Research and Simulation on Biomass Energy Generation System

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Table 3 Example fuel properties of compressed wood and compresed bark

Table 4 Example boundary conditions for updraft gasifier

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Acknowledgement

We sincerely thank and acknowledge the valuable advice of

Our supervisors:

Dr. Ha How Ung

Dr. Almon Chai

Our course coordinator:

Dr. Basil Wong

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Abstract

Gasification and pyrolysis process in a biomass gasifier is very much affected by the airflow inside the reactor. In order to improve the efficiency of the gasification and pyrolysis process of a gasifier, in which time of reaction is reduced and maximum energy and desired gas fuel are produced, raw biomass material needed to follow a strictly designated path to go through the process. Therefore the design of a reactor is very important as it will determine how biomass is being gasified.

In this project, we are going to look into two major types of gasification reactor design – updraft and downdraft gasifiers for how the air will flow through the reactor. Both reactors have their respective processing sequence and advantages in drying the biomass and gasification. We will try to model the pyrolysis and gasification process using several parameters of both thermodynamics and fluid mechanics terms. Variables values determined will later be set as the boundary conditions for the set up of Computational Fluid Dynamics analysis using computer software.

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Introduction

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Biomass fuel

Biomass fuel is solid organic mass that can be used as fuel to produce energy in chemical form or heat. Biomass fuel faces several problems in dominating the energy fuel market, as solid mass is not easy for transportation and domestic usage, comparing to the conventional liquid and gas fuel. Therefore, the biomass conversion process acts as bridging process to convert solid fuel to liquid and gaseous fuel for its advantages.

There are two major types of biomass that can be used as feedstock for energy production unit, i.e. wet biomass (e.g. starches, manures) and dry biomass (woody and agricultural materials). For the wet biomass, the best way to for conversion will be biochemical reaction which operates at lower temperature and longer time. Whereas for dry biomass, thermochemical process will suit well and require much shorter time for production, but higher operating temperature.

Biochemical

Thermochemical

Process

Digestion, fermentation

Pyrolysis, gasification, combustion, liquefaction

Feedstock

Sugarcane, starch. corn

Cellulose stock, wood municipal solid waste

Reactor type

batch

Continuous

Reaction time

2 days

7 minutes

Water use

3.5-170 litres/litre ethanol

By-products

Distiller’s dried grain

Syngas/electricity

Yield

450 litres/ton

265-493 litres/ton

Technology maturity

>100 in U.S. plants

Pilot plant

Figure 21 Comparison between biochemical process and thermochemical conversion process

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Biomass conversion process

Biomass conversion process refers to all the processes during conversion of solid biomass material to other product in either liquid or gaseous forms. In this paper, we are going to investigate on thermochemical conversion process only. Biomass thermochemical conversion is divided among 3 main processes: pyrolysis, gasification, and combustion. Each process takes different chemical component as input and produce different product. Basically, the three processes are in continuous form but in different phase, where pyrolysis happened before gasification process and gasification precede the combustion. Three processes could happen in the same time too providing the condition meet the requirement for the reaction.

Pyrolysis, which is considered the first stage in the three conversion processes, convert solid biomass material to both solid, liquid and gaseous outcome product. General reaction equation for pyrolysis simplifies the reaction process for various input material:

[pic 2]

Gasification will succeed the pyrolysis process and continue to convert the products to gaseous fuel. Combustion process happened all the time during pyrolysis and gasification process for a small portion of biomass to generate heat for both the process to happen. General reaction equation for combustion:

[pic 3], -393,770kJ/kmol

General reaction equation for gasification:

[pic 4]

Producer gas reaction: [pic 5]

Heavy oil gasification: [pic 6]

Shift reaction: [pic 7]

Temperature