[Gasification] Glaubers Salts for Thermal Storage

Fri Apr 4 11:25:00 CDT 2008

Hi Richard,

Typically, the working fluid is water or water laced with glycol to suppress
the freezing point. The fluid is circulated from the hot side (solar
collector or CHP low-value heat stream through a heat exchanger), to a
second heat exchanger that extracts the heat as warmed air. Any heat excess
to heating needs is banked in the Glaubers vault, usually through a network
of pipes that transfer the heat of the working fluid to the salts which
surround them. The normal state of the salts is typically frozen and thawing
is accomplished by adding sufficient heat to overcome the heat of fusion of
the salts in the vault.

The salts in the vault, which are typically dissolved in a 33% W/W solution,
are liquid above 90F, provided that sufficient heat has been added to them.
I didn't calculate what the sensible heat capacity of the liquid solution
is, but it's somewhere between 0.7 and 1 BTU/lbm*degF.

The disadvantage with using pure water as a thermal storage smas is that
even though its heat capacity is great (1 BTU/lbm*degF), its phase-change
heat of fusion (144 BTU/lbm) comes at 32F, which is not very useful in space
heating applications. So, to get an equivalent useful heat from water alone,
one must rely solely on sensible heat, requiring high top-end temperatures
which imply higher system heat losses in the entire system.

Mark

-----Original Message-----
From: Richard Haard [mailto:richrd at nas.com] 
Sent: Friday, April 04, 2008 8:52 AM
To: mark at ludlow.com; Discussion of biomass pyrolysis and gasification
Cc: 'Ken Basterfield'
Subject: Re: [Gasification] Glaubers Salts for Thermal Storage

Is there a freezeup safety advantage for using glaubers ?
On Apr 4, 2008, at 6:22 AM, Mark Ludlow wrote:

> Hi Ken,
>
> True enough, but the attraction with Glaubers is the low temperature  
> change
> of phase (32C). There's no harm in depending entirely on sensible  
> heat, as
> you suggest, and when your sulfate is liquid, the solution is 2/3  
> water
> which you can heat to 90C if you like. Solar space heating systems  
> using
> sulfate typically didn't run that warm on the top end (I've only  
> seen one).
> The example I used could run at a constant 32C.
>
> (I'm not trying to sell these!)
>
> Mark
>
> -----Original Message-----
> From: Ken Basterfield [mailto:ken at basterfield.com]
> Sent: Friday, April 04, 2008 12:38 AM
> To: mark at ludlow.com; 'Discussion of biomass pyrolysis and  
> gasification'
> Subject: RE: [Gasification] Glaubers Salts for Thermal Storage
>
> Hello Greg & Mark
> 5 tonne of water would give you 1,100,000 Btu if cycled over a  
> sensible 90C
> to 35C ( underfloor heating ) and it is much cheaper than any phase  
> change
> chemical. It can also be used as its own transport mechanism.
> 5t ~ 11,000lb through 90-35C i.e. 55C range  is 99F range so  
> 99x11000 ~
> 1.1MBtu
> KISS
> Ken
>
>
>
> I've stopped 2,021 spam and fraud messages. You can too!
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>
> -----Original Message-----
> From: gasification-bounces at listserv.repp.org
> [mailto:gasification-bounces at listserv.repp.org] On Behalf Of Mark  
> Ludlow
> Sent: 04 April 2008 07:48
> To: info at cangas.ca; 'Discussion of biomass pyrolysis and gasification'
> Subject: Re: [Gasification] Glaubers Salts for Thermal Storage
>
>
> Greg,
>
> I am thinking of sodium sulfate--what you get when you mix sodium  
> hydroxide
> (lye) and sulfuric acid. You can dissolve it at a 1:2 ratio with  
> water if
> the water is warmed but as it starts to freeze at 90F it gives off  
> 83 BTU/lb
> of heat for every lb. that freezes. If you have 5-tons of it and  
> some way to
> heat it to its liquid phase and extract the heat, you could recover  
> 830,000
> BTUs of heat, just from the change of liquid to solid. Of course it  
> takes an
> equal amount of energy to make it liquid again. 8.3 therms is worth  
> about
> $12 in natural gas terms so it's fairly effective as a moderate  
> temperature
> thermal battery for home heating. Plus, it's cheap. The expense is  
> in the
> heat exchangers that transfer heat between the salt and your working  
> fluid
> (likely water/glycol in AK). Lots of things have been tried; many  
> work, more
> or less.
>
> I misspoke when I said it was corrosive. It's not.
>
> I think it would work well when your district heating system is down  
> for
> tinkering, Greg.
>
> Mark
>
> -----Original Message-----
> From: gasification-bounces at listserv.repp.org
> [mailto:gasification-bounces at listserv.repp.org] On Behalf Of Greg  
> Manning
> Sent: Thursday, April 03, 2008 10:38 PM
> To: 'Discussion of biomass pyrolysis and gasification'
> Subject: Re: [Gasification] Glaubers Salts for Thermal Storage
>
>
> Correct me if I'm wrong, but we use this as "tractor salts" for rear  
> tires,
> it can't freeze, and is as dense as rock by itself.
>
> "Calcium & Water"
>
> Greg Manning
>
>
>
>
>
> -----Original Message-----
> From: gasification-bounces at listserv.repp.org
> [mailto:gasification-bounces at listserv.repp.org]On Behalf Of Tom Miles
> Sent: Thursday, April 03, 2008 11:34 PM
> To: 'Discussion of biomass pyrolysis and gasification'
> Subject: [Gasification] Glaubers Salts for Thermal Storage
>
>
> Can someone respond to an inquiry about Glauber's slats for thermal  
> storage?
> I received the following today:
>
>
>
> "We are getting ready to install thermal storage to augment our  
> gasifying
> wood boiler and solar hot water systems, and I was wondering if you  
> could
> give me a thumbnail sketch of the viability for Glauber's salt as  
> opposed to
> water.  Any special considerations that you are aware of?  Can you  
> point me
> to any successful residential applications that you know of?  Thanks  
> a lot
> for you help. "
>
>
>
> The application is in the interior of Alaska.
>
>
>
> Regards,
>
>
>
> Tom Miles
>
>
>
>
>
>
>
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