[Gasification] which prevention take care to use esp for filtration of producer gas

Fri Dec 28 11:17:05 CST 2007

which prevention take care to use esp for filtration of producer gas

On Dec 26, 2007 11:30 PM, <gasification-request at listserv.repp.org> wrote:

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> Today's Topics:
>
>   1. Re: heat exchanger / boiler design book (Toby Seiler)
>   2. Re: heat exchanger / boiler design book (Mark Ludlow)
>   3. Re: heat exchanger / boiler design book (Greg Manning)
>   4. Re: heat exchanger / boiler design book (andrew)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 25 Dec 2007 18:24:13 -0800 (PST)
> From: Toby Seiler <seilertechco at yahoo.com>
> Subject: Re: [Gasification] heat exchanger / boiler design book
> To: list at sylva.icuklive.co.uk
> Cc: gasification at listserv.repp.org
> Message-ID: <437855.36803.qm at web38201.mail.mud.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
>
> Andrew,
>
>  Please clear up something for me.  Not long ago there was a discussion
> about heat exchanger design that I did not understand the principles members
> put forth.  Specifically I have believed that minimization of the boundary
> layer effect would increase the heat transfer, know to me as wiping the
> surface.  Your forth element, surface texture, would have a large effect as
> would flow, (ranging from laminar to turbulent) were increased or decreased
> (given other parameters remained the same).
>
>  I think the argument was made that turbulent flow transferred better.
>  That's what I didn't understand.  I have always thought that laminar flow
> over the surface were more efficient at the transfer and that more molecules
> would be moved if laminar low were maintained.  Please clarify that for me
> as a general principle, if you have it at hand.
>
>  For example;  the fire tubes of a boiler will often contain swirling fins
> that cause a circular or spiraling flow.  Both residency time and surface
> contact are extended and the centrifugal force is a factor.  The wiping
> action reduces the boundary effect and also extends the flow path, giving
> more contact and transfer.  Flow would be laminar however.  It has long been
> my belief that making turbulent flow led to hot spots (much increased
> boundary layer in places), less flow and ultimately less system efficiency.
>  This has led me to believe that a cyclone and heat exchanger combined would
> be efficient, especially with hot gas heat being transfered to a wood fuel.
>
>  Have a good New Year!
>
>  Toby Seiler, Seilertechco
>
>
> ---------------------------------
> Be a better friend, newshound, and know-it-all with Yahoo! Mobile.  Try it
> now.
>
> ------------------------------
>
> Message: 2
> Date: Tue, 25 Dec 2007 19:58:43 -0800
> From: "Mark Ludlow" <mark at ludlow.com>
> Subject: Re: [Gasification] heat exchanger / boiler design book
> To: "'Discussion of biomass pyrolysis and gasification'"
>        <gasification at listserv.repp.org>
> Message-ID: <003101c84773$9c123830$d436a890$@com>
> Content-Type: text/plain;       charset="us-ascii"
>
> Toby,
>
> "Swirling fins" do not increase residence time. Mass flux remains
> constant.
> They increase the velocity of the gases which increases their Reynolds
> Number which increases the probability that flow will be turbulent.
>
> Observe the difference in velocity profiles between laminar and turbulent
> flow. The velocity profile for laminar flow is parabolic, meaning that the
> core of the flow-stream (portion of greatest mass transfer per unit of
> time)
> has much higher velocity than the "tails" of the parabola. Therefore, much
> less heat is transferred to this part of the flow stream because it has a
> short residence time (and it is further removed from the heat-transfer
> surfaces).
>
> Fully-developed non-laminar flow streams have a flatter velocity profile.
> This is because there are fluid molecules moving in all directions at once
> and the velocity profile described is a two-dimensional average of these
> velocities. In general, higher fluid velocities imply higher rates of heat
> transfer. The faster the velocity, the thinner the boundary layer through
> which heat transfer that is purely conductive becomes.
>
> Higher velocity fluid streams also tend to result in less fouling of heat
> exchange surfaces.
>
> Mark
>
> -----Original Message-----
> From: gasification-bounces at listserv.repp.org
> [mailto:gasification-bounces at listserv.repp.org] On Behalf Of Toby Seiler
> Sent: Tuesday, December 25, 2007 6:24 PM
> To: list at sylva.icuklive.co.uk
> Cc: gasification at listserv.repp.org
> Subject: Re: [Gasification] heat exchanger / boiler design book
>
> Andrew,
>
>  Please clear up something for me.  Not long ago there was a discussion
> about heat exchanger design that I did not understand the principles
> members
> put forth.  Specifically I have believed that minimization of the boundary
> layer effect would increase the heat transfer, know to me as wiping the
> surface.  Your forth element, surface texture, would have a large effect
> as
> would flow, (ranging from laminar to turbulent) were increased or
> decreased
> (given other parameters remained the same).
>
>  I think the argument was made that turbulent flow transferred better.
> That's what I didn't understand.  I have always thought that laminar flow
> over the surface were more efficient at the transfer and that more
> molecules
> would be moved if laminar low were maintained.  Please clarify that for me
> as a general principle, if you have it at hand.
>
>  For example;  the fire tubes of a boiler will often contain swirling fins
> that cause a circular or spiraling flow.  Both residency time and surface
> contact are extended and the centrifugal force is a factor.  The wiping
> action reduces the boundary effect and also extends the flow path, giving
> more contact and transfer.  Flow would be laminar however.  It has long
> been
> my belief that making turbulent flow led to hot spots (much increased
> boundary layer in places), less flow and ultimately less system
> efficiency.
> This has led me to believe that a cyclone and heat exchanger combined
> would
> be efficient, especially with hot gas heat being transfered to a wood
> fuel.
>
>
>  Have a good New Year!
>
>  Toby Seiler, Seilertechco
>
>
> ---------------------------------
> Be a better friend, newshound, and know-it-all with Yahoo! Mobile.  Try it
> now.
> _______________________________________________
> Gasification mailing list
> Gasification at listserv.repp.org
> http://listserv.repp.org/mailman/listinfo/gasification_listserv.repp.org
> http://gasifiers.bioenergylists.org
> http://info.bioenergylists.org
>
>
>
>
> ------------------------------
>
> Message: 3
> Date: Wed, 26 Dec 2007 00:35:42 -0600
> From: "Greg Manning" <a31ford at inetlink.ca>
> Subject: Re: [Gasification] heat exchanger / boiler design book
> To: <mark at ludlow.com>, "Discussion of biomass pyrolysis and
>        gasification"   <gasification at listserv.repp.org>
> Message-ID: <GGEBLFNJNOGGJGNEDBJJEEPHMAAA.a31ford at inetlink.ca>
> Content-Type: text/plain;       charset="windows-1250"
>
>
>  Mark, Toby, and List.
>
>  WOW ! Mark, you answered many questions I had, and I was just lurking...
> Thank you !
>
> Greg Manning
>
>
>
>
> -----Original Message-----
> From: gasification-bounces at listserv.repp.org
> [mailto:gasification-bounces at listserv.repp.org]On Behalf Of Mark Ludlow
> Sent: Tuesday, December 25, 2007 9:59 PM
> To: 'Discussion of biomass pyrolysis and gasification'
> Subject: Re: [Gasification] heat exchanger / boiler design book
>
>
> Toby,
>
> "Swirling fins" do not increase residence time. Mass flux remains
> constant.
> They increase the velocity of the gases which increases their Reynolds
> Number which increases the probability that flow will be turbulent.
>
> Observe the difference in velocity profiles between laminar and turbulent
> flow. The velocity profile for laminar flow is parabolic, meaning that the
> core of the flow-stream (portion of greatest mass transfer per unit of
> time)
> has much higher velocity than the "tails" of the parabola. Therefore, much
> less heat is transferred to this part of the flow stream because it has a
> short residence time (and it is further removed from the heat-transfer
> surfaces).
>
> Fully-developed non-laminar flow streams have a flatter velocity profile.
> This is because there are fluid molecules moving in all directions at once
> and the velocity profile described is a two-dimensional average of these
> velocities. In general, higher fluid velocities imply higher rates of heat
> transfer. The faster the velocity, the thinner the boundary layer through
> which heat transfer that is purely conductive becomes.
>
> Higher velocity fluid streams also tend to result in less fouling of heat
> exchange surfaces.
>
> Mark
>
> -----Original Message-----
> From: gasification-bounces at listserv.repp.org
> [mailto:gasification-bounces at listserv.repp.org] On Behalf Of Toby Seiler
> Sent: Tuesday, December 25, 2007 6:24 PM
> To: list at sylva.icuklive.co.uk
> Cc: gasification at listserv.repp.org
> Subject: Re: [Gasification] heat exchanger / boiler design book
>
> Andrew,
>
>  Please clear up something for me.  Not long ago there was a discussion
> about heat exchanger design that I did not understand the principles
> members
> put forth.  Specifically I have believed that minimization of the boundary
> layer effect would increase the heat transfer, know to me as wiping the
> surface.  Your forth element, surface texture, would have a large effect
> as
> would flow, (ranging from laminar to turbulent) were increased or
> decreased
> (given other parameters remained the same).
>
>  I think the argument was made that turbulent flow transferred better.
> That's what I didn't understand.  I have always thought that laminar flow
> over the surface were more efficient at the transfer and that more
> molecules
> would be moved if laminar low were maintained.  Please clarify that for me
> as a general principle, if you have it at hand.
>
>  For example;  the fire tubes of a boiler will often contain swirling fins
> that cause a circular or spiraling flow.  Both residency time and surface
> contact are extended and the centrifugal force is a factor.  The wiping
> action reduces the boundary effect and also extends the flow path, giving
> more contact and transfer.  Flow would be laminar however.  It has long
> been
> my belief that making turbulent flow led to hot spots (much increased
> boundary layer in places), less flow and ultimately less system
> efficiency.
> This has led me to believe that a cyclone and heat exchanger combined
> would
> be efficient, especially with hot gas heat being transfered to a wood
> fuel.
>
>
>  Have a good New Year!
>
>  Toby Seiler, Seilertechco
>
>
> ---------------------------------
> Be a better friend, newshound, and know-it-all with Yahoo! Mobile.  Try it
> now.
> _______________________________________________
> Gasification mailing list
> Gasification at listserv.repp.org
> http://listserv.repp.org/mailman/listinfo/gasification_listserv.repp.org
> http://gasifiers.bioenergylists.org
> http://info.bioenergylists.org
>
>
> _______________________________________________
> Gasification mailing list
> Gasification at listserv.repp.org
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>
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>
> ------------------------------
>
> Message: 4
> Date: Wed, 26 Dec 2007 10:59:03 +0000
> From: andrew <list at sylva.icuklive.co.uk>
> Subject: Re: [Gasification] heat exchanger / boiler design book
> To: gasification at listserv.repp.org
> Message-ID: <200712261059.03812.list at sylva.icuklive.co.uk>
> Content-Type: text/plain;  charset="iso-8859-15"
>
> On Wednesday 26 December 2007 02:24, you wrote:
>
> >   I think the argument was made that turbulent flow transferred
> > better.  That's what I didn't understand.  I have always thought
> > that laminar flow over the surface were more efficient at the
> > transfer and that more molecules would be moved if laminar low
> > were maintained.  Please clarify that for me as a general
> > principle, if you have it at hand.
>
> Mark has provided a better answer than I could but I visualise it
> this way, a laminar flow requires the least power to drive it and
> can be viewed as concentric layers passing down the tube. Assuming
> the flow starts out at a uniform temperature then the
> outside "circle" in contact with the tube surface gives up its heat
> first. It is then a colder surface which can only gain heat from the
> hotter middle sections by conduction, so in effect it insulates the
> tube. If the flow is made turbulent, with mixers or "turbulators"
> then the gases give up their heat uniformly along the tube obeying a
> direct relationship to delta T for the heat transfer, all other
> variables remaining the same.
>
> <snip>
>
> >   It has long
> > been my belief that making turbulent flow led to hot spots (much
> > increased boundary layer in places), less flow and ultimately less
> > system efficiency.
>
> Intuitively I feel the opposite because with turbulent flow the
> mixing of the primary flow is good , so that at any point along the
> length of the tube the temperature remains the same at any point
> across the section.
>
> > This has led me to believe that a cyclone and
> > heat exchanger combined would be efficient, especially with hot
> > gas heat being transfered to a wood fuel.
>
> I cannot visualise what you are considering, are the wood particles
> entering the cyclone with the gas and then being separated, dry, by
> the cyclone? This is a different case and is a direct drying effect
> rather than transferring heat between two fluids with a heat
> exchanger surface in between.
>
> Cyclones do consume power, anyone with a vacuum cleaner that works on
> this principle, Dyson is a popular brand in UK, will appreciate the
> pressure drop associated with them compared with a standard filter
> type vaccum cleaner.
> >
> >   Have a good New Year!
>
> A happy new year to you and all [gasification] contributors too!
>
>
>
> ------------------------------
>
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> End of Gasification Digest, Vol 18, Issue 21
> ********************************************
>