ventilatiom of boilers water feed pumps!!!

[etchyHA]

hi

]i ve asked to ventilate boilers water feed pumps there are 3 pumps each 4MW I/POWER any ideas or experience at this issue wil be good

thanx for advance

 

[etchyHA]

sorry i ment boilers feed water pump room! thanx again

 

[imok2]

Is it just me or are the questions these past few months in need of some serious logic in explanation of what the poster is asking? (confused)

 

[SAK9]

Imok2,

I am with you on this.I beleive this forum is for exchange of ideas and experience among serious professionals in the industry.It is definetly not the place for a bunch of lazy guys who want the easy way out!

This has been a trend of late as you rightly noted.The only way to correct things is to ignore such questions.That way we can ensure that they do not stay in the main page for long!

 

[etchyHA]

iam not lazy as u tink i dont log in every day to see all forum and i dont know if it was sent before .

the boiler's pump room is for power plant and have been

ventilated by 3-fresh fans it's cap.1150 m3/hr the pumps are 3 MW each the f.fans doesnt work the designer put them at a south wall not far from the boiler all i asked for is a hand of help what should i do ?put a specific coling unit to overcome icrease of heat? put more fresh and exhaust fans ??

sorry for the disturbance and i ll search on the old forums at this site

 

[Drazen]

OK, try to be little more specific - I don't understand why you say that fans are close to boilers if we are talking about pump room? Are boilers in next room close to that one?

You have problem wih heat drawn in by fans during hot weather? The reason for ventilation appears to be pump motors heat rejection?

 

[etchyHA]

yes the boiler is next thing after pumps room this room tempretaure is so high .i am thinking about put 3 other exhaust fans at north wall with same cap. of the fresh.fans but how can i get rid of the incresment of heat
transfered due to hot weather ?

 

[Drazen]

Let's go to basics: why ventilation of pump room is needed?! Pumps don't need fresh air to work, just cooling of motors - maybe that was some designer's idea: to lower room temperature in winter by introducing fresh air.

But in summer, these fans should be switched off, probably by temperature controller. Air changes should be reduced to absolute allowable minimum during such weather (this room is not permanently occupied, so it can be rather low figure, compared to work of 3 big fans). If temperature rise is too high, room AHU should be added, dimensioned according to that minimal air quantity, not according to big fans capacity!

 

[MintJulep]

Ok, you have an idea of the load in the room.

What is the maximum temperature that the room can be?

What is the temperature of the available air that will be used for ventilation?

Required ventilation rate is then pretty simple to calculate.

 

[willard3]

Again, there's not enough design information......

Do all 3 pumps run at the same time?
Are the pump motors high efficiency?
Are the motors open drip-proof?
How are the motors controlled, by variable speed drives?
Are the cooling/ventilation and combustion air loads combined for the fans?
Do the boilers operate year 'round and what is their function.

Hard to solve the problem if the problem is not clearly stated.....

 

[imok2]

MintJulep and Willard3, The questions you ask is my point. If someone is asking a question then he/she should be as SPECIFIC as they can be, without the responders trying to "pull teeth". :>)

 

[MintJulep]

Imok,

I agree, the OP's question is poorly asked, and has the characteristic of "please do my job for me because I have no understanding of fundamentals".

 

[etchyHA]

okay

* yes the three pumps working at the same times and there is another one stand by

**the motor efficiency are high

*** i dont know what is the drip-off motor is it a motor kind?

**** boiler are operating year around and it is useda at producing electricity.

sorry i dont know what do u mean by" Are the cooling/ventilation and combustion air loads combined for the fans?"

 

[waross]

Gentlemen;
The poster has stated 3 pumps running at a time.
Size 3mw or 4 mw.
Let's go with 3 times 4 mw. that's 12 mw.
Assume the efficiency at 90%. The heat rejection will be 10% of 12 mw or 1.2 mw.
Or
Assume an efficiency of 85%. The heat rejection will be 15% of 12 mw or 1.8 mw.
If someone in the forum will now suggest a reasonable temperature rise and a corresponding ventilation rate we can give etchyHA a couple of reasonable figures for his fan capacity.
It will be etchyHA's responsibility to determine the actual efficiency of the motors and possibly scale our suggestions to match actual site conditions.
When I am frustrated by poor information, I try to remember that this is an international forum and english may not be the posters first language.
I also try to remember that I follow the forums to both gain new information and to offer help to others.
respectfully

 

[MintJulep]

The motor namepleate may say 4 MW, but that does not mean that the motors are actually drawing 4 MW. Power is proportional to the cube of pump flow, so if the motors are oversized for the pumps, or the pumps are not running a rated capacity, the power may be much less.

A motor of this size very likely has provisions for, or options for forced external cooling.

You don't start a 40 MW motor across the line, so there are probably some sort of drives that have power conversion losses to consider.

 

[waross]

MintJulep
If you would like to help that would be nice.
If you want to pick nits;
Losses are related to but not proportional to power.
Power is proportional to the cube of pump flow AT CONSTANT PRESSURE. An increase in flow is often a result of decreased back pressure.
Running three out of four pumps of this size on a power boiler, it is safe to assume that the pumps are loaded and sized properly.
Provisions for forced external cooling?? Are you confusing motors with transformers? If a motor is designed for external cooling it will have external cooling, not "provisions for". Other than water cooled motors, ther heat rejection is independent of the cooling method. If a motor is rejecting 0.4 mw of heat it doesn't matter if it's open drip proof, TEFC or whatever. 0.4 mw is still 0.4 mw.
It is not common practice to hang a starter or drive on the wall beside a 4 mw pump. The drives will be in the electrical equipment room.
etchyHA;
If you know the rated efficiency of the motors, please post it.
Also, what is the temperature of the outside air and what is the maximum temperature you would like to limit the inside air to?
respectfully.

 

[MintJulep]

To maintain a space containing a 1 megawatt heat source 10 degrees F above the temperature of the ventilating air requires a bit over 526000 cubic meters/hour

 

[waross]

MintJulep
Thank you for your response. It is exactly what I would have hoped for. I hope it is of use to etchyHA.
Respectfully

 

[quark]

When the motor and the driven machine or in a controlled space, the standard formula is to consider IP of the motor rather than the inefficiency, for heat calculation (I am not sure why it is so, till date).

So going as per the standard equation,

Q(BTU/hr) = BHP x 2545/eff. or IHP/2545

If IP is 4MW (i.e 4000000/745 = 5369 HP),
Q = 5369 x 2545 = 13664105 Btu/hr

For a 10F dT, 13664105 = 1.08 x cfm x 10 or flowrate is 1265195 cfm or 2151693 cu.m/hr

For three pumps, it is 6455076 cu.mtr/hr or 3795585 cfm.

That would take a 1000 HP motor (if there is no much duct work)

Personally, I would rather pray God (atheists should excuse me) to send twisters to the boiler pump room 24x7

 

[etchyHA]

thank you quys for all your help

waross
rated eff.=.75
o/T=40C
max. temp at room =30:35 c