[Stoves] Bulk density of LPG vs pellets -- and WHY it matters

Tue Feb 13 14:04:23 CST 2018

Thanks so far to Steven and Crispin.

> You can guess that the LPG (46 MJ/kg) is about 2.7 times the energy of 
> the pellets (17 MJ/kg), however the empty mass of the tank is about 
> equal to the gas contents. Thus the energy content per transported kg 
> is only 1.35 times that of the wood.
The above is by weight.   Great.

And we need to factor in the empty space between the cylinders.  I will 
GUESS that the space between cylinders is about equal to the volume 
(space) of the cylinder (allowing also for the space of the base and the 
top handle/valve of the LPG cylinder) .  That would cut the transported 
of LPG in about half BY VOLUME.   So again the energy content of the LPG 
is 1.35  times that of the pellets.

If so, then either by weight or by volume in the cargo area of a 
delivery truck, the fossil fuel transport for an equal distance would be 
1.35 times as much energy delivered as that of pellets.

But as Steven pointed out (below), the empty cylinders need to be "back 
hauled" from the community, with extra cost of loading and unloading.  
So MAYBE we can call the transport cost to be equal for LPG and pellets 
for equal journeys.

But if the refill station is twice as far away as is the source of the 
pellets (or vice versa), the cost of transport of the further-sourced 
fuel is double in terms of the driving time and double the 
fuel-of-transport costs.

Crispin, my interest is specifically for "regular" densified wood 
pellets, not for torrified pellets that cost more to make and have less 
of the original wood-energy in them (in terms of boimass input, not in 
terms of energy per kg.).   And torrification is at more centralized 
locations than is the basic pelletizing operations.

I agree that if the pellets are consumed in TLUD pyrolytic gasifiers 
with the production of charcoal, the ENERGY releasd is about a third 
less than if the pellets were burned all the way to ash.  This loss is 
countered by the value of the charcoal, whether for later burning or as 
char that somebody in the destination community finds to be desireable, 
perhaps to be biochar or for water filters or other.

For the comparative discussion of LPG or pellets for new stoves in a 
community, the decisive factors are NOT only with the transportation.  
The decisive factors include:

A.  fossil fuel (and CO2 positive) vs renewable fuel (and CO2 
neutral,--- or negative if biochar goes to the soil).

B.  Additional transport:  If the LPG is bulk-trucked or even piped to 
the cylinder loading point, but the pellets are made near the loading 
point, the PPG becomes more expensive.

C.  Cost per MJ of energy:   The WLPGA (World LPG Association) 
presentations point out that biomass is less expensive per MJ than is 
wood.  But we are dealing with pelletized wood, which has incurred extra 
processing costs.  But I suspect that the pellets are still 
significantly less expensive per MJ than would be the LPG.

D.  Supply of the original materials (oil and wood/biomass):   Much 
depends on the geographic location.  But where wood and other biomass 
suitable for pelletizing are sufficient for continual supply, the 
reliance on petroleum to yield LPG or to have LPG from sources of 
natuarl gas is a negative for LPG.

Currently LPG is rather plentiful in the world.   Very unequally 
distributed, but there is much of it.  Middle-east oil and North America 
natural gas from fracking are the main sources.   That will rise and 
fall, for sure, but not known when.

Wood and other suitable biomass for pellets is also rather plentiful, 
and more widely distributed.  What would be useful would be small (not 
tiny or micro) pelitizing facilities that are either (or both) 
relatively inexpensive for continual operations to serve appropriately 
sized areas/communities OR semi-portable pelletizers, being able to be 
moved closer to the sources of the biomass, perhaps seasonally.

Why does this interest me (and you)?   Because processed, uniform, clean 
to handle, dense pellets of biomass are such a great fuel for the 
forced-air TLUD stoves that can give  justifiably serious competition to 
LPG.   The Mimi-Moto and the FAAbulous TLUD-FA stoves will eventually 
established a major project (with large numbers of users), quite 
possiblly in a peri-urban area where they will replace charcoal stoves, 
and where LPG never had much of the action.

Stay tuned.

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu
Skype:   paultlud    Phone: +1-309-452-7072
Website:  www.drtlud.com

On 2/13/2018 12:41 PM, Crispin Pemberton-Pigott wrote:
>
> Dear Paul
>
> Perhaps you could consider transporting torrefied pellets 
> <https://www.pellet.org/images/5%20-%20Bahman%20Ghiasi.pdf> instead of 
> raw wood (21 MJ/kg). Not only is it more energy per ton, it is more 
> likely not to be damaged by moisture. That link has some interesting 
> info BTW.
>
> You can guess that the LPG (46 MJ/kg) is about 2.7 times the energy of 
> the pellets (17 MJ/kg), however the empty mass of the tank is about 
> equal to the gas contents. Thus the energy content per transported kg 
> is only 1.35 times that of the wood.
>
> In terms of cost the wood should be cheaper, delivered.
>
> If you are turning the wood into char and not burning it, the cost 
> advantage will be lost. I presume you have a plan to offset that.
>
> Regards
> Crispin
>
And Steven Law wrote:
> A few thoughts for consideration:
> 1. LPG is a fossil fuel that emits GHG while wood pellets are a renewable fuel when made of sustainable forest products
> 2. the weight of the LPG containers is considerable for transportation purposes since they have to be transported twice in order to be used once, whereas the wood pellets only have to be transported once and the truck can be used to transport something else during the return trip
> 3. the shape of the LPG containers does not lend themselves to easy stacking and will waste a lot of space in the truck whereas wood pellets can be stacked quite densely and there won't be any wasted space on the truck
> 4. the LPG containers will degrade over time and may eventually leak or explode whereas this will never happen with wood pellets
> 5. the LPG will not likely keep money in the local community, but rather the money will be exported from the community to pay for the imported fuel, whereas wood pellets will likely keep money in the local community and provide local jobs and tax revenue
> 6. the ash from burning wood pellets can be used as a soil fertilizer to grow more food in the community
>
> I hope these few thoughts lend themselves to a more community based holistic view to the problem with a triple bottom line approach, rather than a single bottom line calculation with the primary motivation to be maximizing profit for LPG companies.
>
> -----Original Message-----
> From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On 
> Behalf Of Paul Anderson
> Sent: 13-Feb-18 10:15
> To: Stoves and biofuels network <Stoves at lists.bioenergylists.org>
> Subject: [Stoves] Bulk density of LPG vs pellets
>
> Dear Stovers and friends,
>
> I hope that someone can provide an answer to this question:
>
> The situation:  A fuel for cooking needs to be transported to 
> communities in somewhat remote locations.   There are roads that at 
> least allow a pickup truck to go in and out year-round.  The people 
> have access to locally sources woody biomass fuel, but are interested 
> in having some better stoves with processed fuels.   In particular, 
> they are considering LPG in standard bottles/tanks that are brought in 
> full, and empties are taken back.    They are also considering  
> pellets that are in typical 40 pound (~18 kg) bags, with local sales 
> in smaller quanties.   Consider initially that the pellets are made in 
> the same location where the LPG bottles are refilled.  (We can 
> consider different distances of transport later, if of interest).  
> (also, there will be some differences if different sizes of LPG 
> bottles or pellets in super-sacks are used, but that is not of much 
> interest in this initial
>
> discussion.)
>
> The question:  How much energy can be transported in each delivery 
> trip, and which becomes the most economical -- or are they about the 
> same? The LPG has more energy per kg of fuel, but must be transported 
> in metal containers that are cylindrircal and occupy much space.   The 
> pelelts are in bags that can be stacked (such as on a pallet of pellets).
>
> Boilse down to:   LPG in bottles vs pellets in sacks.
>
> My thanks to everyone who contributes to answering this question.
>
> Paul
>
> --
>
> Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
>
> Email: psanders at ilstu.edu <mailto:psanders at ilstu.edu>
>
> Skype:   paultlud    Phone: +1-309-452-7072
>
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