Basis: 100 g of total biomass mixture + gasification air) Table 5.3 Simulation results for biomass mixture gasification.
O UTLINE AND S COPE OF THE T HESIS
Exploring the possibilities for the production of Fischer-Tropsch liquids and streams via biomass gasification. Isothermal kinetics modeling of the Fischer-Tropsch synthesis over the spray-dried Fe-Cu-K catalyst.
I NTRODUCTION
After grouping the states into different regions, the distribution of electricity generation is shown in Figure 2.2. Another motive for exploring renewable energy sources for electricity generation is the fluctuating economics of conventional sources.
B RIEF H ISTORY OF R ENEWABLE E NERGY E FFORTS IN I NDIA
Ministry of New and Renewable Energy [19]
In 1981, the Government of India established the Department of Non-Conventional Energy Resources (DNES) for the development, demonstration and application of renewable energy. MNRE is the flagship ministry of the Government of India (and the only one of its kind in the world) dealing with matters related to the development and promotion of renewable energy in India.
Important policies of Government of India for renewable energy
National Electricity Policy (2005): This policy recognized the role of renewable electricity in areas where grid connectivity was neither cost-effective nor feasible. The policy also encouraged the use of renewable energy even where grid connectivity exists, provided it is cost-effective.
State-of-the-art on renewable energy front
India's global position in renewable energy production / utilization is evident and is likely to grow in the future. The financial allocation for renewable energy has increased from 0.1% in the 6th plan to 28.1%.
B IOMASS P OWER IN I NDIA
- Biomass as a coal substitute
- Biomass resources and utilization
- Conversion of biomass to electricity: Technical options
- Biomass gasification efforts in India [22,23]
Further studies showed that about 15-20% of agricultural waste can be made available for energy production without affecting actual use. More detailed information on these installations can be obtained from the company's website.
T ECHNOLOGY FOR B IOMASS G ASIFICATION
- Chemistry of biomass gasification
- Biomass pretreatment and properties
- Fixed bed gasification [25,28-29]
- Fluidized bed gasification [25-26]
- Post-treatment of producer gas
Thus, the tar content in the producer gas is lower in the downstream design than in the upstream design. Second, the total residence time of the generator gas in the high-temperature region is small.
E CONOMICS OF B IOMASS G ASIFICATION
Factors affecting cost of power generation
As mentioned earlier, the main capital cost of biomass power projects includes the cost of the gasifier, engine generator, civil construction, biomass preparation unit, electricity distribution network and electrical connections and pipelines at the gasifier installation site. . The contribution of different components to the total capital cost of the gasifier of different capacities and using dual fuel or 100% gas engine is depicted in Figure 2.7. Economies of scale (i.e. total capital cost per kW of installed capacity or unit capital cost) also show an interesting variation with the dual fuel or 100% output gas engine, as depicted in Figure 2.8.
Unit capital costs show a sharp reduction with capacity for a dual fuel engine, while capital costs for gasifiers using 100% producer gas are only marginally reduced with a capacity increase from 5 to 40 kW.
Feasibility of low to medium scale units (5–100 kW systems)
Breakeven price approach: Breakeven price of the pilot fuel used in dual fuel generator sets can be used as a measure of the financial viability of biomass gasifier. However, the results of this approach depend on the definition of the break-even price used. The "unit price of diesel" which is in the denominator of the second quarter in the.
Siemons [53] determined the gasifier “feasibility region” based on the breakeven price for diesel for a given capacity factor and biomass price.
Economics of large scale units (500 kW–5 MW)
Bharadwaj [4] has reported a cost model for assessing the economic feasibility of biomass gasifiers at this scale of operation. In addition to the annual capital costs of the gasifier and its operation, this model also takes into account the transport costs of biomass. At about a certain specific fuel consumption rate as a low to medium scale gasifier, the 5 MW unit is expected to consume 150-200 tons of biomass per hour. day.
It is clear that the contribution of the transport cost factor to the total operating cost increases as the capacity of the plant increases.
C ASE S TUDIES
The use of biomass-gasified electricity has reduced the load on the electricity grid by more than 70%. The number of consumers of this facility is approximately 4000 and the rate is fixed at Rs.30 per household per month. The specific fuel consumption and tariff structure are the same as Odanthurai, but the cost of purchasing biomass is much higher at Rs.800/ton of dry wood.
Gosaba and Chottomollakhali have been electrified by the West Bengal Renewable Energy Development Authority with the installation of biomass gasifiers.
B IOMASS G ASIFICATION : G LOBAL P ERSPECTIVE
Updraft Gasifiers
Similar installations have been made in Chottomollakhali village of Sundarbans with a population of 9219 (total 1726 households). In June 2001, four units of 125 kW capacity each were set up in this village at a cost of Rs. To meet the fuel requirement of the gasifiers, 10 ha of land has been planted at a cost of Rs.
The tariff structure is similar to Gosaba Island and the total number of beneficiaries of this enterprise is 225 (1 industry, 74 commercial and 150 households).
Downdraft Gasifiers
Fluidized bed gasifiers
- Ahlstrom Pyrofow CFB Gasifier
- TPS CFB Gasification Process
- Batelle/FERCO Project
- Brazilian BIG-GT Project
- Biocycle Project
- Hawaii Biomass Gasification Facility Project
- Vermont Biomass Gasification Project
- Varnamo Project
- ARBRE Plant
- FOSTER WHEELER Installation at Lahti
- BioCoComb Project (Zeltweg, Austria)
- Amer Project
- BINAGAS Project
- Other Installations
Tar cracking was carried out in another CFB gasifier of similar size. The tar cracking catalyst was dolomite at 900oC. The gasifier power range is 5-20 MWth, dominated by the moisture content of the biofuel (fir bark). The plant's fuel flexibility has been expanded to include RDF and grasses as additional fuels.
The operation of the plant was tested for approx. 650 hours with 3000 tons of wood residues at IGCC conditions.
![Figure 2.10: Schematic flow sheet of the Grieve-in-Chianti biomass gasification plant (adopted from [87])](https://thumb-ap.123doks.com/thumbv2/azpdfnet/10485966.0/86.892.125.777.131.783/figure-schematic-sheet-grieve-chianti-biomass-gasification-adopted.webp)
O VERVIEW AND C ONCLUSIONS FROM I NDIAN P ERSPECTIVE
Social and environmental benefits: Decentralized production based on biomass gasification is likely to create employment opportunities in rural areas. In: Biomass Gasification and Pyrolysis: State-of-the-art and Future Prospects (Ed. Bridgwater AV), Newbury: CPL Press; 1997. In: Recent Progresses in Biomass Gasification and Combustion (Ed. Paul PJ, Mukunda HS), Bangalore: Interline Publishing; 1993.
A review of the socio-economic and environmental benefits of biomass gasification-based plants: lessons from India.
I NTRODUCTION
Predictions from semi-equilibrium version of thermodynamic models of gasification agree more closely with experimental results. We hereby present an overview of the literature that has been published in the field of mathematical modeling of biomass gasification / gasifiers. The literature reviewed in this chapter also includes some experimental studies that also suggest a suitable kinetic model (either empirical or semi-empirical) for the process.
However, it gives an idea of the history as well as the state-of-the-art of the topic of biomass gasification modeling.
L ITERATURE IN THE 1990 S AND B EFORE
The model could correctly predict the effect of heat flow in determining the composition of raw coal gas from a fixed-bed gasifier. 7] have tried to optimize the biomass gasification process as a precursor for methanol production using equilibrium calculations. Wang and Kinoshita [10] have developed a kinetic model for biomass gasification based on the mechanism of surface reactions.
In the following section, we have summarized the literature in the area of modeling biomass gasification (and related processes, such as tar cracking) published in the last decade and a half.
L ITERATURE IN THE P AST O NE AND H ALF D ECADE
The approach of Gao and Li (2008) is similar to that of other authors, as it is assumed that biomass pyrolysis is instantaneous and that the volatiles released in this work are decomposed into an equivalent amount of CO, CH4 and H2O. The coupled ODEs were solved using the Runga–Kutta method for the pyrolysis region and the finite difference method for the reduction region. The model gives the axial profile of different types of generator gas along with temperatures. The influence of these parameters on the amount, composition and calorific value of the generator gas was evaluated.
This model can predict the final composition and temperature of the producer gas.
I NFERENCE AND J USTIFICATION OF P RESENT T HESIS
Stoichiometric and non–stoichiometric models
Although the literature in the field of biomass gasification modeling is quite voluminous, most published studies have used either stoichiometric equilibrium models or kinetic models. Effect of gasification agent on the performance of solid oxide fuel cells and biomass gasification systems. Synthesis, modeling and exergy analysis of biomass gasification with atmospheric air for the Fischer-Tropsch process.
Stoichiometric equilibrium modeling of biomass gasification: Validation of artificial neural network temperature difference parameter regression.
Thermodynamic Optimization of Biomass Gasification
I NTRODUCTION
In this chapter, we discussed the issue of biomass gasifier optimization for the above two applications. As mentioned in Chapter 3, there are two approaches for modeling and optimizing biomass gasifiers, viz. In addition, these models predict the marginal (maximum) capacity of the carburetor for a given range of temperature, air, or equivalent ratio, and pressure.
In the next section, we have provided the essential equations and solution algorithm of the model.
- Basic Equations
- Numerical Iterative Solution
X and P denote the total number of moles in the gas phase and the total pressure, respectively. The number of substances in the gas phase and the condensed phase at equilibrium are denoted by m and s, respectively. The method involves a search for a minimum value of the free energy G of a system (or equivalently G/RT as given in equation 4.1) subject to the mass balance relationship as auxiliary conditions (as given in equation 4.3).
Note: G = Gibbs free energy; g = chemical potential; H = enthalpy (heat content); Kf = formation equilibrium constant; P = total pressure; p = partial pressure; R = ideal gas constant; T = absolute temperature; x* = number of moles in the initial mixture; yo = initial guess of the number of moles in the equilibrium mixture; Cp = heat capacity at constant pressure as a function of temperature; ∆fH298o = heat of formation at 298.15 K; (Go−H298o )/T = free energy function; (Ho−H298o ) = heat content function; the superscript o refers to the standard thermodynamic state; subscript 298 refers to the reference temperature (25 oC = 298.15 K); signature p.
S IMULATION P ARAMETERS AND P ERFORMANCE Y ARDSTICKS
- Biomass Type
- Gasification Medium
- Temperature and Pressure of Gasification
- Performance Yardsticks
This is especially the case when the amount of hydrogen in the production gas from biomass needs to be increased. Regarding the first application, the benchmark for assessing the suitability of the producer gas is LHV (lower heating value) or the net heat content in the gas that can be obtained by combustion in engines. Therefore, we established the gasifier performance measures as: (1) hydrogen content of the production gas; (2) carbon monoxide content of producer gas; (3) H2/CO molar ratio; (4) LHV of the production gas.
Finally, we have also determined the theoretical efficiency of the carburetor for various operating conditions.
R ESULTS
- Trends in H 2 and CO Formation with Different Gasifying Conditions
- Trends in Carbon Distribution
- Trends in Hydrogen Distribution
- Trends in LHV
- Trends in H 2 /CO Molar Ratio
- Trends in Efficiency
For AR = 1 (when air in stoichiometric production is supplied to achieve complete oxidation), of course no production of CO (which is a result of partial oxidation) is seen. 4) For a given temperature, production of CO shows a maxima with air conditions. With increasing air ratio for any gasification temperature, the proportion of carbon that remains unconverted to CH4 decreases. The overall trend in the distribution of carbon among the four products is the same as in the case of gasification with air alone.
Consequently, fraction of carbon converted to CH4 decreases rapidly with increasing air ratio for air gasification than gasification with air-steam mixtures.
D ISCUSSION
- Optimum Parameters for FT Synthesis
- Optimum Parameters for Decentralized Power Generation
Considering the additional costs associated with air-steam mixtures, it appears that air is the most suitable gasification medium. Overall, the optimal combinations or sets of operating parameters for gasifier operation for FT synthesis are: AR = 0.2 to 0.4, temperatures oC, gasification medium: air. Therefore, operating the gasifier above 700 oC would mean excessive energy input that is not rewarded.
Overall, the optimal parameters for gasifier operation for distributed power generation are: temperature ~ 700–800 oC, AR = 0.3–0.4 and gasification medium: air.
C ONCLUSIONS
The most important characteristic of the producer gas from the point of view of energy generation is its lower heating value (LHV). The optimal values of gasifier operation parameters for FT synthesis were found to be: AR. Interestingly, the optimal set of parameters for gasifier operation for both FT synthesis and decentralized power generation closely overlap.
Therefore, the production gas generated by these parameters could be used for both applications.
SAMPLE CALCULATION FOR EQUILIBRIUM MODEL
Stoichiometric Air Requirement
![Figure 2.4: Schematic of an updraft biomass gasifier (adopted from [27])](https://thumb-ap.123doks.com/thumbv2/azpdfnet/10485966.0/61.892.174.744.110.739/figure-2-schematic-updraft-biomass-gasifier-adopted-27.webp)
![Figure 2.5: Schematic of a downdraft gasifier (adopted from [27])](https://thumb-ap.123doks.com/thumbv2/azpdfnet/10485966.0/62.892.178.740.111.713/figure-2-5-schematic-downdraft-gasifier-adopted-27.webp)
![Figure 2.6: Schematic of a crossdraft biomass gasifier (adopted from [27])](https://thumb-ap.123doks.com/thumbv2/azpdfnet/10485966.0/64.892.155.771.120.813/figure-2-schematic-crossdraft-biomass-gasifier-adopted-27.webp)
