Describe the concept of ‘Hydrogen Economy’
- Future energy system in which hydrogen plays a central role
- Shift from traditional energy sources
- Potential to significantly reduce greenhouse gases
- Hydrogen to be produced from renewable or low carbon sources such as electrolysis of water using renewable electricity, steam reforming with carbon capture and storage (CCS), biomass gasification, or other emerging technologies.
Major issues associated with ‘Hydrogen Economy’
- Cost: mostly due to the energy intensive nature of current hydrogen production methods
- Infrastructure: Infrastructure for production, transportation, and distribution is under developed
- Energy efficiency: The production, storage, and utilization of hydrogen involve energy losses at each stage, reducing overall energy efficiency
- Scalability and Scale-up: Scaling up hydrogen production to meet the requirements of various sectors would require significant investment, research, and development
- Sustainability: Hydrogen produced from fossil fuel-based processes, such as steam methane reforming without carbon capture, can still result in greenhouse gas emissions.
- Safety: Hydrogen is highly flammable and has specific safety considerations.
- Public Acceptance: The general public’s awareness and acceptance of hydrogen as an alternative energy carrier may pose a challenge.
CRISES - Cost, Infrastructure, Energy efficiency, Scalability, Safety, Sustainability
List the current methods used to produce hydrogen from biomass
Thermochemical vs Biological
Thermochemical:
- Gasification
- Pyrolysis
- High pressure aqueous
GPH
Biological:
- Anaerobic digestion
- Fermentation
- Metabolic processing
AFM
Advantages of the ‘Hydrogen Economy’
Elimination of pollution caused by fossil fuel
Elimination of greenhouse gases
Elimination of economic dependence
Distributed and localized production
Explain biomass gasification
Gasification is a thermochemical process that converts biomass into syngas. Which can be further processed to separate and purify hydrogen.
Undergoes pyrolysis
Oxygen-deficient environment must be created, favoring the production of syngas rather than complete oxidation / complete combustion
What is syngas?
Syngas, short for synthesis gas, is a mixture of gases primarily composed of hydrogen (H2) and carbon monoxide (CO). It is produced through various processes, including biomass gasification, coal gasification, or steam reforming of natural gas. Syngas is a versatile fuel and feedstock that can be used in a range of applications.
Explain pyrolysis
The thermal decomposition of the organic material in the absence of oxygen. This results in the release of volatile compounds, including gases and tars.
The gasification reactions
In the presence of heat and limited oxygen, the volatile compounds released during pyrolysis react with steam (H2O) or carbon dioxide (CO2) to produce syngas. The main reactions involved are:
C + H2O → CO + H2
C + CO2 → 2CO
C + 2H2O → CO2 + 2H2
These reactions are endothermic, meaning they require heat energy to proceed.
What are the 5 types of biomass?
W - Woody Biomass : Woody biomass refers to biomass derived from trees and woody plants.
A - Agricultural Biomass: Agricultural biomass comprises biomass residues and byproducts generated from agricultural activities.
G - Energy Crops: Specifically cultivated for their high biomass yield and energy content.
E - Algae: microscopic aquatic organisms that can convert sunlight, water, and carbon dioxide into biomass through photosynthesis.
O - Organic Waste: refers to biomass derived from organic materials that are discarded or considered waste. This includes food waste, agricultural waste, forestry residues, and municipal solid waste.
Explain ‘anaerobic digestion’
Anaerobic digestion is a biological process that utilizes microorganisms to break down organic matter in the absence of oxygen, resulting in the production of biogas. Biogas is a mixture of gases, primarily composed of methane (CH4) and carbon dioxide (CO2), with smaller amounts of trace gases such as hydrogen (H2), nitrogen (N2), and hydrogen sulfide (H2S).
Explain ‘fermentation’ for the production of H2 from biomass
Fermentation involves the use of microorganisms to convert organic matter into H2 gas. It is a natural metabolic process that occurs in the absence of oxygen (anaerobic conditions).
Explain ‘Metabolic Processing’ for the production of H2 from biomass
The utilization of specific metabolic pathways and enzymes within microorganisms to produce H2 gas. Different metabolic pathways can be employed by microorganisms to convert organic matter into H2.
Explain what ‘Biogas’ is
A renewable energy-rich gas produced by the breakdown of organic matter in the absence of oxygen, a process known as anaerobic digestion. It is primarily composed of methane (CH4) and carbon dioxide (CO2), with trace amounts of other gases such as nitrogen (N2), hydrogen sulfide (H2S), and small quantities of other volatile organic compounds.
What are the 4 steps of producing hydrogen via steam reforming?
- Feedstock pre-treatment : removes impurities which may deactivate the catalyst used
- Catalytic steam reforming : feedstock is introduced into a reformer, which contains a catalyst, typically based on nickel (Ni). Steam reforming reaction takes place
CH4 + H2O -> CO + 3H2 (endothermic, requires high temp)
Heat required, generated by: CH4 + 2O2 -> CO2 + 2H2O
- Water - Gas shift reaction : Used to turn the undesired CO into H2
CO + H2O -> CO2 + H2 (exothermic reaction, occurs at lower temp than previous reaction)
- Gas clean-up : Purification steps are often taken at the end such as pressure swing adsorption or membrane separation to remove trace amounts of CO
F.I.R.E.H2O. O
Biological hydrogen production:
- Dark fermentation : relies on anaerobic bacteria to break down organic matter in the absence of light. Through a series of biochemical reactions, these bacteria produce hydrogen as a byproduct.
- Photobiological Hydrogen Production: Certain photosynthetic microorganisms and algae have the ability to produce hydrogen through photosynthesis. Under specific conditions, they can divert their metabolic pathways to generate hydrogen gas instead of oxygen.
Explain the Palladium membrane separation process
- operate via pressure driven diffusion across palladium membranes
- exhibit high permeability to hydrogen while selectively blocking the passage of other gases
- Palladium is very expensive
- H2 molecules in contact with the Pd membrane dissociate into monatomic hydrogen and pass through the membrane. When on the other side the monatomic hydrogen recombines back into molecular H2
Describe the extraction of shale gas via ‘fracking’
Stage 1: Drill down to shale level
Stage 2: Water sand and chemicals pumped to a pressure of approx 1500 lb/inch^2, forcing the rock apart releasing the gas in the pores
Stage 3: Liquid pumped out of well, sand keeps the rock separated allowing gas to seep out of the broken shale layer to be piped to the surface.
What is ‘Shale gas’ ?
Shale gas is methane (natural gas) which is trapped in impermeable shale rock deep underground
What are the advantages and potential risks of ‘Fracking’ ?
Advantages:
- Increased energy production
- Economic benefits (i.e job creation)
- Reduced carbon emissions (produces lower co2 emissions than coal when combusted)
- Energy transition support
IREE
Risks and concerns:
- Water contamination
- Air pollution
- Seismic activity
- Habitat and wildlife disruption
WASH
How can ‘Shale gas’ be utilized for producing hydrogen?
Steam methane reforming
What are two current methods of purification of hydrogen?
- Pressure swing adsorption
- Pd membrane separation
How does pressure swing adsorption work?
The process involves cyclic changes in pressure to selectively remove impurities from a gas stream.
Adsorption based on molecular weight at high P
Beds composed by zeolites, silica, and carbons
H2 = 99,99%
What are some current methods of hydrogen storage?
- Compressed gas storage
- Liquid hydrogen storage (specialized storage facility)
- Metal Hydride
- Chemical Hydride
What are some current methods of hydrogen transport?
- Compressed gas transport
- Liquid hydrogen transport
- Hydrogen pipelines
