Using hydrogen as fuel is an old concept, mostly aligned with the development of fuel cells. In the laboratories it has been proven since the beginning of the 20th century, yet only when the space program adopted it in the 70s, it gained mainstream traction. Then again till now the space program was the only industry justifying its cost.
In order to evaluate it, we ought to compare it with other fuel options, like LNG, which is in vogue at the moment. Its heating value is more than double to that of LNG. In respect to gasoline, 1kg of hydrogen can meet the energy produced by one gallon of gasoline. In short its high performance, coupled with zero greenhouse gases emissions, gives good grounds for the buzz around it.
Nonetheless we need to understand the whole process to be able to establish its environmental value, starting with its production methods. There are several tried and tested production methods already available in the market, such as steam reforming, partial oxidation, coal gasification, thermochemical methods in the biogenic production and electrolysis, with a couple more in the pipelines, like biochemical methods. The 95% of the hydrogen production presently comes from steam reforming.
Steam reforming is an endothermic reaction between mainly natural gas and water in high temperatures between 700°-1000°C. Natural gas contains methane CH4 which reacts with H2O, producing H2 and CO, a middle step gas, known as SYNGAS, further processed to give H2 and CO2 at completion. For every ton of H2 produced in this method, there are 9ton CO2 produced simultaneously. Off course it is fair to mention that the densities of the two gases are quite different, H2 has a 0.089g/l while CO2 has 1.98g/l, therefore if we look at the volume of the two we will see a different ratio. Instead of natural gas LPG can be used or naphtha, but in all cases with steam reforming our source is fossil fuel.
The same applies for partial oxidation, which is using heavy fuel oil in the basic reaction, along with pure oxygen to produce the hydrogen and carbon monoxide. It requires more energy that the former method and yields less product at the end. The main advantage of this method is that it can be a way of burning the heavy fuel oil which is produced while we extract petrol from the ground. The use of heavy fuel oil use is further limited as shipping is slowly turning its back on it, leaving only onshore power plants using it, but its production remains. We need to do something with it, this can be a short term solution.
Looking at the other methods, coal gasification simply uses coal and emits not only CO2 at the very end of the process, but also some nitrogen. Hardly a method with environmental attributes.
In theory thermochemical methods that use biomass as origin material are great as we manage to eliminate waste, coupled with producing power. Yet the source needs to be carefully selected in order to be productive and the waste quantity has to be very large for a noteworthy H2. It is presently lacking in efficiency.
Then there is the most talked water electrolysis, hydrogen produced from water and ending in water, in which case we have theoretically no greenhouse emissions. Practically today the efficiency of conversion is between 70-80% and when Proton Exchange Membrane method is fully established, the efficiency would reach to 82-86%. The only drawback of this method is that it needs 286kJ energy per mole of H2, in order to produce electricity of 237kJ, namely we are inserting more energy that we are getting back. If it is from renewable energy, solar or wind and so forth, then we are definitely on the positive end, but let’s not forget the prerequisite.
As our objective is to truly appreciate the value of hydrogen as a fuel of the future, in respect of its production alone in this post, we can sum the aforementioned below.
- There is great potential of H2 as fuel, its heating value is excellent and fuel cells can be further developed to store energy that will be available when we need it;
- Presently 95% of it is produced by fossil fuel, therefore it is not free of greenhouse gases. If we are developing energy free of greenhouse gases, alternative methods for producing H2 need to become the main source;
- Electrolysis is only truly free of greenhouse gases when it is coupled with renewable energy for its production, as it consumes more energy that the resultant H2 is giving;