NATIONAL FERTILIZERS LIMITED VIJAIPUR GUNA (M.P.)
REPORT ON VOCATIONAL TRANING At (AMMONIA 1 (INSTRUMENTATION (INSTRUMENTATION)) ))
SUBMITTED TO Mr. D. R. Chowdhary (Chief Manager HRD) Mr. R. P. Gupta (Asst. Manager HRD)
SUBMITTED BY Hemant Pathak nd B. Tech (2 Year) Electronics & Communication
ACKNOWLEDGEMENT
I deeply acknowledge my sense of quietude to honorable Mr. D. R. Chowdhary (Chief Manager HRD) Mr. R. P. Gupta (Asst. Manager HRD) and staff for arranging my vocational training in their esteemed organization. I would also like to express my heartily thanks and indebtedness to Mr. B. Roy
(S. R. Manager)
Mr. R. Boipai
(Manager)
Mr. Sudesh Kumar
(Dy. Manager)
Mr. Shiv Prasad
(Asst. Manager)
Mr. Anshul Jain
(Asst. Manager)
Mr. A.K. Dwivedi
(Asst. Manager)
For their deep involvement, invaluable suggestion and continues motivation throughout this period. I am highly obliged to them for always being there in my needs. I cannot escape by giving thanks to all people directly or indirectly helping me for the completion of my training.
AMMONIA PROCESS DESIGN
Ammonia is produced from a mixture of hydrogen and nitrogen in a proportion of approximately approximately 3:1. Natural gas from from Gail is used used as the major major fuel for urea urea production. Hydrocarbon feed is completely desulphurized in the desulphurization section. The desulphurized hydrocarbon is reformed with steam and atmospheric air into process gas in the Primary and Secondary Reformer. Reformer. The gas contains mainly hydrogen, nitrogen, carbon monoxide and carbon dioxide. After that carbon monoxide is converted to carbon dioxide and hydrogen with steam to increase the yield of hydrogen. Then carbon dioxide is then absorbed in GV Section and the sent to ammonia synthesis chamber. The remaining carbon dioxide is then converted to methane in methanator using hydrogen. The purified synthesis gas is compressed to about 220 kg/cm2 and sent to the ammonia synthesis loop where it is converted into ammonia. This formed ammonia is then sent to urea plant for production of urea or sent to ammonia storage unit after passing it from cooling tower (which has a capacity of storing 10000MT). The flow diagram is shown below.
Steam Natural Gas form GAIL CH4
CO, CO2, H2
Desulphurization tank
Primary Reformer
Atmospheric Air
GV Section
CO2, H2, N2
CO to CO2 Converter
Secondary Reformer
CO, CO2, H2, N2
H2, N2
Synthesis Compressor
Absorbed CO2 to UREA PLANT
NH3 Reactor
Ammonia to Urea Plant or to Storage Unit
INSTRUMENTATION The Technology of using instruments to measure and control the chemical and physical properties properties of materials materials is called called Instrumentation. Instrumentation. It is a tool for efficient plant operation in any process industry. Efficiency means increased productivity, cost reduction and increased profitability of operation. When the instruments are used for the measurement and control of industrial manufacturing conversion process is known as process instrumentation. The role of instruments in particularly very pivotal in a fertilizer industry. Where instruments has to keep pace with the new developments to measure , record, analyze and control the highly complex chemical reaction, unit operation taking place at high pressure and temperature. Process plant consists of hundreds or even thousands of control loops all networked together to produce to be offered for sale. Each of these is controlled within a required operating range to ensure the quality of the end product. Each of these loops receives and internally creates disturbance that detrimentally affect the process variables and interaction from other loops in the network provides disturbances that influence the process variable. To reduce the effect of these load disturbance sensor the transmitter collect information about the process variable and relationship to some desired set point. This simple process control loop consists of these elements:1. 2. 3. 4.
Sensing Measurement Controlling element Final control element
MEASUREMENT Measurements have got to be one of the most important equipment in any processing plant. Any decision made on what the plant should do is based on what the measurement tell us. It is the integrated approach of application of knowledge, skill, standard practices to keep all the equipment’s/ equipment’s/ Instruments in healthy condition with their reliability, accuracy, for efficient & trouble free optimum operation of the plant In the context of process control, all controller decision is similarly passed on measurement. This section is going to deal with the instrument equipment normal used to measure and provide signals. We will look at the measurement of these process parameters.
Pressure
Flow
Level
Temperature Vibration PRESSURE
General Theory
Pressure is probably one of the most commonly measured variables in the process plant. It includes the measurement of steam pressure; feed water pressure, condenser pressure, process fluids, lubricating oil pressure and many more. Pressure is actually the measurement of force acting on area of surface. We could represent this as:
The units of measurement are either in pounds per square inch (PSI) in British units or Pascal’s (Pa) in metric. As one PSI is approximately 7000 Pa, we often use kPa and MPa as units of pressure.
Pressure Measurement
The object of pressure sensing is to produce a dial indication, control operation or a standard (4 - 20 mA) electronic signal that represents the pressure in a process. Common Pressure Detectors
Bourdon Tubes Bourdon tubes are circular-shaped tubes with oval cross sections. The pressure of the medium acts on the inside of the tube. The outward pressure on the oval cross section forces it to become rounded. Because of the curvature of the tube ring, the bourdon tube then bends as indicated in the direction of the arrow. Due to their robust construction, bourdon are often used in harsh environments and high pressures, but can also be used for very low pressures; the response time however, is slower than the bellows or diaphragm. Differential Pressure Transmitters
Most pressure transmitters are built around the pressure capsule concept. They are usually capable of measuring differential pressure (that is, the difference between a high pressure input and a low pressure input) and therefore, are usually called DP transmitters or DP cells. Figure illustrates a typical DP transmitter. A differential pressure capsule is mounted inside housing. One end of a force bar is connected to the capsule assembly so that the motion of the capsule can be transmitted to outside the housing. A sealing mechanism is used where the force bar penetrates the housing and also acts as the pivot point for the force bar. Provision is made in the housing for high- pressure fluid to be applied on one side of the capsule and low-
pressure fluid on the other. Any difference in pressure will cause the capsule to deflect and create motion in the force bar. The top end of the force bar is then connected to a position detector, which via an electronic system will produce a 4 20 ma signal that is proportional to the force bar movement. DP Transmitter Application A DP transmitter is used to measure the gas pressure (in gauge scale) inside a vessel. In this case, the low-pressure side of the transmitter is vented to atmosphere and the high-pressure side is connected to the vessel through an isolating valve. The isolating valve facilitates the removal of the transmitter. The output of the DP transmitter is proportional to the gauge pressure of the gas, i.e., 4 mA when pressure is 20 kPa and 20 mA when pressure is 30 kPa.
STRAIN GAUGES The strain gauge is a device that can be affixed to the surface of an object to detect the force applied to the object. One form of the strain gauge is a metal wire of very small diameter that is attached to the surface of a device being monitored.
For a metal, the electrical resistance will increase as the length of the metal increases or as the cross sectional diameter decreases. When force is applied as indicated in Figure 8, the overall length of the wire tends to increase while the cross-sectional area decreases. The amount of increase in resistance is proportional to the force that produced the change in length and area. The output of the strain gauge is a change in resistance that can be measured by the input circuit circuit of an amplifier. amplifier.
The change change in the process process pressure pressure will will cause a
resistive change in the strain gauges, which is then used to produce a 4-20 mA signal.
FLOW MEASUREMENT There are various methods used to measure the flow rate of steam, water, lubricants, air, etc., in a nuclear generating station. However, in this module will look at the most common, namely the DP cell type flow detector. Also in this section we will discuss the application of a square root extractor and cut-off relay plus the possible sources of errors in flow measurements and different failure modes that can occur.
Flow Detectors
Orifice Plate
The orifice plate is the most common form of restriction that
is
used
measurement.
in An
flow orifice
plate is basically a thin metal plate with a hole bored in the center. It has a tab on one side where the specification of the plate is stamped. The upstream side of the orifice plate usually has a sharp, edge. With an orifice plate in the pipe work, static pressure increases slightly upstream of the orifice (due to back pressure effect) and then decreases sharply as the flow passes through the orifice, reaching a minimum at a point called the vena contracta where the velocity of the flow is at a maximum. Beyond this point, static pressure starts to recover as the flow slows down. However, with an orifice plate, static pressure downstream is always considerably lower than the upstream pressure. In addition some pressure energy is converted to sound and heat due to friction and turbulence at the orifice plate. Figure shows the pressure profile of an orifice plate installation.
Advantages and Disadvantages of Orifice Plates Advantages of orifice plates include: • High differential pressure generated • Exhaustive data available • Low purchase price and installation cost • Easy replacement
Disadvantages include: • High permanent pressure loss implies higher pumping cost. • Cannot be used on dirty fluids, slurries or wet steam as erosion will alter the differential pressure generated by the orifice plate.
LEVEL MEASUREMENT Accurate continuous measurement of volume of fluid in containers has always been a challenge to industry. This is even more so in the nuclear station environment where the fluid could be acidic/caustic or under very high pressure/temperature. We will now examine the measurement of fluid level in vessels and the effect of temperature and pressure on this measurement. We will also consider the operating environment on the measurement and the possible modes of device failure.
Open Tank Measurement The simplest application is the fluid level in an open tank. Figure shows a typical open tank level measurement installation using a pressure capsule level transmitter
Closed Tank Measurement Should the tank be closed and a gas or vapour exists on top of the liquid,
the gas pressure must be compensated for. A change in the gas pressure will cause a change in transmitter output. Moreover, the pressure exerted by the gas phase may be so high that the hydrostatic pressure of the liquid column becomes insignificant. For example, example, the measured measured hydrostatic head in a
boiler may be
only three meters (30 kPa) or so, whereas the steam pressure is typically 5 MPa. Compensation can be achieved by applying the gas pressure to both the high and low-pressure sides of the level transmitter. This cover gas pressure is thus used as a back pressure or reference pressure on the LP side of the DP cell. One can also immediately see the need for the three-valve manifold to protect the DP cell against these pressures.
Effect of Temperature on Level Measurement Level measurement measurement systems that use differential pressure ΔP as the sensing method, are by their their very nature affected affected by temperature temperature and pressure. Recall that the measured height H of a column of liquid is directly proportional to the pressure P exerted at the base of the column and inversely proportional to the density ρ of the liquid. H α P/ρ Density (mass per unit volume) of a liquid or gas is inversely proportional to its temperature. ρ α 1/ T Thus, for any given amount of liquid in a container, the pressure P exerted at the base will remain constant, but the height will vary directly with the temperature. HαT
Effect of Pressure on Level Measurement Level measurement systems that use differential pressure ΔP as the sensing method, are also affected by pressure, although not to the same degree as temperature mentioned in the previous section. Again the measured height H of a column of liquid is directly proportional to the pressure PL exerted at the base of the column by the liquid and inversely proportional to the the density ρ of the liquid: H α PL/ ρ Density (mass per unit volume) of a liquid or gas is directly proportional to the process or system pressure Ps. ρ α Ps Thus, for any given amount of liquid in a container, the pressure PL (liquid pressure) exerted at the base of the container by the liquid will remain constant, but the height will vary inversely with the process or system pressure. H α 1/Ps Most liquids are fairly incompressible and the process pressure will not affect the level unless there is significant vapour content.
TEMPERATURE MEASUREMENT Every aspect of our lives, both at home and at work, is influenced by temperature. Temperature measuring devices have been in existence for centuries. The age-old mercury in glass thermometer is still used today and why not? The principle of operation is ageless as the device itself. Its operation was based on the temperature expansion of fluids (mercury or alcohol). As the temperature increased the fluid in a small reservoir or bulb expanded and a small column of the fluid was forced up a tube. You will find the same theory is used in many modern thermostats today. In this module we will look at the theory and operation of some temperature measuring devices commonly found in a generating station. These include thermocouples, thermostats and resistive temperature devices. Thermocouples (T/C) and resistive temperature devices (RTD) are generally connected to control logic or instrumentation for continuous monitoring of temperature.
Thermostats are used for direct positive control of the
temperature of a system within preset limits
TEMPERATURE MEASURING INSTRUMENTS:1. Mercury – in – Glass Thermometers. 2. Bimetallic Thermometers. 3. Pressure-Spring Thermometers. 4. Thermocouples. 5. Resistance Thermometers. 6. Pyrometers.
Resistance Temperature Detector (RTD) Every type of metal has a unique composition and has a different resistance to the flow of electrical electrical current. This is termed termed the resistively resistively constant for that metal. For most metals metals the change in electrical resistance resistance is directly proportional proportional to its change change in temperature temperature and is linear over a range of of temperatures. temperatures. This constant factor called the temperature coefficient of electrical resistance (short formed TCR) is the basis of resistance resistance temperature temperature detectors.
The RTD can can
actually be regarded as a high precision wire wound resistor whose resistance varies with temperature.
By measuring measuring the resistance resistance of the metal, its
temperature can be determined. Several different pure metals (such as platinum, nickel and copper) copper) can be used in the manufacture of of an RTD. A typical RTD probe contains a coil of very fine metal wire, allowing for a large resistance change without a great space requirement. Usually, platinum RTDs are used as as process temperature monitors because of their accuracy and linearity. To detect the small variations of resistance of the RTD, a temperature transmitter in the form of a Wheatstone bridge is generally generally used. The circuit compares the RTD value with three known and highly accurate resistors.
RTD using a Wheatstone bridge
Advantages of RTD:
The response time compared to thermocouples is very fast. In the order of fractions of a second.
An RTD will not experience drift problems because it is not self- powered.
Within its range it is more accurate and has higher sensitivity than a thermocouple. In an installation installation where long leads are required, the RTD does not require special extension cable.
Unlike thermocouples, radioactive radiation (beta, gamma and neutrons) has minimal effect on RTDs since the parameter measured is resistance, not voltage.
Disadvantages:
Because the metal used for a RTD must be in its purest form, they are much more expensive than thermocouples.
In general, an RTD is not capable of measuring as wide a temperature range as a thermocouple.
A power supply failure can cause erroneous readings
Small changes in resistance are being measured, thus all connections must be tight and free of corrosion, c orrosion, which will create errors.
Among the many uses in a nuclear station, RTDs can be found in the reactor area temperature measurement and fuel channel coolant temperature.
Failure Modes:
An open circuit in the RTD or in the wiring between the RTD and the bridge will cause a high temperature reading.
Loss of power or a short within the RTD will cause a low temperature reading.
Thermocouple (T/C) A thermocouple consists of two pieces of dissimilar metals with their ends joined together (by twisting, soldering or welding). When heat is applied to the junction, a voltage, in the range of mili-volts (mV), is generated.
A thermocouple is
therefore said to be self-powered. Shown in Figure is a completed thermocouple circuit.
The voltage generated at each junction depends on junction temperature. If temperature T1 is higher than T2, then the voltage generated at Junction 1 will be higher than that at Junction 2. In the above circuit, the loop current shown on the galvanometer depends on the relative
magnitude
of
the
voltages at the two junctions.
Advantages of thermocouples: thermocouples:
Thermocouples are used on most most transformers. transformers. The hot junction junction is inside the transformer oil and the cold junction at the meter mounted on the outside. With this simple and rugged installation, the the meter directly directly reads the temperature rise of oil above the ambient temperature of the location.
In general, thermocouples are used exclusively around the turbine hall because of their rugged construction and low cost.
A thermocouple is capable of measuring a wider temperature range than an RTD.
Disadvantages of thermocouples:
If the thermocouple is located some distance away from the measuring device, expensive extension grade thermocouple wires or compensating cables have to be used.
Thermocouples are not used in areas where high radiation fields are present (for example, in the reactor reactor vault). Radioactive radiation radiation (e.g., Beta radiation from neutron activation), will induce a voltage in the thermocouple wires. wires. Since the signal signal from thermocouple thermocouple is also a voltage, the induced voltage will cause an error in the temperature transmitter output.
Thermocouples are slower in response than RTDs
If the control logic is remotely located and temperature transmitters (millivolt to milli- amp transducers) are used, a power supply failure will of course cause faulty readings.
Bimetallic Strips A bimetallic strip is constructed by bonding two metals with different coefficients of thermal expansion expansion (Figure 10). If heat is applied to one end of the strip, the metal with the higher coefficient of expansion will expand more readily than the lower one. As a result, the the whole metallic strip will bend in the direction direction of the metal with the lower coefficient.
FINAL CONTROL ELEMENTS There are many types of final control elements including valves, dampers, feeders, louvers, and variable speed drive devices, although in general the vast majority of final control elements found in the industrial control world are pneumatically actuated valves. CONTROL VALVE
A valve with actuator that automatically, fully or partially opens or closes the valve to a position dictated by signals transmitted from controlling instruments can be called as a control valve. Importance of Control Valve
•
The actual purpose of the final control element is to regulate the flow of the process fluid strictly in accordance with the dictates of the controller output (PD). In other words the valve must move to a position represented by the value of the PD. The faster and more more accurately the valve valve follows these these dictates the better the control variance becomes.
•
The importance of the final control element cannot be overestimated. Many people mistakenly believe that the valve is not really critical to the control performance.
DISTRIBUTED CONTROL SYSTEM The old system in CPP Plant was single loop controller based, which came in beginning of year 1984, at the time of Vijaipur-1 project. The system is now almost 30 years old and fast moving towards abolescence and non-availablity of spears. LIMITATIONS OF OLD SYSTEM:-
1. Non-working data acquisition system. 2. Non reliable recording with high maintenance cost. 3. Optimization through cascaded loops not possible. 4. Non redundant system. 5. Un-predictive failure due to ageing problem. WHY WE NEED DCS???
Earlier a conventional split Architecture type SINGLE LOOP CONTROLLER named as SLPC . The basic process control system for any hazardous chemical/ petrochemical process plant shall have a high rate of reliability and availability as the loss of control can create an unsafe situation.
WHAT IS DCS??? It is a process control system that uses a network to interconnect interconnect
sensors,
controllers, operator, terminals and actuators . DCS typically contains several computers for controls and uses proprietary interconnections.
DCS SYSTEM
This system includes both the field area , we also call it as the Hazardous area and the safe area. The hazardous area includes the transmitters from which field cables carrying signals are fed to the junction box where the cables are combined in a simplified form so that cables will be arrange in a proper manner. Then this system is divided in two cabinet system 1. Marshaling cabinet 2. System cabinet
Marshaling cabinet system:The field cables are fed to a safety barrier. The barriers supplies +24VDC power to the field transmitters. The barrier separates the hazardous area and the nonhazardous area. The MTL barriers are used in CPP plant. The barrier supplies 24VDC power but receive 4-20mA signal and a digital signal from the field transmitters. Then this 4-20mA signal is fed where this signal is converted into 1-5VDC signal and this signal is transmitted to the input card, which is located at the I/O i.e., END of this cabinet.
System cabinet:It consist of analog to digital converter if the signal is in form of analog it convert it to digital or vice versa also. Then this signal is fed to FCS(field control station) or controller CS3000 . This cabinet includes different I/O card, card, power supplies, CPU, communication modules, bus controllers. All the field instrument like transmitters and control valves are wired to these controllers. Then there is Operator station where the process of monitoring and operating is done. Communication bus are used to communicate between controllers and
operator station station and then then a ETHERNET ETHERNET cable is used to to connect engineering station and other supervisory sup ervisory computers. And at last if needed to convert the current of 4-20mA into pneumatic signal 0.22
1kg/cm . This pneumatic signal helps in operating the control valve, which is a final control element.
FCS (Field Control Station):
Used to control the process. All the instruments and interlocks created by software reside in the memory mem ory of the FCS. All the field instruments like l ike transmitters and control valves are wired to the FCS. o
Reliable controller
o
Cost-effective and capable I/O subsystem
HIS (Human Interface Station)
Used to monitor the process and to operate various instruments. o
o
The operator station based on Windows XP or Windows2000. (Both are selectable.) HIS provides easy & flexible operation .
ENG (Engineering Station) o
Engineering Station is used to do the engineering builder for all the stations like HIS, FCS, CGW etc. ENG is a PC loaded with Engineering software.
Communication Bus: Used to communicate between the FCS and the OPS o
V-Net (Communication Bus) Real-time control bus. V-NET is a used for communication between HIS, FCS, CGW. Max 64 Stations can can be connected on V-net.
Transmission speed: 1 GBPS o
ETHERNET (Communication Bus) - it is a standard network in CS3000 to connect HIS, ENG and supervisory computers Transmission speed: 100 MBPS
PROGRAMMABLE PROGRAMMABLE LOGIC CONTROLLERS (PLC)
This training introduces the basic hardware and software components of a Programmable Programmable Controller (PLC). It details the architecture and basic instruction set common to all PLC’s. Basic programming techniques and logic designs are covered. This training describes the operating features of the PLC, the advantages of the PLC over hard-wired control systems, practical applications, troubleshooting troubleshooting and maintenance of PLC’s. PLC’s. INTRODUCTION TO PLCS Major Components of a Common PLC
POWER SUPPLY
From SENSORS
I M NO PD UU T L E
PROCESSOR
Pushbuttons , contacts,
PROGRAMMING DEVICE
OM UO TD PU UL TE
To OUTPUT Solenoids, contactors, alarms
Processor
The processor module contains the PLC’s microprocessor, microprocessor, its supporting circuitry, and its memory system. The main function of the microprocessor is to analyze data coming from field sensors through input modules, make decisions based on the user’s defined control program and return signal back through output modules to the field devices. Field sensors: switches, flow, level, pressure, temp. transmitters, etc. Field output devices: motors, valves, solenoids, lamps, or audible devices. The memory system in the processor module has two parts: a system memory and an application memory.
I/O Module
•
•
The I/O interface section of a PLC connects it to external field devices.
•
The main purpose of the I/O interface is to condition the various signals received from or sent to the external input and output devices.
•
Input modules converts signals from discrete or analog input devices to logic levels acceptable to PLC’s processor.
Output modules converts signal from the processor to levels capable of driving the connected discrete or analog output devices. Advantages of PLCs:
Less wiring.
Wiring between devices and relay contacts are done in the PLC program.
Easier and faster to make changes.
Trouble shooting aids make programming easier and reduce downtime.
Reliable components make these likely to operate for years before failure.
PROGRAMMING OF PLC
Normally Open (NO)
Normally Closed (NC)
Power flows through these contacts when they are closed. The normally open (NO) is true when the input or output status bit controlling the contact is 1. The normally closed (NC) is true when the input or output status bit controlling the contact is 0.
AND OPERATION
B
C
Rung
Each rung or network on a ladder program represents a logic operation. In the rung above, both inputs A and B must be true (1) in order for the output C to be true (1). OR OPERATION
Rung B
In the rung above, it can be seen that either input A or B is be true (1), or both are true, then the output C is true (1).
ESD (Emergency Shut Down) To protect people, environment and equipment’s safety systems are used that have to fulfill many more criteria their simply performing safety functions.
Safety:- Safety systems have always confirm to the latest standards such Availability: - If the process is to be cost effective, then they must run continuously. It is not accepted for them to stop because of error in the system. Cost Saving: - The startup costs combined with reliability maintenance and upgrade costs determine the cost effectiveness of a safety system. Openness: - The level of networking in automation solutions is growing all the time. At the same time, there is growing demand to reduce the numbers of different bus system.
