Method and furnace for incinerating organic substances, such as sludge, resulting from the treatment of industrial or agricultural waste or waste water

Abstract

The present invention relates to a method for incinerating organic substances in a fluidized bed incinerator furnace, said organic substances resulting from the treatment of waste water, industrial or agricultural waste, such as sludge, in particular sewage treatment plant sludge, said furnace comprising a casing in the lower part of which there is a granular bed, preferably a sand bed, which constitutes a fluidization zone Zf, said organic substances being introduced as fuel into said fluidization zone Zf, and air being injected as oxidant from a windbox through a fluidization dome located at the top of said box into said sand bed, said air passing through channels provided in said fluidization dome, said furnace being configured to treat a nominal value Vn of the volume Vmo of the organic substances to be treated. The invention consists in that the method comprises a step of adjusting the volume of said fluidization zone Zf as a function of the volume Vmo of the organic substances to be treated, in which step, when the volume Vmo of the organic substances to be treated is less than the nominal value Vn, the volume of said fluidization zone is reduced from an initial volume Vfi to a reduced volume Vfr, and the air flow rate is reduced by sealing the air channels so that only the channels leading into the thus reduced fluidization zone Zfr are operative.

Description

[0001] The present invention relates to a furnace for incinerating organic matter, such as sludge, resulting from the treatment of industrial or agricultural waste or wastewater, and more particularly to a fluidized sand bed furnace, as well as a method for incinerating organic matter such as sludge.

[0002] The fluidized bed incineration furnace includes a casing, in the lower part of which there is a granular bed, preferably a sand bed, which constitutes the fluidization zone, and sludge is injected as fuel into the fluidization zone. Below the fluidized bed is a wind box that receives preferably heated fluidization air through a radial inlet. The upper part of the wind box supports a fluidization dome. This fluidization dome is an important part of the furnace because the fluidization air is distributed through channels, such as those provided with blowing nozzles, passing through the dome.

[0003] The operating principle of the fluidized bed furnace is to suspend pre-calibrated particles of preferably sand by a fluid that can be preheated or not. The physics and thermodynamics of fluidization have been widely described in reference books such as "Fluidisation engineering" by Daizo Kunni and Octave Levenspiel, "Fluidisation" by Max Leva or Nichols. The fluidization dome separates the fluid manifold and the fluidized particles. It allows for a good distribution of the fluid through the blowing nozzles or fluidization tuyeres that constitute the channels to the fluidization zone.

[0004] The fluidized sand bed is heated to the incineration temperature (750 - 850 °C) and constitutes an extremely turbulent medium in which the heat exchange reaches a very high transfer coefficient. Through the turbulence of the sand, the organic matter, usually dewatered sludge, supplied to the base of the bed at one or more points decomposes very rapidly, evaporation occurs instantaneously, and partial combustion of the organic matter takes place with the fluidization air acting as an oxidant.

[0005] Generally, a dense fluidized bed with or without bed overflow is used, which has a stable expanded bed height (taking into account the loss of sand due to wear). This is because the mineral matter of the sludge has a very small particle size compared to the particles of the sand in the bed, such that all the mineral ash is pneumatically driven into the upper region of the furnace and then into the emission duct for soot (fly ash).

[0006] The incineration method implemented in this type of furnace thus allows the destruction of organic matter trapped in a mineral and / or liquid matrix, such as sludge from sewage treatment plants or sludge resulting from the treatment of industrial or agricultural waste or wastewater. This is the most widely used method for achieving such destruction while meeting the standards related to regulations.

[0007] The sludge burned in this type of furnace is generally pasty and still contains a lot of water at the outlet of the traditional dehydration system. The water content in the sludge is generally 55% to 85% of the raw material product. In the furnace, the redox reaction is carried out by reacting the organic matter as fuel with the expanding fluid as the oxidant (in most cases air).

[0008] Since the sludge to be treated generally still contains a lot of water, which highly cools the bed and the furnace, the organic matter of the sludge with only high calorific value may not be sufficient to maintain the furnace at 850 °C, which is its minimum operating temperature.

[0009] Thus, depending on the quality of the sludge, the furnace may require the injection of auxiliary fuel (natural gas, biogas or fuel oil or charcoal or any type of organic residue with a calorific value of organic matter higher than 15,000 kJ / kg) to maintain the temperature required by regulations, which is 850 °C in France.

[0010] However, when the water content of the organic matter is low, the sole input heat from the organic matter of the sludge can avoid the use of this auxiliary fuel during incineration.

[0011] The present applicant also proposes an improved method for recovering energy from the soot to obtain more dehydrated sludge through partial evaporation of the water part and to achieve a balance in the demand for auxiliary fuel between water and organic matter.

[0012] However, to start the furnace, auxiliary fuel is generally always used, generally gas or fuel oil for example. This fuel injection is carried out in the bed, preferably in the lower part of the bed, above the fluidization grid, above the dome, in the first third separating the fluid and the bed.

[0013] However, the need for consumption of auxiliary fuel cannot be completely eliminated at present. One of the reasons for this defect is that the amount of organic matter to be incinerated, such as sludge, to be treated is often very less than the nominal value used for sizing the furnace.

[0014] In fact, the construction project of the incineration workshop must meet the technical specifications that generally require incinerating sludge with a given output at the start of operation and a very high output in the future (such as 10 or 20 years) much higher than at the start to anticipate growth. Between these two cases, the sludge flow rate may double, while the incineration furnace has a flexibility of at most 1 to 1.6 for the range of sizes it has selected.

[0015] Often, during the start-up phase, the sludge flow rate is much less than the target amount required for the furnace design. Thus, to start operations, a furnace with dimensions corresponding to the start-up flow rate would be needed. Then, as operations evolve towards the target sludge flow rate, it would be preferable to replace this start-up furnace with a furnace whose dimensions are suitable for handling the target sludge flow rate. Given the costs involved, this solution is excluded.

[0016] Thus, furnaces are generally designed to operate in two modes during start-up operations, according to future operations:

[0017] - Either process the sludge production for a given period (generally one week) over several days to reach the operating conditions of the furnace.

[0018] - Or distribute the sludge production, for example, over a one-week period to continuously process the sludge, which means operating at a lower hourly rate and generally less than the minimum flow rate that the furnace accepts for optimal efficiency and / or to maintain self-heating.

[0019] In both cases, auxiliary fuel is used as a supplement:

[0020] - Either to keep the furnace hot during the non-incineration phase (called the maintenance phase). Keeping the furnace hot is achieved around 800 °C + / - 50 °C in the sand bed, which also allows keeping the equipment downstream of the furnace hot and limits the amplitude of the thermal cycles that can damage the equipment.

[0021] - Or during incineration, to fill the energy deficit caused by the reduced flow rate of the sludge and thus the organic matter of the inherent energy source, and also due to greater heat losses in the soot. In fact, the flow rate of the air present is then higher than the stoichiometric ratio for sludge combustion.

[0022] This stoichiometric ratio corresponds to the air flow rate strictly necessary to ensure complete combustion (or oxidation) of the fuel. In fact, any excess air generates energy losses because it is additional mass to be heated.

[0023] One solution could lie in reducing the amount of air to be sufficient for the amount of sludge and to reach a stoichiometric ratio close to 1.

[0024] However, there is a lower limit to the amount of air that allows the fluidization of the particles (here especially sand). This air is injected into the furnace at the base of the sand bed. Below this minimum flow rate, the sand is poorly fluidized and no longer functions for breaking up the sludge injected in the form of a column with a diameter of 50 mm to 250 mm (especially approximately 100 mm). In a furnace of given dimensions, the variation in the air flow rate between the maximum and the minimum is 60%, which corresponds to a variation in the sludge flow rate of 60% (by varying the excess air, with an error of a few percent), in other words, the sludge flow rate can vary from 1 to 1.6. This furnace design range with the maximum operating dimensions corresponding to the operating capacity of the furnace with a nominal sludge production (denoted as X) allows operation at a reduced capacity of up to 60%, i.e., at a sludge flow rate up to 60% lower than the nominal capacity of the furnace, while maintaining an air-sludge ratio favorable to good combustion and good fluidization.

[0025] If the flow rate is too low, it also cannot ensure the combustion of the volatile substances in the sand bed. The temperature of the sand decreases and is no longer uniform, which can create dead zones and pose a risk of agglomeration of the sand that could cause the entire fluidization of the bed to stop.

[0026] For example, by changing the matrix of the fluidized bed, it is also possible to consider reducing the particle size and thereby allowing a reduction in the air flow rate required for fluidization. There are existing such solutions, but they are still difficult to implement and may be insufficient: even in the same furnace dimensions, the capacity range could potentially increase from 1 to 1.6 to 1 to 2.0.

[0027] The main limitation of such a solution becomes apparent when the extreme production rates (current and future) cannot be scaled to a single furnace dimension.

[0028] To overcome these drawbacks, the present invention thus proposes to be able to vary the fluidization air flow rate according to the volume of sludge to be treated, without affecting the quality of the fluidization of the sand bed, and if necessary this is temporary. In other words, the present invention consists in providing a furnace whose dimensions are defined at a fluidization dome of, for example, 2.93 m according to future production targets (generally operating at a low rate of its dimensions), and whose dimensions can be temporarily changed to those of a smaller-sized furnace, for example, for the startup of the furnace, the diameter is reduced to 2.34 m.

[0029] Thus, by combining the minimum operating rate of the furnace with its reduced volume and air flow rate with the maximum rate of the furnace with its initial volume and flow rate, the maximum capacity range of a furnace of a given dimension from 1 to 1.6 is extended to a range of 1 to 3 for the sludge flow rate (for a small-sized furnace) and 1 to 2 (for a large-sized furnace).

[0030] To this end, an object of the present invention is a method for incinerating organic substances in a fluidized bed incinerator furnace, the organic substances being composed of organic substances captured in a mineral and / or liquid matrix, in particular from the treatment of wastewater, industrial or agricultural waste, such as sludge, in particular sewage treatment plant sludge,

[0031] The furnace includes a housing, and in a lower part of the housing there is a particle bed, preferably a sand bed, which constitutes a fluidization zone Zf,

[0032] The organic substances are introduced as fuel into the fluidization zone Zf, and air is injected as an oxidant from a windbox through a fluidization dome located at the top of the box into the sand bed,

[0033] The air passes through channels provided in the fluidization dome,

[0034] The furnace is configured to handle a nominal value Vn of the volume Vmo of the organic substances to be treated,

[0035] The method includes a step of adjusting the volume of the fluidization zone Zf and advantageously the air flow rate entering the fluidization zone Zf according to the volume Vmo of the organic substances to be treated. In this step, when the volume Vmo of the organic substances to be treated is less than the nominal value Vn, the volume of the fluidization zone is reduced from an initial volume Vfi to a reduced volume Vfr, and the air flow rate is reduced by sealing the air channels so that only the channels leading to the thus-reduced fluidization zone Zfr are operative.

[0036] Advantageously, the method according to the present invention makes it possible to define a reduced fluidization zone volume Vfr by reducing the volume of the fluidization zone Zf and by restricting the channels of the fluidization dome to the channels operative in the reduced fluidization zone Zfr, which allows an incineration treatment that is as optimized as possible relative to the volume Vmo of the organic substances to be treated, and which is suitable for operating conditions with a small organic substance flow rate.

[0037] Thus, when the volume of the sludge to be treated is less than the nominal value of the volume of the sludge to be treated and the furnace of dimension X reaches the lower limit of fluidization, the volume is reduced, which corresponds to an intermediate dimension of the furnace or fluidization zone of dimension X-1, and the air channels are sealed so that only the channels leading to the reduced fluidization zone are operative.

[0038] Moreover, advantageously, this regulation of the volume of the fluidization zone is preferably a temporary volume reduction. Thus, the method then includes a supplementary volume regulation step in which, once the volume Vmo of the organic matter to be treated approaches or reaches the nominal value Vn, the initial volume Vfi of the fluidization zone adapted to treat the organic matter to be treated at the nominal volume Vn is restored, and advantageously the initial air flow rate into said zone is also restored by releasing the air channels of the previously sealed fluidization dome. In this way, the incineration method can be implemented while limiting the consumption of fuel and thus of auxiliary fuel.

[0039] The method can advantageously be applied to existing working furnaces and also to future projects (furnaces under construction or to be constructed). Thus, the plug-in is installed in the form of a kit, which has a shape complementary to the part of the furnace casing that delimits the fluidization zone Zf and extends from the fluidization dome against said part of the casing at a height less than or equal to the height of the fluidization zone.

[0040] Thus, by arranging means for reducing the volume of the fluidization zone Zf, at least the volume of the fluidization zone is reduced, said means consisting of a plug-in in the form of a kit, which has a shape and height complementary to the part of the furnace casing that delimits the fluidization zone Zf, extends from the fluidization dome against said part of the casing, and delimits an internal volume corresponding to the reduced volume of the fluidization zone.

[0041] According to an alternative of the method, by installing the plug-in over the entire height of the furnace, it is also possible to reduce the volume of the furnace casing above the fluidization zone. Advantageously, reducing the volume of the casing above the fluidization zone can allow for improved ash discharge and limit heat losses. By this alternative, the energy and economic efficiency are further improved.

[0042] For the purposes of the present invention, the kit is a cylindrical element, the shape of which corresponds to the cylindrical shape of the fluidization zone. However, the fluidization zone of the furnace generally has a frustoconical shape, and the kit is also frustoconical.

[0043] According to this embodiment, the thickness of the wall of the kit can be constant or variable, in particular progressive, which defines the inner diameter of the kit, which corresponds to the reduced diameter of the newly reduced fluidization zone Zfr defined by the kit.

[0044] The kit is advantageously installed along the wall of the fluidization zone in the furnace and extends from the fluidization dome, covering the air channels provided through the fluidization dome at the periphery of the fluidization dome and terminating below the thickness of the kit, which reduces the air intake into the reduced fluidization zone. The kit also constitutes a sealing means.

[0045] Advantageously, the reduced fluidizing air volume flow rate can thus be expressed according to the following formula, which corresponds to the same formula for the nominal case and takes into account the flow rate of the organic matter to be processed:

[0046] Φv’ = Φb’ x S x MV x Coef1 x Coef2, where

[0047] Φv’: fluidizing air flow rate in kg / h

[0048] Φb’: raw sludge flow rate in kg / h (raw sludge is water and dry matter, and dry matter is mineral matter and organic matter).

[0049] S: proportion of dry matter in the organic matter in %

[0050] MV: proportion of organic matter in the dry proportion in %

[0051] Coef1: stoichiometric ratio corresponding to the amount of air in kg / h for burning 1 kg of organic matter, the stoichiometric ratio being 5 to 10 depending on the type of organic matter

[0052] Coef2: 1.01 to 1.4 for the excess air desired to ensure complete combustion of the organic matter.

[0053] The "raw sludge", also referred to as "wet sludge", refers to a mixture of the input dry matter and water. The dryness of these raw sludges is preferably 18 to 35%, generally about 22 to 26%.

[0054] According to a further more preferred embodiment, the housing has a frustoconical shape with an angle of 0° to 45° relative to the vertical direction at the fluidization zone, and the plug or kit preferably has a frustoconical shape:

[0055] - Its outer diameter Dext is equal to the diameter of the frustoconical part of the housing at the height of the added cone:

[0056] Dext = D1, which can vary over the height H, where

[0057] D1: inner diameter of the fluidization zone of the housing designed for the future production;

[0058] H: height of the zone where the dynamic development of particle fluidization takes place

[0059] - Its inner diameter Dint is equal to the outer diameter of the added frustoconical part minus twice the thickness A of the kit

[0060] Dint = Dext - A × 2, where A: is the thickness of the inserts added to the periphery of the fluidization zone to reduce the diameter of the fluidization zone, and this thickness can be constant or variable, especially progressive, and advantageously ranges from 0.15 to 0.7 m, preferably from 0.25 m to 0.35 m.

[0061] - The height H of the frustum cone is selected such that: H = B + C,

[0062] where B corresponds to the height of the particle bed at rest, B ranges from 0.3 m to 1.5 m, preferably equal to approximately 1 m, and

[0063] C corresponds to the dynamics, i.e., the desired turbulence in the sand bed, which ranges from 0 to 2 m, preferably from 0.3 to 0.5 m. This turbulence or dynamics corresponds to the projection height of the particles.

[0064] The reduction in the air flow rate is advantageously achieved by sealing the air channels located around the fluidization dome and terminating below the means for reducing the volume. The means for reducing the volume advantageously serves as the means for sealing the air channels.

[0065] Thus, for the purpose of maintaining particle fluidization, the volume Vfr of the fluidization zone is preferably reduced by the annular volume of a material that can resist temperature and wear added around the fluidization zone. For example, this annular volume of the wall inserted against the wall of the housing constitutes an insert or a kit.

[0066] It is also possible to consider inserts installed in the fluidization zone above the fluidization dome but not along the wall of the fluidization zone to reduce the volume of the fluidization zone and reduce the air flow rate by sealing a part of the air channels.

[0067] An example of a material that can resist wear and high temperatures is refractory concrete or refractory bricks.

[0068] According to the following formula, the volume flow rate Фv’ of the fluidizing air in the fluidization zone with reduced volume is thus reduced proportionally to the initial air flow rate Фv and the thickness of the cylindrical element:

[0069] Φv' = Φv x ((D1 - 2A) / D1) 2 , where,

[0070] D1: the inner diameter at the base of the fluidization zone of the housing designed for future production, in m

[0071] A: the thickness of the element added to the periphery of the fluidization zone to reduce the diameter of the fluidization zone, and this thickness is generally from 0.2 m to 0.7 m, preferably from 0.25 m to 0.35 m.

[0072] One object of the present invention is also a furnace for incinerating organic matter, said organic matter consisting of organic matter captured in a mineral and / or liquid matrix, in particular from the treatment of waste water, industrial or agricultural waste, such as sludge, in particular sewage treatment plant sludge, said furnace having a casing, in the lower part of which there is a fluidized bed of particulate matter, preferably sand, and said furnace further comprising, at least from bottom to top:

[0073] A bellows, the upper part of which supports a fluidization dome having channels through which air from the bellows is distributed in a fluidization zone Zf corresponding to the particulate bed,

[0074] At least one organic matter supply device and at least a supplementary fuel injection device, arranged to supply the fluidization zone,

[0075] - Above the fluidization zone Zf there is an expansion and afterburning zone, the top arch of the casing being located above said expansion and afterburning zone, at which there is a discharge duct for the combustion products,

[0076] The furnace is constructed to treat a nominal value Vn of the volume Vmo of the organic matter to be treated, and

[0077] The furnace is characterized in that it comprises means for reducing the volume of the fluidization zone from an initial volume Vfi to a reduced volume Vfr, and means for sealing the air channels, said means for sealing the air channels being constructed to reduce the input air flow rate by only activating the channels leading to the reduced fluidization zone Zfr when the volume Vmo of the organic matter to be treated is less than the nominal value Vn of the volume of the organic matter.

[0078] Thus, when the volume Vmo of the organic matter to be treated is less than the nominal value Vn (usually from 30% to 80% of Vn), the furnace can operate in an optimized manner because the volume of the fluidization zone is reduced from the initial volume Vfi to the reduced volume Vfr, and the injected air flow rate is reduced by sealing a part of the air channels to only activate the channels leading to the thus reduced fluidization zone. The furnace according to the present invention allows the implementation of the above-described incineration method.

[0079] Very advantageously, the reducing means and the sealing means can also be disassembled so that when the volume Vmo of the organic matter to be treated is close to or equal to the nominal value Vn, the reducing means and the sealing means can be removed and the initial volume Vfi and the number of air channels in the fluidization zone can be restored.

[0080] Thus, the volume of the fluidization zone and the volume of air blown into it can be reduced in order to treat in an optimized manner a volume Vmo of organic matter less than the nominal value Vn, while maintaining the dimensions of the furnace for future use.

[0081] Advantageously, the device for reducing the volume of the fluidization zone and the device for sealing the air passage are the same.

[0082] According to a preferred embodiment, the reducing and sealing device consists of inserts mounted in the fluidization zone of the furnace in the form of a kit, the kit having a shape complementary to the part of the casing that defines the fluidization zone, and extending from the fluidization dome against said part of the casing to form an additional wall doubling the wall of the fluidization zone and sealing the air passage provided in the dome periphery in the dome.

[0083] When the zone of the casing is cylindrical, the kit can thus be cylindrical. Preferably, when the fluidization zone has a frustoconical shape, the reducing and sealing device consists of a frustoconical kit capable of resisting wear and temperature. It is embedded in the existing frustoconical zone up to the fluidization grid base. Thus, the cross-sectional area at the fluidization grid is reduced, and at the same speed, the fluidization air flow rate is advantageously reduced.

[0084] The thickness of the insert, such as a cylindrical or frustoconical kit, is proportional to the reduction in the air flow rate desired for burning sludge or other waste. Preferably, its thickness corresponds to the thickness of the fluidization nozzle ring located at the periphery of the fluidization dome. In fact, the dome can consist of a sequence of concentric rings respectively carrying air passages for, for example, fluidization nozzles, ejectors. The thickness of the insert is thus chosen to define the reduced volume Vfr of the fluidization zone and the reduced cross-sectional area of the fluidization dome.

[0085] The thickness of the kit, which can be constant or variable, preferably progressive, is thus advantageously chosen to define the reduced volume Zfr of the fluidization zone and the reduced cross-sectional area of the fluidization dome, and the thickness of the kit is proportional to the reduction in the air flow rate desired for burning sludge or other waste.

[0086] Thus, preferably by adding an annular volume of material capable of resisting wear and temperature around the fluidization zone, the volume Vfr of the fluidization zone is reduced, for example, this annular volume of the wall inserted against the wall of the casing forms the insert or kit.

[0087] According to an embodiment of a furnace according to the present invention, the device for reducing the volume extends beyond the fluidization zone over the entire height of the furnace. This also limits the volume of the furnace casing. This reduction in the volume of the casing above the fluidization zone can allow for improved energy and economic efficiency, especially by improving ash discharge and limiting heat losses.

[0088] According to an embodiment, the reducing and sealing device is inserted into an existing furnace to optimize the operation of the existing furnace with respect to the nominal quantity of organic matter to be treated that has not yet been reached.

[0089] Alternatively, the reducing and sealing means are provided during the construction of the furnace to allow the operation to be enabled.

[0090] Advantageously, the reducing and sealing means extend along the wall of the fluidization zone and, through its thickness, reduce the diameter of said zone while sealing the channels provided in the fluidization dome and located above said fluidization dome. These reducing and sealing means can be placed on existing furnaces but can also be deployed on furnaces under construction to optimize the fuel consumption of self-activation.

[0091] They are easily added by constructing a base part (an additional wall added to the fluidization zone Zf) after the final construction or during the initial construction. They can thus be disassembled just as easily to restore the overall volume of the furnace required for the nominal flow rate of the organic matter (especially sludge) for which it is designed.

[0092] The material used to implement this wall can have a quality similar to that of the refractory inner wall of the furnace. This is, for example, a refractory brick that generally includes at least 20% alumina (preferably 42 to 45% alumina) to resist the wear exerted by the sand in motion. They are generally joined with caulking cement.

[0093] Alternatively, refractory concrete, especially refractory concrete including 30 to 35% by weight of alumina based on the total weight of the concrete, can be used to implement this additional wall. In this case, the concrete can be projected or molded against the inner wall of the fluidization zone. Such a material allows the use of the reducing means for about 1 to 2 years in the operating conditions of the furnace, but generally has a lower strength than the material constituting the furnace itself, which helps to break these reducing means when the initial volume Vfi is to be restored. Preferably, the material for the reducing and sealing means having a lower strength than the material constituting the furnace itself can thus be refractory concrete with an alumina content of 30% to 35% by weight based on the total weight of the concrete, while the concrete used to implement the furnace itself preferably has 40 to 42% alumina. The inserts forming the wall can thus be implemented with a less costly material.

[0094] The furnace according to the invention is advantageously implemented with the same materials and processing tools as those used for constructing the interior of the furnace.

[0095] These materials are generally refractory bricks and / or refractory concrete, or a combination of the two. The reducing and sealing means can be prefabricated in the factory before being installed in the furnace, or they can be manufactured in situ, i.e., in the furnace, by assembling bricks in the furnace, projecting or molding concrete to form the additional walls constituting the kit.

[0096] The kit is composed of additional walls inserted into the walls of the fluidization zone and can be made of refractory bricks or concrete. The techniques for installing and removing refractory materials for manufacturing and removing this additional temporary wall are the same as those for performing maintenance work or disassembling refractory walls, that is, by loosening the bricks or cutting the bricks into small, easily transportable pieces for discharge.

[0097] The present invention will now be described in more detail with reference to the accompanying drawings, which show:

[0098] Figure 1 : A longitudinal sectional view of an incinerator furnace according to the present invention in the nominal operating mode;

[0099] Figure 2 : Figure 1 A longitudinal sectional view of the furnace in the enabled operating mode.

[0100] As can be seen in Figure 1 the furnace 1 for incinerating organic matter (such as sludge) from the treatment of industrial, agricultural waste or wastewater has a housing 11 usually made of refractory concrete. In the lower part of this housing, there is a fluidized particle bed, preferably a sand bed 2.

[0101] The furnace also includes a windbox 3 that receives preferably preheated fluidizing air through a radial inlet 31. The upper part of the windbox 3 supports a fluidization dome 4 that constitutes an important part of the furnace 1. In fact, it is through this dome 4 that the fluidizing air from the windbox 3 is distributed by means of channels provided in the dome 4, and through this dome, the air from the windbox 3 is distributed in a part of the housing called the fluidization zone Zf 5 corresponding to the position of the sand bed 2.

[0102] In this fluidization zone Zf 5, there is at least one sludge supply device 6 and at least one supplementary fuel injection device 7. In some furnaces, the sludge supply device is implemented above the fluidization zone. A supply device 10 is also provided to introduce sand into the furnace. Above the fluidization zone 5, there is an expansion and afterburning zone 8, and the top arch of the housing 11 is located on top of the expansion and afterburning zone, where there is a discharge duct (not shown) for combustion products.

[0103] The furnace 1 is configured to handle a nominal value Vn of the volume Vmo of the sludge to be treated.

[0104] At the fluidization zone Zf 5, the wall of the furnace 1 has the shape of a frustum of a cone, with its largest upper base located on the side of the housing 11 and its smallest lower base located on the side of the fluidization dome 4.

[0105] The fluidization zone 5 thus defines a volume located above the fluidization dome 4, in which the sand bed 2 is present, and this fluidization zone is provided with injectors 51.

[0106] Thus, under the action of the heated air coming from the bellows 3 and passing through the fluidization dome 4, the displacement of the sand bed 2 that can only move towards the top of the furnace 1 is achieved. The upward velocity is related to the injected air flow rate and the lower cross-sectional area of the frustum cone.

[0107] The upward velocity determined for the nominal treatment value is typically 0.75 m / s for good fluidization of the sand and 1.2 m / s to avoid excessive sand entrainment. Preferably, the velocity is 0.9 m / s.

[0108] The furnace 1 is thus dimensioned for the sludge treatment nominal value Vn. However, often during the production start-up phase of this type of furnace 1, the sludge volume is usually much smaller than the desired target nominal value for which the furnace 1 is designed.

[0109] To enable the furnace 1 to operate in an optimized manner even during the production start-up phase, i.e., when the sludge volume Vmo to be treated is less than the nominal value Vn of the sludge volume to be treated, the volume of the fluidization zone zf 5 is reduced from the initial volume Vfi to a reduced volume Vfr, and the air channels are sealed to make only the channels leading to the reduced fluidization zone 5' operative.

[0110] For such an implementation, devices for reducing the volume of the zone 5 and for sealing the air channels, which are configured to make only the channels leading to the reduced fluidization zone 5' operative, are placed in the fluidization zone Zf 5.

[0111] As can be seen in Figure 2 the part of the outer shell 11 defining the fluidization zone Zf 5 has a plug supported thereon, which is in the form of a frustum-shaped kit 9. The kit extends from the fluidization dome 4 to a height H2 that is less than or equal to the height H1 of the frustum-shaped part of the outer shell 11.

[0112] The kit 9 has an outer diameter Dext that corresponds to the inner diameter D1 of the fluidization zone 5 and varies according to the height H2 of the plug 9, and a smaller inner diameter Dint that corresponds to twice the value of the diameter Dext minus the thickness A of the plug 9. Thus, the volume of the resulting fluidization zone Zfr 5' is reduced.

[0113] Since this volume Vfr is reduced, the volume of the sand is also reduced. The air volume flow rate is then restricted by sealing the air channels with the plug 9 that is partially located on the fluidization dome 4. The frustum-shaped effect also allows, through the frustum-shaped part of the outer shell, the recovery of the load of the frustum-shaped element. The cross-sectional area at the fluidization dome 4 is reduced, and at the same air velocity, the fluidization air flow rate is reduced.

[0114] The thickness A of the frustoconical plug 9 is proportional to the reduction of the air flow rate desired for the combustion of the organic matter to be treated (sludge and / or other waste).

[0115] The volume flow rate of the fluidizing air in the fluidization zone 5' with reduced volume Vfr thus decreases proportionally to the initial flow rate according to the following formula:

[0116] Φv’ = Φv x ((D1 - 2A) / D1) 2 , where

[0117] D1: The average inner diameter at the base of the fluidization zone of the housing designed for future production

[0118] A: The thickness of the element added to the periphery of the fluidization zone to reduce the diameter of the fluidization zone, the thickness is generally 0.2 to 0.7, preferably 0.25 m to 0.350 m.

[0119] To determine the air flow rate required when the volume of sludge to be treated is less than the nominal value, the formula is:

[0120] Φv’ = Φb’ x S x MV x Coef1 x Coef2, where

[0121] Φv’: The fluidizing air flow rate in kg / h

[0122] Φb’: The raw sludge flow rate in kg / h

[0123] S: The proportion of dry matter in the sludge (raw) in %

[0124] MV: The proportion of organic matter in the dry proportion in %

[0125] Coef1: The stoichiometric ratio corresponding to the amount of air in kg / h for burning 1 kg of organic matter, the stoichiometric ratio is 5 to 10 according to the type of organic matter

[0126] Coef2: For the excess air desired to ensure complete combustion of the organic matter, it is 1.01 to 1.4.

[0127] Thus, according to an embodiment of the method, a furnace is implemented with a diameter of the fluidization zone of 2.83 m (dimension X) and is configured to process at least 963 kg MS / h. Such a furnace operates with a preheated fluidization air flow rate of, for example, 550 °C from 6700 Nm3 / h (for a minimum blowing air velocity for fluidization of ~0.75 m / s) corresponding to a sludge dry matter flow rate of, for example, 963 kg MS / h to 10750 Nm3 / h (maximum fluidization velocity of ~1.2 m / s) corresponding to a flow rate of 1550 kg MS / h. The oxygen content is the same in both cases.

[0128] The activation of the furnace is characterized in that for flow rates far below the minimum flow rate of 600 kg MS / h, a fluidization air flow rate of 4250 Nm3 / h would be sufficient, and thus, a furnace with a smaller size (dimension X - 1) would be required. If this flow rate is distributed over seven days a week and applied to a furnace of the original size (X), the fluidization velocity for such a constructed furnace of this type would be 0.47 m / s, which is too low in terms of the turbulence in the bed.

[0129] Two solutions are feasible. In the first case, with the minimum flow rate (963 kg MS / h) for which the furnace is constructed, the sludge is processed 3 to 4 days a week, and the gas consumption required during sludge incineration is 19 kg / h. On the other hand, the furnace temperature is then maintained during the remaining period of the week, which corresponds to a large natural gas consumption of approximately 40 kg / h.

[0130] In the second case, with a high air flow rate of 6700 Nm3 / h, the sludge is processed seven days a week to meet the minimum fluidization air velocity of 0.75 m / s to have the required turbulence in the sand bed. The excess air causes losses and highly increases the consumption of auxiliary fuel, such that the consumption changes from 19 kg / h (as in the previous case, in the incineration for 3 to 4 days) to 46 kg / h of natural gas for 7 days to compensate for the losses. The operator selects this solution to protect the equipment downstream of the furnace.

[0131] The method of the present invention is then implemented by adding a plug with a thickness of 300 mm at a height of, for example, 1.3 m, reducing the dimension of the fluidization zone to a diameter of 2.23 m. The air volume is then adapted to the sludge volume while maintaining good turbulence in the furnace. The flow rate can be reduced to 4200 Nm3 / h to meet the minimum turbulence velocity of 0.75 m / s in this newly reduced fluidization zone. The excess air is reduced, and advantageously, the natural gas consumption is reduced from 46 kg / h to 18 kg / h.

[0132] The method of the present invention not only allows an operating saving of approximately 100,000 euros per year but also advantageously limits CO 2 emissions (616 t of CO per year) 2No longer released into the atmosphere).

[0133] In certain already existing waste treatment plants, for an estimated investment of 30,000 to 70,000 euros, the implementation of an incineration furnace according to the invention allows for annual savings of 50,000 to 200,000 euros in terms of natural gas that can be used as fuel. The invention thus offers significant economic advantages and is at the same time easy to implement, whether in existing or new facilities.

Claims

1. A method for incinerating organic substances in a fluidized bed incinerator furnace, said organic substances being composed of organic substances captured in a mineral and / or liquid matrix, The furnace includes a housing, in the lower part of which there is a particle bed, which constitutes a fluidization zone Zf. The organic substances are introduced as fuel into the fluidization zone Zf, and air is injected as an oxidant from a wind box through a fluidization dome located at the top of the box into the particle bed. The air passes through channels provided in the fluidization dome. The furnace is configured to handle a nominal value Vn of the volume Vmo of the organic substances to be treated. It is characterized in that, The method includes the step of adjusting the volume of the fluidization zone Zf and the air flow rate entering the fluidization zone Zf according to the volume Vmo of the organic substances to be treated. In this step, when the volume Vmo of the organic substances to be treated is less than the nominal value Vn, the volume of the fluidization zone is reduced from an initial volume Vfi to a reduced volume Vfr, and the air flow rate is reduced by sealing the air channels so that only the channels leading to the thus-reduced fluidization zone Zfr are in operation.

2. The method according to claim 1, It is characterized in that, Adjusting the volume of the fluidization zone is a temporary volume reduction.

3. The method according to claim 2, It is characterized in that, The method includes a supplementary volume adjustment step. In the supplementary volume adjustment step, once the volume Vmo of the organic substances to be treated approaches or reaches the nominal value Vn, the initial volume Vfi of the fluidization zone suitable for treating the organic substances to be treated and the initial air flow rate are restored.

4. The method according to any one of claims 1 to 3, It is characterized in that, A plug-in is installed in the form of a kit (9), which has a shape complementary to the part of the housing (11) of the furnace that defines the fluidization zone Zf (5) and extends from the fluidization dome (4) against the part of the housing (11) at a height (H) less than or equal to the height (H1) of the fluidization zone (5).

5. The method according to any one of claims 1 to 3, It is characterized in that, By installing a plug-in that extends over the entire height of the furnace, the volume of the housing of the furnace above the fluidization zone is also reduced.

6. The method according to claim 4, It is characterized in that, The housing (11) has the shape of a frustum of a cone with an angle of 0° to 45° with respect to the vertical direction at the fluidization zone (5).

7. The method according to claim 4, It is characterized in that, The kit (9) has the shape of a frustum of a cone, and: - Its outer diameter Dext is equal to the diameter of the frustum of the cone of the housing (11) at the height of the added frustum of the cone: Dext = D1, which can vary at the height H, where, D1 is the inner diameter of the fluidization zone of the housing designed for future production, and H is the height of the region where particle fluidization develops dynamically, -- Its inner diameter Dint is equal to the outer diameter of the added frustum of the cone minus twice the thickness A of the kit. Dint = Dext - A×2, where A is the thickness of the element added around the fluidization zone to reduce the diameter of the fluidization zone, and the thickness is from 0.15 to 0.7 m. -- The height H of the frustum cone is selected such that: H = B + C, where B corresponds to the height of the particle bed at rest, B is from 0.3 m to 1.5 m, and C corresponds to the dynamics, i.e., the desired turbulence in the particle bed from 0 to 2 m.

8. The method according to claim 1, characterized in that, the organic matter comes from the treatment of wastewater, industrial or agricultural waste.

9. The method according to claim 1, characterized in that, the organic matter is sludge.

10. The method according to claim 1, characterized in that, the organic matter is sewage treatment plant sludge.

11. The method according to claim 1, characterized in that, the particle bed is a sand bed.

12. The method according to claim 7, characterized in that, the thickness A of the element added around the fluidization zone is from 0.25 m to 0.35 m.

13. The method according to claim 7, characterized in that, the height B of the particle bed at rest is equal to about 1 m.

14. The method according to claim 7, characterized in that, the desired turbulence C in the particle bed is from 0.3 m to 0.5 m.

15. A furnace (1) for incinerating organic matter, the furnace having a housing, in the lower part of the housing there is a fluidized particle bed (2), and the furnace further comprises: a bellows (3), the upper part of the bellows supporting a fluidization dome (4), the bellows having channels through which air from the bellows (3) is distributed in a fluidization zone Zf (5) corresponding to the particle bed (2), at least one organic matter supply device (6) and at least one supplementary fuel injection device (7), arranged to supply the fluidization zone, above the fluidization zone Zf (5) there is an expansion and after - combustion zone (8), the top arch of the housing (11) being located above the expansion and after - combustion zone, and at the top arch there is a discharge duct for combustion products, the furnace (1) being configured to handle a nominal value Vn of the volume Vmo of the organic matter to be treated, characterized in that the furnace (1) comprises means for reducing the volume of the fluidization zone Zf (5) from an initial volume Vfi to a reduced volume Vfr, and means for sealing the air channels, the means for sealing the air channels being configured to reduce the input air flow rate by only activating the channels leading to the reduced fluidization zone Zfr (5’) when the volume Vmo of the organic matter to be treated is less than the nominal value Vn.

16. The furnace (1) according to claim 15, characterized in that, the means for reducing the volume Vf of the fluidization zone Zf and the means for sealing the air channels are the same.

17. The furnace (1) according to one of claims 15 and 16, characterized in that, The reduction and sealing device consists of inserts mounted in the fluidization zone Zf in the form of a kit (9), the kit having a shape complementary to the part of the housing (11) that defines the fluidization zone Zf (5) and extending from the fluidization dome (4) against said part of the housing (11).

18. The furnace (1) according to claim 17, characterized in that the thickness A of the insert (9) is chosen to define the volume Vfr of the reduced fluidization zone and the reduced cross-sectional area of the fluidization dome, the thickness A of this insert (9) being proportional to the reduction in the air flow rate desired for the combustion of the organic matter, the desired air flow rate being defined by the following formula: Φv’ = Φb’ × S × MV × Coef1 × Coef2, where Φv’: fluidization air flow rate in kg / h, Φb’: organic matter flow rate in kg / h, S: proportion of dry matter in the organic matter (as received) in %, MV: proportion of organic matter in the dry proportion in %, Coef1: stoichiometric ratio corresponding to the amount of air in kg / h for the combustion of 1 kg of organic matter, this stoichiometric ratio being between 5 and 10 depending on the type of organic matter, Coef2: excess air desired to ensure complete combustion of the organic matter, being between 1.01 and 1.4, this air flow rate is also defined by the following formula: Φv’ = φv × ((D1 - 2A) / D1) 2 , where D1: average internal diameter at the base of the fluidization zone (5) of the housing designed for future production, Φv: nominal fluidization air flow rate in kg / h, A: thickness of the insert (9) added to the perimeter of the fluidization zone (5) to reduce the internal diameter of the fluidization zone (5), this thickness generally being between 0.15 m and 0.7 m.

19. The furnace (1) according to one of claims 15 and 16, characterized in that the reduction and sealing device is inserted into an existing furnace.

20. The furnace (1) according to one of claims 15 and 16, characterized in that the reduction and sealing device is provided during the construction of the furnace (1).

21. The furnace (1) according to claim 17, characterized in that the insert (9) consists of an additional wall made of refractory material inserted into the wall of the fluidization zone (5).

22. The furnace according to claim 21, characterized in that the materials used are refractory bricks, concrete.

23. The furnace (1) according to one of claims 15 and 16, characterized in that the reduction and sealing device can be disassembled.

24. The furnace (1) according to one of claims 15 and 16, characterized in that the device for reducing the volume extends beyond the fluidization zone over the entire height of the furnace.

25. The furnace (1) according to claim 15, characterized in that the organic matter comes from the treatment of wastewater, industrial or agricultural waste.

26. The furnace (1) according to claim 15, characterized in that the organic matter is sludge.

27. The furnace (1) according to claim 15, characterized in that the fluidized particle bed is a sand bed 28. The furnace (1) according to claim 18 characterized in that the thickness of the insert (9) added to the periphery of the fluidization zone (5) is from 0.25 m to 0.35 m

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