Sunday, March 30, 2008
Display problem ? Click HERE
In site experiencing summer and winter, normally the air cooler (heat transfer area) will be designed based on maximum ambient air temperature during summer. However, ambient air temperature will drop significantly during winter and those air cooler handling wet gas (saturated with water vapor or free water found in vapor phase) will potentially experience hydrate formation as the fluid temperature cooled below the hydrate formation temperature of fluid. How the tackle this kind of issue ?There are few practical means to tackle hydrate formation downstream of air cooler which only occur during winter.
(i) Manual shutdown of fans
Install a temperature transmitter with low temperature alarm (LAL) downstream of air cooler outlet to monitor the fluid temperature. In the event the fluid temperature decrease as the ambient temperature is dropped, once it reaches the LAL set point and triggers alarm, operator may stop some motors (fan) to reduce forced air flow and reduced heat removal from air cooler. As this action required operator attention and uncertainties in fluid composition, it is recommended to provide more margin on the set point i.e 10 degC above hydrate formation temperature.
(ii) Auto-Control Air Flow
Install a temperature transmitter with low temperature alarm (LAL) downstream of air cooler and Variable Speed Drive for air cooler motors so that the vapor temperature is maintained at some margin (e.g. 5 degC) above hydrate formation temperature. In this way, the fluid temperature is maintained by controlling air flow (controlling motor speed) via air cooler tubes,hence the heat removal from process fluid.
You may aware that other than above mentioned benefit, there are other benefits as discussed in Variable Frequency Drive (VFD) helps in Many Aspects (click here).
VSD control is one the effective means in controlling air cooler outlet temperature. There are other means of controlling the temperature as discussed in Air Cooled Heat Exchanger Control using Variable Pitch Fans.
(iii) Inject Hydrate Inhibitor upstream of Air cooler
This is one of the common method in controlling hydrate formation. However, the continuous consumption of hydrate inhibitor could lead to high life cycle cost of the plant and may not be attractive at all. Apart, there are other problems associate with hydrate inhibitor (i.e. methanol, MEG, TEG, etc). If methanol is used, it will stay in vapor form and follow the vapor to downstream processing facilities. Methanol is not easy to be removed from the gas phase and methanol-water mixtures when it is knocked out as liquid in cold section. If MEG /MEG is used, it potentially poison downstream equipment such as membrane and form a contaminant in gas phase.
Apart, some may consider to provide a bypass around the air cooler so that hot fluid from upstream of air cooler warm with fluid outlet of air cooler and expecting mixture is above hydrate formation temperature. This will ONLY help in fluid downstream of mixing, but hydrate formation still occur upstream of mixing point. Hot bypass DOES NOT HELPS !
Another aspect one shall remember is mal-distribution of air flow within the air cooler tube bundle would lead to some tubes experience higher air flow compare to other tubes and results fluid in some tubes experience temperature lower than hydrate formation temperature. Hence, whenever the hydrate temperature is lower than minimum ambient temperature, mal-distribution of air flow within tube bundle shall be analyzed in detail. Moreover if the fluid entering air cooler is two phase gas liquid flow, phase separation at the distribution header would even worsen above scenario.
Related Post
- How much heat removal by natural convection when Air Cooler fan off
- Success story of turbulator in Air Cooled Heat Exchanger
- Heat Transfer Coefficient For Air-Cooled Heat Exchangers
- Air Cooled Heat Exchanger Control using Variable Pitch Fans
- Design of Quiet Air-Cooled Heat Exchangers
- Should Forced Draft or Induced Draft Air Cooler be employed on offshore platform ?
Labels: Air Cooler, Fan, Heat Exchanger
Friday, March 28, 2008
Display problem ? Click HERE
Earlier post "Quatitatively compare Variable Speed Control (VSC) with Conventional Flow Control in Pumping system", PumpSave has been introduced to estimate energy saving when apllying a variable speed control in a pump.
Recommended Utility :
PumpSave is a tool developed by ABB to enables you to estimate energy (money) saving when apply Variable Speed Control (VSC) compare to traditional control such as throttling control, On/Off control and Hydraulic control. In addition, it provides financial indicators (e.g. Payback period, annual saving, NPV, etc) to assess the benefits of adopting Variable Speed Control (VSC).
If you still do not aware of the benefits of Varaible Speed Drive (VSD), read earlier post in "Variable Frequency Drive (VFD) helps in Many Aspects"
Similarly Variable Speed Control (VSC) can be used in controlling a fan for air cooler.
FanSave has been developed by ABB for comparing AC drive control against traditional flow control methods in fans and estimate savings you can achieve by replacing outlet damper, inlet vane or pitch control methods with VSC. Similarly FanSave provides financial and environmental indicator for justification.
Try it out and share your experience with many others here...
Related Post
Try it out and share your experience with many others here...
Download FanSave (Click here)
Download FanSave Operating manual (Click here)
Related Post
- Quatitatively compare Variable Speed Control (VSC) with Conventional Flow Control in Pumping system
- Variable Frequency Drive (VFD) helps in Many Aspects
- Pump Pressure Versus Head
- Why Centrifugal pump NPSH required increases with flow ?
- Tips for Centrifugal Pump
- Consider energy saving by optimizing the pump control
Labels: Energy, Environment, Fan
Sunday, December 9, 2007
Natural Convection PhenomenonAn air-cooled heat exchanger fan off, heat transfer by natural convection may continuous where the air movement is resulted by the air density difference between cool ambient air and hot air (near tube with hot process fluid) within the tube bundle and duct. Natural air cooling may leads to some adverse and process problem. Two major examples are
1) waxy fluid crystallized & solidified and water freezing in air-cooled heat exchanger
2) Inability for vapor to condensed results vapor passing across air-cooled heat exchanger
Process design engineer shall address above scenarios as part of the design and understanding ability of natural air cooling becomes important.
Natural Convection Heat removal by Induced Draft & Forced Draft Fan
Works carried out by Berryman (1983) and Henry (1988) has shown that heat removal from induced draft and forced air cooler in the range of 20-40% and 5-15% (of normal heat duty) respectively. The percentage is increased with wind velocity. Refer to following image.
Higher heat removal is expected in induced draft compare to forced draft. This could be caused by the location of fan and fan blades. In forced draft (where fan is located below the tube bundle), fan blades will create disturbance of air flow and affect proper air distribution across the tube bundle and leads to lower heat removal. Disturbance of air flow may increases the possibility of vortex (air recirculation) formation between the fan blades and tube bundle. Air recirculation will reduce net cool air intake into tube bundle and lower heat removal.Credit During Fan Off
Apart from process issue as discussed, natural air cooling by air-cooled heat exchanger during fan off and/or shutdown condition will help to reduce process fluid temperature. In the event of power failure which lead to fan off, residue hot gas may continue pass through air-cooled heat exchanger and results downstream system temperature continue to rise. Natural convection will partially cool the hot gas. Determining quantity of heat removal by natural convection for CAPEX optimization and maintaining plant integrity is getting critical in this context. API has provides some allowance in natural convection. Per API STD 521, section 5.6.4 Air-Cooler fan failure, partial condensing capacity of 20% - 30% of normal duty can be taken for natural convection of air-cooled heat exchanger. However, API STD 521 has not differentiated allowance for induced draft and forced draft fan.
Additional Thought
Considering Berryman and Henry studies, credit statement in API STD 521 and still air condition, the reasonable heat removal by natural convection during fan off for induced and forced draft may be 20% and 5% of normal duty respectively.
Besides, as the reasonable heat removal only 5% for forced draft, it has minimum incentive for further optimization and process designer can choose to ignore. However, 20% for induced draft is at it lower end and has reasonable incentive for further optimization, thus process designer may consider take the allowance but shall always confirm with final design during detailed design and fabrication.
Related Topic
- Success story of turbulator in Air Cooled Heat Exchanger
- Heat Transfer Coefficient For Air-Cooled Heat Exchangers
- Air Cooled Heat Exchanger Control using Variable Pitch Fans
- Design of Quiet Air-Cooled Heat Exchangers
- Should Forced Draft or Induced Draft Air Cooler be employed on offshore platform?
Labels: Air Cooler, Fan, Forced Draft, Induced Draft
Sunday, August 19, 2007
There are several ways of controling process fluid temperature of an Air Cooled Heat Exchanger. They are tabulated as follow :
i) Fluid bypass (manual)
ii) On-off fan operation (manual)
iii) Two-speed fans (manual or automatic)
iv) Louvers or shutters (automatic)
v) Variable pitch fans (automatic)
vi) Variable speed fans (automatic)
ii) On-off fan operation (manual)
iii) Two-speed fans (manual or automatic)
iv) Louvers or shutters (automatic)
v) Variable pitch fans (automatic)
vi) Variable speed fans (automatic)
Out of all methods, variable speed fans control is considered the most reliable as compare to others. Nevertheless, R.C. Monroe from Hudson is proposing variable pitch fans...Read more in the following article.
R.C. Monroe
Hudson Products Corp. Houston, Texas
Further Reading
Labels: Air Cooler, Fan, Heat Exchanger
Saturday, August 18, 2007
Many industrial facilities are required to meet stringent noise requirements. These requirements are imposed to protect workers’ hearing and/or to meet community ordinances. The facility designer must pay careful attention to the noise level of all industrial equipment, including air-cooled heat exchangers.
Air-cooled heat exchangers are a source of plant noise. Therefore, it is important to design each unit to produce the minimum amount of noise while still meeting the thermal requirements at a reasonable cost.
This paper discusses the major noise sources of an air-cooled heat exchanger, the factors affecting the noise from each source, and how the source affects the overall noise level of the air-cooled heat exchanger.
Further reading
Labels: Air Cooler, Fan, Heat Exchanger
Friday, August 17, 2007
Tuf-Lite
Axial Flow Fans for Air Cooled Heat Exchanger & Cooling tower from HUDSON Product Incorporation (HPC)
Read The Basics of Axial Flow Fans for basic understanding of Axial Fan especially Tuf-Lite series. You may check-out the differences between these 3 generation of Tuf-Lite axial fans with following links :
If you are plant / maintenance or isntallation engineer of axial fans, your may be interested to read Axial Fans Manual, Fan assembly & installation instruction, Field inspection Guidelines and Proper Belt Tension.
Further reading
Labels: Air Cooler, Fan, Heat Exchanger
Thursday, August 16, 2007
Apart from FREE software for download, HUDSON also share other very useful articles in it website...
Basic of Air-Cooled Heat Exchanger (ACHE)
This is very good article for a beginer involve in design and operation of an air-cooled heat exchanger. In this article, many aspects of air-cooled heat exchanger has been discussed. Those aspects include Components in Air-cooled heat exchanger, construction of forced draft fan and induced draft fan air-cooled heat exchnager, tube bundle construction, type of fins, comparison between forced draft fan and induced draft fan, thermal design of air cooled heat exchanger, Typical Heat Transfer Coefficients for Air-Cooled Heat Exchangers, fan selection, controls, etc.
Other very useful articles available for FREE download in HUDSON website are :
Further Reading
Labels: Air Cooler, Fan, Heat Exchanger
Tuesday, August 14, 2007
HUDSON Product Corp. (HPC) a well known Air cooled Heat Exchanger. Establish since 1939, has designed and manufactured air-cooled heat exchanger equipment to serve the oil, gas and petrochemical processing industries. HPC is pioneer in this field, has developed several international recognized air cooled Heat exchanger product :
- Fin-Fan ® Air-Cooled Heat Exchangers
- Hy-Fin ® Extruded Finned Tubing
- Tuf-Lite ® FRP Axial Flow Fans for air coolers and cooling towers.
- Tuf-Lite I I® FRP Axial Flow Fans for air coolers and cooling towers.
FREE Air-cooled Heat Exchanger and Fan rating Softwares available for download :
- Basics of Air-Cooled Heat Exchangers - This software is designed to familiarize users with the types, components, and features of air-cooled heat exchangers.
- Fan-Rating Program - The Tuf-lite Fan Selection Program is designed to assist customers in selecting the appropriate axial flow fan for their application.
Further reading
Labels: Air Cooler, Fan, Heat Exchanger
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 :
- Hot Air Recirculation by Air Coolers (3.6MB)A.Y. Gunter and K.V. Shipes, Hudson Products Corp., Sugar Land, Texas
Labels: Air Cooler, Fan, Forced Draft, Induced Draft
