Organic waste as a biomass resource - Biomass as Energy Source: Resources, Systems and Applications - page 126

and Peacocke, 2000; Cheremisinoff and Rezaiyan, 2005; Di Blasi, 2007; European Comission,
2006; Yaman, 2003).
All pyrolysis products can be used for energy purposes. The liquid and gas products can be
used as vehicle fuel or combusted for production of power and/or heat production. The solid
product, char, can be used as a solid fuel. An advantages of using pyrolysis instead of direct
combustion are reduction of the flue-gas amounts and with that the requirements of flue-gas
cleaning. The same techniques as used for combustion can also be used for pyrolysis. MSW has
been used as feedstock in pyrolysis plants and RDF, waste cocking oil, sludge, rapeseed cake, crop
residues and forestry residues are examples of other organic wastes that have been investigated
for pyrolysis (Cheremisinoff and Rezaiyan, 2005; European Comission, 2006; Hossain et al. ,
2011; Karayildirim et al. , 2005; Puy et al. , 2011; Singhabhandhu and Tezuk, 2010; Smets et al. ,
2011).
Gasification is also a thermo-chemical process but compared to pyrolysis the aim is to convert as
much as possible of the feedstock to gas. The process is also operated at higher temperatures than
pyrolysis (up to 1800 ◦ C for conventional gasification and up to 20,000 ◦ C for plasma gasification
compared to 250 to 800 ◦ C for pyrolysis). The gas mainly consists of CO 2 ,CO,CH 4 ,H 2 ,H 2 O and
small amounts of C 2 -hydrocarbons. (European Comission, 2006; Gomez et al. , 2009; Ptasinski,
2008; Valleskog et al. , 2008).
The techniques mainly used for gasification are fixed beds, fluidized beds and entrained flow
gasifiers (also called entrained suspension bed gasifiers). Fixed bed gasifiers have a simple design
and give a low calorific gas with high tar content. The fluidized bed gasifier gives the possibility
to a more uniform temperature distribution but the ash content of the fuel can cause slagging
of the bed in the same way as for fluidized combustion of some feedstock's. The entrained flow
gasifiers are operated at high temperatures and need feedstock divided to small particle sizes.
Another technique is the so-called plasma gasification technique where an electrically generated
plasma arc torch is used (Alimuddin et al. , 2010; European Comission, 2006; Gomez et al. , 2009;
Li et al. , 2004, McKendry, 2002).
Several types of organic waste have been tested in different types of gasifiers, for example:

• MSW, RDF, salmon waste, hazelnut shells and wood waste in fixed bed gasifiers (Arena, 2011;
Dogru et al. , 2002; Rowland et al. , 2009; Sheth and Babu, 2009).
• MSW, RDF, forest residues, sawdust, straw, black liquor from pulp production and olive oil
residues in fluidized bed gasifiers (Alimuddin et al. , 2010; Arena, 2011; Göteborg Energi,
2012; Li et al. , 2004; Naqvi et al. , 2010; Palonen et al. , 2006).

• liquid, pasty and granulated rice husk, black liquor from pulp production, and sawdust in

entrained flow bed gasifiers (European Comission, 2006; Chemrec, 2012; Zhou et al. , 2009).

• pelletized RDF from carpet and textile waste and MSW in plasma gasifiers (Clark and Rogoff,

2010; Lemmens et al. , 2007; Willis et al. , 2010).

Pyrolysis and gasification can be combined with combustion of the produced gas for heat
and/or power production. An example of such a plant is a plant being built in Lahti, Finland where
250,000 tonnes of waste from businesses and households will be used to generate 90MW of heat
and 50MW of power per year. It is also possible to further process the gas to vehicle fuels as
for example dimethylether (DME), synthetic natural gas (SNG) and Fischer-Tropsch (FT) fuel.
(Arena, 2011; Chemrec, 2012; European Comission, 2006; European Investment Bank, 2011;
Ptasinski, 2008; Valleskog et al. , 2008).
For pyrolysis the influence of process parameters on the gas and by-product quality and plant
efficiency are of interest for further development. While gasification for gas cleaning, tar reduc-
tion, process operation conditions and increasing plant energy efficiency are development areas.
(Arena, 2011, Cheremisinoff and Rezaiyan, 2005; European Comission, 2006; Kirkels and
Verbong, 2011; Kumar et al. , 2009; Malkow; 2004; Puy et al. , 2011; Smets et al. , 2011).