Efficient Conversion of Solid Biomass into Gaseous Fuel · Efficient Conversion of Solid Biomass...

Efficient Conversion of Solid Biomass into Gaseous Fuel

Dr. Aysha Irshad

Dept. of Chemical Engineering, University of Engineering & Technology, Lahore, Pakistan

Prof. Gordon E. Andrews, Dr. Herodotos N. Phylaktou

Prof. Bernard M. Gibbs

School of Chemical & Process Engineering, University of Leeds

Presented by: Prof. Gordon Andrews

12th ECCRIA Conference, Cardiff University, Cardiff, UK

5th-7th September 2018

Importance of biomass as fuel

• Renewable source

• Carbon neutral if sustainability is maintained

The use of biomass for heat usually involves two stage combustion

Two stage combustion systems include

• moving grate systems

• pellet and chip biomass boilers

• log boilers sometimes called gasification boilers


A. Irshad, G.E. Andrews, H.N. Phylaktou, H. Li and B.M. GibbsSchool of Chemical and Process Engineering, University of Leeds, UK 2

12th ECCRIA The European Conference on Fuel and Energy Research and its Applications 2018 Oct. 5-7, Cardiff University, Wales

• Moving grate systems• Can use wood chips or

pellets or logs• Electricity production

using steam turbine• Two stage combustion

with rich primary orunderfire air and overfireor secondary air tocomplete the combustion.

• Used for generation ofelectricity in the 1 – 50MW range.

Primary air

Secondary airMoving grate two stage combustion – continuous fuel addition

Gasificationzone 1

Oxidation zone 2




Solid biomass combustion system• Solid biomass combustion systems are usually

two staged Rich combustion stage in which

gasification reaction results in theformation of CO & H2

Secondary combustion stage whereexcess air reacts with gases fromgasification stage to burn themcompletely

• Overall excess air is controlled via oxygensensor, in most units primary air is usually a fixed ratio of the overall excess air

• Disadvantage of water cooling of gasification zone

• Fuel added typically once per day

Secondary air hole at throat between gasifier zone and secondary combustion zone

Gasification

Drying

Air Fan

Primary air

Ash

Secondary air combustion

O2 sensor




Efficient Conversion of Solid Biomass into Gaseous FuelA. Irshad, G.E. Andrews, H.N. Phylaktou, H. Li and B.M. Gibbs

School of Chemical and Process Engineering, University of Leeds, UK 5


TGA analysis

Objective

• To optimise the gas yield and thermal efficiency of the first stage of two stage biomass combustion.

Thermal Efficiency = Energy in Gases From the First Stage Gasification rich combustionEnergy in the original biomass on daf basis

This is sometimes called the CGE – combustion gas efficiency

In this work we are using the heat of rich combustion to generate the temperature and to operate in the temperature region that TGA analysis shows that 80% of the volatiles are released from biomass 300 – 500oC, which will undergo rich combustion to generate CO and H2 plusHydrocarbons if there is inefficiency in the rich burning.






12th ECCRIA The European Conference on Fuel and Energy Research and its Applications 2018 Oct. 5-7Cardiff University, Wales

1.

3.

5.

2.

4.

6.

6.Chimney

The Cone Calorimeter withcontrolled atmosphere air box



12th ECCRIA The European Conference on Fuel and Energy Research and its Applications 2018 Oct. 5-7Cardiff University, Wales

1. insulation

2. cooling jacket on load cell

3. Load cell

1

2

3

Cone calorimeter insulatedConfined atmosphere air boxAir supplied through two pipes inBottom of the compartment

Air flow set to achieverich combustion.Gas composition isCO, hydrogen andhydrocarbons.Effectively this is anupward flow gasifier.

Test biomass placed on theLoad cell here

Ash rich zone gasification with 70 kW/m2 radiant heat flux.Air flow 9 g/m2s which is a HRR of 27 kW/m2 5 sticks of ash


A. Irshad, G.E. Andrews, H.N. Phylaktou, H. Li and B.M. Gibbs



Experimental setup of Cone calorimeter

• The cone calorimeter is common equipment in fire research used to determine HRR by oxygen consumption

• Incident heat flux from conical heater isvariable

• Wood and biomass samples were placed ina sample holder 100mm x 100mm x 20-30mm, an insulation of 10-20 mm was placedunderneath the biomass that made totalheight of sample holder 40mm.

• A number of experiments were performedto achieve the gasification conditions in thecone calorimeter enclosure




Pine wood sample arranged in sample holderGas sampler with 20 sample holes



Thermocouples inserted into the wood a different distances fromthe heat source.


Pine wood Dry ash wood Eucalyptus wood

White wood pellets Sunflower shell pellets

China biomass black China biomass skin Corn cobs

Grade B torrified wood pellets

Efficient Conversion of Solid Biomass into

Gaseous Fuel


A range of 9 biomass have been studiedIncluded two supplied to me on a trip to China a few years ago.


Temp. vs time of pine wood gasification at 70 kW/m2 at Øm = 2.8



Near steadyState burning

Most volatiles are releasedat this temperature of the wood at the top surface.Volatiles are being releasedfrom the wood below the surface for a long time afterthe 600s test period shownhere.


Equilibrium calculations

• CEA (chemical equilibrium with applications) programme

by NASA was used to predict the equilibrium composition

for the products of combustion, constant enthalpy and

pressure system HP problem was chosen with Ø values

from 0.5 to 8 with one temperature to start iterations

• Input to the software was,

Elemental composition of the biomass

Standard heat of formation of biomass calculated by

method of Zainal et al. (2001)[2].

2. Zainal, Z.A., Ali, R., Lean, C.H., and Seetharamu, K.N., Prediction of

performance of a downdraft gasifier using equilibrium modeling for different

biomass materials. Energy Conversion and Management, 2001. 42(12): p.

1499-1515.

Pine wood

Equilibrium concentrations and adiabatic flame temperature

of gaseous products as a function of equivalence ratio (Ø)

for pine wood




Equivalence ratio (Ø)

The equivalence ratio is the ratio of the stoichiometric air to

fuel ratio to that of measured air to fuel ratio by mass

Ø𝑚 = 𝐴 𝐹 𝑆𝑡𝑜𝑖𝑐ℎ𝑖𝑜𝑚𝑒𝑡𝑟𝑖𝑐

𝐴 𝐹 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑

Emission index EI ( gspecies /kgbiomass) or

Yields = kgspecies/kgbiomass

EI is related to the volumetric specie concentration C

and exhaust A/F ratio by mass

𝐄𝐈 = 𝐊 × 𝐂 × 𝟏 +𝐀

𝐅

K = Ratio of the molecular weight of gas component to that

of exhaust sample

Hot gas efficiency HGE

𝐻𝐺𝐸 = [{H.H.V of product gases+Sensible heat of the gases}(

MJ

kg 𝑏𝑖𝑜𝑚𝑎𝑠𝑠)

H.H.V of the fuel (𝑀𝐽

𝑘𝑔 𝑏𝑖𝑜𝑚𝑎𝑠𝑠)

]x100

H2 concentration

Water gas shift equilibrium

where K is a function of equilibrium temperature, here a value of 3.5 is used, which

corresponds to Teq 1738 K [1].

]][[

]][[

22

2

HCO

OHCOK

1. Chan., S.H., An exhaust emissions based air-fuel ratio calculation for internal combustion engines. Proc. Instn Mech Engrs, Part D:

Journal of automobile engineering, 1996. 210: p. 273-280.




Biomass C %

daf

H %

daf

N

% daf

S %

daf

O %

daf

VM %

daf

VM %

ar

FC %

daf

H2O

% Ar

Ash

% ar

CV MJ/kg Stoich.

(A/F)(g/g)

Actual Daf actual Daf

Pine wood 48.4 6.1 0.2 0.0 45.4 87.3 81.4 12.7 5.2 1.6 18.8 20.2 5.3 5.7

Ash wood (dry) 48.7 6.5 0.7 0.0 44.1 82.2 74.6 17.8 5.1 4.2 18.3 20.2 5.4 6.0

Ash wood (Wet) 50.6 6.6 0.5 0.0 42.3 84.9 73.6 15.1 9.6 3.6 19.0 21.8 5.5 6.3

Eucalyptus Wood (Pakistan) 52.2 6.0 0.7 0.0 41.1 82.0 71.4 18.0 6.4 6.5 19.2 22.0 5.5 6.3

Acacia Wood (Pakistan) 49.1 6.0 0.3 0.0 44.6 79.9 73.6 20.1 5.8 2.0 19.0 20.6 5.3 5.8

Block wood 51.1 6.6 1.0 0.0 41.3 83.9 76.9 16.1 6.2 2.2 19.4 21.2 5.9 6.4

Sycamore Wood 54 6.8 0.8 0.0 38.4 83.0 72.5 17.0 8.0 4.6 19.9 22.8 6.1 6.9

White Wood processed pellets 48.8 6.0 1.4 0.0 43.8 86.7 79.6 13.3 4.3 3.9 19.3 21.0 5.4 5.9

Grade B torrified wood processed pellets 49.0 6.0 2.8 0.0 42.2 80.5 64.2 19.5 6.7 13.5 17.2 21.6 4.8 6.1

Sunflower Shell processed pellets 49.8 5.8 2.1 0.0 42.3 82.3 74.2 17.7 6.2 3.7 19.4 21.5 5.4 6.0

Mountain ash raw pellets 53.8 6.5 1.0 0.0 38.7 87.0 75.2 13.0 9.7 3.9 19.3 22.3 5.9 6.8

Table 1. Elemental analysis, Proximate analysis, CV and stoichiometric air to fuel ratio for biomass studied




Biomass C %

daf

H %

daf

N

% daf

S %

daf

O %

daf

VM %

daf

VM %

ar

FC %

daf

H2O

% Ar

Ash

% ar

CV MJ/kg Stoich.

(A/F)(g/g)

Actual Daf actual Daf

China’s biomass skin (China) 42.1 5.6 2.0 0.0 50.3 84.1 58.5 15.9 6.9 23.5 11.6 16.7 3.3 4.7

China’s biomass black (China) 51.9 6.4 1.9 0.0 39.8 74.1 25.9 7.5 34.3 12.8 22.0 3.8 6.6

SPF ( Spruce, pine, Fir) raw 53.4 6.6 1.0 0.0 39.0 84.4 75.3 15.6 6.0 4.8 18.6 20.9 6.1 6.8

SPF torrefied 56.0 7.2 1.1 0.0 35.6 79.4 72.8 20.6 5.4 3.0 20.1 22.0 6.8 7.5

Grade B wood 53.4 6.6 2.5 0.0 37.4 85.6 69.6 14.4 7.8 10.8 17.1 21.1 5.7 7.0

Grade B torrified wood 54.5 6.3 2.7 0.1 36.5 81.3 65.2 18.7 5.8 14 17.6 21.9 5.7 7.0

Corn cobs (Pakistan) 45.9 6.0 1.2 0.0 46.8 82.5 69.4 17.6 7.1 8.8 14.8 17.6 4.9 6.9

Wheat straw (Pakistan) 49.0 6.8 1.1 0.2 42.9 84.1 57.3 15.9 5.5 26.3 14.1 20.7 4.2 6.2

Rice husk (Pakistan) 48.4 6.4 1.4 0.0 43.7 80.0 53.7 13.5 6.7 26.2 13.7 20.4 4.0 6.0

• Stoichiometric air to fuel ratio for these biomasses vary from 4.7 to 7.5




Results and discussion

The cummulative mass of the gases flowing up the chimney from the rich burning gasification zone agrees very well with the loss in mass of the biomass.This means that the FTIR calibration is good and all the significant species have beendetermined.




Pine wood rich burning

gasification Steady state

70 kW/m2 radiant heat

Øm with time for pine wood at different air flow rates




Equivalence ratio varied by changing the primary zone air flow – indicated Øm is for the steady state period

Steady state




Pine wood gasification 70 kW/m2 radiant heat

Adiabatic equilibrium

There is zero equilibrium THC so all these THC are rich combustion inefficiency HC and for efficient energy transfer they must make the second stage combustion as a significant partof the biomass energy is in these hydrocarbons. Inefficient transfer of these hydrocarbonsto the burner/ engine / gas turbine reduces the overall thermal efficiency of the process.

CO

Measured




UK standard for domestic water heating boiler is to have minimum thermal efficiency of 86%.

HGE as a function of Øm for pine wood

Heating value as a function of time at Øm = 2.8

MJ/ Kg biomass

Acetylene

Ethylene

Toluene

Benzene

Air flow 19.2 kg/m2s


Xylene

Trimethylbenzene




Heating value as a function of time at Øm = 2.8

MJ/ Kg biomass

Acetylene

Ethylene

Toluene

Benzene

Xylene

Trimethylbenzene




1. Berend Vreugdenhil ERC/TNO Netherlands 12th ECCRIA 2018 Th. 6A 14.002. V.Lavrenov, Russian Acad Sci 12th ECCRIA 2018 Th 5A 12.053. Pedro Abelha ECN/TNO 12th ECCRIA 2018 Th. 5A 11.25

Measurements of biomass gasification gas composition % + CGE%

% 1 1 1 2 3

CO 28 15.6 28%

H2 20 14.1 33.4%

CH4 15 6.9 8.8%

CnHm 3

C2H2 0.3 0.03%

C2H4 2.0 1.6%

Benzene 0.7 6022 ppm

Toluene 0.1 211 ppm

CGE 76% 68-79% 66.8 – 78.3%

CO

H2

THC

Sensible heat

• Towards the end, HV of the gases is increasing showing that more char is present and higher thermalefficiencies can be achieved, In these two tests MLR was quick initially and some char burning zone wasachieved within test time.

Heating value as a function of time at Øm = 2 Heating value as a function of time at Øm = 1.6

HGE = 86%HGE = 90 %

MJ/ Kg biomass,

Pine wood Air = 25.6 kg/m2s Pine wood Air = 31.6 kg/sm2





HGE = 55%Ø = ~4.5

HGE = 80 %Ø = ~6

HGE = 81 %Ø = ~6

HGE = 42 %Ø = ~3.5

MJ/ Kg biomass




Different equivalence

ratios are obtained at

fixed air flow of air due to

differences in the

elemental composition

and physical nature of

the biomass: solid, pellet

or powder.

Air flow 19.2 kg/m2s

Flaming combustion zone

Char burning zone




• Rich burning of pellets have

caused inefficiency and low yield.

• Need to optimise primary

gasification zone to achieve

maximum yield of the gasification

products

EICO / yield g/kg biomass vs time for different biomass




Conclusions:

• There exists an optimum, on an energy conversion basis, equivalence ratio

for the primary gasification zone of two stage burning.

• For pine wood it was 2.8. The results for different biomass indicates that the

optimum equivalence ratio was different for different biomass. This implies

that optimisation of a two stage burner would require the ability to control

the air split as well as the overall excess air. 80% energy conversion from

solid biomass to gas was demonstrated for pine wood at Ø = 2.8.

• The most important gases in order of energy content were CO, H2,

acetylene, ethylene, toluene, benzene, xylene and trimethyl-benzene . There

was no significant methane.

• The cone calorimeter is a good experimental tool to characterise the

combustion and gasification of biomass.




Efficient Conversion of Solid Biomass into Gaseous Fuel · Efficient Conversion of Solid Biomass...

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