Use of bioenergy for wood drying. Measures at Norwegian sawmills to improve bio fuel combustion

Transcription

1 Use of bioenergy for wood drying Measures at Norwegian sawmills to improve bio fuel combustion EDG Seminar, Oslo, 21 May 2008 Henning Horn, Norwegian Institute of Wood Technology (NTI) Norsk Treteknisk Institutt,

2 No bio fuel - no wood drying fun

3 The Norwegian situation Approximately 55 sawmills Woody biomass fired boilers (mainly bark) Low net sales value of woody biomass Bio fuel driers are rarely used The use of a mix of woody biomass with high and low moisture content is common Some sawmills measure moisture content of bio fuels as part of their Energy Management Systems

4 The combustion chamber

5 Important operational parameters in the combustion chamber Air supply Ash or impurities on the grate Bio fuel quality Impurities Moisture content Conformity The three T s : Temperature, time (detention period), turbulens

6 Reduce heat losses to a minimum Boiler efficiency ( η) = Net heat ( Q1 ) Input power ( Q 0 ) Q s Radiation loss Q s Flue gas loss Q s Flow-through loss Q 0 Input power Q 1 Net heat

7 Negative impact of high moisture content (MC) in bio fuel Reduces the combustion temperature Lower primary air supply to the bio fuel Increased level of CO Simplified equation: C + O + H + N CO 2 + CO + H 2 O + NO x

8 Correlation of heating value and bio fuel moisture content Heating value (calorific value) the amount of energy released during complete combustion of the fuel Effective heating value decreases with increased moisture content Equation: e low ( H h ) MC low ev bf H = H +

9 Thermal efficency of bark fired boiler is highly dependent on MC 100 Boiler efficiency [%] Bark moisture content [%]

10 Heating values of bio fuels of Norway Spruce HV, Wood chips HV, Bark Heating value [kwh/lm 3 ] Moisture content [%]

11 Measuring bio fuel MC Bark samples of approximately 500 grams 5-10 samples MC determined by oven dry method

12 Mixing bark and wood chips Q: Which amount of wood chips should be added to the bark volume to maintain the combustion? Average MC of wood chips is constant Average MC of bark is measured and varies Theoretical approach calculating total heating value of the bark/wood chips mix

13 Mixing bark and wood chips HV, Wood chips HV, Bark Heating value [kwh/lm 3 ] Moisture content [%]

14 Mixing bark and wood chips HV, Bark Heating value [kwh/lm 3 ] Moisture content, bark [%]

15 Mixing bark and wood chips HV, Bark HV Mix (90/10), MC Wood chips=23 % Heating value [kwh/lm 3 ] Moisture content, bark [%]

16 Mixing bark and wood chips HV, Bark HV Mix (90/10), MC Wood chips=23 % HV Mix (65/35), MC Wood chips=23 % Heating value [kwh/lm 3 ] Moisture content, bark [%]

17 Indoor vs outdoor storage of unrefined biofuels Generation of heat in bark and wood chips Degree of drying varies by seasonal climate (temperatur, rain, snow, humidity) Mesurements to control temperature and drying of bark stack Wood mould disease

18 1 month outdoor storage of bark, March-April Bark stack of Norway Spruce instrumented to survey temperature developement during storage 22 MC samples taken before and after storage period Survey of outdoor temperature and air humidity Target: To see if MC of bark was decreased significantly

19 1 month outdoor storage of bark, MarchMarch-April

20 1 month outdoor storage of bark, March-April Temperature measurements Temperature [ o C] / Air humidity [%] TT B TT B TT M TT M TT T TT T Tout avg TC 1 - B TC 2 - M TC 4 - T -20 Period (days) -20 AH avg

21 1 month outdoor storage of bark, March-April 68,0 % Measured moisture content of bark before and after storage 67,5 % Moisture content 67,0 % 66,5 % 66,0 % 65,5 % March April Avg. March Avg. April 65,0 % Bark layer bottom Bark layer middle Bark layer top

22 Similar studies of bark and wood chips Päivi Lehtikangas, Raida Jirjis, Storage of Wood Chips and Bark in Northern Sweden, Dept. of Forestry Products, 1998 Target: To see how different storage methods affect the fuel quality of bark and wood chips Outdoor covered / uncovered storage of bark Indoor / outdoor storage of wood chips Storage was initiated in September / October

23 Similar studies of bark and wood chips - results Percent reduction in MC after 1 month storage: Bark; Covered = -0.9 %; Uncovered: % Wood Chips; Indoor = %; Outdoor = -0.8 % Percent reduction in MC after 2 months storage: Bark; Covered = % Uncovered: % Wood Chips; Indoor = %; Outdoor = -1.1% Percent reduction in MC after 8 months storage: Wood Chips; Indoor = %; Outdoor = %

24 Why bark driers are seldom used in Norwegian sawmills Large investment cost Extra handling Low net sales value of bio fuels Feasible if the sawmill want to produce refined products like pellets and briquettes

25 Conclusion Heating value of bio fuels is an important parameter for the operational properties of the combustion plant Implementation of Energy Management System for bio fuels at sawmills is a way to better control the operational challenges Mix of wet bark and wood chips of lower MC can be a way of maintaining stable combustion Storage of bio fuels indoor is preferable Investment in bio fuel dryers can be considered to produce refined assortments