GB2424057A

GB2424057A - Increasing the throughput potential of a rotating cement kiln

Info

Publication number: GB2424057A
Application number: GB0504224A
Authority: GB
Inventors: Desmond Whiteley
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-03-01
Filing date: 2005-03-01
Publication date: 2006-09-13
Also published as: GB0504224D0

Abstract

A lifting device is installed at the lower end of the cooling zone of a rotating cement kiln to lift clinker out from the newly formed clinker bed. Said clinker consisting of nodules and dust containing a stated amount of heat is presented in particular form to the secondary air to the burner flowing up from the cooler and into the kiln. Intercepted stated heat adds to heat intercepted from clinker passing down through the cooler and taken to the burner with the secondary air increases temperature of the burner flame entering the burning zone with the gases of combustion to enhance entropy. Lighter fraction of clinker dust carried up into the burning zone with the gas flow receives heat to become superheated and shares acquired heat with the material bed passing down through the burning zone on landing thereby reducing calcining heat requirement in the burning zone. It is thought that enhancement of entropy and reduced calcining heat requirement in the burning zone will produce substantial increase in throughput from any existing rotating cement kiln.

Description

INCREASING TIJIE THROUGHPUT POTENTIAL OF EXISTING

ROTATING CEMENT KILNS

This invention is for improvements in or related to the manufacture of cementjtjous materials and is particularly concerned with providing an improved method and apparatus for use in the manufacture of cementitious clinker.

A rotating cement kiln comprises an elongate tubular steel body supported on rollers at a small inclination to the horizontal, rotated by means of an electric motor turning a pinion in engagement with a gear ring.

Heat supplied to a kiln may be by a burner using a fossil fuel such as coal, oil or gas, or by a burner consuming chemical or other waste materials.

In the manufacture of cementitjous clinker, hereinafter referred to as clinker, it is known to provide a rotating kiln in which the raw feed material is fed in at one end. The kiln is inclined at an angle to the horizontal such that as the feed material is fed in at the upper end of the kiln and as the kiln rotates, the feed moves slowly down the kiln. As a result of heat being applied to the lower end of the kiln, the feed material is first dried (if the feed is wet), pre-heated and carbon dioxide driven off The resulting material is heated up to calcining temperature in a zone of the furnace known as the burning zone and rendered into a clinker at the lower end of the burning zone known as the sintering zone of the kiln. The clinker being partially cooled in the lower end of the kiln known as the cooling zone before being discharged from the kiln and into an external heat exchanger, hereinafter known as the cooler.

In a dry process' cement kiln it is known for the dry raw feed to be first pulverised, then pre-heated and carbon dioxide driven off in ancillary equipment.

The mainly de-carbonated material being fed in at the upper end of a rotating kiln that consists in conjunction, a burning zone, a sintering zone and a cooling zone.

As result of heat being applied to the lower end of the kiln the dccarbonated feed material is heated up to calcining temperature in the burning zone and rendered into a clinker in the sintering zone. The issuing clinker being partially cooled in the cooling zone of the kiln before discharge into the cooler.

The net amount of heat absorbed to render a dry raw feed into a clinker, per unit weight of clinker formed, is known as the heat of reaction' for that material.

The present invention is applicable to any existing type or size of rotating kiln for use in the manufacture of cementjtjous material, regardless of the type of fuel consumed at the burner. It is mainly concerned with the improvement in heat exchanges that take place at the lower end of the rotating kiln, referred to hereinafter as the kiln.

The clinker is fonned in the sintering zone of the kiln and it is necessary thereafter to cool the clinker for storage and subsequent transportation. The clinker after cooling is subsequently mixed with other materials and ground to a powder in a mill in order to form a cementitious product.

In production, the secondary air to the burner first passes through the cooler. The air enters at the lower end of the cooler and flows up through the cooler contra to the flow of issuing clinker passing down through the body of the cooler. Heat intercepted from the clinker as it moves slowly down through the body of the cooler is transferred to the cooling air passing up through the cooler and carried to the burner where it combines with heat from consumption of fuel at the burner to produce the burner flame temperature.

As a result of heat being applied to the lower end of the kiln, the dccarbonated feed material passing slowly down through the burning zone receives heat until its temperature reaches sintering temperature in the zone of the kiln known as the sintering zone. A chemical reaction takes place, clinker is formed and a known quantity of exothermic heat per unit weight of newly fonned clinker is released into the clinker bed, raising the temperature of the clinker bed to a maximum.

Said exothermic heat is assumed to radiate away from the clinker bed and back up into the burning zone of the kiln to be discounted in calculating the heat of reaction' for the dry raw feed material.

It follows that the newly formed clinker bed is superheated as it leaves the sintering zone and enters the cooling zone of the kiln. As the newly formed clinker bed passes slowly down through the cooling zone, heat may radiate away from the clinker bed and up into the burning zone of the kiln until its temperature falls to sintering temperature when all exothennic heat will have left from the clinker bed. Heat may continue to radiate away from the clinker bed and up into the burning zone of the kiln until its temperature falls to well below sintering temperature before issuing from the kiln and entering the cooler.

Should the issuing clinker still be superheated as it leaves the kiln, then heat intercepted from the issuing clinker and transferred to the secondary air to the burner flowing up through the cooler will contain exothermic heat. As said clinker heat is carried to the burner with the secondary air, the exothermic heat content enhances the flame temperature and satisfies the requirement regarding said heat of reaction' for the dry raw feed material as it enters the burning zone with the gases of combustion.

It is known in the production of clinker for the kiln to be thermally balanced to produce the optimum amount of clinker for minimum fuel expenditure. The burning temperature that produces the necessary temperature pressure to render de-carbonated feed material to a clinker is derived from consideration of the total entropy that arises in the burning zone. This consisting of heat radiated back up into the burning zone from the issuing clinker bed passing down through the cooling zone and heat contained in the burner flame entering the burning zone with the gases of combustion. Once an existing kiln has been thermally balanced, although entropy in the burning zone may be enhanced and throughput potential of the kiln increased accordingly, entropy itself may not be increased.

Since the existing kiln will have been thermally balanced with all heat losses taken into account, then a reduction in any one of those known heat losses will automatically reduce the total fuel requirement at the burner. The resulting increased burner flame temperature and enhanced entropy in the burning zone of the kiln generating an increase in throughput potential that also produces a pro rata reduction in the external radiation heat loss from the kiln's rotating steel shell.

It is thought that by removing an amount of heat from the issuing clinker bed passing down through the cooling zone of an existing kiln, less heat will leave the kiln and enter the cooler with the issuing clinker.

Accordingly, the present invention requires a lifting device to be installed at the lower end of the cooling zone. The lifting device designed to lift up out of the issuing clinker bed a calculated quantity of clinker containing a stated amount of heat. As said kiln rotates, clinker falling from the lifting device by gravity is presented to the secondary air to the burner flowing up out of the cooler in particulate form as a partial curtain over the cross-sectional area of the kiln. The falling clinker consisting of a mixture of clinker nodules and clinker dust. Heat intercepted from the falling clinker adds to the amount of clinker heat intercepted by the cooler and when transferred to the secondary air to the burner, temperature of the burner flame is increased and entropy in the burning zone of the kiln is enhanced.

The removal of stated amount of clinker heat from the clinker bed in the cooling zone results in less heat being carried out of the kiln and into the cooler with the issuing clinker. It follows that a reduction in the temperature of the issuing clinker as it enters the cooler may also have the effect of reducing the temperature of clinker discharging from the cooler. It is further thought that external heat loss from the cooler body may be reduced in consequence.

Accordingly, the present invention requires a lifting device to be installed at the lower end of the cooling zone designed to lift up out of the issuing clinker bed a calculated amount of clinker containing a stated amount of heat. Removal of said heat from the issuing clinker bed in the cooling zone resulting in less heat entering the cooler with the issuing clinker and cooler heat losses being reduced accordingly. Corresponding reduction in fuel requirement at the burner increases the burner flame temperature and entropy in the burning zone of the kiln is enhanced.

An objective of this invention is to enhance entropy in the burning zone of an existing kiln.

Throughput potential of an existing rotating cement kiln is a function of said entropy and internal surface area of the refractory lining in the burning zone of the kiln. The lining being a fixed entity that transfers a calculated amount of heat from the gases of combustion to the decarbonised feed material passing down through the burning zone by conduction, convection, and radiation. Any enhancement of entropy in the burning zone enhances the burning temperature and throughput potential is increased accordingly. Although the existing refractory lining can not be increased directly, it is thought possible to increase its effectiveness by reducing the calcining heat requirement in the burning zone.

Consider again the action of a lifting device located at the lower end of the cooling zone of a kiln. As a calculated quantity of clinker falls from the lifting device in particulate form, a stated amount of heat is transferred from the falling clinker to the secondary air to the burner flowing up into the kiln and said clinker is cooled. The addition of heat to heat intercepted by the cooler, when taken to the burner with the secondary air, increases the burner flame temperature and entropy in the burning zone of the kiln is enhanced, as said.

Production records for the existing kiln provides the percentage of dust contained in the issuing clinker. Hence, the amount of clinker nodules leaving from the lifting device will be known. As the lifted clinker falls through the cooling secondary air to the burner, the clinker nodules land on the issuing clinker bed and leave directly from the kiln and enter the cooler. On entry to the cooler, said clinker nodules have a cooling effect as they share heat with the clinker issuing from the kiln.

As the lifted clinker leaves from the lifting device by gravity and falls through the air flowing up the kiln to the burner, the known amount of clinker dust is carried up into the kiln with the gas flow as far as its natural carry' takes it.

It is thought that as the clinker dust settles out of the gases flowing up through the kiln, the heavier clinker dust will land on the clinker bed passing down through the cooling zone of the kiln. The lighter clinker dust being carried beyond the sintering zone and up into the burning zone to land on the de-carbonated material bed passing down through the burning zone.

Having been cooled in the airflow, the heavier clinker dust has a cooling effect upon the issuing clinker bed passing down through the cooling zone of the kiln on landing. The lighter clinker dust having first been cooled in the airflow, is carried beyond the sintering zone and up into the burning zone of the kiln with the gas flow where it intercepts heat from within the burning zone to become superheated. It then shares its acquired heat with the de-carbonated material bed passing down through the burning zone on landing.

The amount of heat contained in the lighter clinker dust at burning temperature, transferred directly to the material bed passing down through the burning zone, effectively reduces the kiln's calcining heat requirement in the burning zone of the kiln.

An objective of this invention is to reduce the calcining heat requirement in the burning zone of an existing kiln.

The lighter clinker dust leaves the burning zone at sintering temperature and enters the sintering zone contained within the newly formed clinker bed. Heavier clinker dust created by the lifting device landing on the clinker bed as it leaves the sintering zone and moves slowly down though the cooling zone of the kiln.

For thermal balance within the kiln to be preserved, the amount of positive heat contained in the lighter clinker dust as it leaves the burning zone must equate to the amount of negative heat contained in the heavier clinker dust in the cooling zone. This in turn allows the capacity of a lifting device to be calculated since the amended temperature of the clinker bed in the location of the lifting device can be determined.

In production, as the material bed passes down through the burning zone it receives heat from the burner flame until on reaching sintering temperature it is calcined to a clinker in the sintering zone. The newly formed clinker bed plus returning clinker dust passes on down through the cooling zone to a lifting device installed at the lower end thereof A calculated quantity of clinker containing a stated amount of heat is lifted out of the issuing clinker bed and presented to the secondary air to the burner in particulate fonn. Said amount of heat intercepted from the clinker falling by gravity from the lifting device and transferred to the cooling secondary air is taken to the burner together with heat intercepted from the issuing clinker passing down through the cooler. The resulting increase in burner flame temperature enhances entropy in the burning zone of the kiln.

As heat is removed from the issuing clinker bed before it enters the cooler, it follows that the temperature of the clinker entering the cooler is reduced and cooler heat losses are thereby reduced. The resulting reduction in fuel requirement at the burner increases the burner flame temperature and enhances entropy in the burning zone of the kiln.

The combined enhancement of entropy in the burning zone increases throughput potential of the kiln. Increase in throughput potential itself produces a heat saving at the burner due to a pro rata reduction in the external radiation loss from the kiln shell. The resulting reduction in fuel requirement at the burner increases the flame temperature and enhances entropy in the burning zone of the kiln.

As the lighter of the clinker dust created by the lifting device is carried up into the burning zone it receives heat from the burning zone to become superheated, and shares its acquired heat with the material bed passing down through the burning zone on landing. The resulting reduction in calcining heat in the burning zone produces a direct increase in throughput potential for the kiln, and that results in a heat saving due to a pro rata reduction in external radiation loss from the kiln shell. The resulting reduction in fuel requirement at the burner increases the flame temperature and enhances entropy in the burning zone of the kiln.

By virtue of the total increase in the burner flame temperature generated and the consequential enhancement of the entropy in the burning zone, together with the reduction in calcining heat requirement in the burning zone of the kiln, throughput potential of the kiln will be increased.

An objective of this invention is to increase the throughput potential of an existing kiln.

Accordingly the present invention provides a rotating kiln for the manufacture of cementitious material comprising an elongate tubular member mounted for rotation about an axis inclined to the horizontal. Means for feeding material into the kiln and means for permitting the exit of material from adjacent to the lower end of the kiln. Said kiln is characterised in the means for lifting up a calculated quantity of clinker from the newly formed clinker bed at the lower end of the cooling zone to be exposed in particulate form to the secondary air to the burner flowing up into the kiln. The lifting device to be formed of appropriately manufactured refractory bricks rigidly fixed in a ring or rings to coincide with the refractory lining on the internal periphery of the kiln, designed to carry up issuing clinker from the bottom of the kiln and up the side of the kiln. The clinker is free to fall from the lifting device by gravity as a partial curtain over the cross- sectional area of the kiln and back to the bottom of the kiln again. The lighter clinker dust created by the lifting device being carried up into the burning zone by the gases flowing up through the kiln, becoming superheated, and sharing its acquired heat with the material bed passing down through the burning zone of the kiln on landing.

Regardless of size of its lifting capacity, the lifting device is always installed at the lower end of the cooling zone of the kiln.

The cementitious forming materials, which may have been largely decarbonated in ancillary processing equipment if the raw feed materials are dry, are introduced into the body of the kiln at the upper end thereof The exhaust gases leave from the upper end of the kiln and may be assisted from the kiln by an exhaust fan.

The feed material after being dried (if the feed is wet), preheated and de- carbonated, passes down the kiln through a burning zone in which the temperature at the bottom end thereof is sufficient to enable the clinker forming reaction to take place.

The dc-carbonated materials fuse during the reaction and on moving down past the burning zone and into the sintering zone, a chemical reaction takes place and exothermjc heat is released into the newly formed clinker bed. A lifting device installed at the lower end of the cooling zone intercepts a stated amount of heat from the clinker bed, which may still be superheated, and transfers it to the secondary air to the burner, thereby enhancing the burner flame temperature.

Clinker discharges from the kiln and enters the cooler, and in passing down through the cooler, heat may be transferred to the combustion air entering the kiln, improving combustion efficiency at the burner.

In use, as the cement making material flows down the kiln, the lighter portion of the clinker dust created by a lifting device installed at the lower end of the kiln is carried up into the burning zone by the gas flow as far as it's natural "carry" takes it. Said clinker dust intercepts heat from within the burning zone to become superheated, and on landing, shares it's acquired heat with the material bed passing down through the kiln. Thereby reducing the amount of heat required for calcining the dccarbonated raw feed material in the burning zone.

It will be appreciated that in order for the cementitjous clinker to form, the raw feed has to be dried (if the raw feed is wet), preheated, dccarbonated and heated to a sufficiently high temperature in order to calcine the material into a cementitious clinker. It is thought that the combined effect of enhanced entropy and reduction in calcinmg heat requirement in the burning zone will increase the throughput potential of any type or size of rotating cement kiln.

In order to cope with the potential increase in throughput generated by a lifting device, and to prevent a build up of calcining heat in the burning zone, the effective length of the kiln has to be increased. This to be achieved by increasing speed of rotation of the kiln's body in accordance with increase in throughput generated. The flow of clinker through the cooler may also be increased in accordance with increased throughput produced.

It is thought that a kiln having clinker dust created at the lower end of the kiln, and by virtue of the resulting enhanced burner flame temperature, combined with the concentration of heat in the burning zone, will have it's throughput potential increased.

An objective of the present invention is to increase the throughput potential of any existing rotating cement kiln, regardless of type or size and regardless of type of fuel employed at the burner.

Accordingly the present invention provides a rotating kiln for the manufacture of cementitious material comprising an elongate tubular steel member mounted for rotation about an axis inclined to the horizontal. Means for feeding material into the kiln and means for permitting the exit of material from adjacent to the lower end of the kiln. Said kiln is characterjsed in the means for lifting up a calculated quantity of clinker from the newly formed clinker bed at the lower end of the cooling zone to be exposed in particulate form to the secondary air to the burner flowing up into the kiln. Regardless of size of lifting capacity employed a lifting device to be always installed at the lower end of the cooling zone of the kiln. The lifting device is formed of appropriately manufactured refractory bricks and rigidly fixed in a ring or rings to coincide with the refractory lining on the internal periphery of the kiln designed to carry up issuing clinker from the bottom of the kiln and up the side of the kiln. Lifted clinker free to fall from the lifting device by gravity as a partial curtain over the cross-sectional area of the kiln and back to the bottom of the kiln again. The lighter clinker dust created by the lifting device being carried up into the burning zone by the gases flowing up through the kiln, becoming superheated and sharing its acquired heat with the material bed passing down through the burning zone of the kiln on landing.

Rotational speed of the kiln shell to be increased in order to speed the flow of material through the kiln in accordance with the increase in throughput potential engendered by the lifting device employed. Flow of newly formed clinker passing through the cooler also to be increased in accordance with the increase in throughput produced.

Claims

I Claim: A rotating kiln for the manufacture of cementitious material, said kiln comprising in combination:- (a) an elongated tubular steel member with an internal refractory brick lining mounted for rotation about an axis inclined to the horizontal and having a lower end the central cross-section of said tubular member being free from any fixed obstruction to the flow of gases through said tubular member; (b) means for feeding a material into said tubular member; (c) means for permitting the exit of material from adjacent to the lower end of said tubular member; (d) means for intercepting heat from newly formed cementitious clinker from adjacent to the lower end of said tubular member
2. The kiln as set forth in Claim 1 wherein a lifting device is installed at the lower end of the cooling zone of the kiln.
3. The kiln as set forth in Claim 2 wherein the capacity of the lifting device employed intercepts a stated amount of heat from the issuing clinker bed for transfer to the secondary air to the burner.
4. The kiln as set forth in Claim 3 wherein the capacity of the lifting device employed is designed to remove a calculated quantity of clinker from the issuing clinker bed containing said stated amount of heat.
5. The kiln as set forth in Claim 4 wherein the lifting capacity employed produces a designated increase in throughput potential for that kiln of up to 25%.

5. The kiln as set forth in Claim 4 wherein the design of lifting capacity employed produces a designated increase in throughput potential for that kiln.

Amended claims have been filed as follows I Claim: A rotating kiln for the manufacture of cementitious material, said kiln comprising in combination:- (a) an elongated tubular steel member with an internal refractory brick lining mounted for rotation about an axis inclined to the horizontal and having a lower end the central cross-section of said tubular member being free from any fixed obstruction to the flow of gases through said tubular member; (b) means for feeding a material into said tubular member; (c) means for permitting the exit of material from adjacent to the lower end of said tubular member; (d) means for intercepting heat from newly formed cementitious clinker from adjacent to the lower end of said tubular member 2. The kiln as set forth in Claim I wherein a lifting device is installed at the lower end of the cooling zone of the kiln.

3. The kiln as set forth in Claim 2 wherein the capacity of the lifting device intercepts a pre-deterrnined amount of clinker from the issuing clinker bed.

4. The kiln as set forth in Claim 3 wherein the heat content of the clinker leaving the lifting device generates a designated increase in throughput.