The OTS, Story / Lesson for Failing to understand the Importance of the MOV (Motorised Operated Valve) it's OPERATION and STEM POSITION (PART1/2)
Husain A Tinwala
Expertise in Building, Testing and Using (Training) OTS from Training point of view. Opportunities in OTS development, business development, OTS Training development & Reviving dead OTS are welcomed.
In this blog / article I talk about greenfield Refinery project. I had to train on high-fidelity Operator Training simulator (OTS) of unit Heavy Oil Cooling (HOC). In this process the product must be cooled to specified temperature before been sent for storage. This unit receives products from different units of the refinery. The HOC unit’s job is to cool the hot product and send it to Tankfarm. The part which we discuss below is of cooling section.
Do also read the “Story of pressure-drop across Heat Exchanger”
I always intent and give importance of building OTS (Operator Training Simulator) ; from Training point of view. Because absence of a Training Vision will lead to end of life of OTS in 2-3 years of its commissioning. Let's discuss about the MOV (part1) which made my training session difficult.
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Lets Begin!
In Heavy Oil cooling Unit we have Motor Operated Valve (MOV) at the inlet and exit of each and every cooling Heat Exchangers.
About MOV,
These are Motor Operated Valves. Big valves usually for On – OFF or Inching (Throttling) purpose. They are same like other valves with only difference of having motor at top to operate it. More details about MOV can be found on internet. Below is actual picture of MOV.
On Field and DCS Panel the MOV have three positions. OPEN, STOP and CLOSE.
In HOC unit Heat Exchangers, we have diesel flowing in Tube side. In Shell side it could be LSFO, Crude or Atmospheric residue (AR). As shown in diagram,
As shown the inlet and outlet of process line have its own MOV. For easy understanding purpose I have considered only one line at inlet and exit.
The temperature of inlet stream is upto 200+ deg C. When lining up the Heat Exchanger it is very important to slowly heat up the Heat Exchangers.
So we crack Open the inlet valve of Heat Exchanger and wait. As the temperature keeps increasing we slowly keep opening the valve. This ensures the Heat Exchangers gets heated up before been lined up for full flow. This helps in preventing uneven expansion and leakages in Heat Exchanger at gaskets.
So the actual Operation is,
On Field and DCS Panel the MOV have three positions. OPEN, STOP and CLOSE.
During Start up we must operate the MOV’s from the field. In OTS, During operation from the Field panel we realized there is no Stop switch or button. The faceplate had only OPEN or CLOSE option.
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As a result, we had to use Manual valves to regulate the flow through the Heat Exchanger and slowly heat it up.
This resulted in lack of training of the field operators. And the actual SOP could not be replicated.
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Also think even if they fix the issue will I be able to use the MOV? The answer to it is, NO.
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Because, we do not know what percentage has the valve stem travel? We do not have position feedback available in the faceplate. In actual plant we have it on field. So even I press STOP button I do not know whether the valve is 10% or 30% OPEN?
The position feedback option is very important because it assist in knowing percentage of valve Open.?
So on what basis would I press a STOP button if I am not aware of the valve opening. This is the second issue affecting the training.
Brought it in attention of the OTS supplier. Unfortunately they did not implement it for following reasons,
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?So,
I explained them this particular scenario,
If we look in detail at this particular heat transfer case we have two MOV's. One at the inlet of Heat Exchanger and other at Discharge of the Heat Exchanger. Both the MOV's are used in different ways.
MOV 001 :- This MOV is at the inlet of the Heat Exchanger. It is opened very slowly by using OPEN and STOP command at regular intervals. Here the aim is to slowly heat up the Heat Exchanger.
MOV 002 :- This MOV is at the discharge of the Heat exchanger. When we line up the Heat exchanger for services the discharge MOV is OPEN first. And it is completely OPENED at once.
So both the MOV's are used in different ways. One MOV by ON-OFF and other by inching.
Also reasoned simply saying its in p&id so implement it.?
Well the OTS supplier did not updated the faceplate. And as consultants we cant do much then.
Solution: -
For MOV’s one must check and ensure that its all three positions STOP, OPEN and CLOSE are available.?
The OTS supplier must also provide a valve position indicator. Which would assist the field operator in knowing the correct position of the valve.
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The Design of MOV Faceplate in HMI for this case must be as follow,
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Read and understand p&id before making the Faceplate in HMI.
In p&id the MOV will be represented like this.
?Look at the p&id it showcases all the three options. Along with the option of switch to change from LOCAL to remote mode. (The Other associated signals with MOV are removed. For easy understanding.)
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It is also the responsibility of the Model testers (clients). During MAT and SAT of OTS. We must check all the Field panel faceplates. And question oneself does it show the information as in Real plant or p&id ??
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Always remember the field panel faceplates are built by OTS supplier. So the faceplates can always be changed or upgraded.
Will appreciate your Guidance (Your thoughts, proof reading or sharing your experience).
Inviting and sharing to right minded people is applauded.
Thank you!
By:-
Husain Abbas Tinwala
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Have a nice day ahead!