Method of operating an incinerator comprising a device for capturing ash entrained by flue gas

Abstract

A method facilitates operation of an incinerator for solid fuel. The incinerator includes a device for separating ash from flue gas. The method includes collecting ash deposits originating from the flue gas, resulting in collected ash. To improve the flowability of the ash collected, the method further includes introducing a powdery additive material including i) clay and ii) calcium carbonate into the flue gas. At the location where the additive material is introduced, the flue gas has a temperature of at least 700° C. The additive is introduced with a rate R of at least 0.1 times the mass of ash in the stream of flue gas.

Claims

1. A method of operating an incinerator (100), said incinerator comprising: a chamber for incinerating solid fuel in the presence of oxygen-comprising gas, a flue gas channel for passing flue gas emanating from the chamber to an exhaust opening, wherein said flue gas comprises ash, and a device for separating ash from said flue gas into: flue gas having a reduced ash content, and ash; the method comprising: introducing oxygen-comprising gas and a solid fuel into the chamber to incinerate said solid fuel resulting in a stream of flue gas comprising ash; capturing ash from the stream of flue gas comprising ash using the device; collecting ash deposits originating from the flue gas comprising ash from the incinerator resulting in collected ash; and introducing a powdery additive material comprising i) clay and ii) calcium carbonate using an injection port transverse to the flow of flue gas comprising ash into the flue gas comprising ash, wherein: the flue gas comprising ash has, at the location where the additive material is introduced, a temperature of at least 700° C. and is introduced upstream of the device, a powder particle of said powdery additive material comprises granules, each granule comprising a mixture of clay and calcium carbonate, at least 10% by weight relative to the calcium carbonate being calcium carbonate in a form that when characterized by means of Thermogravimetric Analysis under a nitrogen atmosphere with a rate of increase in temperature of 10′ C per minute has decomposed completely when a temperature of 875° C. has been reached; and the powdery additive material is introduced with a rate R of at least 0.1 times the mass of ash in the stream of flue gas comprising ash.

2. The method according to claim 1, wherein at least 40% by weight relative to the calcium carbonate is calcium carbonate in a form that when characterized by means of Thermogravimetric Analysis under a nitrogen atmosphere with a rate of increase in temperature of 10° C. per minute has decomposed completely when a temperature of 875° C. has been reached.

3. The method according to claim 1, wherein: the additive material is introduced using a plurality of injection ports, and the number of injection ports is chosen such that the amount of flue gas per injection port is at least 10.000 kg of flue gas per hour.

4. The method according to claim 1, wherein the solid fuel is a fuel comprising material of non-fossil biological origin.

5. The method according to claim 1, wherein the additive material is introduced in the flue gas comprising ash where the flue gas comprising ash has a temperature in a range from 875° C. to 1050° C.

6. The method according to claim 1, wherein the amount of additive material introduced is controlled in dependence of the ash content in the flue gas comprising ash.

7. The method according to claim 1, wherein the powdery additive material is introduced with a rate R of 0.2 to 5 times the mass of ash in the stream of flue gas comprising ash.

8. The method according to claim 1, wherein: the incinerator is part of a plant, said plant further comprising a unit for the thermal conversion of paper waste material comprising kaolin, wherein the kaolin is thermally treated in a fluidized bed having a freeboard in the presence of oxygenous gas, and the fluidized bed is operated at a temperature between 720 and 850° C. and the temperature of the freeboard is 850° C. or lower to result in the powdery additive material, which is introduced into the flue gas comprising ash of the incinerator.

9. The method according to claim 1, wherein the weight/weight ratio of convertible calcium carbonate to the clay is in the range of 1 to 10.

10. The method according to claim 1, wherein the powdery material has a water content of less than 0.9% wt./wt.

11. The method according to claim 2, wherein at least 70% by weight relative to the calcium carbonate is calcium carbonate in a form that when characterized by means of Thermogravimetric Analysis under a nitrogen atmosphere with a rate of increase in temperature of 10° C. per minute has decomposed completely when a temperature of 875° C. has been reached.

12. The method according to claim 5, wherein the additive material is introduced in the flue gas comprising ash where the flue gas comprising ash has a temperature in a range from 900° C. to 1000° C.

13. The method according to claim 7, wherein R is between 0.3 and 2.

14. The method according to claim 7, wherein R is between 0.4 and 1.2.

15. The method according to claim 9, wherein the weight/weight ratio of convertible calcium carbonate to the clay is in the range of 1 to 5.

16. The method according to claim 9, wherein the weight/weight ratio of convertible calcium carbonate to the clay is in the range of 1 to 3.

17. The method according to claim 10, wherein the powdery material has a water content of less than 0.5% wt./wt.

Description

(1) The invention will now be illustrated with reference to the example section below, and with reference to the drawing wherein

(2) FIG. 1 shows a schematic view of an incinerator;

(3) FIG. 2 shows a Thermogravimetric Analysis (TGA) graph for various calcium carbonate-comprising materials; and

(4) FIG. 3 shows a comparison of the flowability of ash obtained in accordance with the present invention (right) and a control.

(5) FIG. 1 shows a plant comprising an incinerator 100 comprising a combustion chamber 110, a flue gas channel 120, a heat exchanger 130 and an exhaust pipe 140 and a device 160 for separating ash from flue gas, here an electrostatic filter.

(6) A mixture of household and industry derived waste materials is fed from a fuel storage via a hopper on a grate 170. Air is introduced into the combustion chamber 110 via an air supply conduit 180.

(7) Additive material is introduced into the flue gas channel 120 via injection ports 150.

(8) Downstream of a heat exchanger 130, the additive material is separated from the cooled down flue gas comprising ash from the heat exchanger 130 using the device 160 before the cleaned flue gas is vented to the atmosphere via the exhaust pipe 140.

(9) Ash deposited on the heat exchanger 130 is periodically removed and discharged from the incinerator via hopper 190. Ash captured by the device 160 is discharged via hoppers 200.

EXPERIMENTAL SECTION

(10) 1. Characterization of Additive Material

(11) The following materials were used for incineration experiments, and characterised as discussed below.

(12) Powder Size

(13) Laser diffraction was used to measure particle size in the range of 0.1-600 μm. Typically, a solid-state, diode laser is focused by an automatic alignment system through the measurement cell. Light is scattered by sample particles to a multi-element detector system including high-angle and backscatter detectors, for a full angular light intensity distribution. In a typical test, 10 mg of a sample was added to the liquid dispersing medium. The recommended dispersing medium for the samples is isopropyl alcohol. 95% by weight of the particles of the samples A to F described below had a size of less than 100 μm.

(14) Additive material suitable for use in the present invention

(15) —A— Calcium carbonate-containing material produced from deinking paper sludge prepared in accordance with WO0009256.

(16) The material's composition was determined by means of X-ray fluorescence. The material contained 30 mass % of calcium carbonate; 25 mass % of calcium oxide; and 36% of silica-alumina clay in the form of meta-kaolin.

(17) Reference Materials:

(18) —B— Laboratory grade calcium carbonate (laboratory grade calcium carbonate, Perkin Elmer Corporation, Waltham, Mass., USA)

(19) —C' Ground limestone (mercury sorbent, sample obtained from the Chemical Lime Company in St. Genevieve, Mo., USA)

(20) —D— Ground limestone (sample obtained from the Mercury Research Center at 19 Gulf Utility, Pensacola, Fla., USA)

(21) —E— Ground dolomite stone (sample obtained from the USA National Institute of Standards and Technology (NIST) denoted as standard reference material (SRM) 88b))

(22) —F— Ground limestone (sample obtained from the USA National Institute of Standards and Technology (NIST) denoted as standard reference material (SRM) 1d. SRM 1d is composed of argillaceous limestone)

(23) Material Decomposition

(24) TGA measurements were carried out in a nitrogen atmosphere and at a heating rate of 10° C. per minute using a Setaram Labsys EVO TGA apparatus (Setaram Company, Caluire, France).

(25) As can be seen in FIG. 2, where the curves A-F correspond to the calcium carbonate-comprising materials listed above, the decomposition of calcium carbonate occurs at different temperatures. For curve E, it is the second steep downward slope at about 950° C. that relates to the decomposition of calcium carbonate, the first steep slope at about 800° C. relating to the decomposition of magnesium carbonate.

(26) EDX Measurements

(27) Individual particles of the additive material (A) produced in accordance with WO0009256 contain both clay and calcium compounds as can be observed from Energy Dispersive X-ray spectroscopy (EDX) applied in conjunction with Electron Microscopy (EM), both methods are considered known to someone skilled in the art. EDX measurements on even the smallest particles visible in the EM, typically having dimensions of a few micrometers, show that in each particle both calcium- and silica/alumina species are present. The calcium represents the calcium and calcium carbonates present in the additive material, whereas the silica/alumina species represent the clay fraction present in the additive material.

(28) 2. Incineration Experiment

(29) Experiments were performed using an incinerator 100 as schematically shown in FIG. 1.

(30) The incinerator processed a fuel consisting of household and industrial derived waste materials. The incineration resulted in amounts of ash in the flue gas leaving the combustion chamber 170 that are further detailed in the individual experiments 2A, 2B, and 2C described below. The additive applied was produced from a mixture of paper residue and composted sewage sludge in a weight ratio of 85% to 15%, using the method descried in WO9606057. The additive is injected into the flue gas of the incinerator leaving the incineration chamber at a height of more than 15 meters measured from the lowest point of the incineration grate. During each experiment described below in sections 2A, 2B, and 2C, it was observed that no flames reached this height for more than 90% of the duration of the experiment. The first heat exchanger internal—boiler tube—protruding into the flue gas flow, is located at more than 10 meters downstream of the additive injection location. The temperature of the flue gas at the location of the additive injection varied with the solid fuel and the energy production in the incinerator, being between 800 and 1050° C., as further detailed in the individual experiments 2A, 2B, and 2C. Typically amounts of ash and additive injected into the flue gas by means of pneumatic injection through steel injection ports (right-pointing arrow in FIG. 1) of typically 32 mm internal diameter are further detailed in the individual experiments 2A, 2B, and 2C described below. The averaged velocity of the injection air is also further detailed in the individual experiments 2A, 2B, and 2C described below.

(31) 2A. Improved Flowability of Ash (1)

(32) Ash was collected from a waste incinerator plant, that operates several identical incineration furnaces and boilers. One of the furnaces did not apply the additive, and serves as the reference case. The amount of ash collected from the flue gas in the reference case was approximately 400 kg/h. The other furnace applied the additive at a rate of 70 kg/h, which was injected into the flue gas at a temperature of approximately 950° C. by means of four injection ports and a velocity of the injection air of approximately 15 m/s (location indicated with reference number 150 in FIG. 1). The total amount of solids collected from the flue gas was 470 kg/h.

(33) Further operational conditions and material processed in the incinerator were identical within operational variability.

(34) Cups were filled to approximately half full by adding 20 grams of ash (reference case; FIG. 3 left half), and 20 grams of ash obtained with the method using the additive (FIG. 3 right half) with reference number 300 and reference number 330 respectively. The cups were then tilted to observe the moment where the ash or ash+additive mixtures were reaching the point of falling out of the cups. This is indicated by reference numbers 310 and 340 respectively. The material obtained using the method according to the present invention flowed easier—at a lesser tilt of the cup—than the reference material. The required rotation until falling from the cup was approximately 95 degrees for the reference and approximately 80 degrees for the ash plus additive. The cups were then tilted further to observe when the complete amount of ash (reference case) or ash plus additive had fallen out of the cup, as indicated in FIG. 3 by reference numbers 320 (reference ash) and 340 (ash plus additive) respectively. Again, the material flowed easier—at a lesser tilt of the cup—when mixed with the additive. The required rotation to completely empty the cup was approximately 150 degrees for the reference versus approximately 110 degrees for the ash material obtained in accordance with the present invention.

(35) 2B. Improved Flowability of Ash (2)

(36) Ash was collected from the flue gas of a waste incineration plant by means of gravimetric sedimentation (FIG. 1 at reference number 190) and electrofiltration (FIG. 1 at reference number 200). Both ash streams were mixed together before loading in silo-containers (trucks). Without further significant variation, two situations were created. The first situation reflects normal operating procedures, without the application of the additive. The second situation reflects the effect of application of the additive. The normal amount of ash collected without the application of the additive was 120 kg/h. The amount of additive that was applied in the second situation was 80 kg/h. The additive was injected by means of five injection ports into the hot flue gas at a flue gas temperature of approximately 900° C. The velocity of the injection air applied in each injection port was approximately 18 m/s. In both situations, the ash that was collected was stored in a silo, from where trucks were filled for further disposal of the ash.

(37) It was observed that in the first situation (no additive applied), all three fill-openings of the truck had to be used to fully load the truck. This implied that the truck had to move under the silo to position each fill-opening underneath the silo-exit chute. The total loading time was in excess of 25 minutes.

(38) It was further observed that in the second situation (with the application of the additive), only the center fill-opening of the truck had to be used to fully load the truck. It was no longer necessary to move the truck under the silo after it had positioned itself for the center fill-opening. The ash-additive mixture displayed positive flow-properties allowing the mixture to freely flow into the truck. The total loading time was reduced to less than 15 minutes.

(39) TABLE-US-00001 Amount of fill Time until Re-positioning opening applied truck is full of truch on truck min # per truckfill ash - no additive 3 >25 2 ash plus additive 1 <15 0

(40) 2C. Improved Efficiency of Ash Collection

(41) Dosage of 70-100 kg/h of additive to a waste incineration plant into the flue gas at a temperature of 800-1000° C. by means of 4 injection ports at the location indicated in FIG. 1 with the number 150 at a velocity of injection air of approximately 15 m/s, resulted in a significant decrease of solids that passed through the electrostatic precipitator without being removed from the flue gas flow, as indicated in the Table below. The following definitions were applied in the Table below:

(42) TABLE-US-00002 Emission Reduced ash Additive Total ESP from ESP emission kg/h kg/h kg/h Increase efficiency kg/h from ESP No additve 100 0 100 90.00% 10.00 Additive 100 80 180 80% 98.50% 2.70 73%

(43) Ash: The amount of ash particles collected from the electrostatic precipitator filtration on an hourly basis. Measurement is carried out by weighing the amount of ash produced and collected over time by measurement of the amount of ash trucked away from the incinerator for further disposal.

(44) Additive: The amount of additive that was injected into the flue gas at a temperature of 800-1000° C. by means of 4 injection ports at the location indicated in FIG. 1 with reference number 150 on an hourly basis. Measurement is carried out by weighed dosage of the additive by means of the discharge of a weighing bin over time.

(45) Total: The sum of the amounts of ash and additive as defined in the previous two sentences. Measurement is carried out by weighing the amount of ash plus additive produced and collected over time by measurement of the amount of ash trucked away from the incinerator for further disposal.

(46) Increase: The mathematical increase in the amount of solids (ash plus additive) added or present in the flue gas prior to removal from the flue gas by means of the electrostatic precipitator filtration.

(47) ESP efficiency: The measured efficiency of the electrostatic precipitator filtration, as defined from the mathematical division of the difference of the amount of solids present in the (raw) flue gas up-stream of the ESP and the amount of solids present in the (cleaned) flue gas down-stream of the ESP, and the amount of solids present in the (raw) flue gas up-stream of the ESP.

(48) Emission from ESP: The amount of uncollected ash or ash+additive material that leaves the electrostatic precipitator filtration with the flue gas through the exhaust as indicated by reference number 140 in FIG. 1. As can be inferred from the measurement results, the amount of material vented to the atmosphere is significantly (73%) reduced upon the application of the additive in accordance with the invention.