Generation of Electricity from Biomass - Electrical energy from Biomass, combustion, gassification

GENERATION OF ELECTRICAL ENERGY FROM BIOMASS

1.1. INTRODUCTION

Energy is the most vital issue for all living-being on earth. Modern life style has further increased its importance since a faster life means a faster transport, faster communication, faster manufacturing processes etc. All these lead to an increase in energy required for all these modern systems. These energy come from different sources and one of these sources is the biomass or biofuel energy production (generation) source.

1.2. DEFINITION OF BIOMASS

Biomass or Biofuel is a fuel that is developed from organic materials, renewable and sustainable source of energy used to generate electricity or other forms of energy. It is the organic material that is used for the production of energy known as biomass.

1.3. DESCRIPTION OF BIOMASS

The biomass plant is a renewable source of energy because wastes residues will always exist be it in terms of scrap wood, forest resources, manure etc...Developing new energy sources to produce reliable, affordable energy while respecting the environment is one of the top most compelling need of this system.

Most bio-power plants function when wastes is burned and the energy in it released as heat(steam) runs a turbine to make or to generate electricity and also provides heat to industries and home. Biomass is burned directly to produce high pressure steam (heat) that drives a turbine generator to generate or make electricity. In some biomass industries, the extracted or spent steam is used for manufacturing processes or to heat buildings.

In the case of CAMEROON being a developing country, biomass or biofuel is mostly used for domestic purposes such as cooking, smoking, roasting, drying crops etc... For the moment, biofuel is the main source of energy. This is mostly in the form of firewood, charcoal, dung etc. some of the biofuel is used at the industrial level. For example the Cameroon Development Cooperation uses biomass (palm husks and rubber wood) in its oil mills and Tole tea factory. While it is used in the tea factory mostly as a source of direct heat for drying tea leaves, in the oil mill it is used as a direct source of heat for boiling kenels and also, by converting the heat into mechanical energy for the production of electricity.

A simple biomass system shown in the figure below is made up of several key components. For a steam cycle, this includes:

• Fuel storage and handling equipment.
• Combustor/ furnace.
• Boiler, pumps, fans.
• Steam turbine.
• Generator, condenser.
•  Cooling tower, exhaust/ emission control etc.

A general view of a biomass power plant system

1.1.1.      METHODS TO CONVERT BIOMASS TO ELECTRICITY

The figure below shows the general methods and process in the production of energy from biomass.

Different methods and processes for energy production from biomass.

A)    COMBUSTION

Burn the biomass directly which produces heat. The heat production by recovering heat through heat transfer media such as steam and hot water using boilers and heat exchangers is send to the steam turbine which then generates electricity. Combustion can be represented by:
C₆H₁₀O₅ +6O₂---------->6 CO₂ + 5 H₂O + 17.5 MJ / Kg.

Biomass     +   Oxygen (air)              Carbon dioxide   +   water   +     heat.

Combustion process for energy production

A)    GASIFICATION

This is the process of converting biomass solid raw material (e.g. wood) into fuel gas or chemical feedstock gas (syngas).This gasification is also subdivided into other types.

a)      A biomass gasifier takes dry biomass such as agriculture waste and with the absence of oxygen and high temperature produces synthesis gas (CO+H2); also known as pyrolysis of biomass.

b)      Gasification also takes wet biomass such as food waste and manure into methane (CH4) in a digestion tank. Both methane and synthesis gas (syn gas) can be used in a gas engine or a gas turbine for energy production.

c)      Another way to produce electricity from gasification is by using fuel cells. If we have enough purity, we can use fuel cells to produce electricity. The fuel cells break quickly if the gas in any way contains impurities but this technology is not yet commercial.

d)     Biofuel like ethanol, biodiesel and bio-oil can also be used for power production in most types of power generation plants.

The general process of gassification is shown in the figure below.

Overview of gasification process in energy production

1.1. PROCEDURES NECESSARY BEFORE BIOMASS IS INSTALLED

This type of a system is best suitable for a particular application and which depends on many factors including:

-          Availability and cost of each type of biomass (chip, pellets, house waste, forest residues etc.).

-          Competing fuel cost (fuel oil and natural gas).

-          Peak and annual electricity load and cost.

-          Building size and type.

-          Space availability.

-          Operation and maintenance staff availability.

-          Local emission regulation.

1.2. ADVANTAGES AND DISADVANTAGES OF A BIOMASS SYSTEM

1.2.1.      MERITS

-          It has an advantage of dispatchability meaning it is controllable and available when needed.

-          The waste material reduces landfilled disposal and makes more space for everything else.

-          Carbon dioxide which is released when biomass fuel is burnt is taken in by plants.

-          Less money is spent for oil.

1.2.2.      DEMERITS

-          The fuel needs to be procured, delivered, stored and paid for.

-          Also, biomass combustion produces emissions which must be carefully monitored and controlled to comply with regulation.

-          Additional work is needed in areas such as harvesting methods because land used for energy crops may be in demand for other purposes such as farming, conservation, housing etc.

-          Some biomass conversion projects are from animal wastes and are relatively small and therefore limited.

-          In some cases, it is a major cause of pollution.

-          Research is needed to reduce the cost of production for biomass based fuel.

-          Agricultural wastes will not be available if the basic crop is no longer grown.

1.3. CONCLUSION

Biomass system ranges from small stoves used in homes for heating or cooking to large power plant used by centralized utilities to produce electricity. In residential areas, biomass can be used for space heating or for cooking. Here, wood is the common source of fuel, although many different materials are used. In industrial and business, biomass is used for several purposes including space heating, hot water heating, and electricity generation which is the main proponent for this topic. 

By EKETECH