Organic waste as a biomass resource - Biomass as Energy Source: Resources, Systems and Applications - page 116

Outputs from such pre-study activities should be considered with respect to the following
implementation focuses and their outputs; results from these scenarios are the best possible
biogas plant locations concerning the individual scenario topics:
• Focus I on products and co-products utilization : best suitable scenario according to existing
structure (heat, electricity, gas) including lowest demand for new infrastructure (such as grids
for example).
• Focus II on implementation to agriculture infrastructure : best suitable scenario according to
farm locations, farm sizes and digestate utilization for fertilizer demands (with respect to
individual crop breeding strategies). This should consider place of combined waste, energy
crop and agricultural residue utilization.

• Focus III on optimum transporting distance : best suitable scenario according to preferably short

substrate and product transporting distances.
The challenge is to find the best suitable regional combination of all three individual focuses
and scenarios. Depending on the local conditions to be determined beforehand, it is always
somehow an individual decision to define the best suitable scenario or the most relevant focus
for the individual region. For example in a country like Germany with a high number (and in
some regions also a high local density) of biogas plants, the backgrounds are completely different
in comparison to developing countries in terms of renewable energy production. Therefore, it
is always important to think in terms of individual regions and to avoid the transfer of existing
strategies simply from one country or region to another.
After defining the best suitable combination of scenarios the regional substrate-related biogas
potentials should be determined (e.g. as described in section 6.3.3); referring to the resulting
experimental data and the defined utilization and implementation strategies according to the
above mentioned scenarios, regional substitution factors in terms of energy resources and CO 2
emissions can easily be calculated.

6.4 COMBUSTION OF WASTE

Combustion is a mature and well-proven technology that has been used for waste treatment
of many types of wastes such as municipal solid waste (MSW), refuse derived fuels (RDF),
agriculture wastes, wood wastes, packaging waste, industrial waste, hazardous waste, and sludge
from wastewater treatment. Still, there are needs for development making the process more
efficient as an energy conversion process, including improved emission control, plant efficiency
and ash handling.

6.4.1 Technical background
The energy content that can be converted to thermal energy is dependent on the type of waste
fuels. Table 6.5 shows heating values for some organic waste fuels.
The waste combustion plant consists mainly of the boiler and the flue gas cleaning system. The
waste is combusted in the boiler and heat is recovered by boiling water. The steam can then be
used for power production in a steam turbine or for heat production. Heat can also be recovered
from the steam leaving the steam turbine.
The design and operation conditions of a waste combustion plant are dependent on the type
of waste used as fuel. Especially, high concentrations of corrosive substances, as for example
chlorides, are of importance. This is the reason to the usually rather modest steam pressures and
temperatures (commonly around 400 ◦ C and 40 bar) used in waste combustion plants (European
Commission, 2006).

6.4.2 Examples of combustion of waste
Techniques used for combustion of waste are grate furnace, fluidized bed and rotary kiln. Today
grate furnace seems to be the most commonly used technique at least for MSW. For example,