Gasification is a process that converts carbonaceous materials, such as coal, petroleum, or biomass (such as wood), into the simpler elements carbon monoxide and hydrogen by reacting the raw material at high temperatures.
In the temperature range of a regular fire, the majority of the gases are released from the wood in combination with the smoke. Those gases contain about 50% to 80% of the heat content of the wood. This process results in a gas mixture that is often referred to as synthesis gas or syngas or in the case of a wood fuel – woodgas. Wood gas is also called “holzgas”, air gas or blue gas, and is the product of thermally gasifying a biomass material (ie. wood or coal). Wood gas is generated in a high temperature chemical reaction (>700°) between the wood and a limited amount of steam or oxygen. The lack of oxygen keeps the gases from the wood in the form of carbon monoxide, hydrogen and carbon dioxide.
If the reaction is stopped at this stage, the woodgas may be used as a fuel for a number of purposes. The gas may even be cooled and cleaned to remove tars and particulates and used as fuel in a variety of other applications, including engines!
In gasification wood boilers the wood gases don’t just go up and out the chimney, as in the case of standard wood boilers. Instead of this, the reaction is continued and the emitted woodgas is superheated and mixed with air resulting in complete combustion. The heat is then transferred to a boiler for efficient distribution. An additional benefit of the gasification process is that the complete combustion leaves little or no ash.
In general, gasification is very efficient in extracting energy from different types of organic materials, including wood. Extremely high combustion efficiency is obtained by gasification, and thus minimal emissions are caused. With respect to wood boilers, wood gasification means that less wood is required, lower emissions will be seen (and also less smoke), and less ash will be created.
There are several approaches in wood gasification and secondary combustion principles two most common of which are given below:
- Continuous burn: Dual combustion chambers. Many of the European wood gasification models use this technique. These units are designed to operate properly when they burn a load of wood in one continuous burn and transfer the resulting heat to a water storage container where it is stored until the heat is needed.In these systems, the gases flow down through the fire into a secondary chamber where firebrick (or a ceramic material) creates the superheated environment necessary to complete the efficient combustion process. Keeping this secondary chamber at high temperatures is key to the performance of the overall system, hence the need for one continuous burn so that this chamber does not cool and lower the boiler efficiency.
- On-demand burn: Single combustion chamber. During normal operation, a thermal mass maintains the firebox at the extreme temperatures required for complete combustion. This enables the system to operate as an on-demand system and remove the need for the water storage tank in the case of continuous burn.
If you decide to make more use of the fuel you consume for heating, if you want to create less smoke and harmful emissions during burning of your fuel you can consider Gasification Boilers.
Thanks the Techstore Team
