VGB POWERTECH 7 (2020) - International Journal for Generation and Storage of Electricity and Heat

VGB PowerTech 7 l 2020 The Biofficiency Project | Part 1
Tab. 1. Classification of different sources of biomass for energy and investigated feedstock in Biofficiency. Adapted from
Main sector Sub sector Examples Investigated in Biofficiency
Agriculture
Forestry
Organic waste
Dedicated
cultivation
By-products
and residues
Crops for biofuels (corn, sugarcane, rapeseed, oil palm, cassava etc.), energy grasses
(miscanthus, switchgrass), short rotation forests, others
Herbaceous by-products: Straw from cereals, rice, corn, bagasse, empty fruit bunch from oil
palm, prunings from stover, empty corn cobs, etc.
Woody biomass: regeneration orchards, vineyards, olive and oil palm plantations
Other forms: Processing residues such as kernels, sunflower shells, rice husks, animal manure,
foliage
Miscanthus
Wheat straw, empty fruit
bunches
Sun flower husk, digestate
Main product Stems, wood fuel from forests or trees outside forests, woody biomass from landscape cleaning Wood pellets
By-products
and residues
Residues of forest harvest (branches, tops, stumps), residues of wood industry (bark, sawdust,
other wood pieces, black liquor, tall oil, recycled wood)
Municipal solid waste (MSW), food waste from stores, restaurants and households, used kitchen
oil, waste from the food industries (from dairy, sugar, beer, wine, fruit juice industry, olive
oil filter cake, from slaughterhouses), sewage sludge
Spruce bark, fir brushwood
Manure, sewage sludge, olive
pomace, urban leave litter,
road side grass, tomato foliage
to meet strict limits for fine particles, nitrogen
oxide and sulphur oxide emissions.
The project addressed current bottlenecks
in solid biomass combustion, namely increase
deposit formation, corrosion and
ash utilisation by a variety of new, promising
approaches. The goal was to deepen
the understanding of biomass combustion,
to improve biomass pre-treatment technologies,
as well as to contribute to the field of
biomass ash utilisation. The following
main objectives and goals were defined in
order to develop the next generation, biomass-fired
CHP plant:
––
Increase efficiency of CHP plants by elevated
steam temperatures through solving
and understanding of ash-related
problems – slagging, fouling and corrosion.
––
Reduce emissions – i.e. CO 2 , particulates,
CO, NO x , and SO 2 – by efficiency gain,
reduction of impurities and by tailored
plant design.
––
Widen the feedstock for pulverised fuel
(PF) and fluidised bed (FB) power plants
using pre-treatment methods with focus
on the reduction of harmful components
in the biomass (torrefaction, hydrothermal
carbonisation and steam explosion).
––
Optimise the use of additives in the combustion
of solid biomass.
––
Widen ash utilisation and nutrient recirculation,
study new concepts and explore
possible utilisation options based
on in-depth ash characterisation.
The main results of the project are presented
in a series of two technical papers in
VGB Power Tech, whereby in this first part
the focus lies on handling ash-related issues
in biomass boilers and accessing difficult
biomass feedstock for energetic use via
pre-treatment.
2. Accessing difficult biomass
feedstock via pre-treatment
2.1 Available bioenergy carriers
Biomass is organic material that originates
from plants and animals and can be used as
a source of renewable energy. Traditionally,
biomass has always been utilised as fuel
for domestic applications such as heating
and or cooking. Nowadays modern technologies
are available for the energetic utilisation
of biomass. For example, when biomass
is burnt, it releases heat that can be
used in subsequent combined heat and
power generation. Biomass accounts for
roughly two thirds of renewable energy in
the European Union [2]. It plays the most
crucial role in the heating sector, where
biomass is responsible for over 90 % of all
renewable heat generated.
Ta b l e 1 provides a classification of the
different potential sources of biomass for
energetic utilisation. In Biofficiency, biomass
feedstock from almost all these sectors
have been investigated. The selection
was based on availability, cost and potential.
All biomass feedstocks selected in the
Biofficiency project were characterised
thoroughly. The data is available on the
open source database Phyllis II of project
partner TNO.
Due to the transition of the European energy
system towards higher shares of renewable
resources and energy carriers,
there is an increasing demand for biomass
to be used for energy. Hence it competes
with the existing use for production of e.g.
construction materials, pulp and paper,
and even for more novel uses such as chemicals.
Therefore, an important question is
how much sustainable biomass will be
available for bioenergy in Europe in the future.
F i g u r e 1 gives an overview of the
technical and sustainable potentials of the
above-mentioned biomass classes in the EU
by 2020 [3].
Technical potential is the available biomass
for all uses under current framework
conditions with the current technological
possibilities including existing harvesting
techniques, infrastructure and accessibility
and processing techniques.
Potential for energy use is a proportion of
the technical potential after satisfying other
existing and projected competing uses of
the same biomass feedstock.
Sustainable potential constricts energy potential
based on the sustainability criteria.
As seen in F i g u r e 1 , agricultural and forestry
residues represent a large portion of
the available biomass feedstock. Consequently,
these feedstocks are of increasing
interest in the energy sector, due to the
lower associated fuel costs as well as higher
local availability.
Mtoe
500
450
400
350
300
250
200
150
100
50
0
Technical
potential
Potential for
energy use
Manure, Sewage, other waste
Forest residues, wood residues
Forest stemwood
Agricultural waste
Energy crops
Sustainable
potential
Fig. 1. Technical potential, potential for energy
use and sustainable potential (Mtoe) of
fuels for bioenergy in the EU 2020.
Adapted from [3].
However, most of these biomass feedstock
suffer from low bulk density, high moisture
content, low calorific value and their high
hydrophilic nature [4, 5]. With these properties,
multiple problems arise [5]. Firstly,
hydrophilic biomass is subjected to biological
deterioration, limiting the practical
time for storage, a challenge for seasonally
available agricultural residues. Further,
the fibrous nature of biomass materials
brings milling and fuel handling difficulties.
Compared to fossil fuels, biomass often
contains higher amounts of alkali metals
and chlorine, which are responsible for
many undesirable reactions leading to operational
problems in combustion furnaces
and boilers.
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