Quick Links: Ammonia  |  Urea  |  DAP  |  ABC  |  SAP

 
ICI, U.K, technology utilizing steam naphtha reforming process.

The erstwhile engineering firm, Humphreys & Glasgow Ltd., London (now part of Jacobs Engineering, U.S.A.), designed, engineered and constructed the Ammonia and Urea plants.

Naphtha, a petroleum product, is the main raw material for producing Ammonia. It is first desulphurized and passed through primary reformer tubes, filled with catalyst, along with the required quantity of steam to yield a gaseous mixture of Hydrogen (H₂), Carbon Monoxide (CO), Carbon Dioxide (CO₂) and Methane (CH₄). The heat needed to complete the reaction is supplied by burning the fuel Naphtha in the Primary Reformer furnace. The gas is then passed through the Secondary Reformer along with the required quantity of air and steam to yield CO₂. H₂ and Nitrogen (N₂). The remaining CO is converted into CO₂ in two stages and then separated for use in Urea synthesis. The product gases consisting of N₂ and H₂ are compressed to about 180 kg/cm² pressure and passed through the Ammonia Synthesis Converter at about 480’C to produce gaseous Ammonia. This is further condensed and the liquid Ammonia obtained is either sent to the Urea plant or stored in the Horton Sphere.

The annual production capacity is 217,800 MT. (The highest annual production of 220,377 MTs. has been achieved in the year 2002-03.)

 
The Urea Plant is designed based on the CO₂ stripping process, licensed by Stamicarbon b.v., Netherlands. Ammonia (NH₃) and Carbon Dioxide (CO₂) are the main raw materials for Urea production. Initially, NH₃ and CO₂ are passed through a High Pressure Condenser where Ammonium Carbamate solution is formed. This is sent to an Autoclave where a portion of it gets converted to Urea. The unconverted Ammonium Coarbamate is stripped into NH₃ and CO₂ gases in a High Pressure Stripper using fresh CO₂ and then recycled back to the HP Condenser along with fresh Ammonia and dilute Ammonium Carbamate to again form a concentrated solution of Ammonium carbamate. This is a continuous cycle.

The Urea solution that comes from the Stripper is separated and concentrated in a low pressure section consisting of a rectification column, a flash vessel, pre evaporator and two stages of evaporation. The molten Urea solution coming from the final evaporator is taken to a revolving prill bucket at the top of the prill tower. The Urea solution is sprayed in the form of fine droplets by rotation of the prill bucket. The droplets solidify into prills before reaching the bottom of the prill tower as they come in contact with an upward flow of air. The prills are collected and sent for bagging or alternatively for storage in the Silo.

The Urea plant was revamped in March 2002. This resulted in improvement in the product quality with a marginal increase in production quantity. For better control of the operations, a new Distributed Control System replaced the obsolete pneumatic controls.

The Company’s original industrial license was to produce 3,40,000 MT of Urea annually. Subsequent to the revamp, the Government of India has recognised the enhancement in the capacity to 3,80,000 MT per annum. Maximum production of 3,80,000 MT has been achieved in the year 2002-03.

 
To diversify into phosphatic fertilizers, the Company commissioned a DAP Plant in 1986 with a licensed capacity of 1,38,000 MT/year. Imported Ammonia and Phosphoric Acid (H₃PO₄) are the main raw materials. Toyo Engineering Corporation, Japan and Toyo Engineering India Ltd., Mumbai, were the contractors. A shore terminal was set up to receive and store these materials.

Ammonia and Phosphoric Acid react in a Preneutraliser (reactor) to produce slurry of Mono Ammonium Phosphate (MAP). The slurry is then sprayed in a rotary granulator on a rolling bed of recycle seed material with simultaneous ammonisation to produce DAP. The wet granules obtained are dried to less than 1% moisture in a rotary drier and sent for screening. The product is cooled in a fluidised cooler and bagged.

In March/April 2002, the Plant was modernized by installing a pipe reactor system in the granulator with technology from Incur S.A., Spain. The controls have been upgraded to a Distributed Control System. The advantage from the revamp is the flexibility to produce additional fertilizer grades (i.e., 16:20:0 and 20:20:0) apart from DAP of a better quality in terms of size, shape and crushing strength.

With the introduction of improved operation and maintenance techniques and the resultant increase in the on stream efficiency of the plant, production of 2,20,000 MT per annum of DAP and complex fertilizers can be achieved.

The plant is capable of producing 12,000 MT/year of ABC and is based on indigenous technology. The main raw materials, NH3 and CO2, are first bubbled through water in a carbonation tower to form Ammonium Carbonate solution. This solution is fed to a Bi carbonation tower where it is further reacted with CO2 to form slurry of ABC. This slurry is pumped to a centrifuge to separate crystals of ABC from the mother liquor. The wet ABC crystals are dried in a rotary drier and then bagged.
 

 

PROJECT SUMMERY
Project Beginning	October 2005
Date of Mech. Completion	January 2006
Commercial Production	March 2006
Technology License	“Outo Kampu” Germany / F F I L India
LSTK Contractor	Furnace Fabric (India) Ltd., Mumbai
Plant Capacity	33000 MTPA
Project Cost	12 Crores

Manufacture of Sulphuric Acid
The Sulfuric Acid Plant technology is based on double conversion, double absorption contact sulfuric acid process using powder sulphur as raw material. It consists of three principal steps:

1. Combustion of Sulfur to produce Sulfur Dioxide gas. S + O₂ = SO₂

2. Conversion of Sulfur Dioxide gas to Sulfur Trioxide gas in the presence of vanadium catalysts. SO₂ + ½ O₂ = SO₃

3. Absorption of Sulfur Trioxide in sulfuric acid and reaction of water with Sulfur Trioxide to form Sulfuric Acid. SO₃ + H₂O = H₂SO₄

Raw sulphur is melted in pits with the help of steam coils using LP steam of 5kg/cm². This raw sulphur contains impurities like ash and organics which is removed by filtration using ‘Leaf Filter’. The molten sulphur, stored in a Clean pit at 135^oC is charged to the furnace through a sulphur gun which atomises the sulphur. Dry combustion air is introduced into the furnace. Sulphur burns to form sulphur-dioxide.

Sulphur-dioxide is converted into sulphur- trioxide using Vanadium Pentoxide as catalyst in first three beds of conversion maintaining gas inlet temperature of 410^oC to 450^oC at each stage. Third Converter bed outlet is taken to IAT (Intermediate Absorption Tower) where SO₃ is Absorbed in sulphuric acid to produce sulphuric acid. The SO₃ free gases left after this absorption are taken through heat exchanger for further conversion in fourth and fifth beds . Thus five beds of catalyst are used in 5 stages to achieve maximum conversion.

The advantage of this technology is that much better SO₂ to SO₃ conversion efficiencies are obtained due to this intermediate absorption, since the ‘product’ formed i.e. SO₃ has been removed and so the reaction tends to proceed more towards the product side. It is possible to get conversion efficiencies up to 99.8% compared to about 98% of earlier single absorption technology. Such high conversion efficiencies naturally result in lower SO₂ emissions to the environment from the process.

Conversion from SO₂ to SO₃ is Exothermic and heat is removed at each stage to produce steam. Fifth Converter bed outlet after complete conversion (99.8%) passes through final absorption tower to produce Sulphuric acid. Hence the process is called Double Conversion Double Absorption Process.