Materials Science and Engineering for Clean Biomass Cookstoves

Transcription

1 Materials Science and Engineering for Clean Biomass Cookstoves Ömer Doğan Don Ferguson and James Bennett DOE Biomass Cookstoves Technical Meeting January 11-12, 2011 Alexandria, VA.

2 Materials Materials are enabling technology for cookstoves. To make clean, efficient, affordable, widely-used and durable biomass cooking stove, one has to have appropriate materials for the cookstove components. 2

3 Clean Cookstove Materials Structural materials Combustion chamber Insulation and envelope Accessories (grate, skirt, etc.) Functional materials Thermoelectric generator Heat conducting probe Heat sink N. MacCarty, J.Cedar, Proceedings of ETHOS

4 Current Examples of Combustion Chamber Materials Refractory ceramics Prefired refractory shape (refractory fired to final brick ) Plastic refractory (refractory shaped to need) Castable refractory (shape cast) Ceramic fiber (potential backup material) Powdered refractory filler Metallic materials Steel (mild steel, Cr steel, stainless steel) Cast iron 4

5 Materials Selection Criteria for Combustion Chamber Is the material low cost? Can the material be produced locally (in the country)? What type of biomass fuel will the stove use? Will the stove combust or gasify? What is the shape of the temperature profile in the stove? Is heat insulation a requirement? What is the minimum life expectancy? 5

6 FUEL Tapack 6 Sjoerd Nienhuys, Improved Cooking Stove Metal One Pot, August 2010 Treshkin

7 Fuel Types and Potential Flame Temperatures In the absence of moisture and assuming adiabatic (no heat loss) conditions: Mass Fraction Fuels C H O N S Ash Flame Temperature (K) Bituminous Coal Ag Waste (Corn Stover) Wood (Pine) Switchgrass Charcoal Addition of moisture and heat loss will reduce flame temperatures 7

8 Emissions from Biomass Fuel Flames Carbon Monoxide PM: Volatile Organic Compounds (VOC), Poly- Aromatic Hydrocarbons (PAH) Sulfur Dioxide, Hydrogen Sulfide, Aldehydes, Etc. Most of these can be reduced through improved combustion Longer residence times Increased temperatures 8

9 Select Biomass Ash Chemistry, Quantity, and Melting Temperature Property (Wt %) Material Rice Straw Wheat Straw Switch Grass Sugar Cane Trash Douglas Fir Wood % Cl (dry wt biomass) % Ash (dry wt biomass) Oxide (in Ash) - Al 2 O NL 2.8 CaO Fe 2 O K 2 O MgO Na 2 O P 2 O SiO TiO NL 0.1 SO Unknown Melting Temperature ( o C) NL = Not Listed Source: B. Jenkins, R. Bakker, and J. Wei; On the Properties of Washed Straw; Biomass and Bioenergy; vol. 10 (1996), no. 4, pp

10 High temperatures 600 C-900 C (Up to 1100 C reported) Large temperature fluctuations Combustion gas and ash Major gas constituents: CO, CO 2, H 2 O Minor gas constituents: H 2 S, alkaline vapors Ash constituents: Fe 2 O 3, SiO 2, Al 2 O 3, CaO, MgO, K 2 O, Na 2 O, SO 3 Thermal cycling 3-10 cycles per day between room temperature and C Large thermal gradient Near room temperature outside surface to C inside surface Heating / cooling rate Accidental spills and overflows Mechanical stresses Dropping stove while carrying or dropping hard objects on it Fuel handling/inserting Loading with heavy pots 10

11 Hightemperature corrosion Thermal fatigue Thermal shock Creep Wear 11

12 High-Temperature Corrosion Metallic materials High temperature oxidation (scale formation) Scale spallation due to thermal cycling Hot corrosion Ceramic materials Slagging conditions 12

13 Thermal Fatigue Sjoerd Nienhuys, Improved Cooking Stove Metal One Pot, August 2010 Cyclic temperature / cyclic stress Constrains to expansion / contraction Adjacent components at different temperatures and / or made of different materials Phase transformations Fatigue damage (crack initiation and growth) 13

14 Low Stress Creep Intermediate temperatures Stove can be designed so that the load bearing components are not located in the hot zone. 14

15 Wear and Fracture Fuel handling / inserting Dropping stove or dropping hard objects on stove Loss of toughness (temper embrittlement) 15

16 How can we simulate the cookstove operating conditions that influence materials? Computer modeling Laboratory tests Field tests 16

17 Location Fuel type Fuel chemistry User habits Cultural aspects will determine the operating conditions!!! We have to come up either with construction materials that are not sensitive to these variables or with different materials for different locations. 17

18 Materials Production / Fabrication Sheet steel Integrated steel plant Mini-mill (arc melting) Cast irons Foundry Ceramics Refractory plant 18

19 Summary Due to local nature of fuel, there will be more than one solution to the materials problems. High temperatures and cyclical nature of operation may cause thermal fatigue in both metallic and ceramic materials. Combustion gases combined with high temperatures are likely to cause corrosion on metallic materials. Integration between combustion research and materials research is essential. 19