Steinmetz Presentation

Design of a Solar Thermal Kiln for Drying and Gasifying Wood: 

Design of a Solar Thermal Kiln for Drying and Gasifying Wood Stephanie Rubino Steinmetz Symposium 2006 Advisor: Professor Wilk

Presentation Outline: 

Presentation Outline Why Dry Wood? Why Dry Wood in a Solar Kiln? Project Goals Design Parameters of Kiln Solar Thermal Kiln Design Methodology: Process Diagram Schematics Air Collector Analysis/Results Current Status Oven Experiments 1 and 2 Temperature Profile of Poplar

Why Dry Wood?: 

Why Dry Wood? Green wood is an unstable easily deformable material Environmentally beneficial Burning wet wood releases harmful volatiles such as carcinogens Burn cleaner wood to maximize amount of heat released Offset energy cost by efficient use of wood fuels *Burning wood is the largest current use of biomass derived energy.

Why Dry Wood in a Solar Kiln?: 

Why Dry Wood in a Solar Kiln? Increase in caloric content Faster drying time Protection from the elements Capable of drying wood to moisture contents of 6 to 10% Gives wood desirable properties Kiln drying is energy intensive Disadvantage: dependent on weather

Goals of Project: 

Goals of Project Overall Project Goal: Design and construct a prototype solar thermal kiln that can efficiently dry different species of wood in a timely, cost effective, energy conscious, and environmentally friendly manner. Design Goal: Uniformly reduce the moisture content while maintaining the integrity of the wood.

Design Parameters of Kiln: 

Design Parameters of Kiln Energy Supply Sensible Heat: raise temperature of wood to required drying temperature Latent Heat: evaporates water Rate of Drying Mass of wood Avoid internal Defects Temperature Increase the capacity of the air for moisture Relative Humidity Surface evaporation Air Flow Natural convection Air Circulation Continual replacement of properly conditioned air Kiln Size 4’ x 4’ x 4’

Methodology: Process Diagram: 

Methodology: Process Diagram Design Components Air Collector Ductwork Blower T and valves Dampers Incident solar hits air collector Air travels through ductwork to kiln where it is forced out to heat the wood Dampers for temperature control Blower

Schematics: North Face of Kiln: 

Schematics: North Face of Kiln Active/Passive Hybrid Kiln Designed to capture all available solar energy Holes in duct to force air out into kiln More holes towards the bottom due to natural convection

Schematics: South Face of Kiln: 

Schematics: South Face of Kiln Plexiglas on inclined part of face Air forced in from the air collector Expanded metal shelves More surface area exposed Increased air flow Well insulated on bottom, top, and door

Schematics: Air Collector: 

Schematics: Air Collector Insulation: Minimize losses Ductwork to Kiln: Air forced through ductwork into kiln by blower Insulating Air Gap Single Cover Plexiglas: Transparent top for solar radiation absorption Aluminum Duct: Solar absorber, functions to heat the air Control conditions of the air going into the kiln Area of Collector Size of blower determines mass flow rate of air into the kiln

Air Collector Analysis: 

Air Collector Analysis Goals Air temperature leaving collector = air temperature entering kiln Bounds of useful energy gain Preliminary Assumptions Steady state analysis 1D heat transfer Thin duct so collector temperature is uniform Well insulated; no conduction losses Methodology 1st case: no losses to get upper boundary of useful energy into the kiln 2nd case: no cover on air collector to get lower boundary of useful heat; losses taken into account Constraints Practical size limits

Air Collector Analysis: 

Air Collector Analysis

Air Collector Results: 

Air Collector Results Range of Useful Heat 892 W – 252 W Range of Collector Temperatures 376°F – 149°F

Current Status and Progress: 

Current Status and Progress Temperature Data Collection Goals: Rate of wood drying = f(species, MC) Temperature Profile along cross-section of the wood Different species of wood tested in oven 4 groups, varying the temperature of the oven and time in the oven Kiln Assembly Purchased materials Assembly and Testing in Kiln

Wood Fuels to Test: 

Wood Fuels to Test Hardwoods/Angiosperms/Broad Leaf Oak, Poplar Softwoods/Gymnosperms/Coniferous Western Hemlock, Pitch Pine High heating value Highly reactive and oxygenated Purchased by the boardfoot 1’ x 6” x 1” thick

Experimental Set-up: 

Experimental Set-up Wood placed vertically in oven Air circulated from back to front 7 thermocouples oriented along centerlines Center Cross-section

Test 1: T=60°C; t=30 minutes : 

Test 1: T=60°C; t=30 minutes

Test 2: T=70°C; t=30 minutes: 

Test 2: T=70°C; t=30 minutes

Temperature Profile of Poplar: 

Temperature Profile of Poplar

References: 

References Tillman, David A., Amadeo J. Rossi and William D. Kitto. Wood Combustion: Principles, Processes, and Economics. Washington: Academic Press, Inc, 1981. Tillman, David A. Wood as an Energy Resource. New York: Academic Press, Inc. 1978. Henderson, Hiram L. The Air Seasoning and Kiln Drying of Wood. New York: Henderson, 1939. Schobert, Harold H. Energy and Society: An Introduction. New York: Taylor & Francis, 2002. Bodig, Jozef, and Benjamin A. Jayne. Mechanics of Wood and Wood Composites. New York: Van Nostrand Reinhold Company Inc., 1982. Goswami, D. Yogi, Frank Kreith, and Jan F. Kreider. Principles of Solar Engineering: Second Edition. Pennsylvania: Taylor & Francis, 2000. Seip, Ralf. “Experiments with Solar Hot Air Collectors.” Home Power #72. Ralf Seip, 1999. http://www.mtc.com.my/publication/library/drying/contents.html. http://www.eia.doe.gov.

Design Features: 

Design Features Additional Design Options Fresnel lens on air collector to increase effective area Blowers powered by photovoltaics Desiccant to send in dry air to kiln Scalable design Possibly use to dry food and/or crops

Environmental Concerns: 

Environmental Concerns Deforestation Destroying an ecosystem Burning wet wood releases harmful volatiles Carcinogens Smoke Pollution

Experimental Error: 

Experimental Error Temperature Uncertainty Based on initial thermocouple readings Taken as the largest ΔT between any two thermocouples Average taken over the testing days yields a temperature uncertainty of +/- 1°C Moisture Content Reading Uncertainty Hand held Moisture Content Meter reads to 3 significant figures Readings taken upon visual inspection and rapidly change Uncertainty is approximately +/- 0.3%

Dry Wood Applications: 

Dry Wood Applications Combustion Heat Source Generate Steam Wood fired power plants Pyrolysis Breaking down of wood by heat to form charcoal Gasification Conversion of wood into a gaseous fuel Outdoor Wood Boilers