TECHNO-ECONOMIC INVESTIGATION OF BIOMASS GASIFIER INTEGRATED WITH WOOD CHIPPING MACHINE

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.

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

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 — 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

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).

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.

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%).

Trial with 10 kg wood of moisture content ~16%.

Biomass:- wood
Amount of Biomass:- 10 Kg                                                                                          Amount of charcoal:- 500 gm                                                                                        Amount of small wood chips:- 1 Kg                                                                                      Weight of Pot :-1.5 Kg
Amount of Water :- 13.16 Kg (Including Pot).
Starting Time :-3:07 PM.
Flow of gas from Burner :- 3:15 PM
Start burning of burner Time :- 3:17 PM
Burner Stopping Time :-3:27 PM.
Wood not burned completely.
Amount of water left :- 12.82 Kg .(including Pot)
Initial Temperature:- 24°C
Final Temperature:- 68°C

Calculation
Input energy: – Weight x Calorific Value
Amount of wood: – 10 k
Calorific value of wood(siris): – 18.5 MJ/Kg (dry)                                                        Calorific value with 16% moisture                                                                                      Net calorific value = Cv (dry) x (1- MC/100) – (MC/100 x L)

MC : moisture content                                                                                                            Cv (dry) :  dry calorific value = 18.5 MJ/Kg                                                                              L : Latent heat of water vapourisation = 2.26 MJ/Kg

NCV = 18.5 x (1- 0.16) – ( 0.16 x 2.26)                                                                                                 = 15.178 MJ/Kg

Total input energy of wood = 10 x 15.178 = 151.78 MJ                                              Actual energy of wood used : 2.84 x 15.178 = 43.1 MJ

Calorific value of charcoal : – 28 MJ/Kg                                                                                     Input energy of charcoal :- 0.5 x 28 = 14MJ

Input energy of small dry wood chips = 1 x 18.5 = 18.5 MJ

Total input energy = 151.78 + 14 + 18.5 = 184.28 MJ                                                            Energy of wood left unused = 151.78 – 43.1 = 108.68 MJ                                                      Actual input energy = 184.28 – 108.68 = 75.6 MJ

Output energy = m x Cp x ΔT
m= Weight of water left in pot after trial
Cp = Specific heat of water.
ΔT= Temperature difference.
Output energy = 11.32 x 4.2 x 44
= 2091.94 KJ                                                                                                                                  = 2.092 MJ
Vapour energy = amount of water evaporated x latent heat of water vapourisation.
= 0.34 x 2.26
=0.768 MJ

Total output energy = (2.092 + 0.768) MJ
= 2.86 MJ
Efficiency = (total output energy/input energy) x 100

= (2.86/75.6) x 100
= 3.78 % 

The gasification efficiency of 3.78% is too low because of the large amount of unburned wood that gets trapped in the gasifier, improperly produced gas, and heat that is released into the atmosphere in the form of flue gases.