The document describes a new 3-stage gasification scheme for municipal solid waste and biomass. The scheme consists of pyrolysis, combustion, and gasification stages, and can operate normally or in reverse mode by adjusting air blowers. It produces synthesis gas free of tars and dioxins with 30% electrical efficiency. A SWOT analysis found strengths include adequate replacement of fossil fuels while weaknesses include unproven reliability and moderate costs.

1. Development of an innovative
3-stage steady bed gasifier for
municipal solid waste and
biomass
RAVI
KUMAR
2009JE0618

2. CONTENTS
• Introduction
• Materials and methods
 Normal operation
 Reversed operation
• Strategic analysis
• Conclusions
• References

3. INTRODUCTION
• Gasification of biomass, MSW, waste-derived
fuels and residues is used as an thermal
treatment method to produce power and heat.
• Gasification is a thermo-chemical
process, classified between combustion and
pyrolysis, for producing energy.
• Presented in this paper is a new, recently
patented, 3-stage gasification scheme, designed
for all aforementioned types of fuels and for
producing a synthesis gas free of tar and dioxins.

4. • The proposed 3-stage gasification scheme comprises
of three stages:
i) pyrolysis,
ii) combustion and
iii) gasification.
• It is valid for municipal solid waste and any type of
biomass despite differences in chemical
composition.
• The innovation of this 3-stage gasification scheme is
based on the fact that the transition between
normal and reverse operation and vice versa is
achieved only by the proper rotation settings of four
air blowers, thus creating a new model of gaseous
flow management between the three
aforementioned stages.

5. • It can achieve a safe industrial-scale operation
while producing a gas free of harmful
components.
• It is suitable for small- to-medium scale
capacities.
• Overall electrical efficiency of 30% .
• Minimum environmental impacts well below
all existing thresholds.

6. MATERIALS AND METHODS
• Past trials for designing and constructing a
multi-stage gasification scheme were
performed by placing
(i) pyrolysis of fuel as first stage,
(Ii)combustion of Pyrolysis Gases (PG) as
second stage and, finally
(iii)charcoal gasification as the third stage of
the overall process.

7. Normal operation
1. Pyrolysis zone
2. Combustion zone
3. Gasification zone
4. Material feeding system
5. Grate
6. BPA blower
7. Burning hearth
8. Reduction layer
9. Distillation layer
10. Drying layer
11. Pyrolysis gas duct
12. Torch
13. Up-draught stream
14. Down-draught stream
15. Gasification bed
16. Flue gas
17. Discharge system
18. Gas output
19. Gas cooling and cleaning
20. Buffer zone

8. • Burning hearth: Partial combustion of the charcoal is
performed, which provides the energy for the reactions at
the overlaying material layers. The remaining charcoal and
the ash are detached by moving the grate; then, they fall
downwards, pass through the buffer and combustion zones
to, finally, create the fixed bed of the gasification zone.
• Reduction layer: Part of the hot carbon dioxide, which is
produced from the hearth, is reduced via the charcoal into
carbon monoxide.
• Distillation layer: The volatiles of the fuel are separated
through a complicated sequence of pyrolytic reactions, The
solid fragment (charcoal, ash) falls into the reduction
zone, while the hot gases rise through the new incoming
fuel and they dry it.
• Drying layer: Fuel's water content is converted into
vapor, which departs together with the remaining gases.

9. • Most of the tars and dioxins which still exist
into the PG, when they cross the flame of the
torch, are burned and/or cracked.
• The produced synthesis gas is rich in H2 and
CO, has low contents of tars and dioxins and is
suitable for supplying internal combustion
engines.

10. REVERSED OPERATION
1. Pyrolysis zone
2. Combustion zone
3. Gasification zone
4. Material feeding system
5. Grate
6. BPA blower
7. Burning hearth
8. Reduction layer
9. Distillation layer
10. Drying layer
11. Pyrolysis gas duct
12. Torch
13. Up-draught stream
14. Down-draught stream
15. Gasification bed
16. Flue gas
17. Discharge system
18. Gasification zone
19. Gas cooling and cleaning
20. Buffer zone
21. Additional supply of natural gas
or propane
22. Up-draught stream flue gas
stream
23. Down-draught stream flue gas
stream
24. Up-draught stream

11. • Presented in figure is the reversed operation
of the buffer zone, which is achieved by a
modification of the normal operation, in order
to gasify fuels with high water contents and/or
low calorific values.
• During the reversed operation of the buffer
zone, which is achieved by proper operation
settings of the air blowers, the flue gas from
the torch is divided into two streams; the up-
draught stream passes through the buffer
zone and enforces additional heat to the
pyrolysis bed, whereas the down-draught
stream feeds the gasification bed

12. • When feeding the gasifier with high-humidity
fuels, it becomes necessary to provide the
combustion torch with additional external
supply of gas (natural gas or propane) fuel, in
order to have enough energy for heating the
high vapor content which is now present in
the PG.

13. RESIDUE PROCESSING
• AWT- Ash Water Tank
• ECA- Exchanger of
Combustion Air
• EPA-Exchanger of Pyrolysis Air
• ESA-Exchanger of Additional
Steam
• GST-Gas Scrubber Tower
• BGO-Blow of Output Gas
• VSC-Venturi Scrubber

14. • Bottom ash holding - The bottom ash is separated
from the produced gas due to the gravity and
finally dips into a water tank (AWT) and onto a
conveyor belt.
• Heat reallocation - The preheaters of the flue gas
(ECA) and of the PG (EPA) are the devices (heat
exchanger) which implement the heat
reallocation in the system.
• Gas cooling and separation: The necessary
installations and their attributes for cleaning the
produced gas and making it suitable for feeding
an internal combustion engine are summarized
below:

15. • Gas Scrubber Tower (GST): a) Fly ash (>8 μm) is
trapped in this device. b) Gas is cooled down to
near-atmospheric temperature.
• First Baffle Scrubber (BS1): Separation of
different types of gases which exist in the
produced gas, (e.g. hydrochloric acid
(HCl), ammonia (NH3)), which are water-
soluble.
• Venturi Scrubber (VSC): Gas is sprayed with a
potassium-hydroxide (KOH) solution. Small particles
(> 1 μm) are held and sulfur di- oxide is converted to
potassium sulfate (K2SO4).
• Second Baffle Scrubber (BS2): Second stage of
sulfur dioxide conversion.

16. • Droplets holding: Rasching ring columns are
foreseen at the end of the aforementioned
devices (GST, BS1 and BS2) in order to divert
the existing droplets out of the gas flow.
• Fans: At the upper side of each tower of BS1
and BS2, the centrifugal fans BGO1 and BGO2
are respectively located; they balance the
existing pressure drop in the gas cleaning
devices.

17. STRATEGIC ANALYSIS
SWOT analysis for the three-stage gasification scheme
• Strengths
 Potentially adequate to replace fossil fuelled
energy conversion.
 Low volume of produced solid residues.
 Low weight of produced liquid residues.
 Appropriate gaseous flow management in the
direction of low tars, dioxins and emissions.
 Electrical efficiency ~30
 Decentralized technology
 High efficiency rate of the reactor (~76%)

18. • Weaknesses
Reliability not yet proven
Moderate investment cost (~1900€/kWe)
Bureaucratic requirements
Financing issues

19. • Opportunities
Application in small-scale industries which
have available biomass residues
Application in small-medium municipalities-
CHP plant:
 Generated electricity to the grid
 Generated heat to appropriate heat customers
A developing market
Moving into new market segments that offer
improved profits

20. • Threats
Competitors have superior access to channels
or distribution
Change of the existing charging policies
Development of other competitive new
Waste-to-Energy advanced conversion
technologies

21. CONCLUSION
• The innovation of the presented three-stage
gasifier is characterized by the fact that the
transition from normal to reversed operation
is implemented via the existence of a buffer
zone, which is thus creating a new model of
gaseous flow management.
• This model can handle a wide range of
variations in water content and/or
composition of the inserted fuel.

22. REFERENCES
• Antonopoulos,I.S.,Karagiannidis,A.,Elefsiniotis,L.,Perkoulidis,G. and Gkouletsos,A. 2011.
Development of an innovative 3-stage steady-bed gasifier for municipal solid waste and
biomass. Fuel Processing Technology 92 2389–2396.
• http://www.gasification.org/page_1.asp?a=87 as viewed on 20/01/2013
• http://en.wikipedia.org/wiki/Gasification as viewed on 20/01/2013