Page 173 - Energy from Toxic Organic Waste for Heat and Power Generation

Power Generation From Renewable Energy Sources 153

In India, the quantity of biomass and plastic waste produced yearly is almost
nearly about 200 million metric tons and 960 million tons per annum, re-
spectively. Currently, about 90% of the plastic wastes are disposed in landfills
and incineration, but both these methods are not environmental friendly
[7]. To avoid environmental problems caused by the waste plastics and bio-
mass and to meet present energy crises, waste biomass and plastic materials
like low-density polyethylene (LDPE) can be thermally or catalytically con-
verted to obtain useful products like producer gas and fuel oil, respectively
[8]. These fuels can be used in spark ignited (SI) engines very conveniently.
However, CI engines cannot be operated with these fuels alone without a
small amount of liquid fuel injection of diesel and biodiesel due to the fact
that the producer gas and fuel oil will not ignite under the prevailing tem-
perature and pressure conditions.
Alternative fuels include biodiesels of different origin; fuel oils derived
from waste plastics and alcohols can be used in single fuel mode or along
with gaseous fuels in dual fuel mode. Diesel engine performance with blend
of Jatropha oil methyl ester and plastic pyrolysis oil resulted in higher ther-
mal efficiency at higher loads. But this blend operation increased emissions
such as HC, CO, and NO x compared to diesel operation [9]. Some of the
researchers not only used biodiesels, but also used fuel oil along with die-
sel/biodiesel in the blended form. Investigators showed lower performance
with smooth heat release rate with waste plastic oil operation compared to
diesel operation [10]. Moreover, CI engines have an ability to operate at
higher compression ratio and, hence, high-octane number fuels can be con-
veniently used and burnt with the help of liquid fuel injection. Therefore,
partial or complete replacement of fossil fuels for diesel engine applications
is the need of the hour. Major emissions from diesel engines include nitric
oxide (NO x ) and smoke. These pollutants can be overcome by the use of ad-
vanced technologies developed for diesel engines such as hydrogen addition
to producer gas, increasing compression ratio, advancing the injection tim-
ing, use of homogeneous charge compression ignition (HCCI), reactivity-
controlled compression ignition (RCCI), and dual fuel concept as well.
In dual fuel mode of operation, to obtain high-thermal efficiency and
lower nitric oxide and smoke emissions, the charge is well premixed before
compression ignition process. Increased high-octane fuel fraction during
combustion results into 90% soot reduction [11–13]. This is the greatest
benefit over the simple compression ignition combustion. But it is difficult
to control the combustion phasing. However to control the combustion in
HCCI, the combustion is slightly changed to RCCI mode just by altering