WO2000064832A1

WO2000064832A1 - A plant and a process for manufacturing cement and electricity simultaneously

Info

Publication number: WO2000064832A1
Application number: PCT/IN2000/000026
Authority: WO
Inventors: Vinod Chintamani Malshe
Original assignee: Vinod Chintamani Malshe
Priority date: 1999-03-19
Filing date: 2000-03-21
Publication date: 2000-11-02
Also published as: AU5424800A

Abstract

Thermal electricity generating plants face a problem of disposal of fly ash generated by burning low grade coals. In the present invention, rapid cooling of clinker gives rise to glass phase clinker giving rise to a high class cement, utilizes the heat contained in the clinker to generate electricity without information of fly ash. The other major advantage of the present invention besides saving in investment in man power, grinding energy and heat energy and heat energy lost by radiation is ease of fabrication of cement plant as there is a vertical kiln with concurrent flow of clinker with the combustion gases.

Description

A PLANT AND A PROCESS FOR MANUFACTURING CEMENT AND ELECTRICITY SIMULTANEOUSLY

The following specification particularly describes the nature of the invention and the manner in which it is to be performed: -

This invention relates to a plant for and a process for manufacturing high- class cement and electricity simultaneously,.

This process particularly relates to manufacturing high-class cement having no crystalline phase and utilizing exothermic heat of the clinker formation reaction for generating electricity Background And Prior Art

The production of electricity by thermal power stations in many a country primarily depends on coal. In India, due to inherently available poor quality of coal and the departure from shaft mining to open cast mining has reflected in very high ash content in all the varieties of coal used by the industry. A typical thermal power station consumers as much as 25,000 tones of coal every day. If the ash content of the coal is 40% and even if we assume hundred percent utilisation of carbon, typical ash produced by this thermal power plant is 10,000 tones per day. This ash poses serious problems of disposal necessitating investment in utilisation of the fly ash. In spite of serious efforts made by research and development of power stations, the utilisation of fly ash has remained a meagre proportion of the actual production. The fly ash, as of today has a negative cost attached to it. Considering the huge capacity that the country has already created and the one that would be created in future, the thermal power stations are a serious threat to the environment. Alternate fuels such as naphtha or natural gas are very difficult materials to be used for power generation due to the high cost. Secondly, the available resources of coal are so large that they would continue to remain the major source of energy for power generation which means that the country would continue to produce electricity by burning the poor quality coal and simultaneously VC -

PCT-34W produce large quantities of fly ash If uses are not found out for this fly ash, these large quantities would pose seπous problems of disposal causing considerable environmental degradation Thus it becomes essential to generate fly ash as near the cement plant as possible, and eventually merge the two plants.

Indian Pat 17504, 155358, 145715 and 164056, have made an effort to improve the energy efficiency of the process by recycling the energy contained in the clinker as heat by preheating the incoming air and transport it all the way to the fluidized bed calciner. These authors have not laid any special emphasis on rapid cooling requirements of the clinker. Nor have they appreciated the need to recover the heat energy from the clinker in the form of electricity.

Electricity is a basic need for the humanity. Cement has also found a place of pride in the chemical industry. The need for both is increasing in the growing world , more particularly in the developing countries. The new process is therefore applicable in all the parts of the world. In the conventional cement manufacturing process, the heat required to dissociate the lime stone to calcium oxide is about 400 K Cal/Kg clinker and the overall energy requirement in terms of heat energy is about 700 K Cal/Kg clinker. Further 120 kWh energy is required for grinding coal, raw meal and clinker. Of these, about 15 kWh is consumed in coal grinding, about 40 kWh in raw material grinding and balance 45 kWh being required for grinding the cement clinker, balance being required for other rotational energy needs in conveying and air handling

Thus, we see there is a lot of heat energy wasted and there is scope to improve cement plant so as to conserve all heat losses and utilize them for generation of electricity.

We also see that there is a need to utilize fly ash generated in coal based electric plants, but the attempts to put them in cement has shown that there are limitations on its use. And in general use of fly ash in cement is not practiced on large scale mainly because the colour of the cement changes perceptibly which is not acceptable to several users. Also, it reduces the setting speed of the cement and full strength is obtained only after 28 days. There are several deposits of lime stone in the world which are not exactly suited for the production of cement. One of the primary reasons is the dilution occurring due to the ash coming from the coal which needs to be accounted 00/64832

for in the composition. If the amount of ash in the coal is high, the requirement of the purity of lime stone is also higher. Very high purity lime stone is some times added as a "sweetener" to overcome this problem. Cement clinker is widely believed to be a crystalline substance. The observations are on the contrary. For example, a highly crystalline cement clinker is poor in cementacious properties.. Rapidly cooled clinker, particularly the one which is quenched in water shows very high cementacious properties. There have been developments in Japan (Cement Technology and Engineering consultancy, Guide to Japanese Technology 1994-95 P 22-23)where large scale cement production has shifted to cooling of the clinker in fluidized bed thus attaining fairly rapid rates of cooling. A plant operating at 2000 TPD is reported to be operating satisfactorily. The quality of cement produced by rapidly cooling clinker is reported to be superior to standard clinker. It is well known that rapid cooling can not promote crystallization. In this process, clinker particles in the range of 1.8 to 2.5 mm are calcined in fluidized bed kiln at a temperature of 1300-1350 °C for sufficiently long time and it is cooled in another fluidized bed by blowing cold air through it causing it to cool down rapidly. The hot gases so generated are passed on to the clinkering zone of first fluidized bed. Advantages of this process such as utilization of poorer grades of coal due to lower temperature requirement of the clinkering zone and lower energy consumption due to superior insulation and superior heat recovery have been reported.

There are tremendous heat losses in rotary kilns employed in cement plants because of rotary nature of the kiln. Heavy insulation increases load on the rotation energy and poses difficulties of support system design. The cement produced by the plants and processes now in use is having some degree of crystallinity. High-class cement has to have super-cooled cement clinkers in a glassy phase which has more strength development character.

OBJECT

The main object of the present invention is to develop a plant and a process for manufacturing cement and electricity simultaneously in one plant. O 00/64832

Another object of the present invention is to invent a process that would not allow crystallization of molten cement clinker when formed, but will rapidly super-cool it into glassy structure to give high-class cement clinker and eventually, high-class cement and high-class cement concrete having higher strength.

Another object of the present invention is to utilize exothermic heat of clinker formation reaction to generate electricity.

Another object of the invention is to prevent generation of fly ash in coal based electricity generating thermal plants

Another object of the invention is to take calcination reaction to completion so as to have very low amounts of calcium carbonate in the calcined limestone. Utilization of lime stones with less than 78% Calcium carbonate is not feasible due to ash present in the coal. One of the objects of this invention is to use low grade lime stone by simultaneously producing electricity with alternate fuels. This can be done by retrofitting a power generation equipment to an existing cement plant. There are several power stations operating with ashless fuels such as naphtha, natural gas or LPG or LNG. Another object of the invention is to develop process/plant that can be retrofitted to an exiting power station operating with any fuels with the help of additional equipment. Since the calcination of limestone is decarbonation reaction which produces carbon dioxide and burning of coal also generates carbon dioxide, another object in principle is to overcome the effect of carbon dioxide on the calcination reaction rates due to mass action of carbon dioxide.

BRIEF DESCRIPTION OF INVENTION.

Accordingly, the invention is related to a plant for and a process for manufacturing high-class cement and electricity simultaneously, wherein said plant comprises mainly a stationary vertical highly insulated kiln replacing near horizontal rotary kiln in the conventional cement manufacturing plants with high pressure steam boiler driving electricity generators and said process comprising following steps: (i) calcining finely ground preheated limestone powder with addition of finely powdered and/or atomized fuel in a fluidized bed calciner;

(ii) mixing on-line, fresh finely powdered and /or atomized fuel and other finely powdered correcting materials required, to make the required composition of the cement at the end of the process, with the overflow of said fluidized calcined limestone in the form of fine powder produced at the end of step (i)

(iii) passing said fluidized fine powder mix produced at the end of step (ii) into the lower portion of a stationary, vertical, highly insulated kiln, along with fresh air, moving the fluidized bed upwards in said kiln for combusting additional said fuel with particles and promoting cement clinker forming exothermic reaction in the fluidized state, concomitantly raising temperature of the particles and gases beyond melting point of the inorganic substances,

(iv) rapidly cooling said molten cement clinker particles and gases formed in step (iii) in the fluidized state in the lower portion of said stationary, vertical, highly insulated kiln with help of radiant heat exchangers of high pressure steam generators, in the upper portion of the said kiln to form solid cement clinker in fine particulate form, cool said gases and generate high pressure steam;

(v) recovering said cooled solid cement clinker in fine particulate form, formed at the end of step (iv) by particles/ dust collecting systems such as array of cyclones, electrostatic precipitators and bag filters;

(vi) generating electricity by driving generator turbines by high pressure steam

(vii) formed at the end of step (iv);

(viii) grinding said cool cement clinker in powder form obtained at the end of step (v) with additives for making high-class cement of desired composition. DETAILD DESCRIPTION OF THE INVENTION:

Limestone purity depends on other minerals in limestone. The ash content of the coal and its composition and that of the limestone contribute to the clinker composition.

Limestone generally contains about 97.5 % CaCO₃ which loses 43.7 % of its weight on ignition forming about 54.6 % of CaO with about 1 % SiO₂ and about 1 % MgO.

For cement plants, "cementacious rock" type limestone having silica as impurity is used. 3 parts of limestone and 1 part of clay are usually mixed for cement manufacture.

The final product is expected to have at least 68% CaO.(C) 22-23 % SiO₂ (S) ,5-7 % AI₂O₃ (A), 4-6% Fe₂O₃,(F) (N F > 1.2 - 1.4 ) MgO - 1%, SO₃ - 1%

The fly ash obtained on burning coal in electricity generating plants has composition which is variable depending on the coal used and is generally as follows:

S1O2 , 55-60 %

Fe₂O₃, 5 - 10 %

CaO, 5%

Na2θ, K2O minimum

There are four basic compounds in cement. Tri calcium Silicate, (C3S), Di calcium Silicate (C2S), Tri calcium Aluminate (C3A) and Calcium alumino ferrite(C4AF)

C3 S - 50 -60

C2 S - 20 -30

C3A - 5

C4AF - 5-7 00/64832

The coal consumption / 1 clinker in the plant of present invention may be up to 300 Kg, (0J40 - 0J50 t for cement making and 0J50 t/t clinker for power generation) this may contain up to 35 - 40 % ash which means ash content would contribute 12-13 % to cnker. The balance 87% should have 68 CaO as CaCO₃ This means lime stone of 78 % purity is required. If such high purity limestone is not available, duel fuel firing may be resorted to. Thus the energy required for decarbonation alone may be provided by burning coal which is equal to 1675 Kcal/Kg CaO. When we add to this specific heat of solids CaO + Ash (0.25 Kcal/Kg/ °C) + radiation losses + heat carried away by gases, the energy requirement works out to 1420 Kcal/ Kg. Clinker. Of this exothermic heat of clinkerisation reaction (3CaO + S1O2 ) is available which is 990 Kcal/Kg CaO or = 670 Kcal/ Kg of clinker since the CaO content of the clinker is about 68% leaving about 750 K Cal / Kg clinker to be generated by burning coal.

If up to 100% decarbonation of calcium carbonate is to be carried out it is highly favorable that CO₂ concentration in heating medium should be low. This can be best achieved by bypassing the gases used for clinkerisation reaction, to energy recovery and feeding fresh air for decarbonation reaction. Thus if CaCO₃purity is 90 %, requirement of lime stone / Kg clinker is 1.35 Kg. Net Heat requirement is 3324 Kcal + specific heat of gases, solids + losses = 4000 Kcal which would be provided by 0.66 Kg of coal of about 20 % ash, making up non-CaO portion to 10 + 13.2 = 23.2 %. CaO content would be 67.5 % of the mix.

The hot solids at 1000 to 100 °C would be further mixed with alternate fuels such as LPG, mineral oil, vegetable oils or natural gas, to raise the temperature of the mix by another 500 °C. Once the solid are heated to 1500°C, exothermicity of clinkerisation reaction would boost the gas temperature by another 1000°C,

Cyclone preheaters are devices to exchange heat between solids and gases. A series of 5 to 6 preheaters is arranged to cause counter current flow of solids (downwards) with fluids (upwards). Fluid bed calciner is the device used for carrying out decarbonation reaction of lime stone as in conventional cement plants.

CaCO₃ + ΔH -» CaO + CO₂ + 140 Kcal

This reaction requires 140 Kcal /g mole heat. Almost all the heat is provided by burning coal in this zone of the equipment when finely powdered preheated fuel is fed along with coal. -

Composition of fly ash varies with source. Generally it contains 60 -70 % S1O2,

10-15 % AI₂O₃, 10 % , Fe₂O₃, and balance alkali and alkaline earth metals

Na, K, Ca, Mg, etc.,)

The desirable composition of cementacious raw mix is

CaO 65-68 %

SiO₂, 22-23 %

Fe₂O₃, 6 - 7 %

AI₂O₃ 4 - 7 %

MgO <1%

Additional Coal or Alternate Fuel:

Maximum requirement of alternate fuel would be to raise the temperature of the precalcined premix to 1450 °C. The exothermic heat of reaction of 3CaO + Siθ₂, (= 670 Kcal/Kg of clinker ) would further increase the temperature of solids by about 1200 °C causing temperature of the inorganic mix to cross 2600°C. At this stage, either coal or alternate fuel or mix of these can be used • depending on the quality of the lime stone available. We shall now consider energy balance in this process: Theoretical requirement for clinkerisation is 400 - 420 Kcal./ Kg Clinker which can be generated by burning 0 145 -0J55 kg. Coal /Kg clinker ( Energy consumption is about 750 KCal./ Kg clinker ; 700 for best plants) which means 17-18 % coal is required for burning of 1 Kg clinker (of a coal which would generate 4200 - 4500 Kcal. / Kg heat value and may have up to 34% ash). Based on this coal and operating conditions one requires about 10% excess air to attain complete combustion which ammounts to 1.5 NM³ air/Kg clinker. The theoretical requirement of calcination of lime stone is about 400-450 K Cal/Kg clinker. The requirement of energy for cement making is about 750 K cal. /Kg clinker. Of this, 400 to 450 K Cal/Kg is required for decarbonation , 70 to 80 K Cal / kg. Clinker are radiation losses, cooler losses are 100 -115 K Cal/Kg clinker, about 45-50 K Cal/Kg Clinker are lost with exit gases, and about 50 K Cal/ kg are lost with clinker.

In the new process, 0J 4 Kg of a coal with 4500 K cal / kg calorific value and- 34% ash content is used for decarbonation process in the fluidized bed calciner. The overflowing solids at 1100 ° C are mixed with additional 0.14 Kg coal and 1.5 NM³ air . the combustion of the coal attains a temperature in excess of 1800 °C. the exothermic heat of reaction to form clinker (670 Kcal/kg clinker) raises the temperature of solids and gases well above 2700 °C . Total wight of solids is thus 1 kg clinker + 0,05 kg ash and total weight of gases is 1.79 Kg. The heat recovered from 1 Kg. Clinker and ash is 526 K cal and from gases is 430 K Cal. At 70 % conversion efficiency, this ammounts to 0.88 KWH of electricity/ Kg clinker. Heat input form 0.28 Kg coal with 4500 k cal/Kg heating value is 1260 K cal. Heat out put is comosed of following components. Heat of decarbonation 420 K cal/ Kg clinker

Electricity generated ( 0.88 Kwh) 668 K cal/Kg clinker

Heat with gases from preheater 50 K cal /kg clinker

Heat from off gases 50 K cal/ kg clinker

Heat with clinker 54 K cal/ Kg clinker

Radiation losses 18 K cal / Kg clinker

The temperature of the gases at the precalciner out let may be 330 °C in the case of 5 stage preheaters and 300 ° C in the case of 6 stage preheaters. Radiation losses which are 70 -80 K Cal./ Kg clinker for conventional rotary kiln due to the nature of the equipment could be brought down to only 18 K Cal/ kg clinker with the help of suitable insulation.

In this process, additional fuel is deliberately burned so as to attain the high temperature required for clinkerisation. The heat so produced and the exothermic heat of clinker formation is recovered in the form of electricity with the help of conventional power generating equipment. It is possible to show 00/64832

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by elementary calculations that a 70 Mega Watt thermal power station can produce about 2000 t of fine clinker / day PROCESS VARIABLES

The following are the desirable variables of the process and their range of variation.

The preheated limestone powder used in step (i) is generally passing through 60 mesh, preferably passing through 100 mesh.

The fuel used in step (i) is chosen from solid fuels such as coal, coke, lignite, and liquid fuels such as furnace oil, diesel oil and gaseous fuels such as liquefied petroleum gas, natural gas, methane and mixtures thereof. In case fuel used in step (i) is solid it is finely ground to pass through 60 mesh, preferably passing through 100 mesh.

In case of liquid fuels the particle size of the atomized fuel is about 50μ - 100μ, preferably 5μ -10 μ. Addition of emulsified water may help this process. The calcining of finely ground preheated limestone powder with addition of finely powdered / atomized fuel is carried out in fluidized bed calciners at temperature 1000 - 1100 °C. The energy in the exiting gases is recovered by 5 or 6 stage cyclone preheaters which are placed in the path of the gases as in the conventional cement plant.

The calcium carbonate content of the calcined product obtained at the end of step (i) is less than 10 % by wt. preferably less than 5 % by wt, The fuel used in step (ii) is same or different, chosen from group of fuels used in step (i).

The contribution of ash remaining after combustion of fuel in step (ii), is considered in planning/deciding what other powdered materials would be necessary to make the required composition of the cement at the end of the process (Silica, Alumina, Iron oxides)

The amount of the fresh fuel added at step (ii) is based on calorie requirement to raise the temperature of the gases for promoting cement clinker forming exothermic reaction in the fluidized state, and for concomitantly raising temperature of the particles and gases beyond melting point of the inorganics. 00/64832

I I

Additional fuel may be added with a iew to generate more electrical energy as per the design of the power station.

In the plant of the present process temperature of the particles and gases in step (iii) in and at the exit of the reaction zone of the kiln, is raised from about

1450 °C - 1500 °C to about 2500 - 2800 °C.

The amount of said fresh air injected at step (iii) moving upwards in the kiln is

10 - 15 % excess over that required for combustion of said fuel in the fluidized fine powder mix produced at the end of step (ii)

The velocity of the fresh air injected at step (iii) moving upwards in the kiln is greater than the settling velocity of the particles in the fluidized bed.

The rate of rapidly cooling molten cement clinker particles and gases formed in step (iii) in the fluidised state in the lower portion of the kiln wit help of radiant heat exchangers of high pressure steam generators, in the upper portion of the said kiln to form solid cement clinker in fine non crystalline particulate form, is 300 - 1500 °C / Sec. Preferably, it is 900 - 1200 °C / Sec.

Additives for making high-class cement of desired composition to the clinkers obtained at the end of step (v) are gypsum 7 - 8.7 % by wt of the said cement clinker, and grinding aids such as triethanol amine or calcium lignσsulfonate in the range of 0.01 - 0.02 % by wt. clinker.

High class Portland cement is manufactured using coal having ash as high as

35 - 40 % both in step (i) for calcination and in step (ii) for clinker formation.

High class refractory calcium aluminate cement is manufactured by the process of present invention using limestone of high purity with iron content not more than 15 ppm , and choosing ash-less fuel in step (i) for calcination and in step (ii) for clinker formation preferably from LPG/ methane / furnace oil or mixture there of, and other additives of step (ii) comprise mainly reactive alumina.

High class white cement is manufactured by the process of present invention using limestone of high purity with iron content not more than 15 ppm, and choosing ash-less fuel in step (i) for calcination and in step (ii) for clinker formation preferably from LPG/ methane / furnace oil or mixture there of, and other additives of step (ii) comprise mainly low iron high purity silica. 00/64832

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Oil well cement is made by the said process by using ash less fuel at both the stages of firing .

Portland cement can also be made with the use of organic ash less fuels with poorer grades of lime stone in which additional ash from the coal does not permit formation of correct composition. (CaCO₃ content <75% and sijica- content more than 15%).

The plant for and a process for manufacturing high-class cement aηd electricity simultaneously of the present invention has a stationary vertical kiln replacing near horizontal rotary kiln in the conventional plants. The stationary vertical kiln is designed to favor formation of cement clinkers in fine particulate form without agglomeration; and rapid cooling of moltep cement clinkers as formed without any crystallization and conservation of heat for utilizing in generating electricity.

Use of vertical stationary kiln provides opportunity to let exhaust out carbon dioxide generated in calciners and allow fresh air in to the kiln, thereby helping calcination reaction to go to completion, and allowing burning of fresh fuel completely in the kiln for promoting clinker formation reaction. DETAILD DESCRIPTION OF THE PLANT OF PRESENT INVENTION: The plant of the present invention will now be described with the help of the accompanying drawing (Fig 1 and Fig 2)

Fig 1 describes a conventional cement plant in which

(1) is a blower

(2) is a preheater with a set of 5 or 6 cyclones

(3) is a calciner

(4) is a rotary kiln

(5) is a clinker cooler

In a cement plant of conventional technology, the kiln feed is prepared with lime stone and other correcting materials such as silica, alumina, iron oxides which are provided by clays or pure ingredients specially required for providing the desired composition of the clinker Allowance is made for the ash content of the coal since it becomes part of the clinker The kiln feed is 00/64832

13

passed down wards in the suspension preheaters (2) in which gases flowing upwards exchange their heat with the solids. The preheated solids are added to calciner (3) which converts the calcium carbonate to calcium oxide . The other ingredients are either chemically unchanged or the clay dissociates to its reactive form by breaking down in its component oxides which become reactable with calcium oxide. The mix is slowly raised to a temperature of 1450-1500 °C in the rotary kiln(4). This is done by firing additional fuel , mostly coal, which is adequate to raise the temperature of the mix to the required reaction temperature where silica can react with lime. The exothermic heat accelerates the process and at times the clinker melts to form a ring of glass on the refractory surface. The new material coming in contact with this molten material gets converted in nodular shape in the size range qf 3-15 Cm. The clinker from the rotary kiln is fed to the clinker cooler (5) for cooling and heat recovery. The large size of clinker does not allow rapid cooling. The time taken by the clinker to reach a temperature where crystallization reactions will freeze is about 10 minutes. In this duratioη, a good part of the material crystallizes. The cooled clinker is taken for grinding in ball mills with additives such as gypsum( up to8%), triethanol amine(0.01 toθ.02% of clinker). The cement is ground to a fineness of about 4000 blain. Fig 2 describes the plant of the present invention for manufacture of high- class cement and electricity simultaneously. In Fig 2,

(6) is a blower

(7) is a preheater with a set of 5 r 6 cyclones

(8) is a calciner

(9) is a additional blower

(10) is lower zone of the stationary kiln wherein additional fuel is ignited

(11) is upper zone of the stationary kiln wherein cement clinker is formed

(12) is a radiant heat exchanger which is super heater

(13) is a high pressure steam boiler.

(14) is economizer

(15) high purity water feed

(16) is high pressure steam outlet for generating electricity 00/64832

14

(17) is first cyclone

(18) is second cyclone

(19) is third cyclone

(20) is electrostatic precipitator

(21) is a bag filter

(22) is suction blower

(23) is stack for discharge of the gases

DESCRIPTION OF THE PROCESS OF THE PRESENT INVENTION With reference to Fig 2 , the process of present invention can be summarized as follows.

Finely ground lime stone along with the other reactants such as silica, alumina and iron oxide designated as kiln feed is fed through the chute to pre heater (7) . The preheated solids are fed to fluidized bed calciner (8) where most of the calcium carbonate is converted to calcium oxide, and are fed to the lower part of the vertical kiln (10). Here additional fuel and air are fed biy blower (9). The combustion products carry over the calcined lime stone with other reactive components and cause them to reach a high temperature enough to melt by the exothermic heat of combustion of fuel and the exothermic heat of the reaction of silica with lime. The gases then pass to the clinkering zone (11) from which the solids and the gases are passed to the heat recovery section. The first part of the section (12) is the super heater followed by the boiler (13), followed by the economizer(14). The high purity water for raising steam is fed through (15) and the high pressure steam js obtained from 16 for generation of electricity. The dust laden gases which have now been cooled to about 300 °C are fed to cyclones (17), (18) and ( t9) for recovery of the clinker. The finer particles are collected by the electrostatic precipitator (20) . The finest of the particles are recovered by the bag filter (21). Blower (22) provides additional suction for maintaining the velocity of the gases in the system and the gases are let out to atmosphere by the stack (23). The clinker dust collected by the equipment (17), (18), (19), (20) and (21) is combined and sent for cement production. The clinker dust is mixed with 8% gypsum , 0.01 % triethanol amine and ground to a fineness of 5000 blain to produce the high class cement. 00/64832

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SALIENT FEATURES OF THE INVENTION.

1. The plant and process of present invention produces cement clinkers in non-crystalline form, the clinkers are cooled rapidly from molten state to glassy state, without giving any time/cnance to form any crystalline phase. The cement formed is calcium silicate or calcium aluminate type and on hydration forms a stronger cement. The glassy structure is more reactive than the crystalline structure. Hence this cement is called "high-class" ' cement

2. The stationary vertical (tower) kiln allows heavy insulation and there is no limit on its diameter as in rotary kiln. The heat losses by radiation from the kiln surface are reduced considerably.

3. Agglomeration of molten clinker particles is common in rotary kiln with attendant problems of ring formation, failure of refractory, formation of hot spots and consequent stoppage of the production of the plant. This does not happen in stationary vertical kiln of the present invention, because collision of particles is prevented by air flow upwards, there by giving clinkers in fine powder form.

4. The exothermic heat of reaction of _t Calcium Oxide and Silica or Alumina raises the temperature of the gases and the particles in the vertical kiln beyond melting point of inorganics, and needs no extra fuel for this as in rotary kiln.

5. The gas flow in the vertical kiln of the invention is co-current with the flow of solids and therefore recovery of the heat energy at the cooling zone in the upper part of the vertical kiln is rapid, thus preventing any crystalline phase formation in cooling cement clinkers.

6. The thermal electricity generating plants based on coal firing when based on the plants of the present invention there is no ash disposal problem . In the process, ash is not formed , but high class cement clinker is formed.

7. Several facilities in cement plant and electricity generating plants are common, and therefore the plant of present invention reduces investment and running costs for both the plant by suitably resizing the equipment.

8. Clinkers produced by the process of present invention are in the form of fine particles, and therefore grinding energy required for making cement 00/64

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from the clinkers is less than that in the clinkers produced in the conventional cement plant.

9. Existing electricity plants can be augmented to produce cement and existing cement plants can be augmented to produce electricity as a result of this invention.

10. Low grade lime stone- which have just adequate CaCO3 content for cement making can also be used without using coal as a fuel if integrated with a thermal power station operating on naphtha or LPG or any other low ash fuel

EXAMPLES.

The process of the invention will now be illustrated with the help of Examples.

The Examples are by way of illustration only and in no way restrict the scope of the invention. All the examples are based on the qualitative work done at different sites.

EXAMPLE 1:

Lime stone (CaCO₃ 78-90 %) was ground with correcting materials such as silica, alumina, iron oxide or clay material which provides all the three components, to -100 mesh size in a ball mill and preheated by passing through a series of 6 cyclone pre- hβater. The residence time in the pre-heater is from 15 - 20 sec. The outcoming limestone and other ingredients (the correcting materials described earlier) were at about 1100°C, when near complete conversion of CaCO₃ to

CaO had taken place. The calcined lime stone from the fluidized bed calciner was added to the additional fuel, at the rate of 0J4 Kg coal ( with 34% ash content) / Kg clinkering material with a supply of fresh air at the rate of 1.5

NM³ air (10% excess over theoretical requirement). The fresh fuel was ignited as the precalcined kiln feed was mixed with the fuel and air. The high temperature of the pre calcined kiln fed helped to attain the combustion temperature rapidly. The flame temperature reached 1800 °C and the reaction of clinkerisation raised the temperature of solids to 2700-2800 °C

The combusting gas and dust mixture was allowed to flow through an insulated pipe, which provided empty space for reaction, for 1 second before it entered heat recovery system. The heat absorbed was recovered as high O 00/64832

17

pressure steam in high-pressure boilers. The enthalpy of the steam was 760 K Cal/Kg clinker which is equivalent of 0.58 KW/h of electrical energy at 70% efficiency ( For 0J 4 Kg of additional coal burned) . The reaction mass was collected in fly clinker recovery system comprising a set of cyclones followed by electrostatic precipitator followed by bag filters made of glass cloth . The gases may be preconditioned to improve the efficiency of electrostatic precipitators by addition of ethylene glycol or diethanol amine which also works as a grinding aid for grincmg of cement clinker. The clinker was ground with additives such as triethanol amine(0.01%) and gypsum(8%) for making Portland cement composition. The cement powder so produced was mixed with 45 % of its weight of water, formed into 1-cm diameter cylinder, and cured in humid atmosphere for extended duration. The cylinders were tested for the cold crushing strength and the results are shown in Table 1 be|ow.

Table 1 Day CCS

Kg/cm² 1 180 - 200

3 350 - 400 7 600 - 700 28 800 - 900

CCS = Cold crushing Strength

Example 2

The process of Example 1 was repeated with following changes:-

Thβ kiln feed was prepared using a high purity lime stone and reactive alumina obtained from a typical alumina industry was added as the reacting material. The impurity level of iron was controlled below 15 ppm. The silica and Na₂O and K₂O were controlled below 1 %

The fuel used in this case was a gaseous fuel and a liquid hydrocarbon fuel or a combination thereof which had no ash. 00/64832

18

The product clinker in this case was a refractory cement clinker with high refractory properties.

Example 3

The process of Example 2 was repeated with following changes:-

The purity of the lime stone used was high with iron content less than .15 ppm.

The kiln feed was prepared by using high purity silica. The fuel used was gaseous and liquid hydrocarbon as in Example 2. The clinker produced was a white cement grade clinker.

Example 4

In this case, the clinker as produced in Example 1 was co ground with granulated slag produced by a steel plant in the ratio of 34 parts clinker, 8 parts gypsum and 58 parts granulated slag with grinding aid such as triethanol amine or calcium lignosulfonate. The resultant cement had excellent setting properties.

Example 5

In this case , the cement clinker produced as in example 1 was co ground with fly ash produced by a power station using a low grade coal. The grinding aid and the gypsum were as used in example 1. The resulting cement gave. excellent setting properties on hydration and curing for 28 days.

ADVANTAGES OF THE INVENTION

Combination of the process generating electricity with cement making plant has several advantages: a. From the electricity generation point of view, disposal of fly ash is no more a problem. b. Some of the equipment required such as coal handling, preparation of powder, grinding , is shared by both the plants. c. Some personnel requirement is also shared. d. Proper location of this combined plant would help in reducing transport costs in case of cement plant and transport losses in case of electricity generation plant. e. Cement obtained by this process is better in setting time, hydration properties and in strength, than cement obtained by normal process. f. The overall capital requirement is lowered to almost half. g. The rotary kiln the conventional equipment is totally eliminated, h. Clinker is obtained in a fine powder form which is easily ground. i. Very rapid cooling from 2600°C to 200 °C in 2-3 Sec. Compared to 10 - 15 minutes in conventional plants produces almost completely glassy clinker which has much superior hydration properties. j. The over all heat energy and grinding energy required for this process is considerably lower as compared to the conventional process primarily because several operations become common and in case of clinker grinding it requires far less energy compared to conventional clinker which is very hard and lumpy in nature.

As a result of savings in energy, manpower and investment, the cost of production of both, the cement and the electricity are considerably reduced.

Claims

00/6483220Claims:

1. A plant for and a process for manufacturing high-class cement and electricity simultaneously, wherein said plant comprises mainly a stationary vertical highly insulated kiln replacing near horizontal rotary kiln in the conventional cement manufacturing plants, followed by high pressure steam boiler driving electricity generators and said process comprising following steps: i)calcining finely ground preheated limestone powder with addition of finely powdered / atomized fuel and other powdered materials required, to make the required composition of the cement in a fluidized bed calciner; ii)recovering the heat of the off gases with fresh incoming feed. iii)mixing on-line, fresh finely powdered / atomized fuel at the end of the process, with the overflow of said fluidized bed calciner containing calcined limestone in the form of fine powder produced at the end of step (i) iv)passing said fluidized fine powder mix produced at the end of step (ii) into the bottom of a stationary, vertical, highly insulated kiln, along with fresh air, moving the fluidized bed upwards in said kiln for combusting said fuel particles and promoting cement clinker forming exothermic reaction in the fluidized state, concomitantly raising temperature of the particles and gases beyond melting point of the inorganics; v)rapidly cooling said molten cement clinker particles and gases formed in step (iii) in the fluidized state in the lower portion of said stationary, vertical, highly insulated kiln with help of radiant heat exchangers of high pressure steam generators, in the upper portion of the said kiln to form solid cement clinker in fine particulate form, cool said gases and generate high pressure steam; vi)recovering said cooled solid cement clinker in fine particulate form, formed at the end of step (iv) by particles/ dust collecting systems such as array of cyclones, electrostatic precipitators and bag filters; vii)generating electricity by driving generator turbines by high pressure steam formed at the end of step (iv); 21

(ix) grinding said cool cement clinker in powder form obtained at the end of step (v) with additives for making high-class cement of desired composition.

2. A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in claim 1 wherein, said finely ground preheated limestone powder used in step (i) is passing through 60 mesh, preferably passing through 100 mesh.

3. A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in claim 1 or 2 wherein, said fuel used in step (i) is chosen from solid fuels such as coal, coke, lignite, and liquid fuels such as furnace oil, diesel oil and gaseous fuel such as liquefied petroleum gas, natural gas, methane or any other fuel. Or mixture thereof

4 A plant for and a process for .manufacturing high-class cement and electricity simultaneously as claimed in any claim 1-3 wherein, when said fuel used in step (i) is chosen from solid fuels such as coal, coke, lignite, said finely ground fuel powder is passing through 60 mesh, preferably passing through 100 mesh.

5. A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1-3 wherein, when said fuel used in step (i) is chosen from liquid fuels such as furnace oil, diesel oil the particle size of the atomized fuel is about 10 μ -100 μ, preferably 10μ -20 μ.

6..A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1 -5 wherein said calcining of finely ground preheated limestone powder with addition of powdered and or / atomized fuel is carried out in a series of 5 - 6 cyclone fluidized bed calciners;

7 A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1-6 wherein, calcining temperature in said fluidized bed calciner in step (i) of claim 1 is 1000 - 1100 °C

8 A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1-7 wherein, calcium carbonate content of the calcined product obtained at the end of step (i) of claim 1 is less than 10 % by wt. preferably less than 5 % by wt, 00/64832

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9 A plant for and a process for manufacturing high-class cement and. electricity simultaneously as claimed in any claim 1 - 8 wherein, said fuel used in step (ii) is same or different, chosen from group of fuels used in step (i) of claim 1 .

10 A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1 -9 wherein, contribution of ash remaining after combustion of fuel in step (ii) of Claim 1 , is considered in other [finely powdered] materials required, to make the required composition of the cement at the end of the process.

11 A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1- 10 wherein, the amount of the fresh fuel added at step (ii) of claim 1 is based on calorie requirement to raise the temperature of the gases and said inorganics for promoting cement clinker forming exothermic reaction in the fluidized state, and for concomitantly raising temperature of the particles and gases beyond melting point of the inorganics;

12 A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1- 11 wherein said temperature of the particles and gases in step (iii) of Claim 1 in and at the exit of the reaction zone of said stationary., vertical, highly insulated kiln, is raised from about 1550 °C- 1650 °C to about 2500 - 2800 °C.

13 A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1- 12 wherein, the amount of said fresh air injected at step (iii) of claim 1 moving co-currently upwards in said kiln is 10 - 15 % excess over that required for combustion of said fuel in said fluidized fine powder mix produced at the end of step (ii) of Claim 1

14 A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1- 13 wherein, the velocity of said fresh air injected at step (iii) moving co-currently upwards in said kiln is greater than the settling velocity of the particles in said fluidized bed.

15 A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1- 14 wherein, the rate of rapidly cooling said molten cement clinker particles and gases formed in step (iii) in the fluidised state in the lower portion of said stationary, vertical, highly insulated kiln with help of radiant heat exchangers of high pressure steam generators, in the upper portion of the said kiln to form solid cement clinker in fine non crystalline particulate form, is 300 - 1500 °C / Sec.

16 A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1- 15 wherein, the rate of rapidly cooling said molten cement clinker particles and gases formed in step (iii) in the fluidised state in the lower portion of said stationary, vertical, highly insulated kiln with help of radiant heat exchangers of high pressure steam generators, in the upper portion of , the said kiln to form solid cement clinker in fine non crystalline particulate form, is 900 - 1200 °C / Sec.

17 A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1- 16 wherein, said additives for making high-class cement of desired composition added during said grinding of said cool cement clinker in powder form obtained at the end of step (v) are gypsum 7 - 8.7 % by wt of the said cement clinker, and grinding aids such as triethanol amine or ethylene glycol 0.01 - 0.02 % by wt. ^•

18 A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1- 17 wherein, coal with 40 % ash is used in step (i) of claim 1 for calcination and in step (ii) for clinker formation to give high class Portland cement.

19 A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1- 18 wherein, fuel used in step (i) for calcination and in step (ii) of claim 1 for clinker formation is coal with 35 -40 % ash to give high class Portland cement.

20 A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1- 19 wherein, limestone used in step (i) of claim 1 is of high purity with iron content not more than 15 ppm , fuel used in step (i) of claim 1for calcination and in step (ii) of claim 1 for clinker formation is chosen from LPG/ methane / furnace oil or mixture thereof, and other additives of step (ii) of claim 1 comprise mainly reactive 00/64832

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VC -PCT-3-00 alumina to manufacture hjgh class refractory calcium aluminate cement as shown in example 3

21 A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1- 20 wherein, limestone used in step (i) is of high purity with iron content not more than 15 ppm , fuel used in step (i) for calcination and in step (ii) for clinker formation is chosen from LPG/ methane / furnace oil or mixture thereof, and other additives of step (ii) comprise mainly low iron high purity silica to manufacture high class white cement as shown in example 2.

22 A plant for and a process for manufacturing high-class cement and electricity simultaneously as claimed in any claim 1- 21 wherein plant used has a stationary vertical kiln replacing near horizontal rotary kiln in the conventional plants.

23. A process and a plant as claimed in claim 1-22 wherein the partial pressure of carbon dioxide in the calcination zone is lowered by isolation of the gases produced in the burning zone of the conventional cement making process.

24. A process and a plant as claimed in claim 1-22 wherein the clinker is recovered to produce electricity through radiant heat transfer to raise high pressure steam.

25. A process and a plant as claimed in claim 1 -23 for manufacturing high- class cement and electricity simultaneously wherein said stationary vertical kiln favors formation of cement clinkers in fine particulate form without agglomeration, and favors rapid cooling of molten cement clinkers as formed without any crystallization and favors conservation of heat for utilizing in generating electricity.

26 A plant for and a process for manufacturing high-class cement and electricity simultaneously, substantially as herein described in the text, in the examples and in the fig. 2 of the accompanying drawing, and Portland cement, high or low alumina refractory cement and white cement, granulated slag cement and flyash pozzolona cement manufactured using the plant and the process of the present invention as exemplified in Examples 1 2, 3 4 and 5