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Posted by andrew on June 20, 2011, 8:07 pm
 
Winston wrote:


Even the greases can be converted fronm the triglycerides to methyl esters.
I'm told the glycerine by product digests well.

The H2S reacts with damp rusty iron to produce iron sulphide

Fe2O3(s) + H2O(l) + 3 H2S(g) → Fe2S3(s) + 4 H2O(l)

It's regenerated in air

2 Fe2S3(s) + 3 O2(g) + 2 H2O(l) → 2 Fe2O3(s) + 2H2O(l) + 6 S(s)

Pinched from Wikipedia and this latter reaction is exothermic.

http://en.wikipedia.org/wiki/Hydrogen_sulfide

The chap I know doesn't do this but uses bacteria in the biodigester to
precipitate out the sulphur. Evenso the weak link in the system has been
the 120kW converted industrial engine.

Basically the unless you start with a fairly pure form of carbon, like steam
coal, the limits of the reaction temperatures prevent producing a tar free
gas. Tar kills engines. Wood starts off with a high massflow per unit of
energy available. This means lots of oil changes and gas clean up systems
that cost more than the gasifier. If you do use steam coal then your gas is
basically CO which has a low flame speed which severely derates an engine.

After the low hanging fruit of high head hydro power and turbines in
windspeeds in excess of 7metres/sec it looks to me like these renewable
technologies involve an overall cost in excess of four times the cost of
conventional grid electricity here in UK.

AJH

Posted by Winston on June 20, 2011, 9:55 pm
 
andrew wrote:

And most efficiently.

(...)


"In order to regenerate iron(III) oxide, the container must be
  taken out of service, flooded with water and aerated."

Sounds like delaying the process of venting the H2S rather
than preventing the venting of H2S.  I suppose I could just
recycle the saturated swarf.....


That is intriguing!  Tell me more!


Does one really need 160 HP?
Sounds like a good use of an engine parted out of a car.
Right now, I could make my electricity meter stop
incrementing if I had a source of ~1.4 HP 24/7
(or ~14 HP for 2.4/7)

In the last 5 years, I have *given away* two cars that had
suitable engines in them.


There was a very low tech filter as part of the gasifier plans I
cited a couple days ago:
http://www.gengas.nu/byggbes/contents.shtml

Would that not be sufficient?


At the moment.  Things change; I notice that the cost of electricity
is not on a downward trend.

http://www.data360.org/dsg.aspx?Data_Set_Group_Id97

As I inferred from Zach's OP, one should have many parallel alternatives
available.  Using only hydro or solar space heat or solar hot water or wind
or geothermal or tidal power or solar steam or biodiesel or wood or methane
or algae or photovoltaics is just silly.

:)

--Winston



Posted by andrew on June 21, 2011, 9:47 pm
 Winston wrote:


In practice two columns would be used alternately.

I thought you just wanted it out of the biogas stream because it causes
problems with engine corrosion.

I think it is a proprietary system but have a look at:

http://www.grobergreen.com/bio-digester-performance-for-october-2010/

which seems similar. I imagine the degree of control is non trivial.

In his case yes, he uses about 25kW(e) and exports the rest but his grid
interconnect only takes 100kW(e), he burns any excess gas for heating.


Apart from the loss of efficincy of scale being significant.

Consider there are 8766 hours in a year and these gensets run for a very
high proportion of that at 1500 rpm. My van is doing 35mph at 1500 rpm so
in a year that equates to continous running for 306810 miles, so far it has
actually clocked 198,000 miles in 8 years with only servicing but I don't
think it would have done 1.5 times that in a year without problems.


I doubt it, in the days when gasifiers were used it was forced by a lack of
supply, so just as Newcomen's engine paid even at 1/4% connversion
efficiency they were willing to pay a high price and that price was in
using lots of labour and frequent engine servicing. We get far more from
modern fuels and engines with next to no maintnance costs, I manage on 2
oil changes a year and little else on the engine front.

The gasifiers that are in everyday use in India also have an environmental
cost in disposing of the filtrate. The Allpowerlabs crowd are addressing
these issues and making good progress but...


Yes similar to our experience but 30% lower prices than we pay, I have
experienced a 10% rise in the past 12 months for electricity and 14%
increase has just been announced.

I suspect Zach and many americans have much more space to play with
alternatives than the average suburban englishman.

AJH

Posted by Winston on June 21, 2011, 10:57 pm
 andrew wrote:

OIC.  Like a condensate filter in a compressed - air
       system.  Sort of.


Yes. Ideally, I want to cheaply and conveniently rid the system of
SO2. Snap in a filter and toss it annually. (Ideally)


Thanks!  Very interesting. Normally, vegetable grease and oil do not
contain sulphur.  I expect his efficiency would increase dramatically
and his SO2 remediation problems would all but disappear if he switched
feedstocks.  (You knew I was going to say that.)


I don't understand.
The car engines were capable of ~85 kW.
That isn't so far from 120 kW, yes?


Congratulations on your van's reliability!

Stationary engines benefit from better working conditions than
their mobile cousins, overall.


That was just a trend indication.  I've been paying U$.13 a kWHr for
quite a while now, here in the California Bay Area.
It is only going to get more expensive as inflation takes hold.


That's why it is critical for intrepid experimenters to create practical
low cost energy sources that can be optimized for cost and space.

(IMHO)

--Winston

Posted by Curbie on June 19, 2011, 6:23 pm
 Z,

I like Winston's methane idea better then gasifiers which have been
known to start fires and on occasion explode, I don't know anyone that
recommends that small DIY gasifiers run unattended.

Cooking gas, space & water heating, refrigeration, fuel for ICEs;
methane has a lot of uses for those who have the bio resources.

A redo of John Fry's book:
http://large.stanford.edu/courses/ph240/cook2/docs/methane_digesters.pdf
... I have the original pdf and a methane spread-sheet for DIY if you
want them.

Jean Pain's book may also be of particular interest to you, he uses
forest wastes.
http://transitiontownlincoln.org.uk/wp-content/uploads/2011/03/Another-Kind-of-Garden.pdf

Curbie


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