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Chemical Process Technology

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Chemical & Process Technology

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Friday, September 28, 2007

Displayed problem ? ....Click HERE

Heat exchanger sleeving, a money-saving technology generally associated with the electric power industry, is drawing increasing interest from engineers in the chemical process industries (CPI), as well.



Sleeving consists of expanding thin tubes (sleeves) into the tubes of a heat exchanger. The expanding process produces a residual, interfacial fit pressure between the outside surface of the sleeve and the inside surface of the tube. The sleeves may be short, for instance about 6 to 16 in., or may extend for the full straight length of the tubes. Typical sleeve thicknesses are 0.01 to 0.03 in., depending upon material of construction and thickness of the original tubes. In addition to the expansion step, sometimes the inner end of the sleeves is welded to the inside wall of the tube.

In tubular heat transfer equipment in power plants, sleeving has long been used for one or more of these purposes:

  • To reduce the prospect of inlet-end tube erosion (short sleeves for this purpose are also called ferrules, and their use is called ferruling)
  • To restore tubes to service that had been plugged by plant personnel because of known perforations in discrete, identifiable locations
  • To restore tubes to service that had been plugged because their walls had become excessively thin
  • To bridge failures in discrete locations of tubes that are otherwise intact; for example, if a tube has a circular crack just beyond the inner face of the tubesheet
Before applying sleeving to similar problems at CPI plants, it is useful to be aware of the sleeving methods and equipment available, be able to determine how sleeves affect the heat transfer performance of heat exchangers, and be able to calculate the changes in pressure drop through the tubes.

Related Topics

Heat Exchangers: Selection, Rating and Thermal Design, Second Edition




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posted by Webworm, 10:38 PM | link | 0 Comments |

Thursday, September 27, 2007

Heat Exchanger design is one of the common activities in plant design. However, although Heat Exchanger is designed in proper manner and follow most of the good engineering & design procedure, yet you might fails to achieve the desired performance by a wide margin. With an understanding of some common reasons why this might happen, designers can avoid these problems in the first place, and troubleshooters can recognize the root causes quickly.

Heat Exchanger Duty : Going for Gold
by David Butterworth
(Click HERE to download)

Exchangers for single-phase operation, condensing and boiling are considered in that order here; but as we shall see, exchangers often handle a combination of these, and it is not always obvious which process is causing the problem. In fact, some of these problems are quite unexpected and can even take experienced designers by surprise. It must be recognized that the most important cause of problems in exchangers is excessive fouling. Other articles, books, and conferences have been dedicated to this problem, so fouling will not be addressed here. Instead we consider those exchangers that have failed for some reason other than fouling.

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posted by Webworm, 7:11 AM | link | 0 Comments |

Wednesday, September 26, 2007


In the earlier post, <<Hydraulic Design of Liquid Piping Systems >>, it presented the concepts in hydaulic study such as Bernoulli's theorem, pressure head, static head, velocity head, acceleration head, static head loss, dynamic head loss, etc. All this are related to hydraulic of piping alone. Now, this following article is the extension of above mentioned article.

by John Cheng, PhD, PE
(Click to download)

It extended to pumping liquid from one tank / drum to another tank /drum. It elaborate quite a lot on the pump head-capacity curve and interaction with piping resistance curve. the best features in this article is the STEP-by-STEP of pump hydraulic calculation, available Net Positive Suction Head (NPSHa) determination. This typical form the basis for a pump specification. A process engineer MUST read this and familiar with pump hydraulic.

Apart it also discuss the affinity law, selection guidelines for centrifugal & reciprocating pumps, pump protection methodology, etc.

Related Topics :


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posted by Webworm, 3:35 AM | link | 2 Comments |

Monday, September 24, 2007



Piping is a basic components in the Chemical & Process Plant. Piping connect two different equipment and deliever fluid from one equipment to another equipment. Hydraulic study is essential study to determine a piping is selected with optimium size, lowest line loss and within the available driving force between the equipments. The following article is a revision kit for a process engineer who are dealing with hydraulic study of piping system.
Hydraulic Design of Liquid or Water Piping Systems
by John Cheng, PhD, PE
(Click to download)
This article contain few main chapter and concepts in hydaulic study such as Bernoulli's theorem, pressure head, static head, velocity head, acceleration head, static head loss, dynamic head loss, etc. It also presented calculation of friction factor using Cole Brook-White equation, recommend absolute roughness for several common pipes, how to analyse system change with approximation method, etc.

Related topics :




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posted by Webworm, 9:15 AM | link | 0 Comments |

Thursday, September 20, 2007


In earlier post,<< High Temperature Hydrogen Attack in metal & alloy>> there are some discussion on how hydrogen attack in metal & alloy is initiated and a paper in recent activities in hydrogen attack.

How many of you have ever heard accident caused by High Temperature Hydrogen Attack in metal & alloy ? How severe is this attack ?

By chance, i found an accident of High Temperature Hydrogen attack on Carbon Steel piping at the outlet of a Pressure Relief Valve. This accident happened in the Residue Hydrodesulfurization unit in Japan. This accident has killed five (5) operators and injured three (3) operators.



High temperature gas contain Hydrogen is compressed and fed to furnace and reactor. Heating and reaction taken place in the furnace and reactor and hot product is fed to a separator. Pressure Relief Valve protecting compressor is bypassed the furnace and reactor and connected to downstream of furnace and reactor. Generally the is no flow passing the Pressure Relief Valve discharge and is expected the discharge piping is always under low temperature. Those High temperature hydrogen attack is not expected in the Pressure Relief Valve discharge piping and design has not considered it.

After the incident, investigation has reported that the burst piping is caused by High Temperature Hydrogen Attack. How the piping is exposed high temperature and how the hydrogen can get into this piping ?

If you review details drawing in figure 4 in the report, you will find that the piping burst at the location closed to the main pipe. During normal operation, hot gas is flowing through the main pipe and main pipe is heated to high temperature. Hot main pipe will transmit heat to the branch from Pressure relief Valve with conduction effect. Temperature is gradual reduced with distance from the branch tie-in.

In the event compressor is overpressure, pressure relief valve popped will release high temperature gas with hydrogen rich in it. Whenever it passing through the pipe, hot piping metal will pick-up the hydrogen, react with Carbon in the piping and form Methane and this will weaken the hot carbon steel piping.

One note has not been addressed is that there is residue hydrogen gas in the product line. This continuously expose the branch with hydrogen. Hydrogen pick-up activity is continues during normal operation.

Lesson here is never under-estimated Hydrogen attack in metal and alloy. Whenever dealing with hydrogen, special attention shall be taken for those non- continuous operating lines.

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posted by Webworm, 11:26 PM | link | 0 Comments |

Tuesday, September 18, 2007

2ph_relief

This is another of excellent workbook related to Emergency Relief System recommends to those engineer who works (design, engineering, operation) in Oil & Gas platform, Chemical & Process plant, Refinery, Chemical plant, etc. Again in particular for SAFETY & LOSS PREVENTION engineer...

WBCRRSS

Workbook for Chemical Reactor Relief System Sizing

Prepared by Janet Etchells & Jill Wilday

The workbook is to provide information on methods available for the sizing of emergency relief systems for exothermic runaway reactions in liquid-phase chemical reactions. This work mainly written for SAFETY & LOSS PREVENTION engineers who are dealing with Chemical relief with reaction and shall have good basic experiences in Chemical reaction Kinetics and fluid flow.

This workbook is available FREE for download from HSE UK.

Related topics

If you benefits from this post, buy me some sweets



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posted by Webworm, 8:31 AM | link | 2 Comments |

Sunday, September 16, 2007




This is one of excellent book that i always wanted to recommend to many of you, typically those engineer who works (design, engineering, operation) in Oil & Gas platform, Chemical & Process plant, Refinery, Chemical plant, etc.
This is a must have book specifically for those works as SAFETY & LOSS PREVENTION engineer...




Emergency Relief System Design Using DIERS




Emergency Relief System Design Using DIERS Technology
The Design Institute for Emergency Relief Systems (DIERS) Project Manual
By: Fisher, H.G.; Forrest, H.S.; Grossel, S.S.
Part of the PREFACE...
A consortium of 29 companies formed the Design Institute for EmergencyRelief Systems (DIERS) in 1976 under the auspices of the AIChE to evaluateexisting methods to design pressure relief systems for runaway reactions andto develop additional technology as needed. Approximately $1.6 million wasspent acquiring test data and documenting applicable methods for the designof emergency relief systems suitable for the discharge of two-phase vapor-liquid flow. Of particular interest was the prediction of when two-phase flowwould occur and the extent of vapor-liquid swell.
DIERS did not set out to add another two-phase flow computation procedure to the many that already existed. Rather, the goal was to identify methods that could be used to size safe, but not overly conservative, relief systems for two-phase vapor-liquid flow for flashing or frozen viscous or nonviscous fluids.
Techniques for sizing an emergency relief system for runaway reaction include:
  • Direct empirical scaling of experimental data obtained in vessels witha very lower thermal inertia.
  • Semi-theoretical graphical or analytical design methods.
  • Computer simulation of incidents and flow through relief systems.
This project manual is primarily intended
  • to provide a record of the DIERS research project.
  • to help organizations acquire, assimilate and implement the vastamount of DIERS information and technology by serving as both areference and training tool.
  • to illustrate ERS design methodology by means of selected sampleproblems.
  • to serve as a text for the AIChE/DIERS Continuing EducationCourse entitled "Emergency Relief System Design Using DIERS Technology."
If you have subscribed to KNOVEL...Click HERE
If you want to own ONE...Click HERE

Related reading

  • Requirement of overpressure protection devices on system design to PIPING code



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posted by Webworm, 1:22 AM | link | 0 Comments |

Saturday, September 15, 2007



This is a video clip shows launching of a ship at yard...

Click here for URL...




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Friday, September 14, 2007


High Temperature Hydrogen Attack (HTHA) is a form of degradation caused by hydrogen reacting with carbon to form methane in a high temperature environment.

C + 4H --> CH4

The methane forms and stays in grain boundaries and voids however it does not diffuse out of the metal. Once it accumulated in the grains and voids, it expands and forms blister , weaken the metal strength and initiate cracks in the steel.

High-strength low-alloy steels are particularly susceptible to this mechanism, which leads to embrittlement of the bulk parent metal (typical C-0.5 Mo steels). The embrittlement in the material can result in a catastrophic brittle fracture of the asset.

Following is a picture of Blistering in metal due to High Temperature Hydrogen Attack.



This paper summarizes the research and investigation activities related to HTHA, including the general information about HTHA.

Recent Activities On
High Temperature Hydrogen Attack


"Exisitng C-0.5Mo steel in hydrogen service is still our concern in industries. High Temperature Hydrogen Attack (HTHA) has been one of the major problems in petroleum and petrochemical industry because of its effect. Since the original Nelson Curves was suggested in 1949 to define the operating limits for steels used in hydrogen service to avoid HTHA, a number of research and investigation activities on HTHA have been carried out mainly in The United States and Japan.

In USA, API summarized these data as Publication 941 – “Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants” in 1970 and, since then, it has been widely used for material selection in hydrogen service, operation and maintenance in petroleum and petrochemical plants. In Japan, some organizations such as JSM, JPVRC and PVT have been tackling HTHA problems since 1970’s, and they suggested some assessment procedures for HTHA. Importance is how to evaluate this equipment to keep plant integrity.
"

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posted by Webworm, 3:30 AM | link | 0 Comments |

Thursday, September 13, 2007

There are some confusion or argument if over perssure protection devices e.g. Pressure Relief Valve, rupture disc, etc, shall be provided on a pressure containing part which designed to PIPING code i.e. ASME B31.3.

Some engineers interpreted that as long as the pressure containing part designed to PIPING code i.e. ASME B31.3, you got the waiver from overpressure protection.

Above statement may be true :
- if the INVENTORY capture in the system is LOW and associated RISK is LOW.
- if the system is TOTALLY FREE from overpressure scenario i.e. external fire, solar heating, etc. For example buried pipeline.

Requirement of PSV shall NOT be 100% judged from the design code itself. The RISK and CONSEQUENCE e.g. INVENTORY associates risk & consequences shall come into consideration to define if a overpressure protection i.e PSV is required.

Good engineering practices such as SHELL DEP 80.45.10.10-Gen, section 2.2.2, has provision of waiver of overpressure protection if made-of small inventory (<500 Liters), containing non-toxic fluid and fluid initial boiling point is higher than maximum ambient temperature.

Related reading









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posted by Webworm, 6:51 PM | link | 0 Comments |

Wednesday, September 12, 2007

In earlier post << DISTILLATION : Alcohol Distillation >> and << World Class Home Distillation >>, I have recommended some information on Making of Alcohol for those who are interested...

Now i would like to bring you <> directed by Ryan vanDijk.














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posted by Webworm, 9:07 AM | link | 0 Comments |

Monday, September 10, 2007

H2_Em

Earlier post << Hydrogen present and it's impact to metallurgy >> has discussed on how Hydrogen attack metal or alloy by reducing its ductility (ability to deform) and some preventive measures. This post will provide listing of standard test method used to a material potentially (or already) expose to hydrogen embrittlement.

Standard Test Methods (NACE, ASTM)
  • NACE TM0177 - laboratory testing of metals for resistance to sulfide stress cracking in H2S environments.
  • NACE TM0284 - evaluation of pipeline and plate steels for resistance to stepwise cracking.
  • ASTM G129 - slow strain rate test for determination of environmentally assisted cracking.
  • ASTM G142 - tension tests in hydrogen environments.
  • ASTM G146 - hydrogen induced disbonding of stainless clad steel plate in refinery hydrogen service.
  • ASTM F-326 - method for electronic hydrogen embrittlement test for cadmium electroplating processes.
  • ASTM F-519 - method for mechanical hydrogen embrittlement testing of plating processess and aircraft maintenance chemicals.
  • ASTM A-143 - practice of safeguarding against embrittlement of hot dip galvanized structural steel products and detecting embrittlement.
  • ASTM B-577 - hydrogen embrittlement of deoxidized and oxygen free copper.

Some guidelines for use of test methods :

  • General purpose - Slow strain rate test methods. Conservative results is expected.
  • High strength material - Constant load test method
  • Low strength material - Non-stressed coupons exposed to testing fluid
  • Material exposed to Hydrogen environment at high temperature - Special testing to be handled by specialist.
Related reading









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posted by Webworm, 3:32 AM | link | 0 Comments |

Sunday, September 9, 2007

embritt_title

In one of the field development project, the feed composition contain trace amount of hydrogen (H2). What extra pre-cautions that we needs to take care as compare to other hydrocarbon gases? One of the problems that shall always be taken care is Hydrogen embrittlement and material selection.

What is H2 embrittlement ?
H2 embrittlement is the embrittlement of metal or alloy involves hydrogen ingression in to metal or alloys matrix and significantly decrease it’s ductility (ability to deform), cause metal or alloys crack and catastrophic failure at stresses below normal yield stress level of the attacked material.

How H2 cause metal or alloys lose it ductility ?
Whenever metal or alloys expose to fluid contains hydrogen, hydrogen will dissolved in solid metal to give up it electrons to metal and form hydrogen nucleus which is very small. Small nucleus hydrogen will stay in the metal or alloys matrix, it probably will meet with another nucleus hydrogen and combine and form molecule Hydrogen. Molecule Hydrogen will expand and cause metal or alloys cracking in micro scale. This partially reduce it tensile strength. Expansion of molecule Hydrogen in metal or alloys matrix will displaced it metal further and decrease its ductility.

How H2 is introduce into metal or alloy matrix ?
Hydrogen can be introduced into metal or alloy :

  • manufacturing & making of metal or alloy
  • welding
  • contact with fluid contains hydrogen
  • electroplating
  • cathodic protection
  • rusting (corrosion)
  • phosphating
  • pickling

Metal cracking cause by H2 embrittlement
Following are some images shows cracking caused by h2 embrittlement.

H2_embrittlement_cracking_High_stregnth_area


H2_embrittlement_cracking_Boiler

H2_embrittlement_cracking_SS


How to minimize or avoid H2 embrittlement ?
There are number of ways to minimize or avoid H2 embrittlement :
a) minimize amount of residual H2 in metal or alloy during fabrication
- Cleaning, preheating, keep dry during welding
- avoid rapid heating and cooling
- Post Weld Heat Treatment of metal or alloy

b) minimize amount of H2 pick up by metal or alloy during operation
- avoid using chemical or additive generating H2

c) Use high resistance to H2 embrittlement material e.g. aluminium, plastic, etc
d) Use low strength metal or alloy
e) Use plating or coating process with low or no hydrogen generation



Further reading





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posted by Webworm, 6:57 AM | link | 0 Comments |

Thursday, September 6, 2007

hitran_flow

In one the recent depleted field debottlenecking project, new Booster Compression unit will be installed to boost the depleted well fluid pressure to meet high delivery pressure while maintaining the production forecast market demand.

As this unit will be installed on existing platform, space and weight constraint are the MAJOR issues. Many efforts have been implemented in order to reduce new installation space and weight. One of them is to reduce the Lube Oil Cooler Size.

How to reduce lube oil cooler size while meeting duty and flow ?

Turbulator


The following image demonstrates a wire matrix turbulator by hiTRAN


inkflow

Wire matrix turbulator, known as a HiTRAN® Matrix Element, is inserted into inner tube of Heat Exchanger. The basic principle is to promote fluid mixing, convert laminar flow to turbulence flow pattern, maintaining turbulence flow pattern and improve tube-side heat and mass transfer.

From above image,
- region (A) is laminar flow conditions
- region (B) is turbulence caused by the use of hiTRAN matrix tube Inserts

See below the comparison between Compressor lube oil cooler (Air-Cooled Heat Exchanger) with and without turbulator :

Number of tube rows above each other 5* (with turbulator) 10*
(without turbulator)
Width 4* m(with turbulator) 7.3* m (without turbulator)
Length 7.9* m (with tubulator) 12.2* m
(without turbulator)
Height 7.2* m (with turbulator) 9.3* m (without turbulator)

* For reference only

Turbulator has significantly reduce the space consume and weight and it ensure the project to proceed to installation phase. Idea of using turbulator is one of the success story in debottlenecking project especially those have space and weight constraints.

Further Reading









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posted by Webworm, 5:59 PM | link | 0 Comments |

Tuesday, September 4, 2007

Just back from long vacation...Will continue my posting...

Milt Beychok from www.air-dispersion.com has shared a schematic flow diagram of a typical GAS PROCESSING that depicts the various unit processes and the flow of intermediate product streams that occurs between the inlet Gas with associate condensate as feedstock and the final end products. This image has given a brief idea how gas/condensate goes through separation and purification. Products included Condensate, C2, C3, C4, Light gas (high C1), and side product elementary Sulfur.



NatGasProcessing

Click image to view original











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posted by Webworm, 9:46 PM | link | 2 Comments |