22MEX01 Renewable Energy Sources

Unit V

Direct Energy Conversion Systems and New Energy Sources

Direct Energy Conversion Systems: MHD Generators Thermoelectric Power Generation.

New Energy Sources: Hydrogen Generation Storage - Transport and Utilization - Applications - Power Generation Transport - Hydrogen Economy - Safety Issues - Fuel Cell Principle Types.

Magnetohydrodynamic (MHD) System

• A magnetohydrodynamic system deals with the behavior of electrically conducting fluids (like plasma, liquid metals, or saltwater) flowing in the presence of a magnetic field.
• Lorentz Force - When a conducting fluid flows across a magnetic field:

MHD System- Working

• Ionized Gas or Conducting Fluid is Introduced
• A high-temperature plasma or liquid metal (like mercury, sodium, or ionized gas) is made to flow at high speed through a duct or channel.
• Seeding in MHD is the process of adding easily ionisable salts to the working fluid to increase its electrical conductivity; common seeding materials include potassium carbonate, cesium carbonate, potassium sulfate, and cesium sulfate.
• Strong Magnetic Field is Applied
• Magnets placed around the duct create a magnetic field perpendicular to the direction of the fluid flow.
• Motion of Conducting Fluid Generates Electric Current
• Due to the interaction between the fluid flow and the magnetic field, the charged particles experience the Lorentz force, producing an electric current in the perpendicular direction.
• Electrodes Collect the Generated Current
• Electrodes placed on opposite sides of the duct pick up the induced electric current.
• Electrical Power is Delivered Without Moving Parts
• The collected current is fed directly to an external circuit or grid, making MHD a direct energy conversion system

Open-Cycle MHD System

Closed-Cycle MHD System

Hybrid MHD and Steam Part Open Cycle system

MHD System

Advantages

• No moving mechanical parts
• Higher theoretical efficiency
• Less mechanical wear
• Suitable for high-temperature systems

Challenges

• High magnetic field requirements
• Material limitations at high temperatures
• Ionization and fluid conductivity issues
• High system cost

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HYDROGEN

• Hydrogen is an energy carrier, not an energy source
• While hydrogen is the most abundant element, most is chemically bound as hydrocarbons, carbohydrates or water
• Energy is needed to extract the hydrogen
• It can be produced from various sources as 90% of the materials contains hydrogen atoms.
• Water is an important source for hydrogen production using electrolysis

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Why hydrogen is important

• Hydrogen is ~75% of the known universe
• On earth, it’s not an energy source like oil or coal Only an energy carrier like electricity or gasoline — a form of energy, derived from a source, that can be moved around
• The most versatile energy carrier

- Can be made from any source and used for any service

- Readily stored in large amounts

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Present uses of hydrogen�

• Most used in petroleum refining and petrochemical production (93%)

other uses

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• • metal processing (2.7%)

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• • manufacture of electronics components (1.5%)

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• • food processing (.7 %)

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• • manufacture of glass (.3%)

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• • utility power generation (.2%)

HIGH EFFICIENCY� & RELIABILITY

ZERO/NEAR ZERO�EMISSIONS

ADVANTAGES OF A HYDROGEN

• Hydrogen can produce up to 3x as much energy as natural gas
• 9 million metric tons hydrogen / year

- Enough to power 20-30 million cars or 5-8 million homes

• While in use, hydrogen emits no carbon dioxide, only in production
• Can be generated from water as waste and solar energy: both inexhaustible energies
• Drivers using it can save money through hydrogen fuel over a long period of time
• Water is MAIN byproduct
• Weighs less than hydrocarbons

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HYDROGEN ENERGY CYCLE

16

The First Question:

Where Does Hydrogen Come From?

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95% of hydrogen is currently produced by steam reforming

Partial Oxidation

Steam Reforming

Electrolysis

Thermochemical

Fossil Fuels

Water

Biomass

currently most energy efficient

requires improvements

not cost effective

requires high temperatures

Gasification

Microbial

requires

improvements

slow

kinetics

CURRENT HYDROGEN PRODUCTION

• Current hydrogen production
• 48% natural gas
• 30% oil
• 18% coal
• 4% electrolysis
• Global Production
• 50 million tonnes / yr
• Growing 10% / yr
• US Production
• 11 million tonnes / yr

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HOW IS HYDROGEN PRODUCED?

• Reforming fossil fuels
• Heat hydrocarbons with steam
• Produce H₂ and CO
• Electrolysis of water
• Use electricity to split water into O₂ and H₂
• High Temperature Electrolysis
• Experimental
• Biological processes
• Very common in nature
• Experimental in laboratories

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HYDROGEN PRODUCTION

ELECTROLYSIS OF WATER

STEAM REFORMING

• Most common method of producing commercial bulk hydrogen.
• Most common method of producing hydrogen used in the industrial synthesis of ammonia.
• It is the least expensive method.
• High temperature process (700 – 1100 °C)
• Nickel based catalyst (Ni)
• At 700 – 1100 °C and in the presence of a nickel based catalyst (Ni), steam reacts with methane to yield carbon monoxide and hydrogen.

CH4 + H₂O → CO + 3 H₂

• Additional hydrogen can be recovered by a lower-temperature gas-shift reaction with the carbon monoxide produced. The reaction is summarized by:

CO + H₂O → CO₂ + H₂

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COAL GASIFICATION

THERMOCHEMICAL PRODUCTION OF HYDROGEN

• When water is heated to above 2500 ^oC, it separates into oxygen and hydrogen in a process known as thermolysis.
• However, at such high temperatures, it is difficult to prevent the oxygen and hydrogen from recombining to form water.
• Thermo chemical water-splitting cycles can lower the temperature and help separate oxygen and hydrogen products to produce pure hydrogen gas.
• These cycles can improve the efficiency of hydrogen production from 30% for conventional electrolysis to around 50% efficiency
• One of the most promising cycles so far is the sulfur-iodine (S-I) cycle.

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SULFUR-IODINE THERMOCHEMICAL CYCLE

• Sulfur dioxide (SO₂ ) and iodine (I₂) are fed into the cycle as chemical catalysts.
• A catalyst lowers the activation energy of a reaction without being used up by the reaction.
• Step 1

I₂ + SO₂ + 2H₂O 2HI + H₂SO₄

• The reaction is run at 120 degrees C. The hydrogen iodide and sulfuric

acid are separated, usually by distillation.

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STEP 2

• Generation of oxygen and regeneration of SO2.

H₂SO4 H₂O + SO₂ + 1/2 O₂

• This reaction is run at 850 degrees C.

STEP 3

• Generation of hydrogen and regeneration of I

2HI H₂ + I₂

• This reaction is run at 450 degrees C.

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PHOTOBIOLOGICAL

• This method involves using sunlight, a biological component, catalysts and an engineered system.
• Specific organisms, algae and bacteria, produce hydrogen as a byproduct of their metabolic processes.
• These organisms generally live in water and therefore are biologically splitting the water into its component elements.
• Currently, this technology is still in the research and development stage and the theoretical sunlight conversion efficiencies have been estimated up to 24%.

BIOMASS PRODUCTION OF HYDROGEN

• Hydrogen can be produced numerous ways from biomass.
• Biomass is defined as a renewable resource made from renewable materials. Examples of biomass sources include:

- switch grass

- plant scraps

- garbage

- human wastes

• Gasification of biomass could be a way of extracting hydrogen from these organic sources.

• The biomass is first converted into a gas through high-temperature gasifying.
• The hydrogen rich vapor is condensed in pyrolysis oils.
• These oils can be steam reformed to generate hydrogen.
• This process has resulted in hydrogen yields of 12% - 17% hydrogen by weight of the dry biomass.
• When biological waste material is used as a feedstock, this process becomes a completely renewable, sustainable method of hydrogen generation.

DRAWBACKS

• Extreme Cost
• Right now only 4% of production is being used from electrolysis
• Rest is from fossil fuels
• Hydrogen uses fossil fuels in production and in return, creates greenhouse gases
• Hard to store
• Hydrogen can react with metals it’s stored in and cause leaks
• Need to be able to produce at least ten times more in order for hydrogen powered vehicles to be normal

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HYDROGEN STORAGE & TRANSPORTATION

HYDROGEN STORAGE

• Compressed gas storage

- stored in cylinders

• Liquid storage.

- cryogenic storage, liquid hydrogen boils at -273^o C, Highly flammable, High cost.

• Line pack system.
• Underground storage.
• Metal hydrides.

HYDROGEN TRANSPORTATION

• Pipeline transportation.
• Liquid hydrogen transportation.
• Metal hydride transportation.

UTILIZATION OF HYDROGEN GAS

• Residential uses
• Industrial uses
• Alternate transport fuel
• Alternative fuel for aircraft
• Electric power generation

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FUEL CELL

• A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent.
• Fuel cells are different from batteries in that they require a constant source of fuel and oxygen to run, but they can produce electricity continually for as long as these inputs are supplied.

COMPONENTS OF FUEL CELLS

• Fuel electrode (anode)

- Porous nickel electrode

• Oxidant electrode (cathode)

- Porous carbon electrode

• Electrolyte .

- KOH

• Catalyst .

- Nickel , silver

HOW DO THEY WORK?

• Fuel (H₂) is first transported to the anode of the cell

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• Fuel undergoes the anode reaction

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• Anode reaction splits the fuel into H⁺ (a proton) and e^-

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• Protons pass through the electrolyte to the cathode

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• Electrons can not pass through the electrolyte, and must travel through an external circuit which creates a usable electric current

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• Protons and electrons reach the cathode, and undergo the cathode reaction

CLASSIFICATION OF FUEL CELL

• Hydrogen fuel cell
• Fossil fuel cell
• Hydrocarbon fuel cell
• Alcohol fuel cell
• Hydrazine fuel cell

REGENRATIVE FUEL CELL

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