Thursday, July 12, 2007
Wednesday, July 11, 2007
Factors and Criteria for Vent Stack Design
Vent and flare stack are used dispose waste gas in safe and enviroment friendly manner. Flare stack is probably preferred as compare to vent stack if the release fluid contain HC from environmental point of view e.g. impact to greenhouse effect for 1 mole of C1 is about 20 times of 1 mole of CO2. However, flare stack may be costly.
For a vent stack, at least 3 main criteria shall be met :
i) Toxic / flammable component well dispersed and meeting health and safe level during Normal operation (Nor. Op.) and emergency situation (Emer. Op.). very much subject to components / species in vent gas. Local regulations will probably indicate the limits of various components. In additional, Material Safety Datasheet (MSDS) will probably indicate the limits. PHAST, FRED, etc can be used for dispersion study.
ii) Radiation due to ignition of lightning (Emer. Op.). In the event, vent gas is HC and potentially ignited by lightning, radiation study shall be conducted to ensure radiation at the receptor (human) point is meeting criteria e.g. 6.31 kW/m2. In addition to the radiation level, the temperature of receptor (equipment) shall not damage the equipment. FLARESIM, FRED, etc can be used for radiation study.
iii) Noise level at receptor meeting noise criteria during Normal operation (Nor. Op.) and emergency situation (Emer. Op.). Noise level at receptor (human) is meeting criteria e.g. 115 dBA with background noise. Keeping in mind, some plant owner may impose more stringent requirement i.e. 90 dBA @ receptor (human). FLARESIM, FRED, etc can be used for noise study.
If some spill over control PCV tie to vent header and release continuously into vent stack, fluid exit temperature may be a concern in some environment sensitive area.
API 521 has recommended Mach = 0.5 and this value is probably a good start for vent diameter determination. Vent stack height will subject to above criteria, location of vent stack, plant layout, wind speed, wind direction, etc. Modeling vent stack with inclusion of vent diameter and height using software as mentioned will be conducted in order to ensure meeting all criteria as mentioned earlier.
Monday, July 9, 2007
ProMax from BR&E - Renowed Process Simulator in Gas Treating Industry
Looking at this particular logo, i am sure many of you know what it mean...
BR&E - Bryan Research & Engineering Inc, has been in the oil and gas industry for years. My first contact with BR&E was 10 years ago.
Bryan Research & Engineering incepted in 1974, renowed process simulation software, ProMax having its ability to predict the performance of gas processing, refining and petrochemical processes.
ProMax capabilities includes Amine Sweetening, Glycol Dehydration, Equipment Rating/Sizing, Crude Oil Refining, LPG Recovery and Caustic Treating.
FREE articles (AMINE related) available BR&E site :
Addition of Static Mixers Increases Treating Capacity in Central Texas Gas Plant
Alternative Flow Schemes to Reduce Capital and Operating Costs of Amine Sweetening Units
Analysis of Amine Solutions by Gas Chromatography
Analysis of Various Flow Schemes for Sweetening with Amines
Converting to DEA/MDEA Mix Ups Sweetening Capacity
Decreasing Contactor Temperature Could Increase Performance
Design & Operation of a Selective Sweetening Plant Using MDEA
Design Alternatives for Sweetening LPG's and Liquid Hydrocarbons with Amines
Dome's North Caroline Plant Successful Conversion to MDEA
Improved Absorber-Stripper Technology for Gas Sweetening to Ultra-Low H2S Concentrations
Influence of Ammonia on Gas Sweetening Units Using Amine Solutions
Optimization of Amine Sweetening Units
Optimization of New and Existing Amine Gas Sweetening Plants Using Computer Simulation
Selecting Amines for Sweetening Units
Selective Absorption Using Amines
Solubility of Hydrocarbons in Physical Solvents
Sweetening LPG's with Amines
The Use of MDEA and Mixtures of Amines for Bulk CO2 Removal
Treat LPGs with Amines
Unique Acid Gas Enrichment Application
Using Mixed Amine Solutions for Gas Sweetening
The Impact Of Acid gas Loading On The Heat Of Absorption And VOC and BTEX Solubility in Amines Sweetening units
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Sunday, July 8, 2007
Simulate Trayed & Packed bed column in HYSYS
Somedays ago...somebody raise a very simple question. He is doing revamping of existing amine absorber column. This column contains trayed and packed bed section. He is using HYSYS process simulator. How shall he simulate it in HYSYS ?
Yeah...probably a very simple question to those who has experiences with HYSYS. I know i can simply response to him saying that please refer to HYSYS manual...but still i take a little of my time to elaborate.
Amines absorber column may contains trays and packing for some design reasons...Can HYSYS simulate combined tray and packed bed column ?
Yes...you may do so with following steps...
- Go to Tools/Utilities
- Select "Tray sizing" option
- Choose the tower in your flowsheet that you want to size, add (define) two column sections - one for trays and other for packing.
- In the Design tab, from drop-down list find the packing type that matches your tower internals. There are additional packing data shall be enterred.
I purpose pack this information here for ease of everybody...
Further reading
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Saturday, July 7, 2007
Correct model and thermo package in Amine system simulation using HYSYS
Amine is a solvent widely used in removal of H2S and CO2 in natural gas. They are generally called gas sweetening and acid gas removal. Generally H2S and CO2 absorb and react with amine in the absorption tower will then be regenerated in the regeneration tower. Regenerated amine will then return back to absorption tower. H2S and CO2 flashed from regeneration tower will be send to thermal oxidizer (TO) and it will then be destroyed in the TO. In case the H2S is significant, the H2S will normally sent to Sulfur Recovery Unit (SRU) to recover Sulfur as byproduct.
There are number of software such as ASPEN HYSYS, SULSIM, PROMAX, AMSIM, etc available in the market which have been widely used by process engineer to simulate the entire amine loop. In HYSYS, there are Li-Mather model and Kent-Eisenberg model available for amine system. Which model shall be used ? There are ideal and non-ideal thermo package, which thermo should be used ?
Li-Mather is a fundamental and rigorous model whilst Kent-Eisenberg method is more empirical. With sufficient study and field data backup with Li Mather model and limitation of Kent-Eisenberg method (limited working envelop), it is advisable to use Li-Mather method for design purpose. Designer can always advisable to counter check with Kent-Eisenberg method.
The non-ideal themo package is taking into accounts of kinetic effects. Hence, non-ideal thermo package is generally adopted in the event feed contains significant amount of CO2 (slow reaction). As for feed dominant with H2S, then they should be minimal impact to the results as the reaction is fast.
Friday, July 6, 2007
How to differentiate MASS lower heating value and Volumetric Lower heating value (gas) in HYSYS ?
LOWER HEATING VALUE
Is there any different between MASS lower heating value (kJ/kg) and lower heating value (gas)(VOLUMETRIC) (MJ/m3) in Aspen HYSYS ?
Yes...there are some differences...
MASS lower heating value (kJ/kg)
There are indeed two representations of Lower Heating Values in Aspen HYSYS. By default, HYSYS calculates the LHV on a molar basis as the sum of the heat of combustion (at 25C and 1 atm) multiplied by the mole fraction for each component in a mixture :
LHV = sum(x[i] * Heat_of_Combustion[i])
The heat of combustion in the above equation is a pure component property that comes directly from the HYSYS database. As a consequence, HYSYS will report
In the events we do not know the Heat of combustion for hypothetical components, i may always suggest to represent the hypothetical compenent with nearest Molecular weight component in HYSYS standard library. From Science perspective, these figures are different but from engineering point of view, there are more or less similar...make equilavent between them is acceptable.
Lower heating value (gas)(VOLUMETRIC) (MJ/m3)
The second representation of the Lower Heating Value is calculated on a volumetric basis in much the same way as above, but with data from ISO 6976:1995(E). This calculation includes data for the following components (at 15C and 1 atm) :
Ammonia, Argon, CO, CO2, H2S, H2O, Hydrogen, Oxygen, Nitrogen, n-alkanes (C1 through n-C30, including i-C4 and i-C5), Ethylene, Propene, Cyclopentane, Cyclohexane, M-Cyclopentane, M-Cyclohexane, Benzene, Toluene, E-Benzene, 124-M-Benzene, Methanol, EGlycol, TEGlycol.
If the stream contains components other than these, then data for the hydrocarbon with the nearest molecular weight is used. If the molecular weight is greater than decane, then the data for decane is assumed.
Thursday, July 5, 2007
Simulation of Compact Heat Exchanger...
An interesting thesis related to Compact Heat Exchanger i found recently which shared by Arturo J.Pascheco-Vego
This dissertation investigates enhancement in accuracy of heat rate predictions in compact fin-tube
heat exchangers . The sources of error from a conventional approach based on correlating heat transfer coefficients, sometimes of 25 - 30%, are studied first. These include the idealized assumptions in the procedure by which correlations are found, the data compression that occurs through the correlation process, and the multiplicity of solutions for a proposed correlating function obtained using local regression
Arturo J. Pascheco-Vega, UNI of NOTRE DAME
Further reading
- CFD in Compact Heat Exchanger
- Compact heat exchanger Increased performance, optimized area utilization, reduce CAPEX & OPEX
- ALFA LAVAL - Plate technology and Designing Plate & Frame Heat Exchanger
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