As Snr. Instrument and Control Engineer that supports the operation. In this case study, the writer supports the Corrosion and Inspection Team. On certain occasions, a study will be performed to support their objective. The case study is to provide cool fluid to the cooling probe in order to simulate the potential TLC in the subsea multiphase pipeline. This led to increasing the integrity of the subsea multiphase pipeline.
This is not a daily task for an instrumentation engineer. However, a variety of instrumentation devices or equipment includes electronic, pneumatic, and hydraulic therefore in certain cases the equipment is categorized as instrumentation. The writer provides options and schemes to solve their problem.
I. BACKGROUND
As part of the mitigation of ToLC in the pipeline, VCI (Volatile Corrosion Inhibitor) will be injected. To monitor the effectiveness of VCI injection, a cooling probe needs to be installed. The cooling probe will simulate the potential TLC in the subsea multiphase pipeline, which is achieved by cooling the probe which simulates the cooling effect of seawater. With this new method, can continuously monitor the ToLC rate and furthermore evaluate the chemical performance that has been applied.
II. Objective
Trial vortex tube performance to achieve cool down inside cooling probe with the temperature at 10-20 degC.
III. Methodology
The methodology to cool down inside the cooling probe could be a number of possibilities to cool down the probe. The writer proposes using a vortex cooling product from Vortec (https://www.vortec.com/en-us/vortex-coolers). The selected model vortex tube requires a continuous gas supply 11 SCFM with pressure inlet available. The cold fraction is expected 90%.
This is sample measured on manufactured laboratories for 208-15-HSS tube at 100 psig:
Cold fraction (%)
Valve open
100
0°-full closed
90
90° counter clockwise
80
210° CCW
70
380° CCW (one full turn plus 20°)
60
570° CCW (one and a half full turns plus 30°)
50
750° CCW (two full turns plus 30°)
The cold fraction is to predict the temperature drops and rises in the vortex tubes for various inlet temperatures. The cold fraction will determine the opening valve at the hot end.
Backpressure exceeding 5 psig (0.3 barg) will reduce the performance of the vortex tube.
The cooling fluid is using nitrogen from a bottle of nitrogen. As consequence, the instrument air is not available on the platform. The drawback of using a rack of bottled nitrogen on an offshore platform is logistic issues. Since it is not intended for continuous operation but rather for evaluation in certain periods of time.
To control the desired cold temperature, cold airflow and temperature are easily controlled by adjusting the slotted valve in the hot air outlet. Opening the valve reduces the cold airflow and the cold air temperature. Closing the valve increases the cold airflow and the cold air temperature. Adjusting the valve will alter the cold fraction; the maximum cold fraction could be achieved at 90% cold fraction. To achieve 90% cold fraction valve is turned 90° counter clockwise.
Since the supply is using a rack of bottle nitrogen, inlet pressure to vortex tube is not constant and it will decrease continuously. Thus it will affect the outlet temperature in both the cold and hot ends as per table 1. The temperature range is represented in table 1. The table is derived from absolute ratio table 3.
Cold Fraction
90
PSIG/BAR
OC
1.4
Temperature Cold End
25.106
Temperature Hot End
121.133
2.8
Temperature Cold End
18.122
Temperature Hot End
163.036
4.1
Temperature Cold End
18.122
Temperature Hot End
172.347
5.5
Temperature Cold End
16.958
Temperature Hot End
179.913
6.9
Temperature Cold End
15.795
Temperature Hot End
181.659
8.3
Temperature Cold End
15.212
Temperature Hot End
184.569
9.7
Temperature Cold End
14.631
Temperature Hot End
185.733
Table 1
Pressure inlet is maintained by pressure regulator valve (set @6.9 barg). Outlet pressure regulators will fluctuate around 6.9 barg – 5.88 barg according to the flow rate curve. Hence outlet cold end will fluctuate at 14oC-18oC.
To protect vortex tube from excess pressure, Pressure Safety Valve (PSV) at the inlet line vortex tube is installed to avoid inlet pressure above 10.3 barg.
With selected vortex tube and cold fraction set 90% cooling capacity yield 640 BTU/Hr.
Inside the cooling probe, 2 heat transfer convection occur, namely natural convection and forced convection. However, in this cooling system, only force convection is considered. Natural convection is ignored since the focus is the cooling surface temperature of the element sensor.
Force convection at the surface cooling probe is calculated using assumption 80OC at surface temperature and flow cool air at 15OC which resulted in loss heat rate 77.876 BTU/Hr. Thus using a cooling capacity 640 BTU/Hr is adequate to maintain 15 – 20OC at the surface of the element sensor to create condensation
The performance of the vortex tube is depending on the stability of inlet pressure and flow rate. Replacement of bottle nitrogen is calculated based on the performance vortex tube. The performance of vortex tube is optimum when the flow rate is maintained at more or less 11 MMSCFD. To maintain the optimum flow rate range, bottle nitrogen should be replaced when pressure below 17 barg.
It is estimated that for 8 hours of sampling, it requires 6 bottles of nitrogen to supply the vortex tube at 11 SCFM.
The convection heat transfer of the cooling probe is complicated since it involves fluid motion as well as heat conduction. The convective heat transfer coefficient “h” strongly depends on the fluid properties and roughness of the solid surface, and the type of fluid flow (laminar or turbulent).
The case of cooling probe heat transfer is similar to flow over a flat plate. This analogy is adopted since heat transfer is focused on the bottom of the sensor surface.
It is found that the Nusselt number can be expressed as:
where L=D=Diameter
For isothermal surface plates, the local Nusselt number for turbulent is:
Assumptions:
It is assumed that the velocity of the fluid is zero at the surface; this assumption is called no-slip condition. As a result, the heat transfers from the solid surface to the fluid layer adjacent to the surface by pure conduction, since the fluid is motionless.
Which is valid for 5 x 105 < Re < 107 and 0.6 < Pr < 60. The fluid properties are evaluated at the free-steam temperature T∞, except for µs which is evaluated at surface temperature.
Heat Loss required (Please refer to Calculation Note – Attachment 1)
This is one of my case studies to calculate the volume vessel of a Diesel Tank.
The purpose of the scope of work was to improve diesel fuel management as part of a fuel management improvement campaign.
The objective is to convert measurement height liquid in Diesel Tank to volume basis (in liter). The level transmitter type was DP(Differential Pressure) transmitter using hydrostatic pressure to measure the level.
According to process calculation of vessel diesel tank.
(Partial liquid volume of the tank with ellipsoidal head).
where
It was Putting this equation direct to DCS (TDC3000) one function of arccos was not available
Option I :
Using the trigonometry function found on the list of Built-in Arithmetic
This approach is manipulating the original equation using the available function on the controller PCS, unfortunately, it becomes more complicated, but the advantage it has no error
Option II:
Using the Regression Linear approach.
Option III: Totalizer
Totalizer is one feature that is available in flow computers. This totalizer has a function to accumulate the volume.
Error in option I and option II originated from % error measurement and % error calculation due to error measurement. That is the reason why it doesn’t match the sounding table
On the other hand, totalizers don’t respect the shape of the vessel. Therefore it could minimize the error resulting from measurement, However, the outlet of the vessel should be equipped with a totalizer the outlet
Thus the remaining volume vessel is Qremain=Qin-Qout.
This should be written in the PLC to retrieve the value in the control room along with the push button start and stop.
The scope of this project was to obtain tangible efficiency turbines through mass balance water input and output by the deployment of flow rate sensor from various point measurement inlet and outlet at Water Treatment Plant for Power plant (Coal). The application was for monitoring only. No control sequence or safety shutdown system involves.
Among these flowmeters, a specific case that drains our attention. It was solving the open channel flowmeter on the outfall unit from the condenser. The water cycle operation is never expected to shutdown, either 2 x 50% or 2 x 100% operation of power generation. This situation contributes to the complexity of hydraulic structure/weir installation.
An open channel flow meter is not frequently part of the scope project not many as flow meter carried in closed conduits that flow completely the piping system. In this article, I would walk you through to capture the problem encounter during the installation hydraulic structure of open channel flow meter. In the end, it will influence the selection sensor for open channel flowmeter to enable the installation and to eliminate the possibility of failure.
Weir, as seen in the construction design, is essentially a dam built across an open channel over which the liquid flows. It simple based on the design especially when selecting rectangular weir without end constructions. I overlooked the weir thickness requirement and installation method. The installation method is so crucial in order to place the weir as a hydraulic structure.
The requirement thickness should be calculated by a structural engineer in regard to force exerted on the weir. Moreover, the installation method should review by construction engineer since the water flow could not be stopped, only in certain circumstances, the water flow will undergo low flow rate.
The other difficulties factor is we don’t have structure or installation engineer, so we fully trust the responsible for structural and installation scope to the contractor. It was not all the contractor’s mistake since we didn’t request any calculation and installation procedure document.
All the explanation below is related to the projects.
II. PLC and HMI
I was in-charge for programming, designing, and configuring both Programmable Logic Controller (PLC) and Human Machine Interface (HMI). Although there is A comprehensive guide selection of PLC is available in relevant details such as IEC 61131-1 and IEC 61131-2.
In common practice especially for PLC package in an existing plant, PLC is selected based on, as follows:
Hazard and operability study (HAZOP) to identify the requirement of safety integrity level for the PLC
The capability to cope the application.
Project budget.
Certain population PLC on the User/Company premises.
Service availability PLC product on the country.
In this project, the PLC selection was toward to no.4 besides the project budget. It was agreed to use PLC Simatic S7-1200 CPU 1214C. S7-1200 is sufficient for the specified application. The main application was to monitor flowrates on different locations at demineralize water systems. There is no control and safety requirement for the shutdown process.
Nowadays, PLC developer is competing to create integrated automation software with one engineering environment and one software project for all automation tasks. Siemens has built an integrated software portal named as TIA portal. This is a Control Engineering 2012 Engineers’ Choice award winner. As a user I admit, it was really convenient and easy using Step 7 professional and RT advance. However if you are a new learner, it is recommended to read the guideline to familiar the program blocks. Selection engineering software depends on the controller model. Actually, STEP 7 Basic is sufficient. However, since the plant has various Siemens controllers into it is decided to use STEP 7 Professional.
Whether it’s the inexperienced or experienced writing the PLC program, simple ladder logic, and a step sequence is often the best solution. It was developed using ladder logic and function block diagram, Step 7 utilize grouping the ladder logic name as a network.
After deciding the PLC brand, there are several factors to be considered such as.
Power supply quality
PLC Program
Signal transmission
Conformance to Hazardous Area
II.1 Power Supply Quality
AC voltage is the main source power, vendors provide module AC to DC with various power wattage. Each power module will supply PLC rack. It will power the I/O module either through the back plane or cables. Most cases, field instrument is using dedicated AC to DC power supply. Power supply quality is important for a steady condition for the I/O module either analogue or digital module.
It should carefully evaluate when PLC power supply is the same source with an inductive load such as a motor. Power quality should be one of the considerations when utilizing 4-20mA analogue input. Power quality refers to the ability of electrical equipment to consume the energy being supplied to it. A number of power quality issues including electrical harmonics, poor power factor, voltage instability and imbalance impact on the efficiency of electrical equipment. Equipment instability and failure.
Below is a simplified interconnection diagram, one of example when power quality could interfere 4-20 mA signal and flickering digital signal. The symptoms analogue fluctuation and flickering always occur whenever the density sensor connected to the AI Module.
At first sight, we suspect it comes from inductance coupling between cable AC and analogue, digital wiring (24VDC). Although the arrangement cable inside the cabinet has been separated between AC and 24VDC. The distance is adequate to minimize inductance coupling using a cabinet with a width of 800 mm.
We also suspect from grounding issues. We have to provide proper grounding for the power supply PLC and power supply converter 220VAC to 24VDC. Since not all companies segregate between instrument grounding and power grounding only equipment with source 220VAC is connected to dispatch grounding.
In the end, we figure out that the problems are caused by power quality due to harmonics. So we decided to use AC to AC converter. It solves the problem.
II.3 PLC Program
PLC program of this project consists of:
Scaling complete with simulation input
Alarm (High only, High-high provides but not use since no emergency action applied for flowrate)
Totalizer
This program is a standard basis for a flowmeter. The scaling and alarm function block could be combined (as seen in figure 1). The function block is created by user from the basic function block.
Not all user function block requires developing from scratch. Siemens has provided additional add-on libraries available on their website. One of the examples is Totalizer.
II.3.1 Memory Capacity
The size of memory capacity depends on several factors even the style of programming could affect memory capacity. Deciding memory capacity is vital when the plant is continuously extended or expanded.
The other factor of memory capacity as following:
The number of input-output, number of variables, constant, and contribute to consume memory IO.
System architecture with other devices.
The individual style programming and programming language.
The Complexity of the application. Scaling, mapping, and alarm are typical or standard program. One of the examples complexity programs could be is represented in the control loop method. Feedforward, Close loop, 2 degrees of freedom control etc.
II.3.2 Scaling 4-20mA to Engineering Unit
Raw value as a representation of 4-20mA could have a different minimum or maximum value among the modules. The value to be determined based on the function purpose. Below are different full-scale ranges among the module.
The engineering unit scale between PLC and transmitters should be the same. Thus, a linearity relation between 4-20 mA and the engineering unit is created. 4 mA as lower range value and 20 mA as upper range value.
However, you need to decide the unit and scale to be sent from the transmitter.
In the example of a Magnetic flow transmitter, the information conveyed in 4-20mA could be presented in either velocity or flowrate. If you choose a velocity, in consequence, the flowrate equation should be created in PLC program.,
If the engineering unit scale between PLC and flow transmitter is different the linearity between the devices will be different. In addition, errors contribute to non-linearity. There is four error that contributes
Zero
Error
Span
Error
Linearity
Error
And
the combination above
In case
this happens, the display in the transmitter and HMI will be different.
II.3.3 Totalizer
Totalizer is used to determine the accumulative flowrate during a certain period. For example, “in the last 60 seconds, there have been 30 gallons of water flowing by the sensor.”
To obtain consistency accumulation during certain periodes, Totalizer should be considered as an interrupt. Thus regardless of the complexity of the program. It would give high priority to maintain a consistency time period.
One you should aware of when implementing Totalizer in the PLC program. The raw value should be limited for instance 0 to 27648. Over and under this value, it should be identified as an error. The error should not consider as a value in totalizer. It should hold totalizer or give input value 0 on the totalizer function block. Over and under range, the value could be used to identify short or loose cable wiring.
II.4 Signal Transmission
Selecting signal transmission to convey the information Besides conventional 4-20mA, the other option is to use HART. HART protocol offers a number of advantage however there are drawback should be considered.
Much technical literature is available to explain HART protocol in detail. The compatibility between HART and 4-20 mA wiring. Field transmitter complete feature HART enables to ease of calibration system.
Several advantage when using HART Protocol as following :
Not necessary to provide scaling analogue function block
Totalizer is not requiring defining the PLC program. Totalizer is available on certain field instruments. PLC will send a command to start and stop the Totalizer.
Besides the primary variable, the other parameter could be obtained. Other parameter known as a secondary variable, tertiary variable This variable could retrieve by three classes of HART commands:
Universal commands
Common Practice commands
Device-Specific commands
If there were concerns about hazardous areas, HART protocol is claimed to be more intrinsically safe.
Therefore, it is depicted that HART has an advantage over conventional 4-20mA. There are several things to be considered in order to use HART
Do they possess Asset Management
SystemCPU (processing unit) and AI cards should be compatible. For Siemens PLC, HART is using ET200. This series is far compared to the S7-1200 series
Version to be check
Selection of cabling system – Peer to peer or multi-drop.
Installing or enabling resistor 250 ohm. Scaling is not required even you could retrieve 3 data parameter simultaneously named as
PV; Primary Variable
SV; Secondary Variable
TV; Tertier Variable
II.5 Hazardous Area
Mostly, PLC is located in a safe area i.e. technical room, meanwhile, the field transmitter is located in a hazardous area. Hazardous area certification for field transmitters should be inline with the wiring. When using conventional 4-20mA, the wiring in the hazardous area needs to be check. Mostly, when the PLC and the field transmitter have different hazardous areas.
III. HMI
Human Machine Interface is a user interface or dashboard that connects a person to a machine, system, or device. It is stand-alone and independent from the existing DCS system.
The selection of HMI is based on the architecture of the application. The architecture of HMI/SCADA will determine the license to be purchased. There is more detail, for selection HMIa . Below are several overviews
Independent/Stand Alone. The license either development or runtime license.
SCADA Based, If SCADA is selected next it to decide the sharing data., DDE Server, OPC or combination
SCADA based definitely require development license
Web client
This
project is using Wincc RT Advance
There is an option based on feature and scale-able of
Basic
Comfort
Advanced
Professional
The reason to deploy Wincc RT Advance it has minimum features to covers the flowmeter application. In general, the HMI consist of
Representation displays such as P&ID. Symbol and coloring mostly based on the industries. The company could also produce specification and regulation for symbol and coloring
Alarm management, it will be guided through ISA. Alarm animation is important for operator to identify situation.
Inhibit
Logging, (logging of process values and alarms). Please be aware logging Options for WinCC runtime Advance
Trending, Individual trending each flow transmitter
III.1. General Alarm
General Alarm has different tone for specifics events. Indeed, it is different between Company. To notify all attendant in the plant. Each area is equipped with annunciation.
This project didn’t integrate with existing General Alarm
III.2 Alarm
In industries where process hazard analysis results in minimum SIL 2. It requires 2 systems separated. Process Control System and Safety shutdown system.
When these systems exist. Grouping occurrence of alarm based on the system. PCS covers high and low alarm while SSS generate alarm High-high and Low-low. High-high and low-low alarm have consequence action to the process closing the valve or stopping the pump.
As stated, this application only for monitoring there is an alarm rule that could be waived. No intervention by maintenance personnel is required. High-high and a low-low alarm is not mandatory thus reset alarm through acknowledge is not mandatory either. The alarm logging is available.
The other feature does not require are
Maintenance inhibit
Start-up Inhibit
III.2.2 Alarm Animation WinCC
Alarm animation is important for an operator to know the condition of the plant. Usually, each company has different specifications for color and shape to animate the process plant.
It could be similar to the same type of business or industries.
I found that the way to represent alarm animation assign to a variable on WinCC advance is kindly different from other software HMI. Usually, the shape contains 2 tags or 1 structure tag.
Usually, I use structure to group alarm for one tag i.e.
PT001.HH with set point 90% of the maximum range
PT00.HH with set point 70% of the maximum range
PT001.L with set point 30% of the maximum range
PT001.LL with set point 10% of the maximum range
The other way is to generate dedicated variable i.e
PAH001
PAL001
The alarm is discrete 1 or 0; True or False. Meanwhile RT Advance uses integer value to generate different level alarms. The way to generate an alarm on RT advance is kindly different from what I use on other HMI. RT Advance use integer value to generate different level alarms
Faceplate
A faceplate is a configured group of displays and operator objects. The “data exchange” with the display and operator objects contained in the faceplate is performed via an interface at the created faceplate. The properties of the used display and operator objects are assigned to the individual objects in the “faceplate editor”. Faceplates can be managed and modified in a central library.
This project use faceplate as seen below. No control applied on the faceplate. No universal standard for a faceplate. It is custom depends on the application. In this project, the faceplate consists of
Individual trend flowmeters
Individual log measurement
Individual totalizer
IV. FLOW TRANSMITTER
All flowmeter is connected to the new dedicated PLC and HMI. It is stand-alone and independent from the existing DCS system.
In a standard basis, selecting flowmeters usually based on the
Accuracy requirement (for fiscal service or not)
Type of fluid and other fluid parameters
Installation constraint. Equipment that can be reached for inspection, repair, or monitoring from permanent platforms is more likely to be inspected, calibrated, and replaced than equipment that requires climbing with a safety harness or scaffold.
There were 3 types of flowmeters used in this project
Vortex flowmeters, operate under the vortex shedding principle, where an oscillating vortexes occur when a fluid such as water flow past a bluff (as opposed to streamlined) body. Vortex mostly uses in application of steam.
Magnetic flowmeters, this type of flowmeter is very common for water service due to the dominant conductivity parameter.
The ultrasonic flowmeter as a secondary device. The ultrasonic level meter is not only used for the level meter but it could use as a parameter to determine flowrate of open channel water. The equation will be embedded in the PLC program. For this application, it implements for the open channel consist of culverts and open channel.
Each flowmeter has a different method to obtain the flowmeter value. Each will have a different equation.
In the case of open channel flowmeter, there are several methods. The primary device for ultrasonic flowmeters are:
Weirs
Flumes such as Parshall flumes, Cutthroat Flume
IV.1 Rectangular Weir
In the first design, we use rectangular weir for the simplicity design
Flow rate equation based weir method, Q = 6620(L-02.H)H1.5,
Where :
Q = flowrate
H = head on the weir
L = crest length of weir
K = constant dependent upon units
IV.2 Cutthroat flume
There is a similar method as Parshall flume named as a cutthroat flume. In this project, the cutthroat flume is applied to measure flowrate at sewerage as a primary device.
W=KW1.025Han = CHan
Q=free flow rate(cfs / m3/s)
K=flume discharge constant (varies by flume length/units)
C=flume discharge constant (varies by flume length/throat width / units)
W=throat width
Ha = depth at the point of measurement (feet / meters)
n = discharge exponent (depends upon throat width)
The constant flowrate equation Parshall flume is determined by the selection range of flowrate and the dimension of open channel. More detail is available in the link below
There are two ways to obtain flowrate using ultrasonic. In reality ultrasonic only measures the height. The flowrate equation could be configured either in the ultrasonic transmitter or PLC.
Ultrasonic level to produce flowmeter value
IV.1.1 Selection of 4 wire or 2 wire transmitter
The selection 4 wire or 2 wire transmitter is the intention of the user and evaluation actual condition. These transmitters are called “4-wire” or self-powered. The current signal from the transmitter connects to the process variable input terminals of the controller to complete the loop.
Mostly the reason to use 4 wire as follows:
PLC is not available as acquisition data. The transmitter should have displayed on the transmitter so measurement is readable
Three and four-wire devices incorporate an external power supply in order to effectively eliminate the voltage drop placed on the processed signal current loop
Some device is not available as 2-wire. Some sensor requires external power to drive the chemical/mechanical event in the transducer.
V. INSTALLATION
The initial design was proposed using Parshall flume, the idea was to avoid high force when the maximum flow rate through the primary device. However, the member team decided to use weir for the simplicity of the design. It was understandably the main concern of the project team, Parshall flume is not easy to construct. In addition, there were no local vendors able to precast the Parshall flume.
We decide to use Weir to measure the water meter outflow unit. As a reference, I use Flow Measurement Practical Guides for Measurement and Control Handbook published by ISA.
Weir are the simplest, least expensive, and probably most common type of the primary measuring device used to measure flow in open channels.
After sizing the weir, I don’t pay attention to the installation procedure. There are two rectangular channels. The water flow never stops flowing. The only possible scheme is to place it down during the low water flow. Since it is using concrete, I thought with this weight it will easily dip into the water. Moreover, construction and installation are responsible to the contractor. If the contractor confirms they could install it then it became their responsibility. As a team, we really don’t concern about this until the installation start.
The installation method for the primary device for open water is really critical. It is even more important than sizing. If the installation seems impossible then quickly turn to use other methods.
High water flow is a detriment to the weir or Parshall flume structure.
Since we don’t have a data flowrate outlet, the sensing range flowrate only through observation. I was not sure the water flows were in low or normal flowrate, but it is convincing that it would not disrupt the process when laying down the weir structure using a crane.
It is not as expected, when the weir structure dipped into the water as it water tip the bottom weir structure, the hoist cable start swing. The degree hoist cable swing becomes bigger when the weir dipped deeper to water until the crane start to lift from the ground. The installations stops and not continue.
Basically there are two option solution from my knowledge
To find a way for a better method of installation. However, there still a risk if the installation fails again. Moreover, the remaining project budget reveals that there is no room for failing.
Change the flowrate measurement method with an admissible installation scheme.
After gathering information, the most reasonable is option 2. It automatically changes the equation to
Q = A x v
A = surface area
V = velocities
A = length x width where length is similar to height (H). Height(H) will be determined using the ultrasonic sensor. The width of channel is 2 mtr.
Now to determine the method velocity.
The first option is using the non-contact method
Non-Contact Sensor
The velocity could be measured using ultrasonic or laser. Laser velocimeter has a laser diode to determine the stream’s level by emitting an ultrasonic pulse and measuring the time it takes for the an echo to return for the stream’s surface. The transducer is both a pulse transmitter and an echo receiver. Certain manufacturers already provide integrated between velocity sensor and level sensor. Since the ultrasonic is measuring the level. The remaining sensor is the velocity
It could be installed on the surface. Since the flow much turbulence it is and a lot of ripple on the surface. We consult to the vendor, their recommendation is to
Contact Sensor
The Second method contact by immersing the sensor
The other could be installed inside the water. The sensor is installed at the bottom of the channel.
Not many vendors provide this sensor. I search on the internet, that moment I only find Mainstream Measurement. It sells variety product of sensor in immersed water.
The velocity sensor is designed to operate immersed in the liquid and is installed at the bottom of the channel where the measurements are to be taken. Below are photos during the installation of velocity sensor immersed in water.
We finally complete the project. Thank you for all the team who participate in this project especially my colleague construction engineer (Mr.Chris) who design the structure to hold the immersed velocity sensor. It was critical to complete this project.
For companies that business lies in upstream industries where continuously to explore new reservoirs to deliver the amount of gas according to a contract agreement. Exploring new potential reservoir, installing wellhead and tie-in the flow line to existing manifold called well connection. Well-connection is the heart that pumps the company (upstream industries) to operate and run. The various engineering work of well-connection is repetition and could be grouped based on typicality. Since well-connection is repetitive work and a tight schedule, often it is overlooked. Improvement is always open if we have comprehensive knowledge of technology.
Improvement along with cost reduction will have outcome optimization. For a mature exploration field, the term “optimization” plays a major role in cost savings. Optimization is targeted to reduce significant costs either Capex (Capital Expenditure) or Opex (Operating Expenses).
Cost reduction is responsible for all entities in the organization.
As a Senior Instrument and Control Design Engineer, you often encourage yourself to bring a new idea for improvement and delve into the details. On several occasions, improvement is proposed and requested by the production and process department. Other disciplines such as electrical, instrument and control systems will support this request. This particular improvement, it is initiated by self-insight. The objective was to gain self-accomplishment to give added value to the company.
II. OBJECTIVES
For this case improvement and cost optimization is addressed on wellhead and wellhead flow line measurement which is part of well-connection work.
III. EXISTING DESIGN
III.1. WELLHEAD
Below are the typical schematic connection to measure pressure and temperature on the wellhead x-mass tree. The Wellhead platform is located remote where no electrical power is available. The measurement uses a paper chart recorder. The paper chart recorder movement is either powered by internal batteries or mechanical key wounding. Paper chart recorders (well-known brand Barton) are measuring and recording wellhead parameters as follows:
Annulus Pressure (Casing Pressure)
Tubing Pressure (Production Pressure)
Tubing Temperature (Production Pressure)
III.2 FLOWLINES
Whilst the typical measurement flow rate (compensated) on flow line as seen below. Measure parameters are as following:
Differential Pressure (inH2O)
Pressure upstream Flow Element(static, barg)
Temperature flowline (degC)
Within this configuration, NUFLO Scanner 2000 is using internal battery 7.2V 17Ah. The internal battery is not rechargeable. The internal battery should be continuously expedited. The other problem is a decision when to purchase the internal batteries in order not too long place in storage. Guidelines for storing batteries should be followed to avoid excessive self-discharge.
IV. THE IMPROVEMENT and OPTIMIZATION
Based on the two device measurement on wellhead and flow line, it could be integrated only using NUFLO Scanner 2000 as schematic connection below
This improvement is to optimize the capability of NUFLO Scanner 2000. NUFLO Scanner 2000 able to receive additional 2 analogue input if it utilizes additional cards (expand I/O).
2 Analogue input will be assigned for:
1 ea analogue input to be assigned for Pressure Tubing (production)
1 ea analogue input to be assigned for Pressure Annulus (casing)
The remaining tubing temperature will utilize the RTD sensor currently being used for the temperature flow line. Meanwhile, RTD on the temperature flow line will be replaced with a temperature gauge. You will instantly notice, the temperature is different between the wellhead and the flowline. The temperature on the flowline is lower than the temperature on the wellhead. If we use input temperature from the wellhead it will affect the flow rate calculation. But this difference is not significant and it is acceptable.
Since this application is not for metering purposes but rather to control manual choke valve opening. In addition, throughout the well life cycle, fluid density is held constant, thus temperature will not main factor for flow rate compensation.
The other option is to use temperature on wellhead only for recording, not as input for flow rate compensated equation. The temperature for flow rate compensated is considered as constant, set by the metering team.
Both pressure sensor for pressure casing and tubing signal is conveyed with an output of 4-20mA. As stated previously, an existing configuration is using internal power. In order NUFLO Scanner 2000 could be as loop power two wires, it will require an external power supply 24VDC.
The external power supply 24VDC is provided by the lithium-ion battery power pack. It is rechargeable meanwhile internal battery is not rechargeable.
The lithium-ion battery power pack should be equipped with a protection feature such as a protection circuit that limits the peak voltage of each cell during charge and prevents the cell voltage from dropping too low on discharge. In addition, the cell temperature is monitored to prevent temperature extremes. The maximum charge and discharge current on most packs are is limited to between 1C and 2C. With these precautions in place, the possibility of metallic lithium plating occurring due to overcharge is virtually eliminated.
V. ADVANTAGE & DISADVANTAGE
Despite improvements with its advantages, any modification has its drawback to be considered. Often disadvantage comes from other aspects which not related to improvement.
The following are advantage of this improvement
Paperless
Higher accuracy reading due to digitizing reading
All data parameters are recorded for up to 30 days
Meanwhile the disadvantage as following
High initial cost for battery power pack (including charger)
Additional work for carrying battery power pack for recharge
To define who will be responsible to maintain the lithium-ion battery pack, electrical team or the instrumentation team.
Not yet found a product that conforms to hazardous area certification for this battery type. Hence, it should be located outside zone 2 (non-classified area
VI. POWER CONSUMPTION
The remote wellhead platform does not have an electrical source. External power will be provided by power pack batteries. Batteries power packs are very custom, in order to able to select the battery power pack. Power consumption should be calculated.
Based on the average lifetime of an internal battery, the average current consumption NUFLO Scanner 2000.
Note :The average lifetime of the internal battery could result different if you control the update rate. So this calculation result might be different depends on the update rate requirement.
1 ea lithium-ion battery pack with 24VDC and 46.99 Ah may have different weights among the manufacturer. Battery lithium-ion with a capacity of 40 – 50Ah 24VDC would weigh around 11 – 13 kg. It is considered heavy. In this design, I decided to select batteries with weights 5 up to 7 kg. However, within this selection weight, the capacity will be rated 20 – 25 Ah. The selection of battery weight is related to the charging method. The expected duration of the lifetime will reduce up to 45 days.
VII. CHARGING METHOD
A lithium-ion battery is critical during charging. This is why I decide no automatic charging onsite. Moreover, power by solar panels is not considered since this material is highly attractive for thievery. If the batteries have reached minimum level voltage, then the batteries will be carried out to onshore (accommodation) for recharging. Since the charging is onshore, attention should be address to consider the weight of batteries to be hand carry.
1 ea lithium-ion battery pack will cover 1 NUFLO Scanner 2000 with associated sensors. Yes, you could increase capacity Ah by configuring parallel but since this installation is in a hazardous area it would be safer not to configure batteries in parallel or series. Parallel/series battery configuration has the possibility to generate a spark when fixing or dismantling the connection bar. So I recommend only using an individual battery pack. As possible the location battery should be categorized as a non-classified area (outside zone 2).
Onsite, batteries will continue to discharge. Therefore, the lithium-ion battery pack should be facilitated with a battery management system in order to maintain the voltage does not go below the minimum voltage. When the battery has reached the minimum it should able to give an indication to the operator and it will automatically cut power to the device (load) in this case NUFLO Scanner 2000 and accessories sensors.
VIII. BILL OF MATERIAL
Next are selection material to perform the modification
IX.CAPITAL COST
I could not provide comprehensive capital cost. This capital cost intended for comparison. I didn’t consider the cost of man-hour to perform this modification.
The gain of improvement is estimated USD 1788.45 (USD 5500 – USD 3711.55). Usually, this value is small compared to overall well-connection work. However, if in 1 year at least there are 50 well connections, this saving is worthy.
This price quote was in 2018
Conventional Barton Chart approximately $ 5500 USD
X. IMPLEMENTATION
I have not yet implemented this improvement and optimization due to the procurement company policies of batteries. Company has restricted import product directly without any local agent. We are trying to solve this issue. Hopefully in the future, I could update the result.
I remember my experience as trainer for chemical injection (CI) system on 2016. The attendees were operator, maintenance, and inspection/corrosion team. The course was focused on technical issue.
The course details related to various elemental aspects of the chemical injection system from design of the system including valves, pumping, monitoring, and delivery . It cover in depth of
The various design aspects of the equipment
involved.
How to operate and monitor the performance of
chemical injection packages.
We create pretest and post test to ensure the participant obtains benefit from the course.
Besides to transfer knowledge, the objective of this
workshop and training is to increase level competence and reduce number of
problems during normal operation.
Mostly on our site, chemical injection system is use to protect flow line pipes from corrosion. The chemical injection will maintain corrosion rate below allowable rate. It is injected on the X-mass tree upstream choke valve.
Chemical injection system will be tailor to meet the specific requirement. The schematic shown are typical schematic use to protect flow lines. So it might be different schematic CI for different application.T
The schematic is taken for SkoFlo catalog
Understanding the equipment involved play important role. If one equipment failure it will affect the entire performance. Even wrong setting on back pressure regulator (BPR) would disrupt the performance.
In our facilities, chemical injection system could be
categorized of two types, as following.
Multi injection system
Single injection
The basic different of this system is how to set the flow rate.
In multi injection system flow rate are set individually on the flow control valve. This flow control valve is a pressure independent flow control valve. Once the valve is set at a desired flow rate, that flow rate is maintained even though the pressure conditions upstream and/or downstream of the valve may change considerably.
For single injection, flow rate is control using adjustment pump stroke length and stroke rate, without necessity to install flow control valve and back-pressure regulator. Pump should size properly in order to achieve target flow rate.
In addition, back pressure regulator and flow control valve is utilized for single injection with over capacity pump (based stock on hand) where injection flow rate is difficult to achieve using adjustment of pump stroke length and stroke rate.
Equipment of chemical injection system based on the schematic consist of
Chemical injection pump
Back pressure Regulator
Pressure Safety Valves (PSV)
Gauge drum
Dampener
Pressure Gauge
Flow control Valve
Note: Back pressure Regulator and Flow Control Valve is using a well-known brand SkoFlo
A.PUMP
Pump is reciprocating positive displacement pumps. The pump could be pneumatic driven or electrical driven. In multi injection system, pump will be operated based on highest well flowing pressure. Meanwhile stroke length and stroke rate is set at the total flow rate require for each well. Pump discharge pressure is recommended to set at: highest well pressure + 200 up to 400 psi + 13.8 barg
Note: +14 barg is really specific for flow control valve manufactured by SkoFlo valve
B. BACK PRESSURE REGULATOR (BPR)
It is specially
design for multi injection; however it could be used for single injection if
the pump is overcapacity.
Since on multi injection system, pump will deliver flow rate at total flow rate from each well, so overflow to the system network injection will occur. Back pressure regulator will dispense the overflow chemical injection back to the tank. I suggest the back pressure regulator is set at 80% of pressure safety valve.
Set point BPR is not regularly to be adjusted. Set point of BPR is also to maintain differential pressure between injection line and wellhead pressure at minimum 13.8 barg.
This is one of
requirement of flow control valve which require minimum differential 14 barg
between upstream and downstream to obtain stable injection flow rate.
C. FLOW CONTROL VALVE
It is design to
regulate injection flow rate for each flow line. Unlike other control valve
where flow will alter as system pressure changes, this specific flow control
valve maintains a constant differential pressure across a fixed calibrated
orifice, thus resulting in a constant flow through that orifice. As
differential pressure is independent of system pressure changes, the flow rate
is stable in all field conditions. However minimum 200 psi (13.8 bar) dP across
the valve is required for the flow rate ranges.
D.PRESSURE SAFETY VALVE (PSV)
Pressure safety valve is not based on API 520. This safety valve has similar function as back pressure regulator, but it has different intention. BPR is intended for normal operation it will open and close regularly.
Meanwhile PSV will open for particular case, e.g.
Blocked outlet by any isolation valve
Clogged CI Injection line lead to over pressure
Therefore, PSV set pressure is at maximum allowable pressure / Wellhead shut in pressure.
During the training session, we heard many problems
regarding chemical injection system from our operation e.g.
Pumps not working,
Plugging on the flow control valve,
Seat inside flow control valve disintegrate
Corrosion rate exceeded, etc.
My recommendations for these kinds of problems were
a. If pumps not working
Many causes could result pump not working. However, before examining the pump. I recommended checking pressure gas regulator + filtering regularly, since the supply is from hydrocarbon gas where water content might high. This would reduce the pump pressure discharge, after prolonged use without regularly drain the filter, this condition could lead the pump stop working.
b. Seat inside flow control valve damage / disintegrate.
This could occur if the flow control valve is located near the pump. Water hammering effect could occur during calibration where closing the valve handle adjustment rapidly. I recommended placing the flow control valve near the injection point. In addition it will optimize function of dampener.
I also find action by personnel which degrade the performance
of multi injection system.
First, changing pump flow rate by lowering backpressure
regulator set point. This action will affect the minimum differential pressure
require by flow control valve if not properly calculated.
Second, bypassing one of the flow control valve due to plugging. This action will affect the entire injection flow rate to each flow line. By bypassing one flow control valve will disrupt the network pressure. The injection fluid will tend to route to the lowest pressure, in this case the line with bypass flow control valve. In consequence, the other injection line will not meet the required injection flow rate.
Third, Increasing orifice flow control valve intentionally. By increasing the orifice (Cv), it will change the original design of the flow control valve. The manufacturer has engineered and carefully selected the spring, chamber upstream and downstream, and the stem flow control valve. Increasing orifice will change the inherent Cv . In the end this action will disrupt the network pressure. Same consequence found on second cause.
Besides the problems, I receive valuable feedback from the trainee about the chemical injection system. Most of the concerns are not written on technical datasheet, catalog, even manual.
We summarize
and make conclusion in order to maintain the performance and lifetime of the
pump, as following
If pump stroke is at the maximum 45 spm, the
pump spring will often break below 1 month.
We decide to limit the stroke rate at maximum 40 spm.
If stroke length shorten below half size of stroke length. It will often break the spring.
So we decide to maintain the stroke length at minimum 0.5
Low speed of stroke/minute is more preferable than high stroke/minute in delivering the same flow rate
Instrumentation and Control System 