HISTORY OF FACT

Mans history is replete with revolutions, responsible for molding his system of thought and shaping his modes of living. Revolutions have, more often than not, emerged out of crisis-situations it was one such crisis situation that guided the enlightened perception of a far sighted visionary to form FACT. Yes! The FERTILISER AND CHEMICALS TRAVANCORE LIMITED-popularly known as FACT-was indeed a revolution when it was established as the first large scale fertilizer factory in the country. Since then, it has played a major role in creating fertilizer consciousness among our farmers, and giving a positive direction to the modernization of agriculture in India. And that, of course is an interesting story-a story of never ending challenges and constructive responses.

The beginningThe 1940,s were a time of critical food shortage in our country. The traditional approach to cultivation was not of much help in finding a solution to this problem. And nitrogenous fertilizer had not yet arrived on the agriculture scene in sufficient quantities to make any perceptible impact. A revolution was indeed necessary to change the status quo. And when it came, it did through the vision of Dr. C.P. Ramaswami Aiyar, the Dewan of the former Travancore State, who mooted the idea of increasing food production by the application of fertilizer as a long term solution to food problem. To give concrete shape to his idea, he sought the help of Seshayee Brothers Ltd. Industrialist known for their pioneering work. And Indias first large-scale fertilizer plant was set up in 1944 at Udyogamandal on the banks of the river periyar in Kerala State. The new venture of course had to go through many teething troubles. For instance, the raw materials necessary for the production of ammonium salts were not available in the state. But this deficiency was overcome by adopting a revolutionary method known as the FIREWOOD GASIFICATION PROCESS.

28However, initial difficulties not withstanding, the plant at Udyogamandal went into commercial production in 1947, with the slated capacity to manufacture 50,000 tonnes of Ammonium Sulphate (10,000 tonnes of N). This was followed by the production of SUPERPHOSPHATE in a new plant with a capacity of 44,000 tonnes. A sulphuric acid plant of 75 tonnes per day was also installed which was considered large going standard at that time. Meanwhile the inner dynamics of FACT was finding another expression in the formation of new unit with the help of the State Government and Methur Chemical & Industrial Corporation Ltd., for the production of caustic soda which later become todays Travancore-Cochin Chemical Ltd., a Kerala Government undertaking. This indeed was a big leap forward as it replaced all the imports of that product, saving a considerable amount of foreign exchange. FACT was the first to use its by- product, chlorine, as hydrochloric acid to produce Ammonium Chloride. These by-products produced by FACT paved the way for setting up of other industrial units around the FACT complex viz. Hindustan Insecticide Ltd., Indian Rare Earth Ltd., etc.

Expansion

In the late 50s, the Udyogamandalam Division launched its first expansion with an outlay of Rs. 3 crores. Highlights of the period were the installation of two plants to produce Phosphoric Acid and Ammonium Phosphate (16:20 Grade). The second stage of expansion involving Rs. 2 crores saw the replacement of the Firewood Gasification Process and the Electrolytic Process by the Texaco Oil Gasification Process for which a new plant was set up.

FACT became a Kerala State Public Sector Enterprise on 15th August

1960. On 21st November 1962, the Government of India became the major shareholder. The 2nd stage of expansion of FACT was completed in 1962.

The 3rd stage of expansion of FACT was completed in 1965 with setting up of a new Ammonium Sulphate Plant.FACT has been a pace-setter in marketing evolving a continuous and comprehensive package of effective communication with farmers and promotional programmes to increase the fertilizer consciousness among our farmers. In fact, FACT was the first fertilizer manufacturer in India to introduce the village adoption concept since 1968 to improve agricultural productivity and enhance the overall socio-economic status of farmers. FACT has a well organized marking net work, capable of distribution over a million tones of fertilizers.With the licensing of Cochin Division in 1966 FACT further expanded and by 1976 the production of sulphuric acid, phosphoric acid and Urea was started. In 1979 Production of NPK was commercialized.

Technical Divisions

FACT Engineering and Design Organization (FEDO) was established in1965 to meet the emerging need for indigenous capabilities in vital areas of engineering, design and consultancy for establishing large and modern fertilizer plants. FEDO has since then diversified into Petrochemicals and other areas also. It offers multifarious services from project identification and evaluation stage to plant design, procurement project management, site supervision, commissioning and operating new plants as well as revamping and modernization of old plants. FEDO received international accreditation ISO 9001 2004 for quality system standards covering areas of consultancy, design & engineering services for construction of large fertilizer, petrochemicals, chemicals and related projects including purchasing, construction, supervisor, inspection and expediting services.FACT Engineering Works (FEW) was established on 13th April 1966 as a unit to fabricate and install equipment for fertilizer plants. FEW was originally conceived as a unit to fabricate and install equipment for FACTs own plants. Over the year it developed capabilities in the manufacture of class I pressure vessels, heat exchangers, rail mounted LPG tank wagons etc. It has a well equipped workshop approved by Lloyds Register of Shipping, further; this division has excelled in laying cross country piping fabrication and installation of large penstocks for hydel units in Kerala.The Cochin Division of FACT, the 2nd production unit was set up at Ambalamedu and the 1st phase was commissioned in 1973. The 2nd phase of FACT Cochin Division was commissioned in 1976. The project was designed to produce Ammonia which would be converted to Urea and also to produce high analysis, water soluble NP fertilizers. This division comprises of a number of large capacity plants to produce Ammonia, Urea, Sulphuric Acid, Phosphoric Acid and Fertilizers like FACTAMPHOS 20-20 and DAP 18-46.FACT has also a Research & development Department which carries out research related to fertilizers. This Division is also capable of doing fundamental research in areas of fertilizers and chemicals technology. So far FACT R & D has taken 17 patents in areas like Sodium Fluoride, Sulphuric Acid and Ammonium Phosphate.FACT took a major breakthrough, when its 50,000 TPA plant of Caprolactum was commissioned in 1990 as a major diversification plan from our traditional field of fertilizers and allied chemicals. The plant with a capacity outlay of Rs. 368 crores utilizes the most modern technology and the product is acknowledge as one of the best in the world. It also produces 2, 25,000 tonnes per Ammonium Sulphate as co-product.Subsequently, FACT set up a 900 TPD Ammonia plant at Udyogamandal with an investment of Rs 618 crores. This replaced the old Ammonia plant of Udyogamandal Division. The plant commissioned in 1998.FACT has been entering into a Memorandum of Understanding, (MOU) with the ministry of chemicals and fertilizers every year. This is as per the guidelines of DPE, Ministry of finance GOI. The objective of FACT is to achieve excellence in performance as per the MOU agreement.

DIVISIONS OF F.A.C.T

Udyogamandal Division

FACT commenced operation at Udyogamandal with the commissioning of a50,000 tonnes per annum Ammonium Sulphate Plant in 1947. In the decades that followed multi stage expansion programs were undertaken bringing in the latest technologies of the day which were quickly mastered and successfully implemented. Today the division is 40 year old small capacity plants and 10 year old state of the art technology plants. The latest addition to this unit was a 900 tonnes per day Ammonia Complex set up with an investment of RS 618 crores. FACT Udyogamandal division is certified to ISO 14001, the environmental system standards.

Cochin Division

FACT Cochin Division was set up in the 1970's at Ambalamedu, 30 km from Udyogamandal and adjacent to the Cochin Refineries. Phase-I of the division saw the setting up of an integrated Ammonia urea complex utilizing Indian Engineering skills. A large scale complex fertilizer plant of 485,000 TPA was set up as phase-II. Sulphuric acid and Phosphoric acid plant of economy scale were also set up.

Petrochemical Division

FACT diversified into petrochemicals in 1990 with the production of Caprolactum. This versatile petrochemical product is the raw material for the manufacture of nylone-6, which finds extensive application in textiles, tyre cord and engineering products. Thanks to its high quality, the product has been acknowledged as among the best in the world. The division is located adjacent to the Udyogamandal division. Co-product Ammonium Sulphate is transferred to the fertilizer plant of Udyogamandal division for processing.

FACT Engineering & Design Organization (FEDO)

FACT Engineering & Design Organization (FEDO) was established in 1965 for utilizing the considerable indigenous plant building expertise accumulated by FACT in its process of nurturing the nascent chemical fertilizer industry. FEDO is today one of India's premier project engineering organization, catering to a wide spectrum of industries like petrochemicals, refining, pharmaceuticals, hydrometallurgy etc as well as petroleum storage, environmental engineering, offsite facilities etc. The division undertakes project execution on consultancy and turnkey basis, handling the intricacies of the technology sourcing, design and engineering, hardware procurement and construction with practiced ease. FEDO is ISO 9001 certified.

FACT Engineering Works (FEW)

Established in 1966, FACT Engineering Works was originally conceived as a unit to fabricate and erect equipment for fertilizer plants. Over the years, it developed capabilities in the manufacture of Class I Pressure Vessels, Heat Exchangers, Columns, Towers etc. required for the fertilizer, petrochemical and petroleum industries. FEW received ISO 9002 Certification in 1998.

PRODUCTS & PRODUCT MIX

PRODUCTSAmmonium Sulphate - Udyogamandal DivisionAmmonium Phosphate / Complex fertilizers / Factamfos -Udyogamandal Division & Cochin Division Caprolactum-Petrochemical Division Biofertilizers - Research & Development Division

Exported Products

Caprolactum - Petrochemical DivisionAmmonium Sulphate - Udyogamandal Division

Byproducts

Nitric Acid & Soda Ash - Petrochemical Division Gypsum - Udyogamandal Division & Cochin Division Carbon Dioxide Gas Udyogamandal

Intermediary Products

Ammonia - Udyogamandal & Cochin DivisionSynthesis Gas - Udyogamandal DivisionSulphuric Acid - Udyogamandal & Cochin DivisionOleum - Udyogamandal DivisionSO2 Gas - Udyogamandal DivisionPhosphoric Acid - Udyogamandal & Cochin Division

PRODUCT MIX

Straight Fertilizers

Ammonium Sulphate - Containing 20.6% N in Ammonical form and 24% sulphur, an important secondary nutrient.

Ultraphos - FACT markets imported Rock Phosphate containing 32% P2O5 under the brand name "Ultraphos". This high analysis fertilizer is found suitable for application especially in Coconut/ Rubber/ Oil Plam/ Tea Plantation.

Complex Fertilizers

Factamfos 20:20:0:15 - NPK complex fertilizer - Factamfos or Ammonium Phosphate contains 20% N in ammonical form, 20% P in water soluble form and 15% sulphur; a secondary plant nutrient, which is now attaining great importance in agriculture. Factamfos also can be used for foliar spraying.

NPK Mixtures

NPK Mixtures - FACT prepares crop specific standard mixtures for all crops in Kerala and also special NPK mixtures for plantation crops like Tea, Coffee, Cardamom, Rubber etc.

Rose Mixture - A fertilizer tonic for Roses.

Vegetable Mixture - A special blend exclusively prepared for vegetable. Garden Mixture - A special nutrient combination for both flowering and foliage ornamental plants.

Imported/ Traded products - FACT has entered into direct import of MOP and also trading of Imported Urea.

Bio fertilizer - FACT produces and markets 'N' fixing Bio fertilizers - Rhizobium, Azospirillium and 'P' solubilising bio fertilizer - Phosphobactor.

CHEMICALSAnhydrous Ammonia - FACT produces Ammonia of over 99.96% purity. Sulphuric Acid - FACT has one of the largest plants in Asia and it manufactures Sulphuric acid of 98% purity.

Caprolactum - It is the raw material for Nylon-6. The product quality of FACT Caprolactum is among the best available in the world.

Nitric Acid and Soda Ash - Small qualities of these are obtained from Caprolactum plant as byproduct

MANUFACTURING METHODS FOR SULFURIC ACID

As described above, sulfuric acid is an important raw material for phosphate fertilizer production and to a much lesser extent for nitrogen and potassium fertilizers. World production of sulfuric acid was about 121 million tons in 1977 and about half of this production was used in the fertilizer production.About 58% of the worlds production was based on elemental Sulfur, 25% on Pyrite and 17% on other sources. Of the other sources, the principal one was the by-product sulfuric acid recovered from smelting operations.

In general terms, the sulfuric acid is produced by catalytic oxidation of sulfur dioxide to sulfur trioxide, which is subsequently absorbed in water to form sulfuric acid. In practice the sulfur trioxide is absorbed in sulfuric acid which is kept at a controlled concentration (usually 98%) by the addition of water.

There are no major variations of commercial interests on this mentioned chemistry. There are alternatives as to source of Sulfur dioxide and method of conversion to sulfur trioxide. The two most common methods for the conversion of sulfur dioxide to sulfuric acid are

1. Lead Chamber Process:2. Contact Process

Lead Chamber Process:

This is an old process and was introduced in Europe in near the middle of 18th century. This method uses nitrogen oxides as oxygen carrying catalysts for the conversion of sulfur dioxide to sulfur trioxide. The reactions which produce the sulfur trioxide and sulfuric acid take place within the huge lead chambers or in packed towers which may be substituted for the chambers. Chambers process produced acid of concentration less than80 %.The major disadvantage includes the limitations in throughput, quality andconcentration of the acid produced. All known new plants uses the Contact process although some older Chamber process plants may still be in use.

Contact Process:

In the contact processes, the sulfur dioxide is converted to sulfur trioxide by the use of metal oxide catalyst. Platinum was once widely used as catalyst but because of its excessive first cost and susceptibility to poisoning, it has been largely replaced by vanadium oxide. The vanadium pentaoxide is dispersed on a porous carrier in a pellet form. The characterstics of the catalyst which can be used are mentioned as follows:

1.Porous carrier having large surface area, controlled pore size and resistance to process gases at high temperature; in pellet form if used in fixed bed and powdered form if used for fluidized bed. Ex- Alumina, silica gel, zeolites.2. Active catalytic agent:Vanadium pentaoxide in this case. Preparations are generally kept secret for thecompetitive reasons but they usually consist of adding water soluble compounds to gels or porous substrates and firing at temperature below the sintering point.3. Promoter:Alkali and/or metallic compounds added in trace amounts to enhance the activityof the catalytic agent. Advantages of the V2O5 catalyst1. Relatively immune to poisons.2. Low initial investment and only 5% replacement per year.

Disadvantages of V2O5 catalyst1. Must use dilute SO2 input (7-10%).2. As a catalyst it is less active and requires high oxygen or sulfur dioxide to giveeconomic conversions3. Requires larger converters and thus higher initial investment.

Now the SO3 gas is passed to an absorption tower where it is absorbed in recirculating concentrated acid. There are many variations in the contact process depending upon the types of raw materials available and other considerations; also a number of engineering variations are in use by many different design/construction firms offering services in this field.

Main disadvantages of the contact process are that concentrated acid (98%) of high purity can be produced directly and that compact plants of quite high capacity have now become rather common place.

THE PRODUCTION OF SULFURIC ACID BY CONTACT PROCESS:

RAW MATERIALS: One of the early raw materials for the sulfuric acid was sulfate of iron or vitriol. By heating the solid sulfate and condensing the fume an oil of vitriol resulted. The rectified oil of vitriol (ROV) is concentrated acid and the brown oil (BOV) is about 77% Sulfuric Acid. The raw materials for sulfuric acid manufacture are chiefly Sulfur, Pyrites, Spent oxide, anhydrite and gases from the smelting of metalliferous ores, from the purification of natural gas and from refining operations.CHEMISTRY OF SULFURIC ACID PRODUCTION:

The equations governing the production of sulfuric acid are:

S + O2SO2+ -70 KCal

(solid) (gas)

SO2 + 1/2 O2SO3+ -23.50 KCal

SO3 + H2O H2SO4 + -32 Kcal

The first reaction expressing the combustion of sulfur is strongly exothermic; sulfur on burning gives about one third of the heat of combustion of coal, and this heat raises the temperature of combustion gases roughly in accordance with the graph as shown

This heat is high in temperature and there is plenty of it, consequently it is worth utilizing and the hot gases are led across pipes through which the water passes. The water is heated, steam is raised and the gases are cooled. This is the arrangement in the water tube boiler. In the fire tube boiler the hot gases pass through the tubes which are surrounded with water.

The second equation is also exothermic and its apparent that the equation gives a decrease in volume, three volumes become two volumes and this reaction would be aided by pressure. High conversions are however, obtainable with catalysts at 400 to 500C with a small excess of oxygen and the use of pressure.

The third equation represents the absorption of sulfur trioxide to form sulfuric acid. It is exothermic and the absorbing sulfuric acid has to be cooled continuously; the heat is available at a relatively low temperature and is not worth recovering. Sulfuric acid is used for the absorption of sulfur trioxide as it has been found in practice that sulfur trioxide and water form a mist, which is difficult to separate from the gas and that under these conditions the absorption, is not complete. The strength of the acid is best about 98%.

SULFUR HANDLING AND STORAGE:

Sulfur used for the production of sulfuric acid is practiced to handle as solid in bulk, from ship to wagon and from wagon to cool off and solidify; it can then be broken up and shovelled into wagons for disposal. It consists of carbonaceous matter and inorganic ash.Although commercial sulfur is over 99% sulfur, the impurities present as dust in the plant gases tend to be filtered out by the catalyst and a blanket or layer of hardened dust on the catalyst detracts from the efficiency of conversion. In consequence some manufacturers filter the molten sulfur through leaf filters to remove some of the impurities and so obtain a longer period before the plant has to be shut down for cleaning away the dust and sieving the top layers of the catalyst from it. However, the filter leaves have to be removed for the replacement of the filtering medium and for the removal of the accumulated sludge, and these unpleasant operations, together with the installation cost of the equipment, have to be weighed against the benefits of having slightly less dusty gases.

SULFUR BURNING:There are several types of burners for sulfur. One is revolving cylinder containing pool of molten sulfur which is combusted by the passage of air over its surface. Another type is a brick lined vertical cylindrical vessel in which is erected a pile of fire brick in the form of a pyramid, and on to this structure molten sulfur is pumped to be met by a stream of co- current dry air for its combustion. A third variety is in the form of a burner similar to an oil burner.

The quantity of air is regulated to give between 8 to10% SO2.

In the starting up the plant with a vertical burner the fire-brick is first heated by the burning of a fuel gas. The gas, when a sufficiently high temperature has been reached is cut off and the liquid sulfur is pumped over the brick-work. A measured amount of air is passed down the burner and the sulfur burns to sulfur dioxide providing sufficient heat in normal operation to raise the temperature of the gases to some 810-900 C. If the air contains 21% oxygen and sulfur is burned to give 10% sulfur dioxide gas, then 11% oxygen and 79% nitrogen will form the residual gases. Some excess oxygen is necessary over and above that required to combine with the sulfur and the sulfur dioxide. Out of the 11% oxygen, 5% will be required to combine with the dioxide to form the trioxide leaving an excess of 6%. This is adequate but if attempts were made to have a 14% sulfur dioxide gas then 14% from the 21% oxygen would be taken up in forming sulfur dioxide and another 7% would be required to convert the dioxide to trioxide. This would leave no excess oxygen and an excess has shown to be essential for a good conversion of the dioxide.When sulfur burns, the gases rise to a temperature depending on the dioxide concentration; with 8% sulfur dioxide the temperature is about 750C. In the diagram, the gas temperatures are plotted against the dioxide concentrations. To withstand these temperatures the burner is brick lined and the area of the brickwork radiates heat and helps to burn the sulfur completely in the time given by the volume of the burner for the passage of the gases.

The composition of the gas can be varied by altering either the air or the sulfur to the burner. The very hot gases containing the ash from the sulfur are led straight into the waste heat boiler.

THE WASTE HEAT BOILER:

The object of the waste heat boiler is to utilize the heat in the gases to generate steam. A water tube boiler consists of tubes among which gases pass, the tubes being full of water. The gases heat the tubes which in turn raise the temperature of the water. The boiler is in the form of cylinders connected by hairpin shaped tubes arranged across the path of gases. The tubes are kept filled with water (to prevent burning) and are connected at the top to a steam drum, a cylindrical vessel in which water is kept at a constant level by an automatic feeding device. The steam drum, where the water boils, is above the tubes and serves to supply water to the boiler and for the release of steam. The surface area of the water inside the drum must be sufficient to minimize the carryover of the spray with steam which is led off from the top of the drum and then through super heater tubes by which the steam is heated several degrees above its condensation temperature to give it superheat and make it free from droplets, dry and suitable for use in turbines or other steam engines. The water circulates from the steam drum to the sludge drum, another cylindrical shaped vessel at the bottom of the boiler, from which the solids, deposited from the evaporating water, are sludged out and the solid content of the boiler water controlled. The water circulates through the hairpin tubes upwards to another cylindrical drum and then passes from this intermediate drum upwards again through another set of hairpin tubes to the steam drum. The pressure under which steam is generated depends upon the purpose for which it is to be employed.

There are the usual auxiliaries which are associated with a boiler, the feed pumps for pumping the feed water into the drum against the boiler pressure, the feed water preparation tank where phosphates and alkali are added to the water to prevent boiler corrosion, and the economizer which heats the boiler feed water near to the temperature of the water in the boiler drum. The feed water is sometimes preheated by exhaust steam from the boiler feed pumps before being heated in the economizer. Preheat may be to100C and the final temperature of the feed water say 215C. The economizer and the super heater obtain their heat from the sulfurous gases at convenient points in the processusually from the converter after the second and third stages. Cold water in the economizer tubes could cause local condensation from the sulfurous gases and result incorrosion. After the first stage of conversion there is another waste heat boiler similar in construction to the first boiler but smaller and the two boilers use the same steam drum. The inlet gas temperature to the converters should be 380-400C and the waste heat boiler is designed to take away the heat from the gases until their temperature is in this range. This reduction in temperature is about 400C and corresponds to several tons of steam an hour form the moderate size sulfur burning plant.

The temperature of the exit gases is controlled by a by-pass on the waste heat boiler. The amount of heat evolved is dependent upon the quantity of sulfur and the temperature on the proportion of sulfur dioxide in the gases. The higher the temperature, the higher is the proportion of heat which is to be removed. It is best to gauge this so that the waste eat boiler by-pass in normal operation is almost shut.

The waste heat boiler design takes into consideration the following factors. The area of the tubes must be adequate to take the requisite amount of heat from the gases. This is dependent upon the amount of heat transferred per unit of tube area, which itself is dependent upon the velocity of gases over the tubes and the temperature difference between the gases and the boiler water

GAS DRYING:

It has been found in practice that if moisture is present in the gases before conversion, a sulfur trioxide mist will form after the converters, which is extremely difficult to absorb in the acid absorbers. There are several theories to account for this. It may be that the sulfur trioxide particles are surrounded by a film of acid and the aggregates are sufficiently small to pass through the absorbers and out into the atmosphere, giving rise to inefficient absorption and causing a local nuisance. There mists can be destructive to vegetation, damaging to buildings and extremely unpleasant to life in the vicinity. It is therefore essential to use dry air for sulfur burning or install special plant for absorbing the mist, which is a difficult proposition.

Air is dried in a drying tower which uses strong sulfuric acid for this purpose. The tower consists of a mild steel vertical cylinder lined with acid-resisting brick and packed with ceramic rings. The acid is distributed down the tower and air is blown upwards counter- current to the acid by a blower which also serves to give the air sufficient for it to pass through the whole of the sulfuric acid plant to atmosphere after the absorbers.

The vapor pressure of water above acids of high concentrations at ordinary temperatures can be extremely low and consequently under the right conditions (95-98% H2SO4 at35C or less) the acid removes nearly all the water vapor in the air that is down to30mg/m3.

The tower has to be of a sufficient diameter not to require a significant pressure drop for the gases to pass through it and to have an adequate surface area of packing for the absorption of water from the air to take place in the time which the gases take to pass through the tower volume. Consequently the gas velocity up the tower must be small, and this will determine the minimum diameter of the tower. The amount of acid used in the tower has to be significant to wet the surface of the packing without flooding and not to become so dilute that its vapor pressure becomes appreciable. The amount of water in air at a given temperature and relative humidity is known and hence the minimum quantity of 98% acid on the drying tower can be calculated.

It is common practice to use acid from the absorption section on the drying tower; the heat of dilution is then removed on the absorption coolers but coolers are sometimes provided on the drying section with a bleed-off to the absorption circulation system.

GAS FILTRATION:

The gas from the burners after passage through the waste heat boiler contains ash from the sulfur and some scale from the waste heat boiler and gas lines. These solid impurities are best removed before the gases enter the converter; otherwise the dust accumulates on the layers of catalyst and causes channeling through the catalyst layers, irregular contact and pressure drop.

The filter consists simply of the wide diameter vessel filled with the filtering medium which is commonly the lumps of quartz. The vessel is of squat cylindrical shape in mild steel. The gases pass downwards to assist in the removal of the solids at a velocity which is slow because of the wide diameter of the vessel. When the filter is first put into service, the pressure drop is several m atmospheres, but when it is ready for opening and cleaning, this pressure drop rises to some 100m atmosphere. The interval between removals of dust depends on the ash content of the sulfur; a filter usually lasts three to six months and this period would be extended if the molten sulfur were also filtered before burning.

In many cases the gas filtration unit may not be present and thus this step may be treated as the auxiliary unit, depending upon the requirement. In the flow sheet given, the gas filtration unit is not shown.

CONVERSION:

The converter is a reactor and its objective is to combine the sulfur dioxide with the residual oxygen in the gases to form sulfur trioxide. The conversion is aided by a catalyst and the more sensitive the catalyst the lower the temperature at which the conversion takes place and more favorable the equilibrium but in general sensitive catalyst are more readily poisoned. In practice it is necessary to have a catalyst which is sufficiently robust to resist poisoning but is active enough to give good conversion at about 400C. The converter consists of a tall cylindrical vessel of sufficient diameter (generally 3.5 to5.5m) to give a low gas velocity, inside which there are three or four trays for quantities of catalyst. Between the catalyst sections there are devices for cooling the gases to keep the temperature entering the later catalyst sections in the region of 405 to 440C. The first catalyst pass contain relatively little catalyst because the reaction is rapid and the temperature rises sharply; the second a little more, and the last stages most of the catalyst, where both the sulfur dioxide and oxygen are less concentrated.

After the passage through the first catalyst tray when the gas temperature has risen from about 410C to over 600C, the gases pass into an external waste heat boiler to raise steam and bring the gas temperature down to 430C and at this temperature the gases enter the second catalyst tray. On passing through the catalyst the temperature again rises but this time not so much, and after the second tray sufficient heat can be removed by superheating the steam raised in the waste heat boilers. The super heater tubes are led from the boiler into a space underneath the catalyst bed in the path of the gases. The temperature is again brought down to about 430C and after the third pass the gases are similarly cooled. In the final section, which contains most of the catalyst, the temperature rise is small as the reaction has been brought near the equilibrium value in the previous passes and only relatively small amounts of sulfur dioxide and oxygen remain to react. After leaving the catalyst the gases are at 400 to 450C; they are passed through the economizer where the temperature is reduced to a lower value. The gases then pass through an air cooler to the absorbers.

The catalyst consists of vanadium in the form of small pellets or cylinders. The total volume is arranged to give the time of contact necessary for the reaction to take place. The speed of the reaction depends on the activity of the catalyst. A conversion of sulfur dioxide to trioxide of between 98 and 99 % is achieved.

The equilibrium is given by

(PSO3)KP = (PSO2) (PO2)

(PSO2) (PO2) should be as high as practicable to give a good value for (PSO3). If there is excess of oxygen (PO2) will increase in value but too great an excess will diminish (PSO2) initially. On some converters, air is introduced between the converter stages which acts as a cooling medium and provides the additional excess of oxygen.

Below 400C the reaction is very slow but above 630C the reaction is fast but the equilibrium is becoming unfavorable, the reaction goes more quickly the higher the temperature, but the equilibrium becomes unfavorable. The aim in running the converter is to maintain a pattern of temperature which experience has shown will give the optimum conversion. These temperatures depend on the catalyst activity, gas strengths and other factors

The running of the converter consists in close observance of temperatures, the pressure drops and the sulfur dioxide conversion. The temperature rise across the catalyst is the measure of the amount of reaction taking place. Pressure drops across the bed of catalyst, if they are abnormally high, indicate a partial blockage and channeling through the catalyst, which would be accompanied by a small temperature rise. A high pressure drop across the first pass may necessitate shutting down the plant and screening the top layer of the catalyst which has possibly become choked with dust.

ABSORPTION

The gas leaving the reactor is cooled further in a heat exchanger as mentioned above and before entering the absorption tower where the Sulfur trioxide is absorbed in a recirculated stream of concentrated sulfuric acid. The sulfuric acid is maintained at desired concentration (usually 98% H2SO4) by the addition of water and its temperature is controlled in the desired range of 70 to 90C measured at the tower inlet by cooling the recirculated acid.

Some of the acid goes to the air drying tower mentioned previously where the moisture from the incoming air supplies some of the water needed in the reaction. Since, the heat released in this step is at a low temperature level, little use can be made of it.

In the above mentioned Single Absorption process, the recovery of the sulfur as sulfuric acid is 97-98% and the remainder is lost to the atmosphere as Sulfur dioxide. In many countries, the discharge of this amount of Sulfur dioxide to the atmosphere is environmentally unacceptable. Therefore most of the plants use a Double Contact Double Absorption Process (DCDA)

The gas after passing through three catalyst bed goes to the first absorption tower where the Sulfur trioxide is removed. The gas is then reheated to about 420C, passed through the fourth catalyst bed, then cooled and sent to a second absorption tower.

2SO2 + O2 2SO3In the reaction removal of the reaction product sulfur trioxide facilitates more efficient conversion in the last catalyst bed. The DCDA process reduces the sulfur dioxide loss to less than 2Kg of sulfur dioxide/ ton of the sulfuric acid. High efficiency mist eliminators are also required to limit the loss of sulfuric acid mist to less than 0.05Kg/ton of sulfuric acid.

Thus the recovery in a DCDA plant should atleast be 99.8%.

THE TAIL GAS:

The gas from the absorption section contains about 0.15 % sulfur dioxide which oxidizes in part to sulfur trioxide and forms mist. At this concentration, corresponding to a conversion efficiency of over 98%, the effluent is tolerable and no further treatment of gas is required. In exceptional cases where the oxygen content is low or for other reasons where the conversion is down, the gases can be scrubbed with ammonia liquor and then treated by electrostatic precipitator.

STORAGE:

The last part of the sulfuric acid plant is the storage and the pumping system. The tanks are large flat cylinders which are sometimes of more than 1000 tons capacity. The pumping of acid is commonly done by the centrifugal pumps, the submerged glandless type on smaller tanks where the shaft can be less than about 10ft in length. The absence of gland leaks makes for a neat and clean pumping section. The storage installation should be calculated to maintain continuity of supply, if this is required, during the shutdowns of the acid plant and to cater for peak demands.

DEVELOPMENTS:

The use of the DCDA system adds 10 to 15% to the cost of the plant in comparison with the older Single Absorption Process. It also uses more energy and produces less steam or other recoverable energy. An alternative which is less expensive is to recover the sulfur dioxide from the single absorption plant by ammonia scrubbing. Scrubbing the gas with the ammonia solution produces an ammonium sulfite solution which is then acidulated with sulfuric acid. The liberated sulfur dioxide is returned to sulfuric acid plant and a concentrated ammonium sulfate solution remains which may find use in a fertilizer industry.

Operation of the sulfuric acid plant has some advantages,

1. The equipment is smaller and less expensive2. Less Catalyst is required.3. Equilibrium condition and reaction rates are more favorable in the conversion and absorption steps.The solubility of sulfur dioxide in sulfuric acid increases with the increase in pressure and with the decrease in temperature. In a conventional plant operating at 1 atm and with an acid temperature 110C, the solubility of sulfur dioxide in sulfuric acid is only 8ppm. However, increasing the pressure to 8 atm and lowering the temperature to 49C, the sulfur dioxide solubility is increased to 190ppm.Under these condition a substantial amount of sulfur dioxide can be transferred in the acid stream to the air drying tower and then to the incoming air stream. Many authors have pointed out that there is no theoretical limit to the amount of sulfur dioxide that can be recycled or recovered; it depends on the rate of recirculation of the acid between the absorber and the air drying towers.

Ammonium Sulphate

Ammonium sulfate was once the leading form of nitrogen fertilizer, but it now supplies a relatively small percentage of the world total nitrogen fertilizer because of the rapiud growth in use of urea, ammonium nitrate. The main advantages of ammonium sulfate are its low hygroscopicity, good physical properties (when properly prepared), chemical stability and good agronomic effectiveness. It reaction in the soil is strongly acid forming, which is an advantage on alkaline soils and for some crops such as tea; in some other situations its acid forming character is a disadvantages. Its main disadvantages is its lower analysis (21%N), which increases packaging, storage and transportation costs. As a result, the delivered cost at the farm level is usually higher per unit of nitrogen than that of urea or ammonium nitrate. However, in some cases, ammonium sulfate may be the most economic source of nitrogen when the transportation at low cost, or when a credit can be taken for its content.

Ammonium sulfate is available as a byproduct from the steel industry (recovered from coke oven gas) and from some metallurgical and from chemical processes.

Commercial form, storage and transportation:

Fertilizer grade ammonium sulfate specifications normally indicate a minimal nitrogen content, which is usually not less than 20.5%. limitations on free acidity and free moisture are also generally demanded; typical figures are 0.2% for free H2SO4 and 0.2% for free H2O. occasionally, maximal values for certain organic or inorganic impurities may also be specified for byproduct material.Several factors contribute to trouble free storage of ammonium sulfate and other fertilizers. First, the product should be of uniform crystal size and should contain a low percentage of lines. It should be dry and preferably have below 0.1% free moisture. No free acidity should be cooled with dry air under controlled condition after drying, particularly when the ambient temperature and humidity are sufficient high to cause subsequent moisture condensation after cooling in a bulk storage pile or in sealed bags. Ammonium sulfate is commonly shipped in polyethylene or paper bags.The majority of its production is coming from coking of coal as a byproduct. Ammonium sulphate is produced by the direct reaction of concentrated sulphuric acid and gaseous ammonia and proceeds according to the following steps.

1. Reaction of Ammonia and Sulphuric Acid:

Liquid ammonia is evaporated in an evaporator using 16 bar steam and preheated using low pressure steam.The stiochiometric quantities of preheated gaseous ammonia and concentrated sulphuric acid (98.5% wt/wt) are introduced to the evaporator crystalliser (operating under vacuum). These quantities are maintained by a flow recorder controller and properly mixed by a circulating pump (from upper part of the crystalliser to the evaporator)

2. Crystallization

The reaction takes place in the crystallizer where the generated heat of reaction causes evaporation of water making the solution supersaturated. The supersaturated solution settles down to the bottom of crystalliser where it is pumped to vacuum metallic filter where the A. S crystals are separated, while the mother liquor is recycled to the crystalliser.

3. Drying of the wet Ammonium Sulphate Crystals

The wet A.S crystals are conveyed (by belt conveyors) to the rotary dryer to be dried against hot air (steam heated) and then conveyed to the storage area where it naturally cooled and bagged.The following presents the process block diagram for ammonium sulphate production.

EVAPORATORSAn evaporator is a heat exchanger shell and tubes.The essential parts are an evaporator heating chamber and the evaporation chamber.The bundle of tubes corresponds to a camera and the frame corresponding to the other chamber.The casing is a cylindrical body inside which is the beam pipe.The two chambers are separated by the solid surface of the tubes through which heat exchange takes place.The shape and arrangement of these chambers, to ensure that its efficiency is maximum, resulting in different types of evaporators.We can classify the evaporators into two groups:-Horizontal Tube Evaporators.The heating steam is saturated steam that gives its heat of condensation and out as liquid water at the same temperature and pressure input.The evaporator tube is called horizontal because the tubes are arranged horizontally.In the next evaporator, the heating chamber is formed by the horizontal tubes, which are supported by two plates.The steam enters the tubes and condenses to give up its heat of condensation.There can be no condensate steam, which is removed by a purge.The evaporation chamber comprises a vertical cylindrical body, closed bases, the solvent evaporated with an outlet at the top and another outlet for the concentrated solution at the bottom.. These evaporators are usually of iron or steel plate with a diameter of approximately 2 meters and 3 meters high.The diameter of the tubes is usually 2 to 3 inches.

The following evaporator enters the steam inside the tubes, and heat transfer fluid flowing over the tubes, the steam condenses.From the evaporator and the concentrated solution leaves the solvent evaporated.

-Vertical Tube Evaporators.Are so called because the tubes are placed vertically within the casing.The evaporator is located belowevaporatoris calledStandard,which is one of the best known.Evaporation takes place inside the tubes, leaving the top and the solvent evaporated from the bottom of concentrated solution.The steam heater comes on to the beam pipe and exits as condensed water.

Theevaporatorbasketbellow, which then is another type of vertical tube evaporator, in which the body is conical.This type of evaporator is used when the aim is to bring the evaporation in the end, that is all evaporated the solvent of the solution diluted to obtain crystals.You can also call Crystallisers.The crystals formed are collected at the bottom.The heating element is a compact body that can be removed for cleaning.

Multiple effect evaporator

A multiple effect evaporator consists of a series of evaporators, where the first effect evaporator is the first and so on. During the operation, the steam produced in the first effect is used as heating steam in the second effect.

Methods of feed in the multiple effects:-Feed Direct.The feed enters the first effect and follows the same sense of movement that the steam, leaving the product in the final effect.The liquid circulates in the direction of decreasing pressure and does not need to apply auxiliary power to the liquid pass effect in the other.Only needed two pumps, one for introducing the liquid in the first effect and another to extract the product of the last effect.

-Feed upstream.The liquid evaporates and enters the final effect leaves concentrated on the former.The liquid concentrate and the steam heater circulates in the opposite direction.Here the fluid circulate in the direction of increasing pressures and this requires the use of pumps in each pump to effect the dissolution of a concentrated effect to the next.This represents a considerable mechanical complication that adds to the work done to the pumps at pressures below atmospheric.So, if there are other reasons, we prefer the direct feed system.

- Diet mixed.When a part of the power system is direct and the other party is in opposition.This system is useful if you have very viscous solutions.If we use the pure direct current, we find that the latter effect, where the temperature is lower, the viscosity of the concentrated solution increases, which reduces significantly the overall coefficient, U, for this purpose.To counteract this, use the power to counter or mixed.The diluted solution enters the second effect and follows the direction of feeding directly after passing the final effect of the first to complete evaporation at high temperature.

- Feed in parallel.When feed enters simultaneously for all purposes and meets the liquid concentrate in a single stream.It is a system used in the concentration of common salt solutions, where crystals deposited makes it difficult to provide the feed directly.

In general, we decide for a power system, it is necessary to make a calculation before evaporation performance for each of the systems.

If the input temperature of the food is quite lower than the boiling point in the first effect, in the case of direct currents all the heat that occurs in the first effect is intended to heat the food (heat sensitive) and very little to produce steam, which cause poor performance in the overall process of multiple effects.In this case it is preferred to the circulation counter.

To the contrary, when the solution enters the system at temperatures above the boiling point of the final effect will be more convenient food directly as the solution to enter the final effect on partially vaporize, producing a mist that does not have utilities later, then the solution cool to room temperature evaporation of the last effect and then the warming should go into each end.Centrifugal blowersCentrifugal blowers provide directional air flow by maximizing static pressure, making them optimalfor spot cooling and for air flow through a duct. Alternatively, their high suction can be used to hold anobject in position or their directed air flow can be used to move objects.

FeaturesSince the exhaust outlet is reduced to focus air to a specified direction, these blowers are used for spot cooling. The static pressure is also high,which makes them a suitable choice when cooling equipment through which air cannot flow easily or when blowing air using a duct.

SULPHUR BURNERS

There are basically two types of sulphur burners in use in sulphur burning acid plants; Sulphur Guns using an atomizing spray nozzle and Rotary Cup Burners.Two fluid atomizing nozzles are not commonly used.

1.Sulphur GunsA sulphur gun consists of a steam jacketed pipe with a atomizing spray nozzle mounted on the end.The steam jacketed pipe is long enough to place the spray nozzle at the front on the furnace an serves to keep the gun cool and maintain the sulphur in the molten state. Early sulphur guns used a standard Spraco type nozzle screwed onto the end of the sulphur gun.More sophisticated design are now available but the all work on the same principal.An atomizing spray nozzle is a device which breaks up a mass of liquid into a multitude of droplets, serving the general purpose of increasing the surface area.Spray nozzles create droplets by using the energy in a pressurized liquid to break up the liquid stream into droplets as the liquid passes through an orifice.In this case, the formation of droplets and the increase in surface area allows for the efficient and thorough combustion of sulphur in the sulphur furnace.Spray nozzles require a high pressure drop to effectively atomize the molten sulphur.Pump delivery pressures for molten sulphur are typically 690 kPag (100 psig) or higher.Spray nozzles with fixed orifice sizes are limited in their turndown ability.Typically the flow of molten sulphur is controlled by an upstream control valve.As the valve is closed a greater portion of the pressure drop is taken across the valve reducing the pressure at the spray nozzle.The effectiveness of the spray nozzle is greatly reduced as the inlet pressure is reduced.To overcome this problem the orifice in the spray nozzle must be changed to a smaller size.This requires a stoppage in the plant in order to change the spray nozzle.This problem is partially overcome by having multiple sulphur guns installed in the furnace.As plant production is reduced, sulphur guns are taken out of service so pressure at the spray nozzle is not significantly reduced.For small plants, multiple sulphur guns are not as practical or necessary as in larger plants.Some sulphur gun designs have been developed where the control of sulphur flow is done right at the spray nozzle.This eliminates the turndown problem of fixed orifice spray nozzles.A control rod runs down the length of the sulphur gun and extends through the spray nozzle orifice creating an annular space for sulphur flow.To increase sulphur flow, the control rod is extracted increasing the size of the annular space (i.e. orifice area).The advantage is that high pressures are maintained right at the inlet of the spray nozzle providing for good atomization at all flow rates.One disadvantage is that as the size of the orifice is reduced, the nozzle is more prone to blockage.

Rotary Cup BurnersA rotary cup burner consists of a spinning cup spinning at high speed which atomizes the molten sulphur. The spinning cup is driven by an electric motor through a drive belt system. Sulphur is fed to the burner at a low pressure (< 1 bar g) compared to a pressurized spray nozzle. The high speed rotating cup ensures that the sulphur is atomized to a high degree. The result is a short intense flame that provides for complete combustion of the sulphur to sulphur dioxide. The burner permits a high specific furnace load (2 Gcal/m) compared to the pressurized spray nozzle (0.75 Gcal/m).Since the burner does not rely on a high pressure drop, burner turndown ratios of 1:5 are possible the need to change any spray nozzles. The capacity of the burner is controlled by a control valve on the molten sulphur line. Typical burner capacities range from 5 to 600 tpd of sulphur.The burner can also be used to burn fuel oil during the preheating step and can be quickly switched over to sulphur when required. In FACT naphtha is used as fuel in the furnace.