Heating – Processes of heating or heater operation – Including passing – treating or conveying gas into or through...
Reexamination Certificate
2000-07-06
2001-12-04
Wilson, Gregory (Department: 3749)
Heating
Processes of heating or heater operation
Including passing, treating or conveying gas into or through...
C432S072000, C110S345000
Reexamination Certificate
active
06325620
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of reducing volatile pollutants which are released during the heating of cement raw meal or the like, in particular sulphur oxides, sulphur compounds and similar volatile compounds, in the exhaust gases from a heat exchanger system, according to the preamble to claim
1
.
BACKGROUND OF THE INVENTION
It is generally known that during heating and burning of powdery raw materials, such as cement raw meal or the like, exhaust gases are produced in the gas suspension heat exchanger system which, depending upon the nature and origin of the raw materials contain a greater or lesser proportion of volatile pollutants, such as sulphur oxides, sulphur compounds and similar volatile compounds, which have been released during the heat treatment. Due to corresponding environmental protection requirements it is increasingly necessary to ensure that the emissions of the said pollutants in the exhaust gases from the heat exchanger are reduced. Efforts are therefore being made to develop appropriately or to extend the methods intended for heating and burning of the said raw materials (and the correspondingly designed apparatus and devices) with a view to reducing the said pollutant emissions in the exhaust gases from the heat exchanger.
SUMMARY OF THE INVENTION
Thus for example a method is known from WO87/04698 for reducing the emission of sulphur oxide formed during the heating of raw meal in a gas suspension preheater during cement manufacture and/or of volatile organic compounds in the exhaust gases from the heat exchanger. In this case in order to form and release the sulphur oxide from the sulphur compounds, the raw meal coming from the uppermost preheating stage is heated with at least one hot gas stream in a separate heating device to a temperature range of between 280 and 700° C., particularly between 380 and 500° C., and for this purpose this heating device is preferably provided with its own firing arrangements or burners. Whilst the exhaust gas from this heating device which is leaving the device and is enriched with sulphur oxide or the like can be subjected to secondary purification for precipitation of the pollutants and/or can be returned to the kiln system, the raw meal which is separated from it in a separator is delivered to a cyclone stage of the preheater so that it can be further heated in the usual way in this preheater. The heating device alone, which has to be provided additionally and which requires not only a corresponding heating section but also a suitable separator, corresponding control arrangements and in general its own firing arrangements, leads to extremely high additional design and investment costs; furthermore, this additional heating device requires relatively large quantities of hot gas and the space required for its installation is considerable.
The object of the invention therefore is to create a method of the type set out in the preamble to claim
1
which, on the one hand, is distinguished by a relatively marked reduction in the pollutant emissions in the exhaust gases from the heat exchanger and also by a reliable mode of operation and, on the other hand, by relatively low investment costs for the appertaining apparatus parts.
This object is achieved according to the invention by the method steps set out in the characterising portion of claim
1
.
Advantageous embodiments of the invention are set out in the subordinate claims.
In the method according to the invention, first of all, in a first method step, at least a part-quantity of the raw meal preheated to approximately 300 to 400° C. is drawn off from at least one upper preheater stage and is mixed together in a mixing zone with a selectable fraction of raw meal which is already highly heated and of such a size that the raw meal mixture obtained is adjusted to a mixing temperature which releases the pollutants and in the course of this at least volatile sulphur oxides, particularly sulphur dioxide (SO
2
), are bound to calcium oxide (CaO) contained in the highly heated raw meal and converted into calcium sulphate (CaSO
4
) and/or similar gypsum compounds, whilst at least any carbon monoxide (CO) formed here is removed from the raw meal mixture by means of a carrier gas. Thus due to the mixing together of the two said raw meal fractions the raw meal mixture which is formed is brought to a mixing temperature which corresponds to the volatilisation or expulsion temperature for the pollutants. Thus this can be carried out in a mixing zone of relatively simple construction and with the aid of a correspondingly large fraction, which can be drawn off simply, of the raw meal which is already highly preheated—for example in the lowest stage of the gas suspension preheater and/or in a calcination zone disposed downstream thereof—as a result of which additional hot gas heating sections, firing and burner arrangements and the like which—by comparison with the known construction described in the introduction—are costly and require a great deal of space are avoided.
In the mixing zone which is provided according to the invention, due to the setting of the necessary mixing temperature of the raw meal mixture which is formed, sulphur dioxide and other pollutants contained n the delivered raw meal are volatilised or released, so that the sulphur oxides which are released or formed, particularly sulphur dioxide (SO
2
), is immediately bound to the calcium oxide (CaO), which has been brought into the mixing zone with the raw meal fraction which has already been highly heated and at least partially calcined, and converted to gypsum or corresponding gypsum compounds, particularly calcium sulphate (CaSO
4
). The fraction of the raw meal which has already been highly heated and is to be introduced into this mixing zone is advantageously of such a size that, on the one hand, this fraction is large enough for the partially preheated raw meal fraction delivered from an upper preheating stage to be brought to the necessary mixing temperature; on the other hand, however, care must be taken to ensure that this fraction of the highly heated raw meal contains a sufficient quantity of CaO or CaO particles in order to be able to bind all released sulphur oxides in the mixing zone and to convert them in the aforementioned manner.
Carbon monoxide (CO) volatilised in this mixing zone and similar volatile combustible substances, in so far as they are formed or released in the mixing zone, are essentially not incorporated into the raw meal mixture and can be drawn off out of this mixing zone in a relatively simple manner with a carrier gas stream.
According to a further method step according to the invention the raw meal mixture together with the sulphur oxides is conveyed out of the mixing zone and for it to be further heated and at least partially calcined it is introduced into a preheater stage, the temperature of which is higher than in the upper preheater stage from which the partially preheated raw meal has previously been drawn off. Thus the sulphur oxides incorporated into the raw meal mixture or the gypsum fractions thereof are introduced into a corresponding preheater stage and proceed—during the further preheating and calcining of this raw meal mixture—through the rest of the preheater and into the kiln, since the gypsum containing the sulphur oxides is stable in the further heating process. Thus this means that the pollutants which are released, formed or converted in the mixing zone in the manner according to the invention can be drawn off or passed on in an extremely reliable manner so that emission thereof into the exhaust gases from the gas suspension preheater
1
can be prevented in a relatively simple and yet very reliable manner.
In a method in which the gas suspension preheater is a cyclone preheater with a plurality of cyclone stages which are disposed substantially one above the other and in which the cement raw meal is heat-treated at temperatures which increase from the top downwards, and in which the highly preheated cement raw meal coming out of the low
Krupp Polysius AG
Muramatsu & Associates
Wilson Gregory
LandOfFree
Method of reducing volatile pollutants in the exhaust gases... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of reducing volatile pollutants in the exhaust gases..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of reducing volatile pollutants in the exhaust gases... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2579106