**3.2 Energy content and equivalents of biogas**

Biogas is an odorless and colorless gas that burns with a clear blue flame like natural gas but has a lower calorific value of 20–26 MJ/m<sup>3</sup> (537–700 Btu/ft<sup>3</sup> ) compared to natural gas whose caloric value is 39 MJ/m<sup>3</sup> (1028 Btu/ft<sup>3</sup> ) [6, 33, 94]. Energy equivalents of biogas are presented in **Table 5**.


#### **Table 5.**

*Energy equivalents of biogas [77, 90, 91].*

*Biogas as a Sustainable Fuel and Feedstock: Properties, Purification, and Applications DOI: http://dx.doi.org/10.5772/intechopen.114268*


#### **Table 6.**

*Calorific value of common gaseous fuels.*

From **Table 5**, it is noted that biogas has a higher energy value than manure briquettes, but it has a lower energy content than fossil fuels. But it is a potential substitute for fossil fuels and cuts down on forest clearance at the same time.

The calorific value of the biogas generally varies between 22.5 and 25 MJ/m<sup>3</sup> , or 6.25 and 10 kWh/m3 assuming methane has heating value of 35.8 MJ/m<sup>3</sup> . The energy content can be further enhanced if the raw biogas is upgraded to biomethane [24, 25]. Biogas with 55% CH4 has an average calorific value of about 21.5 MJ/m<sup>3</sup> , compared to pure methane (CH4), which has a calorific value of about 35.56 MJ/m<sup>3</sup> , which is one of the main reasons for upgrading by removal of carbon dioxide (CO2) from raw biogas [4, 5, 70]. **Table 6** shows the energy value of biogas compared to other fuels like butane, natural gas, and propane.

From **Table 6**, it is noted that biogas has the lowest calorific value compared to methane, propane, butane, natural gas, and biomethane. Therefore, upgrading to biomethane can improve its calorific value making it more competitive thermodynamically.
