Patent Publication Number: US-2011070549-A1

Title: System for ash recycling

Description:
The present invention relates to a method and an apparatus for the efficient operation of combustion plants for fossil raw materials and/or waste incineration plants. 
     The main aspect is in this context, in particular, to implement operation which takes care of the material, so that the action of wear with regard to at least one of the components of the combustion plant is reduced, as compared with the prior art. 
     These objects are achieved by means of a method according to the steps of patent claim  1  and an apparatus according to the features of patent claim  7 . Further advantageous refinements of the invention are specified in the dependent claims and also in the description. 
     The method according to the invention is distinguished in that at least the following steps are carried out: 
     a) extraction of the ash from a combustion boiler,
 
b) (if appropriate) solidification of the ash,
 
c) comminution of the ash, and
 
d) feed of at least part of the ash into the combustion boiler from the front, the hardness of the ash being set in a directed manner during step a) or b).
 
     The heat from the flue gases which is generated as a result of combustion is absorbed in such plants by means of heat exchangers and is used further. It is proposed here that the extraction of the ash from the combustion process takes place either continuously and/or discontinuously. For a discontinuous extraction of the ash, to be precise, the trigger time point adopted was the effectiveness of the heat exchange in such combustion plants in the following heat exchanger spaces and/or the degree of slagging of the heat exchangers. 
     The invention departs from this traditional idea by proposing a hitherto disregarded characteristic quantity of the extraction of the ash (type and/or extent). In this case, the hardness of the ash is taken into account, where, in particular, “hardness” means the strength of the ash lumps. The aim is, by means of the method, in particular, to extract the ash, or cause it to solidify, with a lower hardness than has hitherto been customary. The wear affecting the following components can consequently be reduced, or other components can be used. For this purpose, it is regularly necessary to observe or monitor at least one property of the ash inside the combustion boiler and/or outside it and then to exert influence upon the degree of hardness of the ash with the aid of an actual control loop. 
     In particular, it is considered advantageous that the ash has a mean hardness bandwidth of less than 4 prior to step d). The hardness bandwidth is an indication of the strength of the ash which is customary among specialists in this field. A hardness bandwidth of 1 to 10 is regularly referred to in this technical sector, 10 corresponding to the degree of hardness of a diamond. The bottom ash in coal-fired power stations has hitherto been in the range of 5 to 8. In particular, it is proposed here, to be precise, that a hardness bandwidth in the range of 2 to 3 be set with regard to coal. 
     Furthermore, it is proposed that, additionally, fuel, in particular coal, be fed between step b) and c). This also means, in other words, that, for example, ash (for the first time) and coal are processed by means of the same disintegrator. Consequently, precisely for such a coal disintegrator, the wear can be drastically reduced; for example, by 15 to 20%. 
     Furthermore, it is considered advantageous that, to carry out step a), internal cleaning of the combustion boiler is performed. That is to say, at desired time points, the inner surfaces of the combustion boiler are at least partially cleaned off and the ash thereby generated is extracted from the combustion boiler. In other words, it also means that internal cleaning initiates or reinforces the extraction of the ash from the combustion boiler at desired time points. 
     Finally, it is also proposed that internal cleaning comprises a treatment of the ash with water. The water acting into the ash or onto the ash leads, on the one hand, to a smaller lump size of the ash to be extracted and, moreover, can bring about some “softening” of the caked, sometimes even sintered, ash slag (reduction in the hardness bandwidth). If appropriate, solvents may also be added here, which makes it possible to “soften” the ash, while adhering to environmental regulations. 
     Furthermore, it is most especially preferred that at least one operating parameter of the combustion boiler is detected and is compared with a characteristic value which is characteristic of the hardness bandwidth of the ash, treatment of the ash in the combustion boiler and/or extraction being initiated when a threshold value is reached. In this case, therefore, in particular, a directed monitoring of the operating parameters of the boiler and/or of the characteristic value of the ash is proposed. Threshold values resulting from tests can then be used for control in which the treatment of the ash on the inside and/or extraction are/is therefore initiated when the threshold value is reached. 
    
    
     Particularly for implementing the method described according to the invention here, an apparatus is also proposed, which comprises a combustion plant having at least the following elements:
         a storage boiler with an outlet for ash,   (at least) one conveyor for transporting away and cooling the hot ash,   (at least) one disintegrator for the cold ash, and   (at least) one inlet of the combustion boiler for the ash, these elements cooperating in such a way that a circuit (recirculation) is formed (at least partially) for the ash.       

     It is considered highly advantageous that the apparatus is additionally provided with sensors and cleaning means (for example, in the manner of water lance blowers for the combustion boiler), and a (data-oriented) control is provided. 
     Moreover, the method affords especially great advantages in an apparatus in which the ash is routed via a coal conveyor and a coal disintegrator. 
     The invention and also the technical background are explained by means of the accompanying  FIG. 1 . This shows diagrammatically, and non-restrictingly, a possible set-up of an apparatus  3  according to the invention, such that it is suitable, in particular, for carrying out the method described here. 
     The apparatus  3  comprises the centrally illustrated combustion plant  1  with the combustion boiler  2 . The material burnt in the lower region of the combustion boiler  2  by means of the burners  20  settles on the insides of the combustion boiler  2  and/or on the heat exchangers  16 . To monitor this settling and/or the slagging of these components, various sensors  9  are positioned in or on the combustion boiler  2 . The measurement data from the sensors  9  are monitored by the control  11  via control lines  12 . At given trigger time points, cleaning means, illustrated here in the manner of a water lance blower, are activated, so that the ash is removed. 
     The ash occurring during normal combustion and also the ash which is removed from the inside of the combustion boiler  2  by the cleaning means  10  are extracted via the outlet and discharged onto a conveyor belt  17  of a conveyor  6 . The hot ash is moved toward a mill  19  with the aid of the conveyor  6  which has an air-tight housing  18 . Moreover, the cooling of the ash on the conveyor belt  17  takes place, for example, with the aid of an air supply  4  which generates a contradirectional air stream toward the inlet  5  because the combustion boiler  2  is regularly operated under a vacuum. To set the hardness bandwidth and/or to set a directed cooling behavior, a water supply  15  may additionally be provided, by means of which water can be discharged onto the cooling ash. 
     After the ash has passed through the mill  19 , it is discharged onto a coal conveyor  12 . There, it is intermixed with coal coming from a coal reservoir  21  and is fed jointly to a coal disintegrator  13 . A further reduction in the lump size is achieved there. The mixture of ash and coal which is pretreated in this way is fed anew via the inlet  8  of the combustion boiler  2 . A circuit is thus implemented at least for part of the ash. 
     REFERENCE SYMBOLS 
     
         
           1  Combustion plant 
           2  Combustion boiler 
           3  Apparatus 
           4  Air supply 
           5  Outlet 
           6  Conveyor 
           7  Disintegrator 
           8  Inlet 
           9  Sensor 
           10  Cleaning means 
           11  Control 
           12  Coal conveyor 
           13  Coal disintegrator 
           14  Control line 
           15  Water supply 
           16  Heat exchanger 
           17  Conveyor belt 
           18  Housing 
           19  Mill 
           20  Burner 
           21  Coal reservoir