanger combined with a hot gas circuit. The heat pipe, the thermosiphon and the hot gas pipe come from the fireplace. According to another feature, the air supply, at the outlet of the humidifier, is subdivided into a primary air supply duct arriving under the hearth grate and a superheated wet secondary air supply duct arriving at the level of the furnace. development of the flames of the solid fuel bed. This air supply is particularly important for fuels developing a flame above the bed, fuels developing a flame under the fuel bed and embers in the case of reverse combustion wood boilers. In particular, the primary air supply and the secondary air supply can be provided by a different heat and mass exchanger, which makes it possible to regulate the moisture content of each air flow, differently, depending on the needs of the combus. - or the nature of the fuel. According to another characteristic, the primary supply duct, humid, superheated, as well as that of superheated wet secondary air, are each provided with a sensor for measuring primary and secondary air flow rate and / or the temperature of this air. This information is transmitted to a central management unit that manages the operation of the boiler. For the same reasons, the primary duct and the superheated humid air secondary duct are provided with flow control means.

The adjustment will be further refined if the inlet of oxidizing dry air upstream of the mass and heat exchanger is provided with a device for measuring the characteristics of the dry air entering the mass and heat exchanger.

According to another feature, the fireplace is equipped with a flame support device creating a hot spot located in the home to support the flame in case of excessive humidity and / or insufficient temperature of the home. This flame support device is advantageously constituted by a small supply of dry combustion air located on a point of the hearth, an electrical resistance, a blowing of hot air, especially at a high temperature higher than that of ignition and located on a point of the fireplace, an electric arc or an independent burner of fuel and combustion air.

According to another advantageous characteristic, the boiler comprises an outlet condenser traversed by the flue gases and which comprises a scrubber with a washing water circuit connected to the washing water circuit of the mass and heat exchanger treating the flue. combustion air.

The outlet condenser with its scrubber can advantageously be constituted by the outlet chimney which will be equipped with a scrubber with a bottom to recover the heated wash water and thus feed the exchanger wash water circuit. mass and thermal.

Drawings The present invention will be described in more detail below with the aid of various examples of solid fuel and condensation boilers shown very schematically in the accompanying drawings in which: FIG. 1 is a basic diagram of a boiler with According to the invention, FIG. 2 is a diagram of a second embodiment of a solid fuel and condensation boiler according to the invention, FIG. 3 is a diagram of a third embodiment of FIG. 3A is a detail of a variant of the third embodiment according to FIG. 3, FIG. 4 is a diagram of a fourth embodiment of a boiler with According to the invention, FIG. 5 is a diagram of another embodiment with an alternative flame support device, FIG. diagram of a boiler with two heat exchangers and air mass, Figure 7 is a diagram of another embodiment of the boiler with a heat exchanger and thermal fumes in the flue gas chimney. DESCRIPTION OF EMBODIMENTS OF THE INVENTION According to FIG. 1, the subject of the invention is a solid fuel and condensation boiler consisting of a hearth 1 with a grate 11 receiving a solid fuel bed CS surmounted by a heat exchanger primary 2 connected to a primary heating circuit 21. The hearth 1 is supplied with primary air under the fuel bed, through the gate 11 by adjustable registers 111; it is supplied with secondary air over the fuel (CS).

The combustion air of the hearth 1 is provided by a supply fan 5 followed by a heat and air heat exchanger 6 connected to the primary air circuit C1 and secondary C2 through a superheater 65 raising the temperature of the moist air and desaturator. At the outlet 22 of the primary heat exchanger 2, the combustion gas circuit comprises an extractor 3 supplying a condenser recovery exchanger 4 connected to a secondary heating circuit 41. The fumes then pass through a mass and heat exchanger for flue gases. then escape. In more detail, the mass and heat exchanger 6 is provided with an inlet 61 at the bottom, connected to the fan 5 and an outlet 62 at the top with a scrubber 63. The bottom 64 of the exchanger 6 recovers the wash water. The purpose of the mass and heat exchanger 6 is to humidify the combustion air in order to enhance the water vapor content of the fumes and to improve the dew point temperature and the condensation performance. The superheater 65, which raises the temperature of the moist air at the outlet 62 of the mass and heat exchanger 6, and the desiccation is supplied with energy from the hearth 1 or the produced heating water or steam if the boiler produces steam. The superheater 65 supplies the air circuits C1, C2. The hearth 1 receiving the humid air is preferably equipped with a flame support device 9 which creates a hot spot located in the hearth 1 to support the flame in case of excess humidity and / or insufficiency the temperature of the fireplace. This flame support device 9 is of negligible power with respect to the power of the boiler. It has a supply of fresh air and dry independent that allows him to maintain a local flame. This flame support device 9 may also be a direct supply of dry ambient air 491 and / or 492 located on a point of the hearth, an electrical resistance or a high temperature air blast or an electric arc holding a point hot. The ashes of the hearth 1 are recovered in an ashtray 112 from which they are discharged automatically by a device not shown. The condenser recovery exchanger 4 comprises exchange surfaces 42 intended to cause the condensation of the water vapor of the fumes provided with watering and water spraying means on surfaces intended to exchange by condensation to reinforce the thermal exchange by contact of this water with the fumes and to wash soot and particles that can be deposited. This washing is controlled periodically by a valve 44 of a rinsing circuit 43.

The condenser recovery heat exchanger 4 is connected to the inlet 71 in the lower part of the mass and heat exchanger of flue gases 7 whose outlet 72 in the upper part evacuates the fumes in the chimney. The mass and heat exchanger of flue gases 7 comprises at the top a scrubber 73 for washing the flue gases before they are discharged from the installation. The heated wash water is thus recovered at the bottom 74 of the mass and heat exchanger of flue gases 7. The heat and mass exchanger 6 and the mass and heat exchanger of flue gases 7 are connected by a washing circuit 8 formed of a forward leg 81 and a return leg 82 each equipped with a pump 83, 84 and filters 85, 86. The filters 85, 86 keep the water clean and free of particles, avoiding the transmission of particles in the fumes . These filters 85, 86 are for example simple settling tanks equipped with automatic sludge extractors. The forward leg 81 connects the bottom 74 of the mass and heat exchanger of fumes 7 to the washer 63 of the exchanger 6 and the return branch 82 connects the bottom 64 of the exchanger 6 to the scrubber 73 of the mass and heat exchanger 7. The washing water is circulated by the pumps 83, 84. The flue flushing circuit 43 of the secondary heat exchanger is derived from the circuit 8 supplying the mass and heat exchanger with flue gases. The solid fuel boiler described above is connected to a control unit 100 which manages the operation of the supply fan 5, the extractor 3, the circulation pumps 83, 84 according to the needs to be met by the boiler as well as temperature and gas flow measurements in the boiler. The primary air circuit C1 is equipped with a flow sensor 101. The secondary air circuit C2 is also equipped with a flow sensor 102. The primary air flow rate and the secondary air flow rate are regulated by regulators 104, 105 such as butterflies. The output of the supply fan 5 is also regulated by a regulator 106 such as a butterfly and the temperature of the air at the outlet of the fan is detected by a temperature sensor 103.

The superheated wet primary and secondary air flow sensors 101, 102 perform velocity, pressure, temperature and humidity measurements. The information thus collected is supplied to the central unit 100 which determines the equivalent flow rate of dry combustion air. This information is supplemented by the measurements made by the sensor 103 of the dry combustion air upstream of the air washer 63 of the mass and heat exchanger of air 6. According to one characteristic of the invention, the circuit of the - Vage 8 includes a device for adding treatment chemicals to prevent corrosion and / or reduce the rate of emission of gaseous pollutants by adding additives, for example from ash or soot and water from ashes or soot in case of wet ash systems. FIG. 2 shows a second embodiment of the solid fuel and condensation boiler, substantially identical to the first embodiment, except for the part relating to the superheater 265. According to this embodiment, the superheater 265 is constituted by a heat pipe or a thermosiphon. The end 266 of this superheater is located at the hearth 1 above the CS fuel bed to be heated in the case of a thermosiphon by a boiling liquid tank. A pipe 267 connects this hot spot 266 to a heat exchanger 268 placed in the moist air pipe 270 at the outlet of the mass and heat exchanger air 6. Depending on the case, it may consist of several elements in parallel , In particular independent and interchangeable with branches 267a, b, c deriving from the pipe 267. The other elements of the installation identical to those of the embodiment of Figure 1 bear the same references and their description will not be repeated.

FIG. 3 shows a third embodiment of a solid fuel and condensation boiler similar to the second embodiment of FIG. 2, with instead of the heat pipe or the thermosiphon, a superheater 365 connected to the air duct 370 and formed of a heat exchanger 368 fed by a duct 367 with the fumes of the hearth 1, returning through a duct 369 in the flue gas outlet 22 of the fireplace 1 upstream of the extractor 3. These fumes circulate in the rising direction through the exchanger 368. The duct is subdivided into several branches 367a, b, c in the exchanger 368 to emerge by the branches 369a, b, c joining the duct 369.

According to the variant shown in Figure 3A which relates only to the superheater 365A, the flow of fumes is in the opposite direction, the hot fumes arriving through the conduit 367 from the hearth pass through the heat exchanger 368 in the downward direction for better collection - The condensate and evacuate directly at this level by the branches 369a, b, c and the conduit 369 which receives the output 22. The other elements of the installation identical to those of the embodiment of Figure 1 bear the same references and their description will not be repeated.

FIG. 4 shows a fourth embodiment in which the flame support device 490 is constituted by an inlet of combustion air, directly from the fan 5 via a pipe 491 under the grid 11 and / or a pipe 492 arriving above of the grid 11 and the fuel bed CS to create preferential combustion points at two locations CS1 and / or CS2 of the fuel bed CS. The other elements of the installation identical to those of the embodiment of Figure 1 bear the same references and their description will not be repeated.

FIG. 5 shows another embodiment in which the flame support device 590 is constituted by an auxiliary burner supplied with unhumidified air and opening into the hearth 1 above the CS fuel bed. The other elements of the installation identical to those of the embodiment of Figure 1 bear the same references and their description will not be repeated. FIG. 6 shows another embodiment of the boiler with two heat and mass exchangers 6A, 6B, separate, one 6A for the primary air duct C 1 and the other 6B for the air duct secondary C2. These two heat exchangers and masks 6A, 6B are each powered by a fan 5A, 5B. The two heat exchangers 6A, 6B are provided with separate scrubbers 63A, 63B and separate superheaters 65A, 65B. The scrubbers are connected to the washing liquid circuit 8, which moreover comprises the heat and smoke heat exchanger 7.

The primary air ducts C1 and secondary air C2 can thus provide primary air and secondary air with different moisture contents and equivalent dry air flow rates perfectly controlled by each fan 5A and 5B.

The other elements of the installation identical to those of the embodiment of Figure 1 bear the same references and their description will not be repeated. FIG. 7 shows another embodiment of the invention in which the mass and heat exchanger of flue gases 7A is constituted by the flue gas chimney. The other elements of the installation identical to those of the embodiment of Figure 1 bear the same references and their description will not be repeated. In general, in the various embodiments shown in FIGS. 2-7, all the elements of the embodiment of FIG. 1, although taken up with the modifications described above, are not necessarily represented or referenced by detailed way. The boiler installation according to the invention is particularly suitable for boilers with a power of 100 kW to several MW.25 NOMENCLATURE 1 Fireplace 2 Primary exchanger 21 Primary heating circuit 22 Smoke outlet boiler 3 Extractor 4 Heat exchanger condenser 41 Secondary heating circuit 42 Condensing heat exchanger 43 Flue gas cleaning system 44 Valve 5, 5A, 5B Air supply fan 6, 6A, 6B Mass and heat exchanger for air 61 Heat exchanger inlet 62 Exit 63, 63A, B Scrubber 64 Bottom 65, 65A, B Superheater 7, 71 Heat and flue gas heat exchanger 71 Inlet 72 Outlet 73 Scrubber 74 Bottom 8 Wash liquid circuit 81 Outflow branch 82 Return pipe 83, 84 circulation of washing liquid 85, 86 Filters 9 Flame support 11 Grid 111 Registers 112 Ashtray35 100 Control unit 101, 102, 103 Temperature, humidity and pressure flow sensor 104, 105, 106 Flow regulator 265 Superheater 266 Superheater / hot spot end 267 Line 267a, b, c Branch lines 268 Heat exchanger 270 Wet air pipe 365, 365A Superheater 367 Inlet line 367a, b, c branches of the pipe 367 368 Exchanger 369 Exit line 369a, b, c Branch lines 369 370 Humid air line 490 Flame support / combustion air inlet 491 Line 492 Line 590 Flame support / auxiliary burner C 1 Primary air circuit C2 Secondary air system CS Solid fuels30

Claims (11)

CLAIMS1 °) Solid fuel boiler equipped with a fireplace comprising at least two separate primary and secondary air supplies, boiler characterized in that the air supply (5) is equipped with a mass heat exchanger and air (6) for humidifying the combustion air and raising the water vapor content of the flue gases, and a superheater (65) downstream of the mass and heat exchanger of air (6) and before the entry of humidified air in the hearth (1), to raise the temperature of the humid air and to desaturate it. 2) solid fuel boiler according to claim 1, characterized in that the superheater (65, 265, 365) is supplied with energy from the furnace or the heating water produced by the boiler or steam duit by the boiler. 3 °) solid fuel boiler according to claim 1, characterized in that the air supply at the outlet of the humidifier is subdivided into a superheated wet primary air supply duct (Cl) arriving under the grate ( 11) of the hearth (1) and a superheated wet secondary air supply duct (C2) arriving at the level of the flame development of the solid fuel bed (CS). 4 °) solid fuel boiler according to claim 3, characterized in that the superheated wet primary air supply duct (Cl) is provided with a sensor for measuring primary air flow, temperature, humidity and pressure (101) and the superheated wet secondary air supply duct (62) is provided with a secondary air flow rate sensor for temperature, humidity and pressure (102). 5 °) solid fuel boiler according to claim 3, characterized in that thee primary duct (Cl) and the secondary duct (C2) superheated wet air are provided with adjustment means (104, 105). Solid fuel boiler according to claim 1, characterized in that the oxidizing dry air inlet (61) upstream of the mass and heat exchanger (6) is provided with a measuring device. (103) characteristics of incoming dry air and flow rate. Solid fuel boiler according to claim 1, characterized in that the firebox (1) is equipped with a flame support device (9) creating a hot spot located in the firebox (1) to support the flame. case of excess humidity and / or insufficient temperature of the hearth. 8 °) solid fuel boiler according to claim 7, characterized in that the flame support device (9) is an electrical resistance, a hot air blow at high temperature, an electric arc or an independent burner. fuel and combustion air (490) or a point supply of dry ambient air. 9 °) solid fuel boiler according to claim 1, characterized in that it comprises a condenser recovery exchanger 4. 10 °) solid fuel boiler according to claim 1, characterized in that the boiler comprises a mass exchanger and flue gas heat exchanger (7) traversed by the flue gas and which comprises a scrubber (73) with a water circuit of washing (8) connected to the washing water circuit of the mass and heat exchanger of air (6) treating the combustion air. 11. A solid fuel boiler according to claim 1, characterized in that the superheater (65) is a device selected from the group consisting of a heat exchanger combined with a heat pipe heat exchanger combined with a thermosiphon (265) or a heat exchanger combined with a heat exchanger. hot gas circuit (365), the heat pipe, the thermosiphon and the hot gas pipe coming from the furnace (1).