Energy from waste

Sir: The production of energy from waste qualifies for due attention by our energy planners.

The waste-to-energy (WTE) phenomenon converts the chemical energy stored in municipal, as well as in industrial solid waste and garbage into heat, steam, and electricity. Normally, this solid waste is disposed off in barren lands, the process being termed as landfill, but this practice is now regarded as environmentally undesirable.
During 1999, a European Union directive banned the land filling of combustible solid waste in order to control methane emissions, avoid non-productive use of land, and prevent water and soil contamination. This has led to adoption of a number of state-of-the-art waste-to-energy (WTE) technologies, including incineration and gasification, which transform solid waste into versatile fuels suitable for steam generation.
The steam, in turn, drives a turbine-generator train and electric power so produced flows into a power transmission network. Net electrical output could be roughly 550 to 600 kWh/ton of solid waste. Both in Europe and the US, WTE plants play an important role as high-efficiency energy producers and enjoy a lion’s share towards renewable energy generation.
However, the grass is not so green and a lot of operational bottlenecks and functional complications are associated with WTE plants. Besides the inherent benefits of using solid waste as a fuel, a number of challenges and by-product management issues emerge when WTE plants are installed. The availability of municipal solid waste is unpredictable and inconsistent. Its composition is highly variable, including a mix of organic, inorganic and toxic constituents. During combustion, these hazardous components pose health and safety risks. The heavy ash contents of resultant flue gases could lead to slagging, fouling, clotting and corrosion, which will eventually need huge investment to ward off these ill effects. The pollutant emissions produced during the incineration process call for stringent air quality controls. On a per-MWh basis, overall CO2 emissions from incinerators typically exceed those of coal-fired plants due to high moisture content. That is why the US Environmental Protection Agency has not allowed construction of new solid-waste-energy recovery plants since 1990 and no commercial-scale gasification facilities have been built in the US for a long time. This has stagnated capacity enhancement of existing WTE plants in the US.
Furthermore, difficulties in solid waste handling, variations in fuel quality, delicacy of process control and increased maintenance requirements complicate the operation of WTE plants. High slagging and fouling rates necessitate frequent removal of ash deposits, while aggressive chemical conditions lead to accelerated rates of erosion and corrosion. At present, solid waste incinerators are more costly to build and operate than coal-fired plants and other base-load generation.
Nevertheless, role of WTE plants in producing clean, affordable, reliable, and sustainable electricity cannot be underestimated. Our energy planners and decision makers have to study all the pros and cons of waste-to-energy technologies and come up with the most feasible solution to combat power shortages all over the country.
ENGINEER M HAFEEZUR RAHMAN
Jubail, Saudi Arabia