2. Introduction
Gasification is a process that converts organic or fossil based
carbonaceous materials mainly into carbon monoxide,
hydrogen and carbon dioxide
Today there is a huge demand for fuel because of the
increasing population. Biomass is renewable resource and is
available very easily. It is the third among the primary energy
sources after coal and oil
The gasification of biomass allows the production of a
synthesis gas or “syngas”, consisting primarily of H2, CO, CH4,
CO2 and N2, which further has a variety of uses
3. Introduction
A thermodynamic analysis of the process of biomass
gasification was conducted to find the Thermoneutral Points
(TNP’s) for different gasifying agents for different compositions
of the input streams to the gasifier
Reaction TNP’s (R-TNP’s), Process TNP’s (P-TNP’s) with and
without Heat Exchanger were calculated and product gas
compositions at TNP’s were analysed for syngas production,
syngas ratio, %CO2 conversion and heat utilities during the
course of this study
4. Introduction
It is assumed that the exit products of the coal gasifier are in
thermodynamic equilibrium.
HSC Chemistry software is well known software that uses
the Gibbs free energy minimization algorithm to find the
equilibrium product composition from a feed mixture and
has been used in gasification studies earlier
[Kumabe K, Hanaoka T, Fujimoto S, Minowa T, Sakanishi K.
Co-gasification of woody biomass and coal with air and
steam. Fuel 2007;86:684–9.]
We have also used HSC Chemistry 5.11 for our calculations
5. Literature Survey
We downloaded many abstracts and shortlisted around 80
relevant abstracts
We sorted out the shortlisted abstracts in the following
divisions
- Thermodynamic Analysis
- Experimental
- Modelling
- Reviews
- Theoretical
6. Biomass Selection
We chose Rice husk as the biomass to be gasified.
Composition by weight: 47.8% C, 5.1% H, 38.9% O, 0.1% N
(Ref : Jenkins, B.M. & Ebeling, J.M, Correlation of physical &
chemical properties of terrestrial biomass with conversion,
symposium, Energy from biomass & waste, Pg no-371)
Weight for 1 mole of rice husk is calculated to be 25.105 grams
We calculated the compositions in moles for one mole of
carbon in biomass as follows,
For 1 mole carbon, 0.6402 moles of H2, 0.3052 moles O2,
0.0008 moles N2
Temperature range considered in this study is 500-1000 °C
7. Methodology
PART A : R-TNP Analysis
For a particular feed condition, we calculated the output
composition of the reactor using 'Equilibrium Compositions'
module of HSC Chemistry 5.11 at temperatures ranging from
500 to 1000 °C, with intervals of 50 °C and constant pressure
of 1 bar
Using those compositions and 'Reaction Equations' module of
HSC Chemistry 5.11, we calculated the reaction enthalpy at
respective temperatures
8. Methodology (cont.)
PART A : R-TNP Analysis
By plotting the graph of Enthalpy vs. Temperature we
calculated the R-TNP's of the reaction
We calculated the product gas compositions at the R-TNP's
and analysed the parameters: Syngas, Syngas Ratio, %CO2
Conversion, Heat utility (without HE), Reduced Heat Utility
(with HE)
9. 1. Gasifying Agent: CO2
We defined the parameter CCBR (CO2 to Carbon in biomass
molar ratio)
We varied CCBR in the input of the gasifier. Values of CCBR
are: 0, 0.5, 1, 1.5, 2, 2.5, 3, 4, 5
From the graphs of enthalpy change vs. temperature for all
the CCBR, we found that thermoneutral points (TNP’s) can
be obtained for all the CCBR considered except 0 and 0.5
Thermoneutral temperature decreased with increase of
CCBR
14. Gasifying Agent: CO2 - Trends
Syngas, Syngas Ratio and % CO2 conversion decreased with
increase in CCBR
Heat utility (without HE) increased linearly with increase in
CCBR
However, Heat utility (with HE) decreased then remained
constant with the increase of CCBR
22. 2. Gasifying Agent: H2O
We defined the parameter HCBR (H2O to Carbon in biomass
molar ratio)
We varied HCBR in the in the input of the gasifier. Values of
HCBR are: 0, 1, 2, 3, 4
From the graphs of enthalpy change vs. temperature for all
the HCBR, we found that no thermoneutral points can be
obtained for any of the HCBR considered
24. 3. Gasifying Agent: CO2 & H2O
We defined the parameter GaCR (Gasifying Agents to
Carbon in Biomass molar ratio)
We varied GaCR from 1 to 4 in the input of gasifier and
considered different combinations of CCBR and HCBR for
each GaCR
For GaCR = 1, R-TNP’s were obtained only for 1/0
For GaCR = 2, P-TNP’s were obtained only for 2/0
For GaCR = 3, P-TNP’s were obtained for 3/0, 2.5/0.5
For GaCR = 4, P-TNP’s were obtained for all combinations
which had CCBR greater than or equal to 3
31. GaCR = 4 - Trends
R-TNP first slightly decreased with HCBR then increased
Syngas increased (from 1.9124 to 2.0298 moles per moles of
Biomass) with increase in HCBR
Syngas ratio showed a maxima (of 0.403) at HCBR = 0.714
% CO2 conversion first decreased then increased with increase
in HCBR
Heat utility (with HE) increased with increase in HCBR
However, Heat utility (without HE) first decreased slightly and
the increased with increase in HCBR
38. Methodology
PART B: Process TNP Analysis (without HE)
We calculated the Biomass preheating value for temperatures
between 500 to 1000 °C, with intervals of 50 °C.
Cp value of Rice husk was taken as 2.094 J/gK [Kaupp (1984)]
We then calculated the preheating value of gasifying agents
(CO2 and H2O) for respective temperatures. Cp value of CO2
and H2O was taken from Perry's Chemical Engineers'
Handbook 7e
We then calculated the Process enthalpy (without Heat
Exchanger) as the sum of Reaction enthalpy, Biomass
preheating and Gasifying Agents preheating
(Figure 1)
40. Methodology (cont.)
PART B: Process TNP Analysis (without HE)
We plotted the graph of Process enthalpy without heat
exchanger vs. Temperature and calculated the P-TNP's without
HE
We calculated the product gas compositions at the P-TNP's
and analysed the parameters: Syngas, Syngas Ratio, %CO2
Conversion, Reaction Enthalpy at P-TNP's
41. 1. Gasifying Agent: CO2
We varied CCBR in the input of gasifier from 0 to 5
From the graphs of enthalpy change vs. temperature for all
the CCBR, we found that TNP’s can be obtained for all the
CCBR except 0 and 5
45. Gasifying Agent: CO2 - Trends
P-TNP’s, Syngas and %CO2 conversion decreased with
increase in CCBR
Syngas Ratio showed a minima (of 0.469) at CCBR =2.056
Reaction Enthalpy at P-TNP’s was calculated and it showed a
decrease with increase in CCBR
50. Process TNP’s without Heat Exchanger
-120
-110
-100
-90
-80
-70
-60
-50
0.5 1 1.5 2 2.5 3 3.5 4
Enthalpy(KJ)
CCBR
Reaction Enthalpy at P-TNP's
51. 2. Gasifying Agent: H2O
We varied HCBR from 0 to 4 in the input of gasifier
From the graphs of enthalpy change vs. temperature for all
the HCBR, we found that TNP can be obtained only for HCBR
= 1, in the range of 500-1000 °C
HCBR
TNP
oC
CO2(g)
moles
CO(g)
moles
H2O(g)
moles
H2(g)
moles
CH4(g)
moles
N2(g)
moles
C
moles
Syngas
moles
Syngas
Ratio
% CO2
Conv.
1 580.012 0.4341 0.2164 0.5254 0.7704 0.1721 0.001 0.1775 0.9868 3.56 47.46
53. 3. Gasifying Agent: CO2 & H2O
We varied GaCR from 1 to 4 in the input of gasifier
For GaCR = 1, P-TNP’s were obtained for all the
combinations of CCBR and HCBR considered
For GaCR = 2, P-TNP’s were obtained for three combinations
2/0, 1.5/0.5, 1/1
For GaCR = 3, P-TNP’s were obtained for two combinations
3/0, 2.5/0.5
For GaCR =4, only 1 P-TNP was obtained for 4/0
60. Gasifying Agent: Both -Trends
P-TNP’s and Syngas production decreased with increase in
HCBR for both GaCR 1 and 2
Syngas ratio showed an increase with increase in HCBR for
both the GaCR
Reaction enthalpy at P-TNP’s decreased with increase in
HCBR
61. Process TNP’s without HE at GaCR = 1 & 2
500
520
540
560
580
600
620
640
660
680
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
TNP(oC)
HCBR
P- TNP's
GaCR 1
GaCR 2
62. Process TNP’s without HE at GaCR = 1 & 2
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
syngas(moles)
HCBR
Syngas
GaCR 1
GaCR 2
63. Process TNP’s without HE at GaCR = 1 & 2
0
0.5
1
1.5
2
2.5
3
3.5
4
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
SyngasRatio
HCBR
Syngas ratio
GaCR 1
GaCR 2
64. Process TNP’s without HE at GaCR = 1 & 2
-120
-100
-80
-60
-40
-20
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Enthalpy(KJ)
HCBR
Reaction Enthalpy at P-TNP's
GaCR 1
GaCR 2
65. Methodology
PART C: Process TNP Analysis (with HE)
We calculated the Product Gas Cooling Energy released at
respective temperature. Product gas consisted of CO2(g),
CO(g), C, H2O(g), H2(g), CH4(g) and N2(g). Cp values of all the
components were taken from Perry's Chemical Engineers'
Handbook 7e
We then calculated the Process enthalpy (with Heat
Exchanger) as the sum of Reaction enthalpy, Biomass
preheating, Gasifying Agents preheating + Product Gas
Cooling (Figure 2)
67. Methodology (cont.)
PART C: Process TNP Analysis (with HE)
We plotted the graph of Process enthalpy with heat
exchanger vs. Temperature and calculated the P-TNP's with
HE
We calculated the product gas compositions at the P-TNP's
and analysed the parameters: Syngas, Syngas Ratio, %CO2
Conversion, Reaction Enthalpy at P-TNP's
68. 1. Gasifying Agent: CO2
We varied CCBR in the input of gasifier from 0 to 5
From the graphs of enthalpy change vs. temperature for all
the CCBR, we found that TNP’s can be obtained for all the
CCBR except 0
72. Gasifying Agent: CO2 - Trends
P-TNP’s, Syngas production, Syngas ratio and % CO2
conversion decreased with increase in HCBR
Reaction enthalpy at R-TNP’s increased and went from
exothermic region to endothermic region
Reaction enthalpy for CCBR = 2.68 was zero. Thus, R-TNP
and P-TNP is same for CCBR 2.68
78. 2. Gasifying Agent: H2O
We varied HCBR in the input of gasifier from 0 to 4
From the graphs of enthalpy change vs. temperature for all
the HCBR, we found that TNP’s can be obtained for all the
HCBR except 0
81. Gasifying Agent: H2O - Trends
P-TNP’s and Syngas Production decreased with increase in
HCBR
Syngas ratio and % CO2 Conversion increased with increase
in HCBR
Reaction enthalpy at P-TNP’s decreased with increase in
HCBR
86. Process TNP’s with Heat Exchanger
-60
-55
-50
-45
-40
-35
-30
1 1.5 2 2.5 3 3.5 4
Enthalpy(KJ)
CCBR
Reaction Enthalpy at P-TNP's
87. 3. Gasifying Agent: CO2 & H2O
We varied GaCR from 1 to 4 in the input of gasifier
For all the GaCR, P-TNP’s were obtained for all the
combinations of CCBR and HCBR considered
99. 3. Gasifying Agent: Both - Trends
Syngas decreased with increase in HCBR
Syngas ratio increased with increase in HCBR
% CO2 conversion and Reaction enthalpy at P-TNP’s
decreased with increase in HCBR
104. Conclusions
Sandeep et. al. varied SBR (Steam to Biomass Ratio) from
0.75 to 2.7. The hydrogen yield is found to be 104 g/kg of
biomass at SBR of 2.7. Significant enhancement in H2 yield
is observed at higher SBR compared with lower range SBR
REF: Sandeep, K., Dasappa, S., Oxy–steam gasification of
biomass for hydrogen rich syngas production using
downdraft reactor configuration
International Journal of Energy Research – 2013
In our study, for SBR = 3, hydrogen yield is found to be
130.45g/kg of biomass
105. Conclusions
Exothermal regions were obtained in the biomass
gasification with no oxygen in the input stream
Biomass Gasification can be done auto thermally even
without any input of external oxygen or air
Inbuilt oxygen content in biomass is large enough to carry
out the gasification process
The product gas for some of the feed conditions can be
used for Fischer Tropsch process in petroleum industries
106. GaCR
CCBR/
HCBR
Syngas
(moles)
without HE
Syngas
Ratio
without HE
Syngas
(moles)
with HE
Syngas
Ratio
with HE
1 0/1 - - 1.905 1.806423
2 1.5/0.5 0.822 1.216828 - -
2 1/1 0.6785 2.931054 1.9021 1.072682
2 0.5/1.5 - - 1.8972 1.923267
3 2.5/0.5 0.587 1.269037 - -
3 1.5/1.5 - - 1.8895 1.328978
3 1/2 - - 1.8874 2.116064
4 2.5/1.5 - - 1.8804 1.070469
4 2/2 - - 1.8799 1.578031
4 1.5/2.5 - - 1.8786 2.327901
Syngas Ratio between 1 to 3
For Fischer Tropsch