Fin Fan Coolers Pitch Control

[askme]

Dear Friends;

I wonder if some of you are aware of the fin fan coolers pitch control. This mechanism is used to adjust the fan blade oreintation to be more telted and hence increases or decreases the air flow.

My question; is this installation cost effective and can be used for energy conservation?

Thanks

 

[TD2K]

Yes, it reduces the air flow and thus power requirement by the fan. I don't know how it compares to other options like speed control.

 

[speco]

Dear Askme,

TD2K is right. There is some energy savings to be had by using auto-variable pitch fans. However, I believe the cost of variable-frequency drives has come down to the point where A-V fans are no longer the preferred method of control. I work with air-cooled exchangers all the time, and it's been years since anyone has asked for an A-V fan on their coolers, at least the ones that I have seen. VFDs are very common now.

Regards,

speco (

http://www.stoneprocess.com)

 

[Montemayor]

Your question encompasses two points and the corresponding answers are:

1) You, as the owner-operator is the only entity in position to confirm that the installation of variable pitch fans is "cost effective". You are the only one who can identify the total capital and operating costs involved in your part of the world and your working conditions. You, therefore, are the only one who can define "cost effectiveness" for your organization. Perhaps the cost of capital is more - or perhaps less - than in other parts of the world. We don't know, and we can't tell. The only one who can make a credible Return On Investment (ROI) based on a Discounted Cash Flow (DCF) analysis is you. That's the way I define whether a project is cost effective or not. I recommend you do the same.

2. As TD2K and Speco point out, there are energy savings involved in employing a variable-pitch fan. However, the magnitude of the savings (& of the ROI) depends greatly on the local cost of energy and the amount of variable heat load that you have in your process. Again, only you know these facts.

Anyone contributing to this thread can only assert the quality of energy savings potentially existing in a variable-pitch fan. However, we can't quantify the degree of savings - and much less magnitude of the attractiveness of those savings. Without any hard and factual basic data that is all anyone can say. Sorry.

 

[appy1]

Askme,

This is very useful control to reduce power consumption, infact many of finfan cooler in petrochemical company employed this with substantial reduction in power consumption.i have seen reduction in motor horsepower by 20% by keeping pitch closed as against fully open. But this depends on your discreation as that may increase o/l stream temperature.
we employed pitch adjustment as an interlock with finfan o/l stream temperature and hence it works mostly as VFD and added to this when during night hours, when outside temperature is relly low (in tropical countries), all pitch turns to zero, even then o/l stream temperature goes down, in that case it is simple to stop one of the fan and still control is in your hand with pitch opening 60 to 70% and o/l temperature in the range.
I think this helps.

 

[Zoobie]

I think all the respondents thus far have given 'spot on' advice. Your evaluation will be very heavily dependent on geography (ie local climate) in addition to accounting for process effects. While it may not apply to you, I would consider in the economics the effects of maintenance. I have an application where fan pitch is manually adjusted on each fan twice a year (and there are a lot of fans). That is because the seasonal variations are so extreme here that max air flow is needed in the summer but in the winter the air is so much more dense that the fan motors trip. If I were evaluating this for my situation I would take a credit for several thousand dollars in addition to the power savings. Of course once you bring maintenance into the picture you have to consider the flipside...will things need to be fixed more often?

 

[RogerH]

One additional point of view when it comes to pitch control vs an alternative as VFD. VFD is easy to check function by a tachometer e.g. if one wants to maximise cooling wheras pitch control can be trickier to check , without shutting down the fan.
Maintenance cost to my experience is higher with pitch control than compared to VFD's.
Have replaced some pitch control based fans only based on maintance cost and problems to get them reliable with VFD.
Looking from the process side e.g. balancing a multiple bank fin-fan exhanger I found VFD to control the temperature better than e.g. pitch control. The control issue have got me "sold"on VFD in favour of any other control including Pitch.

 

[abutt116]

Somebody could tell me about process air heater (shell and tube) design (air heating with steam) calculations.

Thanks.

 

[ScottyUK]

It is commendable that you are looking for ways to improve the efficiency of your plant.

Variable pitch fans are really an outmoded technology in most circumstances, unless you have either very large - multi megawatt - fans or your process has some peculiarity precluding use of a VSD-induction motor combination. The remarkable precision of speed control and the greatly reduced mechanical stress on the fan during acceleration are two of the key advantages of the VFD. The cost of a VFD has fallen enormously as they have become accepted as commodity items and increased production volumes have allowed economies of scale to be passed on to the user.


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