Hydrogen is a clean and versatile energy carrier with applications in various industries, including transportation, chemical manufacturing, and energy production. One promising method for hydrogen production is through the utilization of pyrolysis gas, which is generated from the thermal decomposition of biomass such as rice straw, wheat straw, wood, and maize straw. This process not only leverages renewable resources but also aligns with global efforts to reduce carbon emissions and transition to sustainable energy systems.
Pyrolysis Gas and Its Composition
Pyrolysis gas, also known as syngas, primarily consists of carbon monoxide (CO), hydrogen (H2), carbon dioxide (CO2), methane (CH4), and other light hydrocarbons (CxHy). The composition of pyrolysis gas depends on the feedstock and process conditions. Common feedstocks for pyrolysis include:
- Rice Straw: High in cellulose and hemicellulose, yielding a rich mix of hydrocarbons and hydrogen.
- Wheat Straw: Similar to rice straw, with slightly higher lignin content, contributing to biochar production.
- Wood: High calorific value, producing consistent pyrolysis gas.
- Maize Straw: Moderate cellulose and lignin content, yielding a balanced composition of bio-oil, biochar, and gas.
Hydrogen Production Process
The production of hydrogen from pyrolysis gas involves three interconnected reactors: the fuel reactor, the steam reactor, and the air reactor. Each reactor operates under specific conditions to achieve 100% conversion of the involved chemical species.
- Fuel Reactor
In the fuel reactor, the pyrolysis gas reacts with iron(III) oxide (Fe2O3) at high temperature and pressure, producing carbon dioxide (CO2), water (H2O), and reduced iron oxide (FeO). The reaction is as follows:
Reaction:
CO2+ CO+ CH4+ Fe2O3 → CO2 + H2O + FeO
Conditions:
- Temperature: 900°C
- Pressure: 10 atm
At these conditions, Fe2O3 is completely reduced to FeO, ensuring the maximum conversion of 100 % Fe2O3 into FeO and pyrolysis gas into CO2 and H2O.
- Steam Reactor
The reduced iron oxide (FeO) from the fuel reactor is fed into the steam reactor, where it reacts with water (H2O) to produce hydrogen (H2) and magnetite (Fe3O4). The reaction proceeds as follows:
Reaction:
FeO + H2O → Fe3O4 + H2
Conditions:
- Temperature: 700°C
- Pressure: 10 atm
Under these conditions, FeO is completely oxidized to Fe3O4, resulting in 100% conversion of water into hydrogen gas. At the required condition.
- Air Reactor
In the air reactor, magnetite (Fe3O4) reacts with oxygen (O2) from air to regenerate iron(III) oxide (Fe2O3). The reaction is as follows:
Reaction:
4Fe3O4 + O2 → 6Fe2O3
Conditions:
- Temperature: 850°C
- Pressure: 10 atm
At these elevated conditions, Fe3O4 is fully converted back to Fe2O3, completing the cycle and ensuring the continuous operation of the system.
Advantages of the Process
- High Efficiency: Each reactor achieves 100% conversion, minimizing losses and maximizing hydrogen production.
- Renewable Feedstocks: The use of biomass-derived pyrolysis gas ensures sustainability and reduces dependency on fossil fuels.
- Environmental Benefits: The closed-loop system significantly lowers carbon emissions compared to traditional hydrogen production methods.
- Versatility: The process can utilize various types of biomass, making it adaptable to regional agricultural residues.
Key Conditions and Observations
- In the fuel reactor, Fe2O3 is completely reduced to FeO at 900°C and 10 atm.
- In the steam reactor, FeO is entirely converted to Fe3O4 at 700°C and 10 atm, producing high-purity hydrogen gas.
- In the air reactor, Fe3O4 is fully oxidized to Fe2O3 at 850°C and 10 atm, ensuring the efficient recycling of iron oxides.
Conclusion:
As by using this process the hydrogen produced in the air reactor yield of 40% of the total reactants consumed and the product is 99% pure hydrogen. As the temperature of the outlet hydrogen gas stream is 700C is sent to expander to reduce the pressure and temperature to cool down.at temperature of 400C and pressure reduced to 10atm to 1atm
