Technology is moving swiftly in the biomass industry and there are plenty of resources out there that will easily confuse you. If not you, then definitely me. Many articles and videos will leave you with more questions than answers. This is precisely what happened to me as I scoured the web trying to understand the process of gasification of biomass. So now I will share with you some of the questions in my head for which I have found answers.
First of all, let me start with the fact that gasification typically falls under two categories based on whether you are utilizing a wet biomass (i.e. manure, food waste, slaughter house waste) or dry biomass (i.e. wood waste, crop residue, urban solid waste). If it is wet, typically it is more advantageous to go through a biochemical process to extract energy out, typically as a liquid fuel. This is how the ethanol is produced that is in your gasoline right now. If you have dry biomass, the biomass process is typically a thermochemical conversion. That is a fancy way of saying that you heat up the biomass, which is a solid, and convert it to a combustible gas that is much more useful. So if you were tricked into thinking that biomass conversion was only from a solid to a liquid via a biochemical process or solid to a gas via a thermochemical process, you now know that biomass can be converted through either of these processes. Biochemical and thermochemical processes are completely different in every way, but they are both considered gasification and produce a useful fuel out of biomass as an end result. Confusing? Yeah me too.
So now that we have a grip on the different types of gasification process, we are going to safely put aside the biochemical process used on wet biomass and talk only about the gasification process of dry material. This process is similar to just burning wood or straw or whatever you have, but there is added complexity to the system. With gasification, the end goal is not to get thermal energy (heat) out of the wood. The end goal is to get the biomass to releases combustible gases contained within itself that can be captured, cleaned and able to be used much like natural gas is used today.
In order to get these gases to be released from the material, we apply heat that will break down the components of the material until you are left with carbon as a solid (approximately 20% of material by weight) and volatile gases (mostly hydrogen and carbon monoxide). The gases released are captured and can be used to create liquid fuels, to run engines, turbines for electricity, or simply for heating.
I am leaving out a lot of technical details about the gasification process, but if you watch the embedded video, you can learn about the very specific chemical reactions that are taking place inside of the combustion chamber. It’s a lengthy video but well worth it.
The one thing I want to leave you with is the biggest thing I learned about gasification. If you are as clever as I am, you might say to yourself, ‘If I have to supply energy (heat) in the first place to get the gases to be released in a gasification system, isn’t that counterproductive? After all, if the goal is to get usable energy as an end product, Why would I want to spend a bunch of energy to get it?’ Excellent question. This stumped me for days. Here is the answer: When you begin a gasification process, you must at first supply heat to get the process started. What many resources fail to mention is that the charcoal that is produced inside becomes very hot and eventually self-sustaining based on the chemical reactions taking place. At that point, an external heat source is no longer needed. The inputs become fuel and air and the outputs become a blend of combustible gases (known as syngas) and water. If you run the process efficiently, all the tars and other impurities are completely burned up and you are left with very little residue.
Hopefully I have given you some insight into your learning about gasification and what it is and cleared up some confusion. There are many processes and designs out there. The biochemical processes that we did not talk much about is a newer technology and is ever evolving. The thermochemical process is much better known. In fact, you can see a bunch of do-it-yourselfers creating gasifiers in their garages on YouTube videos. Both processes have a place in the energy needs of tomorrow and are guaranteed to become more efficient with time.
Understanding Biomass 