Trees are felled at the rate of 27 football fields per minute worldwide. The World Bank says garbage is overcoming the developing world. The two forces simply spell doom for humanity.
In Kenya, institutions such as schools, hospitals, universities, prisons and hotels contribute significantly to the deforestation and garbage problems. They use a lot of wood fuel for their heat energy needs. They also generate a lot of garbage due to their big populations.
Of great interest and surprise, however, is that both problems can be greatly reduced by appropriate technologies to convert combustible trash to heat energy and by efficiently harvesting the smallest amount of heat energy generated by burning firewood for fuel.
The above institutions consume a lot of hot water. To heat water, a lot of heat energy is needed because water has a very high specific heat capacity — of 4.2MJ/kg°C. That’s the heat energy (measured in mega joules) needed to raise the temperature of a litre of water by one degree Celsius.
A kilogramme of well-dried and good quality firewood generates about 19MJ of heat energy. The combustible garbage from institution and municipalities produce about 12MJ of heat energy of every kilogramme burnt. In simple maths, 2kg of combustible trash can generate the same amount of heat energy as 1kg of good quality firewood.
That means combustible trash is not a problem but a good source of heat energy. We can save trees and slow down deforestation. We will also reduce the problem of garbage, which results in a clean environment and a healthy nation.
A solar water heater uses the sunlight temperature, which is about 18°C per six hours a day to warm the water in Kenya. Any combustible material will generate heat temperatures to the tune of 400°C and above. So what is missing is small-scale technologies to efficiently tap this heat energy resource and make good use of it in the institutions.
If solar water heater technologies can make use of 18°C temperatures, what about 400°C that is available 24 hours, seven days a week?
Utilisation of combustible trash ha been done efficiently on a large scale to generate power — as is the case in the Ethiopian plant recently commissioned by the Chinese. The big investor may not be interested in small plants, and that is why governments in the developing world need to encourage appropriate technologies for the purposes.
If combustible materials can generate temperatures of 400°C, then by having appropriate technologies other sources — such as bamboo culms, sawdust, rice husks and sugarcane bagasse — can be used as fuel. That would relieve the huge pressure on firewood fuel and reduce destruction of forests.
We have already developed and tested the technology. Let’s use it.
PETER IKUA, via email.