Advanced Thermal Treatment

Gasification can be seen as between pyrolysis and combustion in that it involves the partial oxidation of a substance. This means that oxygen is added but the amounts are not sufficient to allow the fuel to be completely oxidized and full combustion to occur. The temperatures employed are typically above 750ºC. The main product is a syngas, which contains carbon monoxide, hydrogen and methane. Typically, the gas generated from gasification will have a net calorific value (NCV) of 4 - 10 MJ/Nm3. The other main product produced by gasification is a solid residue of non-combustible materials (ash) which contains a relatively low level of carbon.

[For reference, the calorific value of syngas from pyrolysis and gasification is far lower than natural gas, which has a NCV of around 38 MJ/Nm3.]

Incineration usually involves the combustion of unprepared (raw or residual) MSW. To allow the combustion to take place a sufficient quantity of oxygen is required to fully oxidise the fuel. Typically, incineration plant combustion (flame) temperatures are in excess of 850ºC and the waste is converted into carbon dioxide and water. Any non-combustible materials (e.g. metals, glass) remain as a solid, known as Bottom Ash, that contains a small amount of residual carbon.

The products produced from pyrolysing materials are a solid residue and a synthetic gas (syngas). The syngas is a mixture of gases (combustible constituents include carbon monoxide, hydrogen, methane and a broad range of other volatile organic compounds). The syngas typically has a net calorific value (NCV) of between 10 and 20 MJ/Nm3. If required, the condensable fraction can be collected by cooling the syngas, potentially for use as a liquid fuel.

 

What really is Incineration

Incineration usually involves the combustion of unprepared (raw or residual) MSW. To allow the combustion to take place a sufficient quantity of oxygen is required to fully oxidise the fuel. Typically, incineration plant combustion (flame) temperatures are in excess of 850ºC and the waste is converted into carbon dioxide and water. Any non-combustible materials (e.g. metals, glass) remain as a solid, known as Bottom Ash, that contains a small amount of residual carbon.