1 Storage of comminuted and uncommunited woody biomass, its effect on fuel quality and modeling for natural wind drying Muhammad Afzal 1, Alemayehu Bedane 1, Shahab Sokhansanj 2 Muhammad Afzal 1, Alemayehu Bedane 1, Shahab Sokhansanj 2 1 Faculty of Forestry and Environmental Management,UNB 2 Department of Chemical and Biological Engineering, UBC CSBE Annual Conference, Brudenell River Resort Prince Edward Island, July 12-15, 2009

2 1.1 Background  Wood biomass is a source of energy  Biomass storage plays an important role in forest industry  Better storage can result in low moisture and high energy content in the fuel  Forest biomass residue can be stored either in the form of chipped or compacted into bundles  Identifying the best storage method would be helpful to improve forest harvesting operation

3 1.2 Objectives ► Identify the best method for wood biomass storage ► Examine the changes in woody biomass properties during the storage period ► Provide a drying model for predicting moisture and temperature profiles inside the storage piles

4 2.1 Material and Methods ► Material  Brown forest biomass of White Birch (Betula papyrifera)  One of the most commonly available species in Atlantic Canada  Stored for one year (Aug Aug. 2008)

5 ► Methods : Experimental Piles Wood chipsWood chips  Covered pile  Covered with tarp- prevents rainwater from penetrating into it  Underneath covered pile  Prevents moisture penetration into the piles from the ground  Uncovered pile  Have adequate air flow from all directions Each pile has an average of 3m heightEach pile has an average of 3m height

6 ► Bundles  Old slash of birch was compacted into twelve bundles  Each bundles, average 3m in length, 0.5m in diameter and about 50 kg in weight  Loose Slash  the wood biomass was collected and stored loosely to have adequate airflow for natural air drying

7 2.2 Sampling techniques ► ► At regular interval samples were taken to determine ► ► moisture content ► ► heating value ► ► ash content ► ► CNS composition ► ► Data collected during the storage period by using data loggers to measure the daily ► ► temperature in the piles ► ► ambient temperature ► ► relative humidity

8 2.3 Heat and mass transfer model  Fick’s diffusion law  Heat balance equation  Initial conditions  Boundary conditions

9 ► Assumptions for the model  The wood sample is homogenous and the thermophysical properties are constant  The initial moisture and temperature distribution in wood was uniform  Perfectly compacted wood bundles so that heat and moisture do not get directly inside the piles  No heat generation inside the wood piles

Results and Discussion ► Changes in Moisture Content (MC)  Bundles  IMC ~29.50 %(db)  MC showed an increasing trend during the first 6 months Max. avg. ~80% (db)  MC ~40% db between Feb. – May 2008  FMC ~50% db at the end of the drying period

11 ► Wood chips Covered wood chip pilesCovered wood chip piles  IMC ~59.5% (db)  MC has been decreasing during the storage period  uniform drying in all part of the piles  FMC ~15% d.b at the end of the drying period

12 ► Underneath covered and Uncovered wood chip piles  both had IMC ~59.5%  An increasing trend during the whole storage period  higher MC at the top part of the pile  at center and bottom part of the piles showed approximately the same value of MC  FMC is ~149% and 166% for Underneath covered and Uncovered piles, respectively

13 ► Loose slash wood biomass storage  IMC~ % (db)  non-uniform MC trend in the piles during the storage period  higher MC is at the top part  the FMC ~67% at the end of the storage period ► Moisture content versus time in loose slash pile

14 ► Changes in Calorific Values  Slightly higher loss of HV was observed in wood chip piles  Very low change in HV in bundles Storage method Avg. initial Caloricficvalue(MJ/Kg) Avg. calorific value after the six months (MJ/Kg) (MJ/Kg) Avg. calorific value after one year (MJ/Kg) Bundles Covered wood chips Underneath covered wood chips chips Uncovered wood chips Loose slash

15 ► Changes in ash content  Higher ash content change observed in wood chip piles  Low ash content change occurred in bundles and loose slash piles Storage form Avg. initial ash content (%) Avg. ash content after 6 months (%) (%) Avg. ash content after 1 year (%) Bundles Covered woody chips Underneath covered woody chips chips Uncovered woody chips woody chips Loose slash

storage form C (%)N (%)S (%) initial avg. value after storage initial avg. value after storage initial avg. storage after storage bundles covered wood chips Underneath covered wood chips Uncovered wood chips Loose slash  Change in CNS composition  Higher sulphur content change observed in wood chip piles after storage 16

17  Underneath covered woody chips pile  Covered woody chips pile ► Temperature changes in the pile  the same pattern with the ambient temperature during the whole storage period  slight difference in different form of wood chip piles and bundles of wood chip piles and bundles

18  Temperature profile for uncovered wood chips pile  The bottom part of the piles had higher temperature during low ambient temperature  Temperature inside in all part of the bundles had slightly the same magnitude comparing to wood chips pile  In general woody chips pile has a high internal temperature than bundles due to low thermal conductivity of wood chip  Self heating was not observed in the piles during the storage period  Bundles temperature profile

19 ► Drying Model simulations  The model equations were solved using Finite Element Method (FEM) and depending on the moisture contents, average values:  It was simulated with the ambient temperature and relative humidity recorded during the experiment  Due to influence of rain during the storage, only moisture profile model for covered wood chips piles was done

20 ► Covered wood chips pile ► Modeling of moisture profile

► Temperature in covered wood chips pile ► Temperture in uncovered wood chips pile

22 ► Modelling of temperature profile in Bundles

Conclusions  Moisture content had a significant change through out the storage period  Rate of moisture increase was low in bundle storage but in undeneath and uncovered wood chips was higher  Covered wood chip piles  MC continuously decreasing during the storage period  uniform moisture content profile  Higher loss of calorific and dry matter was observed in wood chip piles than in bundles

24 Cont…  In general the storage of biomass in bundles can reduce the moisture contents and loss of calorific value. However, in case of wood chip piles proper covering can reduce moisture content.  The proposed drying model closely predicted the moisture and temperature profiles.

Acknowledgment ► ► Financial assistance from NSERC and help from the research assistants and staff in the logistics of the experiment is greatly appreciated.

26 Thank you !!