National Institute of Technology, Rourkela In partial fulfillment of the requirements of

This is to certify that the seminar report on SIMULATION OF PROCESS PARAMETERS AND BED-HYDRODYNAMIC STUDIES FOR GASIFICATION OF FLUIDIZED BED BIOMASS WITH ASPEN PLUS submitted by Mohit Mohan Sahu at National Institute of Technology, Rourkela under my supervision and is worthy of Bachelor of Technology (Chemical Engineering) degree from the Institute. Fluid bed gasification is one of the potential sources for the production of clean and environmentally friendly fuel. The ASPEN PLUS simulator is a robust tool to investigate the behavior of a process and can be easily used to access various aspects such as the feasibility of an operation, the effect of operating parameters on the performance of a gasifier.

In this project work, the effects of temperature, steam to biomass ratio, pressure and equivalence ratio on product gas composition and carbon conversion efficiency of a fluidized bed biomass gasifier are studied. 2 Plot of product gas composition versus steam to biomass ratio 3 Plot of product gas composition versus higher steam to biomass ratios 4 Plot of product gas composition versus air flow rate. 6 Plot of carbon conversion efficiency versus equivalence ratio 7 Plot of product gas composition versus equivalence ratio.

9 Plot of variation of carbon conversion efficiency with steam to biomass ratio 10 The schematic diagram of the cold model. 13 Plot showing pressure drop across the bed in relation to bed height at minimum fluidization and turbulent fluidization conditions for sample 1 dolomite.

INTRODUCTION

ADVANTAGES OF FLUIDIZED BED GASIFICATION

Fluidized bed gasifiers are more tolerant of feedstock variations compared to other types of gasifiers.

DISADVANTAGES OF FLUIDIZED BED GASIFICATION

LITERATURE REVIEW

Gasifying Medium
Operating Pressure Used
Mode Of Heating
PHYSICO-CHEMICAL REACTIONS [1]
COMPOSITION OF GAS YIELD [1]
EFFECT OF FEED PROPERTIES ON GASIFICATION [1]

Fuel Reactivity
Volatile Matter
Moisture

DESIGN CONSIDERATIONS [1]

Gasifier Efficiency
Bed Materials

PREVIOUS WORK

Based on the gasification medium used, fluidized bed gasifiers are classified into the following types:-. The pyrolysis or degassing process separates water vapor, organic liquids and non-condensable gases from the char or solid carbon of the fuel. The composition of the developed products depends on the temperature, pressure and composition of the gas during discharge.

The ash content does not determine the composition of the product gas, but it has a profound influence on the practical operation of the gasifier. It is an unavoidable parameter that must be removed in solid or liquid form depending on the design of the gasifiers, the temperature profile and the melting point of the ash produced. Moisture content is a crucial factor for the gasification process as high moisture content of fuels can lower the temperature inside the gasifier, which can hinder the kinetics of gasification reactions which need high temperature because they are endothermic.

In thermal applications, the gas is not cooled before combustion and the sensible heat of the gas is also useful. The fluidized bed gasification material is mainly composed of inert solid particles and some fuel particles at various stages of gasification. As the temperature and equivalence ratio increase, the efficiency of carbon conversion increases because it is accompanied by oxidation and breakdown of molecular bonds in the biomass, resulting in greater conversion of solid carbon to gaseous molecules.

In the simulation they used two CSTR reactors for gasification showing the bed zone and the free zone. They used FORTRAN codes to simulate CSTR reactors and then under different operating conditions checked the performance of the gasifier. Increasing the equivalence ratio first increases the carbon conversion efficiency and then decreases after an optimum value.

Biomass particles in the mm size range do not affect the product gas composition. CO2 remained almost constant and CH4 remained zero for oxygen factor in the range of 20-50%. The injection of steam causes an increase in the formation of CO and H2, but it also reduces the gasification efficiency.

9] in 2010 highlighted char conversion and tar elimination as decisive factors for fluid bed gasification plants because the main loss from the plant is carbon i. 11] in 2004 observed a large difference in the amount of tar produced and the composition of tar, which basically depends on formation conditions as primary tars consisting of cellulose, hemicellulose, lignin-derived products, secondary tars including phenols and olefins.

SIMULATION AND MODELING

ASPEN PLUS SIMULATION

12]: Kinetic model: here we can simulate the reaction conditions at different times and places, which will make it suitable for reactor amplification design and optimization of operating parameters. Equilibrium model: it only predicts final reaction product distribution but gives no idea about the instantaneous product distribution along with geometrical dimensions. In this particular simulation, we will consider both reaction kinetic parameters and bearing hydrodynamic aspects.

KINETIC PARAMETERS

ASPEN PLUS MODELLING

Biomass Decomposition
Volatile Reactions
Char Gasification

The ASPEN PLUS yield reactor, RYIELD, was used to simulate food decomposition. The ASPEN PLUS Gibbs reactor, RGIBBS, was used for the combustion of volatiles under the assumption that volatile reactions follow Gibbs equilibrium. Carbon partially constitutes the gas phase, which participates in de-evaporation, and the remaining carbon constitutes part of the solid phase (char) and then undergoes carbon gasification.

The SEPARATION COLUMN model was used upstream of the RGIBBS reactor to separate volatiles and solids to carry out reactions.

Table 5: Experimental set up parameters used in the simulation [4]

SIMULATION FLOWSHEET [4]

SIMULATION MODEL ANALYSIS

Effect of Variation of Steam Flow (at lower flow rates and higher steam to biomass ratios) on Product Gas Composition
Effect of Variation of Steam Flow (at comparatively higher flow rates and lower steam to biomass ratios) on Product Gas Composition
Effect of Temperature at Constant Steam to Biomass Ratio and Air Flow Rate on Product Gas Composition
Effect of Equivalence Ratio on Product Gas Composition and Carbon Conversion Efficiency
Effect of Pressure on Product Gas Composition
Effect of Steam to Biomass Ratio on Carbon Conversion Efficiency

The work for the present report was only carried out in the cold model unit due to the time constraint. In the cold model unit, the hydrodynamic properties of bed materials to be used in the real mode were studied, i.e. The pressure drop and minimum fluidization characteristics were determined for the different biomass samples with different bed materials in the cold model unit and then using these values as operating conditions for the hot model unit, the actual gasification reaction must be carried out.

Finally, the composition of the product gas from the Hot Model unit must be determined. In this case, experimentation is essentially limited to studying the hydrodynamic characteristics of the bed in a cold fluidized bed model carburettor unit. A fixed amount of bed material is taken into the screw feeder and the time taken to feed until it reaches the minimum height inside the fluidized bed reactor is recorded, i.e.

The pressure drop across the bed, at the inlet, under minimum fluidization conditions and turbulent conditions is recorded with a certain bed height. The time is then measured for each 1.0 cm increase in bed height and the same process is repeated until the entire feed material is discharged from the screw feeder into the fluidized bed reactor.

Table 7: Dependency of product gas composition on steam flow rate

TERMS AND DEFINITIONS

PROPERTIES OF DOLOMITE

EXPERIMENTAL ANALYSIS

DISCUSSIONS

CONCLUSION