Hydrogen production from biomass
Yesterday at the Hydroverse Convention in Essen I was again confronted with this topic...
Some basics
The elementary analysis of the biomass is decisive for the consideration of the utilization paths. How much carbon, how much hydrogen, but also how much oxygen does it contain?
The presentation by Phydades shows the range very well.For a first consideration, an average value was taken.
What tends to be overlooked is the high percentage of oxygen, which will already produce a high percentage of CO (at high temperatures) or CO2 (at low temperatures) even in a pyrolysis without combustion air. see Boudouard reaction
Now, a first basic consideration has been carried out to show what yields can be produced in the ideal case of a complete conversion, knowing full well that reality will lie in between.
The cases
For all cases, it was assumed that no other medium, such as air or steam, was supplied. The following show cases have been considered:
The results
Depending on the process, between 1.6 MWh (HTC) and 3.3 MWh (syngas) must be externally supplied for 1,000 kg for the conversion. However, this also results in very different products in terms of energy.
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Options
H2 production could be increased by injecting steam. In the process, the carbon would also be converted into CO or CO2. However, there is no either-or here; both gases are produced. In addition, there are hydrocarbons, the classic tars. There are various approaches to reducing this problem.
Methanol production, on the other hand, could be increased by injecting hydrogen, since there would still be sufficient carbon and oxygen. The crux of the production is that it is a catalytic process at higher pressures. Catalysts are very sensitive to calaysator poisons, such as sulfur.
Acetic acid production could be increased only slightly by adding oxygen. However, there is a critical temperature window here, as acetic acid decomposes at temperatures as low as 320°C.
HTC conversion will produce very small amounts of hydrogen or methane, depending on the H/O ratio. In fact, strong contaminations occur in the water phase here, so that it cannot be used as a fertilizer.
Mass "balance"
The following interesting figures on world annual productions can be found:
Have I made a mistake here?
Conclusio
The production of hydrogen from biomass seems interesting at first glance, since it is hydrogen from renewable sources. However, the production process generates significant amounts of CO2.
Therefore, it is important to look closely at the environment:
Thus, no simple answer is possible, what is the right use of the available raw material!
Personally, I prefer living trees....
Zelfstandig/ vrijwillig Coach-Toekomstdenker in de Transitie naar een Fossielvrije, Circulaire, Bio-based Economie
1 年Your statement that you prefer "living trees" demonstrates your lack of knowledge about the balance of nature, biodiversity and sustainable forestry in the transition from fossil to a biobased economy. Don 't worry! Forrests are dying now due to ignorance within the forestry business and are burning down due to lack of insurance and loss prevention practices in this branche.
Sustainable fuels and chemicals from biomass or CO2
1 年Quite an oversimplification there Dirk Gerlach because when producing hydrogen from biomass residues (NOT LIVING TREES) we avoid the use of natural gas adding more CO2 to our system. If done right it would include storing the biogenic carbon, which generates negative emissions. So not only avoiding additional carbon ending up in the atmosphere. Also reducing the carbon in the atmosphere. It’s a win win! And on top of it, amongst the cheapest forms of renewable hydrogen!!
Mentor of TRAVELLERS in The 2021 Challenge
1 年Thanks. Again it is remarkable that you don't recognize heat as a harmful emission. Personally I think hydrogen is no solution while the numbers are huge and will become even bigger in the future. Dig one layer deeper in the fundamentals of natural sciences and you will find CM. And suddenly you realize that it is all much simpler.