Colours of Hydrogen
The world is increasingly looking at Hydrogen to solve the emission problems of fossil fuels. Hydrocarbon to Hydrogen is the new mantra for policy makers across the world. Many countries are developing policies and infrastructure to usher in the Hydrogen economy. In this multi-part series we will look deeper at Hydrogen, the various methods of producing it, the economics of producing it, the technologies around storing and transporting it and finally the policy measures around it.
This week, we look at the colours of Hydrogen – the various ways that Hydrogen is produced.
Hydrogen is the most abundant element in the Universe and therefore on Earth as well. But it is almost never found in its elemental form on Earth. Hydrogen or H2 is almost always found in some compound form. Water is the most abundant example. But all types of fossil fuels are also some form of H2 compound, hence hydrocarbons. It is the hydrogen component of the hydrocarbon that provides the energy. When any hydrocarbon is burnt, hydrogen provides the energy and carbon is emitted as the pollutant.
Since it is always in some compound form, it must be extracted from the “ores”, so to speak. So water, oil, coal and H2-based-gases are some manner of an ore to elemental hydrogen.
The various colours of hydrogen are the various techniques used to produce hydrogen, the type of “ore” used and the type of energy used to extract H2 from that “ore”.
Black / Brown Hydrogen: Sourced from lignite or Coal with fossil fuels providing the power
Source is lignite or coal. Fossil fuels are used to extract H2 from Coal. Coal especially brown coal like lignite is preferred to black coal, because brown coal has a relatively higher oxygen content. This makes it easier to gasify coal. Coal gasification means converting coal into a gaseous form that can then be burnt as a fuel to generate energy[1]. The output is H2 and carbon compounds, usually CO2, CO. This is the most polluting form of producing H2. When these emissions are captured using Carbon Capture or Sequestration techniques, then it may be more environment friendly, but that is far into the future.
But from an economics point of view it is still a fairly viable method.
Grey Hydrogen: using Methane and Steam Methane Reforming (SMR)
Currently, this is the most widely used and the cheapest technique to produce H2. It uses methane (CH4) in the natural gas to extract H2. In SMR, methane reacts with high-temperature (700C-1000C) steam in the presence of a catalyst under 3-25 bar pressure. This produces H2, CO and CO2. In the next stage called the “Water gas shift reaction” CO and steam react in a presence of a catalyst to produce more H2 and CO2. In the final step of “pressure swing absorption” CO2 and other impurities are removed leaving behind pure H2[2].
SMR can be used on ethanol, propane and gasoline.
H2 from SMR can be used to power Fuel Cell Electric Vehicles. The GHG emissions for generating H2 from Petrol under SMR is still lower than emissions from using petrol directly in an internal combustion engine vehicle.
Blue Hydrogen: this is Grey Hydrogen + Carbon Capture and Storage[3]
In Grey Hydrogen, CO and CO2 that were byproducts of the process were emitted into the atmosphere. In Blue Hydrogen, instead of letting these emissions off in the open it is stored using CCS techniques. CCS means storing the GHG emissions in depleted oil wells or other similar reservoirs. CCS is a complex and an expensive technique. While its potential seems significant, it may will be years before it is economically viable.
Green or Yellow Hydrogen: H2 produced from electrolysis of water powered by Renewable Energy (RE) (green) or purely solar (yellow)
In Green Hydrogen water is split using electrolysers into H2 and Oxygen (O). An electrolyser has a cathode (negatively charged) and anode (positively charged). The electricity is provided by Solar / RE energy. Since there is zero emission in the production of H2 and in the production of the requisite electricity, this is the greenest and most environment friendly method of generating H2. Most governments are developing policies to achieve this ideal.
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Green H2 method is the best way to produce H2. It also seems to be the best way to achieve the “1-1-1” goal of 1 kg of H2 at $1 in 1 decade (by 2030)[4].
Pink / Red / Purple Hydrogen: When RE is replaced by Nuclear power, Green H2 becomes Pink H2.
While there are no direct GHG emissions from this process, nuclear waste is a far more hazardous waste to manage. Managing, especially storing, nuclear waste plans for thousands of years of safe storage. The whole of human civilization is just about 10,000 years. Against that, planning for “safely” storing a nuclear waste for between 10,000 years and 1,00,000 years seems quite fantastic bordering on impossible.
With over 18 years of advisory and engineering experience across 25GW of renewables, Arbutus Consultants Pvt Ltd. could be your partner of choice in your renewable energy journey. Please reach out to us at [email protected] to find out how we may be of assistance.?
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