GB2449699A

GB2449699A - Rotary kiln for manufacturing cement clinker

Info

Publication number: GB2449699A
Application number: GB0710503A
Authority: GB
Inventors: Desmond Whiteley
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-06-01
Filing date: 2007-06-01
Publication date: 2008-12-03
Also published as: GB0710503D0

Abstract

A rotary kiln for the manufacture of cement clinker comprises an elongated tubular steel member with an internal refractory brick lining, an inlet feed, an exit adjacent to a lower end of the tubular member, and means for intercepting heat, and thus cooling, the newly formed cement clinker at the exit. Preferably, the temperature of clinker issuing from the kiln is reduced by lengthening a burner pipe, thus minimising entropy in a burning zone and reducing the throughput potential of the kiln. A lifting device may be installed at the lower end of a cooling zone of the kiln, where intercepted heat from the lifted clinker leaving the device may enhance entropy in the burning zone of the kiln. The clinker dust created by the lifting device may be carried up through the kiln in particulate form with the gas flow, with the lighter clinker dust being carried up into the burning zone of the kiln where it releases its acquired heat. Preferably, the acquired heat reduces the calcining heat requirement in the burning zone of the kiln such that the combined enhanced entropy and reduced calcining heat requirement increases and restores the throughput potential of the kiln to its original level.

Description

MODIFICATION OF EXISTING DRY PROCESS' CEMENT KELNS This nyen.tionis for

improvements in or related to the manufacture of cethethitioffs 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 the rotating 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 cementitious clinker, hereinafter referred to as clinker, it is known to provide a rotating kiln in which the dry raw feed material is 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 de-carbonated 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 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.

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 size of dry process' kiln for use in the manufacture of cementitious 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 formed 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. 2"

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 de-carbonated 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 formed 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 sintermg temperature when all exothermic 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. 3..-

It is known in the production of cementitious 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 througb the cooling zone and heat contained in the burner flame entering the burning zone with the gases of combustion. Once a 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 then be increased.

The kiln having been thermally balanced with all heat losses taken into account, a reduction in any one of those known heat losses will automatically reduce the total fuel requirement at the burner resulting in increased burner flame temperature and enhanced entropy in the burning zone of the kiln.

With a lifting device installed at the lower end of the cooling zone of a kiln it is thought that clinker heat intercepted from the lifted clinker will add to clinker heat intercepted from the cooler and increase the amount of heat taken to the burner with the secondary air. Thereby enhancing entropy in the burning zone of the kiln.

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

Accordingly the present invention provides a kiln for the manufacture of cementitious material comprising a processing plant for the preparation of dry raw feed material and 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 installation of a lifting device at the lower end of the cooling zone designed to lift up a calculated amount of clinker from the newly formed clinker bed. This to be exposed in particulate form to the secondary air to the burner flowing up into the kiln.

Since the issuing clinker leaves a lifting device containing heat, the amount of said heat depends upon the capacity of said lifting device for thermal control of the kiln. Hence, a Format consisting of a series of a known kiln's operating details and calculations based upon standard cement technology, already used to analyse the working of various types of rotating cement kilns, has been expanded to study the observed effects of installing lifters at their lower ends. Said Format being used to determine the capacity of any lifting device installed at the lower end of the cooling zone. It is clear from the calculations that the lifting device intercepts clinker heat from the lifted clinker to be taken to the burner where it enhances the burning temperature. Then the lighter clinker dust carried up into the burning zone intercepts heat from the burning zone and said heat carried down to the material bed reduces calcining heat requirement in the burning zone on landing.

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

By virtue of a lifting device installed at the lower end of the cooling zone it is thought that by enhancement of entropy and reduction of calcining heat in the burning zone throughput potential of the kiln will be increased.

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

FOR A KILN TO REACH MAXIMUM THERMAL EFFICIENCY, TEMPERATURE OF THE

ISSUING CLINKER AS IT LEAVES THE KILN HAS TO BE AT A MAXIMUM AND SAID

CUNKER MAY WELL BE SUPERHEATED. IT FOLLOWS THAT FOR THE DRY PROCESS' KILN IN PARTICULAR PERCENTAGE OF DUST CONTENT IN THE ISSUING CLINKER ENTERING THE COOLER MAY BE VERY HIGH. HENCE, WHEN THE INSTALLATION OF A UFTING DEVICE AT THE LOWER END OF A DRY PROCESS' KILN WAS CONSIDERED, IT WAS REAUSED THAT THE BURNING TEMPERATURE GENERATED MAY WELL RISE TO AN UNACCEPTABLE LEVEL. IT WAS ALSO NOTED

THAT THE HIGH LEVEL OF CUNKER DUST TAKEN UP INTO THE BURNING ZONE

WOULD REQUIRE ROTATIONAL SPEED OF THE KILN BODY TO BE INCREASED IN

ORDER TO PREVENT A BUILD-UP OF HEAT IN THE BURNING ZONE. THE

IMPUCATIONS BEING FOR COSTLY AMENDMENTS TO ANCILLARY EQUIPMENT

REQUIRED FOR BOTH KILN AND COOLER. IT WAS THEREFORE THOUGHT UNUKELY FOR A LiFTING DEVICE DESIGNED PURELY TO INCREASE THROUGHPUT POTENTIAL OF THIS KILN TO FIND FAVOUR WITH THE CEMENT INDUSTRY.

However, it is thought that the theory behind the lifting device may be incorporated in an amendment to this kiln. Hence, by lengthening the burner pipe, or by other means, temperature of issuing clinker leaving from the kiln may be reduced to a new assumed temperature that is to be designated, thereby minimising entropy in the burning zone whilst throughput potential is reduced accordingly.

An objective of this invention is to reduce the temperature of the issuing clinker.

With temperature of the issuing clinker reduced as it leaves the kiln a lifting device is installed at the lower end of the cooling zone. Heat intercepted from the lifted clinker as it falls from the lifting device in particulate form enhances entropy in the burning zone. 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 enhanced entropy and reduction in calcining heat in the burning zone producing a direct increase in throughput potential for the kiln.

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

after temperature of issuing clinker has first been reduced.

By virtue of first minimising entropy in the burning zone and then enhancing entropy and reducing calcining heat in the burning zone, throughput potential of the kiln will be restored.

An objective of this invention is to restore throughput potential of the kiln to normal.

Accordingly, the present invention requires a kiln to be modified with the temperature of the issuing clinker on leaving the kiln reduced by approved means to minimise entropy in the burning zone. A lifting device installed at the lower end of the cooling zone, following the Format below, is designed to lift up out of the issuing clinker bed a calculated quantity of clinker containing a calculated 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 failing 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. With new total entropy in the burning zone and said reduced calcining heat in the burning zone, throughput potential of the kiln is restored to its original level.

Consider the explanatory notes and details of THE FORMAT below:- (a) From operating statistics of an existing dry process' cement kiln to be modified, Tables (A'), (B') and (C') are drawn up and used to determine the existing Burning Temperature [Item (28)], Tables (B') and (C') being taken from standard tables. Table (A') applies only to the kiln to be modified.

(b) The assumed new reduced temperature of the issuing clinker [Item (1 2a)] is used to determine the new Burning Temperature [Item (28a)}, using the same tables as above.

(c) Resulting percentage reduction in throughput potential is derived from consideration of the two Burning Temperatures above [Item (34)].

(d) Assumed [Item (36)] is to be amended until a recalculated percentage increase in throughput potential [(Item 79)] is in full agreement with the percentage reduction in throughput potential [Item (34)].

(e) Regardless of its capacity the lifting device is always installed at the lower end of the cooling zone of the kiln.

THE FORMAT

(1) Throughput of Existing Kiln. tons/day (1) (2) Heat of Reaction for the dry raw feed material KC/Ib (2) (3) Recognised types of fuel employed in a Cement Kiln in the production of O.P.C.:-(a) Coal (b) Gas (c) Oil (d) Waste-derived liquid (e) Waste oil (f) Tyres (g) Paper, plastic and packaging (h) Meat and bone meal (MBM) (k) Processed sewage pellets (PSP) (3) (4) Standard Calorific Value of fuel used KC/Ib (4) (5) When llb of this Fuel is burnt with % excess air:-(5) (6) Gases of Combustion consist of:- (i) Sulphur dioxide lb (ii) Carbon Dioxide lb (iii) Nitrogen lb (iv) Any other gas lb (v) Water lb (vi) Air lb (6) (7) TOTAL = lb (7)

(8) Table (A')

Drawn up from Standard Heat Tables for the constituent gases forming the Gases of Combustion in the Kiln to give Total Heat in the Gases of Combustion at various high temperatures for the particular Kiln when lib of the fuel employed is consumed at the Burner. (8)

(9) Table (B') (9)

Standard Heat Table for Air.

(10) Table (C') (10)

Standard Heat Table for Clinker.

(11) Heat requirement @ Primary Burner KCIIb clinker produced. (11) (12) Clinker issues from Kiln to Cooler @. C. (12) (10) Referring to Table (C'):-(10) (13) Clinker issuing from Kiln to Cooler contains KC/lb clinker. (13) (14) Total of Cooler (clinker and radiation) Losses = KCIIb clinker. (14) (15) Clinker heat returned to the Kiln = ((13) -(14)) = KCI1b clinker. (15) (16) Primary Burner consumes (11)1(4) = lb fuel per lb clinker. (16) (17) Total heat @ Burner = (11) + (15) = KCIIb clinker (17) (18) Equivalent heat @ Burner = (17)/(16) = KC/lb fuel (18) (8) Referring to Table (A'):-(8) (19) Flame Temperature = C. (19) De-carbonated raw fed receives heat from the burner flame until its temperature reaches the sintering temperature of 1370 C. On formation of cementitious clinker a chemical reaction takes place and 99.96 KC exothermic heat is released into the clinker bed producing an instantaneous increase in clinker temperature to 1630.16 C. Thereafter, heat radiates away up into the burning zone as the clinker bed passes down through the cooling zone before issuing from the kiln and into the cooler.

(20) Clinker formed on entry to sintering zone 1370 C. (20) (21) contains 345.08 KC/lb clinker produced. (21) (22) Newly formed cementitious clinker in sintering zone 1630.16 C. (22) (23) contains 445.04 KC/lb clinker produced. (23) Reconciling Entropy in the Burning Zone:- (24) Burner Flame - [(7) x (16) x (17)] x [(19)] = (24) (25) Radiation from Clinker Bed - [(23) -(13)] x [((22) + (12)}/2] = (25) (26) Total = (26) (27) Total Heat in Burning Zone [(7) x (16) x (17)] + [(23) -(13)] = (27) (28) Hence Burning Temperature = 1(26)/(27)1 = C. (28) After Modification.

(12a) Clinker issues from Kiln to Cooler @ C (12a) (13a) Clinker issuing from Kiln to Cooler contains KC/Ib clinker (13a) Reconciling Entropy in the Burning Zone: (24) Burner Flame -[(7) x (16) x (17)] x [(19)] = (24) (25a) Radiation from Clinker Bed -[(23) -(13a) x [((22) + (12a)}/2] = (25a) (26a) Total = (26a) (27a) Total heat in Burning Zone -[(7) x (16) x (17)] + [(23) -(1 3a) = (27a) (28a) Hence, Modified Burning Temperature = [(26a)/(27a)] = (28a) NOTES.

(30) Percentage of dust in issuing clinker % (30) (31) Percentage of nodules in issuing clinker = % (31) (32) Secondary air to the burner enters the kiln with [15.6 + (15)] = KC/lb air (32) (9) Referring to Table (B'):-(9) (33) Secondary air to the burner enters the kiln @ C. (33) (34) Reduction in throughput potential = 11 -[((28) + 273)/((28a) + 273}]4] x 100% = % (34) The lifting device raises clinker out of the issuing clinker bed to fall down by gravity and pass through the secondary air to the burner flowing up into the kiln in particulate form. The heavy clinker nodules fall directly out of the kiln and into the cooler whilst the clinker dust is carried up into the kiln with the airflow. The heavier clinker dust settles out to fall on the clinker bed passing down through the cooling zone. The lighter clinker dust is carried by the gas flow up into the burning zone where it assimilates heat to become superheated before landing on the de-carbonated feed material passing down through the burning zone. After sharing its acquired heat with the feed material, the lighter dust passes through the sintering zone and re-enters the cooling zone with the issuing clinker bed at sintering temperature. For thermal stability in the kiln, the amount of heat carried out of the burning zone with the lighter dust must equal the cooling effect of the heavier clinker dust on the clinker bed in the cooling zone on reaching the lifting device. It follows that maximum temperature at the sintenng zone, and at the lifting device, will be reduced.

(36) Assumed amount of heat removed from issuing clinker bed by a lifting device and transferred to the secondary air to the burner: -. KCIIb clinker. (36) (37) Total heat in Secondary Air to the Burner = [(32) + (36)] = KC/lb air. (37) (9) Referring to Table (B'): (38) Temperature of Secondary Air arriving @ the Burner C. (38) (10) Referring to Table (C'):-(10) (39) Clinker dust carried up into the Kiln by the Secondary Air temperature (38) C contains...KC/lb clinker. (39) Lifting capacity (Z) is calculated from details given above of the existing kiln to be modified, supplied or assumed. The calculations are to be repeated as necessary until the amount of clinker heat (36) removed from the issuing clinker bed by the lifting device and taken to the burner with the secondary air generates an increase in throughput potential that coincides with the specified increase in potential of(34) %.

As (Z) lb clinker issues from the lifting device, it contains (13a) KCIIb clinker @ (12a) C.

As cooling Secondary Air to the Burner enters the Kiln from the Cooler it contains (32) KC/lb air (33) C and intercepts a further (36) KC from the (Z) lb clinker leaving from the lifting device.

Eiuating Entropy: (Z) x (13a) x [(12a) + (38)]/2 (from lifted clinker) = (36) x [(38) + (33) ]12 (transferred to Secondary Air) (40) Hence, Lifting Capacity (Z) = lb clinker. (40) The amount of clinker (Z) removed from the clinker bed by the lifting device consists of a mixture of clinker nodules and clinker dust. The percentage of clinker dust (30) is available from production records of the existing rotating cement kiln to be amended.

(41) (Za) = (40)x(31) = lb clinker. (41) (42) [(Zb) + (Ze)] = (40) x (30) = lb clinker. (42) Thermal Balance in the kiln requires the amount of heat (39) KCIIb clinker contained in (Zb) lb heavier clinker dust landing on the clinker bed in the Cooling Zone to be equal to the amount of heat (21) KCI1b clinker contained in (Zc) lb lighter clinker dust entering the Cooling Zone from the Burning Zone, therefore.- (43) (Zb)/(Zc) = (21)/(39) = (43) (Zb) = (Zc) x (43) (Zc) + (Zc) x (43) = (Zc) x [1 + (43)] = (42) (44) (Zc) = (42)/El + (43)] = lb clinker. (44) (45) (Zb) = (42) -(44) = lb clinker. (45) Note. The Sintenng Zone moves as required to thermally balance the kiln.

Consider entropy at the Sintering Zone: (47) 1.0 x (23) x (22) = Newly formed clinker (44) x (21) x (20) = Lighter clinker dust Total = (47) (48) Tsz = (47)/[(1.0 x (23) + ((44) x (21))] = C. (48) (10) Referring to Table (C'):-(10) (49) Newly formed cementitious clinker leaving the sintering zone @ temperature (48) C. contains KC/lb clinker. (49) Consider entropy at the lifting device:-.

(50) 1.Ox(13a)x(12a) = (44)x(21)x(20) = (45) x (39) x (38) = Total (50) (51) Heat content at the lifting device:- [(1.0 x(13a)) + {(44) x (21)) + ((45) x (39))] (51) (52) Hence, Tid = (50)1(51) = C. (52) (10) Referring to Table (C'):-(10) (53) Clinker issuing from Lifting Device @ temperature (52) contains KCIIb. (53) (54) As (Z)lb clinker issues from the lifting device it contains (53) KC/Ib clinker @ (52) C.

Cooling air enters the kiln containing (32) KC/Ib @ (33) C and intercepts (36) KCIIb clinker heat from the (Z) lb clinker leaving from the lifters.

Hence, total heat in cooling air = (37) KC @ (38) C.

quating entropy: (Z) x (53) x ((52) + (38)}/2 = (36) x ((38) + (33)}/2 (Z) = [(36) x ((38) + (33))/2] [(53) x ((52) + (38))/2] (Z) = Liftin2 Capacity lb. (54) (55) (Za) Clinker nodules = (54) x (31) = lb. (55) (56) [(Zb) + (Zc)] Clinker dust = (54) x (30) = lb. (56) (57) It is assumed that intercepted clinker heat from the Cooler will remain the same and all clinker dust carried up into the kiln with the Secondary Air to the Burner @ (38) C will contain (39) KC/lb.

i.e. (Zb) x (39) = (Zc) x (21) Hence, (Zb)/(Zc) (21)1(39) = (57) (58) (Zb) = (Zc) x (57) (Zc) x (57) + (Zc) = (56) (Zc) = (56)/{(57) + 1) = lb lighter clinker dust. (58) (59) (Zb) = (56) -(58) = lb heavier clinker dust. (59) (60) Reduction in the amount of heat carried into the Cooler with the issuing clinker: = [(55) x{(53) -(39))] = KC/1b clinker. (60) The lighter clinker dust (ic) has the effect of reducing the maximum temperature of the newly formed cementitious clinker bed in the sintering zone, and temperature of the clinker bed at the lifting device is also reduced by the combined effect of the heavier and lighter clinker dusts, {(Zb) + (Zc)). It follows that the temperature of the clinker entering the cooler will be reduced and with the cooling effect of the clinker nodules (ia) entering directly into the Cooler, Cooler heat losses will be reduced accordingly.

The majority of the heat entering the Burning Zone of the existing cement kiln is composed of heat (11) KC/lb clinker from consumption of fuel at the Burner. Its temperature being enhanced by heat (15) KC/Ib clinker intercepted by the Cooler when transferred by the Secondary Air to the Burner. Heat radiated back up into the kiln from newly formed cementitious clinker passing down through the Cooling Zone adds to the total of heat entering the Burning Zone and completes the total amount of entropy in the Burning Zone required to produce the existing throughput.

It follows that in order to increase throughput from an existing cement kiln that is already operating in thermal balance at seemingly maximum throughput, it is necessary to enhance total entropy in the Burning Zone. To do this, a lifting device is installed at the lower end of the Cooling Zone to remove a measured amount of heat (36) KC/Ib clinker from the clinker bed, just before it discharges from the Kiln and enters the Cooler. This amount of heat is transferred to the Secondary Air to the Burner where it enhances the Flame Temperature on entry to the Burning Zone with the Gases of Combustion.

Temperature of the clinker issuing from the Kiln is reduced and Cooler heat losses are reduced accordingly. Corresponding fuel saving at the Burner (60) KC/lb clinker enhances the Burner Flame Temperature.

Notes.

(i) Supply of feed to kiln and discharge of newly formed clinker from cooler remains constant.

(ii) Total heat at the Burner remains constant.

(iii) Return of clinker heat from the Cooler is assumed to be as existing unJess amended in accordance with the Cooler's operational manual or consultation with the manufacturer.

(61) Total fuel @ Burner = (11)-[(60) + (36)] = KC/lb clinker. (61) (62) Primary Burner consumes (61)1(4) = lb fuel per lb clinker produced. (62) (63) Total clinker and fuel saving = {(60) + (36) + (15)) = KC/lb clinker. (63) (64) Total heat @ Burner = (61) + (63) KC/lb clinker. (64) (65) Equivalent heat @ Burner = (64)/(62) = KCI1b fuel. (65) (8) Referring to Table (A'):-(8) 14: (66) Final Flame Temperature C. (66) Lighter clinker dust (58) lb enters into the Burning Zone @ (38) and contains (39) KCIIb clinker.

Reconciling Entropy in the Burning Zone: (67) Burner Flame -(7) x (62) x (64) x (66) = (67) (68) Radiated Clinker Heat - {(49) -(53))x {1.0+ (56)) x {(48) + (52))/2 = (68) (69) Lighter Clinker Dust -(58) x (39) x (38) = (69) (70) Total = (70) Total Heat in Burning Zone:- (71) (7) x (62) x (64) + {(49) -(53))x {1.0 + (56)) + (58) x (39) (71) (72) Hence, Final Burning Temperature = (70)1(71) = C. (72) (73) Increased Temperature Pressure = [{(72) + 273)}/{(28a) + 273)]4 = (73) (10) Referringjo Table (C'):-(10) (74) Heat in clinker @ temperature (72) C = KCIIb. (74) (75) Hence, clinker heat carried down to material bed = ((74) -(21)) x (58) = KC/Ib. (75) (76) Known Sintering Heat Reuuirement in Burning Zone = KC/Ib clinker. (76) (77) Sintering Heat requirement in the Burning Zone is reduced to (76) -(75) = KC/lb clinker. (77) (78) When a lifting device is installed at the lower end of the cooling zone, intercepted heat from the newly formed clinker bed increases the thermal pressure within the burning zone by times (73). At the same time the lighter clinker dust created by the lifting device reduces the calcining heat requirement in the burning zone by (75) KCI1b clinker from (76) KCI1b clinker to (77) KC/lb clinker.

Hence, thermal pressure in the burning zone increases by (73) x (76)/(77) = times. (78) (79) Hence, Throughput Potential increases by:-1(78)-1.01 x 100% = % (79) The cementitious forming materials after being largely de-carbonated in ancillary processing equipment 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 is finally dc-carbonated as it 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 de-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 exothermic heat is released into the newly formed clinker bed. A lifting device installed at the lower end of the cooling zone intercepts a determined amount of heat from the clinker bed 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 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 "cany" 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 de-carbonated raw feed material in the burning zone.

It will be appreciated that in order for the cementitious clinker to form, the raw feed has to be preheated, dc-carbonated 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 calcining heat requirement in the burning zone will restore the throughput potential of any type or size of dry process'cement kiln where the burner pipe has been lengthened to reduce temperature of the issuing clinker. It is further thought that lowering the temperature of clinker issuing from the kiln will improve kiln performance by reducing dust content, raising flame temperature, lowering burning temperature and producing incidental heat saving. 16'

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 characterised in the means to reduce the temperature of the clinker as it issues from the kiln. Said kiln is further 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. 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 on landing. Said kiln is further charactensed in that calcining heat in the burning zone is reduced by the action of the clinker dust created by a lifting device. Flow of materials through kiln and cooler are not affected. 17:

Claims

IClaim: 1. 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 the temperature of the clinker as it issues from the kiln is reduced by a lengthening of the burner pipe or by other suitable means to present a preffered new lower clinker temperature as it issues from the kiln.
3. The kiln as set forth in Claim 2 wherein the new temperature minimises entropy in the burning zone of the kiln.
4. The kiln as set forth in Claim 3 wherein the minimised entropy in the burning zone reduces throughput potential of the kiln.
5. The kiln as set forth in Claim 4 wherein a lifting device is installed at the lower end of the cooling zone of the kiln.
6. The kiln as set forth in Claim 5 wherein intercepted heat from lifted clinker leaving the lifting device enhances entropy in the burning zone of the kiln.
7. The kiln as set forth in Claim 6 wherein clinker dust created by the lifting device is carried up the kiln with the gas flow.
8. The kiln as set forth in Claim 7 wherein the lighter clinker dust is carried up into the burning zone of the kiln and shares its acquired heat on landing.
9. The kiln as set forth in Claim 8 wherein the acquired heat reduces calcining heat in the burning zone of the kiln.
10. The kiln as set out in Claim 9 wherein combined enhanced entropy and reduced calcining heat in the burning zone increases throughput potential of the kiln.
11. The kiln as set out in Claim 10 wherein the reduction in throughput potential in Claim 4 is equalled by the increase in throughput potential in Claim 10 restoring throughput potential of the kiln to normal.