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Chemical Process Technology

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Chemical & Process Technology

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Tuesday, July 31, 2007






Above question started with a simple query raised in the Chemical Resource Forum.

"Plate Type Heat Exchangers V/s STHE - We are planning to replace an existing Shell & Tube HE with a Plate Type HE as the existing one is not offering the desired effect. The duty of the HE is attached. Since one of the fluid handled contains solids, can a PTHE handle it? I would like to know if similar retrofits have been carried out and what are the precautions to be taken while opting for such a change ? "

How do you interprete above question from engineer perspective ?




How do you interprete "fluid handled contains solids" ?




The process may contains solid can be
(a) high concentration, small particle size or;
(b) high concentration, large particle size or;
(c) low concentration, small particle size or;
(d) low concentration, large particle size



Above combination may end-up with different heat exchanger which best suit their own need. Thus, whenever specify solid in fluid, concentration (wt% or ppmw) and particle size (micron or mm) are required to be spelt out so that other (vendor , consultant) can provide the most cost effective solution whilst meeting process demands.

Can PHE take fluid with solid in it ?

PHE is having a very unique feature where narrow channel and proper engineered cross-sectional areas promote turbulence and high heat transfer (convective) capabilities. High turbulence has the potential of removing scale stick on the plate. However, present of solids in fluid promote pluggage in the narrow channel and ultimately results NO flow.

(Click image for better view)


What are the option can be suggested here ?

Probably first and ordinary option is relook into the root-cause of under-performed STHE by analyses the STHE construction, review maintenance frequency and methodology, etc and check if there is oppurtunity to modify existing STHE to increase heat exchange performance.

Somehow if it has to be replaced, there are some type of heat exchanger which properly suitable for "fluid contain solids". There are :

Spiral HE (Alfa Laval , Sentry)
Self-Cleaning HE (KLAREN)

Further reading :













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posted by Webworm, 2:54 AM | link | 0 Comments |

Saturday, July 28, 2007



CHEMICAL ENGINEERING magazine shared the following useful information....
<<
HEAT TRANSFER >>
Some of you may already aware of this table. However, i would like to park here for the benifits of :
  • those who still don't know
  • those lazy to do filing
  • those who knew but failed to locate it again
This sheet contains very useful Heat Transfer Equations which commonly use by many engineers, designers, educators, students, etc. The equations include :
  • Basic equations For Conduction, Convection & Radiation
  • Basic equations use in Shell-and-Tube-Heat-Exchanger
  • Basic equation for Batch Heating
  • Basic equations for Steady State Heat Flow by Conduction
Further Reading










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posted by Webworm, 9:08 PM | link | 0 Comments |

Friday, July 27, 2007



PSV is a final safeguarding device to prevent equipment or system from catastrophic failure. However, this device may not protecting equipment and/or system from FIRE attack. We may only rely on other active and passive protecting system to safeguard the system.
A wet gas KO drum operate at LOW pressure & LOW temperature. External FIRE (regardless of POOL or JET fire) heating up it gas via metal wall. As gas is low in heat transfer (~ 7 - 20 kW/m2), the heat absorbed by vessel wall do not dissipate into gas fast enough and tends to stay in the metal wall. Vessel wall (flanges, gasket, etc) probably failed before the internal pressure reached it PSV set pressure.

JET FIRE
Installing PSV does not protecting the vessel from Fire attacks regardless of pool nor jet fire. Practically, we shall shift the focus to :

  • emergency depressurization system

  • high SIL instrumented protective system

  • fire proofing system

  • high firewater spray density
Jet fireis initiated from flanges leakage, cracked pipe, damaged of some fitting attached to large pipe, etc. It subject to

  • internal pressure at release point

  • flame direction

  • relative distance between release point and impinged vessel
Jet flame contain very high momentum which impacting to the impinged vessel (but reduce according as pressure depleted), etc. There are many other transient parameters evolve with time such as wind speed, wind direction, etc.
Fire impinged area may expose to very high localised heat flux (>300 kW/m2), as the flame travel around the vessel, the heat flux reduced accordingly. Many documents e.g. "Guidelines for Protection of Pressurised Systems Exposed to Fire", by Scandpower Risk Management AS, quoted jet fire heat flux of 300 kW/m2 is just an average heat flux.
As indicated in latest API Std 521, section 5.16 "...a relief device might not prevent vessel failure from jet fire impingement.", those sizing PSV protecting a vessel may not needs to consider jet fire heat flux.
POOL FIRE
In conclusion,

  1. PSV will only be sized for pool fire using the API 521 equation

  2. Focus on emergency depressurization. Use jet fire heat flux rather than pool fire heat flux. CAUTION : if you use HYSYS, the model only use API 521 equation. Some configuration is required to estimate depressurization rate based on jet fire heat flux.

  3. While conduct depressurizations study, ensure maximum allowable working pressure due to reduce wall stress (reduce according to time) is always above internal pressure exert on the vessel wall.

  4. Increase wall thickness or apply external fire proofing if necessary.

  5. Conduct Scenario and Quantitative Risk Analysis, Jet fire flame pattern analysis etc if above measures are too excessive









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posted by Webworm, 7:05 AM | link | 1 Comments |

Thursday, July 26, 2007



Today i read an article in HYDROCARBON PROCESSING, June 2007,
<< MINIMISING FACILITY FLARING >>
and found a site related to FLARE...A site for International Flare Consortium (IFC).
The International Flare Consortium (IFC) was formed to address the gaps in science with respect to emissions from flares and to establish best practices. The landmark studies of the 1980s provided much useful information but did not account for the effect of wind. More recent wind-tunnel work in Canada was limited to simple production flares. To date there is no systematic study of the effect of fuel composition on performance of flares.



The goals of the IFC are:

  • Provide emission factors for production and refinery flares, including the effect of steam rate, composition and flow rate of fuel, and wind speed.
  • Establish optimal operating conditions, maximizing combustion efficiency and minimizing pollutant emissions.
  • Set operating envelope outside of which flares should not be operated.
One very interesting article available FREE to public from IFC :

<< Reaction Efficiency of Industrial Flares >>

"This paper compares and contrasts reaction efficiency findings on properly designed and operated industrial flares with those of rudimentary field flares and shows that the results on the latter hardly apply to the former. We review the most significant of the contributions to flare emissions research of the last three decades and provide the background perspective of researchers who were directly involved in leading and executing the 1980's flare efficiency studies that formed the foundation for future studies. These landmark studies demonstrated that properly designed and operated industrial flares are highly efficient and led to the codification in the United States Environmental Protection Agency's 40CFR60.18 General Requirements for Flares of the conditions that ensure the proper operation of industrial flares."

One of the interesting parameter that i have always been looking for is the Flare combustion efficiency...from this article...98% combustion efficiency and it is supported by a well known organization.

For those would like to made to reference...here is the place.









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posted by Webworm, 8:42 AM | link | 0 Comments |

Wednesday, July 25, 2007


Just read a news by Bette Lawler, AICHE Director of Operations,

"Dear AIChE Member:A number of members have reported that they have received calls from a group claiming to represent AIChE or CCPS asking them to participant in a Survey about Process Safety. Neither organization is conducting such a survey. It is not yet clear how many members may be being contacted or how their information has been obtained. There is concern, in light of recent Terrorist Activity, that this may be an attempt to determine security vulnerabilities in the chemical process. The FBI has been notified and is investigating. If any member receives such a request, please make an effort to determine the person's identity, and immediately notify Scott Berger ccps@aiche.org or call AIChE at 212-591-7319."
If happened that you received such survey request, please take serious notes and consideration on providing information.
Please copy above news and inform your lovely friend...










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posted by Webworm, 8:35 AM | link | 0 Comments |

Tuesday, July 24, 2007



A strong debate taken place in a project that i am working on...........
Should we install Forced Draft (FD) Air Cooler or Induced Draft (ID) Air Cooler on an offshore platform ?
Induced draft fan is generally prefer from air cooling perspective as forced generally more prone to hot air recirculation. However, this potential expose maintenance group to hot air and huge resistance given by the operation & maintenace team.
Benefits / advantages of using forced draught fan are :
  • Maintainability - Forced draught fan easier to maintain, better accessibility and handling of fans & drive-assembly
  • Power - Lower power consumption for forced draught fan
  • Vibration - Less prone to vibration due to shorter fan shaft employed for forced draught fan
  • Cost - Lower initial cost and more economical to maintain for forced draught fan
  • Space - Forced draught fan require less space, especially lesser plot width


However, disadvantages of using forced draught fan are :

  • Inlet air distribution - Less uniform air distribution and higher tendencies of hot air recirculation
  • Noise - Forced draught fan has higher noise level
  • Control - Less controllability as compare to Induced draft fan

Conclusion from the debate is FORCED DRAFT fan will be installed only after Hot Air Recirculation Analysis using CFD has been carried out to definitely confirm air temperature will not accumulate and affect the air cooler performance.

Further reading :










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posted by Webworm, 6:33 AM | link | 0 Comments |

Monday, July 23, 2007



CHEMICAL ENGINEERING magezine also shared the following articles within the community...If you are still fresh in Chemical and Process Industrial, I would recommend you read the first article by Jenniffer. It is simple and practical...Process / Plant expert like some of you...please proceed to second article. There are more consolidatred and philosophical / conceptual kind of approaches...
Jennifer Keith
Flow Technology, Inc
This article provides an overview of flowmeter selection criteria and practical advice for evaluating common meter designs and for pairing the right instrument technology with various flow-measurement applications is offered. Intangible factors shall also be considered which include familiarity of plant personnel, their experience with calibration and maintenance, spare parts availability, and mean time between failures at the particular installation site.
Gernot Engstler
Endress + Hauser
High demand from chemical process industry (CPI) has pushed the manufacturer to provide high performance instrumentaion and flowmetering solutions include tools for the entire life cycle of a flowmeter.
From engineering, commissioning and start up to operations and maintenance, advanced diagnostics and onsite device-verification features help to maximize plant availability, instrument reliability and cost savings. Flowmeter instrumentation can even provide process status and analysis information that can be used to increase product quality and process efficiency. In addition to requiring high performance, users increasingly look for sensors that are easy to install, commission, use and maintain. Flowmeters that are tailored to the specific requirements of an industry or application can reduce the complexity and costs of operation. In this article, we look at some of the advanced functions of flowmeters.
Further Reading









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posted by Webworm, 4:30 AM | link | 0 Comments |

Sunday, July 22, 2007


CHEMICAL ENGINEERING magazine shared the following useful information....

<<

FLOWMETER SELECTION >>, by Rebekkah Marshall

Briefly discusses general selection criteria, flowmeter accuracy and turndown...









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posted by Webworm, 9:49 PM | link | 0 Comments |

Saturday, July 21, 2007



Tubular Exchanger Manufacturers Association (TEMA) has developed a series of fouling factor for Shell and Tube (S&T). These fouling factor are generally higher than Plate Heat Exchanger (PHE), why not use S&T fouling factors to size PHE ?
Isn't this approach conservative and guarantee the performance ?

Reason being...

  • Oversized Plate Heat Exchanger (PHE) required extra CAPEX and extra Space for oversized PHE
  • Tubulence minimise fouling tendencies in correctly sized PHE. Oversized PHE results low actual velocity and increase potential fouling and inefficient heat transfer
  • HTRI studies showed PHE fouling significant lower than Shell & Tube Heat Exchanger (S&T)...factor of 6.7

GUIDELINE : Do not oversized PHE more than 25% against required area.

Further reading :











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posted by Webworm, 1:50 AM | link | 0 Comments |

Friday, July 20, 2007


If you plant / maintenance engineers, you probably interested to the following articles...

POLARIS, a Heat Exchanger manufacturer from Denmark. POLARIS supply Plate-and-Frame, Brazed, Safety-Pair Double-Wall Plate, Semi-Welded Plate and Free-Flow Plate Heat Exchangers.
FREE Operation and Maintenance Manual Available for download from POLARIS

Simpel operation guideline presented in the manual for Brazed Heat Exchanger. It covers how a brazed heat exchanger is operated, application, specification and advantages of brazed heat exchanger, installation guide, start-up & shutdown as well as cleaning procedures.

Plate-and-Frame Heat Exchanger Operation and Maintenance Manual
This manual briefly discusses a Plate Heat Exchanger Construction, function and characteristic, the gasket design, installation and start up procedures, maintenance & cleaning procedures.
Further reading...









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posted by Webworm, 8:20 AM | link | 0 Comments |

Years come and go...But today is just a little bit special...

~ 20072007 ~

Double Match...
It happens only once in a lifetime ..
I wish you a very Wonderful Day !









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posted by Webworm, 2:14 AM | link | 0 Comments |

Wednesday, July 18, 2007




As discussed in previous post, Carbon Dioxide (CO2) is known as one of industrial waste gas causing global warming...there are number of measures are implemented to reduce global warming. CO2 reduction measures are CO2 capturing, reinjection into aquifer, injection into reservior for well maintenance, gas injection for enhanced oil recovery (EOR), etc.
Co2 being captured will be injected in the reservior. The injection can be as high as 300-400 atm which is higher than the critical pressure of Co2.
How does Co2 in Supercritical looks like ?
The following image (running in sequence) shows liquid Co2 under pressure boiled and transform itself to supercritical fluid (SCF).

CLICK IMAGE...
Source : Nottingham University
See also Video Clip (Better view by Windows Media Player or equivalent)
Further Reading










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posted by Webworm, 9:46 PM | link | 0 Comments |

Tuesday, July 17, 2007



"Cooking a Vessel"

Have you ever heart of this term in Process Engineering ???

This term probably mean heat up (and circulate when possible) a solution inside a dirty or impure vessel for the sake of dissolving or simply rinsing out the internals prior to sweeping it with a semi-pure fluid and conditioning the vessel for production service.
This is a necessity when you done internal work inside a distillation column, for example, during an annual turn-around and there are traces of grease, oils, and gasket adhesive and other "goodies" inside the assembled and repaired internal parts. In order to ensure that all these impurities are not mixed in with the finished product, the column, reboiler, condenser, associated vessels and all their internals are "cooked" with a hot fluid - usually a solvent or a hot caustic solution - in order to rinse and sweep out all undesired impurities left in the vessels after human entry.Other Forum members may have the same terminology for other techniques used in their plants.
Source : Art Montermayor
During precommissioning / commisioning phase, some system may required acid cleaning in order to remove grease, oil, corrosion stuff, welded slag, etc. Through acid cleaning, it may oxidize metal surface layer so that it form a strong and corrosion resistance layer for vessel protection. Sometime, it called passivation and "cooking a vessel" in layman term.









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posted by Webworm, 1:24 AM | link | 0 Comments |

Monday, July 16, 2007



Let's some interesting articles from Dr.R. Shankar Subramanian, University of Clarkson
How to Design a Shell-and-Tube Heat Exchanger

A lot has been written about designing heat exchangers, and specifically, shell-and-tube heat exchangers. For example, the book by Kern (1) published in 1950 details basic design procedures for a variety of heat exchangers. Since the publication of that book, with the advent of computers, design procedures have become sophisticated even though the basic goals of design remain the same. Because it is possible to specify an infinite number of different heat exchangers that would perform the given service (heat load), we have to identify the specific heat exchanger that would do it subject to certain constraints. These constraints can be based on allowable pressure drop considerations either on the shell-side or on the tube-side or both, and usually include that of minimizing the overall cost. An article in 1979 by Taborek (2) outlines how heat exchanger design techniques evolved over the years since the appearance of the book by Kern. More recent developments are discussed in numerous articles in the magazine “Chemical Engineering.”
Here is a step-by-step approach to specifying a new shell-and-tube heat exchanger. We shall focus on sensible heat transfer, and make extensive use of Chapter 11 in Perry’s Handbook (3). From hereon, references to page numbers, table numbers, and equation numbers are from Perry’s Handbook.
R. Shankar Subramanian,
University of Clarkson









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posted by Webworm, 4:29 AM | link | 0 Comments |

Sunday, July 15, 2007



Wanna to share some findings today...some notes from Dr. Shankar Subramanian, University of Clarkson.
Heat Transfer to or from a Fluid Flowing Through a Tube

A common situation encountered by the chemical engineer is heat transfer to fluid flowing through a tube. This can occur in heat exchangers, boilers, condensers, evaporators, and a host of other process equipment. Therefore, it is useful to know how to estimate heat transfer coefficients in this situation.
We can classify the flow of a fluid in a straight circular tube into either laminar or turbulent flow. It is assumed from hereon that we assume fully developed incompressible, Newtonian, steady flow conditions. Fully developed flow implies that the tube is long compared with the entrance length in which the velocity distribution at the inlet adjusts itself to the geometry and no longer changes with distance along the tube.
R. Shankar Subramanian,
University of Clarkson
Heat transfer in external flow
External flows occur when the fluid is confined in such a large channel or container such that it can be considered practically unbounded in extent when considering heat transfer to a stationary solid surface. The ideal starting point for this is flow over a flat plate that is long and wide. We know that in this situation, for flow at large values of a suitably defined Reynolds number, a boundary layer forms on the surface in which the velocity varies from zero (no slip) at the solid surface to the value in the free stream. Outside the boundary layer, viscous forces are entirely negligible, and potential flow can be assumed to prevail. Potential flow means flow in which the vorticity is zero and viscous forces are neglected.
R. Shankar Subramanian,
University of Clarkson









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posted by Webworm, 10:17 AM | link | 0 Comments |

Thursday, July 12, 2007















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posted by Webworm, 8:41 AM | link | 0 Comments |