Method for operating a combustion plant

Technical field

p0001The present invention relates to a method according to the preamble of claim 1. It also concerns a firing plant for performing the method.

State of the art

p0002For combustion in conventional construction of the fuel is injected through a nozzle into a combustion chamber where it is burnt with supply of combustion air. Basically, the operation of such furnaces is possible with a gaseous and / or liquid fuel. When using a liquid fuel, the NOx, CO, UHC emissions (UHC = unsaturated coal-water substances) the vulnerability is concerning in terms of a clean burning superficially that the atomization of the fuel a high degree of mixing (gasification) with the combustion air must reach. When using a gaseous fuel, therefore, the combustion with a substantial reduction of the pollutant emissions expires. Meanwhile, for combustion plants with boilers but have gas-powered burner, despite the many advantages, not to enforce such right. The reason for this may be that the logistics for gaseous fuels makes an elaborate infrastructure per se necessary. Therefore, if the combustion installations created with liquid fuel, so the quality of combustion regarding deeper pollutant emissions is overweight depends on whether it is possible to achieve an optimal degree of mixing between fuel and combustion air, ie, whether complete gasification of the liquid fuel guarantees is. The way a premix, which acts upstream of the actual burner head has not led to the goal, because in such a configuration must be feared always that a flashback of the flame can take place inside the premixing. While it is true that premix burners have become known which work with 100% excess air, so that the flame can be operated just before the point of deletion. But here is important to remember that for combustion allows for the boiler efficiency, a maximum excess air by 15%, thus ensuring the use of such burners in atmospheric combustion no optimal operation. the farther even if the necessary degree of gasification of the liquid fuel could be achieved approximately, so would be at the high flame temperatures, which are known to be responsible for the formation of NOx emissions, has not yet been acted upon. The desired combustion at low flame temperatures and with a homogeneous fuel / air mixture can not be achieved with the become known from the prior art options.

Summary of the Invention

p0003The invention aims to remedy this. The invention, as characterized in the claims, the object is an object with a method and a firing system of the type mentioned in the pollutant emissions, in particular as regards the NOx emissions to minimize, this both when using a liquid fuel, a gaseous fuel, as well as in a mixed operation with said fuel.

p0004Being founded on the invention idea differs from the classical principles in that the graduation is exclusively carried out by 2-fold addition of fuel and recirculated flue gas in the air excess area. In the first stage the combustion air via a heat exchanger an aerodynamically stabilized premix burner is supplied. Depending on the design of the heat exchanger, the combustion air can be preheated to about 400 ° C, resulting in the combustion of oil to a very good pre-evaporation. The combustion air ratio in this so-called lean stage is about 2.1, corresponding to approximately 11% residual oxygen, whereby at flame temperatures of about 1300 ° C, NOx emissions, the atmospheric case, be less than 1 vppm. On the way to the second stage of the heat medium is removed, so that when it enters the second stage, the temperature is still about 1000 ° C. There is preferably further via an annular chamber fuel / flue gas mixture is injected until a residual oxygen content of about 3% is reached in the exhaust gas axially offset. The injected mixture is thereby ignited by the hot flue gases from the first stage. The full combustion is achieved then in the combustion chamber at a temperature of about 1400 ° C.

p0005The essential advantage of the invention is the fact that the arrangement of the injection openings of the fuel / flue gas mixture control a time delay of ignition in the combustion chamber, thus affecting the oxygen content during the burnout, such that at optimum trim of the system, the expected NOx emissions are, vppm with complete burn-out, between 5-8. According to current knowledge, this value marks the theoretical lower limit for the near-stoichiometric combustion of fossil fuels.

p0006Another advantage of the invention is to be seen in that the first stage caloric conditioned flue gas combustion air can be supplied to the one hand to influence the pre-heating temperature and on the other hand, the residual oxygen content to reduce further if necessary after the second stage.

p0007Advantageous and expedient further developments of the inventive task solution are defined in the further claims.

p0008In the following an embodiment of the invention will be explained in more detail with reference to the drawings. All elements which are required for direct understanding of the invention are omitted. The direction of flow of the various media is indicated by arrows. Identical elements are provided in the various figures with the same reference numerals.

Brief Description of Drawings

p0009It shows:<dl id="dl0001"><dt>Fig. 1</dt><dd>a boiler system for staged combustion,</dd><dt>FIG. 2</dt><dd>a premix burner in the design, cut as a "double-cone burner" in perspective and in accordance with</dd><dt>FIGS. 3-5</dt><dd>corresponding sections through different levels of the premix burner according to FIG. 2.</dd></dl>

WAYS TO CARRY OUT THE INVENTION, COMMERCIAL recoverability

p0010Fig. 1 shows a boiler plant, which is divided into a skim stage 1 and a near-stoichiometric stage 2. The lean stage 1 consists essentially of a premix burner 100 with a downstream combustion chamber 122, in which prevails a flame temperature of about 1300 ° C. The premix burner 100 is operated with a liquid 112 and / or gaseous fuel 113th The combustion air 115 for the premix burner 100 is a mixture 6, which consists of fresh air and 3 of recycled, calorically conditioned flue gas. 4 The degree of mixing is maintained on the air side by a controllable throttle valve 7, which air unconditioned 3, thus obtained at ambient temperature. The flue gas 4 originates from a flue gas manifold 8, which is derived from the flue gases from the near-stoichiometric stage 9 the second These fumes 9 fall at a temperature of about 300 ° C, and they are cooled in said flue gas distributor 8 through a heat exchange system 10 to about 260 ° C. This cooled flue gases 4, and the fresh air are mixed upstream of the premix burner 3 100 and compressed in a compressor 11 acting there, wherein the temperature of the compressed air / flue gas mixture is approximately 260 ° C. Subsequently, this mixture is further processed by a further 6 122 induced by the heat exchange wall the combustion chamber, which is versinnbildlich by the arrow 16, caloric, such that the combustion air 115 to about 400 ° C flows for the premix burner 100 therein. The outflow side of the combustion chamber 122 is an annular chamber 12, which is already one of the near-stoichiometric level. 2 In this ring chamber 12, NOx emissions flow through the slightly cooled hot gases from the lean level 1, which is operated with combustion air 115 at about 11% O2, whereby at a flame temperature of about 1300 ° C in atmospheric case less than 1 vppm lie. Further, this ring chamber 12 is perforated with a number of Eindüsungslöchern 13 through which a fuel / flue gas mixture flowing in the fourteenth This mixture 14 is composed of a proportion of the flue gas 4 from the flue gas distributor 8 and out of a further portion of wood to heating 15, which is preferably a gaseous fuel. On the way to near-stoichiometric stage 2 the hot gases provided in the lean stage 1 is withdrawn 16 heat through the aforementioned heat exchange, so that when it enters the annular chamber 12 still prevails a temperature of about 1000 ° C. The injected by axial displacement into the annular chamber 12 fuel / flue gas mixture 14 reduces the residual oxygen content of the conditioned hot gases from the lean level 1 to approx 3%. Furthermore, the injected into the annular chamber 12 mixture 14 undergoes by the hot gases of about 1000 ° C self-ignition, the complete burnout takes place subsequently in the boiler combustion chamber 17 at a temperature of about 1400 ° C. After leaving the boiler combustion chamber 17, the flue gases 9 still has a temperature of about 300 ° C, a portion of which, as already explained above, be introduced into the flue gas manifold eighth The not diverted flue gases 18 are vented through a chimney 19 at the lowest temperature outside. For optimum control of the various media, which induce a complete combustion within the near-stoichiometric stage 2, are the expected NOx emissions between 5-8 vppm what present state of knowledge represents a lower limit for the near-stoichiometric combustion of fossil fuels.

p0011To better understand the structure of the premix burner 100, it is advantageous if the individual cuts are used according to the figures 3-5 at the same time to FIG. 2. Furthermore, so as not to make unnecessary cluttering Fig. 2, are in their baffles schematically shown in FIGS 3-5 121a, 121b has only hinted added.

p0012In the following reference is made in the description of Fig. 2 as necessary to the remaining figures 3-5.

p0013The premix burner 100 of FIG. 2 consists of two hollow conical partial bodies 101, 102 which are offset from each other nested. The offset of the respective center axis or longitudinal axis of symmetry 201b, 202b of the conical sectional bodies 101, 102 provides on both sides, in mirror-image arrangement, one tangential air inlet slot 119, 120 free (Fig. 3-5), through which the combustion air 115 in the interior of the premix burner 100, that is, into the conical cavity 114th The conical shape of the sectional bodies 101, 102 shown in the flow direction has a certain fixed angle. Of course, depending on the operational use, a trumpet, the sectional bodies 101, 102 have in the flow direction an increasing or decreasing conicity similar respectively. Tulip. The latter two forms are not included in the drawing since they are nachempfindbar to the skilled artisan. The two conical part bodies 101, 102 each have a cylindrical top portion 101a, 102a which are also analogous to the conical part bodies 101, 102 offset angles to one another, so that the tangential air inlet slots 119, 120 100 are present over the entire length of the premix burner. In the region of the cylindrical initial part is a nozzle housed 103 whose injection 104 of which coincides approximately with the narrowest cross-section of the conical hollow space formed by the conical sectional bodies 101, 102 114th The Eindüsungskapazität and the nature of this nozzle 103 is determined by the predetermined parameters of the respective premix 100. Of course, the premix can be purely conical, ie without cylindrical initial parts 101a, 102a to be executed. The conical part bodies 101, 102 further have a respective fuel pipe 108, 109, which are arranged along the tangential inlet slots 119, 120 and is provided with injection openings 117 through which a gaseous fuel is preferably 113 injected into the flowing through there combustion air 115 as this the arrows are intended to symbolize the 116th These fuel lines 108, 109 are preferably at the latest at the end of the tangential inflow, placed before entry into the conical cavity 114, this in order to obtain an optimal air / fuel mixture. Combustion space end 122, the outlet opening of the premixing burner 100 through a front wall 110, in which a number of holes 110a are provided. The latter come into operation when necessary, and ensure that the dilution air or cooling air is fed 110b the front part of the combustion chamber 122nd Furthermore, this air feed ensures flame stabilization at the outlet of the premix burner 100. This flame stabilization is important when it comes to support the compactness of the flame due to a radial flattening. In the zoom out through the nozzle 103 fuel is a liquid fuel 112, which may be enriched with at most a recirculated exhaust gas. This fuel 112 is injected at an acute angle into the conical cavity 114th From the nozzle 103 to THEREFORE forms a conical fuel profile 105, which is enclosed by the tangentially inflowing rotating combustion air 115th In axial direction, the concentration of the fuel 112 is continuously reduced by the inflowing combustion air 115 to an optimal mixing. If the premix burner 100 is operated with a gaseous fuel 113, then this is preferably about Oeffnungsdüsen 117, the formation of this fuel / air mixture directly at the end of the air inlet slots 119, 120 is concluded. In the injection of the fuel 112 through the nozzle 103 is in the region of the vortex, that is achieved in the area of ​​the reverse flow 106 at the end of the premix burner 100, the optimum homogeneous fuel concentration over the cross section. Ignition takes place at the apex of the reverse 106. Only at this point can a stable flame front 107 arise. A back of the flame into the interior of the premix burner 100 as latent is the case with known premixing, whereas with complicated flame holders remedy is there wanted is not to be feared here. If the combustion air 115 is additionally preheated or enriched with a recirculated exhaust gas, as this aids the vaporization of the liquid fuel 112 sustained before the combustion zone is achieved. The same considerations also apply if supplied via lines 108, 109 instead of gaseous liquid fuels. When designing the conical sectional bodies 101, 102 regarding cone angle and width of the tangential air inlet slots 119, 120 are narrow limits to be observed, so that the desired flow field of the combustion air 115 with the flow zone 106 can adjust the output of the premix 100th Generally it can be said that a reduction of the cross section of the tangential air inlet slots 119, 120, the backflow zone 106 further upstream shifts, which then, however, comes the mixture ignites earlier. After all, it should be noted that once fixed backflow 106 is positionally stable per se, because the swirl number increases in the flow direction in the area of ​​the conical shape of the premix to 100. The axial velocity within the premix burner 100 can be changed by an appropriate, not shown feeding an axial combustion air flow. The construction of the premix burner 100 is further excellently, to change the size of the tangential air inlet slots 119 120, whereby a relatively large operational range can be detected without changing the overall length of the premix 100th

p0014From Fig. 3-5 now the geometric configuration of the baffle plates 121a, 121b is shown. You have a flow introduction function, which extend, according to their length, each end of the conical sectional bodies 101, 102 in the direction of inflow over combustion air 115th The canalization of the combustion air 115 in the conical cavity 114 can be obtained by opening or closing the guide plates 121a, 121b optimized to placed in the conical cavity 114 in the region of the inlet of this channel pivot 123, in particular, this is necessary when the original gap size of the tangential air inlet slots 119, 120 is changed. Of course, these arrangements may also be provided dynamic static electricity by forming requires excessive baffles an integral part with the conical part bodies 101, the 102nd Also, the premix can be 100 operated without baffles, or it can be another tool for this vogesehen.

LIST OF REFERENCE NUMBERS

p0015<dl id="dl0002"><dt>1</dt><dd>First combustion stage, Magerstufe</dd><dt>2</dt><dd>Second Verbrennnungsstufe, near-stoichiometric stage</dd><dt>3</dt><dd>air</dd><dt>4</dt><dd>conditioned flue gas</dd><dt>6</dt><dd>Air / flue gas mixture</dd><dt>7</dt><dd>throttle</dd><dt>8th</dt><dd>Flue gas distributor</dd><dt>9</dt><dd>Flue gases from stage 2</dd><dt>10</dt><dd>heat exchanger</dd><dt>11</dt><dd>compressor</dd><dt>12</dt><dd>annular chamber</dd><dt>13</dt><dd>Eindüsungslöcher</dd><dt>14</dt><dd>Fuel / flue gas mixture</dd><dt>15</dt><dd>fuel</dd><dt>16</dt><dd>heat exchanger</dd><dt>17</dt><dd>Boiler furnace</dd><dt>18</dt><dd>Fumes fireplace</dd><dt>19</dt><dd>fireplace</dd><dt>100</dt><dd>burner </dd><dt>101, 102</dt><dd>subfield</dd><dt>101a, 102a</dt><dd>Cylindrical Angangsteile</dd><dt>101b, 102b</dt><dd>Longitudinal axes of symmetry</dd><dt>103</dt><dd>fuel nozzle</dd><dt>104</dt><dd>fuel injection</dd><dt>105</dt><dd>Brennstoffeindüsungsprofil</dd><dt>106</dt><dd>Backflow (vortex breakdown)</dd><dt>107</dt><dd>flame front</dd><dt>108, 109</dt><dd>fuel lines</dd><dt>110</dt><dd>front wall</dd><dt>110a</dt><dd>air holes</dd><dt>110b</dt><dd>cooling air</dd><dt>112</dt><dd>liquid fuel</dd><dt>113</dt><dd>Gaseous fuel</dd><dt>114</dt><dd>conical cavity</dd><dt>115</dt><dd>combustion air</dd><dt>116</dt><dd>Fuel injection</dd><dt>117</dt><dd>fuel nozzles</dd><dt>119, 120</dt><dd>Tangential air inlet slots</dd><dt>121a, 121b</dt><dd>baffles</dd><dt>122</dt><dd>combustion chamber</dd><dt>123</dt><dd>Fulcrum of the baffles</dd></dl>