FI98854C - Method and burner for the combustion of liquids and solids with a wide particle size distribution - Google Patents

Description

98854

METHOD AND BURNER FOR COMBUSTION OF LIQUIDS AND SOLIDS WITH A WIDE PARTICULATE SIZE DISTRIBUTION

The invention relates to a method for the combustion of liquid and solids with a wide particle size distribution in a controlled manner using a vortex chamber, in which the substance is fed into the vortex chamber tangentially together with the air flow and thus generates a vortex, which selectively delays The invention also relates to a burner implementing the method.

Conventional flame combustion of powdery materials has been based on grinding the combustible material into fine dust which has been burned in a flame formed outside the actual burner. The maximum delay time allowed for flame combustion, i.e. the time in which the particle must have time to burn completely, is clearly less than 1 second and usually only a few tenths of a second. In order to stabilize the flame and keep the flame length reasonable, the combustible material had to be ground to a size of less than 0.1 mm. Grinding has taken place in a separate mechanical mill. Grinding biofuels to a particle size suitable for flame combustion is much more problematic than, for example, grinding coal. Grinding biofuels to dust combustion consumes 25 energy 1-5 MJ / kg, which is far too much from an economic point of view. Milled peat must also be ground before it can be used for flame combustion. Especially in smaller units ·· *; dust incineration, which requires efficient grinding, has been economically tm * - • f uncompetitive and has also required the use of quite *. * * 30 expensive fluidized bed incinerators. It can be said that the lack of a cheap combustion technology solution has been one of the factors that has weakened the economic competitiveness of peat and: · biofuels.

m m mmm • m · • · · 35 The problem with dust combustion is the short reaction time of the particles, which 1; · therefore the material to be combusted has to be ground very finely.

::: Stability conditions for dust burners are strict due to the very low mass of the ignition zone. Adequate and even dryness of the combustible dust is also a condition for stable combustion. For safety reasons, dust burners usually need to be secured with support flames using oil or 2 98854 gas. The dust combustion system thus requires drying, grinding, stabilization burners and the actual dust burners of the material to be burned. In small units, such a system is not economically competitive.

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The incineration method, which is already known and has been used in practice in the past, is the so-called sulasyklonipoltto. In cyclone burners, all the combustion air is introduced into the cyclone and they have generally operated at such a high temperature that the ash accumulated in the cyclone 10 has been removed as a melt. The problems with cyclone burners have been e.g. temperature control. Too low a temperature has led to an uncontrolled growth of the slag layer accumulating on the walls of the cyclone, and at high temperatures the service life of the protective liners of the cyclone has remained too short. Due to the large number of patients with combustion heat-15, the nitrogen oxide emissions of cyclone burners are also high and exceed the permissible emission limits. For these reasons, cyclone combustion is hardly used anymore.

A solution has been sought to the costs 20 and technical problems of the dust and cyclone combustion described above, e.g. fluidized-bed technology. Unfortunately, however, despite advances in fluidized bed technology, it appears that its economic competitiveness remains poor in small units. Floating :: layer technology is divided into so-called. bubbling fluidized bed (BFB) and 25 circulating mass technology (CFB). In the latter through the combustion chamber .j. a large solids stream flows, which is separated in a cyclone and f M »j. returned to the bottom of the vertical combustion chamber. CFB- * ···. combustion requires complex equipment including an air distribution chamber with nozzle bottoms, a vertical reaction chamber, a cyclone, and a solids recovery equipment. CFB combustion and cyclone combustion t ♦ ♦ * ·· ^ thus have in common that both techniques include, as an essential 5: * component, a cyclone which provides a selective delay time for coarse particles. In CFB combustion, the particle delay time is determined. primarily according to the conditions of the vertical chamber (riser).

35 In cyclone combustion, the particle delay time is formed solely by the conditions of the cyclone. Another essential difference between CFB combustion and: conventional cyclone combustion is the amount of solids stored in the system. In CFB combustion, the amount of solids in the system is 3 98854 very much higher than in cyclone combustion, and almost without exception, CFB combustion uses other solids in addition to fuel, which make up the bulk of the system solids. The purpose of the high solids content is to improve the stability of the system and, in some applications, to reduce emissions. It is clear that CFB combustion does not operate above ash sintering temperatures. In cyclone combustion, the amount of solids is very small and the burners usually operate in the molten ash area. Both combustion techniques have obvious advantages and certain uniformities. The question therefore arises as to whether it is possible to combine the technical simplicity of cyclone combustion with the process technical advantages of CFB combustion. This invention relates to a process in which the key advantages of a CFB reactor are achieved in a simple vortex chamber. Poor quality liquid fuels also pose a technical problem with combustion-15. The present invention seeks to solve these problems of the prior art.

The characteristic features of the method according to the invention are set out in the appended claim 1 and the characteristic features of the corresponding burner are set out in claim 6. Other advantages and embodiments of the invention will become apparent below.

With the method according to the invention, coarse fractions, solid and poor quality liquid fuel 25 can be burned efficiently and at low cost. In the process according to the invention <; In this system, the vortex chamber is used for the simultaneous chemical and physical processing of the material to be treated.

. ·· ·. Later, the invention is referred to as a description of its operation • · ·

Chemi Mechanical Reactor (CMR), which works as follows. Rough,. The 30-fraction fuel is fed with oxygen-containing gas to »« · CMR. The oxygen to fuel ratio is clearly adjusted • · * * · '* on the substoichiometric side so that the temperature in CMR'. * · *: Is preferably between 600 and 750 C. The most typically oxygen-containing gas is air, with 35 airflows directed to CMR. for dry fuel, the amount is 30 to 50% of the total amount of combustion air. The oxidizing gas is introduced into the CMR tangentially, creating a vortex in the CMR that prevents coarse particles from leaving the CMR. As a result, 4 98854 CMRs are enriched in solid material which circulates strip-like along the sheath of the CMR. Due to the internal vortex of the CMR, the temperature-fragile particles collide with each other and with the walls of the CMR and thus grind into finely divided particles. When the particles fall below a limit depending on their physical state, they leave the CMR. The CMR vortex is adjusted to allow the passage of particles with a sufficiently short reaction time in flame combustion. In CMR, the residence time of large particles becomes large, while the finely divided material is rapidly removed from the CMR. It is clear that such a selective residence time is advantageous for combustion.

Based on the above, the following advantages are achieved in CMR: 15 l. Thanks to the abundant solids circulation and sub-stoichiometry, the temperature control is easy and precise.

2. The solid vortex formed inside the CMR evens out the circumferential temperature differences and protects the structure from overheating.

20 3. By chemical and thermal treatment of the combustible material, the energy consumption required for grinding is obtained significantly. :; small.

4. The amount of solids accumulating inside the CMR will stabilize the flame securely, so no support combustion is required.

25 5. A high power density (MW / m3) is achieved in CMR.

6. Organically bound nitrogen is released under reducing conditions, • ♦ · so the formation of nitrogen oxides is minimized.

7. CMR can be implemented as a non-refrigerated • steel structure without material problems.

• · ·::: 30. ···. The burner according to the invention can also act as a carburetor. In this case, • · · I .. # it is better to talk about the reactor instead of the burner.

The invention will now be described with reference to the accompanying figures, which show a burner according to the invention.

Figure 1 shows a side view of the burner in partial section.

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Figure 2 shows a cross-section of the burner of Figure 1 from point II-II.

Figure 3 shows the parts of the burner in an axonometric view.

Reference numeral 1 denotes a vortex chamber (CMR chamber) into which the fuel is introduced by means of carrier air from a pipe 11 together 12 through a direction tangential to the vortex chamber 1. The end of the vortex chamber 1 has a flange 8.1 with which it is attached to the end 8.2 of the secondary chamber 6. A vortex chamber outlet pipe designated as intermediate channel 4 is inserted through these ends 10. This extends somewhat into the secondary chamber 6. At one end, the outlet channel 5 of the secondary chamber 6 extends partially over the intermediate channel 4, whereby an annular gap channel is formed between them. Secondary air is introduced through a pipe 2 and a joint 3, which 15 is also oriented parallel tangentially to the unit 12. The burner is fixed, for example, to the boiler wall from a flange 7.

In order to ignite the burner, electric resistors 22 and an oil nozzle 9 are connected around the vortex chamber 1. Naturally, gas can also be used for igniting 20. In the middle of the vortex chamber 1, at the front end, there is a thermocouple protection tube 21, inside which the thermocouple itself is installed to measure the temperature of the vortex chamber 1 (CMR chamber).

25 In Fig. 3, the vortex chamber and the secondary air system are separated from each other and the vortex chamber 1 is rotated by about 901 with respect to the situation of Figs. 1 and • · · 2. The intermediate pipe 4 is here attached to the flange 8.2 of the secondary chamber 6 and for this purpose the flange 8.1 of the vortex chamber 1 has a hole 15. Figure 3 does not show electrical resistors,: 30 temperature sensors or an ignition burner.

• · · • · 1 • · · I .. The main dimensions of a pilot unit and 2 MW burners are as follows: s · ··· •

Pilot 2MW Unit; 35 CMR chamber diameter 200,800 mm CMR chamber length 150,600 mm

Exhaust pipe diameter 50 225 mm 6 98854

Sawdust properties:

Water / dry matter mass ratio 0.06 0.06

Maximum particle size 5 5 mm

Avg. particle size 1 1 mm 5

Airflow to CMR / stoichiometric airflow:

Minimum 0.4 0.35

Maximum 1.2 1.2 10 Bite feed:

Maximum 4.0 110 g / s

Minimum 1.7 20 g / s

Minimum power density 5 1.33 MW / m3

Maximum power density 11 6.6 MW / m3 15

Flame length:

Maximum 400 mm

Minimum 150 mm 20 In the vortex chamber 1, i.e. in the CMR chamber, the sub-stoichiometric combustion The amount is controlled so that the temperature is between 600 and 750 ° C. This generally corresponds to 25 to 35% of the oxygen consumption taking place in the vortex chamber. It is essential that the secondary air flow is a concentric ring flow, most preferably it is a vortex ring flow around the primary flow as shown. It is also important ... that the outlet channel 5 is so close to the end 8.2 that a pressure drop occurs between them • · · * which equalizes the ring flow. 1 ·: The ratio of the length to the diameter of the vortex chamber 1 (CMR chamber) is • · ·: 30 most preferably between 0.8 and 1.2. The length of the secondary chamber 6 is most preferably 30 to 50% of the length of the vortex chamber chamber 1. Foreign ···. the channel 4 and the secondary chamber outlet channel 5 most preferably overlap t · 20 to 30% of the diameter of the intermediate channel. The diameter of the intermediate channel 4 is most preferably 25 to 35% of the diameter of the vortex chamber 1.

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In the vortex chamber, i.e. the CMR reactor, it is not primarily a question of separation, but of processing the solid particles into a gaseous compound and small coke particles. These all exit the vortex chamber through the intermediate channel.

In some cases, it is preferable to use an inert granular material in the vortex chamber that improves the grinding of the solid fuel and increases the heat capacity of the chamber to even out combustion. The use of an inert substance can often be arranged so that it is fed only to the extent that it leaves the vortex chamber to a small extent.

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Claims (11)

A method of controlled combustion of liquid and of such solids having a wide particle distribution, by means of a cyclone chamber, according to which the method is measured tangentially in the cyclone chamber (1) together with the air flow and the material flow is swirled away from the center, characterized in that a vortex is formed between the tangential feed stream and the central feed stream, by means of which a selective delay time is obtained for the coarser particles, so that the size of the outgoing particles decreases to a size smaller than the set limit size, and that the air feed is divided into two phases, in which during the first phase the substance to be burned is measured together with a sub-oximetric amount of air in the cyclone chamber (1) while maintaining the temperature below the ash melting point and during the second phase a secondary air stream is supplied in an annular stream with the same center around the current flowing out of the cyclone chamber. 20 Process according to Claim 1, characterized in that the ratio of oxygen to fuel in said first sub-stoichiometric combustion is controlled so that the temperature is between 600 - 750 ° C. 3. Method according to claim 1 or 2, characterized in that 25 - 35% of the oxygen consumption takes place in the cyclone chamber. • t Method according to claim 1, 2 or 3, characterized in that the secondary air stream is formed as a vortex with the same center and in the same direction as the primary stream. Method according to any of claims 1-4, characterized in that inert granular material is also fed into the cyclone chamber. A burner for carrying out the method according to claim 1, which burner comprises a cylindrical cyclone chamber (1) with tangential fuel and air connections (11) and a central discharge channel, hereinafter referred to as an intermediate channel (4). ), characterized in that the burner comprises a secondary chamber (6) arranged with the same center after the cyclone chamber (1), which secondary chamber comprises a tangential secondary air coupling (3) and an outlet duct (5) with the same center and said intermediate duct (4) extends to a portion from the secondary chamber (6) as the secondary chamber discharge duct (5) extends from the opposite end partially to the intermediate duct (4), forming an annular space for the supply of the secondary air stream around the main stream. Burner according to claim 6, characterized in that the ratio between the length and diameter of the cyclone chamber (1) is in the range 0.8 - 1.2. Burner according to claim 6 or 7, characterized in that there is electrical resistance around the cyclone chamber for heating the cyclone chamber and further in the primary air connection an oil / gas nozzle for igniting the burner. Burner according to claim 6, 7 or 8, characterized in that the length of the secondary chamber (6) is 30 - 50% of the length of the cyclone chamber (1). 0 '25 Burner according to any one of claims 6 - 9, characterized in that the intermediate channel (4) and the secondary chamber's output channel (5) overlap each other by 20 - 30% of the diameter of the intermediate channel. . ··· 30.. 11. Burner according to any one of claims 6-10, characterized in that the diameter of the intermediate channel (4) is 25 - 35% of the diameter of the cyclone chamber (1). 35