Heating – Having condition responsive control – Analyzer or composition sensor of work – work atmosphere or...
Reexamination Certificate
1999-09-27
2001-02-06
Wilson, Pamela (Department: 3742)
Heating
Having condition responsive control
Analyzer or composition sensor of work, work atmosphere or...
C432S014000, C432S058000, C432S106000, C106S752000, C106S758000
Reexamination Certificate
active
06183244
ABSTRACT:
TECHNICAL FIELD
The invention relates to producing cement clinker using high sulfur fuel.
BACKGROUND
Cement clinker is produced by sintering a raw material, such as limestone mixed with silica alumina and ferrous or ferrique oxide, that is homogenized and fed into a rotary kiln. The production may take place using a dry, semi-wet, or wet process, where the type of process refers to the amount of water added to the raw material. In the dry process, dried limestone, the raw material, passes through a series of cyclones and preheaters that heat the raw material, and a precalciner that further preheats and precalcines the raw material. The heated and precalcined raw material then enters a rotary kiln in which it is sintered in a sinterization or klinkerization reaction to form cement clinker. The cement clinker is then cooled in a grate cooler and discharged.
In a wet process, the raw material is mixed with water to form a slurry having a water content of approximately 35-40%. The slurry then is passed through a long rotary kiln having a series of different zones (or chambers) of reaction to form cement clinker.
A typical wet process kiln has a fuel consumption per kilogram (“kg”) of clinker produced of between 1,300 and 1,500 kilocalories (“kcal”), depending on the water content of the slurry fed to the kiln. The fuel consumption is approximately 175% of the consumption of a dry process rotary kiln that is equipped with a preheater and precalciner. A kiln having a capacity to produce 1,500 tons of clinker per day typically has a diameter of between four and five meters and a length of between 135 and 150 meters.
The semi-wet process of producing cement clinker involves using a slurry of raw material and water in which the water content is in the range of approximately 15% to 20%. The kiln is equipped with filters that remove a portion of the water through a process known as slurry dewatering.
SUMMARY
In one general aspect, an apparatus for producing cement clinker using a high sulfur fuel includes a wet rotary kiln, at least one sulfur analyzer, a controller, and a burner installed in the kiln. The wet rotary kiln has a first end and a second end and is operable to process a slurry of a raw material and water received at the first end to produce cement clinker. The sulfur analyzer is operable to produce a measure of the sulfur content of the cement clinker. The controller is operable to receive the measure from the sulfur analyzer and to control a concentration of oxygen in the kiln based on the measured sulfur content. The burner is installed in the kiln at the second end and is operable to burn a high sulfur fuel.
Embodiments may include one or more of the following features. For example, the apparatus may include an exhauster mounted to the kiln at the first end and operable to pull air through the kiln, and the controller may be operable to control the concentration of oxygen in the kiln by controlling the speed of the exhauster based on the measured sulfur content. The controller may be operable to control the concentration of oxygen in a sintering zone of the kiln by controlling the speed of the exhauster based on the measured sulfur content.
The high sulfur fuel may contain less than 4.5% sulfur and, in some implementations, may contain approximately 4.5% to 7% sulfur. The slurry may include approximately 35% to 40% water in a wet rotary kiln and approximately 18% to 20% water in a semi-wet rotary kiln.
The slurry further also may include a second high sulfur fuel. The second high sulfur fuel may contain more than approximately 4.5% sulfur and, in some implementations, may contain approximately 4.5% to 7% sulfur.
The kiln may include a heating zone for heating the slurry, a decarbonation zone for decarbonating the slurry, and a reaction zone for reactions in the slurry. The second high sulfur fuel combusts and burns in the kiln in the heating zone, the decarbonation zone, and the reaction zone.
The apparatus may further include a variable speed weigh feeder to add the second high sulfur fuel to the slurry to form a mud, and a slurry feeder to feed the mud into the kiln at the first end. The speed of the weigh feeder is controlled by the controller to adjust a concentration of carbon monoxide in gases exiting the kiln. The kiln also may include a drying zone equipped with chains for heating and drying the slurry.
The kiln includes a sintering zone for sintering the raw material, and the oxygen provided in the kiln at the sintering zone may be up to 6% in excess, whereby the temperature at which there is a decomposition reaction of calcium sulfate is raised to approximately 1500° Celsius. The apparatus further includes a carbon monoxide analyzer operable to measure the carbon monoxide concentration in the gas flowing from the exhauster and the controller is operable to receive the carbon monoxide measure, to turn off the burner if the measured carbon monoxide concentration exceeds approximately 0.6%, and to maintain the carbon monoxide measure at a preset level by controlling the speed of the weigh feeder.
In another general aspect, a method of producing cement clinker using high sulfur fuel includes introducing a slurry of a raw material and water into a wet rotary kiln, combusting a high sulfur fuel in the wet rotary kiln, passing the mixture through the kiln in the presence of the combusting fuel so as to sinter the raw material to form a sintered material, measuring a sulfur content of the sintered material, and controlling an excess concentration of oxygen in the kiln based on the measured sulfur content.
Embodiments may include one or more of the following features. For example, the high sulfur fuel may contain more than approximately 4.5% sulfur and, in some implementations, may contain less than 7% sulfur. The method may further include feeding a second high sulfur fuel to the slurry of raw material and water to form a mud before introducing the mud into the kiln. The second high sulfur fuel may contain more than approximately 4.5% sulfur and, in some implementations, may contain approximately 4.5% to 7% sulfur. The mixture of water and raw material may contain approximately 35-40% water in a wet process and approximately 18-20% water in a semi-wet process.
The method may further include controlling a feed rate of the second high sulfur fuel added to the mixture to control the measured oxygen and carbon monoxide content of the gas exiting the kiln. The method may still further include measuring a carbon monoxide concentration to control a feed rate of the second high sulfur fuel introduced into the kiln. The method also may include combusting the second high sulfur fuel to consume at least a portion of the excess oxygen.
In the method, controlling the excess concentration of oxygen may include maintaining the concentration at a level up to approximately 4.5 to 6%. The excess concentration of oxygen in the kiln may be controlled to produce a sintered material having a SO
3
concentration less than approximately 3.5%.
The method also may include maintaining an oxidizing atmosphere in at least a portion of the kiln to reduce NOx emissions to a level below 200 mg per normal cubic meter. The method also may include maintaining a circulation of SO
2
in the kiln at less than 80 kg per hour to eliminate calcium sulfate and calcium sulfite deposits in the interior of the wet rotary kiln. The method may further include reducing the concentration of SO
2
in the kiln by creating SO
3
by using calcium sulfite (CaSO
3
) as an intermediate oxidizing catalyst. The wet rotary kiln may include a sintering zone and controlling the oxygen concentration in the kiln may include providing excess oxygen in at least the sintering zone to prevent decomposition of calcium sulfate below approximately 1500° Celsius. In the method, the excess oxygen balances the sulfur entering the kiln and leaving in the sintered material.
The use of high sulfur fuel in a wet rotary kiln by controlling oxygen in the kiln's sintering zone based on sulfur in the cement clinker provides considerable advant
Cement Petcoptimizer Company
Fish & Richardson P.C.
Wilson Gregory A.
Wilson Pamela
LandOfFree
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