Heating – With heating gas conveying – agitating – scattering or...
Reexamination Certificate
2000-06-02
2001-07-10
Wilson, Gregory (Department: 3749)
Heating
With heating gas conveying, agitating, scattering or...
C432S014000
Reexamination Certificate
active
06257877
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a kiln plant and a method for manufacturing cement. The kiln plant comprises a kiln for burning clinker, a cooler, a calciner followed by a separation cyclone and a burning compartment which is fed tangentially with tertiary air from the cooler. Completely or partially calcined material is routed from the bottom of the burning compartment to the calciner to which exhaust gases from the kiln are also vented.
It is a recognized fact that a number of advantages may be achieved by constructing a calcination zone equipped with an extra burning compartment which is exclusively fed with tertiary air from the cooler.
A plant of this type is described in our EP-A-103423. From this patent is known a plant (SLC-S) for calcination of cement raw materials, in which due allowance has been made for the inherent difficulty in achieving a complete burn-out of the fuel which is utilized in the calciner. In this plant the raw material is fed, after being preheated, to a burning compartment (
4
) in which it is calcined in hot air from the cooler (
2
). The tertiary air from the cooler flows centrally up through the bottom of the burning compartment (
4
) which means that there is an upward flow centrally in the burning compartment and a downward flow along the sides of the burning compartment. The raw material is fed at the lower end of the burning compartment and is distributed subject to the action of the turbulent flow encountered across the entire length of the burning compartment.
From U.S. Pat. No. 4,014,641 is known a plant for the calcination of cement raw materials in which the quantity of nitrogen oxide in the exhaust gases of the kiln is reduced by generating a zone in the kiln discharge duct to which reducing gas is fed. Hot air from the cooler and hot gas from the kiln are via a duct (
5
) and a duct (
13
), respectively, routed to a cyclone preheater (
14
,
15
,
16
,
17
) in which raw material is preheated in counter-current to the hot gas from the cooler and from the kiln. In the area of the kiln discharge duct which is located below the feed duct (
5
) from the cooler, reducing conditions are generated by introducing reducing gases via a duct (
12
). The reducing gases are formed in the calciner (
8
) since the air volume which is fed to the calciner is sufficient to cause gasification of the fuel in the calciner but insufficient to cause complete burn-out of the fuel in the calciner (col. 4, lin. 1-5). A disadvantage of this plant is that fuels which are difficult to ignite and slow-burning such as petcoke, anthracite and other grades of coal with a low gas content cannot be utilized in the calciner since they would produce a substantial unburned coke residue which would be precipitated and led to the rotary kiln, subsequently giving rise to problems in terms of sulphur expulsion and formation of cakings.
From U.S. Pat. No. 5,364,265 is known yet another calcining system in which the NO
x
emission is limited by formation of reducing gases, viz. Co and H
2
, in a burning compartment (
20
). The coke formed in the burning compartment during this process exhibits quite distinctive reactive properties. However, optimization of this method is relatively difficult to achieve in respect of ensuring minimum NO
x
emission given that very few parameters can be controlled during operation. The firing process in the burning compartment depends entirely on the desired degree of calcination of the raw meal. At the same time, the complexity of the plant structure is relatively high.
From our international patent application No. PCT/DK 97/00029 is known a method for reducing the NOx rate of emission from a plant. The object of this invention is to provide a method for operating a kiln plant with a reduced NO
x
emission rate, while, simultaneously, providing the option of using fuel with a low reactivity, such as petcoke, anthracite and other grades of coal with a low gas content in zones with a relatively low temperature. This object is obtained by regulating the fuel input rates in three different zones, with exhaust gases being fed to one zone from the two other zones in a way ensuring minimization of the NO-content in the exhaust gases from the zone to which exhaust gases are vented from the two other zones.
The object of the present invention is to provide a kiln plant and a method for manufacturing cement. The kiln plant is of a relatively simplified construction and it may advantageously burn fuel with a low reactivity, such as petcoke, anthracite and other grades of coal with a low gas content in the calcining zone where the temperature is generally at a low level.
BRIEF SUMMARY OF THE INVENTION
According to the present invention, a kiln plant for manufacturing cement, said plant comprising a kiln, a cooler, a calciner with subsequent separation cyclone, a burning compartment provided at its upper part with a central burner, and featuring below the burner a tangential inlet through which hot gas is fed, via a duct, from the cooler to the burning compartment, said duct being provided with an inlet for raw meal, the lower part of the burning compartment being provided with a connection to the calciner, and a second connection directing the exhaust gases from the kiln to the calciner; is characterised in that the height h
1
-h
2
of the upper part of the inner volume of the burning compartment, between the tip of the burner and the upper edge of the tangential inlet, being the uppermost point of entry of hot gas from the cooler is at least ⅓D, where D represents the diameter of a cylinder having the height h
1
-h
2
and the same volume as the upper part of the inner volume of the burning compartment; and in that the height of the lower part of the inner volume of the burning compartment, h
3
-h
4
, being situated between the lower edge of the tangential inlet, being the lowermost point of entry of hot gas from the cooler, and the outlet from the burning compartment, is at least D.
This object is thus obtained, when the burning compartment is cylindrical by locating the tangential inlet of the burning compartment so that the height of the upper part of the inner volume of the burning compartment, h
1
-h
2
, which is located below the burner tip and above the upper edge of the tangential inlet, is at least ⅓D and so that the height of the lower part of the inner volume of the burning compartment, h
3
-h
4
, which is located between the lower edge of the tangential inlet and the outlet from the burning compartment, is at least D. Preferably, the height of the upper part of the inner volume of the burning compartment, h
1
-h
2
, should be at least ⅔D and the height of the lower part of the inner volume of the burning compartment, h
3
-h
4
, should be at least {fraction (3/2)}D.
This will result in that a space with a high temperature and a low content of raw materials will be generated over the tangential inlet of the raw material suspension. This will ensure improved ignition and combustion characteristics of low-cost and gas-deficient grades of coal.
The invention also includes a method for manufacturing cement in a plant according to the invention, wherein the raw materials are preheated and then subjected to at least partial calcination in a burning compartment which at its upper part is provided with a central burner; where raw materials are fed to the burning compartment via a tangential inlet suspended in hot gas from a cooler; the partially calcined material is passed from the lower part of the burning compartment via a connection to a calciner, the gas/material suspension is passed from the calciner to a separation cyclone, in which a separation of gas and material is effected, and where exhaust gases from the kiln are directed to the calciner via a second duct, CHARACTERIZED IN THAT the height h
1
-h
2
of the upper part of the inner volume of the burning compartment, between the tip of the burner and the upper edge of the tangential inlet, being the uppermost point of entry of hot gas from the coole
Baker & Botts L.L.P.
F. L. Smidth & Co.
Wilson Gregory
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