SE0900536A1 - Solid fuel combustion process and plant - Google Patents

Description

10 15 20 25 30 2 step. In other words, the afterburner is divided into two stages: a first stage with one lower combustion temperature, e.g. 950 ° C, and a second step with a higher combustion temperature, e.g. 1200 ° C. Flue gas chane | en achieves a strong speed increase of the flue gases, which together with the additional supply of combustion air in the canal provides a renewed combustion which burns out substantially all of the burned organic material in the fuel and its gases.

Another insight is that for efficient combustion, a continuous combustion should be maintained. conditions for the lower and higher temperature ranges in the furnace and afterburner clean. The oven and the afterburner then need to have an effective heat insulator and heat storage lining, ie. the liner may need to have a certain minimum thickness.

This minimum thickness may vary depending on the lining material chosen and the size, but for a typical waste incineration plant may need to amount to about 1.3m in the afterburner and about 0.5m in the rotary kiln. Thereby an even temperature and an efficient combustion are achieved in the process. Thus need nor is additive fuel such as oil or gas used to keep the process going.

The maintenance of the state of continuity can be further regulated by selective return of combusted flue gas to the furnace from a flue gas outlet at the plant. The can also be regulated in other ways, e.g. by adjusting the amount entered fuel for the prevailing type of fuel.

The lower temperature range can range between about 950 and 1100 ° C and the higher temperature range between about 1100 and 1200 ° C. In one embodiment of the invention, unburned residues may be incorporated into through an open bottom of the first stage of the afterburner.

Unburned residues in the second stage of the afterburning chamber can be taken off the particle bed at a bottom of the second stage.

Furthermore, the lining of the oven may have a varying height for exposure to a temperature. porous underside of the fuel in the furnace, so that colder fuel does not form an insulation against the temporary bottom of the rotary kiln. The hot gas in the oven can then be re access all sides of the fuel. If the height varies in the circumferential direction, sliding parts of the lining also make it easier to carry and mix the fuel in the so that all parts of the fuel will surely come into contact with the oxygen-poor the combustion gas.

Although the furnace is specially designed to burn solid fuel, it can also burn fluid fuels. 10 15 20 25 30 3 Other features and advantages of the invention may be set forth in the claims and the following description of embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a schematic sectional view of a part of a plant according to the invention ningen; and FIG. 2 is a sectional view taken along line 2 - 2 of FIG. 1 DETAILED DESCRIPTION OF EMBODIMENTS In the schematic representation of FIG. 1 shows an incineration plant with a rotatably mounted furnace 10 fed from a line 32 with fuel 40 in shape of e.g. household waste through a feed screw 30. As indicated can at start-up and at requirements during operation the furnace 10 is also fed with gaseous and liquid fuels through fuel lines 34, 36 connected to the furnace 10. To the furnace 10 can also through a line 38 is returned combusted flue gases that have passed the plant.

As indicated in FIG. 2, the furnace 10 may have a steel jacket 20 which may have an outer diameter of typically about 4m and its length can then be about 17m. The 10 feeding of the oven 22 comprises refractory blocks 24, 26 (FIG. 2) with varying varying heights the high blocks 26 can typically have a height or thickness d of about 0.5 m. Especially the high ones the blocks 26 may in a manner not shown also be inclined with respect to the furnace 10 axis of rotation to facilitate the transport of fuel through the furnace in a screwed manner 10. In addition to facilitating the access of combustion gases to the fuel 40 at the moment lower sides, the higher blocks 26 serve to carry, spread and mix it solid fuel 40 in the furnace, so that the initial combustion process safely reaches all parts of the fuel 40. Furthermore, the furnace 10 typically tilts about 4 degrees down towards an inlet in a afterburner 50.

In a typical combustion process, the furnace 10 is rotated by a known drive (not shown). device at about 1 rpm and it then takes about 1 hour for freshly fed fuel to gases to primary flue gas / combustion gas and other particles entering a first, 60, of two stages 60, 80 in the afterburner 50. Unburned material in the form of residual ash and metals with a high melting point and ceramic materials fall into e.g. a water tank 62 in the bottom of the first stage 60 and is discharged therefrom for further handling by means of a conveyor 64, such as a screw conveyor. 10 15 20 25 30 4 According to the invention, the afterburner 50 as well as the furnace 10 have a large mass. said (total typically about 1500 tons), ie. a thick covering or liner 52, of e.g. Fire- solid ceramic material, such as brick material, or casting materials, which serve as insulation and heat storage and thus be able to maintain the high temperatures in a state of continuity with small oscillations during operation of the plant. ln- the cladding 52 in the afterburner 50 can typically have a thickness D of about 1.3m.

The heat losses due to the lining of the afterburning chamber 50 can typically be approx 200 kcal / m 2 / h, while those in the oven 10 may be about 1700 kcal / m 2 / h; the oven has less amount of refractory and insulating material as otherwise its weight would be too high.

To facilitate the maintenance of the liner 52 in the afterburner 50, its inner surface layer may consist of relatively thin refractory blocks 56 with a thickness of about 40 mm, whereby the underlying thicker blocks 54 do not need to be replaced. taken when renovating the afterburner 50. In the afterburner 50 years further arranged a partition 72 which divides the afterburner 50 in its two stages 60 and 80.

In the example shown, the partition 72 also extends a bit horizontally between the two stages 60 and 80 of the afterburning chamber to define an elongate one passage in the form of a flue gas duct or flame port 70. However, the partition 72 may also include a simple vertical or inclined wall layer of refractory material with a shorter flue gas duct (not shown).

In the flue gas duct 70 there is an inlet 72 for combustion air which is fed with by means of a fan 74 which typically provides an air flow at a speed of approx 30m / s.

Through the arrangements described above, the facility can be considered to be divided into a primary combustion unit A with an oxygen-poor, gasifying combustion environment and a secondary combustion unit B with an oxygen-rich, highly combustible combustion unit environment At an outlet 82 for the flue gases from the second stage 80 of the afterburning chamber 50 In the example shown, a boiler in the form of a gas-liquid heat exchanger 90 is connected. In the heat exchanger 90, steam is generated which can drive a turbine 92, which in turn can drive a generator 94 for electrical energy.

At an outlet for the flue gases from the boiler 90 there may be a suction fan 96 for create a sufficiently negative negative pressure to drive the flue gases through the plant ningen. 10 15 20 25 30 5 In connection with the facility, there may also be a number of different, not shown components, such as a flue gas purifier, and other components for handling solid, liquid and gaseous residues which are generated or otherwise need to be be handled in connection with the operation of the facility.

During operation of the plant, a state of continuity is thus maintained in the furnace 10 and the afterburner 50. To achieve an optimal such state of operation and a complete combustion process is ensured the following: 1) 2) In the primary combustion unit A, an initial prevails combustion conditions in the form of partial pyrolysis in a gasifying, oxygen-poor environment which is produced is burned at a substantially constant lower temperature of about 950-1100 ° C. Thereby, the fuel 40 can be almost completely gasified so that it leaves a minimal amount of residual ash of about 4-5% that falls down it vertical shafts formed by the first stage 60. By comparison, conventional furnaces of the prior art are considered to leave 20-30 ° / ° residual ash. Restas- may also include high melting point solids in the fuel, such as glass and metals, which in the lower temperature are prevented from melting take and damage adhere to the liner 52. In the secondary combustion unit B there is still a final combustion burning condition with a substantially constant elevated temperature of approx 1100-1200 ° C. The elevated temperature is achieved by partly The fuel gas generated A accelerates at a high rate (typically about 30 ° C) m / s) according to Bernouilli's principle in the cross - section reduced flue gas duct, partly combustion air is blown at high speed across the combustion gas through the fan ten. As indicated above, then in the narrow passage 70 per unit time much a large amount of O 2 in a welding torch-like flame effectively interact with very large amounts of combustible CO in the fuel gas for conversion to CO 2 in the resulting, heated and combusted flue gas leaving the effluent the combustion chamber 50. Upon entering the larger volume in the second stage 80 of the afterburner 50, the flue gas velocity is reduced. Any remaining solid residues, such as magma, fall on the second stage 80 bottom near the boiler 41 and cooled there to solid phase. To make it easier removal of such residues, which may form a glassy film 10 15 20 25 30 6 bottom, this bottom may have a layer in the form of a particle bed 84 of barley of clay, such as chamottle clay.

To sense the state of operation of the facility can, as schematically indicated in FIG. 1, a number of temperature sensors 12 are placed in suitable places laying as. The temperatures sensed by the sensors 12 are signaled via signal transmitters. connections, such as signal lines 14, to a computer 16, such as a system control computer. ningen. The computer 16 can then, with the aid of the temperature information, compare the prevailing the state with a desired state of continuity embedded in a software. In case of deviations between states, for example, the computer 16 may increase or decrease the reflux of cold flue gas through line 38, by controlling a valve 98 in line 38 via a signal bond 18. If, for example, a larger proportion of plastic material with a high energy content (typically 9-10 against normally about 2.5 Mcal / kg) temporarily occurs in the fuel, return flow can that of cold flue gas need to be increased to lower the average temperature in unit A down to at least 1100 ° C. If, on the other hand, the temperature sensors 12 signal that the the risk of cooling to a temperature below the steady state, the return the flow of cold flue gas is restricted and possibly also the furnace 10 and the afterburner 50 temporarily need to be supplied with extra fuel via lines 34 and / or 36.

This is also controlled in a manner known per se by the computer 16 via other signal connections 14, 18, which schematically indicates FIG. 1.

When starting up a cold plant until the state of operation, can in the oven 10, the gaseous or liquid fuels supplied through the lines are burned 34, 36. In addition, for this purpose, in the afterburning chamber 50 both steps 60, 80 is one or more gas or oil burners 58 (only one oil burner is shown in FIG. 1) in connection with the walls of the afterburner 50.

The above detailed description is primarily intended to facilitate understanding and any limitations of the invention are not to be construed as such. The modifications which will become apparent to one skilled in the art upon review of the specification may be without departing from the spirit of the invention or the scope of the following patent requirement.

Claims (13)

7 PATENT REQUIREMENTS A method of burning solid fuel (40) through a rotary kiln (10) and an afterburner (50) connected to the furnace, comprising feeding the fuel at an end of the furnace (10); characterized by initial combustion of the fuel (40) in an oxygen-poor environment in a lower temperature range in the furnace (10) and in a first step (60) of the afterburning chamber (50) to produce combustible flue gas therein; increasing the velocity of the flue gas through a narrowed passage (70) between the first stage (60) and a second stage (80) of the afterburning chamber (50); and forced introduction of combustion air into the displaced passage (70) for final combustion in a higher temperature range of the flue gas in the passage (70) and in the second stage (80) of the afterburning chamber (50). A method according to claim 1, comprising maintaining a state of continuity for the lower and higher temperature ranges in the furnace (10) and the afterburner (50) by a heat insulating and heat storing liner (22, 52) of the furnace and the afterburner of a particular minimum thickness. A method according to any one of the preceding claims, comprising maintaining a state of operation for the lower and higher temperature ranges by selectively returning combusted flue gas to the furnace (10) from a flue gas outlet. A method according to any one of the preceding claims, comprising maintaining the lower temperature range between about 950 and 1100 ° C and the higher temperature range between about 1100 and 1200 ° C. A method according to any one of the preceding claims, comprising receiving unburned residual products through an open bottom in the first stage (60) of the afterburning chamber (50). 8 A method according to any one of the preceding claims, comprising picking up unburned residual products on a particle bed (84) at a bottom of the second stage (80) of the afterburning chamber (50). A method according to any one of the preceding claims, comprising exposing a temporary underside of the fuel (40) to flue gas in the rotary kiln (10) by varying the height of a liner (22) of the kiln. A solid fuel combustion plant (40) comprising a rotatable horizontal furnace (10); an afterburner (50) connected to the furnace; characterized by a primary combustion unit (A) comprising the furnace (10) and a first stage of the afterburning chamber (50) for initial combustion of the fuel in a low oxygen environment in a lower temperature range in the furnace (10) and in the first stage (60) for generating of combustible flue gas therein; a secondary combustion unit (B) comprising a narrowed passage (70) for increasing the velocity of the flue gas between the first stage (60) and a second stage (80) of the afterburning chamber (50), and an inlet (72) for forced introduction of combustion air into the narrowed passage (70) for final combustion in a higher temperature range of the flue gas in the passage (70) and the second stage (80) of the afterburning chamber (50). Plant according to claim 8, wherein the inlet (72) is directed radially into the narrowed passage (70). A plant according to claim 8 or 9, comprising a fan (74) for blowing the combustion air through the inlet (72). Plant according to any one of claims 8-10, comprising a return line (38) for selectively returning combusted flue gas to the furnace (10) from a flue gas outlet. 9 A plant according to any one of claims 8-11, comprising an open bottom of the first stage (60) of the afterburning chamber (50) for receiving unburned residual products therethrough. Plant according to any one of claims 8-12, comprising a varying height of a liner (22) of the furnace (10).