 |
  |
|
 |
|
 |
|
 |
|
|
|
|
|
|
Dear All Biomassers: The message below from my good friend Tom Milne, Bob Evans and all anouncing a new report on hydrogen needs to be put in context. Speaking as a fuel scientist, I hope I may be permitted a personal diatribe in this forum. If you are emotionally convinced that hydrogen is the world's best fuel, and wish to stay convinced, delete this message. . ~~~~~~~~~ HYDROGEN has been known and used since the early part of the 19th century. It is easy to make in the laboratory from iron and HCL or by electrolysis. Hydrogen is unique amongst the elements with outstandingly good and bad properties. As a fuel it has the highest Mass Energy Density of any fuel by a large margin, so liquid hydrogen isn't too bad a fuel if you can afford the cost and keep it well insulated. As a gas it also has a very low Volume energy density (same as CO, 1/3 that of methane). It is an important component of synthesis gas (CO + H2) and producer gas (CO + H2 + N2). Hydrogen also has a flame velocity (2.83 m/s in air compared to .5 m/s for methane, propane etc.). For this reason it is a difficult automotive fuel, since stoichiometric combustion produces "hydrogen knock". However, it has the widest flamability limits so can be burned very lean for better efficiency. Another hydrogen problem I haven't heard discussed is that it contracts chemically 1/3 on burning according to H2 + 1/2 O2 [1.5 moles or voumes] ===> H2O [1 mole] by contrast, methane gets full value, since CH4 + 2 O2 [3 moles] ===> CO2 + 2 H2O [3moles] ~~~~~~~ Hydrogen is an important chemical for converting vegetable oils to margarine etc. and is widely used in large chemical plants. Electrolysis of water to make hydrogen is only 72% efficient (due to high overvoltage), and conversion of heat to electricity is typically 30% efficient, so electrolysis is 18% base efficiency. Hydrogen can be made from methane and hydrocarbons using steam reforming and the water gas shift reaction - probably 80% efficient. So for 150 years pure hydrogen was only used by quartz workers. However, many gases, including our producer gas, can contain large fractions of hydrogen - 18% in our current producer gas at CPC. ~~~~~~~~ So how has hydrogen risen so high in research circles as a target fuel? It all started with "The Hydrogen Economy" about 1970. At that time we were naively told that nuclear electric power would be too cheap to meter in a short time (Ha!). But you can't run a car on electricity so we would still need a "fuel tank". Since power had no cost, hydrogen from water would have no cost! Voila. I remember hearing these arguments at the first "Hydrogen Economy" conference held appropriately at the Playboy Club in Miami about 1974. We have since become disenchanted with the nuclear energy side of this argument, but dreamers still talk of hydrogen combustion being "non polluting" and therefore the ultimate fuel. Today's cars are amazingly clean compared to those of the smoggy ''70s, so they are relatively "non polluting" in the atmospheric sense. However our current fossil fuels do increase atmospheric CO2 levels so can be considered "polluting" from a global warming perspective. Don't worry, the oil will be gone soon at the present rate of usage/wastage. For a REALISTIC view on hydrogen, check out.. http://www.nrel.gov/ncpv/hotline/pdf/hydrogen_economy.pdf Your Skeptical Fuel Scientist, TOM REED BEF GASWORKS ----- Original Message ----- From: "Milne, Thomas" <thomas_milne@nrel.gov> To: "Milne, Thomas" <thomas_milne@nrel.gov>; <gasification@crest.org>; <stoves@crest.org>; <bioenergy@crest.org> Sent: Friday, May 24, 2002 12:36 PM Subject: GAS-L: RE: Biomass to Hydrogen Report Web Address > > > > -----Original Message----- > > From: Milne, Thomas > > Sent: Friday, May 24, 2002 11:27 AM > > To: 'gasification@crest.org'; 'stoves@crest.org'; 'bioenergy@crest.org'; > > 'hydrogen@pete.URI.edu' > > Subject: FW: Biomass to Hydrogen Report Web Address > > > > Interested parties may access our recent IEA report, "Hydrogen from > > Biomass--State of the Art and Research Challenges", at the WEB address > > listed below. The authors would welcome corrections or additions to > > references, as a supplement for Year 2002 is planned. > > > > Tom Milne, Carolyn Elam and > > Robert Evans. > > > > > > -----Original Message----- > > From: Elam, Carolyn > > Sent: Thursday, February 28, 2002 11:10 AM > > To: Milne, Thomas > > Subject: Biomass to Hydrogen Report Web Address > > > > http://www.eren.doe.gov/hydrogen/iea/pdfs/hydrogen_biomass.pdf > > - > Gasification List Archives: > http://www.crest.org/discussion/gasification/200202/ > > Gasification List Moderator: > Tom Reed, Biomass Energy Foundation, Reedtb2@cs.com > www.webpan.com/BEF > List-Post: <mailto:gasification@crest.org> > List-Help: <mailto:gasification-help@crest.org> > List-Unsubscribe: <mailto:gasification-unsubscribe@crest.org> > List-Subscribe: <mailto:gasification-subscribe@crest.org> > > Sponsor the Gasification List: http://www.crest.org/discuss3.html > - > Other Gasification Events and Information: > http://www.bioenergy2002.org > http://www.crest.org/articles/static/1/1010424940_7.html Bioenergy > http://www.crest.org/articles/static/1/1011975339_7.html Gasification > http://www.crest.org/articles/static/1/1011975672_7.html Carbon > >
| |||||||||||||||||||||||||
