Duct/fan sizing over long distance 3

[bjs1234]

Hi all, I'm working on a project which will move flue gas from a plant to a processing plant some distance away. In planning for a worst case scenario, we need to move the gas up to 10 km by pipe. Due to its properties and potential water content, high pressure transport is not an option. Sizing a fan for approx. 75,000 m^3/hr is giving me some trouble given the pressure drop over this distance.

What is the maximum delta-P across a fan if in series? I cannot seem to find an easy guide to getting rough estimates. I can easily calculate pressure drop across the line using ASPEN Plus and know that several boosters will probably be needed along the way, even if a very large (1.5 m) diameter pipe were used.

Thanks for any advice.

 

[DRWeig]

bjs,

You should be able to get a blower for whatever delta-pressure you want. What sort of static pressure limit do you want to keep in your duct? What sort of velocity limit?

Let us know!

Goober Dave

 

[bjs1234]

Hi Goober Dave,

Thank you for the reply. To be honest, I am not sure what a typical static pressure limit would be. We have not specified the materials of construction for the pipe, but are considering corrosion resistant stainless steel and possibily even fiber glass options. Ideally, we would have one or more blowers which would be able to work in such a way to mitigate the frictional losses.

Here is what I imagine:

Inlet (1 atm) -> Fan/Blower (2 atm output)-> Pipe Length X (1 atm outlet due to frictional losses) ->Fan/Blower (re-up to 2 atm)-> and continue until the end of the process.

As a new chemical engineer, I am just not sure where to begin.

Thanks again, I appreciate it!

 

[MintJulep]

10 kM of 1.5 M diameter stainless pipe!

Please post who you are giving the order to before you actually award it so that we can all buy stock.

Where to start?

Either start by picking a pipe size, work out the pressure drop and select fans accordingly.

Or, select fans and then design a pipe size to match the available pressure.

You should really do a life-cycle calculation - but pumping costs are going to be huge - so the lower pressure drop (bigger pipe) the better in the long run.

 

[bjs1234]

Haha. 1.5 m was sort of a worst case scenario.

"select fans and then design a pipe size to match the available pressure" <-- this is what I am not sure how to do. How to select fans? How does static pressure of a fan, or a fan curve, or any available data translate into how much frictional pressure drop it can overcome?

Thanks!

 

[MintJulep]

The static pressure of a fan IS the pressure drop the fan can overcome.

 

[bjs1234]

OK, thanks. That's what I feared. I mean, if I have a 1 atm pressure drop, that is a lot of inches of water in static pressure from a fan. Hmmm...

 

[DRWeig]

BJS,

In that pressure range, we call 'em blowers or compressors instead of fans, even though they may just look like huge fans. I have worked with some waste treatment plant aeration blowers that were designed for 300,000 m^3/h at 0.5 atm -- so roughly twice the motive power of your hypothetical 75,000 m^3/h at 1.0 atm. Each machine delivered about 2800 KW at the shaft and had a 5000 KW electric motor. That's the order of magnitude of the energy need you're looking at.

Like MintJulep said, this is worth doing cost-optimization analysis. Don't worry at first about having to put blowers in series, that's a detail for later. I wish I could give you a quick method to follow, but I've never gone beyond a few hundred meters with my work...

I would advise finding a consultant with some experience in tunnel ventilation or something?

Let's see if anyone else pitches in, though -- this forum has really amazed me with its breadth of experience.

Good on y'all,

Goober Dave

 

[bjs1234]

I am now considering a multistage centrifugal blower. I found this one from HSI as an example (PDF -

http://specs.topspotservices.com/hsi/downloads/246.pdf).

At my flow rate (50000 m^3/hour), it discharges 24 psig. I know this is an enormous blower and probably very expensive. I will have to get in touch for a quote. But in other regards, what are the typical concerns in running this type of blower? How much moisture can safely remain in the flue gas? With a fan, I was not concerned. With a compressor, I would be very concerned. I am not sure what to think with this system.

Thanks again-- invaluable help has been given so far.

 

[SAK9]

To get you started assume 1.5 pa/meter that would be 1500 pa/km.Start with a radial 3000 pa blower, put in a booster at 3km from the first put a third one at 6km and put a 1000Pa for the final stage ie 3x3000pa+1x1000pa.Since this is flue gas,I am assuming the entire duct will be of welded construction.3000 pa would not be much for a welded circular duct.

 

[DRWeig]

Such an interesting challenge!

As far as the fact that it's flue gas, it'll be laden with moisture. Ideally, it would be nice to keep it hot and light for the whole trip, but it's not an ideal situation -- condensation will have to be dealt with somehow, and the blower materials need to be able to handle the corrosives in there too...

I'll keep watching, this is an incredibly challenging flue problem!

Goober Dave

 

[bjs1234]

Hi SADK9,

I like the way you are thinking about breaking the problem into parts. For a radial blower, I have not been able to find one with a capacity of more than a couple of thousand CFM. I need about 30,000 CFM. Is it still a reaslistic option? Am I looking at the wrong places? Thanks.

DRW: True, RE corrosion resistant materials.

Thanks everyone.

 

[SAK9]

See the attached catalogue.At the top of the range they seem to deliver 20000 cfm at around 5 psi.Maybe you need two identical 15000 cfm blowers in parallel.

 

[bjs1234]

Does anyone have an order of magnitude price estimate for the following:

http://specs.topspotservices.com/hsi/downloads/246.pdf

$100s of K, or millions?

Thanks.

 

[saplanti]

My guess for moving flue gas (probably it is at high temperature) for such a long distance with duct is not a good idea.

You had better discuss this with a process engineer first. On the way the temperature will drop down and corrosion will be a big problem, the duct material will be very expensive. Of course the type of flue atmosphere is an issue here, you have already mentioned the water content.

Therefore, from my experience the distance should be a short as possible to treat/process the gas. If it is definit to deliver the flue gas to that distance you may need to provide a couple separator/filter stations in between to eliminate the water content.

In case the elevated temperature of the flue gas you need to reduce the temperature to an acceptable level before entering the compressors . Additionally, compressor manufacturers will ask you to filter the gas before accepting into the compressors for the life expectancy of the compressors.

Regards,

Ibrahim Demir

 

[willard3]

You should first find a manufacturer that will fabricate a fan/compressor that will work in an atmosphere with sulfuric/nitric acids and lots of moisture.

There are fan manufacturers (Buffalo Forge and etc) that will produce custom pressure/flow fans to suit you.

You should also familiarize yourself with fan control as starting fans in series can be tricky.

There are consultants who do nothing but large ventilation projects and you may do better hiring one for this project.

 

[fredt]

This is a more complex problem than it appears. The issue of suitable fan(s) is not the major problem as other respondents have stated fan suppliers will provide a suitable machine to suit the specific requirements but fan suppliers do not design systems like this - it is a specialist business. The effects of compressibility and leakage along the length are the main reason for the complexity and it is likely that several fans would be needed at intervals along the duct. It is a common issue in the ventilation of long tunnels during construction but is further complicated by the flue gas. At another level gas pipelines have similar issues but operate at much higher pressures. Good luck.

Fred