Tuesday, November 11, 2008

Adjusted Method For Compressor Settle Out (with Vapor & Liquid) Using HYSYS

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Since the release of "Simple Method For Compressor Settle Out Using HYSYS", some readers of Chemical & Process Technology raised a question. The proposed method has considered all in VAPOR, how shall this method apply in case of present of VAPOR and LIQUID in Compressor Suction drum and Air Cooler Downstream ?

It is correct that the simple method is simplified version for VAPOR only Settle out condition. Nevertheless, minimum adjustment to the method enable the method to be used for condition with VAPOR and LIQUID. First refer to following image.





Step 1 : Compressor Suction. Estimate physical volume of vapor (Vv1) and liquid (Vl1).
Step 2a : Compressor Suction. Separate Compressor Suction Inlet (stream 1) with 2-phases (vapor & Liquid) with Separator unit operation.
Step 2b : Copy Compressor Suction Inlet Vapor (stream 2) condition and composition to a new stream Actual Compressor Suction Inlet Vapor ((stream 4). Adjust Mass flow of this stream until the Actual Volumetric Flow equal to Vv1.
Step 2c : Copy Compressor Suction Inlet Liquid (stream 3) condition and composition to a new stream Actual Compressor Suction Inlet Liquid (stream 5). Adjust Mass flow of this stream until the Actual Volumetric Flow equal to Vl1.
Step 2d : Mix Actual Compressor Suction Inlet Vapor (stream 4) and Actual Compressor Suction Inlet Liquid (stream 5) to form Compressor Suction (stream 6).

Normally the Compressor Discharge stream is superheated and no liquid is expected.

Step 3 : Air Cooler Downstream. Estimate physical volume of vapor (Vv3) and liquid (Vl3).
Step 4a : Air Cooler Downstream. Separate Air Cooler Downstream Outlet (stream 7) with 2-phases (vapor & Liquid) with Separator unit operation.
Step 4b : Copy Air Cooler Downstream Outlet Vapor (stream 8) condition and composition to a new stream Actual Air Cooler Downstream Outlet Vapor (stream 9) . Adjust Mass flow of this stream until the Actual Volumetric Flow equal to Vv3.
Step 4c : Copy Air Cooler Downstream Outlet Liquid (stream 10) condition and composition to a new stream Actual Air Cooler Downstream Outlet Liquid (stream 11). Adjust Mass flow of this stream until the Actual Volumetric Flow equal to Vl3.
Step 4d : Mix Actual Air Cooler Downstream Outlet Vapor (stream 9) and Actual Air Cooler Downstream Outlet Liquid (stream 11) to form Air Cooler Downstream (stream 12).

The remaining steps are same as "Simple Method For Compressor Settle Out Using HYSYS" by adjusting Settle Out Cond Actual Volumetric Flow same as Vv1+Vl1+V2+Vv3+Vl3.

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Sunday, November 9, 2008

CO2 Corrosion Using Freecorp Model

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In earlier posts "Quick Estimation of CO2 Corrosion Rate" and "CO2 Corrosion Rate Estimation Using M-506 Model", two simple model i.e the DeWaard Milliam model and Norsok M-506 model have been introduced. The DeWaard Milliam model is just a simple chart while the M-506 model has been programmed into a software and available FREE for download.

In this post, another CO2 corrosion rate estimation software FREECORP will be introduced. FREECORP has been released for use by the corrosion research community. It was developed by scientists and programmers at Corrosion Center using publicly available knowledge of oil pipeline corrosion and it is distributed under GPL (General Public License) for FREE use by researchers, practitioners, and students of corrosion phenomena.

"FREECORP V1.0 is a simple corrosion model, strongly rooted in theory, which has been developed exclusively based on public knowledge. Currently, this model is capable of predicting uniform corrosion of carbon steel at a single point in an environment containing carbon dioxide, acetic acid, oxygen, and/or hydrogen sulfide. Iron carbonate film formation, a key factor in carbon dioxide corrosion, is simulated using an empirical correlation to improve the accuracy of corrosion rate prediction. Contributions to corrosion of various corrosion species can be calculated, which enables the exploration of dominant corrosion mechanisms in the corrosion process. Furthermore, polarization curves for each individual electrochemical reaction, net cathodic and anodic reactions and polarization sweeps can be optionally displayed. In a case of hydrogen sulfide corrosion, film formation is calculated and concentration profile of H2S across mass transfer layers on steel surface is displayed."


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Friday, November 7, 2008

Hot Tapping and Online Valve Change out

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Plant debottlenecking and upgrading may involve some hot work and new tie-ins on existing facilities. To facilitate safe construction of new tie-ins, conventionally the existing system will needs to be shutdown and decommission to allow safe hot work. Production loss and inventory loss will incur a large cost for a simple modification. Thus, hot tap technology has been created to facilitate construction of new hot tap while allowing continue production and zero inventory loss. Read more on "Hot Tapping and Line Stopping Without Shutdown Services". You may view the the detailed hot tapping procedure by click this link.

In normal operation of a plant, certain unavoidable phenomena such as equipment wear and tear, corrosion, decay, etc would lead to valve deteriorate and required to be replaced / changed out. Similarly, this activities would lead production shutdown and inventory loss in order to carry out the change-out activities. Now a new technique has been introduced to remove and replace a ball valve without shutting down the plant. It has been successfully implemented in changed-out of a 6" ball valve located on a live cryogenic tank. This surely and significantly reduction in production and inventory losses. In principle, it apply the similar hot tapping procedure to carry out the valve change-out. Read more on "Ground-breaking procedure on live propane tank avoids costly shutdown".

Applying hot tapping and valve change-out with live plant, it is a significant challenge to all parties involve. Several factors shall be in consideration :

i) Safety Analysis - The entire hot tapping work shall be properly analysed. All stringent safety analysis i.e PHA, HAZOP, etc shall be properly conducted and documented.

ii) Competent operator - The entire works shall be carried out by a team of competent operator. In some counties, the group of people shall have license to carry such activities.

iii) Cost - The hot tap activities is highly hazard and require high technology to conduct this activities. This will results a high cost.

Although hot tapping and online valve change-out is very attractive, nevertheless, there are still many established oil and gas operator keep them away from using this technology. The main concern still the risk involve and confident and success stories for these techniques. Having said that, it no doubt is a technique may be considered in special case.

What do you think ?

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Thursday, November 6, 2008

Simple Method For Compressor Settle Out Using HYSYS

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Compressor emergency blowdown is commonly initiated after compressor system shutdown. The compressor shutdown will also lead to Compressor System Suction shutdown valve (SDV) and Discharge SDV to shut close and the anti-surge and/or capacity control valve open. Compressor discharge with high pressure and hot, air cooler and downstream high pressure and cold and suction vessel low pressure and cold will be settled-out prior to blowdown.

How to estimate the settle out condition ?

Settle-out of compressor system can be conducted using HYSYS. The main concept is constant mass and volume before and after settle-out. It is assumed the settle out is carried out adiabatically.

Following are some steps can be used to obtain the settle-out condition. Let start with following image.



Step 1 : Calculate physical volume of Compressor Suction (V1), Compressor Discharge (V2) and Air Cooler Downstream (V3).

Step 2 : Setup the system as per above image by correct Compressor Suction, Compressor Discharge and Air Cooler Downstream operating condition and composition.

Step 3 : Adjust Compressor Suction, Compressor Discharge and Air Cooler Downstream Mass flow until the respective Actual Volumetric Flow same as V1, V2 and V3.

Step 4 : Set Balance (BAL-1) for Mole & Heat

Step 5 : Adjust Settle-out Cond stream pressure until the Actual Volumetric Flow same as V1+V2+V3.

Thus, the settle out condition can be extracted from the Settle-out Cond stream.

Do you aware of other method ? Why not share with us ?

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Tuesday, November 4, 2008

Saturate Dry Gas With Water in HYSYS Using SATURATE Extension

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Wetting a dry gas using 3-phase Separator unit operation in HYSYS has been discussed in "Saturate Dry Gas With Water in HYSYS". It is a simple but ordinary way and useful. Aspen HYSYS (previously Hyprotech) has generated a simple extension called SATURATE extension to perform same function. See below image.



Locate SATURATE Extension
The SATURATE extension does not come with HYSYS installation file. It can be downloaded from ASPENTECH Support Website. Click here to locate the HYSYS extension. (for register user only).

Register & Access SATURATE Extension
Once the SATURATE extension is downloaded, it shall be registered in HYSYS. Unzip the saturate.edf and saturate.dll files to a convenient directory on your hard disk. Go to Tools … Preferences, then choose the Extensions tab, click the Register an Extension button, then navigate to the location of the saturate.dll file. Local Administrator privileges are required in order to register an extension. The Saturate Stream Unit extension should then appear under the Extensions category of the Add Operation window. (Accessible via Flowsheet … Add Operation, or by pressing F12.)



Obtain Water Content
Once the SATURATE extension is open, above tab will be shown. Just set the the unit to lb/mmcf at Standard condition, the water content in lb/mmscf can be found.

Find Under Saturate Water Content
If one to find the Water Content at 80% Humidity, just simply change the Humidity input to 80. Water content at under saturate condition will be shown.

Applicability
This extension only support HYSYS 2.4.1 onwards.



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Sunday, November 2, 2008

Saturate Dry Gas With Water in HYSYS

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A loyal reader in Chemical Process Technology raised a question. I have a dry gas composition. As the gas is produced from reservoir, it is saturated with water. How to simulate in the HYSYS simulator ? How to calculate water content in wet gas ?

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From hydrocarbon - water equilibrium analysis, you will find that as you increase water content in dry gas, the water will mix with dry gas until the dry gas is saturated with water. Once it is saturated with water, any addition of water into the water saturated gas (normally called wet gas) will knock-out as free water in aqueous phase. This can be easily modeled in any process simulator like HYSYS.

Below image shows Dry gas stream is mix with Water in a 3-phase Separator unit operation. To saturate the Dry gas with water, the only requirement is increase the Free Water flow until the aqueous flow (Free Water) starts to knock off free water. In this case, an ADJUST unit is used to adjust the water flow until zero flow.



To find water content (in lb/mmscf), first check out the Water Mass Flow in Wet gas from composition, change the basis to mass flow. See following image.




Then find the Molar flow in MMSCFD. See following image.



In above example, the Water Mass Flow is 1233.6 kg/h (2719.6 lb/h) and Molar Flow is 1005 mmscfd. Thus,

Water content = (2719.6 x 24) / 1005 = 64.93 lb Water / mmscf Gas.

If you have better method, let us know.

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Saturday, November 1, 2008

Simple but Effective Approach to Hazard Analysis in Oil & Gas Industry

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Simple update to IEM Members or those who are practicing Engineering in MALAYSIA...

It has been a standard industrial practice to carry out hazard analysis for hazardous operations. However, accidents still happen and occasionally, the consequential losses are alarming. In many cases, the accidents could have been prevented if the hazard analysis had been more effectively completed or if the analysis findings (information pertaining the hazards and their controls) are communicated and hence, appreciated by everyone. In response to this, the Bowtie technique was invented and is being increasingly adopted in the oil & gas industry. It is simple and can be applied for all types of hazard such as fire/explosion, environmental pollution, work-related accidents, transportation accidents, security threat, health hazards and may others. It is suitable for other industries as well e.g. construction, fabrication, manufacturing, aviation, shipping etc. The Bow-tie technique emphasises on a pragmatic approach to identify not only hazard controls but also measures required to ensure the effectiveness of the identified controls. The overall findings are graphically presented in a bowtie-like skeleton that allows easy understanding and communication.

A talk on “The Bowtie Technique – Simple but Effective Approach to Hazard Analysis in Oil & Gas Industry”, organised by Oil, Gas and Mining Technical Division has been scheduled.

Date : 22 November 2008 (Saturday)
Time : 9.30 am to 10.30 am
CPD : 2 Hours (approved by BEM)
Venue : Conference Hall, Bangunan Ingenieur, Petaling Jaya
Speaker : En. Syed Zaidul Hamzah





*Any queries, please contact sec@iem.org.my.

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