Hydrogen From Biomass

Biomass

Biomass, mainly in the form of wood, is the oldest form of energy used by humans. Traditionally, biomass has been utilized through direct combustion, and this process is still widely used in many parts of the world. The most important biomass energy sources are wood and wood wastes, agricultural crops and their waste by-products, municipal solid waste, animal wastes, waste from food processing, and aquatic plants and algae. Energy from biomass fuels is used in the electric utility, lumber and wood products, and pulp and paper industries. Currently, much research has been focused on sustainable and eco-friendly energy from biomass to replace conventional fossil fuels.

The chemical structure and major organic components in biomass are extremely important in the development of processes for producing derived fuels and chemicals. Biomass energy (bioenergy) utilization has gained particular interest in recent years due to the progressive depletion of conventional fossil fuels that calls for an increased use of renewable energy sources.

 

Contribution of Biomass in Global Energy Supply

Biomass can be considered as the best option and has the largest potential, which meets energy requirements and could insure fuel supply in the future. Biomass energy resources are potentially the world’s largest and most sustainable energy source, a renewable resource comprising 220 billion oven-dry tons (about 4500 EJ) of annual primary production. Currently, much research has been focused on sustainable and eco-friendly energy from biomass to replace conventional fossil fuels. 

Biomass can be converted to a number of secondary energy carriers (electricity, gaseous, liquid and solid fuels and heat) using a wide range of conversion routes. The conversion routes to fuels and electricity can be distinguished in thermal, chemical and biochemical conversion routes. There have been developed thermo chemical conversion technologies such as pyrolysis, gasification, liquefaction, and supercritical fluid extraction for maximizing liquid yields.

 

Biomass Feedstocks for Hydrogen Production

The use of renewable biomass as a major feedstock for hydrogen production has received considerable attention in recent years. Hydrogen can be generated from biomass, but this technology urgently needs further development. The production of hydrogen from biomass is already economically competitive today. Hydrogen from biomass has many advantages:

(i)               independence from oil imports,

(ii)             net product remains within the country,

(iii)            stable pricing level,

(iv)            peace keeping, and

(v)             the CO₂ balance can be improved by around 30%.

Two types of biomass feedstock are available to be converted into hydrogen:

(i)               dedicated bioenergy crops, and

(ii)             less expensive residues, such as organic waste from regular agricultural farming and wood processing (biomass residues).

The list of some biomass material used for hydrogen production is given in Table 1. In general, biomass from energy crops, such as sweet sorghum, can be used as raw material for hydrogen production. Biomass, especially organic waste, offers an economical, environmental-friendly way for renewable hydrogen production.

Biomass Species	Main conversion process
Bio-nut shell	Steam gasification
Olive husk	Pyrolysis
Tea waste	Pyrolysis
Crop straw	Pyrolysis
Black liquor	Steam gasification
Municipal solid waste	Supercritical water extraction
Crop grain residue	Supercritical fluid extraction
Pulp and paper waste	Microbial fermentation
Petroleum basis plastic waste	Supercritical fluid extraction
Manure Slurry	Microbial fermentation

Table 1: List of some biomass material used for hydrogen production.

 

Hydrogen Production Routes from Biomass

The methods available for the hydrogen production from biomass can be divided into two main categories: thermo-chemical and biological routes. The major biomass-to-hydrogen pathways are shown in Fig. 1. Hydrogen can be produced from bio renewable feedstocks via thermo chemical conversion processes such as pyrolysis, gasification, steam gasification, steam reforming of bio-oils, and supercritical water gasification. Biological production of hydrogen can be classified into the following groups:

(i)               bio-photolysis of water using green algae and blue-green algae (cyanobacteria),

(ii)             photo-fermentation,

(iii)            dark-fermentation, and

(iv)            hybrid reactor system.  

Fig 1: Pathways from biomass-to-hydrogen

The advantage of the thermo-chemical process is that its overall efficiency (thermal to hydrogen) is higher (~ 52%) and production cost is lower. The yield of hydrogen that can be produced from biomass is relatively low, 16-18% based on dry biomass weight.

In the pyrolysis and gasification processes, water gas shift is used to convert the reformed gas into hydrogen, and pressure swing adsorption is used to purify the product. Comparison with other biomass thermo-chemical gasification such as air gasification or steam gasification, the supercritical water gasification can directly deal with the wet biomass without drying, and have high gasification efficiency in lower temperature. The major disadvantage of these processes is the decomposition of the biomass feedstock leading to char and tar formation.

Processes	Hydrogen yield (wt%)	Hydrogen/biomass energy contents
Pyrolysis + catalytic reforming	12.6	91
Gasification + shift reaction	11.5	83
Biomass + steam + except heat (theoretical max.)	17.1	124

Biological hydrogen production processes are found to be more environment friendly and less energy intensive as compared to thermo chemical and electrochemical processes. Biological production of hydrogen (biohydrogen) as a by-product of microorganism metabolism is an exciting new area of technology development that offers the potential production of usable hydrogen from a variety of renewable resources. There are three types of microorganisms of biohydrogen generation: cyano-bacteria, anaerobic bacteria, and fermentative bacteria.

 Hydrogen Production from Biomass Gasification

Gasification of biomass has been identified as a possible system for producing renewable hydrogen, which is beneficial to exploit biomass resources, to develop a highly efficient clean way for large-scale hydrogen production, and has less dependence on insecure fossil energy sources. Gasification technologies provide the opportunity to convert renewable biomass feedstocks into clean fuel gases or synthesis gases. The synthesis gas includes mainly hydrogen and carbon monoxide (H₂ + CO) which is also called as bio-syngas. Bio-syngas is a gas rich in CO and H₂ obtained by gasification of biomass. Hydrogen production is the largest use of syngas. Biomass can be converted to bio-syngas by non-catalytic, catalytic, and steam gasification processes. Steam gasification is a promising technology for thermo chemical hydrogen production from biomass. The yields of hydrogen from the pyrolysis and the steam gasification increase with increasing of temperature. In general, the gasification temperature is higher than that of pyrolysis and the yield of hydrogen from the gasification is higher than that of the pyrolysis.

Cost of Hydrogen Production from Biomass

Hydrogen production by gasification and pyrolysis of biomass are not generally considered economically competitive with SMR (Steam Methane Reforming) processes. The price of hydrogen obtained by direct gasification of lignocellulosic biomass, however, is about three times higher than that for hydrogen produced by SMR. It is found that, the cost of producing hydrogen from biomass ranges from 10 to 14 US $, with a net higher heating value (HHV) energy efficiency of 56-64%. It is believed that in the future biomass can become an important sustainable source of hydrogen. Biomass residues are the cheapest feedstocks. Because of the low sulphur content of biomass, a sulphur removal system is not likely to be required. Several studies have shown that the cost of producing hydrogen from biomass is strongly dependent on the cost of the feedstock. Hydrogen from biomass gasification is not expected to develop in the near term due to costs, lack of demonstrated technology and lack of widespread hydrogen market and infrastructure. For a more long-term view of price competition, it is necessary to include both the variability in feedstock prices and the likely use of CO₂ capture and storage (CCS) in fossil-based processes.

Role of Biomass Gasification in the Future Hydrogen Supply

Biomass has been recognized as a major world renewable energy source to supplement declining fossil fuel resources. It will play an important role in the future global energy infrastructure for the generation of power and heat, but also for the production of chemicals and fuels. The dominant biomass conversion technology will be gasification, as the gases from biomass gasification are intermediates in the high-efficient power production or the synthesis from chemicals and fuels. Biomass gasification offers the earliest and most economical route for the production of renewable hydrogen. Environmentally Compatible Energy Strategies (ECS) project has developed a long-term hydrogen-based scenario (B1-H₂) of the global energy system to examine the future perspectives of fuel cells. The scenario illustrates the key role of hydrogen in a long-term transition towards a clean and sustainable energy future. According to this scenario, biomass gasification will become a dominant technology in the future.

Hydrogen can be generated from biomass, but this technology urgently needs further development. The production of hydrogen from biomass is already economically competitive today. Hydrogen production from biomass has major challenges. There are no completed technology demonstrations. It is believed that in the future biomass can become an important sustainable source of hydrogen. Due to its environmental merits, the share of hydrogen from biomass in the automotive fuel market will grow fast in the next decade.

Conclusions

Hydrogen produced through a range of renewable primary energy sources such as wind, biomass, and solar energy is ideal for gradually replacing fossil fuels. The use of renewable biomass as a major feedstock for hydrogen production has received considerable attention in recent years.

Biomass and biomass-derived fuels can be used to produce hydrogen sustainably. Biomass gasification offers the earliest and most economical route for the production of renewable hydrogen.

Gasification of biomass has been identified as a possible system for producing renewable hydrogen, which is beneficial to exploit biomass resources, to develop a highly efficient clean way for large-scale hydrogen production, and has less dependence on insecure fossil energy sources. Gasification of biomass will become one of the dominant technologies by the end of the 21st century.

 

References

1)     Milne TA, Elam CC, Evans RJ. Hydrogen from biomass- state of the art and research challenges, Report for IEA, IEA/H2/ TR-02/001. Golden, CO: National Renewable Energy Laboratory; 2002

2)     Caputo AC, Palumbo M, Pelagagge PM, Scacchia F. Economics of biomass energy utilization in combustion and gasification plants: effects of logistic variables. Biomass Bioenergy 2005; 28:35e51.

3)     Hoogwijk M, Faaij A, Eickhout B, de Vries B, Turkenburg W. Potential of biomass energy out to 2100, for four IPCC SRES land-use scenarios. Biomass Bioenerg 2005; 29:225e57.

4)     Havva Balat, Elif Kirtay, Sila science & energy company, University Mah, Trabzon, Turkey. Hydrogen from Biomass- Present scenario and future prospects. 7416-7426