Exergy and energy analysis

1. Introduction
 Biomass has great potential as a renewal and clean
energy for producing electricity from combined
cycle.
 Biomass gasification involves the production of
gaseous fuels by partial oxidation of solid fuel.
 Gasification is a degradation process consisting of
a sequence of thermal and thermochemical
processes.
 The gasification of biomass is an attractive
technology for combined heat and power
production.

2. Renewable Energy Resources
Availabilty across the world [1]

3. Gross Residual availability from
crop production in india [1]

4. Two major groups of Biomass [2]

5. IGCC Systems
 IGCC is an acronym for Integrated Gasification
Combined Cycle.
 The major purpose of IGCC is to use hydrocarbon
fuels in solid or liquid phases to produce electrical
power in a cleaner and more efficient way via
gasification, compared to directly combusting the
fuels.
 The ultimate goal for IGCC is to achieve a lower
cost of electricity (COE) than conventional
pulverized coal (PC) power plants and/or to be
competitive with natural gas-fired combined-cycle
systems with comparable emissions.

6. Integrated Gasification
Combined Cycle Power Plant[3]

7. Types of Gasifier [3]
1. Downdraft Gasifiers
 The downdraft (also known as co-current) gasifier is
the most common type of gasifier
 The flow of air and gas is downwards (hence the name)
through the combustion and reduction zones. The term
co-current is used because air moves in the same
direction as that of fuel, downwards.
 A downdraft gasifier is so designed that tar, which is
produced in the pyrolysis zone, travels through the
combustion zone, where it is broken down or burnt. As
a result, the mixture of gases in the exit stream is
relatively clean

9. Updraft Gasifier
 In updraft gasifiers (also known as counter-
current), air enters from below the grate and flows
upwards, whereas the fuel flows downwards.
 An updraft gasifier has distinctly defined zones for
partial combustion, reduction, pyrolysis, and
drying.
 The resulting combustible producer gas is rich in
hydrocarbons (tars) and, therefore, has a higher
calorific value, which makes updraft gasifiers
more suitable where heat is needed, for example
in industrial furnaces.

11. Fluidized Bed Gasifiers
 In fluidized bed gasifiers, the biomass is
brought into an inert bed of fluidized material
(e.g. sand, char, etc.).
 The fuel is fed into the fluidized system either
above-bed or directly into the bed, depending
upon the size and density of the fuel and how
it is affected by the bed velocities.
 During normal operation, the bed media is
maintained at a temperature between 550 °C
and 1000 °C.

13. Entrained-flow gasifiers
In entrained-flow gasifiers, fuel and air are
introduced from the top of the reactor, and
fuel is carried by the air in the reactor.
The operating temperatures are 1200–1600
°C and the pressure is 20–80 bar.
Entrained-flow gasifiers can be used for
any type of fuel so long as it is dry (low
moisture) and has low ash content.
Due to the short residence time (0.5–4.0
seconds), high temperatures are required
for such gasifiers.

15. Advantages and disadvantages
of different Gasifier types [1]

16. Reactions involved in a
gasification process at 298K and
1atm [8]
 Heterogeneous reactions:
1. C(s) + ½ O2 → CO ∆H = -110.5 MJ/kmol
2. C(s) + CO2 → 2CO ∆H = +172.0 MJ/kmol
(Gasification, Reverse Boudouard Reactions)
3.
4. C(s) + H2O (g) → CO + H2 ∆H = +131.4 MJ/kmol
(Steam-Char Gasification)
5.
6. C + 2H2 → CH4, ∆H = -87.4 MJ/kmol
(Hydrogasification, Direct Methanation)
7.

17. Homogeneous reactions:
 CO + ½ O2 → CO2 ∆H = -283.1 MJ/kmol
 CO + H2O (g) → CO2 + H2 ∆H = -
41.0 MJ/kmol (Water-gas shift)
 CO + 3H2 → CH4 + H2O ∆H = -205.7 MJ/kmol
(Methanation)
 CHmOnNoSpClq → aCO+ bH2+ cCH4+ dC2H2+ eN2+ fHCl+
gH2S+ hCO
(Volatile cracking)
 CH4+ ½ O2 → CO + 2H2 ∆H = -35.7MJ/kmol
(Volatiles gasification via CH4)
 C2H2 + O2 → 2CO + H2 ∆H = -447.83 MJ/kmol
(Volatiles gasification via C2H2)
 H2 + ½ O2 → H2O ∆H = -242MJ/kmol

18. Characterstics of Some
Commercial Gasifiers

19. Design and Calculation [4]
The general chemical formula for biomass
feedstocks given by Ca0Ha1Oa2Na3The global
gasification reaction in the biomass gasifier can be
written as:
Ca0Ha1Oa2Na3 + wH2O + a4(O2 + 3.76N2) +
a5H2O→b1CH4 + b2CO+b3CO2 + b4H2 +
b5H2O+b6N2
For every single atom of carbon in fuel, the
coefficient a1 becomes one.

20. Cont…
 The coefficients a2, a3, and a4 are the H/C, O/C, and
N/C mole ratios, respectively

21. Cont…

22. Cont…
Now our general equation of biomass become
C1H1.56O0.52N0.088 + 0.24H2O + 0.084(O2 + 3.76N2)
+ 1.284H2O→b1CH4 + b2CO+b3CO2 + b4H2 +
b5H2O+b6N2
Taking atom balances on carbon, hydrogen, oxygen,
and nitrogen
C balance: 1 = b1 + b2 + b3
H balance: 1.56 + 2*1.284 = 4b1 + 2b4 + 2b5
O balance: 0.52 + 2*0.084 + 1.284 = b2 + 2b3 + b5
N balance: 0.088 + 2(3.76) 0.084 = 2b₆

23. Cont…
There are six unknowns and four equations, so there
is a need for two equations developed from
equilibrium reactions.
Methane reforming CH₄+ H₂O = CO+ 3H₂
Water shift reaction CO + H₂O = CO2+ H₂
 b₃, b₄, b₅, b₆ are converted in terms of the
coefficient b₁ and b₂
 Values are substitute in the equation of k1 and k2

24. Cont…
k₁ = b1/b4
2
k2 = b₃b₄/b₂b₅
As we know that equilibrium constant depends on
temperature
So, formula of calculaiting k₁ and k2

25. Cont…
Now the values of k₁ and k2 are
Gasifier Temperature and are 784.0485K and 6bar

26. Cont…
 The simplification of equation k₁ forms a quadratic
equation in terms of b1 and b₂ represented by the
function f (b1, b₂), similarly the simplification of the
equation of k₂ forms another function represented by
g(b1, b₂).
 A numerical method is used to solve the b1 and b2
from the above two equilibrium constant equations.
Therefore, approximate initial values of b1 and b2 are
taken to start the iteration of the numerical method. By
Taylor’s series expansion method

27. Cont…
 The values of h and k are the desired degree of
accuracy in the coefficients of b1 and b2,
respectively. In the above equations fo= f (b1 ,b2)
and go=g (b1 ,b2), respectively are solved to get the
values of h and k. If the desired degree of accuracy
is not obtained, this iteration is repeated with the
new values for the coefficients. They are as
follows:

28. Cont…
 This is repeated up to the desired accuracy. All the
six coefficients _b1-b6__ in the partial oxidation
reaction are calculated by the iteration.

29. Cont…

30. Cont…

31. Cont…

32. Refrences
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biomass gasification systems for power generation (<200kW class): A
review, “Renewable and Sustainable Energy Reviews,no.117,2020.
[2] P.Basu, Biomass Gasification, Pyrolysis, and Torrefaction,
Practical Design and Theory, 2nd ed., London:Academic
Press,Elsevier,2013.
[3] M.Parvez, “Investigation on thermodynamics behaviour of apple
juice waste and sugarcane bagasse gasified fuelled combined cycle
power generation system, “Biofuels,2017.
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031801-1,2009.

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integrated gasification cogeneration system for combined pro
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[8] T. Wang and G. Stiegel, Integrated Gasification Combined
Cycle (IGCC) Technologies, Woodhead Publishing, 2017.

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biomass gasification combined cycle (IBGCC)
power generation concept: the gateway to a
cleaner future," Allied Environmental
Technologies, vol. I, p. 1–22, 1999.
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gasification combined cycle opportunities using
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Alstom’s industrial gas turbines," in Proceedings
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35.  [11] D. Souza and M. Santos, "A feasibility study of an
alternative power generation system based on biomass
gasification/gas turbine concept," Fuels, no. 78, p. 529–
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