THE PATENTS ACT, 1970
FORM 2
COMPLETE SPECIFICATION
SECTION 10

METHOD OF RECOVERING HIGH PURITY
CONDENSATE FROM SODA ASH EFFLUENT, FILTERING
SODA ASH EFFLUENT SOLIDS AND CONVERTING
THESE SOLIDS INTO CEMENT CLINKER
TATA CHEMICALS LIMITED
HAVING ITS REGISTERED OFFICE AT
BOMBAY HOUSE, 24, HOMIMODY STREET,
FORT, MUMBAI - 400 001.

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

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This invention relates to a method of recovering high purity condensate from waste heat. Soda ash effluent solids are then filtered, washed (with high purity condensate generated), treated and converted into cement raw materials for use in cement clinker manufacture.
PRIOR ART :-
Under the prior art, all synthetic soda ash plants use the Solvay process and generate soda ash effluent. During the process generally 8-9 kilolitres of effluent is generated per tonne of soda ash. This effluent contains 25000 to 30000 mg/litre of suspended solids, which are usually discharged into the nearby water bodies. Many soda ash plants in the world are facing closure due to their inability to handle effluent solids. The discharged effluent solids contain unreacted lime (calcium oxide), ash, unburnt calcium carbonate, silica and other calcareous materials. Therefore a need was felt to find out effective ways to separate these solids from the effluent, recycle them into some manufacturing process and to make them re-useable in a value added product.
BACKGROUND OF THE INVENTION :-
Under this invention the applicants have devised a novel method of first recovering high purity condensate from waste heat of soda ash effluent then separating solids through filtration and treating effluent solids (effluent cake) by washing and drying so as to make them suitable for use as raw material for cement clinker. By the use of the aforementioned process the applicants generate approximately 800
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tonnes per day (TPD) of effluent solids when soda ash production is about 2800 TPD.
The process used under this invention consists of the following steps and is undertaken to separate solids from the effluent and to produce additional capacity of cement clinker : -
1. Sea water desalination plant using waste heat from soda ash effluent.
2. Effluent solids separation (filtration and treatment).
3. Expansion of clinker capacity for utilizing the effluent
solids.
As these solids mainly contain lime, unburnt calcium carbonate, silica and other calcareous materials, extensive laboratory and pilot trials were conducted for treating the effluent solids and to make them suitable for using as raw material for cement plant. Under the present invention an unique process has been devised to separate the solids involving chemical treatment, use of filtering aids and large size membrane filter presses thereby turning these effluent solids into a form whereby they can be readily handled. Large amount of high purity water is required for the process to wash the solids to minimize the chloride concentration below 0.2%. These solids can then be mixed with limestone and fed to a cement kiln.
DESCRIPTION OF THE INVENTION :-
Soda ash plants using Solvay process generate about 8-9 kilolitres of effluent per ton of soda ash produced. The effluent produced in the soda ash plant is hot in nature and is available at 104 degrees
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centigrade. This effluent contains 25000 - 30000 mg/litre of solids which is high in chloride content. The solid effluent at 104 degrees centigrade is first subjected to sea water desalination plant.
SEA WATER DESALINATION PLANT USING WASTE HEAT FROM SODA ASH EFFLUENT
The effluent solids when separated from the effluent contain high chloride, which is to be reduced to make them suitable for feeding as raw material to cement plant. For reducing the chloride, the cake formed in the process is washed with copious quantities of good quality of water. Approximately 4,000,000 liters of good quality of water is required every day for processing the entire solid effluent. As this much quantity of water is not available, a desalination plant utilizing waste heat from the effluent vapors generated in the flash vessels has been installed. This new desalination plant can generate 4,800,000 liters per day of distilled water utilizing vapor from Soda Ash Effluent Treatment Plant.
The sea water desalination plant has been engineered by M/s. Kehems-Entropie, who are leaders in this field. The technology is unique as this utilizes vapor generated from the flash vessels of effluent treatment plant. The desalination plant, as shown in Fig 1, consists of two parallel streams each having four successive cells at decreasing vacuum from cell 1 to cell 4. This system works on the principle of successive decreasing absolute pressure and correspondingly lowering the evaporation temperature for example the vapor from flash vessel at 80 degrees centigrade is cooled down to 74 degrees centigrade in cell 1 tube bundle externally sprayed by raw seawater. The heat released during condensation allows part of this
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raw seawater to evaporate at a temperature / pressure of 65 degrees centigrade / 0.25 bar absolute. The vapor produced from cell 1 then goes through cell 2 where it is condensed, thus evaporating part of cell 2 raw seawater at a temperature / pressure of 60 degrees centigrade / 0.20 bar absolute. The same process goes on in cells 3 and 4. The vapor produced in cell 4 at 51 degrees centigrade / 0.13 bar absolute goes to the raw seawater and cooling seawater condensers where it is condensed. The flash condensate from cell 1 is extracted directly by means of flash condensate pump. The water condensed in each cell from cell 2 goes through an interconnecting U-shaped tube to the next cell and finally to the condensers. From condensers, the water (which is distilled water) flows by gravity to the seal pots from where it overflows to the storage tank. The distillate pump then pumps the distillate water. In a similar way, the part of the sprayed seawater which has not been evaporated in each cell goes through an interconnecting U-shaped tube to the next cell to be finally blown from cell 4 by means of brine reject pump. The vacuum in the plant is maintained by two independent steam ejector systems. Single stage steam ejector system for cell 1 and two stage steam ejector system for the rest of the plant. These vacuum systems pump the air coming from the dissolved gases in the feed water and the unavoidable small leaks at the gaskets.
The solid effluent which is now at 70 degrees centigrade is collected in a tank and is then subjected to an effluent solids treatment plant
EFFLUENT SOLIDS FILTRATION PLANT
The solid effluent which is at 70 degrees centigrade consists of calcium oxide, calcium sulphate, magnesium bicarbonate, aluminium
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oxide etc. as solids and calcium chloride, sodium chloride in dissolved form. Effluent solids filtration project was proposed to recover the solids with less than 40% moisture and chlorides less than 0.2% from hot effluent and use it as a raw material in the cement plant, which will reduce the consumption of the chemical grade limestone.
The basic engineering is indigenously developed after extensive Laboratory & Pilot Plant study, utilising the vertical plate and frame automatic pressure filter supplied by M/s. Larox of Finland and High Rate and High Compression Thickeners from M/s. Supaflo of Australia and its distributors M/s. McNeilly, Bangalore.
The applicants are generating about 8-9 kilolitres of effluent per tonne of soda ash which is recovered in the Ammonia Recovery Section of Soda Ash Plant. The effluent is collected in a tank from where the effluent is pumped to Effluent Solids Filtration Plant, as shown in Fig. 2. The plant is divided into two parallel streams each having a capacity to handle 50% of effluent generated in the first stage of treatment. Each stream consists of one 21M dia High Compression Thickener, one 21M dia High Rate thickener, 3 carbonators, 3 filters, and air compressors with accessories. A common carbon dioxide blowing system with conditioning towers for carbonation, raw water feeding system for washing of cake and cake conveying system for feeding the cake to cement plant are also part of this treatment plant.
1. Thickeners Section
Fifty percent of the effluent slurry is fed to the High Compression Thickener, where the effluent solids are concentrated to 25% by
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weight. The concentrated slurry is repulped with seawater for diluting the chloride content and fed to the High Rate Thickener. Part of the clear liquor from the High Compression Thickener is proposed to be pumped to salt works for increasing the production of gypsum and salt. Balance liquor is proposed to be evaporated for the recovery of vacuum salt and calcium chloride solution. The underflow of the High Rate Thickener containing 16% by wt. effluent solids is transferred to a tank from there it is pumped to Carbonators. The overflow from the High Rate Thickener is disposed off to sea.
2. Carbonation Section
In the carbonation section, the thickened effluent slurry from the High Rate Thickener is carbonated in 3 reactors in series operation. Carbonation of the slurry is required to convert active calcium oxide present in the slurry, which is not suitable for cement plant to calcium carbonate. The carbonation of slurry also helps in better filtration of the slurry. The carbon dioxide gas required for the carbonation is tapped from the existing cement plant kiln stack, cooled and compressed in blowers. The pH of the carbonators outlet slurry is monitored continuously to ensure complete carbonation of slurry. The carbonated slurry from the 3rd carbonator is collected in filter feed tank.
3. Filtration Section
The carbonated slurry is filtered in two separate filters in a sequential automated operation in batch mode. In each sequential automated operation undertaken in batch mode sufficient quantity of slurry is pumped to the filter where solids are filtered in two stages. In the first stage the slurry is pressed at 7 bar pressure
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and washed with good quality water. During the second stage the washed cake is further pressed at 16 bar pressure. Compressed air is used for both pressing operations as well as for drying the effluent cake to the desired moisture level. The cake with desired chloride content is conveyed to the cement plant Dryer Crusher by a belt conveyor.
EXPANSION OF CLINKER CAPACITY FOR UTILIZING THE
V
EFFLUENT SOLIDS
This is the third and the final step wherein the treated effluent solid cake as obtained and as more particularly described hereinabove, is subjected to a kiln wherein it gets fully utilised. Chemical grade reject limestone from existing soda ash plant and cement grade limestone available in the near vicinity is added to the kiln thereby expanding the clinker production capacity from the present related capacity of 1000 TPD to 2500 TPD.
In this process the effluent solids are mixed with other raw materials in the following proportions and are fed to the kiln.
Material TPD Source
Chemical grade limestone 1085 Presently available from the
Soda Ash plant
Cement grade limestone 1816 From nearby sources
Effluent solids 800 From Effluent solids
separation plant
Fly Ash 75 From Mithapur power plant
Sandstone 96 From nearby sources
Total 3874
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The existing plant's facilities is upgraded to handle raw rnaterials and other equipment are added to increase the plant capacity to 2500 TPD Clinker.
When supplied with 800 TPD Soda Ash effluent solids the existing Cement plant's clinker capacity will stand upgraded from 1000 TPD to 2500 TPD. A new 60M-dia circular stacker reclaimer is put up to blend various grades of Limestone and fed into a bin. This is conveyed to the existing raw mill. Alongwith limestone, other ingredients such as sandstone and clay are added. The ground material is conveyed the existing CF SILO.
Filter cake Crusher Drier:
The separated solids from the Soda Ash effluent is in the form of cake containing some moisture. This is conveyed from the Effluent solids separation plant by a belt to a bin and fed by a box feeder to the crusher drier where the cake agglomerates, is broken up and dried by the new Calciner string pre-heater gases. The dried powder is fed to the CF SILO. Fly ash from a separate bin is fed into the CF silo to achieve proper Raw Mix composition.
On-stream analyzer:
To analyze the composition of the various components flowing into the Kiln feed system an on-line X-ray analyzer is provided.
New Calciner String with 4 stage pre-heater:
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A new calciner string with 4 stage pre-heater will calcine the Raw Mix fed from the same CF SILO. The pre-heater gases will provide heat to the crusher drier. The existing kiln and 6 stage pre-heater will continue to operate at present production rates.
Coal Mill:
A New Coal mill is added beside the existing unit to meet the additional fuel requirement of the new Calciner string. Both units will work in parallel.
Kiln modification and new clinker cooler:
The 60.6 meter long rotary kiln shell is extended by 3.4 meters and the old Planetary (UNAX type) coolers is removed. A new (COOLAX type) Grate cooler is placed at the kiln discharge to cool the product clinker. Deep Pan conveyor will convey the clinker to the existing as well as a new 10000 ton clinker silo. The new silo will have extraction facilities for transportation.
Alkali bypass:
The filter cake will contain small amounts of chlorides, which are detrimental to the kiln and preheater operation. Equipment is provided to by pass 10% of the kiln exhaust gases and quench them in a conditioning tower. The bypassed gas is dedusted in an ESP.
TYPICAL EXAMPLES
1.
Average feed solid concentration 13-14%
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Steps operated time
Feed to Filter 60 sec
First pressing 90 sec
Cake wash 300 Sec
Second pressing 150 Sec
Air drying 30 sec
Cake discharge 240 Sec
Total time 15.5 Minutes
Average quantity of discharge Cake 1.4 Tons

Analysis of Cake
Sample no 1 2 3 4 5
Contents (wt%)
Moisture 23 37.1 33.7 31.1 33
Chloride 1.35 1.47 1.40 1.08 1.2
CaO 0.56 1.12 1.12 0.84 0.8
CaC03 62.5 68.0 58.5 66.5 61
CaS04 15.55 10.72 16.1 11.73 15
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We claim:

condensate from waste heat of soda ash effluent then separating the solids from the soda ash effluent through filtration, and treating effluent solids by washing with high purity condensate generated and drying so as to make them suitable as raw material for use in cement clinker manufacture.
2) An invention as claimed in claim 1 above wherein solids from the soda ash effluent are first subjected to a seawater desalination plant which results in the formation of distilled water; then the solids with less moisture content are subjected to effluent solid filtration plant wherein they are treated, washed and dried so as to make it suitable for use as raw material in a cement plant.
3) An invention as claimed in claims 1 and 2 above wherein the solid effluent at 104 degrees centigrade is first subjected to sea water desalination plant which consists of two parallel streams each having four successive cells at decreasing vacuum from cell 1 to cell 4 which reduces the vapour to 74 degrees centigrade in cell 1 which is externally sprayed by sea water resulting in condensation and the release of heat which inturn allows part of this sea water to evaporate at a temperature /pressure of 65 degrees centigrade / 0.25 bar absolute.
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4) An invention as claimed in claim 3 above wherein the vapour
produced from cell 1 then goes through cell 2 where it is condensed
thus evaporating part of cell 2 raw seawater at a temperature /
pressure of 60 degrees centigrade / 0.20 bar absolute with same
procedure of successive decreasing of absolute pressure and
corresponding lowering of vapour followed resulting in formation
of vapour in cell 4 at 51 degrees centigrade / 0.13 bar absolute which goes to the raw seawater and cooling seawater condensers where it is condensed.
5) An invention as claimed in claims 3 and 4 above wherein the flash condensate from cell 1 is extracted directly by means of flash condensate pump and the condensed water in each cell from cell 2 goes through an interconnecting U-shaped tube to the next cell and finally to the condensers wherefrom the water (which is distilled water) flows by gravity unto the seal pots from where it overflows to the storage tank and distilled water is pumped out.
6) An invention as claimed in claims 3, 4 and 5 above where part of the sprayed sea water which remains un-evaporated in each cell goes through an interconnecting U-shaped tube to the next cell to be finally blown from cell 4 by means of brine reject pump.
7) An invention as claimed in claims 3, 4, 5 and 6 above wherein solid effluent treated through the seawater desalination plant is produced at 70 degrees centigrade which gets collected in a tank and is then subjected to an effluent solids treatment plant.
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8) An invention as claimed in claims 1 and 7 above wherein the effluent collected in a tank is pumped to an effluent solids filtration plant divided into two parallel streams each having a capacity to handle 50% of the effluent with each stream consisting of 21M dia High Compression Thickener, 21M dia High Rate Thickener, 3 carbonators, 3 filters and air compressors.
9) An invention as claimed in claim 8 above wherein 50% of the solid effluent slurry is fed to the High Compression Thickener where it is concentrated to 25% by weight and the same is repulped with seawater to reduce the chloride content and then fed to the High Rate Thickener wherein part of the liquor is proposed to be pumped to salt works for increasing the production of gypsum and salt and the balance liquor is proposed to be evaporated for the recovery of vacuum salt and calcium chloride solution and the underflow of the High Rate Thickener which contains 16% by wt. of the effluent solids is transferred to a tank and pumped to carbonators and the overflow is disposed of into the sea.
10) An invention as claimed in claim 9 above where the thickened effluent slurry is carbonated in 3 reactors to convert calcium oxide present therein into calcium carbonate which inturn helps in better filtration of the slurry which is then collected in a filter feed tank and subjected to 3 filters in sequential automated operation in batch mode thereby filtering the solids in two stages. In the first stage the slurry is pressed at 7 bar pressure and washed with distilled water and in the second stage the washed cake is further pressed at 16 bar pressure and dried. The effluent cake with desired chloride content is conveyed to the cement plant wherein it gets fully used.
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11) An invention as claimed in claim 10 above wherein the effluent solid cake is subjected to a kiln to which is added chemical grade reject limestone thereby expanding the clinker capacity to 2500 tonnes per day.
12) An invention as claimed in claims 1 and 2 above wherein 800 TPD effluent solids are mixed with 1085 TPD chemical grade limestone, 1816 TPD cement grade limestone, 75 TPD fly ash, 96 TPD sandstone and fed to the kiln to get the desired 2500 TPD of cement.
Dated this 14th day of March 2005
For Tata Chemicals . Ltd., By their Advocate Attorneys,

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ABSTRACT OF THE INVENTION
This invention relates to a novel method of recovering high purity condensate from waste heat of soda ash effluent then separating the effluent solids through filtration and treating them by washing and drying so as to make them suitable for use as raw material for cement clinker. The process used under this invention, undergoes 3 steps to separate solids from effluent and to produce additional capacity of cement clinker viz. 1) Seawater desalination plant using waste heat from soda ash effluent, 2) Effluent solids filtration plant and 3) Expansion of clinker capacity for utilizing the effluent solids. By the use of this process, large amounts of distilled water is generated and the effluent solids are used as a raw material in the manufacture of cement.
1 4 MAR 2005
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