1. INTRODUCTION

KRIBHCO is a co-operative fertilizer company, which is produced the urea. KRIBHCO was incorporated on 17th April 1980 as a national level cooperative society jointly promoted by Government of India & agricultural co-operative all over the country.                          

1.1. Area & Location

The KRIBHCO (Hazira) unit is located around 15KM west of Surat & lies on the north bank of river Tapti. An all weather road from Surat to Hazira connect the plant site with the city. A canal belongs to irrigation department is running on the north side of the plant side is the feeding water from Ukai. A separate 66 KV lines vav substation  supplies power to site. A railway feeder line approximately 35 km long has connected the site with the Mumbai Ahmadabad main line. The total cost of plant is Rs.890 corers.

1.1.2 Technical features

The KRIBHCO Hazira plant in two phases produces a total of 1.45 million tons of urea per annum. The main plants consists of two ammonia plants, each of 1350 MTD capacity & four urea streams each of 1190 MTD capacity.

1.1.3 Performances

FINANCIAL

The Society has achieved excellent financial results for the financial year 2004-2005.The Society earned pre-tax profit of Rs. 185.83 crores during the year and a post tax profit of Rs. 140.59 crores. The net worth of the society is 2060.39 crores as on March 31, 2005. The Society has paid the highest dividend amount in the cooperative sector in the country.

PRODUCTION

KRIBHCO Plant in their 19th year of  commercial operation have produced 18.06 lakh MT of Urea and 10.92 lakh MT of Ammonia in the year 2004-2005 which corresponds to 104.41% and 108.90% of reassessed capacity of Urea and Ammonia  respectively. The production of urea during the year is the highest since inception. Society has broken several other records also in various fields. The cumulative Urea and Ammonia production since inception crossed 32 million MT and 19 million MT respectively has consistently occupied the first position the country for similar plants.

Fig1:- Overview of KRIBHCO, Surat

2.         UREA PLANT

 2.1        Urea Process description

The main final product in the KRIBHCO plant is Urea. For Urea basic need is Ammonia and carbon dioxide. These both come from Ammonia plant. In Urea plant different process is made to both this get Urea as final product.

2.2        Urea synthesis  

Liquid ammonia and carbon dioxide gas are two raw material for the manufacturing of urea. The reaction of the ammonia and carbon dioxide has to be carried out under high pressure and temperature to first form ammonium bicarbamate, a portion of which dehydrate to form urea and water according to the following reactions :-

2NH3 + CO2 = NH2COONH4 + 38000 Kcal moles ………..…..1

NH2COONH4 = CO NH22 + H2O  7700 KcalKg mole……2

Here the first reaction is highly exothermic and rapidly goes to completion and second is endothermic and is always incomplete. The overall reaction and heat has to be removed continuously for the equilibrium reaction to the process.

The conversion of ammonia carbamate to urea is depends upon

1. Reaction temperature and pressure

2. Molar ratio of ammonia and carbon dioxide gas water and carbon dioxide of feed  

    reactants and residence time.

The conversion increases with the increase of temperature. Since the presence of water tends to shift the equilibrium reaction in the backward direction. The pressure employed depends upon the temperature of reaction and has to be kept higher then the dissociation pressure of ammonium carbamate at that temperature. Higher ratio of ammonia and carbon dioxide increases conversion and also helps minimizing the corrosion    

2.3        Concentration and Prilling

Urea solution obtain in the last stage of the decomposition is normally of about 72%  to 75% strength. This is concentrated to produce urea of 99.7% concentration before prilling special care is essentially taken while concentrating the urea solution to limit the formation of biuret as it is considered harmful for the agricultural applications.especially for use in the plastic industry, the technique of crystallization under volume is adopted.

The method commonly employed is to carry out concentration of urea solution in one or two stage using conventional shell-tube type evaporators operating under voearne orin a talling film type swept evaporator. Melted yrea is then so spread from the top of the prilling tower using either multistage sprayer or at a prilling bucket. The prills get dried and cooled while falling, counter to a column of air rising upwards.

The urea prills thus get dried and cooled while falling, counter current to a column of air rising upwards. The urea prills thus produced contains biuret contents of 0.6% to 0.9%. depending upon the type of the evaporators, their location and pipe routing etc. the prills are collected at the urea silo or directly for bagging.

2.4        Application of Urea Plant

1. The fertilizer grade is used for the purpose of agricultural use in field in granular form due to its free floating characteristics. It is also used for making mixed fertilizers of different grades.
2. The feed grade urea is used as animal feed or as a supplement in some of the advanced countries.
3. The technical grade urea is the multi picture of the thermosetting resin. It is also used for the other chemicals pharma products etc.

3.        AMMONIA PLANT

3.1        INTRODUCTION

There are two streams of ammonia each of 1350 MTD capacity based on the renowned KELLOGG high pressure reforming technology. The gas obtain from the O.N.G.C, will be desulphurised, mixed with steam and passes on to the battery of tubes in a furnace called primary reformer where in the gas steam mixture is passed through the bed of nickel catalyst as well as heated externally to a temperature of 818 degree Celsius to reform the hydrocarbons into CO, CO2 and hydrogen. This partially reformed gas mixture is passed on to the secondary reformer  where in the air is added in stochiometric proportion to supply the nitrogen as well as to complete the reforming. The reformed gas passes through the high temperature and low temperature shift converters wherein the carbon monoxide is converted into the carbon dioxide. The CO2 is then removed from the gas mixture in the CO2 removal section employing the latest modified ben field process. The gas mixture is then methanted to remove the final traces of C0, Carbon dioxide. The gas mixture contains nitrogen and hydrogen in the ratio 1:3 is then compressed in synthesis gas compressor to a pressure of 20 atm and passed over the catalyst filled ammonia converter to synthesis ammonia. The ammonia formed is refrigerated to -30 degree centigrade and stored in atmospheric storage tank.

The waste heat generated during the process at the various stages of the exothermic reactions utilized to produce steam at 105 atm. pressure. This coupled with that from auxiliary boiler in the main reformer furnace provide power for all the drivers ion the ammonia plant as well as satisfied the process steam requirement, making the plant self sufficient, independent and reliable and energy efficient.

Fig2:- Process diagram of Ammonia Production

3.2        PROCESS DISCRIPTION

The manufacturing of the ammonia involves the following basic steps:-

1. DESULPHURISATION: Pre treatment of nature gas feed for removal of the sulphur, which is a poison for catalyst use in the ammonia plant.

2. REFORMING: Reforming of the desulphurised natural gas mixture of hydrogen and carbon oxides and additional of air in between two stages of reforming.

3. CO-CONVERTER: Conversion of CO into carbon dioxide.

4. CARBONDIOXIDE ABSORPTION & REMOVAL OF CARBON DIOXIDE: By absorption in alkaline absorbent.

5. METHANATION: Final purification of the gas in a methanator to give a pure synthesis gas.

6. AMMONIA SYNTHESIS: Compression of pure sysnthesis gas & sysnthesis of ammonia from hydrogen and nitrogen.

7. REFRIGERETION: Separation & purification of ammonia to get the final ammonia product.

4.        OFFSITE PLANT

DM PLANT (WATER TREATMENT PLANT)

4.1        INTRODUCTION:

Water which is required for industrial process use is available from two sources; surface supplies and underground supplies.

Natural water is likely to contain different concentration of the following salts :-

1. Alkaline salt such as bicarbonates and carbonates of Ca, Mg, Na.
2. Natural salt such as sulphate, chlorides and nitrates of Ca Mg, Na.

Other dissolved impurities such as silica, CO and metals like iron may also be present to a losser extent. The dissolved salts of Ca and Mg make the water hard.

This hard water, sulphate, chloride and carbonates of Ca, Mg, and Na are responsible for corrosion in boiler system. In view at there difficulties caused by impurities in water. DM water in high pressure boilers should have the following specifications:

Conductivity     0.3 micromhos\cm

Sio2 (silica)       0.01 ppm

Hardness            Nil

4.2        PROCESS   DESCRIPTION:

The DM plant travels the filtered water, received from water pre- treatment plant . The plant consists of four streams each designed for an output of 180 meter of demineralised water per hour .

The plant consist of following units :

1. Filter water storage
2. Filter water pump
3. Activated carbon filters
4. Strongly acidic cations units
5. Weakly basic anion units
6. Strongly basic anion units
7. Mixed bed units
8. DM water storage
9. DM water pump
10.  Acid and alkali storage and handling equipment.

4.3        STEPS  FOLLOWED  IN DM WATER  PLANT:  

Steps followed in DM water plant are as follows:

1. Removal of chlorine by passing the water through activated carbon                              

      filters.

2. Demineralisation through strongly acidic cation & (SAC) weakly basic anion. (WBA) and strongly basic anion (SBA) exchangers.
3. Removal of carbon-dioxide present in the decarbonised water in atmospheric forward craft type de-gassers.
4. Polishing of the demineralised water through mixed bed units consist of a mixture of strongly acidic and strongly basic ion exchange resins acting effectively as a series of demineralising pairs.

5.        FIELD INSTRUMENTATION

5.1        Level Measurement

Level measurement is one of the oldest measurements. Liquid level refers to the position or height of a liquid surface above a datum line. Level measurements are made to ascertain the quantity of the liquid held within a container. The measurement of industrial process level parameters is of great importance in the industrial field. Level affects both the pressure and rate of flow in and out of the container and as such its measurement and/or control is an important function in a variety of processes. Hence, the quality may be affected in case of error in the process fluid level.

1. RADAR TYPE LEVEL MEASUREMENT

Fig3. Radar Type Level Measurement

1.1        Operation:-

• The radar type transmitter utilizes linearly polarized microwave beam to detect the level. It operates by generating a pulse and measuring the time it takes for the echo to return.
• Transmitter is mounted on top of the tank. The time of the travel is an indication of the depth of the vapor space above the liquid in the tank.
• Temperature compensation is essential in this type of level measurement because the velocity of the wave is proportional to the square root of the temperature.
• This device can be used for both continuous and point measurement. Point measuring detectors are used for measurement of gas-liquid, liquid-liquid or gas-solid interface.

Fig4. Level Measurement

1.2        Advantages:-

• These types of detectors are non-contacting type. They do not have to make physical contact to measure the level.
• They have no moving parts.
• The reliability of the result is independent of changes in the composition, density, humidity, moisture content, electrical conductivity, or dielectric constant of the process fluid.
• Accuracy is high.

1.3        Disadvantages:-

• The radar type transmitter is subject to much interference, which affects the strength of the echo it receives. The echo can be weak due to dispersion and absorption.
• Expensive.
• Temperature compensation is essential.
• The dirt, irregular and slope surfaces affect the accuracy of the measurement

2. SIGHT GLASS LEVEL MEASUREMENT

Fig5. Sight Glass Level Measurement

Fig6. Level Measurement

1. Operation

• The sight glass (also called a gauge glass) is one of the widely used instruments. It is used for continuous indication of liquid level within a tank.
• It consists of a graduated tube of toughened glass which is connected to the         interior of the tank at the bottom in which the water level is required.
• Liquid level in the glass tube matches the level of liquid in the tank. As the level of liquid in the tank rises and falls, the level in the sight glass also rises and falls accordingly. Thus, by measuring the level in the sight glass, the level of the liquid in the tank is measured.
• In sight glass, it is not necessary to use the same liquid as in the tank. Any other desired liquid also can be used.
• When it is desired to measure liquid level with the liquid under pressure or in vacuum, the sight glass must be connected to the tank at the top as well at the bottom, otherwise pressure difference between the tank and sight glass would cause false reading .In this case, the glass tube is enclosed in protective housing, and two valves are provided for isolating the gauge from the tank in case breakage of the sight glass.
• A sight glass in high pressure tanks is used with appropriate safety precautions.

2.2        Advantages:-

• Direct reading is possible.
• Special designs are available for use up to 3160 C and 10,000 psi.
• Glassless designs are available in numerous materials for corrosion resistance.

2.3        Disadvantages:-

• It can be read only where the tank is located, which is not always convenient.
• Accuracy and readability depend on the cleanliness of the glass and fluid.
• Overlapping gauges are needed for long level spans.
• Since sight glasses are located on the outside of the tanks, the liquid in the sight glass may freeze in cold weather even though the liquid inside the tank does not and thus, it may cause error in the reading.

5.2        PRESSURE MEASUREMENT

Pressure measurement is undoubtedly one of the most common of all the measurements made on systems. In company with temperature and flow, pressure measurements are extensively used in industry, laboratories and many other fields for a wide variety of reasons. Pressure measurements are concerned not only with determination of force per unit area but are also involved in many liquid level, density, flow and temperature measurements. Measurement of pressure is also needed to maintain safe operating conditions, to help control a process and to provide test data. Nearly all industrial processes use liquids, gases or both. Controlling these processes requires the measurement and control of liquid and gas pressures. Thus, pressure measurement is one of the most important of all process measurements.

1. C-TYPE BOURDEN TUBE PRESSURE MEASUREENT

Fig7. C-Type Bourden Tube

1.1        Principle:-

• The Bourdon tube is the most frequently used mechanical type pressure gauge because of its simplicity and rugged construction.
• The action of the Bourdon gauge is based on the deflection of a hollow tube caused by the applied pressure difference.
• It covers ranges from 0-15 psig to 0-100,000 psig, as well as vacua from 0 to 30 inches of mercury.

1.2        Construction and Working:-

• The pressure responsive element of a Bourdon gauge consists essentially of a metal tube, called Bourdon tube, oval in cross-section and bent to form a circular segment of approximately 200 to 300 degrees.
• One end of the tube is closed but free to allow displacement under deforming action of the pressure difference across the tube walls.
• The other end of the tube is fixed and is open for the application of the pressure which is to be measured.
• The tube is soldered or welded to a socket at the base, through which pressure connection is made.
• The figure shows the schematic arrangement of a complete Bourdon tube gauge.
• As the fluid under pressure enters the Bourdon tube, it tries to change the section of the tube from oval to circular, and this tends to straighten out the tube with a consequent increase in its radius of curvature i.e. free end moves away from the centre.
• The free end of the tube is connected to a spring loaded linkage which amplifies the displacement and transmits it to the angular rotation of a pointer over a calibrated scale to give a mechanical indication of pressure.
• The tip of the Bourdon tube is connected to a segmental lever through an adjustable length link. The lever length also may be adjustable.
• The segmental lever end on the segment side is provided with a rack which meshes to a suitable pinion mounted on a spindle. The segmental lever is suitably pivoted and the spindle holds the pointer, as shown in figure.
• A hairspring is sometimes used to fasten the spindle to the frame of the instrument to provide the necessary tension for proper meshing of the gear teeth, thereby freeing the system from backlash (lost motion). Any error due to friction in the spindle bearing is known as ‘lost motion’.
• Bourdon tubes are made of a number of materials, depending upon the fluid and the pressure for which they are used, such as phosphor bronze, alloy steel, stainless steel, ‘Monel’ metal, and beryllium copper. The material chosen to fabricate a Bourdon tube will relate to the instrument sensitivity, accuracy and precision.
• For adequate reliability, the materials for Bourdon tubes must have good elastic or spring characteristics.
• Bourdon tubes are generally made in three shapes:

• C-type
• Helical type
• Spiral type

1.3        Advantages:-

• Their cost is low.
• They have simple construction.
• It is capable to measure gauge, absolute and differential pressures.
• They have been time-tested in applications.
• These tubes are available in a wide variety of ranges, including very high ranges.
• They are adaptable to strain, capacitance, magnetic and other electrical transducers.
• They allow high accuracy, especially in relation to cost.

1.4        Disadvantages:-

• They have low spring gradient (i.e. below 50 psig).
• They have a slow response to pressure changes.
• They usually require geared movement for amplification.
• They are susceptible to shock and vibration.
• They are susceptible to hysteresis.

5.3        FLOW MEASUREMENT

In Instrumentation system and process control flow measurement is an important method for the measurement of flow rates of different process variables. Flow measurement devices are widely useful in various industrial applications to measure the flow rates of liquid , different fluids, vapours , gases, slurries etc. the fluid matter may be clean or dirty, wet or dry.

By mechanical means the flow measurement system or device operates by placing an obstruction in the fluid path. Due to this obstruction pressure gets changed with respect to rate of flow. The differential pressure sensor is used to measure the pressure before and after the obstacle. This differential pressure provides the rate of flow.

Flow measurement can also be possible by electrical methods like allowing the liquid to flow in a magnetic fields, change in the resistance of an element placed in fluid path etc. The developed Electrical voltage is calibrated so as to read the proportional rate of flow.

1. TRANSIT TIME ULTRASONIC FLOWMETER

1.1        Operation

• The Ultrasonic waves are transmitted from transducer A to transducer B and vice-versa.
• These transducers are placed into or onto the pipe line and both work as a transmitter and receiver.
• An ultrasonic oscillator is connected to generate the ultrasonic pulses and applied to transducer A or B, which ever acts as transmitter. Similarly one of them acts as a receiver.
• The flow of fluids is measured by measuring the time elapsed for an ultrasonic pulse to travel through pipe section.
•   ∆T = 2D.v.cosφ/c*c

2.        DOPPLER SHIFT ULTRASONIC FLOWMETER

Fig.8 Ultrasonic Flow Measurement

2.1        Operation

• The ultrasonic wave is transmitted through the pipe wall into the fluid.
• Some part of the ultrasonic wave is reflected by the bubbles or particles in the fluid.
• The reflected waves are detected by the receiver transducer placed at the pipe wall.
• According to Doppler principle if the reflectors are travelling at fluid velocity, the frequency of reflected wave is shifted in proportion to the flow velocity.

5.3        Advantages

• No moving part is involved in process or system so no chance of sparking and arcing.
• Installation is possible without shutting down the process.
• Design can be altered or changed according to flow rates.
• Suitable for corrosive, erosive, slurries and viscous fluids.

5.4        Disadvantages

• The pipeline should be tight.
• High cost.
• Maximum operating temperature for ultrasonic flow meter is 100 degree centigrade.
• Air bubbles or solid particles present in the liquid may affect the accuracy of the system.

5.4        Current to Pressure Convertor:

Air supply (Pressure)

4-20 ma

Fig9. I/P Convertor

1.1        Principle:-

• In order for an electronic control signal to operate a pneumatic instrument (such as an electronic controller operating valve), the electronic signal must be changed into pneumatic signal.
• This is accomplished by using I/P converter or current to pneumatic transducer.
• I/P converters accept 4 to 20 mA and provide a pneumatic output of 3 to 15 psi.
• However, an essential characteristic of a transducer is that it is able to produce an output signal that is proportional to the input.

1.2        Operation:-

• Figure shows I/P converter in which a coil is positioned in the field of a fixed permanent magnet.
• The coil magnet mechanism converts the signal to motion by the interaction of the two magnet fields.
• One field surrounds the permanent magnet and the other field surrounds the force coil.
• The magnetic field in the coil is produced due to the current flowing through the coil.
• The lines of flux of the magnetic coil are concentrated in the magnet.
• An increase in the input current forces the coil to move because of the intensified magnetic field surrounding the coil. A decrease in the current causes the coil to move in the opposite direction.
• The coil movement changes the baffle-nozzle relationship.
• A change in the nozzle back pressure is sensed by a diaphragm in the relay. The movement of diaphragm positions a valve. This valve position determines the signal output value from the relay.
• A balance force on the beam is provided by the feed back bellows.
• A spring pivot provides a pivot point for the beam. As the coil moves up, the baffle moves toward the nozzle.

CONCLUSION

During my training at KRIBHCO, Surat I learned & improved my practical knowledge & also got a chance to learn & apply, theoretical knowledge in my training period.

In my vocational training as a trainee helped me to gain knowledge  as per my  technical subjects  & how these concepts is applied in the industry practically. During these days I also learned how we can work in industry as well as in professional environment.

In training as a trainee I develop my skills and improved my knowledge as per my subjects. Here I learned as a team to achieve a definite goal in a desired period of time on a professional front.  The experienced I gained there, will help me to work more efficiently in the corporate world.