WO1987004698A1

WO1987004698A1 - Process and device for reducing the release of the sulfur oxide and/or volatile organic compounds formed during the heating of raw meal in the pre-heating circuit, in particular in the suspension-type heat exchanger in cement manufacture

Info

Publication number: WO1987004698A1
Application number: PCT/AT1986/000069
Authority: WO
Inventors: Ludwig Kwech; Rainer Hoffmann; Harald Harmuth
Original assignee: Perlmooser Zementwerke Aktiengesellschaft
Priority date: 1986-02-11
Filing date: 1986-10-30
Publication date: 1987-08-13
Also published as: EP0256021A1; ATA34786A; AT384177B

Abstract

According to the process, the formation and release of sulfur oxide and/or of the volatile organic compounds occurs only in a partial gas flow in a separate heating device and not during the heating of the raw meal in the total gas flow, as is normally done in the known process of gas suspension. The exhaust gases from the heating device are subjected to further purification and/or returned to the heating device at the temperature at which a reaction and fixation of the sulfur oxide and/or of the organic compounds or their decomposition products takes place. The device for implementing the process comprises a rising duct (4) or a fluidized bed downstream of which is a cyclone separator (36).

Description

Methods for reducing the emission of sulfur oxide formed during the heating of the raw meal in the preheating system, in particular in the floating heat exchanger during cement production, and / or of volatile organic compounds and device for carrying out the method

The present invention relates to the reduction of the emission of sulfur oxide and / or of volatile organic compounds formed during the heating of the raw meal in the preheating system, in particular in the floating gas heat exchanger during cement production. According to the invention, these emissions are reduced in that the sulfur oxide and or the volatile organic compounds are released in a partial gas stream, in particular a suspended gas heat exchanger, and are preferably fed back to the furnace system for integration during the cement firing process.

Today, cement clinker is usually produced largely using the suspended gas heat exchanger process, in which finely ground zeolite powder is preheated in a single-strand or multi-strand heat exchanger using the sensible heat of the furnace exhaust gas and possibly a further combustion in suspension in the flue gas is then precalcined, depending on the procedure, or given to the rotary kiln immediately after preheating, is burned in the rotary kiln to form the desired clinker phases, after which the clinker is cooled in a clinker cooler. The heat exchanger mentioned is usually a (often 4-stage) arrangement of cyclones which are successively flooded by the flue gas, the raw meal being fed into the gas line to the top cyclone, in which the flue gas is heated, after separation in the cyclone of the next lower stage, where heating takes place again, etc. It is customary to partially calcine the preheated hot meal in the gas line between the inlet of the furnace and the bottom cyclone of the heat exchanger, or also predominantly if fuel is introduced further. We also use our own pre-caicinators, which largely calcinate the hollow before entering the furnace. Conventional heat exchanger designs differ in the number of floods through which the flue gas to the calciner or furnace inlet flows in parallel, and in the type of flour guidance which can be carried out separately for each flood or can also cross from one to the other.

It is a feature of the cement firing process that numerous elements and trace elements contained in the raw cement meal pass quantitatively or predominantly into the cement clinker. This also applies in particular to the alkalis and then also to the sulfur of the cement raw metal when it reaches zones of higher temperature within the process, for example the calciner, the riser channel between the kiln inlet and the lower heat exchanger cyclone or the kiln inlet itself. In this case, the sulfur gets into the rotary kiln itself and, in the conventional raw meal chemistry, the process can usually be controlled in such a way that the sulfur in the form of sulfate is incorporated into the clinker by means of sufficiently oxidizing conditions in the combustion zone and the process is carried out ¬ leaves with the clinker. In contrast to this, compounds which are released in the upper heat exchanger regions at relatively low temperatures which are not sufficient for integration can, according to the current state of the art, only be incorporated in the heat exchanger by additives or after the heat exchanger as part of the exhaust gas utilization become. In addition to volatile organic substances, sulfidically bound sulfur, depending on the mineralogy and structure of the raw meal, is released at least partially, but often to a large extent or completely, in the heat exchanger in the form of sulfur oxide. sets and oxidizes, especially in a temperature range between 380 ° C and 500 ° C. An integration of this sulfur oxide by the raw meal itself then no longer takes place due to the low temperature, but can, according to current practice, only by adding additives, in particular burnt and slaked lime, to the raw meal or to the upper heat exchanger stages and to plants the exhaust gas routing, as well as without additives by integration in the mill drying.

In contrast, it is the basic idea of the present invention to ensure the release of sulfur oxide or volatile organic substances in only one partial gas stream of the entire process - thus not in the course of heating the raw meal with all the flue gas in the known floating gas process - depending on the request after the process has been selected, post-cleaning can be carried out to reduce the emission, which is preferably done in the combustion plant itself even in areas of higher temperature, for example can be carried out in the lowest heat exchanger stage, in the calcining device or in the stovepipe.

The inventive method for reducing the emission during the heating of the raw meal in. Preheating system, in particular in the suspended gas heat exchanger in the cement production of sulfur oxide and / or volatile organic compounds, is accordingly characterized in that the formation and release of the sulfur oxide from the sulfur compounds and or the release of the organic compound of the raw meal at least partially with a portion gas flow takes place in a separate heating device and that the exhaust gas leaving this device, enriched with sulfur oxide and / or the organic compounds or their decomposition products, is subjected to a post-purification for separation and / or is returned to the existing furnace system in a temperature range, in which is a reaction and integration of the sulfur oxide and / or the organic compounds or their decomposition products. According to an advantageous variant of the method according to the invention, the raw meal is heated in the device provided for the release of the sulfur oxide and / or the volatile organic compounds by supplying one of the existing heat exchanger system and / or the furnace inlet area and / or the furnace head and / or the amount of hot gas removed from the clinker cooling device.

Advantageously, the exhaust gas enriched with sulfur eπdd and / or the organic compounds is returned to that area of the furnace system in which the deacidification of the CaCO- takes place, preferably to the calciner.

According to a further variant of the method according to the invention, the exhaust gas enriched with sulfur oxide and / or the organic compounds is fed to an independent flue gas scrubber according to a conventional method.

A further, expedient embodiment of the method according to the invention provides that the exhaust gas enriched with sulfur oxide and / or the organic compounds is fed to the furnace at the furnace outlet, preferably as secondary air.

A particularly advantageous variant of the method according to the invention is characterized in that the heating of the raw meal in the separate device provided for the release of the sulfur oxide and / or the volatile organic compounds in its entirety or, in combination with the above-mentioned heating of the raw meal with hot gas , partly by its own firing device, preferably its own burner.

The formation and release of the sulfur oxide is carried OF INVENTION _¬-making according to the designated special device advantageously in a temperature range between 280 ° C and 700 ° C, preferably between 300 ° C and 600 ° C, in particular between 380 ° C and 500 ° C _*

The formation and release of the organic compounds takes place in the separate device provided for this purpose advantageously in a temperature range between 100 ° C. and 500 ° C., preferably 150 ° C. and 00 ° C., in particular between 200 ° C. and 300 ° C. In the method according to the invention, the temperature in the separate device provided for the formation and release of the sulfur oxide and / or the organic compound is advantageously controlled by a separate firing device for the heating device provided for the release of the sulfur oxide and / or the organic compounds and / or a quantity control of the hot gas supplied to this heating device.

According to a further advantageous embodiment of the method according to he find the proportion of the current supplied to the heating apparatus gesondsp- th Rohmehles is in Depending _¬ @ keitvom sulfur -halt of the clean gas regulated. The purpose of this procedure is to minimize the amount of flour supplied to the heating device depending on the actual need due to the current emission, so that the additional heat consumption caused by the amount of flour supplied to the heating device is minimized as far as possible. With this special embodiment, the furnace operation can be economically adapted to the respective raw material situation.

A further expedient embodiment of the method according to the invention provides for the feed of a raw meal partial stream or one or more raw meal components without preheating into the tertiary air, in particular a raw meal partial flow with an increased sulfide content or an increased content of volatile organic compounds. Subsequently, the raw meal partial flow or the raw meal components _* . Part or all of it is fed to the furnace and any remaining portion is removed from the process and ensiled. With this procedure, a simple solution can be found in the event that the sulfide or the volatile organic bistands are concentrated in one component. This can happen, for example, if the raw meal is made from lime and clay and that Sulfide is concentrated in the lower clay component. In this case, the lime content of the raw meal in the heating device would be virtually ballast and would have an unfavorable thermal effect, whereas the low quantity ratio of the clay to the entire raw meal allows this special solution.

With this method it is then also possible to remove the roasted component from the furnace system and then e.g. to ensilage or to another aggregate, such as a mill. The sensible heat of the tertiary air could e.g. can also be used if this would not be necessary at this point in time for raw material reasons, so that uniform heat utilization for the restoration process is made possible continuously.

According to a further advantageous embodiment of the method according to the invention, a heat exchange is carried out between flue gas after the heat exchanger and tertiary air after the heating device. This special procedure can be advantageous, for example, if the raw material chemistry directly requires the entire raw meal stream to be fed onto the heating device without prior preheating. In this case, a sharp drop in temperature of the entire tertiary air and possibly additional firing can be expected, combined with an increased flue gas temperature after the heat exchanger. To reduce the associated thermal and procedural disadvantages, a heat exchange between flue gas after the heat exchanger and tertiary air after the heating device can equalize the two temperatures. This heat exchange is advantageously carried out indirectly, so that the tertiary air can then be fed back to the calciner.

The present invention furthermore relates to a device for carrying out the method described above, which is characterized in that the device device for releasing the sulfur oxide and / or the organic compounds from the raw meal from a riser and a downstream cyclone.

According to a variant, the device for performing the method according to the invention is characterized in that the device for releasing the sulfur oxide and / or the organic compounds from the raw meal consists of a fluidized bed and a cyclone separator, in particular a circulating fluidized bed with recirculation of the material .

According to an advantageous embodiment of the device according to the invention, the quantity control of the hot gas supplied to the device provided for the formation and release of the sulfur oxide and / or the organic compounds is formed by a bypass bypass of the heating device.

The present invention is explained by way of example in the attached drawings. Show in it

1 shows a schematic representation of a device suitable for carrying out the method according to the invention,

FIG. 2 shows a modification of the device according to FIG. 1, and

3 shows a variant of the device according to FIG. 2.

As can be seen in FIG. 1, the raw cement meal is fed via a feed device 1 to an upper heat exchanger area 2, which receives the flue gas from the lower heat exchanger area 6 via a riser 16. The raw feed material thus reaches the heating device at the desired preheated temperature via a chute 3, a switch contained in the chute 3 optionally dividing the preheated flour into the heating device 4 and the lower heat exchanger area 6 in any desired manner Extent allowed. -

In the event that, for example, to release organic compounds which are volatile at low temperature, a particularly low entry temperature of the raw meal into the heating device 4 is required, which cannot be achieved with the upper heat exchanger area 2, the raw meal can also be obtained directly without preheating the heating device - Device 4 are abandoned. After the heating device, the raw meal passes through a chute 5 i ^{Q to} the lower heat exchanger area 6, which ensures further preheating and precalcination of the raw meal to the desired extent and can be provided with a firing device 21 for this purpose. The preheated and expediently at least to a small extent precalcined flour passes through a chute 7 into the rotary kiln 8 provided with a furnace 20 and after the clinker fire into the clinker cooler 9.

The heating device 4 receives one or more of the gas streams 10, 11, 12, 10 being flue gas and 11 and 12 preheated hot air. The quantity of these gas streams can preferably be regulated; Furthermore, a firing device 22 can preferably provide for the supply of thermal energy. Furthermore, the quantity of flue gas 13 can be regulated, so that the desired quantity of gas can be achieved in the preheating device by regulating the quantities of gas flows 10, 11, 12 and 13 _' or 14 and 13, • or 15 and 13. Furthermore, a blower can be used in the gas line 14, which permits quantity regulation.

The hot gas after the heating device 4 can be supplied via a gas line 14 to the lower heat exchanger area 6, preferably in stages of raw meal extraction, and / or via a gas line 15 to an area 19 which is inside (for example furnace head) or outside the process (eg flue gas cleaning, grinding drying plant). The remaining amount of gas is discharged from the system via the gas line 17 and a blower 18 and can be fed to a further flue gas utilization. FIG. 2 shows a preferred modification of the method, as is used in particular for processing sulfide-containing cement raw meal with the lowest possible sulfur oxide emission.

In this case, the raw meal is fed to the double cyclone 31 of the heat exchanger via a feed device 1 and is already preheated in a riser in front of this cyclone by the flue gas, so that it is then already heated in the reaction chamber 4 via a chute 3 enters, which is supplied with hot air from the furnace head, which is conveyed via a line 32 to a clinker dust separator 33 and from which any proportion which can be selected enters the reaction chamber 4 or via a bypass 3 with quantity control device 35 with Um¬ the reaction chamber 4 and the separator 36 to the precalciner 37 is conveyed. In the reaction chamber 4, with or without additional fuel introduction, the crude meal is further heated and the sulfur oxide is released via a firing device 22, after which the solid is separated from the gas phase in a separator 3 and via a chute 38 in the riser 39 is conveyed in front of the cyclone 40 of the heat exchanger, where the further preheating and ultimately calcining takes place in several stages (further cyclones 41, 42 with chutes 43, 44 and risers 45, 46). The hot gas passes after the separator 36, possibly after being mixed with the bypass amount, into the precalcination device 37. The gas amount control required for temperature control can be provided by control devices (for example flaps or slides), specifically a flap 47 or flaps 47 and 35 additionally with the flap 48 in the riser 49 or with a combination of the flaps 48, 35 and 47 with the blower 50. If the blower 50 is not present, the ^" blower also takes over the pressure loss in the heating device. The precalcination device 37 is fed on the one hand with the preheated flour to the cyclone 42 via a chute 52 and on the other hand with the furnace flue gas via a riser channel 49, and with the hot gas to the separator 36 and possibly bypass 34 through the gas line 53. It is the particular advantage of this process variant that simultaneous release of the COg of the carbonate component of the raw meal and binding of the sulfur oxide from the hot gas stream after separator 36 to the CaO being formed can take place in this precalciner, which is particularly reactive at this point in time is. The precalcination device 37 is charged with fuel via a firing device 5, which provides the necessary energy for the endothermic calcination process. After sufficient deacidification and binding of the sulfur oxide, the raw meal enters the separator 55 and, via a chute 56, the rotary kiln 8. Here, the residual deacidification and clinker phase formation takes place using the fuel heat of the fuel introduced via the firing device 20, after which the cooling takes place in the clinker cooler 9 with simultaneous heating of the cooling air. The entire flue gas of the process occurs after the double cyclone 31 and can be integrated into the exhaust gas utilization, for example mill drying, via a gas line 57 with a blower 51 via a gas line 58.

A variant of the process according to Fig. 2, Fig. _3> them only in that the Gasmengenre¬ gelung in the riser channel 49 towards the kiln inlet to Kalzinierein¬ 37 thereby is made that via a chute 61, a different

Part of the flour of the chute 52 is not integrated into the calcining device 37 but into the riser channel 49. This has the advantage that this enables the pressure loss and thus the amount of gas in this riser to be influenced, and on the other hand the positive effect of cooling the flue gas after entering the oven by the flour with simultaneous preheating or beginning calcining. nation of flour is obtained. This cooling of the gas leads to the condensation of volatile components contained in the gas, in particular alkali metal vapors, on the raw meal, as a result of which blockages of the riser pipe or clogging on its walls are avoided. Because of this positive effect, a combination of the methods of FIGS. 2 and 3 is also sensible, ie the quantity control in the rising channel 49 is carried out by a flap and the incorporation of a partial flour flow, the partial flour flow simultaneously for cooling the gas, avoiding blockages and packing and cooling of the quantity control (flap) takes place.

The implementation of the method according to the invention was tested on the following practical tests:

First of all, with a conventional four-stage suspension gas heat exchanger furnace with a pre-calcining system and a daily output of 2,100 t of clinker, a raw meal with 1.1% total sulfur as SO, based on the loss on ignition loss, and 60% share of sulfide sulfur in the total sulfur was burned to clinker . In this heat exchanger oven, the flue gas was used for mill drying after the heat exchanger fan. An SO _p content of 2603 mg / Nm ^{* was} measured in this test after heat exchanger blowers, a value of 1719 mg / Nm ^{* was} measured in the flue gas chimney when the mill drying system was at a standstill, and operation was carried out there when the mill drying system was operated Measured value of 945 mg / Nm, which corresponds to a 4% inclusion of the SO _p contained in the flue gas in the mill drying zone. In order to minimize the SO _p emissions, an attempt was first made in the conventional way to achieve an SOg bond in the heat exchanger by adding lime hydrate to the raw meal. For this purpose, an hourly amount of 2160 kg of hydrated lime was added to the raw meal and thus fed into the heat exchanger. The SOg content after the heat exchanger fan could thus be reduced from originally 2603 to now more than 1100 mg Nm *. Surrendered in the exhaust stack at standstill of the raw mill now instead of originally 1,719 mg / Nm ^ now 730 mg / Nπr ⁵ and when operating the

Raw mill instead of originally 9 ^ 5 mg Nm ^* now 403 mg / Nu. A further increase in the amount of hydrated lime only resulted in an insignificant reduction in the SO _p content and brought increased operational disadvantages. Obviously there was only a low yield of the hydrated lime, ie the major part did not react with SO _p to bind it, but with the comparatively much higher CO ₂ content of the flue gas and therefore significantly increased the cost of the process. ,

For comparison, a clinker fire was carried out with the same flour using a system according to the method according to the invention, as shown in FIG. 2. In this case, only 95 mg SO _p / Nπr were measured after the heat exchanger fan, 63 mg / Nur in the chimney due to false air intakes and 37 / Nur in the case of raw mill operation. Such a low emission could not be achieved with the conventional methods, ie with the addition of additives, in particular hydrated lime.

Claims

Claims:

1. A process for reducing the emission of sulfur oxide formed during the heating of the raw meal in the preheating system, in particular in the floating gas heat exchanger during cement production, and / or of volatile organic compounds, characterized in that the formation and release of the " Sulfur oxide from the sulfur compounds and / or the release of the organic compounds of the raw meal takes place at least partially with a partial gas flow in a separate heating device and that the exhaust gas leaving this device and enriched with sulfur oxide and / or the organic compounds or their decomposition products is one Subsequent cleaning for deposition and / or the existing furnace system is fed again in a temperature range in which the sulfur oxide and / or the organic compounds or their decomposition products are reacted and incorporated.

2. The method according to claim 1, characterized in that the heating of the raw meal in the device provided for the release of the sulfur oxide and / or the volatile organic compounds by supplying one of the existing heat exchanger system and / or the furnace inlet area and / or the amount of hot gas removed from the furnace head and / or the clinker cooling device.

3. The method according to claim 1 or 2, characterized in that the recirculation of the exhaust gas enriched with sulfur oxide and / or the organic compounds takes place in that area of the furnace system in which the deacidification of the CaCO * takes place, preferably in the calciner.

4. The method according to claim 1 or 2, characterized in that the enriched with sulfur oxide and / or the organic compounds exhaust gas is supplied to an independent Rauchgas¬ scrubbing by a conventional method.

5. The method according to claim 1 or 2, characterized gekennzeich¬ net that the enriched with sulfur oxide and / or the organic compounds exhaust gas at the furnace outlet to the furnace, preferably as secondary air, is supplied.

6. The method according to any one of claims 1 to 5 _» characterized ge indicates that the heating of the raw meal in the device provided for the release of the sulfur oxide and / or the volatile organic compounds in whole or, in combination with the heating of the raw meal with hot gas according to claim 2, in part by its own firing device, preferably its own burner.

7. The method according to any one of claims 1 to 6, characterized ge indicates that the formation and release of the sulfur oxide in the dedicated device provided in a temperature range between 280 and 700 ° C, preferably between 300 and 600 ° C. , in particular between 380 and 500 ° C, takes place.

8. The method according to any one of claims 1 to 6, characterized ge indicates that the formation and release of the organic compounds in the dedicated device provided in a temperature range between 100 to 500 ° C, preferably 150 to 400 ° C, in particular between 200 and 300 ° C.

9. The method according to any one of claims 1 to 8, characterized ge indicates that the regulation of the temperature in the device provided for the formation and release of the sulfur oxide and / or the organic compounds by means of a separate firing device for the release of the sulfur oxide and / or the heating device provided for the organic compounds and / or a quantity control of the hot gas supplied to this heating device.

10. The method according to any one of claims 1 to 9 _», characterized in that the proportion of the raw meal supplied to the separate heating device is regulated as a function of the sulfur oxide content of the pure gas.

11. The method according to any one of claims 1 to 10, characterized in that a raw meal stream or one or more raw meal components is given without preheating in the Tertiär¬ air and is subsequently partly or wholly fed to the furnace and a possibly remaining Proportion is removed from the process and ensiled.

12. The method according to any one of claims 1 to 11, characterized in that a heat exchange is carried out between flue gas after the heat exchanger and tertiary air after the heating device.

13. Device for performing the method according to one of claims 1 to 12, characterized in that the device for releasing the sulfur oxide and / or the organic compounds consists of the raw meal from a riser channel and a downstream cyclone.

14. Device for performing the method according to one of claims 1 to 12, characterized in that the device for releasing the sulfur oxide and / or the organic compounds from the raw meal from a fluidized bed and downstream cyclone separator, in particular from a circulating fluidized bed with recirculation of good.

15. The apparatus of claim 13 or 14, characterized gekenn¬ characterized in that the quantity control of the hot gas provided for the formation and release of the sulfur oxide and / or the organic compounds supplied hot gas is formed by a bypass bypass of the heating device.