RELACIONE LOS RESULTADOS OBTENIDOS CON LAS EXPECTATIVAS DE

75 4.2.6: Hardware Subsystem Specification:

Table 4.2 is the hardware subsystem specification of the envisaged system. It comprises of the components shown in this table.

Table 4.2 Main Features of the Hardware System

ITEM CONTENT

Controller IC Microcontroller

Interface IC Bus Expander

Power Supply 5-10V D.C/220V Ac

Dedicated Input Lines 8

Dedicated Output Lines 16

Input/Output Lines 36

Control Lines 17

Input Mode Digital (3-5V)

Output Mode Digital (3-5v)

Display Type LCD

Text Format Alphanumeric

Operating Temperature 60-70⁰ C

Power Extension Yes, 3

76 Fig 4.1: Block Diagram of SPDC Gas Supply Plant.

a. Well stream heaters

These heats up the incoming flow stream using hot water produced by a control boiler unit.

The purpose is to ensure that the gas/liquid mixture of the stream do not form hydrates as they pass through the inlet pressure reducing valves as shown in figure 4.1

The hydrates are solid in form and are a compound of the hydrocarbon gas and they are produced when the well stream pressure and temperature fall too low.

77 b. Dual inlet manifold

The regulated inlet incoming stream are connected to a dual inlet manifold so that using stop valves, any well stream can be passed to text separator so that the liquid/ gas ratio can be checked and composition analyzed.

The expected operating pressure and temperature of the flow line and of the inlet manifold to the operating inlet separator is 102.8 bar and 45^oc.

c. Inlet separator

This vessel has sufficient volume to allow the well to separate into its liquid and gas components so that they can be separately treated to produce a saleable product. (Figure 4.1) Here temperature, pressure and level is important. Gas and oil are separated. The gas is up and oil is down.

d. Test Separator

The inlet heater manifold is of the dual type and the flow lines from the well head are valved to allow for each to be switched to the test separator (Figure 4.1). The test separator is added as the compositions of the flow stream vary considerably and will change with time. Regular testing is essential to ensure good gas quality.

e. Propane Refrigeration

In this subsystem, hot propane gas returning from both the gas and liquid cooler is scrubbed to remove contamination and passes via a heat exchanger to a lobe type compressor which increases the pressure to raise the liquefying temperature. The pressurized propane then passes through a propane/lube oil separator which removes the compressor lubricant and on to a fin fan cooler then condenses the propane

f. Condensate processing.

The produced liquids from the inlet separator are successively reduced in pressure until the atmosphere pressure is reached. This ensures that the fuel produced liquid (condensate) is stabilized and safe for pumping to the Soku flow station.

The pump increases the pressure to about 55bar at 42^oC and thus ensures that there is no dangerous vapor emitted when the condensate reaches the flow station. The quality of the export

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condensate is controlled using analyzers and if it is not up to standard the system recycles until it is.

g. Gas compression.

A three stage centrifugal compressor driven by a gas turbine is used to increase the pressure of the gas produced during condensate stabilization to a level equal to the NAG from the gas cooler (around 98ba:;)

The Gas Compression also has an input from three locally situated flow stations which produce gas from other fields.

These flow stations are SOKU, EKULAMA AND NEMBE CREEK.

The input pressure to the compressor is around 6 bar and the output pressure around 98 bar which gives a stage compression ratio of 2:5. The estimated flow of gas from the stabilization process and flow station is 65.9mmsefd.

h. Condensate Export Pump

The condensate export pumps are high capacity/high heat pumps. The condensate export booster and export pumps take suction from either the condensate surge drum or the condensate storage tank. The pumps are provided with pressure relieve valves located downstream of the pump relieving of the suction of the export pump. They are set at a design pressure and temperature of 55bar and 42^o C respectively.

i. Dyhedration Teg and Transfer

The Teg tanks are vented to atmosphere. The Teg transfer pumps are local manual stop/start with low low liquid level operation shut down three (OSD 3)pump trip,

In industrial gas process, we have:

i. Normal operating condition ii. Alarm condition

iii. Trip condition

The process control system provides:

i. Centralized control and monitor of facilities from the control room.

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ii. Remote control of valves, motors and process equipment.

iii. Monitor Emergency Shut Down & blow down valve station (open, close). Color of indicator shall be red in an abnormal situation.

iv. Electric drivers status (run, stop) (green indicate operation v. process measurements

 All alarm condition

 All start & stop switches for operation of equipment

 All open & close switched for operation of valves Open loop response: In open loop no controllers are present.

Close loop response: In closed loop response, feedback controllers are present 4.4 The Proposed Design Process

The design methodologies used for the computer-based control systems are not appropriate for the SMS-based control systems, as they do not consider the GSM environment issues such as time delay caused by the call traffic, concurrent user access, GSM-based interface, and SMS-related safety. For example, an SMS-based control system has uncertainty about who the users are, how many users there will be, and where they are. In contrast for a typical distributed control system (DCS) the system load has been determined from conception. SMS-based process control systems have a variable working load. Few of the existing implementations in SMS- based process controls discuss the limitation caused by the GSM environment features such as GSM transmission latency and user isolation. Actually, GSM time delay and multiple users‘

collaboration are two essential issues, which must be addressed in the design of SMS-based control system. The objective of establishing SMS-based process control systems is to enhance rather than replace computer-based process control systems by adding an extra GSM-level in the hierarchy Yang et al (2003).

When designing the architecture for Remote SMS Based Monitoring Control system it would be interesting to bring modularity into the design by using layers as entities that can perform different tasks. So each layer can perform its own jobs and communicate closely with others to make the whole system work seamlessly. Different layers have different specializations, and are responsible for different tasks. Each layer acts independently Yeung and Huang (2001). Figure 4.2 shows the development process of the system. The process began with requirement

80

specification. The requirement is that the product should function properly by being able to control industrial variables and bring them to desired points. The specifications are defined. The components are analysed and the requirement further modified. The proposed system is designed using co-design approach involving hardware and software, The design system is simulated using a simulation tool called proteus ISIS simulation software,. The simulated work is tested for correctness using test data. If the result is correct and meet the specification the aim is achieved. If not the design step is fine toned again.

81 FINAL

REQUIREMENT SPECIFICATION

COMPONENT ANALYSIS

REQUIREMENT MODIFICATION

SYSTEM DESIGN

SIMULATION

DEVELOPMENT &

IMPLEMENTATION

TESTING

MEET SPECIFICATION

PRODUCT

CORRECT RESULT

MINOR CORRECTION

? MINOR CORRECTION

YES

NO RE-DESIGN

NO

NO

YES

Figure 4.2: The Development Process

82 4.4 Steps in Designing the Control Systems.

Figure 4.4 shows the steps involved in developing the control system. Firstly establish the control goal, Identify the variables. In this case the variables are temperature, pressure, level and flow rate. Write the specifications. Establish the system configuration and identify the actuators.

Obtain a model for the process, the actuator and sensor, Describe the controller and the parameter to be adjusted.

Figure 4.3: Steps in Designing Control Systems.

83

Fig 4.4: The Controller Block Diagram

The block diagram in figure 4.4 shows the main parts of a process loop controller:

 Receiver

The receiver converts the signal from the process variable (flow, pressure, etc.) into a signal which is suitable for the controller operating system

 Error Detector

The error Detector detects (finds) any difference between the measured process variable (measured value) and the set point (desired value).

 Control Amplifier

This unit adjusts the output signal to the correcting unit (final control element e.g.

control valve).the correcting unit corrects the error until the error signal is reduced to zero. When there is no error the control amplifier keeps the correcting unit at a fixed position. The operators can switch the system to manual and adjust the output signal by hand.

RECEIVER ^ERROR

DETECTOR

CONTROL AMPLIFIER

R

OUTPUT SIGNAL DESIRED

VALUE

TO CORRECTING UNIT SIGNAL

FROM

MEASURE PROCESS

PROCESS

VARIABLE _VARIABLEE

CONTROLLER

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 Controller Functions

There are up to three ways to adjust the controller. The older systems can be adjusted by a screwdriver. The new systems can be adjusted by changing the computer program.

The adjustments are:

 Proportional band (gain). This controls how much the error signal is amplified.

 Integral (reset). This is adjusted to cancel the final error which may be left after proportional action has finished.

 Derivative (rate). This is only used on slow moving loops (for example, temperature). It gives the system a quick start when an error occurs.

4.5 The Hardware Subsystem Design.

The hardware subsystem of the Gas/Oil Process Control System has data acquisition systems that convert the analog signals from various sensors to digital values that can be read in and processed by the microcontroller. The acquired data of any of the variables is selected, amplified, and converted into a form required by the microcontroller. Attached to the microcontroller are keyboard and the display unit which allow the user to enter set- point values, to read the current values of processed variables and to issue commands. Relays solenoids, D/A converters and other actuators are used to control the process variable under program command.

4.5.1 System Block Diagram

The aim of this work is to develop an SMS based system that will remotely monitor and control industrial process using ANN. Such a system must be equipped with DAS to monitor the condition of the plant, control the variables and in exceptional case report to remote personnel.

The block diagram in figure 4.5 shows the design concept. It has a number of hardware module designed around a standard microcontroller towards achieving this goal. The modules include the input and output interface modules linking the plant being monitored and the controller modules which include the artificial neural network that does the classification and pattern matching.

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Figure 4.5: The block diagram of the design concept of the system [Author]