WO2011104049A1 - Process for the thermal treatment of cement raw meal in a reaction space - Google Patents

Abstract

In the process of the invention, cement raw meal is thermally treated in a reaction space, wherein the reaction space has a bottom having a plurality of compressed air nozzles for the transport of fuels located on the bottom, the compressed air nozzles are arranged both next to one another and behind one another in the transport direction and are divided into separately controllable groups of one or more compressed air nozzles, the compressed air nozzles of one group are activated simultaneously and the following process steps are provided: a. introduction of cement raw meal, b. introduction of fuel, c. addition of combustion air, d. discharge of the offgases formed together with the thermally treated cement raw meal and e. activation of the compressed air nozzles for transport of the fuels located on the bottom. All groups of the compressed air nozzles are activated sequentially over time, with the order being selected so that the predominant part of the immediately successive activations over time is effected by groups which are not directly adjacent in or transverse to the transport direction.

Description

 Process for the thermal treatment of cement raw meal in a reaction space

The invention relates to a method for the thermal treatment of cement raw meal in a reaction space.

In the manufacture of cement clinker, cement raw meal is first preheated in a preheating zone, then precalcined in a calcination zone, and then finishburned in a sintering zone before the fired clinker is cooled in a cooling zone.

Cement production has a very high demand for heat, which has so far been covered mainly by fossil fuels, but in recent times increasingly by lumpy substitute fuels, which are produced in various sectors of industry and the private sector as waste, is substituted inexpensively. As a result, new demands are placed on the reaction technology with regard to the

Litigation, emissions and burnout.

The use of alternative fuels has significantly influenced and changed the process management in the cement industry. To ensure high availability complex process control systems are required. This concerns in particular the

Control of material flows, which can be very versatile when using substitute fuels, and be entered in different places. In general, the entry of the materials takes place by mechanical or pneumatic means. In the reaction chambers, the solid streams are either by means of mechanical devices along a solid floor or in the

Airflow transported.

For the thermal decomposition of solid fuels in particular the combination of separate combustion chamber with calciners in plants for cement production is known. Such combustion chambers are either as Zykloidfeuerung with short

Residence times or as fluidized bed combustion with high demands on the Preparation level of the starting materials carried out. Combustion chambers as rotary kilns or grate firing with moving transport elements are either very expensive or susceptible to faults and offer little opportunity to specifically optimize the combustion process. For the use of alternative fuels, however, it is of essential importance, on the one hand a stationary and homogeneous release of

Ensuring fuel components and on the other hand to be able to adjust the residence time targeted the fuel qualities.

In DE 10 2005 052 753 Al a combustion chamber is described, which uses the principle of Unterschubfeuerung as a transport device and combustion process.

The advantage of the underfeed firing lies in the homogeneous, stationary entry and transport of the fuels. However, this method has the disadvantage that there are high demands on the degree of preparation of the lumped fuels used. In addition, the inhomogeneous distribution of the fuel particles in the fuel bed and the lack of possibility on the

Residence time of the fuels to take effect, disadvantageous.

In DE 10 2004 045 510 AI a combustion chamber is described, which makes it possible to ensure the entry and sales of substitute fuels without additional mechanical installations. The transport of the fuel is carried out by

Activation of compressed air nozzles, which are arranged at the bottom of the combustion chamber.

The invention is based on the object to improve the operation of the compressed air nozzles to the effect that a homogeneous thermal decomposition of the abandoned fuels is guaranteed.

According to the invention, this object is solved by the features of claim 1.

In the method according to the invention, cement raw meal is thermally treated in a reaction space, wherein the reaction space is a floor with a plurality of

Compressed air nozzles for the transport of fuels located on the ground, wherein the compressed air nozzles are arranged in the transport direction both side by side and in succession and are divided into separately controllable groups of one or more compressed air nozzles, wherein the compressed air nozzles of a group are activated simultaneously and the following method steps are provided:

a. Abandonment of cement raw meal,

b. Abandonment of fuel,

c. Addition of combustion air,

d. Removing the resulting exhaust gases together with the thermally treated cement raw meal and

e. Activation of the compressed air nozzles for transporting those located on the ground

Fuels.

All groups of the compressed air nozzles are activated in succession, the sequence being chosen so that the majority of the temporally successive activations are effected by groups which are not arranged directly adjacent to or in the direction of transport.

Further embodiments of the invention are the subject of the dependent claims. According to a further embodiment of the invention, the fuel is at a

Abandoned end of the soil and at least partially transported by the activation of the compressed air nozzles to the other end of the soil. The task of the fuel can be done for example by a screw, a slide, a circulating chain system or pneumatically.

Furthermore, special setting conditions can be provided for special operating conditions. This is the case, for example, during start-up operation, system malfunctions, changes in fuel quality, changes in the type of fuel or when the reaction space is switched off. Here, the activation of the groups of compressed air nozzles take place such that the CO value or the Temperature of the exhaust gas discharged from the reaction space does not exceed a maximum value.

Further advantages and embodiments of the invention will be explained in more detail below with reference to the description and the drawing

In the drawing show

1 is a schematic view of the plant for cement production,

FIG. 2 shows a schematic side view of the combustion chamber, FIG. 3 shows an arrangement of the compressed-air nozzles. The plant for cement production shown in FIG. 1 consists essentially of a preheater 1, a calciner 2, a combustion chamber 3, a rotary kiln 4 and a cooler 5. During operation of the plant cement raw meal 6 is supplied in the upper region of the preheater 1, then preheated in the individual stages of the preheater and finally calcined in the calciner 2 and the combustion chamber 3. Subsequently, the thus pretreated cement raw meal in the rotary kiln 4 to

Fired cement clinker, which is finally cooled in the cooler 5.

The combustion chamber 3 shown enlarged in FIG. 2 has a reaction space 30, a floor 31, a plurality of schematically indicated compressed air nozzles 32 and means 33 for discharging fuel 7. Furthermore, in the area of the ceiling 34 of the combustion chamber 3 means 35 for the task of combustion air 8 and means 36 for the task of cement raw meal, in particular of preheated cement raw meal 6 'are provided. The preheater preheated cement raw meal 6 ', however, can also be supplied together with the combustion air 8 (FIG. 1) to the reaction space 30 (see FIG. 1). The means 33 for discharging the fuel 7, which is, for example, lumped substitute fuel, are for example designed as a screw conveyor, which introduces the fuel laterally into the reaction space 30 in the region of the one end of the bottom 31. For the entry and possibly also for the first transport in the combustion chamber also push beam or a moving floor can be used. A pneumatic entry is also conceivable.

The bottom is formed step-shaped in the illustrated embodiment, wherein five compressed air nozzles 32 are arranged in each riser. The nine existing stages with the associated compressed air nozzles thus result in the arrangement of the compressed-air nozzles shown in Fig. 3. Of course, in the context of the invention, a different number and a different arrangement of the compressed air nozzles can be selected. Also, a substantially smooth, horizontal or inclined floor can be used instead of the staircase-shaped structure. The orientation of the compressed air nozzles is suitably chosen so that, depending on the design of the soil, sufficient transport of the fuels is ensured.

While the fuel 7 at the upper end of the bottom 31 is abandoned, a discharge opening 37 for discharging the resulting exhaust gases is provided together with the thermally treated cement raw meal at the lower end. The combustion chamber 3 is coupled with the discharge opening 37 to the formed as a riser part of the calciner 2. But it is also conceivable that the combustion chamber 3 is connected directly to the inlet region of the rotary kiln 4.

The thermal decomposition of the fuel 7 takes place with the aid of the combustion air 8, which is, for example, hot tertiary air of the cooler 5. By a targeted activation of the compressed air nozzles 32, the fuel 7 is transported in the transport direction 9 to the discharge opening 37, wherein it comes into contact with the combustion air 8 and is thereby thermally reacted. The likewise supplied cement raw meal 6 'is treated thermally and serves if necessary, also for controlling the temperature in the reaction space 30. In the resting phase between two kills further volatile components are expelled from the bed due to the heat of the combustion zone, rise in the combustion zone and burn there after mixing with the hot tertiary air.

The compressed air nozzles 32 are designed as specially designed hot blast nozzles, which are in communication with a compressed air tank. Although it would be conceivable in principle that each compressed air nozzle is assigned to its own compressed air tank, it will often be more practical and above all cheaper if several compressed air nozzles are connected to a compressed air tank.

Upon activation of a compressed-air nozzle, the whirling up of the fuel 7 releases the already formed fuel gas in one fell swoop. If neighboring nozzles are activated immediately one after the other, then locally more fuel is released than oxygen is available for combustion. For this reason, CO would be generated in the exhaust gas in such cases. Therefore, the most important specification is that compressed air nozzles (or all groups of simultaneously activated compressed air nozzles) are activated in chronological succession, the sequence being chosen so that the majority of the temporally consecutive activations by compressed air nozzles or groups that take place in or are not arranged directly adjacent to the transport direction 9. In this way a local, very strong CO development can be avoided.

In the illustrated embodiment, the bottom 31 of nine stages, each with five compressed air nozzles 32. The compressed air pulse is adjusted so that it blows the respective compressed air nozzle 32 associated portion of a stage freely. In this way, the fuel is transported in the transport direction 9 to the discharge opening 37 and thereby decomposed more and more. It is therefore expedient that the activation of the compressed-air nozzles 32 takes place counter to the transport direction 9 by the compressed air nozzles 32 of the lower stages are activated first and those of the upper stages last. In this way it is also ensured that a freely blown area of one stage of the bottom 31 is covered with fuel fuel relatively promptly, although not immediately by a next activation, by the activation of the next higher compressed air nozzle 32. In this way, the soil is thermally protected by the fuel.

Furthermore, one can take into account in the activation of the compressed air nozzles, that sets in the fields 31a to 31c different residence times. This can be useful if one assumes that the fuel has different reaction times during transport. So z. B. conceivable that the drying of the fuel and the outgassing of volatile components at the beginning is fast. In the middle part of the combustion chamber, the solid components of the fuel are then burned. These require more time for reaction, which is why a longer transport time can be set in this area. In the lowest part of the

Combustion chamber are then only flammable substances present, so here an even longer residence time is set to ensure complete burnout. In addition, the volume of fuel to be transported increases from start to finish

From the end of the combustion chamber. The controller must therefore be able to steadily increase the residence times from top to top, without a uniform transport is negligible. Furthermore, the interval time between the temporally successive activation of compressed air nozzles or groups of compressed air nozzles as a function of the process temperature in the reaction chamber 30, in

Dependence of the CO value of the exhaust gas discharged from the reaction space or depending on the temperature of the exhaust gas discharged from the reaction space can be regulated. The method described above is characterized by a very good thermal utilization of even difficult fuels, especially of combustible waste products.

Claims

claims A process for the thermal treatment of cement raw meal (6) in a reaction space (30) having a bottom (31) with a plurality of compressed air nozzles (32) for transporting fuels located at the bottom (31), the compressed air nozzles (32) in the transport direction (9) are arranged both side by side and in succession and are divided into separately controllable groups of one or more compressed air nozzles, wherein the compressed air nozzles of a group are activated simultaneously and the method comprises the following method steps:  a. Abandonment of cement raw meal (6),  b. Abandonment of fuel (7),  c. Addition of combustion air (8),  d. Removing the resulting exhaust gases together with the thermally treated cement raw meal,  e. Activation of the compressed-air nozzles (32) for transporting the fuels located on the ground, characterized in that all groups of the compressed-air nozzles (32) are activated in chronological succession, the sequence being selected such that the majority of the temporally successive activations are effected by groups, which are not arranged directly adjacent in or transverse to the transport direction. 2. The method according to claim 1, characterized in that the fuel (7) at one end of the bottom (31) is abandoned and at least partially by the activation of the compressed air nozzles (32) is transported to the other end of the soil. 3. The method according to claim 1, characterized in that an interval time between the temporally successive activation of the groups is regulated as a function of a process temperature in the reaction space. 4. The method according to claim 1, characterized in that an interval time between the temporally successive activation of the groups is regulated as a function of a CO value of the exhaust gas discharged from the reaction space. 5. The method according to claim 1, characterized in that an interval time between the temporally successive activation of the groups is regulated in dependence on a temperature of the exhaust gas discharged from the reaction space. 6. The method according to claim 1, characterized in that in the start-up operation, system malfunction, changes in fuel quality, changes in fuel type or when switching off the reaction space, the activation of the groups of compressed air nozzles (32) takes place in such a way that a CO value or a Temperature of the exhaust gas discharged from the reaction space (30) does not exceed a maximum value. 7. The method according to claim 1, characterized in that an interval time between the temporally successive activation of the groups and / or a pulse to be generated by compressed air blasts is set. 8. The method according to claim 1, characterized in that a total residence time of the fuels is adjusted by varying an interval time between the temporally successive activation of the groups. 9. The method according to claim 1, characterized in that an interval time for activating adjacent or successively arranged groups is set differently and thereby different residence times in the longitudinal and transverse directions of the reaction chamber (30) can be adjusted. 10. The method according to claim 2, characterized in that the task of the fuel by a screw, a slide, a circulating chain system or pneumatically.