EP0434945B1

EP0434945B1 - Fluid-bed incinerator

Info

Publication number: EP0434945B1
Application number: EP90121485A
Authority: EP
Inventors: Piergiorgio Fontana; Sergio Zuccotti
Original assignee: Italimpianti SpA
Current assignee: IRITECNA SOCIETA PER L'IMPIANTISTICA INDUSTRIALE E
Priority date: 1989-12-28
Filing date: 1990-11-09
Publication date: 1994-12-28
Anticipated expiration: 2010-11-09
Also published as: EP0434945A2; IT8912621A1; IT1236182B; EP0434945A3; DE69015601T2; ATE116420T1; IT8912621A0; DE69015601D1

Abstract

The invention relates to a fluid-bed incinerator comprising a kiln with its combustion chamber being formed with a gas-pervious hearth (6), and which is provided with means (21) for loading into the combustion chamber any refuse to be incinerated above the hearth (6), and with means (4, 5) for feeding through the gas-pervious hearth (6) an upward combustion air flow, and also with means (22) for feeding chemical reagents into the said combustion chamber. According to the invention, the hearth (6) is formed with a centrally located outlet opening (106) which is connected to a delivery duct (9), means (26) being provided for feeding cold air into the combustion chamber in kiln (1), through the delivery duct (9) and the outlet opening (106) in hearth (6), and means (27) being provided for the delivery duct (9) to be put under vacuum by a suction device located in the last section of the delivery duct (9). <IMAGE>

Description

The invention concerns a fluid-bed incinerator comprising a kiln with its combustion chamber containing a gas-pervious hearth, and which is provided with means for loading any refuse to be incinerated into the combustion chamber above the hearth, and with means for feeding an upward combustion air flow through the gas-pervious hearth, and also with means for feeding chemical reagents into the said combustion chamber, whereas the hearth of kiln is formed with a centrally located outlet opening which is connected to a delivery duct means being provided for feeding cold air into the combustion chamber in kiln, through the delivery duct and the outlet opening in the kiln hearth.
A fluid-bed incinerator of this type is known from the document US-A-4.854.249.
The object of the invention is to provide a fluid-bed incinerator according the pre-characterizing part of claim 1, which is of a simple, relatively not expensive construction, and at the same time guarantees such optimum conditions in the fluid hed, that a perfect course of the combustion process and an improved separation of the residual products of combustion will be obtained.
According to the characterizing part of claim 1, the invention attains the aforesaid object by the combination of the following features:

a) the delivery duct consists of a first delivery duct, and of a successive, second delivery duct, and a tubular hub is connected with the outlet opening in hearth, and is received into the counterbored upward end of the first delivery duct, the free downward end of the first delivery duct, the free downward end of the first delivery duct extending into a widened portion in the successive, second delivery duct, and a cold air feeding duct is provided, which opens into the counterbored end of the first delivery duct, preferably at a higher level than the opening at the lower end of the tubular hub;
b) a cold air suction duct is provided, which is connected with the widened portion in the successive, second delivery duct, preferably above the opening at the free end of the first delivery duct, whereby the delivery ducts are put under vacuum.

According to a further improvement, the cold air feeding and suction means are so provided that the fed cold air flow is parted into an upward cold air flow flowing into the combustion chamber in the kiln at a flow rate of 75% of the fed cold air flow, and into a cold air downward flow drawn into the suction means at a flow rate of 25% of the fed cold air flow.
According to the foregoing, cold air renders it possible to have the residual products of combustion cooled, generally from a temperature of about 850°C down to a temperature of about 200-70°C. The fine particle size material forming the mass of the fluid bed, is efficiently separated from the said residual products of combustion owing to the said material being upwardly entrained in the fluid bed. The air that cools the residual products of combustion also allows a certain energy recovery therefrom. This air actually is in a degree of from 10 to 20% of the total air for the fluid-bed process, the combustion air for the incinerating process.
A further feature of the invention resides in that reagents having a fine particle size of about 100 micromillimeters, which in any case is such as to allow the reagents to be partly or entirely drawn along with the flue gases, are preferably fed pneumatically into the combustion chamber, in the inside of the fluid bed, and/or over the fluid bed itself.
Thanks to this feature, a good part of "fresh" reagents, i.e., the reagents that have not yet taken part to any chemical reaction, is drawn along with the flue gases, so that any reagents neutralizing reaction with acid gases can occur not only in the fluid bed but also in the region thereover, in which the combustion of volatiles in the infed fuel mainly takes place. Also, the ashes of the burned refuse will have their softening temperature increased of about 200°C, particularly owing to the action of carbonates, oxides, and hydroxides of alkaline-earth metals, whereby the forming of any agglomerate in the fluid bed, on the surfaces of the fluid-bed-cooling tube nest, on the combustion chamber refractory walls, and around an auxiliary burner which may be provided for a successive flue gas post-heating, is at the same time avoided. Finally, a part of the flue gas-entrained "fresh" chemical reagents is also caused to get into the bag filter at a temperature of 110-150°C, whereby the acid gases neutralising reaction is completed.
The aforementioned advantages therefore contribute to a better utilization of energy and to a better course of the combustion process, thus guaranteeing an ideal operation of the fluid-bed incinerator.
Also other features further improving the above-disclosed fluid-bed incinerator form the object of the invention, and are the subject of the dependent Claims.
The particular features of the invention and the advantages arising therefrom, will appear more in detail from the description.

Figure 1 is a block diagram of a fluid-bed incinerator equipment according to the invention, and comprising a kiln.
Figure 2 is a sectional view through the hearth area of the combustion chamber in the kiln of the fluid-bed incinerator according to the invention.
Figure 3 is an enlarged view showing a detail of the gas-pervious hearth of the combustion chamber in the kiln of the fluid-bed incinerator according to Figure 2.

Referring to Figure 1, the fluid-bed incinerator equipment comprises a kiln 1. The hot gases used for pre-heating the mass of the fluid bed at the time the incinerator is being started, are produced in a generator 2 fitted with a burner 3. Through the ducts 4 and 5, the hot gases and the combustion air are fed underneath the hearth 6 of the combustion chamber in kiln 1, into two annular chambers 7 and 8. Once the fuel self-ignition temperature has been reached, the input of hot gases is stopped, while the feeding of not pre-heated air is being continued. The hearth 6 is made in form of a conical hopper, and is gas-pervious. The kiln 1 is fitted at its bottom area with a duct 9 for delivering the residual products of combustion, which by its top end is connected with a centrally located outlet opening 106 in hearth 6, and by its lower end opens into a vessel 10 for collection of the residual products of combustion. Any particulate matter being entrained by the flue gases to the exterior of the fluid bed, is fed to a cyclone 11 in which most of the entrained dusts are separated from the flue gases. The collected dusts are then delivered into a dust-collecting container 12, or the same are again conveyed into the kiln 1 of the fluid-bed incinerator, while the flue gases containing any residual dusts with a very fine particle size, are introduced into a successive, secondary combustion chamber 13 fitted with a burner 14. The flue gases are then fed to a fume cooler 16. The outlet of the fume cooler 16 is connected to a successive bag filter 17, in which any dusts contained in the flue gases are separated therefrom and delivered into a dust-collecting container 18, while with the aid of an exhauster fan 20, the dust-freed flue gases are vented into the atmosphere through a stack 19.
As it clearly appears in Figure 1, any refuse to be incinerated is loaded into the combustion chamber preferably over the fluid-bed surface S, by suitable refuse-loading means designated by numeral 21. Numeral 22 denotes the reagent feeding means. Reagents are fed into the fluid bed, and/or are fed at such a level thereover, and are of such a particle size that an optimum, reagent-dwelling time within the furnace is achieved, and that the reagents can be then drawn along with the flue gases. Thanks to such a procedure, a good reagent-neutralizing reaction with acid gases, such as HCL, SO₂, HBR, HF, HCN, is ensured not only in the fluid bed, but also in the region over the fluid bed surface S. This turns to advantage, especially in the case of any to-be-incinerated refuse having a high content of volatiles, since the combustion of volatiles mainly takes place above the fluid bed surface S. Moreover, thanks to reagents being drawn along with the flue gases delivered from the kiln, the acid gases absorption takes place along the whole fume line, and a determinate quantity of fresh reagents will get into the bag filter 17, whereby it is possible to have the acid gases neutralising reaction perfectly and efficiently completed. The used reagents may be of different types, and, for example, Ca(OH)₂, Mg(OH)₂, CaO, MgO, CaCO₃, MgCO₃, Na₂CO₃ are preferably used. Also, the ashes of the burned refuse will have their softening temperature increased up to about 200°, particularly owing to the action of carbonates, oxides, and hydroxides of alkaline-earth metals, whereby the forming of any agglomerate is avoided in the fluid bed, on the fluid-bed-cooling tube nest, on the refractory walls of the kiln, and in proximity of the auxiliary, flue gas post-heating burner 14.
Referring to Figure 2, the hearth 6 of the combustion chamber in kiln 1 of the fluid-bed incinerator is, according to the invention, made in form of a gas-pervious conical hopper. The hearth 6 is formed with a centrally located outlet opening 106 which is connected with a downwardly directed tubular hub 23. The tubular hub 23 is fitted into a delivery duct 9 consisting of a first delivery duct 24, and of a successive, second delivery duct 25, and is received into the counterbored upper end 124 of the first delivery duct 24, the downward free end of the first delivery duct 24 being in turn received into a widened portion 125 in the successive, second delivery duct 25. Between the counterbored end 124 of the first duct 24 and the associated tubular hub 23 in hearth 6 an annular chamber T1 is formed, with a cold air feeding duct 26 opening thereinto. Cold air flows into the combustion chamber in kiln 1 through the tubular hub 23 and the associated opening 106, and causes the residual products of combustion to be cooled. At the same time, a certain energy recovery from the residual products of combustion is also obtained, in that the air that cools the residual products of combustion, forms in a degree of 10 to 20%, a part of the combustion air for the combustion process. Also, a better separation of the residual products of combustion from the fine particle size material forming the fluid bed is achieved, owing to this fine particle size material being upwardly entrained.
As shown in Figure 2, the cold air feeding duct 26 preferably opens into the annular chamber T1 at a slightly higher level than the opening at the downward free end of the tubular hub 23, and a suction duct 27 opens into the widened portion 125 in the delivery duct 25, that is, into the annular chamber T2 formed between the said widened portion and the lower end section of the first delivery duct 24. The mouth of suction duct 27 also lies preferably at a higher level than the opening at the downward free end of the first delivery duct 24. By the suction duct 27, into which is drawn part of the air for cooling the residual products of combustion, the delivery ducts 24 and 25 are put under vacuum. Thanks to the particular configuration of the delivery ducts 24, 25, the annular chambers T1, T2, and of the cold air feeding duct 26 and the cold air suction duct 27, the cold air flow fed into the annular chamber T1, is parted into two partial flows, that is, an upward partial cold air flow flowing into the combustion chamber in kiln 1 through the opening 106 in the hearth 6 of said kiln 1, and a downward cold air partial flow which is associated with the residual products of combustion, and is drawn into the suction duct 27. The upward cold air partial flow preferably is about 75% of the fed, total cold air flow, while the downward cold air partial flow is formed by the remaining 25% of the fed cold air flow. The vacuum being thus generated in duct 9, for delivering the residual products of combustion into a collecting vessel 10, allows to prevent that any dust may escape from this duct to the exterior of the vibrating extractor of the residual products of combustion.
As shown in Figure 1, the cold air suction duct 27 feeds cold air to the bag filter, in which the cold air is dust-freed, and together with the purified flue gases is then vented into the atmosphere.
According to a further improvement of the invention, shown in Figure 3, the hearth 6 of the combustion chamber in kiln 1 is gas-pervious, thanks to the provision of a plurality of spaced apart through bores 206 made in the whole extent thereof. In order to prevent any sand-like matter from falling down into the underlying annular chambers 7 and 8, a lamina 28 for holding back this sand-like matter is provided at a distance below each bore 206. The laminae 28 may be made in any suitable manner and, for example, they may consist of substantially Z-shaped platelets which by one of their horizontal arms are secured to the underside of hearth 6. The diameter of these through bores preferably is of about 7 mm, and the hearth must be given an inclination of at least 15°, in order to ensure an efficient downflow of the residual products of combustion through the outlet opening 106.
The advantages as afforded by a fluid-bed incinerator according to the invention, clearly appear from the foregoing. On the one hand, these advantages reside in the special feeding of cold air, which not only guarantees the cooling of the residual products of combustion, but also the separation of the residual products of combustion from the rest of the refuse in the combustion chamber, and a better utilization of energy. On the other hand, the fact of feeding fresh reagents in pulverized form into the combustion chamber in the kiln, does guarantee the presence of said reagents both in the region above the fluid bed, in which the combustion of volatiles takes place, and in the secondary combustion chamber and along the whole fume line, and also in the bag filter, thus ensuring that the combustion-generated acid gases will be entirely cast down. All this renders it possible to improve the fluid-bed combustion process.

Claims

A fluid-bed incinerator comprising a kiln (1) with its combustion chamber containing a gas-pervious hearth (6), and which is provided with means (21) for loading any refuse to be incinerated into the combustion chamber above the hearth (6), and with means (4,5) for feeding an upward combustion air flow through the gas-pervious hearth (6), and also with means (22) for feeding chemical reagents into the said combustion chamber, whereas the hearth (6) of kiln (1) is formed with a centrally located outlet opening (106) which is connected to a delivery duct (9), means (26) being provided for feeding cold air into the combustion chamber in kiln (1), through the delivery duct (9) and the outlet opening (106) in the kiln hearth (6), characterized in that:
a) the delivery duct (9) consists of a first delivery duct (24), and of a successive, second delivery duct (25), and a tubular hub (23) is connected with the outlet opening (106) in hearth (6), and is received into the counterbored upward end (124) of the first delivery duct (24), the free downward end of the first delivery duct (24) extending into a widened portion (125) in the successive, second delivery duct (25), and a cold air feeding duct (26) is provided, which opens into the counterbored end (124) of the first delivery duct (24), preferably at a higher level than the opening at the lower end of the tubular hub (23),

b) a cold air suction duct (27) is provided, which is connected with the widened portion (125) in the successive, second delivery duct (25), preferably above the opening at the free end of the first delivery duct (24), whereby the delivery ducts (24,25) are put under vacuum.
The fluid-bed incinerator according to any of the preceding Claims, characterized in that the hearth (6) of the combustion chamber in kiln (1) is made in form of a conical hopper, and is formed with a plurality of spaced apart through bores (206) for hot gases to flow therethrough, which are made in the whole extent thereof, laminae (28) for holding back any sand-like matter being provided under each bore (206), and at a distance from each bore (206).
The fluid-bed incinerator according to Claim 2, characterized in that the conical hopper forming the hearth (6), is given a minimum inclination of 15°, with its through bores preferably having a diameter of about 7 mm, and that the laminae (28) consist of substantially Z-shaped platelets, with their upper arm being secured to the underside of the said hopper.
The fluid-bed incinerator according to any of the preceding Claims, characterized in that the combustion air feeding means are in form of two ducts (4, 5) opening into the respective one of two concenctric annular chambers (7, 8) provided under the hearth (6).
The fluid-bed incinerator according to any of the preceding Claims, characterized in that the reagent feeding means (22) are so provided, that the reagents are fed directly into the fluid bed, and/or above the fluid bed surface (S).
The fluid-bed incinerator according to Claim 5, characterized in that the said reagent feeding means (22) are of the pneumatic type.
A fluid-bed incinerator equipment, according to any of the preceding Claims, and comprising a kiln (1) with its top outlet being connected to a successive cyclone (11), and then to a secondary combustion chamber (13), to a successive fume cooler (16), and through a bag filter (17) and an exhauster fan (20) to a flue gas and air venting stack (19), characterized in that the cold air suction duct (27) is connected to the bag filter (17), and the chemical reagents are fed by means of the flue gases to the secondary combustion chamber (13) and to the bag filter (17).
A method of operating the fluid-bed incinerator according to Claim 1, characterized in that the fed cold air is parted into an upward flow flowing into the combustion chamber in kiln (1), preferably at a flow rate of 75% of the fed total cold air flow, and into a cold air downward flow drawn upstream of the bag filter, preferably at a flow rate of 25% of the fed total cold air flow.
A method of operating the fluid-bed incinerator according to Claims 6 and 7, characterized in that the fed reagents have a fine particle size, preferably a particle size being lower than 100 micromillimeters, and being however such as to allow the reagents to be partly or entirely drawn along with the flue gases.
A method of operating the fluid-bed incinerator according to any of the preceding Claims, characterized in that the chemical reagents may be, for example, Ca(OH)₂, Mg(OH)₂, CaO, MgO, CaCO₃, MgCO₃, Na₂CO₃, or any combination thereof.