FI87949B - REFERENCE TO A REDUCERING AV QUANTITY EXTERNAL VIDEO BRAENSLEN AV OLIKA BRAENSLEN - Google Patents

Description

87949

The present invention relates to a method for reducing harmful nitrogen oxides from the combustion of various fuels according to claim 1.

The generation of nitrogen oxides during combustion is currently a serious problem in combustion plants using different fuels, such as power plants and heating plants. The emission ceilings for new plants are already strict and will be tightened rapidly in the future.

Efforts have been made to reduce the amount of nitrogen oxides (NOX) in the flue gases released into the air by combustion technology, various additive injections and catalytic means. Various combustion techniques to reduce NOx emissions from combustion include flue gas recirculation, water / steam injection, two-stage combustion, use of low-NOx burners, and phasing of fuel supply. With the help of these methods, approx. 5 ... 50% lower emission values are achieved. For example, from an initial level of 450 mg / MJ, a level of 200 ... 400 mg / MJ is reached. The cost of the methods is 20 ... 35% of the cost of the catalytic methods. Ammonia or urea are most commonly used as nitrogen oxide reducing additives. The result obtained with additional material may be more effective than combustion technology and may be used in conjunction with combustion technology, if necessary. Injection methods are expensive to implement, they can cause corrosion problems in the boiler and at least the use of urea produces nitrous oxide.

Catalytic processes can remove up to Θ0% of NOx compounds, so it is possible to reach levels below 100 mg / MJ. In pursuit of such low emission levels, this technique is often at its most advantageous in combination with a combustion technique that lowers NQX 2 B7949. The investment and operating costs of catalytic processes are high.

Combustion techniques provide only limited results, which means that in new solutions, combustion technology alone is no longer sufficient to achieve the permitted emission limits. Catalytic processes that are more efficient than combustion techniques are very expensive, so their use increases the cost of energy production. The various injection methods are in part relatively inefficient, cause corrosion and, as the injection increases, may cause odor nuisance in the environment.

As such, when using low-NOx combustion technology or fuel staged combustion, the efficiency of the methods is limited by not being able to stage sufficiently steep air without compromising fuel ignition close enough to the burner, rising non-combustible components in flue gases and ash, and flame stability. An increase in the proportion of non-combustible lowers efficiency and causes environmental problems as well as makes it more difficult to use ash. Decreased flame stability poses equipment and personal safety risks due to the risk of explosion.

It is an object of the present invention to provide a reduction in NOx emissions from solid, liquid or gaseous fuels when combusting more efficiently than conventional low-NOx combustion techniques and thus to avoid the use of more expensive, e.g. catalytic, processes.

The invention is based on the fact that the fuel is burned in a very strongly phased manner and forcibly ignited in a very free atmosphere with a flame of a plasma cannon.

More specifically, the method according to the invention is characterized by what is set forth in the characterizing part of claim 1.

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The invention provides considerable advantages.

With the strong phasing allowed by plasma flame ignition, it is possible to achieve NOx emission values as low as with current catalyst technology by combustion technology. This makes it possible to reduce current emission standards by low-cost combustion technology, resulting in large cost savings in new plants compared to catalyst technology. By using plasma, it is possible to use forced ignition of highly free fuel and very strong phasing, thus achieving significantly better NOx reduction than with conventional phase combustion technology. With the method according to the invention it is possible to achieve up to 80% NOx reduction.

By ensuring the stability of the ignition flame and determining the point of ignition of the flame, the use of plasma makes it possible to achieve a good combustion result under very difficult combustion conditions and creates good chances of fuel depletion. The available combustion chamber can be utilized as much as possible because the ignition point of the fuel comes close to the burner, the ignition point can be controlled and the combustion time is made long enough.

In the following, the invention will be examined in more detail with the aid of the accompanying drawings.

Figure 1 schematically shows one burner suitable for applying this method.

Figure 2 shows an experimental arrangement for testing the method according to the invention.

Figure 1 schematically shows a torch operating by means of a plasma cannon 1 which can be used for the application of this method. Coal dust is used as fuel for the burner. The burner has a plasma cannon 1, a fuel supply connection 2, a first auxiliary air supply connection 3 and a second auxiliary air supply connection 4. The fuel supply connection 2 and the air supply connections 3 and 4 are connected to the burner transverse to its longitudinal axis, whereby the fuel to be supplied to the burner and the combustion air is rotated about the longitudinal axis of the burner. This burner is a phase burner in which the combustion of the fuel is controlled by changing the amount of air supplied in different stages 8, 9, 10. In the first combustion stage, the fuel used by the burner is led in front of the plasma cannon 1 to the first gasification zone 8. At this stage, very little air is supplied with the fuel, the amount of air supplied is 5 to 30% of the total amount of combustion air required. The air coefficient in this gasification phase is about 0.05 to 0.3. Since the fuel contains little air in zone 8, the fuel cannot burn completely at this stage 8. However, the hot, high energy density flame of the plasma cannon 1 strongly gasifies the fuel, forming carbon monoxide and hydrogen at the same time as the hot flame of the plasma cannon 1 forcibly ignites a portion of the fuel and the carbon monoxide produced. Combustible carbon monoxide gasifies the above. . efficient use of carbon. The temperature in this zone in zone 8 is in some places 3500 * C and most preferably even above; - 4000 ° C.

The partially combusted and gassed fuel flows forward in the burner to zone 9 and is subsequently supplied with additional air via the first additional air connection 3. The total amount of air supplied with the air of the previous stage 8 is 5 - 50% of the total amount of air. At this stage 9, a large part of the fuel is gasified into carbon monoxide and the water contained in the fuel decomposes into the plasma of the previous stage 8 and the deafness of the subsequent stages 8, 9 into hydrogen and oxygen. The resulting carbon monoxide- and hydrogen-rich fuel mixture is ignited and finally burned in zone 10 by passing more air into the mixture through a second additional air connection 4, whereby the gassed fuel ignites as the air / fuel ratio increases sufficiently.

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Alternatively, the air supplied via the second additional air connection 3 can be used to further gasify the fuel in zone 10, whereby it is ignited to the actual combustion chamber, for example by means of fire air fed to the boiler of the power plant. The total amount of primary and secondary air introduced via the first 3 and second 4 additional air connections is then quite small, each supplying to the fuel at most about 10% of the total amount of air required, but most preferably only about 1 to 5% of the total amount of air. The rest of the required combustion air is brought into the combustion chamber used, for example a boiler.

Phase combustion techniques such as those described above can significantly reduce NOx emissions from combustion. The main difference between the incineration techniques according to the invention and the known incineration techniques is that the incineration method according to the invention makes the phasing sufficient. In order for nitrogen oxides to be reduced effectively, the fuel must be able to gasify efficiently as a mixture containing sufficiently little air. In this case, all the oxygen in the mixture combines with the fuel, not the nitrogen. A sufficiently sub-free mixture can be efficiently gasified only by means of a high energy density flame of the plasma cannon.

The reduction of nitrogen oxides is based on the fact that the conditions in the hot parts of the flame, in particular in the plasma cannon flame, are considered to be strongly reducing by phasing. In this case, the nitrogen oxides formed in the hot flame are reduced to molecular nitrogen. Similarly, phasing keeps temperatures elsewhere in the flame so low that no nitrogen oxides are formed. Because the plasma flame does not require fuel or combustion air, it lacks the oxygen necessary for the formation of oxides and the nitrogen oxides that may be formed under strongly under-free conditions are rapidly reduced. Nitrogen can also be used as the plasma gas without a substantial increase in NOx concentrations, since the nitrogen oxides formed by the combination of 6 87949 combustion air in the plasma flame are rapidly reduced in the first sub-free stages of combustion. An inert gas other than nitrogen can also be used as the Plas bed.

By applying the combustion method according to the invention, the nitrogen oxide emission values achievable by the method were studied. The burner according to Figure 1 was connected to the test boiler 6 as described in Figure 2. In Fig. 2, the fuel and air connections of the burner are marked with the same reference numerals as in Fig. 1. In addition to these, a third air supply connection 5 and a flue gas scrubber 7 are fitted to the boiler 6. The purpose of the experiments was to study the effects of NOx emissions.

The effects of the following factors on the N0X level of the burner flue gases were investigated using the test runs.

Test run No. Variable studied

Test series 1 1 NOx emission level without phasing 2 effect of plasma cannon power, no phasing 3 significance of furnace temperature level, no phasing 4-7 effect of tertiary air addition

Test series 2 8 plasma cannon as shielding gas instead of nitrogen 9 effect of plasma cannon power 10 as plasma gas instead of argon nitrogen 11 effect of addition of tertiary air 12 - 15 ΝΟχ level under optimal conditions determined according to experiments 8-11 7 87949

The air settings of the experiments and the results obtained are shown in Tables 1-4.

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table 1

Test run Duration Tx Vk Vx V2 V3 Vtot No. (min) (C °) (%) (%) (%) (¾) (1 / s) 1 10 1000 25 30 45 0 1280 2 12 1000 25 30 45 0 1280 3 20 850 25 30 45 0 1280 4 10 950 35 14 18 33 880 5 10 1000 26 10 14 50 880 6 15 1050 20 8 10 62 1560 7 7 1100 20 8 9 63 1580

Table 2

Test run Duration Tt Vk V3 V2 V3 See 01 No. (min) (C °) (%) (%) (%) (%) (1 / s) 8 58 1100 26 7 7 60 1390 9 18 1100 21 2 1 76 1710 10 20 1150 20 2 3 75 1710 11a1 »152> 1200 28 3 1 68 1250 11b 1150 22 2 1 75 1600 12 18 1200 25 2 1 72 1400 13 10 1200 28 3 1 68 1260 • - '": 14 13 1200 28 3 1 68 1260.:: 15 10 1200 25 2 1 72 1400 11 In section 11a the amount of tertiary air is less than in section 11b 21 Duration of the entire test run 11: Tx Furnace front temperature (carbon supply control setpoint)

Vk Supply air volume flow V3 Primary air volume flow v2 Secondary air volume flow V3 Tertiary air volume flow

Vt0t Total volume flow 9 87949

Table 3

Test run CO2 CO 02 NO2 η · o (%) (mg / MJ) (%) (mg / MJ) 1 16 5 2.9 415 2 16 2 2.9 410 3 16 74 2.8 390 4 16 46 3.1 260 5 16 51 2.5 135 6 16 43 2.7 85 7 17 39 1.8 70

Table 4

Test run CO 2 CO 2 NO 2 No. (%) (mg / MJ) (%) (mg / MJ) 8a1 »15 70 3.4 110 8b 16 75 2.9 107 9a2> 15 26 3.9 108 9b 16 23 3.5 90 10a3> 15 25 3.1 78 10b 16 24 3.1 80 11a4 »17 38 1.1 63 lib 16 25 2.9 85 12 16 25 2.1 69 13 17 44 2.0 62:. 14 17 58 1.2 57 · * ': 15 17 44 1.0 58 11 In Part 8a the plasma cannon is shielded by air, in Part 8b nitrogen 21 In Part 9a the plasma power is higher than in Part 9b 31 In Part 10a the plasma gas is argon, in Part 10b nitrogen 41 In Part 11a the amount of tertiary air is less than in section 11b ίο 87949

It is clear from the tables below that with strong phasing, NOx emissions are significantly reduced. The lowest emission values are reached when less than 30% of the combustion air is supplied to the burner as a carrier gas and a total of approx. 10% of the combustion air as primary and secondary air.

The combustion method according to the invention can be used for burning other gaseous, liquid or solid fuels in addition to coal dust. The method can be applied to all types of combustion plants, such as boilers, gas turbine combustion chambers and various furnaces. Fuel and air can be supplied to the burner along its axis. There may be more air and fuel supply connections than shown here.

Claims (7)

11 87949 A method for reducing nitrogen oxides from the combustion of solid, liquid or gaseous fuels, the method comprising the steps of phasing the combustion of the fuel, characterized in that. - the fuel is first fed in a strongly under-vacuum to provide reducing conditions to the continuously burning flame of the plasma cannon (1) to the first gasification zone (8) where the fuel is gasified and partially ignited, - additional gas for partial gasification and combustion, - the gassed fuel stream is led to the actual combustion chamber, for example a boiler, burner or the like (6), where it is combusted: Y: to the end. A method according to claim 1, characterized in that a fuel stream containing up to 30% of the total amount of fuel to be burned is introduced into the flame of the plasma cannon · (1) out of the total amount of air required to return. A method according to claim 1, characterized in that additional air is introduced into the partially gasified fuel stream in an amount which, together with the air introduced into the flame of the plasma cannon, corresponds to at most 50% of the total amount of air required to return. 12 87949 Method according to Claim 1, characterized in that the air coefficient in front of the plasma cannon (1) in the first ignition and gasification zone (8) is kept between 0.05 and 0.3. Method according to Claim 1, characterized in that the fuel is fed in front of the plasma cannon (1) by means of an air flow. A method according to claim 1, characterized in that the combustion air is introduced into the fuel stream in four steps: mixed with the fuel to be fed, as primary and secondary air to adjust the degree of gasification of the fuel and finally as combustion air for final combustion of the fuel. A method according to claim 6, characterized in that more than half of the combustion air is fed to the fuel in the last stage. i3 37949