hydrogen as an energy carrier
TRANSCRIPT
Hydrogen As An Energy Carrier
-Zubin [email protected]
Hydrogen factsLightest Most abundantColourlessOdourlessNon-toxicNon-carcinogenic gasNot found by itself on Earth but in its
molecular form combined with anotherchemical as a compound (e.g. water, methane)
How can it be produced?Water electrolysis using any power source including
wind, solar, nuclear powerGasification of CoalAs a by-product from reforming natural gas/biogas
with steamFrom gas or biomass-derived alcohols
ElectrolysisUsing electricity to split water into hydrogen &
oxygenReaction takes place in electrolyzersDecomposition of water (H2O) into oxygen (O2) and
hydrogen gas (H2) due to an electric current being passed through water
ElectrolyzersConsist of an anode and cathode separated by an electrolyte
producing an electrically conducting solution when dissolved in water
Three types of electrolyzers: PEM (Polymer Electrolyte Membrane) Alkaline Solid Oxide
PEM Electrolyzer: Electrolyte is a solid speciality plastic material Electrons flow through external circuit and hydrogen ions
selectively move across the PEM to the cathode Combine with electrons from external circuit to form hydrogen
gas Operates at 70°-90°C
Alkaline Electrolyzer: Use of liquid alkaline solution of sodium or potassium
hydroxide as the electrolyte Transport of hydroxide ions through the electrolyte from
cathode side to anode side Operates at 100°-150°C
Solid Oxide Electrolyzer: Use of solid ceramic material as the electrolyte Selective conduction of negatively charged oxygen ions
at elevated temperatures Operates at much higher temperatures for the
functioning of solid oxide membranes : 700°-800°C
The ProcessHydrogen gas produced at cathode (-ve)
Reduction reaction with electrons from cathode given to hydrogen cations
2H+(aq) + 2e- H2 (aq)
Oxygen gas produced at anode (+ve)Oxidation reaction giving electrons to the anode2H2O (l) O2 (g) + 4H+
(aq) + 4e-
Overall Reaction : 2H2O (l) 2H2 (g) + O2 (g) Twice the amount of hydrogen molecules produced
than oxygen moleculesProduced hydrogen gas has twice the volume of the
produced oxygen gas (assuming equal temp. and pressure for both gases)
The VerdictHydrogen production via electrolysis can result in zero
greenhouse gas emissionsOffers opportunities for synergy with variable power
generationAllows for flexibility to shift production to best match resource
availability with system operational needs and market factorsPossibility of the elimination of curtailing excess energy from
renewable energy generationGrid electricity is not environmentally friendly, energy
intensive, and is not an ideal source for electricity for electrolysis
Renewables integrating hydrogen production through electrolysis is a possible option to overcome these limitations
StorageUsually stored in a liquid or gas stateLiquid hydrogen kept at temperatures bordering on -
253°C in highly insulated tanksAs a compressed gas underground at pressures up to
150 bar (15MPa)Gaseous hydrogen storage is simplest and most
extensively employed for both large and small scale storage
Steel cylinders or special composite material tanks (Li, Mg, C based) are capable of holding the gas at 700 bar
Typical storage: < 1.5% wt H2 , >98.5% wt of cylinderIncrease of % wt of H2: lighter cylinders at higher
pressuresHigh cost of materials required for storageHigh amount of energy is required to liquefy hydrogen
Hydrogen CompressionHydrogen gas requires much larger tanks for its
storage compared to hydrocarbons due to its poor energy density by volume
As a compressed gas usually at pressures up to 200 bar (3000 psi)
Increasing gas pressure improves the density by volume, making for smaller, but heavier container tanks
Compressed hydrogen storage can exhibit very low permeation
Special composite material tanks are capable of holding the gas at 700 bar
Compressed hydrogen is conventionally stored at near-ambient temperatures
“Cold” (sub-ambient but >150K) and “Cryogenic” (150K and below) storage being investigated to achieve higher H2 densities at reduced temperatures
Cost of current compressed gas systems is dominated by composite materials & processing with a significant impact from balance of plant (BOP) components
Hydrogen compressors increase the pressure on the hydrogen and can transport it through a pipe
Approx. 15% of the usable energy from the hydrogen is lost on compression using today’s compression technologies
Also reduces the volume of hydrogen gasExamples:
Electrochemical hydrogen compressor Hydrogen supplied to the anode Compressed hydrogen is collected at the cathode Energy efficiency up to and even beyond 80% Pressures up to 700 bar
Linear compressor Piston moves along a linear track to compress the working fluid Used under cryogenic conditions
UtilizationTo provide electricity and heat through its use in fuel
cellsFuel cells generate electricity from an electrochemical
reaction where oxygen and hydrogen combine to form water
Electricity produced used in a variety of applicationsHeat produced as a by-product used for heating and
cooling purposes
Why Hydrogen?A clean energy carrier produced from any primary
energy sourcePros of Hydrogen as an energy carrier:
Security of Energy Supply Air Quality & Health Improvement Greenhouse Gas Reduction Ensures Economic Competitiveness
Hydrogen SafetyKnowledge gaps have existed for several decades
regarding: Conditions of ignition Flame acceleration Structural protection Ventilation
Public perception and confidence in hydrogen relies on credibility, transparency, and individual benefit
Exhibits wider limits of flammability, high detonation sensitivity, and relative low ignition energy if mixed with air, in comparison to conventional fuels
Codes & Standards regarding Hydrogen Safety: Safety distances Design of buildings & containers for housing hydrogen
equipment Earthing & lightning protection Materials & components used in hydrogen systems
Risks & ChallengesMixtures of hydrogen in are flammable over a wide
range of compositionsEnergy required to ignite a hydrogen/air mix can be
very lowBurns with a flame that is invisible in daylightSmall molecule that can leak very easilyIf released and ignited, it burns with a rapidly moving
flame
ConclusionSophisticated battery for energy
storageHigh potential as a relatively
clean fuel of the futureNegative net energy i.e. it takes
more energy to produce it than it contains
Very low calorific valueRequires larger and heavier fuel
tanksExtraction methods are extremely
energy intensive (e.g.. Electrolysis of water)
Thank You
WindPower Nepal is looking for technical assistance to find out if Hydrogen could be used as a Cooking Fuel in Nepal. For further
information, please write to us at [email protected]