Patent Publication Number: US-2012031312-A1

Title: Apparatus and method for the post combustion of hot material on a conveyor

Description:
FOREIGN PRIORITY CLAIM 
     This Patent Application claims priority to German Patent Application No. 10 2010 033 307.7 filed on Aug. 4, 2010, entitled, “ APPARATUS AND METHOD FOR THE POST COMBUSTION OF HOT MATERIAL ON A CONVEYOR”, the contents and teachings of which are hereby incorporated by reference in their entirety. 
     The present invention relates to an apparatus and a method for the conveyance of hot material, with post combustion of combustible material, on a conveyor which transports combustion residues. The invention is used particularly in plants having at least one combustion boiler, for example plants for the combustion of fossil fuels and/or waste incineration plants. 
     When ash, slag or combustion residues, also designated hereafter as “material”, are being transported away, it is especially important, on the one hand, to achieve by cooling a desired solidification or consolidation for the hot, sometimes still molten materials, so that, in particular, conveyance or further processing of these materials after they have been drawn off from the combustion boiler becomes possible. Furthermore, it is also desirable to subject hot material on the conveyor to post combustion in order to reduce unburnt constituents in the hot material. 
     It was previously assumed that, in order to convey hot materials, it is first necessary to carry out quenching in the water bath (what is known as wet discharge). However, large quantities of water were required for this purpose which, particularly in dry regions, were not readily available. Moreover, the water used had to be purified in a complicated way. Since the 90s, therefore, dry draw-off systems, as they are known, have been adopted. In this case, the hot material is laid onto conveyor belts and is transported further on there, directed cooling of the hot material on the conveyor belts being carried out. These conveyor belts are usually designed so as to be encapsulated with respect to the external surroundings, that is to say housing which prevents the situation where combustion gases arising during the treatment of the material may also readily escape into the surroundings. Also, combustion boilers are operated predominantly with a slight vacuum, so that the combustion gases produced by the material are drawn off towards the combustion boiler by means of a corresponding suction draught. 
     As regards the last-mentioned apparatuses for the conveyance of hot material, it was found that post combustion on the conveyor is often not sufficient, and therefore the material still has a high fraction of unburnt constituents at the end of the conveying road. The result of this is that the ash quality is not sufficient, particularly in terms of a degree of combustion in the hot material, for the further processing of the latter. This refers particularly to the further processing of the hot material in the construction industry. 
     The object of the invention, therefore, is at least partially to solve the technical problems outlined with regard to the prior art and, in particular, to specify an apparatus for the conveyance of hot material out of at least one combustion boiler, which apparatus is distinguished by enhanced, in particular on-demand, destination-oriented and intelligent post combustion of the hot material. Further, a method for the conveyance of hot material out of at least one combustion boiler is also to be specified, which is distinguished by enhanced, in particular on-demand, destination-oriented and intelligent post combustion of the hot material. 
     These objects are achieved by means of an apparatus as described herein and by means of a method described herein. Further advantageous embodiments of the invention are specified herein. It shall be pointed out that the features listed individually herein may be combined with one another in any technologically expedient way and define further embodiments of the invention. 
     The apparatus according to the invention for the conveyance of hot material out of at least one combustion boiler has at least one conveyor for conveying the hot material from a material reception region of the at least one conveyor to a material delivery space of the at least one conveyor along a conveying road, and at least one housing surrounding the at least one conveyor, at least one oxidant feed being arranged in or on the at least one housing along the conveying road at a distance from the material delivery space. 
     The at least one conveyor is preferably designed in the manner of a steel-plate conveyor, in which a multiplicity of steel plates is arranged in a row in an articulated manner, so as to overlap one another, and are moved via (chain) drives or deflecting rollers. The material to be considered for the conveyor belt is, in particular, impact-proof, corrosion-resistant and temperature-proof steels. 
     The at least one conveyor is surrounded by at least one housing. This at least one housing can be connected, in particular gas-tight, to the combustion boiler in the area of the material reception region of the at least one conveyor, the material reception region of the at least one conveyor then being located beneath a material output orifice of the combustion boiler. In the material reception region, the hot material is transferred onto the at least one conveyor. 
     The material reception region is followed in a conveying direction of the hot material by a post combustion zone. Post combustion of the hot material takes place in this post combustion zone as a result of the addition of an oxidant. This oxidant is, in particular, (ambient) air, (ambient) air with a modified oxygen content and/or pure oxygen and/or flue gas. Arranged for this purpose at a distance from the material delivery space or in the region of the post combustion zone, in or on the housing, is at least one oxidant feed by means of which the oxidant can be introduced into the post combustion zone and the oxidant can be brought into contact in the post combustion zone with the hot material. The at least one oxidant feed may be mounted fixedly and/or movably, in particular pivotably, in and/or on the at least one housing. Further, the at least one oxidant feed may have guide elements, such as, for example, guide plates, flow deflection means and/or fans. The post combustion zone usually extends from the material reception region beneath the material output orifice of the combustion boiler as far as a region in which the oxidant no longer causes essentially any post combustion of the hot material. Depending on the flow conditions of the oxidant in the at least one housing, the post combustion zone ends, in particular, directly downstream of the (last) at least one oxidant feed in the conveying direction. 
     The post combustion zone is preferably formed by a cooling zone in which the hot material on at least one conveyor is cooled by a cooling-air stream. In other words, this means that the cooling effect predominates in the cooling zone or even, essentially, significant post combustion no longer takes place. This cooling-air stream is essentially not of the oxidant fed by the oxidant feed, but, instead, an additional cooling-air stream which is fed, in particular, in or near a material delivery space of the at least one conveyor and which can preferably be controlled independently of the feed of the oxidant. Furthermore, the oxidant may have a higher oxygen concentration than the cooling-air stream reaching the post combustion zone. The cooling-air stream enters the apparatus either through a material delivery space of the at least one housing and/or through at least one separate cooling-air stream inlet in the at least one housing in the material delivery space of the at least one conveyor. 
     The material delivery space is, in particular, that space inside the at least one housing which
         commences (directed) downstream of the at least one conveyor belt in the conveying direction, that is to say at the end of the conveying road, and is delimited by the at least one housing,       

     and/or
         commences in the conveying direction with an orifice in the at least one housing, out of which the hot material is unloaded, and is delimited by the at least one housing.       

     It is therefore especially preferable that the oxidant feed arranged nearest to the material delivery space is also arranged in the lateral region of the conveyor or conveyor belt. This ensures, in particular, that the oxidant is added to the material lying on the conveyor. 
     Both the oxidant and the cooling-air stream can flow essentially along the conveying road of the at least one conveyor and preferably opposite to the conveying direction of the hot material, to be precise in the direction of the combustion boiler. In order to prevent the oxidant and/or the cooling-air stream from entering the combustion space of the combustion boiler completely or partially, the oxidant can be removed from the housing through an oxidant outlet at least partially and/or completely before entry into the combustion space of the combustion boiler, and/or the cooling-air stream can be removed at least partially or completely via a cooling-air outlet. The oxidant outlet is in this case preferably arranged in the post combustion zone and the cooling-air outlet in the cooling zone. It should be explained, here, that the cooling-air outlet and the oxidant outlet may, however, also be formed by one common outlet. Moreover, it should be noted at this juncture that the quantity of oxygen entering the combustion space of the combustion boiler via the oxidant and/or the cooling-air stream should not overshoot 1.5% by mass (percent by mass) of the oxygen required for stoichiometric combustion in the combustion space. 
     The apparatus according to the invention is distinguished, then, in that post combustion can be carried out independently of a cooling-air stream by virtue of on-demand, destination-oriented and intelligent activation of an oxidant feed. 
     It should be borne in mind, furthermore, that the at least one oxidant feed and therefore the post combustion zone are at a distance of at least one metre, preferably at least 2 metres and especially preferably at least 3 metres along the conveying road from the material delivery space of the at least one conveyor, thus ensuring a minimum length of a cooling zone. Further, it is also advantageous if a ratio of a first length of the post combustion zone along the conveying road to a second length of the cooling zone along the conveying road is 0.1 to 0.9, preferably 0.3 to 0.7 and especially preferably essentially 0.5. 
     It is especially advantageous if the at least one oxidant feed is connected to at least one hot-air generator. 
     The temperature of the oxidant is increased with the aid of the hot-air generator. This increase in temperature of the oxidant leads to especially intensive post combustion of the hot material on the at least one conveyor in the post combustion zone. The at least one oxidant feed is connected to the hot-air generator, in particular, via temperature-resistant pipelines and/or hose lines. These pipelines and/or hose lines may have at least one oxidant pump. Basically, the oxidant is conveyed out of one or more regions of the combustion boiler which carry exhaust gases and/or out of the surroundings and/or out of a secondary-air stream, provided for the combustion of fuel as in the combustion boiler, through the hot-air generator and the oxidant feed into the housing. The temperature of the oxidant is increased by the hot-air generator preferably to at least 100° C., in particular to at least 200° C. and most especially preferably to at least 300° C. Furthermore, it is preferable to increase the temperature of the oxidant such that the temperature of the oxidant is higher than the temperature of the cooling-air stream upon entry into the post combustion zone. 
     It is especially advantageous if the apparatus has at least one sensor for determining a characteristic value for a degree of combustion of the hot material. 
     This characteristic value for the degree of combustion of the hot material may be, in particular, at least one from the following group: the density of the hot material, the colour of the hot material, the temperature of the hot material, the grain size of the hot material, the consistency of the hot material, the colour temperature of the hot material, the radiated power of the hot material and the ultraviolet radiation (UV radiation) of the hot material. In each case the suitable characteristic value for a degree of combustion of the hot material depends critically on the fuel used in the combustion boiler and can be determined in a simple way by a person skilled in the art by means of routine investigations. Moreover, a sensor known from the prior art and suitable for determining the respective characteristic value must be selected according to the characteristic value. It should be explained, furthermore, that the degree of combustion is the already burnt (percentage) mass fraction or the already burnt (percentage) volume fraction of the hot material. In other words, the degree of combustion means the mass of the hot material minus the mass of unburnt constituents of the hot material as a percentage or the volume of the hot material minus the volume of unburnt constituents of the hot material as a percentage. 
     In the development of the invention, it is proposed that the apparatus have a control which is connected in a data-conducting manner to the at least one sensor and the at least one oxidant feed and which is set up to control the at least one oxidant feed, on demand, as a function of the characteristic value, determined by the at least one sensor, for the degree of combustion of the hot material. 
     This on-demand control of the at least one oxidant feed means, in particular, that the oxidant feed is controlled in such a way that (only and/or exactly) as much oxidant is introduced into the post combustion zone of the apparatus as is sufficient to reach a desired degree of combustion of the hot material. A desired degree of combustion is, in particular, a degree of combustion which is required for specific reprocessing of the hot material. In particular, a degree of combustion of at least 90%, preferably of at least 95% or even most especially preferably of at least 99% should be achieved. For this purpose, the control actuates, in particular, valves and/or oxidant pumps of the at least one oxidant feed. 
     According to a further aspect of the invention, a method for conveying hot material out of at least one combustion boiler is also proposed, which has at least the following steps:
         a) providing hot material from the at least one combustion boiler in a material reception region of at least one conveyor,   b) conveying the hot material from the material reception region of the at least one conveyor to a material delivery space of the at least one conveyor along a conveying road,   c) post combusting the hot material on the at least one conveyor by the on-demand feed of oxidant into at least one housing of the at least one conveyor, the feed of the oxidant taking place into a region of the at least one housing which is located at a distance from the material delivery space of the at least one conveyor, and   d) cooling the hot material by an additional cooling-air stream at least in the material delivery space of the at least one conveyor.       

     According to step a), the hot material of the conveyor is transferred into the at least one conveyor, in particular, through a material output orifice of the combustion boiler in the material reception region which is arranged beneath the material output orifice. Subsequently, in step b), the hot material is conveyed from the material reception region of the at least one conveyor to the material delivery space of the at least one conveyor along the conveying road and is unloaded from the housing in the material delivery space. The feed of the oxidant according to step c) takes place into a region located at a distance from the material delivery region of the at least one conveyor, in particular a post combustion zone, so that post combustion of the hot material of the at least one conveyor is assisted in this region. Moreover, according to step d), cooling of the hot material by an additional cooling-air stream takes place at least in the material delivery space of the at least one conveyor, the cooling of the hot material additionally also taking place in a cooling zone which may extend from the post combustion zone along the conveying road as far as the material delivery region of at least one conveyor. It should be explained that the individual steps are designed, in terms of time, to run in parallel and/or at least partially to follow one another during the conveyance of the hot material on the at least one conveyor. Further, all the explanations and definitions of the features of the apparatus can be transferred to the corresponding features of the method, and vice versa. 
     It is especially advantageous if, in step c), the feed of the oxidant is controlled, on demand, as a function of a characteristic value for a degree of combustion of the hot material. 
     This characteristic value for the degree of combustion of the hot material may be, in particular, at least one from the following group: the density of the hot material, the colour of the hot material, the temperature of the hot material, the grain size of the hot material, the consistency of the hot material, the colour temperature of the hot material, the radiated power of the hot material and the ultraviolet radiation (UV radiation) of the hot material. The in each case suitable characteristic value for a degree of combustion of the hot material depends critically on the fuel used in the combustion boiler and can be determined or calculated in a simple way by a person skilled in the art by means of routine investigations. Furthermore, a sensor known from the prior art and suitable for determining the characteristic value must be selected according to the characteristic value. The control of the feed of oxidant takes place in such a way that the fed quantity of oxidant is increased when the degrees of combustion are too low, in order to increase the intensity of post combustion, until the degree of combustion of the hot material at least reaches the desired degree of combustion. 
     Furthermore, it is advantageous if the characteristic value of the degree of combustion of the hot material is determined by means of at least one sensor. This means, in particular, a continuous determination of the characteristic value for the degree of combustion of the hot material by means of a sensor suitable for the respective characteristic value, particularly in real time, so that a continuous control, adapted to the actual degree of combustion of the hot material, of the feed of oxidant can take place. 
     It is likewise advantageous if the control of the feed of oxidant comprises at least the influencing of one of the following properties of the oxidant:
         temperature of the oxidant,   flow velocity of the oxidant,   flow direction of the oxidant,   mass flow of the oxidant,   oxygen concentration of the oxidant,   location of the feed of oxidant into the housing.       

     These properties of the oxidant are especially suitable for influencing the intensity of post combustion on the at least one conveyor. In particular, it is preferable that at least two or even at least three of the above-mentioned properties are influenced by the control. 
     The temperature of the oxidant is, in particular, that temperature which the oxidant has upon exit from the at least one oxidant feed or upon entry into the at least one housing. The temperature of the oxidant preferably amounts to at least 100° C., in particular at least 200° C. and most especially preferably at least 300° C. The temperature may, in particular, be added in a controlled manner so as to be adapted to the ambient conditions in the housing and/or to the properties of the material. 
     The flow velocity of the oxidant upon exit from the at least one oxidant feed or upon entry into the at least one housing preferably amounts to at least 1 m/s (metre per second), in particular preferably at least 5 m/s and most especially preferably at least 10 m/s. The flow velocity may, in particular, be controlled so as to be adapted to the ambient conditions in the housing and/or to the properties of the material. 
     The flow direction of the oxidant is, in particular, the flow direction of the oxidant along the conveying road in the at least one housing, that is to say either in the conveying direction and/or (partially) opposite to the conveying direction of the hot material, and/or upon exit from the at least one oxidant feed or upon entry into the at least one housing. The flow direction, too, may, in particular, be set to the ambient conditions in the housing and/or to the properties of the material. 
     The mass flow of the oxidant is that mass flow of the oxidant (in kg of oxidant per minute (kg/min)), which flows through the at least one oxidant feed into the at least one housing. The mass flow of the oxidant preferably amounts to at least 50 kg/min, in particular at least 100 kg/min and most especially preferably at least 150 kg/min. The mass flow may, in particular, be added in a controlled manner so as to be adapted to the ambient conditions in the housing and/or to the properties of the material. 
     The oxygen concentration of the oxidant is, in particular, that oxygen concentration which the oxidant has upon exit from the at least one oxidant feed or upon entry into the at least one housing as a percentage by mass. The oxygen concentration will often correspond approximately to that in air, but this does not necessarily have to be maintained as such, instead an (increased or lowered) oxygen concentration adapted to the ambient conditions in the housing and/or to the properties of the material may be added in a controlled manner. 
     The location of the feed of oxidant into the housing is that location inside the post combustion zone where the oxidant from the at least one oxidant feed enters the housing. A plurality of feed locations may therefore be provided. However, it is also possible that a variable feed location (for example, movable in relation to the housing) is present. The delivery of the oxidant can thus also take place so as to be adapted in terms of the position in relation to the housing and as a function of ambient conditions in the housing and/or properties of the material. 
     Furthermore, it is advantageous if the addition of the oxidant and cooling by the cooling-air stream are coordinated with one another. What can thereby be achieved, in particular, is that the quantity of oxygen entered into the combustion space of the combustion boiler via the oxidant and/or the cooling-air stream does not overshoot 1.5% by mass (percent by mass) of the oxygen required for stoichiometric combustion in the combustion space. 
    
    
     
       The invention and the technical background are explained in more detail below by means of the figure. It should be pointed out that the figure shows an especially preferred design variant of the invention, although the latter is not restricted to it. 
         FIG. 1 : shows diagrammatically an example embodiment of an apparatus according to the invention for the conveyance of hot material out of at least one combustion boiler. 
     
    
    
       FIG. 1  shows an apparatus  1  according to the invention for the conveyance of hot material  2  out of at least one combustion boiler  3 . The apparatus  1  has a conveyor  4  for conveying the hot material  2  from a material reception region  5  to a material delivery space  6  along a conveying road  7 . The conveyor  4  is surrounded by a housing  13 . This housing  13  is connected, essentially gas-tight, to the combustion boiler  3  via a material output orifice  14 . The hot material  2  is transferred through the material output orifice  14  out of a combustion space  15  of the combustion boiler  3  onto the conveyor  4  in the material reception region  5 . 
     The conveyor  4  is driven by a drive  22 , so that the hot material  2  is conveyed out of the material reception region  5  along the conveying road  7  to the material delivery region  6  and is delivered from the housing  13 . 
     The material delivery space  6  has arranged in it a cooling-air stream feed  29  in the manner of a valve, pump or fan, which introduces a cooling-air stream  25  through a cooling-air stream inlet  28  in the housing  13  in the material delivery space  6  into the housing  13 . The cooling-air stream  25  flows along the conveying road  7  opposite to the conveying direction of the hot material  2  through the housing  13  and cools the hot material  2  in a cooling zone  27 . The temperature of the cooling-air stream  25  at the end of the cooling zone  27  is so high that cooling of the hot material  2  essentially no longer takes place at the end of the cooling zone  27 . The heated cooling-air stream  25  is discharged from the housing  13  through a cooling-air outlet  30  and/or an oxidant outlet  12  and/or through the material output orifice  14 . In this example embodiment, the cooling-air outlet  30  is located at the end of the cooling zone  27 . 
     The cooling-air zone  27  is followed, opposite to the conveying direction of the hot material  2  along the conveying road  7 , by a post combustion zone  26 . In this post combustion zone  26 , an oxidant  24  is introduced into the post combustion zone  26  via an oxidant feed  23 . The post combustion of the hot material  2  on the conveyor  4  in the post combustion zone  26  is promoted by the oxidant  24 . So that the oxidant  24  can be provided, on demand, in the post combustion zone  26 , (for example) a sensor  10  for determining a characteristic value for a degree of combustion of the hot material  2  is arranged inside the apparatus  1 . This sensor  10  is connected in a data-conducting manner to a control  11  which, in turn, is connected in a data-conducting manner to an oxidant conveyor  8  in the manner of an oxidant pump. The control  11  activates the oxidant pump  8  when the sensor  10  determines characteristic values for a degree of combustion of the hot material  2  which lie below a range for a desired degree of combustion of the hot material  2 . For this purpose, the oxidant pump  8  is connected to a hot-air generator  9  via lines  16 . This hot-gas generator  9  serves for increasing the temperature of the oxidant  24 . In this example embodiment, the oxidant  24  is fed to the hot-gas generator  9  from the combustion space  15  and/or from regions  17  carrying exhaust gas and/or from the surroundings. For this purpose, a first valve  18 , a second valve  19 , a third valve  20 , a fourth valve  21  and a fifth valve  31  are arranged in the lines  16  so as to provide the oxidant  24  on demand. 
     In the present example embodiment, the temperature of the oxidant  24  can be influenced by the hot-air generator  9 , the flow direction of the oxidant  24  can be influenced by an oxidant feed  23  configured so as to be movable and/or pivotable along the conveying road  7  and transversely to the conveying road  7 , the mass flow of the oxidant  24  can be influenced by the cooling-air stream feed  29 , the oxygen concentration of the oxidant  24  can be influenced via the location of extraction of the oxidant  23  (combustion space  15  and/or regions  17  carrying exhaust gas and/or the surroundings), and the feed location of the oxidant  24  can be influenced by a movable configuration of the oxidant feed  23  in the post combustion zone  26 . 
     The present invention is distinguished, in particular, by improved, in particular on-demand, destination-oriented and intelligent post combustion of the hot material. 
     LIST OF REFERENCE SYMBOLS  
     
         
           1  Apparatus 
           2  Hot material 
           3  Combustion boiler 
           4  Conveyor 
           5  Material reception region 
           6  Material delivery space 
           7  Conveying road 
           8  Oxidant conveyor 
           9  Hot-air generator 
           10  Sensor 
           11  Control 
           12  Oxidant outlet 
           13  Housing 
           14  Material output orifice 
           15  Combustion space 
           16  Line 
           17  Region carrying exhaust gas 
           18  First valve 
           19  Second valve 
           20  Third valve 
           21  Fourth valve 
           22  Drive 
           23  Oxidant feed 
           24  Oxidant 
           25  Cooling-air stream 
           26  Post combustion zone 
           27  Cooling zone 
           28  Cooling-air stream inlet 
           29  Cooling-air stream feed 
           30  Cooling-air outlet 
           31  Fifth valve