DESC:-: Complete Specification :-

“Method of using a fluoride-based bath composition for production of clinkers”

Cross references to related applications: This complete specification is filed further to application for patent No. 202231010645 filed on 28-February-2022 with provisional specification, the contents of which are incorporated herein in their entirety, by reference.

Field of the invention
This invention is directed to the cement manufacturing industry. More particularly, the present invention discloses an inventive method for production of clinkers (white cement and gray cement) wherein the temperature for mineralization is reduced by use of a fluoride-based bath composition being sourced from what would have otherwise been a waste in industrial production of aluminum via the Hall–Heroult process.

Definitions and interpretations
Before undertaking the detailed description of the invention below, it may be advantageous to set forth definitions of certain words or phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect, with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. Accordingly the following terms / abbreviations shall refer as under-
“SHC” refers Specific Heat Consumption;
“TPH” refers Tonnage Per Hour
“PMT” refers Per Metric Tonne

Background of the invention and description of related art
The Hall–Héroult process is the major industrial process for smelting aluminum. It involves dissolving alumina in molten cryolite followed by electrolysis of the molten salt bath.

Elemental aluminum cannot be produced by the electrolysis of an aqueous aluminum salt because hydronium ions readily oxidize elemental aluminum. Using molten aluminum salt could have been a solution, however impractical for electrolysis due to high melting points, for example the melting point of aluminum oxide is 2070oC. Pure cryolite has a melting point of 1009 oC. Hence, specially designed compositions are introduced to make the process possible to occur at reduced temperatures and hence amenable to electrolysis.

Among prior art, Aluminum fluoride (AlF3) is usually found to be added to the electrolyte bath so that the electrolysis can happen at temperatures between 940°C and 980°C.The mixture is electrolyzed by passing a low voltage (under 5 V) direct current at 100–300 kA through it. This causes liquid aluminum metal to be deposited at the cathode, while the oxygen from the alumina combines with carbon from the anode to produce mostly carbon dioxide (Reference: Totten, George E.; MacKenzie, D. Scott, 2003. Handbook of Aluminum: Volume 2: Alloy production and materials manufacturing. vol. 2. New York, NY: Marcel Dekker, Inc. ISBN 0-8247-0896-2). Having higher density than the electrolyte solution, the molten aluminum then separates from the electrolyte and settles properly to the bottom of the electrolysis cell.
During the aluminum smelting process, surplus bath material can be generated because of high sodium content in the alumina. Typical composition of this bath material is represented in Table 1 below.

Ingredient Proportion (%)
From To
Na3AlF6 75 80
AlF3 10 12
CaF2 2 4
Al2O3 10 15

Table 1

This surplus is tapped in a liquid form to compensate for electrolyte losses. In its molten form floating in the pot, the bath material mentioned above is hence periodically tapped off to regulate pot fill levels and control the electrical resistance of the electrolyte. This tapped off bath composition is otherwise a waste, and thus a resource awaiting to be claimed advantageously in other industrial processes.

As conventionally known, cement production is an energy-intensive process with thermal energy consumption in the order of 3.3 GJ/tonne of clinker produced, and electrical energy consumption in the order of about 90 – 120 kWh/tonne of cement produced (Giddings, et al, 2000; European Commission [EC] 2001). It is hence a pressing need to bring down the energy budgets of cement manufacturing processes for a more sustainable and green future.

Primary fuel used in cement industry is coal. Cement manufacturing releases a lot of emissions such as carbon dioxide (CO2) and nitrogen oxide (NOx). Consequently, the cement manufacturing industry is under increasing pressure to reduce emissions by reducing coal consumption and hence also securing ecological benefits of conserving non-renewable resources.

Technical issues to be resolved
One industrial process, among many, which form focus of the applicant named herein, belongs to the cement manufacturing industry, specifically the process for production of clinkers (white cement and gray cement), which is riddled with one or more among the following technical issues-
a) High fuel consumption;
b) Requirement of high temperatures in preheater, calciner and burning zone;
c) High power requirements due to torque and fan usage;
d) Sub-optimal Clinker output;
e) Undesirable free lime content of clinker;
f) Undesirable C3S content of clinker;
g) Sub-optimal throughput of the kiln; and
h) Sub-optimal strength of clinker.

State of the art, to the limited extent presently surveyed, does not list a single effective solution embracing all considerations mentioned hereinabove, thus preserving a void to be fulfilled which the applicant named herein has resolved satisfactorily once and for all, by way of the invention to be described in the later part of this document.

Objectives of the present invention
The present invention is identified in addressing at least all major deficiencies of art discussed in the foregoing section by effectively addressing the objectives stated under, of which:

It is a primary objective to provide for improving the methodology for production of clinkers, particularly

It is another objective further to the aforesaid objective(s) to reduce fuel consumption in comparison to that required in conventional clinker production processes.

It is another objective further to the aforesaid objective(s) to obviate the requirement of high temperatures in preheater, calciner and burning zones.

It is another objective further to the aforesaid objective(s) to obviate the high power requirements necessitated due to torque and fan usage.

It is another objective further to the aforesaid objective(s) to improve clinker output.

It is another objective further to the aforesaid objective(s) to minimize, if not eliminate, the undesirable free lime content in comparison to conventional clinker production processes.

It is another objective further to the aforesaid objective(s) to minimize, if not eliminate, the undesirable C3S content in comparison to conventional clinker production processes.

It is another objective further to the aforesaid objective(s) to optimize the throughput of the kiln in comparison to conventional clinker production processes.

It is another objective further to the aforesaid objective(s) to optimize the strength of clinker obtained in comparison to conventional clinker production processes.

The manner in which the above objectives are achieved, together with other objects and advantages which will become subsequently apparent, reside in the detailed description set forth below in reference to the accompanying drawings and furthermore specifically outlined in the independent claims. Other advantageous embodiments of the invention are specified in the dependent claims.

Attention of the reader is now requested to the detailed description to follow which narrates a preferred embodiment of the present invention and such other ways in which principles of the invention may be employed without parting from the essence of the invention claimed herein.

Detailed description
Principally, general purpose of the present invention is to assess disabilities and shortcomings inherent to known systems comprising state of the art and develop new systems incorporating all available advantages of known art and none of its disadvantages.

Accordingly, the disclosures herein are directed towards the establishment of an inventive method for production of clinkers (white cement and gray cement) wherein the temperature for mineralization is reduced by use of a fluoride-based bath composition being sourced from what would have otherwise been a waste in industrial production of aluminum via the Hall–Heroult process.

The present invention thus establishes pluripotent fluoride-based bath composition which is otherwise wasted in aluminum production processes, but can be advantageously utilized applications in which said fluoride-based bath composition is used to serve, in an exemplary use case herein, as a mineralizer.

In the cement manufacturing process, the a raw mix is prepared by admixing limestone, bauxite, laterite, red ocher in different ratios to achieve the desired chemistry needed for making the clinker (white cement & gray cement).

The aforesaid ingredients are first fed into a raw mill to grind the material to a finer size, to thus form a kiln feed, which is fed to the preheaters or suspended calciners to the calciners, and finally charged to the kiln post complete calcination.

Here, the applicant could achieve significant results by using fluorides from tapped bath material as an addition to the raw mix before the raw mill stage or as an addition to the kiln feed before the preheaters or in the alternative, addition along with the fuel from the fuel firing system. Introduction of the synthetic fluoride-based bath composition subject hereof led to the following advantages-
a) Reduction in fuel consumption
b) Reduction in temperatures at preheater, calciner & burning zone
c) Power savings due to lower torque & lower fan usage
d) Increase in Clinker output
e) Reduction in Free Lime content of clinker
f) Increase in C3S content of clinker
g) Increase in strength of clinker.
h) Increased throughput of the kiln if fuel is kept constant

Implementation of the synthetic fluoride-based bath composition subject hereof has been reduced to practice by the applicant named herein, and tested for proof of concept as to native function for Reduction of melting point of limestone, and thus finding utility in clinker manufacturing Kilns, Lime calcination kilns etc.

Reduction to practice / Best mode of performing the invention
In a preferred embodiment, the present invention is intended to be best implemented by the introduction of synthetic fluoride-based bath composition at a metered quantity into the conventional process of manufacturing clinkers, the latter being undertaken as per the following sequence of steps-
a) Selection of raw material.
b) Crushing the material using a Jaw Crusher to a smaller size
c) Crushing the material using an impact mill to a further smaller size
d) Packaging the material to be used at Cement plant
e) Feeding material to a kiln along with the other raw materials in raw mill hopper using a feeding hopper and a dosing machine which comprises of a screw conveyor with VFD to control discharge

In a corollary embodiment, the present invention is intended to be implemented by feeding the material using the dosing system directly in the rotary kiln.

Experimental results
Applicability of the synthetic fluoride-based bath composition subject hereof, as per functionalities listed hereinabove can be understood by way of reference to few experimental studies undertaken by the applicant, specifically in application environment of cement plants for manufacturing clinkers as will be disclosed herein under.

Study 1: Pilot study to determine the % of the fluoride-based bath composition for optimum reduced melting temperature of the Clinker mix

Here, synthetic fluoride-based bath composition of the present invention at different percentages ranging between from 0.05% to 1.0% was added to the clinker raw mix. Temperature of clinkerization was monitored, with observations as shown in Table 2 below.

Sr. No. Clinker Raw Mix (%) Bath composition of the present invention (%) Melting Temp. (oC)

1 100 0.00 1520
2 99.95 0.05 1500
3 99.925 0.08 1450
4 99.9 0.10 1450
5 99.8 0.20 1410
6 99.7 0.30 1400
7 99.65 0.35 1400
8 99.6 0.40 1400
9 99.5 0.50 1270
10 99 1.00 1250
11 98.5 1.50 1230
12 98 2.00 1180
13 97.5 2.50 1150
14 95 5.00 1110
15 90 10.00 1040

Table 2

In this study it was determined that Clinker raw mix has the melting point at 1520oC, which starts reducing as synthetic fluoride-based bath composition of the present invention is added in increasing percentage. From 0.05% to 0.4%, the Clinker raw mix melting temperature decreases gradually from 1520 to 1400°C, and from 0.2 to 0.4% of synthetic fluoride-based bath composition of the present invention, temperature remains at same (1400 oC), but addition of 0.5% synthetic fluoride-based bath composition of the present invention to the raw mix shows a sharp decrease in melting point (from 1400 to 1270 oC - 130 oC decrease). Increasing the % of synthetic fluoride-based bath composition of the present invention, even to double that of 0.5% decreases the melting point only by 20°C (at 1.0%). Hence, it is concluded that the effective decrease in temperature is 1270°C from raw mix melting point (1520 oC), and thus effective optimum addition of synthetic fluoride-based bath composition of the present invention should be between 0.5 to 1.0%, and ideally 0.5% to the raw mix w/w. Also, below 1200°C temperature is not a feasible condition for cement manufacturing operations. This 0.5% synthetic fluoride-based bath composition of the present invention addition may cause much fuel savings by bringing down the melting temperature from 1520 to 1270 oC.

Study 2: Effective saving on fuel costs
Historically, the primary fuel used in cement industry is coal. Hence trials were undertaken in a cement manufacturing facility using coal for heating purposes to melt the clinker raw mix. Data collated is shown in Table 3 below.

Particulars Formula COAL PRICE INR / PMT
A 10,000 11,000 12,000 13,000 14,000 15,000 16,000 17,000 18,000
Kiln Feed (TPH) B 402 402 402 402 402 402 402 402 402
Clinker Production (TPH) C = B/1.58 251 251 251 251 251 251 251 251 251
NCV in Coal D (Actual) 6,700 6,700 6,700 6,700 6,700 6,700 6,700 6,700 6,700
Price per CV E = D / A 1.49 1.64 1.79 1.94 2.09 2.24 2.39 2.54 2.69
Savings--
Savings in SHC (Kcal / Kg) F (Actuals) 18.07 18.07 18.07 18.07 18.07 18.07 18.07 18.07 18.07
Savings in SHC (In INR) G = F * D 26.97 29.67 32.36 35.06 37.76 40.46 43.15 45.85 48.55
Savings due to increase in clinker output (PT of clinker) H (Actuals) 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75
Total Savings I = G + H 27.72 30.42 33.11 35.81 38.51 41.21 43.90 46.60 49.30
Costs
Dosage of FALOX Per Kg of Kiln Feed J (Actual) 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50
Dosage of FALOX Per Kg of Clinker K 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.80
Cost of FALOX PKG L 22.00 22.00 22.00 22.00 22.00 22.00 22.00 22.00 22.00
Cost PMT of Clinker M = K * L 17.60 17.60 17.60 17.60 17.60 17.60 17.60 17.60 17.60

Net Savings PMT of Clinker O = J - M - N 10.12 12.82 15.51 18.21 20.91 23.61 26.30 29.00 31.70

Net Savings Per Hour per Kiln P 2,540 3,217 3,894 4,571 5,248 5,925 6,602 7,279 7,956
Net Savings Per Day per Kiln Q = P * 24 60,964 77,211 93,457 109,704 125,951 142,198 158,445 174,692 190,938
Net Savings Per Year per Kiln R = Q * 330 20,118,047 25,479,497 30,840,947 36,202,397 41,563,847 46,925,297 52,286,747 57,648,196 63,009,646

Table 3 (FALOX = synthetic fluoride-based bath composition of the present invention).

From above results, it can be seen that-
a) Reduction in SHC by 18.07 Kcal / kg on using FALOX
b) dosage of FALOX remained constant at 0.05% of Raw mix.
c) There was an increase in the degree of Calcination at Calciner outlet. The temperature of the calciner outlet was observed to be increased by approximately 50oC.
d) Throughput of the kiln is increased if coal feed remains constant. Due to reduction in energy requirement, the output increases if the same energy is supplied as was conventionally. Correspondingly, the greenhouse emissions also were significantly reduced.
e) There is a reduction in the thermal loading on the burning zone refractories
f) The net saving on fuel is approximately 14 kcal /kg clinker

Throughput of the kiln being increased was validated in various independent trials undertaken by the applicant, results of which are shown in Tables 4A and 4B below indicating an overall saving on SHC of 18.07.

Trial No. Coal used Heat Input Clinker Prod. (TPD) as per BE SHC (Kcal/kg clk) Avg.SHC (Kcal/kg clk)
1 645.7 4177065 6076 687.52 684.5
2 618.6 4151835 6058 685.40
3 590.4 4032631 5927 680.44

Table 4A: Fuel Consumption & NCV when bath composition added

Trial No. Coal used Heat Input Clinker Prod. (TPD) as per BE SHC (Kcal/kg clk) Avg.SHC (Kcal/kg clk)
1 645.7 4158018 6015 691.23
702.6
2 618.6 4245977 6010 706.50
3 590.4 4276105 6023 709.92

Table 4B: Fuel Consumption & NCV when bath composition is not added

Study 3: Scenario analysis based on coal price
Here, trial was conducted in a cement manufacturing facility using coal for heating purposes to melt the clinker raw mix. Data collated is shown in Table 5 below.

Particulars Formula COAL PRICE INR / PMT
A 10,000 11,000 12,000 13,000 14,000 15,000 16,000 17,000 18,000
Kiln Feed (TPH) B 501 501 501 501 501 501 501 501 501
Savings in Coal (TPH) C 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50
Hourly savings in Coal (INR) D = A * C 15,000 16,500 18,000 19,500 21,000 22,500 24,000 25,500 27,000
Consumption of FALOX (0.10% of Kiln Feed) (TPH) E 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50
Cost of FALOX PMT F 24,000 24,000 24,000 24,000 24,000 24,000 24,000 24,000 24,000
Hourly cost of FALOX (INR) G = E * F 12,024 12,024 12,024 12,024 12,024 12,024 12,024 12,024 12,024
Net Savings Per Hour per Kiln H 2,976 4,476 5,976 7,476 8,976 10,476 11,976 13,476 14,976
Net Savings Per Day per Kiln I = H * 24 71,424 1,07,424 1,43,424 1,79,424 2,15,424 2,51,424 2,87,424 3,23,424 3,59,424
Net Savings Per Year per Kiln J = I * 365 2,60,69,760 3,92,09,760 5,23,49,760 6,54,89,760 7,86,29,760 9,17,69,760 10,49,09,760 11,80,49,760 13,11,89,760
BREAK EVEN PRICE K 24,000 24,000 24,000 24,000 24,000 24,000 24,000 24,000 24,000
Savings in Power (KW/PT) L 158.54 158.54 158.54 158.54 158.54 158.54 158.54 158.54 158.54
Clinker output at kiln feed of 501 MT M = A / 1.58 317.09 317.09 317.09 317.09 317.09 317.09 317.09 317.09 317.09
Savings in Unit per ton of Clinker N = L / M 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50
Price per unit of power O 4.50 4.50 4.50 4.50 4.50 4.50 4.50 4.50 4.50
Net Savings Per Hour per Kiln P = M*N*O 713 713 713 713 713 713 713 713 713
Net Savings Per Day per Kiln Q = P *24 17,122 17,122 17,122 17,122 17,122 17,122 17,122 17,122 17,122
Net Savings Per Year per Kiln R = Q *365 62,49,647 62,49,647 62,49,647 62,49,647 62,49,647 62,49,647 62,49,647 62,49,647 62,49,647

Reduction in thermal Loading
BEFORE FALOX
Fuel Rate in Kiln (TPH) S 33.44 33.44 33.44 33.44 33.44 33.44 33.44 33.44 33.44
NCV (Kcal/hour) T 6,900 6,900 6,900 6,900 6,900 6,900 6,900 6,900 6,900
Burning zone cross-sectional area, m2 U
Thermal Loading V = (S*T)/(U*1000) #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

AFTER FALOX
Fuel Rate in Kiln S 32.39 32.39 32.39 32.39 32.39 32.39 32.39 32.39 32.39
NCV T - - - - - - - - -
Burning zone cross-sectional area, m2 U
Thermal Loading V = (S*T)/(U*1000) #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!
Net Savings Per ton of Clinker W = (H + P) / M 12 16 21 26 31 35 40 45 49

Table 5

From this study, it can be seen that-
a) An increase of 1 to 2 % was observed in the C3S content of the clinker.
b) When other factors remain constant, R2O3 content in the kiln may be reduced.
c) Other factors remaining constant, the throughput of the kiln may be increased
d) Reduction in RABH Stack emission (Mg/NM3) is from 27 to 24
e) Reduction in RABH Stack flue gas Nox from 160 to 120
f) Reduction in temperature of Calciner by 45-50 degrees and PH exit temperature by 20-25 degrees

It can be additionally appreciated that, in implementation of the present invention, as the melting point of clinkerization is reduced, the amount of fuel otherwise required to reach conventional melting point of clinkerization is thus saved. This naturally implies reduction in electricity costs needed conventionally for cooling of the clinker so obtained.

From the foregoing narration, an able inventive fluoride-based bath composition is thus provided the use of which leads to process improvements in various applications which significantly score above prior art.

As will be realized further, the present invention is capable of various other embodiments and that its several components and related details are capable of various alterations, all without departing from the basic concept of the present invention. Accordingly, the foregoing description will be regarded as illustrative in nature and not as restrictive in any form whatsoever. Modifications and variations of the system and apparatus described herein will be obvious to those skilled in the art. Such modifications and variations are intended to come within ambit of the present invention, which is limited only by the appended claims. ,CLAIMS:We claim:
1) A method for production of clinkers, comprising-
a) Selection of raw material for production of clinkers;
b) Crushing the raw material using a jaw crusher to a smaller size;
c) Crushing the material using an impact mill to a further smaller size;
d) Packaging the material to be used at cement plant; and
e) Feeding material to a kiln along with the other raw materials, together as the clinker raw mix, in raw mill hopper using a feeding hopper and a dosing machine, further comprising a screw conveyor with variable frequency drive to control discharge
Characterised in that a metered quantity of synthetic fluoride-based bath composition consisting of 75% to 80% Na3AlF6, 10% to 12% AlF3, 1% to 4% CaF2 and 10% to 15% Al2O3 capable of effectively reducing the melting temperature of the clinker raw mix being used for clinker production, thereby achieving-
? Reduction in SHC by 18.07 Kcal / kg;
? Increased temperature of the calciner outlet, thereby increased degree of calcination;
? Increase in throughput of the kiln;
? Decreased greenhouse emissions of the kiln;
? Reduction in the thermal loading on the burning zone refractories; and
? Net saving of 14 kcal /kg clinker on fuel costs for production of clinkers.

2) The method for production of clinkers as claimed in claim 1, wherein the synthetic fluoride-based bath composition is introduced at a concentration ranging between 0.5 to 1.0% w/w of the clinker raw mix.

3) The method for production of clinkers as claimed in claim 1, wherein the synthetic fluoride-based bath composition is introduced at a concentration of 0.5% w/w of the clinker raw mix.

4) A synthetic fluoride-based bath composition capable of reducing the energy-budget of clinker production by up to 18.07 kcal per kg of clinker produced, said composition comprising-
a) 75% to 80% Na3AlF6
b) 10% to 12% AlF3
c) 1% to 4% CaF2; and
d) 10% to 15% Al2O3