Patent Application
20110203534
The present invention relates to a method and to an apparatus for conveying combustion residues along a conveying path out of a combustion chamber in a conveying device. The invention is used in particular in the combustion of raw fossil materials and/or waste combustion plants.
When slag, ash, soot and the like, referred to below as “combustion residues” are transported away, it is of particular importance firstly to solidify or cure the hot materials which are still partially in melt form in a specific manner such that, in particular, said materials can be conveyed or further processed after being extracted from the combustion boiler. Furthermore, it is also desirable to use the energy still located in the hot material and therefore to improve the overall efficiency of the plant or of the combustion boiler.
Although it was initially assumed that quenching in a water bath was necessary for conveying the hot materials (“wet discharging”), “dry extraction systems” have also been used since the 1990s. In this case, the hot material is placed onto conveyor belts where it is transported further, with, if appropriate, afterburning or specific cooling of the hot material partly also being carried out on the conveyor belt. It is immediately apparent here that the materials used in this case, in particular the conveyor belt, have to withstand the high temperatures, the corrosive surroundings and/or the high mechanical loading. Said conveyor belts are generally designed such that they are encapsulated in relation to the outer environment, i.e. have a housing which prevents combustion gases which are still being produced during the treatment of the material from being able to readily emerge into the environment. In addition, the combustion boilers are predominantly operated at a slight negative pressure such that the combustion gases produced by the material can be extracted towards the combustion boiler by means of corresponding suction.
For an extraction apparatus which is usable at high energy and is specifically equipped for the cooling behaviour, reference can be made to EP 0 471 055 B1. It is explained there that it may be expedient to cool the hot material in two separate cooling stages with an intermediate comminution step for the hot material. In particular, a cooling air flow is to be implemented in accordance with the counterflow principle, said cooling air flow being provided at the end of the second cooling stage and at the end of the first cooling stage. Particular effects with regard to the comminution of the hot material and the stratification are explained there, and therefore the overall intention is also to enable more effective operation of the combustion boiler.
According thereto, it is therefore known to transport away the combustion residues by means of conveying devices and in the process (at the same time) also to subject them to additional treatment. Different additional treatments, such as, for example, portioning, separation, comminution of combustion residues, may be required here. For said additional treatments, use may be made, if appropriate, of devices in which the conveying cross section for the combustion residues is reduced, such that there are therefore conveying bottlenecks. The known systems have an occasional tendency to malfunction in the region of said conveying bottlenecks, in particular due to undesirable accumulations of material in the region of said devices.
It is therefore the object of the present invention to at least partially solve the problems arising from the prior art and, in particular, to provide a method and an apparatus with which transportation away of combustion residues is improved. The method is intended in particular to permit fault-free operation of the conveying device and/or of the treatment device (for example a comminutor). Also, a simple construction and cost-effective retrofitting of known systems are to be achieved with the apparatus.
These objects are achieved by a method according to the features of Patent Claim 1 and an apparatus according to the features of Patent Claim 10. Further advantageous refinements of the invention are provided in the patent claims worded as dependent claims. It should be pointed out that the features listed individually in the patent claims worded as dependent claims can be combined with one another in any desired technologically expedient manner and define further refinements of the invention. Furthermore, the features provided in the patent claims are specified and explained in more detail in the description, with further preferred exemplary embodiments of the invention being illustrated.
To achieve the objective, the method according to the invention for conveying combustion residues along a conveying path out of a combustion chamber in a conveying device comprises the following steps:
Step a) relates here in particular to the feeding of the combustion residues onto a conveyor belt which is arranged in the housing of the conveying device. In this case, the housing encapsulates the conveyor belt and the combustion residues transported therein in relation to the environment.
In this (first) housing, a first pressure level is now set during the operation of the apparatus (step b)). This is basically ensured by the combustion boiler which is operated at negative pressure, but, if appropriate, said negative pressure can be set by means of additional suction units, additions of air and/or fans.
During step c), the combustion residues are additionally treated in a treatment device arranged in the conveying path. In this case, the conveying path leads in particular through the treatment device which forms a conveying bottleneck. The treatment device here can have, for example, a comminutor, hammers, grinding mechanisms, flaps, sieves or the like.
The effect now intended to be achieved by step d) is that either certain portions of the combustion residues do not penetrate the treatment device and/or that the combustion residues conveyed through the treatment device are reliably transported away and do not enter the treatment device and therefore the conveying bottleneck again.
The formation of a second pressure level which is lower than the first pressure level in order to set a pressure gradient ensures that the combustion residues cannot enter the treatment device (again) counter to the designated conveying direction. In this case, the pressure gradient is directed from a higher pressure place to a lower pressure place and corresponds at the same time substantially to the conveying direction. For example, the first pressure level can thus correspond to the negative pressure of a combustion chamber which is connected to the housing of the conveying device. In practice, in order to supply the combustion chamber with air, a supply of air is admitted into the housing such that said air can flow into the combustion chamber after flowing through the housing. In the known methods and apparatuses, the negative pressure of the first pressure level frequently gives rise to a state in which combustion residues already conveyed through the treatment device are sucked back again into the treatment device in the opposite direction to the conveying direction. This is the case in particular with very fine ash residues. If the treatment device is designed, for example, as a comminution device for relatively large combustion residues, then there is the risk of said comminution device having malfunctions after a relatively short time because of accumulations of combustion residues.
The present invention solves this problem by introducing a fluid which may preferably comprise at least air, water or water vapour, with a Venturi effect being used to produce a negative pressure which forms a second pressure level downstream of the treatment device. If it is now ensured that the second pressure level is lower than the first pressure level, then a pressure gradient is produced which points from the input side of the treatment device to the output side of the treatment device and therefore in the conveying direction, as a result of which it can always be ensured under all operating states that no combustion residues, such as ash or vapours, are sucked back to the treatment device. In this case, the first pressure level preferably corresponds to the negative pressure of the combustion chamber and the second pressure level corresponds to a lower pressure for producing a suction effect in the direction of the conveying direction of the combustion residues.
For the sake of completeness, it is pointed out that the conveying direction is defined by the journey which the combustion residues make in the conveying device.
In a preferred development of the invention, it is provided that the second pressure level is set between 20 to 600 mbar, preferably between 80 to 150 mbar, lower than the first pressure level. Said pressure levels have proven sufficient and can also be produced in a technically simple manner, for example with nozzle means.
In another advantageous development of the invention, it is provided that the fluid is introduced at a velocity of at least 4 m/sec., preferably at least 10 m/sec. In this case, a negative pressure produced is reinforced on account of the Venturi effect as the velocity increases. Higher velocities can be produced in particular by nozzle means, with the aid of which an outlet velocity of the fluid from the nozzle means can be controlled. In particular, a very precise control of the velocity and of the outlet direction of the fluid is thus possible in a simple manner with the corresponding nozzle means.
In this connection, it is also advantageously provided that the fluid is supplied at a pressure of 4 to 10 bar. The fluid can optionally be supplied in direct form or the intermediate connection of a nozzle means. Among the advantages of this pressure range is that a pressure of 4 to 10 bar can be provided cost-effectively using simple means and at the same time provides a sufficient pressure level for a downstream acceleration of the fluid using nozzle means. Depending on the application, said pressure details are based on the ambient air pressure or the pressure at the outlet side of the nozzle means.
Furthermore, it is provided, according to another advantageous refinement of the invention, that at least the first pressure level, the second pressure level, a temperature or a fluid content in the housing is recorded. This can take place, for example, with measuring means which are arranged at least upstream of, in or downstream of the treatment device. For example, with pressure sensors arranged upstream of and downstream of the treatment device, the correct setting of the desired pressure gradient can be monitored. In another embodiment, it is possible to control the air temperature or the temperature of the combustion residues in order to control the supply of fluid and activity of the treatment device in a predetermined manner and as a function thereof. Furthermore, it is possible to record a fluid content in the housing. It is meant in particular by this that moisture in the housing section between the treatment device and the point at which the fluid is introduced is monitored. This can take place, for example, immediately downstream of the treatment device by arrangement of a measuring means for recording the fluid content such that, in the event of the fluid flow being undesirably conveyed counter to the conveying direction in the direction of the treatment device, this operating state is immediately detected and countermeasures can be taken. Countermeasures of this type may include, for example, controlling the supply of fluid, the supply of air and/or a recycling of gaseous and smoky combustion residues. For example, by increasing the supply of fluid, the negative pressure of the second pressure level can be increased and a conveying back of the combustion residues can be opposed. As an alternative, by increasing the supply of air in the first housing section, the first pressure level can be raised such that the negative pressure formed there is reduced, which likewise opposes a conveying back of the combustion residues counter to the conveying direction. Furthermore, the supply of fluid can finally be completely interrupted if, despite all of the measures, there is the risk of the fluid and of the combustion residues being conveyed back. In addition, it is possible to increase the pressure gradient between the first pressure level and the second pressure level by a recycling of gaseous and smoky combustion residues, which recycling branches off downstream of the treatment device in the conveying direction.
In this case, it is advantageous to at least partially recycle gaseous and smoky combustion residues into the combustion chamber. For example, conducting means for an at least partial recycling of gaseous and smoky combustion residues into the combustion chamber are provided on the housing in the conveying direction downstream of the means for introducing a fluid.
In a likewise advantageous refinement of the present invention, it is provided to monitor at least one region immediately upstream or downstream of the treatment device (i.e. in particular upstream of the nozzle means) for the presence of the fluid and, if the fluid is present, to increase at least the pressure gradient, the recycling or the supply of air or to reduce or interrupt the supply of fluid as a function of at least one recorded measured value.
In order to prevent an unintentional and uncontrolled emergence of, for example, gaseous and smoky combustion residues out of the housing at the end of the conveying device, it is advantageously provided that, downstream of the treatment device in the conveying direction, a fluid barrier is provided at least in the housing or at a housing outlet. This can be achieved, for example, by nozzle means for producing a fluid barrier being provided downstream in the conveying direction at least in the housing or at a housing outlet. A fluid barrier of this type can be composed, for example, of a (hot) air flow or a liquid flow designed in a similar manner to a sprayed liquid curtain. By this means, the emergence of gases, smoke and other particles is efficiently reduced, which is beneficial, for example, to the working safety of operating staff.
Finally, in another advantageous refinement of the method according to the invention, it is also provided that an entry direction of the fluid entering the housing is selected in such a manner that said entry direction has at least one directional component in the conveying direction of the combustion residues. The entry direction of the fluid can be divided for this purpose into different (preferably orthogonal) directional components which, when put together, result in the entry direction. If at least one directional component lies in the direction of the conveying direction, then this assists the transportation of the combustion residues. This is the case in particular if the entry direction of the fluid is at an angle of between 10° and 80° in relation to the conveying direction. In particular angles which correspond, for example, to 30°-60°, are advantageous for this purpose because they produce at the same time a fluid flow which brings about the desired negative pressure, and the fluid flow, owing to its kinetic energy, additionally assists in the conveying of the combustion residues.
The objective according to the invention is likewise achieved by means of the apparatus furthermore proposed by the invention for conveying combustion residues along a conveying path with a conveying device, which has at least one housing, and with a treatment device which is arranged in the conveying path and is intended for treating the combustion residues, wherein downstream of the treatment device, as seen in a conveying direction of the combustion residues, at least one nozzle means is provided for introducing a fluid into the housing, and the fluid is accelerated as it flows through the nozzle means in order to produce a second pressure level in the conveying direction downstream of the treatment device. By means of the nozzle means according to the invention for introducing a fluid into the housing, in particular in the previously described manner, a second pressure level is set in the conveying direction, which pressure level is effectively lower than the first pressure level and thus forms a pressure gradient. The negative pressure produced by the fluid introduced thus ensures a constant conveying of the combustion residues in the conveying direction, as a result of which the reliability of the apparatus is significantly improved.
As nozzle means, use is made here in particular of a system having a plurality of nozzles in the housing at a distance from the treatment unit. If appropriate, the nozzles are designed with a common supply of fluid such that, for example, a pump introduces the fluid via the nozzles into the housing in a manner oriented toward requirements (with regard to period of time and quantity). The distance from the treatment unit is, in particular, in a range of less than 5 m, preferably even less than 2 m or even in the range of 20 cm to 1 m. It is furthermore preferred that the nozzles are distributed over the circumference of the housing, with uniform distribution not being necessary here. The nozzles are preferably arranged in a horizontal plane. The nozzle means are suitable for accelerating the fluid (in particular water) in such a manner that the fluid enters the housing at a sufficiently high velocity in order to generate a suction there away from the treatment device.
In another preferred embodiment of the apparatus according to the invention, it is provided that conducting means for an at least partial recycling of gaseous and smoky combustion residues into the combustion chamber are provided on the housing downstream of the nozzle means in the conveying direction. By this means, (undesired) portions of the combustion residues, such as, for example, fly ash, can be recycled for afterburning in the combustion chamber.
Furthermore, in the case of the apparatus according to the invention according to another preferred embodiment, it is provided that at least one measuring means, which is connected to a control device for controlling the supply of fluid, the supply of air and/or recycling using control or regulating means, is arranged at least in the conveying direction upstream or downstream of the treatment device. In particular, the arrangement of at least one measuring means for measuring moisture upstream of the nozzle means or upstream or in the treatment device permits reliable monitoring as to whether combustion residues and/or fluid are being conveyed back counter to the conveying direction. If such a state is identified, the correspondingly programmed control device, which is, for example, a programmed electronic control device, can carry out corresponding control or regulating measures.
It is likewise particularly advantageous if the control device is designed for determining a pressure gradient. In this case, controlled setting or regulation can also take place as a function of the at least one pressure gradient. If the pressure gradient drops, for example, below a predetermined limit value, the control device can carry out corresponding countermeasures in order to increase the pressure gradient to the desired extent or can introduce protective measures for protecting the apparatus and the operators.
Finally, according to another advantageous development of the invention, it is provided that an air inlet is provided on the housing upstream of the treatment device in the conveying direction. With this preferably controllable air inlet, the supply of air to the combustion chamber and therefore the first pressure level in the housing can be influenced.
The invention is used in particular in combination with one of the following boiler systems: boiler system for improving fossil fuels (coal, brown coal, . . . ), waste combustion plants, etc., with these preferably being operated with the method described here according to the invention and/or being equipped with the apparatus according to the invention. If appropriate, this concept can also be used in other conveying systems having a conveying bottleneck (for example in the manner of a grinder or a comminutor).
The invention and the technical environment are explained in more detail below with reference to the attached figure. It should be pointed out that the figure shows a particularly preferred variant embodiment of the invention, but is not restricted thereto.
Above the treatment device 5 there is an air inlet 10 through which air can flow in the direction of the arrow 11 into the housing 4 from where it passes on into the combustion chamber 1 which is operated at a slight negative pressure. A first pressure level 12 prevails in this region of the housing 4. By contrast, a second pressure level 13 which is characterized by a lower pressure than the first pressure level 12 prevails in the region downstream of the treatment device 5. The second pressure level 13 is produced by introducing fluid 14 (water) through nozzle means 15 in a region below the treatment device 5. The nozzle means 15 are inclined at an angle α with respect to the conveying direction 7 provided at this position. By means of the inclination, the fluid 14 emerging from the nozzle means 15 at the same time produces a negative pressure and, owing to the direction of flow of the fluid, conveys the combustion residues 6 in the direction of the housing outlet 9. Further nozzle means 15 from which a fluid 14 emerges in order to produce a fluid barrier 16 are provided here at the housing outlet 9. This prevents, for example, smoke and gas from undesirably emerging from the housing 4. Such undesirable constituents of the combustion residues can be recycled via a recycling means which leads by means of a valve 17 via a conducting means 18 into the combustion chamber 1. A control device 19 is provided in order to control or regulate the apparatus, said control device being connected via control lines 20 to the air inlet 10, the valve 17, the nozzle means 15 and measuring means 21 at the same time. In this case, the measuring means 21 can be designed, for example, for recording pressure and moisture. If water is used as the fluid 14, then it can be immediately identified with the aid of the measuring means 21 when said fluid has been transported counter to the conveying direction in the direction of the treatment device 5 or even through the latter.
In addition, when the measuring means 21 are designed in order to record pressure, the monitoring of a pressure gradient between a front side 22 and a rear side 23 of the treatment device 5 can be extremely precise. If the pressure gradient between the front side 22 and rear side 23 drops in an undesirable manner, then individual or combined measures can be used either to raise the pressure level 12 by means of additional air 11 or to reduce the second pressure level 13 by introducing additional fluid 14. In addition, it is possible to additionally reduce the second pressure level 13 by recycling combustion residues through the conducting means 18.
With the apparatus designed in this manner, it is possible to ensure continuous and fault-free operation of the treatment device 5.
The present invention is not restricted to the previously described and illustrated embodiment. On the contrary, numerous modifications of the invention are possible within the scope of the patent claims without departing from the area of the concept and range of protection.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 044 709.9 | Aug 2008 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP09/60565 | 8/14/2009 | WO | 00 | 5/10/2011 |
