Sourav BagchiPower EngineeringJadavpur UniversityRoll-001211501006

Hydrogen Generation

• Huge Sources: There is no element in the universe as abundant as hydrogen.

• No Harmful Emission:In fact, when used in NASA’s spaceships, the burned hydrogen gas leaves

behind clean drinking water for the astronauts.• Environment Friendly• Fuel Efficient:

Hydrogen energy is very efficient fuel source than traditional sources of energy and produces more energy per pound of fuel.• Renewable:

We can get Hydrogen by breaking water molecules.

Why Hydrogen is used as Fuel?

Fossil fuels are the dominant source of industrial hydrogen. Hydrogen can be generated from natural gas with approximately 80% efficiency, or from other hydrocarbons to a varying degree of efficiency. At high temperatures (700–1100 °C), steam () reacts with methane () in an endothermic reaction to yield syngas.

In a second stage, additional hydrogen is generated through the lower-temperature, exothermic, water gas shift reaction, performed at about 360 °C.

This oxidation also provides energy to maintain the reaction. Additional heat required to drive the process is generally supplied by burning some portion of the methane.

Steam reforming

The partial oxidation reaction occurs when a sub-stoichiometric fuel-air mixture is partially combusted in a reformer, creating a hydrogen-rich syngas. A distinction is made between thermal partial oxidation (TPOX) [1200°C] and catalytic partial oxidation (CPOX) [800°C-900°C]. The chemical reaction takes the general form:

Idealized examples for heating oil and coal, assuming compositions and respectively, are as follows:

Partial oxidation

Thermochemical cycles combine solely heat sources (thermo) with chemical reactions to split water into its hydrogen and oxygen components. If electricity is partially used as an input, the resulting thermochemical cycle is defined as a hybrid one.

The sulphur-iodine cycle (S-I cycle) is a thermochemical cycle processes which generates hydrogen from water with an efficiency of approximately 50%. The sulphur and iodine used in the process are recovered and reused, and not consumed by the process. The cycle can be performed with any source of very high temperatures, approximately 950 °C, such as by Concentrating solar power systems (CSP) and is regarded as being well suited to the production of hydrogen by high-temperature nuclear reactors, There are other hybrid cycles that use both high temperatures and some electricity, such as the Copper–chlorine cycle, it is classified as a hybrid thermochemical cycle because it uses an electrochemical reaction in one of the reaction steps, it operates at 530 °C and has an efficiency of 43 percent.

Thermochemical cycle

There are three main types of cells-Solid oxide electrolysis cells (SOECs)- SOECs

operate at high temperatures, typically around 800 °C. This has the potential to reduce the overall cost of the hydrogen produced by reducing the amount of electrical energy required for electrolysis.

Polymer electrolyte membrane cells (PEM)- PEM electrolysis cells typically operate below 100 °C and are becoming increasingly available commercially. These cells have the advantage of being comparatively simple and can be designed to accept widely varying voltage inputs which makes them ideal for use with renewable sources of energy such as solar PV.

Alkaline electrolysis cells (AECs)- AECs optimally operate at high concentrations electrolyte (KOH or potassium carbonate) and at high temperatures, often near 200 °C

Electrolysis

The current interest in non-traditional methods for the generation of hydrogen has prompted a revisit of radiolytic splitting of water, where the interaction of various types of ionizing radiation (α, β, and γ) with water produces molecular hydrogen. This revaluation was further prompted by the current availability of large amounts of radiation sources contained in the fuel discharged from nuclear reactors. This spent fuel is usually stored in water pools, awaiting permanent disposal or reprocessing.

The yield of hydrogen resulting from the irradiation of water with β and γ radiation is low (G-values = <1 molecule per 100 electron volts of absorbed energy) but this is largely due to the rapid re-association of the species arising during the initial radiolysis

Radiolysis

Ferrosilicon is used by the military to quickly produce hydrogen for balloons. The chemical reaction uses sodium hydroxide, ferrosilicon, and water. The generator is small enough to fit a truck and requires only a small amount of electric power, the materials are stable and not combustible, and they do not generate hydrogen until mixed.

The method has been in use since World War I. A heavy steel pressure vessel is filled with sodium hydroxide and ferrosilicon, closed, and a controlled amount of water is added; the dissolving of the hydroxide heats the mixture to about 200 °F and starts the reaction; sodium silicate, hydrogen and steam are produced

Ferrosilicon method

The biological hydrogen production with algae is a method of photobiological water splitting which is done in a closed photobioreactor based on the production of hydrogen as a solar fuel by algae. In 2000 it was discovered that if Chlamydomonas reinhardtii algae are deprived of sulfur they will switch from the production of oxygen, to the production of hydrogen.

Photosynthesis in cyanobacteria and green algae splits water into hydrogen ions and electrons. The electrons are transported over ferredoxins. Fe-Fe-hydrogenases (enzymes) combine them into hydrogen gas. Light-harvesting complex photosystem II light-harvesting protein LHCBM9 promotes efficient light energy dissipation. The Fe-Fe-hydrogenases need an anaerobic environment as they are inactivated by oxygen

Photo-biological water splitting

Biomass and waste streams can in principle be converted into biohydrogen with biomass gasification, steam reforming, or biological conversion like biocatalysed electrolysis or fermentative hydrogen production.Fermentative hydrogen productionFermentative hydrogen production is the fermentative conversion of organic substrate to bio-hydrogen manifested by a diverse group of bacteria using multi enzyme systems involving three steps similar to anaerobic conversion. Dark fermentation reactions do not require light energy, so they are capable of constantly producing hydrogen from organic compounds throughout the day and night. For example, photo-fermentation with Rhodobacter sphaeroides SH2C can be employed to convert small molecular fatty acids into hydrogen. The process involves bacteria feeding on hydrocarbons and exhaling hydrogen and . The can be sequestered successfully by several methods, leaving hydrogen gas.

Bio-hydrogen routes

Enzymatic hydrogen generation-Due to the Thauer limit (four /glucose) for dark fermentation, a non-natural enzymatic pathway was designed that can generate 12 moles of hydrogen per mole of glucose units of polysaccharides and water in 2007. The stoichiometric reaction is:

The key technology is cell-free synthetic enzymatic pathway biotransformation (SyPaB). A biochemist can understand it as "glucose oxidation by using water as oxidant". A chemist can describe it as "water splitting by energy in carbohydrate". A thermodynamics scientist can describe it as the first entropy-driving chemical reaction that can produce hydrogen by absorbing waste heat. The use of carbohydrate as a high-density hydrogen carrier was proposed so to solve the largest obstacle to the hydrogen economy and propose the concept of sugar fuel cell vehicles.

Bio-hydrogen routes

• Prof. Bireswar Majumdar for giving me such a good topic.• Prof. Amitava Dutta for suggesting this topic.• http://www.conserve-energy-future.com/

Advantages_Disadvantages_HydrogenEnergy.php• https://en.wikipedia.org/wiki/Hydrogen_production

Acknowledgement