Development of an innovative 3 stage steady bed gasifier slides
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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.
Development of an innovative 3 stage steady bed gasifier slides
- 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