INTRODUCTION
Biomass gasification is the process which converts the wood, crop husks and other agriculture residue into useful gases ( syngas or producer gas) for several uses. The device which is used to do gasification is known as gasifier.
A wood chipper machine plays a crutial role in gasification which convert the wooden logs into small wood chips of desired size. A typical wood chipping machine consists of rotating blades and hammers which converts the raw wood into wood chips of desired size.
Dimensions of gasifier
Length of upper cylinder = 74 cm
Length of lower cylinder = 60.5 cm
Diameter of cylindrical body(outer) = 34.7 cm
Length of feed inlet = 17 cm
Diameter of feed inlet(outer) = 21.3 cm
Thickness of feed inlet = 3.34 mm
Thickness of cylinder (gasifier body) = assume equal to thickness of feed inlet (3.34 mm)
Diameter of air flow pipe (outer) = 60.08 mm
Diameter of air flow pipe (inner) = 49.24 mm
Length of air flow pipe (from blower to burner = 385 cm
Diameter of gas flow pipe (outer) = 11.77 mm
Length of gas flow pipe = 212.5 cm
Length of ignition pipe = 16.3 cm
Diameter of gas removal pipe = 25 mm
Length of gas removal pipe = 49 cm
Distance between two burners = 31 cm
Total no. of burners = 3
Diameter of each burner = 17.5 cm
Height of each burner = 25.5 cm
Calculations
Volume of gasifier = πr^2 h
Radius of gasifier cylinder (r) = d/2
r = (34.7/2) – 3.34
r = 14.01 cm
Total height of gasifier cylinder,h (above grate) = 74 + 30 = 104 cm
Volume = π (14.01)^2 * 104
= 64.09 * 10^-3 cubic m
Density of wood, Albezia lebbeck (siris) = 550 – 660 kg/m^3 ; ( source : wikipedia)
Capacity of gasifier (in kg) = 34.24 kg (considering density 550 kg/m3)
Wood chipping machine
Motor for cutter = 3 hp = 2238 watt
Motor for feeder = 1 hp =746 watt
Size of wood chips
length = 42 mm
diameter = 40 mm (avg.)
Total power consumption of wood chipper = 2.238 + 0.746
= 2.984 kw
~ 3 unit/hr
Machine operating time = 20 minutes
Power consumed by machine = (3/60) * 20
= 1 unit
Weight of wood chips = 10 kg
Wood specification
Wood — Albezia lebbeck (siris)
Type of wood — hardwood
Density of wood — 550 kg/m^3 ( wikipedia)
Moisture content (wet basis) — 35.7 % (need drying)
Colour — light brown
Texture — slightly rough
Challenges faced
The machine getting stuck repeatedly during wood chipping.
Oversized wood pieces caused frequent choking at the cutter blades.
The machine suddenly powered off and didn’t restart for a while. The issue has now been resolved after inspection.
High Moisture Content in Wood Feedstock –
Moisture content was found to be 35.7% (wet basis).
Feeding of wood chips in GASIFIER
Test 1
Testing of gasifier with wood chips of higher moisture content
Result
Combustion takes place instead of gasification as lot of air supplied
Blockage of wood chips seen inside the gasifier.
Test 2
Gasification with limited supply of air and sealing the bottom of gasifier with water to reduce leakage of gas.
Result:-
Gas not formed properly
White smoke come out from burner
Cause: –
High moisture content of wood chips (35%).
Solution :-
Oven drying of wood chips for 4 hours to reduce moisture content below 15%.
