Influence of Feedstock Variables on Selection of Biomass Based CHP Systems

Transcription

1 Influence of Feedstock Variables on Selection of Biomass Based CHP Systems Dr. P. Abdul Salam Associate Professor Energy Thematic Leader - Low Carbon, and Sustainable Production and Consumption Technologies and Management Asian Institute of Technology Regional Workshop on Overcoming Critical Bottlenecks to Accelerate Renewable Energy Deployment in ASEAN+6 Countries June, 2016, Bangkok, Thailand 1

2 Presentation Outline v Overview of CHP System v Biomass feedstocks for CHP system v Key Issues for Biomass Utilization in CHP System v Suitable biomass conversion technologies for CHP system v Conclusion 2

3 CHP System Overview In CHP system thermal energy recovery is the primary goal to Ø Improve system s efticiency (60 to 80%) Ø reduce the fuel consumption & improve energy security Biomass is one of the sources of thermal energy which can be achieved through: Ø Direct combustion/incineration Ø Syngas combustion through gasitication Ø Pyrolysis (bio- oil, bio- char and bio- gas) Ø Biogas combustion through biological conversion Ø Co- Tiring with solid fossil fuels DensiHication, Pyrolysis & torrefaction are the techniques to improve the characteristics of the biomass fuels. The recovered thermal energy can be used for: Heating, Cooling, and Power production 3

4 CHP Applications Feature Typical Customer CHP industrial Chemical, pulp & paper, food, textile, timber, minerals, oil retining sectors etc. CHP commercial / Institutional Hotels, hospitals, large urban oftices, agricultural operations etc. District heating and cooling OfTice buildings, individual houses, campuses, airports, industry etc. within reach of heat network Ease of integration with renewables & Moderate high Low - Moderate waste energy Size MW e 1 kw e - 10 MW e Any Typical prime mover Steam turbine, gas turbine, reciprocating engine (CI), combined cycle (larger systems) Reciprocating engine (SI), Stirling engines, fuel cells, micro turbines Steam turbine, gas turbine, waste incineration, CCGT Source: ttps:// 4

5 Biomass Feedstock for CHP System The availability of a suitable biomass feedstock is the key for the success of biomass- fueled CHP project. Biomass Resources: 1. Wood & Woody biomass 2. Agricultural biomass (Tield & processed residues) 3. Animal & human wastes 4. MSW & industrial wastes 5. Residue derived fuel (RDF) MSW/Sludge waste kitchen Waste Energy Crops Straw Biomass Manure/excreta Empty fruit bunch Sawdust 5

6 Compositional Characteristics of Biomass Fuel type MC VM FC Ash Wood and woody biomass Herbaceous and agricultural biomass Grasses biomass Straw biomass Hulls, shells & other biomass Animal biomass Mixed biomass (wood, agriculture, almond & straw residues) RDF Plastic waste Mixed paper waste Sewage sludge Wood yard waste Coal Bituminous coal Peat Lignite Sub- bituminous Source: Vassilev et al. (2010) 6

7 Key Issues for Biomass Utilization in CHP System Low bulk density, high porosity Ø Road transport accounts ~ 70% of the total delivered biomass- fuel cost Non- homogeneous, larger particle sizes & Fibrous nature Ø Imposes difticulties in maintaining constant feed rates & proper mixing between combustion or gasitication agent with fuel. Ø Causes difticulty in size reduction High initial moisture content Ø Increases Tlue gas volume in combustion & causes low thermal efticiency Ø Increases the volume of syngas need to be treated in gasitication Ø Reduces heating value of product gas & causes problem during combustion in an engine for power production. Tar production in gasi@ication limits the utilization of syngas in gas turbines or engines. Extensive tar cleaning is required. 7

8 Key Issues for Biomass Utilization in CHP System Less carbon & high Oxygen content is responsible for having low heating value compared to solid fossil fuels. Bio- oil has high viscosity & water content (~ 25%) Ø Reduces heating value Ø Exhibits excessive ignition delay i.e., high ignition temp. Ø Have to upgrade bio- oil or modify the existing engines & turbines. High ash content & the presence of Cl, K, N, Na, Si & S, P & Al content in ash are responsible for: Slagging/Fouling Sintering Corrosion Erosion Ø Reduces ash deformation temperature (~<700 o C) Ø Produces corrosive volatiles KCl, HCl & alkali- sulfates. 8

9 Ash: The Crux for Biomass Utilization in CHP System Low silica (SiO 2 ), Low K & High Ca High fusion temp. Example: Woody biomass High silica (SiO 2 ), High K & Low Ca Low fusion temp. Example: agricultural residues High Ca, High P & Low fusion temp. Example: Manures, poultry litters and animal wastes. Mineral Melting temp. ( o C) NaCl 801 KCl 770 K 2 S 470 Na 2 CO K 2 CO CaCl Metallic Al 660 Biomass % Selected minerals in biomass ash SiO 2 CaO K 2 O P 2 O 5 Sawdust Pine sawdust Forest residue Wood pellets (pine) Rice straw Wheat straw Refuse- derived fuel Sewage sludge Coconut shells Sugar cane bagasse

10 Ash: The Crux for Biomass Utilization in CHP System At low melting temperature components present in the Tlue gases impact & deposit on heat transfer surfaces. Typical sticky alkali compounds are NaCl, KCl, Na 2 CO 3, K 2 CO 3 Al is also highly problematic melting temperature of metallic aluminum is 660 o C 8 Slagging in Furnace Fouling in Furnace Fouling in Convective Surfaces 10

11 Ash: The Crux for Biomass Utilization in CHP System Fouling in Superheaters Bed Agglomeration Bed Sintering In FB Systems 11

12 Biomass to Energy Conversion Technologies for CHP System v Direct fuel combustion technologies Fixed bed combustion ü Fluidized bed combustion (FBC) o Bubbling Tluidized bed combustion (BFBC) o Circulating Tluidized bed combustion (CFBC) Pulverized fuel combustion system ü Co- Hiring with coal Auger- fed automatic combustion systems Batch Tiring system Cigar burning system ü Whole tree energy (WTE) system v Indirect fuel combustion technologies ü GasiHication, pyrolysis & AD technologies Syngas/ producer gas or biogas or bio- oil 12

13 Feedstock Requirements for Combustion & GasiHication Method Stoker grate, under Tire stoker boiler Common fuel types Sawdust, bark, chips, hog, fuel, shavings, end cuts, Bagasse, rice husk & others Fluidized bed boiler (BFB or CFB) Bagasse, Wood residue, low alkali content Fuels Co- Tiring: pulverized coal Sawdust, bark, shavings, sander boilers dust Co- Tiring: stoker, FB boilers Sawdust, non- stringy bark, shavings, Tlour, sander dust Updraft FBG Chipped wood, rice hulls, shells, sewage sludge Wood chips, pellets, wood Downdraft, moving bed gasitier scrapes, nut shells CFB, dual vessel GasiTier Wood & chipped agr. residues no Tlour or stringy material size (mm) MC (%) < 50 < 60 < 6 < 25 < < 20 < 50 <

14 Example: GasiHication of MSW for CHP System GasiTication is a better choice than incineration, reasons are: Ø Final product: Syngas, even composition & homogeneous Ø Post- combustion emission control system Ø Syngas is suitable to burn in turbines or reciprocating engines. Ø Provides infertile atmosphere to form or reform of the most toxic chemicals dioxins & furans. Source: syngas.org/uploads/downloads/gtc_waste_to_energy.pdf 14

15 Feedstock Selection for AD Biogas for CHP system q Co- digestion of feedstocks is the adjustment of the carbon- to- nitrogen (C:N) ratio & digester stability (PH value). q Co- digestion of sewage sludge with agricultural wastes or MSW can improve the methane production. q Grasses, straws from wheat, rice, & sorghum are promising feedstock for biogas production. q Manure contains recalcitrant organic Tiber which reduces biodegradability. The addition of Food waste is able to solve the issue. q Thermophilic (55 o C) AD of organic fraction of MSW shows higher micro- organisms growth rate & has the potential to reduce operating time & increase biogas yield compared to mesophilic (35 o C) AD. Source: Ward et al. (2008); Fernández- Rodríguez et al. (2013); Sebola et al. (2014); 15

16 Ø Ø MSW Example: Biogas Production from MSW Dranco Process, Partial stream single- stage Dry anaerobic fermentation system. Soridsep (Sorting Digestion- Separation) integrated waste treatment system for the maximum recovery of recyclables & landtill diversion. Ø Substrate (< 40mm): Restaurant & food waste, dewatered sludges, Energy crops, source separated organics with or without the addition of non- recyclable paper/cardboard. Steam 100% Dry 66% Anaerobic 56% Wet 20% sorting Digestion separation Dranco Process Aerobic stabilization Ø RDF (28%) Ø Ferrous metals (5%) Ø Non- ferrous metals (1%) Biogas (12%) Ø Sand (8%) Ø Fibers (10%) Ø Inerts (8%) Ø Fine rest (10%) Ø Evaporation (5%) Ø Dry matter loss (1%) Ø Stabilized sludge cake (14%) Source: & 16

17 Example: MSW Based CHP System, Dranco Plants BRECHT, Belgium HENGELO, Netherlands Capacity: 50,000 tpy Digester volume: 3,150 m3 Biogas (125Nm3/t) is used in gas engines (3 700 kwel) & Heat is used to produce steam. Capacity: 50,000 tpy Digester volume: 3,450 m3 Biogas is used in gas engines (2 1.2 MW) & Heat is used in district heating network. Source: Murcia (2015) 17

18 v Direct co- Hiring (direct combustion) Coal Biomass Biomass Co- Hiring Options for CHP System Torrefaction (mild pyrolysis, o C) Grinding mill Burner Boiler Furnace v Indirect or external co- Hiring (through gasihication) Coal Grinding mill Burner Biomass Hammer mill & pretreatment GasiTier v Indirect or external co- Hiring (parallel co- Hiring) Coal Biomass Grinding mill Hammer mill & pretreatment Burner (Boiler Furnace) Biomass boiler Steam Steam Boiler Furnace Steam cycle for power generation 18

19 Comparison of Biomass Co- Hiring Technologies Technology variant Energy efticiency with CHP system Capacity factor, % Co- Hiring Technology Direct Co- Hiring Indirect Co- Hiring Parallel co- Hiring 33-42% for traditional system & 44-85% with CHP system %, but typically between 60-80% Typical plant size, MW 10 to 1,000 Up to 1,000 GHG Emissions (emitted/ avoided) by using local biomass resources Other pollutants Lignite co- Ti ring: 950-1,100 gco 2av /kwh e Coal co- Ti ring: 900-1,000 gco 2av /kwh el On average, 15% NOx emissions reductions with 7% co- Ti ring Cost scenario (2010 USD) Investment cost, USD/kW ,000-4,000 1,600-2,500 O&M cost, % of investment per year % of capital costs 5% of capital costs For steam cycle, ~ 4% of capital costs Levelised cost of electricity, USD cents/kwh Source: IRENA (2013) 19

20 CHP Plant Based on Stirling Engine & GasiHier CHP system with updraft and stirling engine with a net electrical efticiency of 17.7% & total energy conversion efticiency of 75.3%. Tar cleaning & cooling of syngas are not required Exhaust heat can be used for Vapor Absorption Chiller System Biomass with 42% moisture 58.7 kg/h, 190 kw Heat loss 2.7 kw Updraft gasihier Producer gas 312 o C Heat loss 2.2 kw Combustion chamber Heater Combustion air 197 kg/h Air Preheater Exhaust gas Cooler 120 o C 38 kw Hot Water Biogas from AD & low- grade biological fuels also can be used as feedstock GasiHication air, 37.1 kg/h Stirlilng Engine Cooling water 76.5 kw Electricity 35 kw Heat loss 2.7 kw 20

21 Biomass Pyrolysis for CHP Application Hemicellulose, Cellulose & Lignin are the major components of biomass materials. Cellulose is the main source of bio- oil, and Hemicellulose & Lignin are the major source of bio- char. Product Pyrolysis type Reactor Bio- char Slow Fixed bed Bio- oil Large scale Medium scale Small scale Bio- gas Fast Fast Flash Slow/ Fast BFB CFB PyRos Heating Method Furnace or kilns Heated recycle gas Wall & sand heating PyRos heating Microwave Electromag netic Temp. ( C) < 3000 Biomass Walnut shell, olive husk, hazelnut shell Agriculture residue, wood chip, fruit shell Forest residue, municipal waste, dry wood, waste tyre Grass, husk, wood dust > 800 Rice husk, Rice straw, wood dust 21

22 Whole Tree Energy (WTE) System for CHP System Ø The waste heat generated in biomass combustion (power generation) is utilized to dry whole trees (short rotation woody crops). Ø A 50 MW power plant requires 18,400 ha of tree (Hybrid Poplar & cotton wood) farms, which is 1% of the land within a radius of 80 km. Example: Plant capacity factor: 86.3% Biomass yield: 11.3 dry ton/ha HHV: 20.2 MJ/kg Fuel supply period: 20 years Power Plant Size (MW) Total Capital Cost ($ million) Power Plant EfHiciency (%) Total Land (ha) Cost of Electricity ($/kwh) , , ,

23 Conclusions o Resource availability (feedstock production, collection & supply) should be ensured. o Biomass characterization is important to select the appropriate biomass energy conversion technology. o Biomass Ash is the major issue in the case of using biomass in combustion based CHP systems. o Integrated approach (co- Hiring & Co- densihication) will maximize the biomass resource utilization. o GasiHication, Pyrolysis & AD are the potential energy conversion technologies to utilize biomass resources efticiently. 23

24 Energy Park at AIT Thank Y ou For more information, please contact: Dr. P. Abdul Salam (salam@ait.ac.th) 24