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Start - Yellow  End- green

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How is energy stored in the gasification process

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How is energy stored in the gasification process

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Syngas comparison vs natural gas vs biogas:
Syngas: Syngas has 50% of the energy density of Natural gas

Biogas: 20 - 26 MJ/m^3

Natural gas: Around 38.3 MJ/m^3

Conclusion:
Both biogas and natural gas have higher energy density as compared to syngas which means they are more energy-dense and more useful.

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Since syngas is a product of gasification, what is syngas?

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Since syngas is a product of gasification, what is syngas?

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Consists of: Hydrogen, carbon monoxide, and carbon dioxide

Biomass | A | B | C
H2 | 7 – 9% | 15 – 17% | 14.9%
CO | 9 – 13% | 21 – 22% | 46.5%
CO2 | 12 – 14% | 10 – 11% | 14.6%
H2O | 10 – 14% | Dry | Dry
CH4 | 6 – 9% | 5 – 6% | 17.8%
C2+ | 0% | 0% | 6.2%
N2 | 47 – 52% | 46 – 47% | 0
Heating value (MJ/m3) | 4.5 – 5.5 | 7.5 | 18

C is the better syngas: Why? How are these components important to syngas composition?

- Most carbon monoxide as compared to the rest which goes through combustion to form carbon dioxide
- It has higher methane which contributes to its high heating value
- 0 nitrogen (%),it uses pure oxygen thus nitrogen does not take up space in the composition of syngas.
- It has relatively high hydrogen which can also go through combustion to form water.

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What are some of their disadvantages and advantages?

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What are some of their disadvantages and advantages?

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++ of fixed bed up draft:
- Simple
- High charcoal burn-out and internal heat exchange, which can lead to low
gas exit temperatures
- High equipment efficiency
- Possibility of operating with many types of feed stock

Disadvantages:
- Channelling in the equipment  can lead to oxygen break-through
- Dangerous and explosive situation
- Necessity to install automatic moving grates
- Problems associated with disposal of tar-containing condensates

++ of fixed-bed down draft:
- It is possible to produce tar-free gas suitable for engine application.
- Suffer less from environmental objections due to lower level of organic components

Disadvantages:
- Unable to operate on many unprocessed fuels
- Suffer from high ash content fuels (slagging)
- Lower efficiency resulting from the lack of internal heat exchange as well as the lower heating value of the gas.

++ of fixed-bed cross draft: (C)
- Economically feasible due to low shaft power of 10kW
- Very simple gas-cleaning train can be employed when using this type of gasifier in conjunction with small engines.

Disadvantages:
- Minimal tar-converting capabilities
- Consequent need for high quality charcoal (Low volatile content)

++ of circulation fluidised bed: (C)
- Easy control of temperature which can be kept below the melting/fusion point of the ash
- Able to deal with fluffy and fine grained materials w/o the need of pre-processing

Disadvantages:
- Erosion can occur on the tubes inside the boiler.
- The uneven temperature distribution could be caused by clogging of the air inlet of the bed.
- Long starting time up to 48 hours.
- High tar content of the product gas

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gasification
advantages:

cost of energy generated through biomass is reduced through the gasification route

it provides a significant life cycle cost advantage over hydrocarbon and ultimately leads to the development of a sustainable energy system

gasification is much cheaper than other energy production methods such as solar energy (gasification is 15-20 times cheaper)

cleaner than direct combustion

better efficiency at small scale

little GHG emissions compared to direct combustion

disadvantages:

rural areas have a lack of access to electricity. causing them to rely on primitive forms of energy like dung and fuel wood.

it has lesser efficiency due to low heating value from lack of internal heat exchange

direct combustion:
advantages:

Low running cost

the biomass treatment is simple

it has a closed carbon cycle, contributing less to global warming and are sustainable in nature

disadvantages:

Low efficiency

Large specific size

production of carbon monoxide from this combustion if in excess can be fatal to people

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Energy storage in gasification process (C)

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Energy storage in gasification process (C)

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Energy stored in CH4, CO, and H2, which are all unstable, means that energy can be stored in these compounds and elements.  CO2 does not store any energy as it is a stable compound, and does not go through combustion.

During the process of Gasification, the exothermic reactions give off heat, which is taken in by endothermic reactions where the energy stored can be burned off to give out energy.

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What are their similarities and difference (K)

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What are their similarities and difference (K)

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Similarities :

all the feed, which is the biomass, is being introduced into the gasifier through the top.

all of the gasifiers produce ash/char (all of them have an ash pit to collect ash or char)

They all require the introduction of air for combustion to take place.

They all have a cylindrical shape which promotes the flow of gases.

Difference :

The flow of air entering

The airflow upwards, downwards and the side of the reactor.

The flow of the producer air

Producer gas is extracted from the top for updraft gasifier

Producer gas is extracted from the bottom for downdraft gasifier

Producer gas is extracted from opposite the air nozzle at the grate

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What is gasification and how does it produce syngas from biomass? (D)

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What is gasification and how does it produce syngas from biomass? (D)

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Gasification is a process that converts biomass- or fossil fuel  into gases (Carbon monoxide, carbon dioxide, hydrogen, methane, carbon dioxide)

in the gasifier - a high temperature/pressure vessel where oxygen and steam directly contact with coal or other feed material causing a series of chemical reactions to occur that convert feed into syngas and ash/slag.

Gas stream cleanup/component separation (Products)

syngas further converted to hydrogen and carbon dioxide by adding steam and reacting over a catalyst in a water-gas shift reactor. when hydrogen is burned, it only created heat and water, resulting in the ability to create electricity with no carbon dioxide in the exhaust gases

Hydrogen made from coal or other solid fuels can be used to refine oil, or make products such as ammonia and fertiliser.

hydrogen enriched syngas can be used to make gasoline and diesel fuel (transportation fuels)

carbon dioxide can be captured from the syngas, preventing the emission of GHGs to atmosphere and enabling utilization (enhanced oil recovery) or safe storage

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Exothermic and Endothermic Processes of Gasification (C)

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Exothermic and Endothermic Processes of Gasification (C)

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Exothermic: Process that gives off heat
Endothermic: Process that takes in heat

drying - endothermic

pyrolysis - endothermic

combustion - exothermic

cracking - endothermic

reduction - endothermic

CO + H2O ↔ CO2 + H2 (water gas shift reaction)

C + CO2 ↔ 2CO (reverse boudouard reaction)

C + 2H2 ↔ CH4  (methanation reaction)

CH4 + H2O ↔ CO + 3H2 (steam methane reforming reaction)

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Since gasifications helps to  converting organic waste (biomass) to energy, what are some of the diffferent methods and what  pros and cons do they have depending on the context of their uses. How should we evaluate the different methods? 

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Since gasifications helps to  converting organic waste (biomass) to energy, what are some of the diffferent methods and what  pros and cons do they have depending on the context of their uses. How should we evaluate the different methods? 

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Fixed-bed up-draft

Fixed-bed down-draft

fixed-bed cross-draft

circulation fluidised bed