7 Components of Biomass Power Plants and Their Functions

Components of biomass power plants are; fuel inlet, combustion chamber, steam generator, electric generator, cooling unit, emissions control, and ash-handling unit.

This article discusses the components of biomass power plants and their functions, as follows;

1). Fuel Inlet (as one of the Components of Biomass Power Plants)

A fuel inlet; also called a 'fuel feeder' or 'fuel feeding system' is part of the equipment used in biomass power plants.

Fuel feeders are very important for handling biomass feedstocks and biofuel, because of the large amount of fuel that is typically needed by these plants, and the need to handle such fuel properly [6].

Basically, the fuel feeder comprises of vessels and conduits that are designed to inject or introduce biomass fuel into the power plant.

The specific design of a fuel feed system for any given biomass power plant may vary widely, depending on cost considerations, scale of the plant, material properties and type of biomass being used, among other factors [9].

The type of biomass that is most commonly used as fuel in power plants is wood, which is often processed to produce pellets that are easy to handle and convert to energy.

It is important to note that the fuel feeder is part of a larger fuel handling system that includes components for fuel refinement and storage. However, it is the most important part of this '£system' as far as power generation is concerned.

The fuel feeder may be advanced an optimized through automation functionality and efficient design. Such optimizations are particularly important for large plants with enormous demand for fuel.

Also, the rate of fuel intake by the feeder may vary based on scale and fuel type; and its value is measured in units of tons per hour.

Fuel feeders are especially important in scenarios with significant complexity, such as hybrid systems that combine bioenergy utilization with other forms of energy like fossil fuels or even solar [6].

2). Furnace/Combustion Chamber/Combustor

The combustion chamber, also called the furnace, boiler or combustor in a biomass power plant, is the component in which biofuel undergoes controlled combustion to yield usable bioenergy in the form of heat.

Biomass is suitable as combustion fuel for heat production and power generation because it is flammable and contains chemical energy that is originally derived from solar radiation and stored in living tissue through photosynthesis.

The combustion process of biomass is the series of physicochemical changes and reactions that occur as biomass fuel is burnt and heat energy is released.

One of the objectives of bioenergy technology innovation in recent years has been to design the combustion chamber or furnace in such a manner that optimizes the process of combustion, and increases energy efficiency of the entire power plant.

In addition to design improvement, efforts are also being made to select plant feedstock that burns with optimal efficiency and minimal environmental impact [5].

Depending on system complexity, the combustion chamber in a biomass power plant can be designed to permit multistage combustion, or cogeneration [7].

Types of combustion chambers or boilers used in biomass power plants are; fluidized bed, fixed grate, and circulating bed types, among others.

The combustion products of biomass are; carbon dioxide, water, and carbon residue. Other products may also be released depending on the specific chemical composition of the feedstock used.

3). Steam Generator (as one of the Components of Biomass Power Plants)

A biomass boiler generates electricity by heating water to produce steam, which is subsequently used to drive a turbine and activate a generator.

The steam generator is the component of a biomass power plant that is designed specifically for handling steam.

It works on the simple principle of fluid temperature-pressure proportionality; whereby increase in temperature of a fluid leads to increase in pressure.

When heat is produced from biomass that is burnt in the boiler/combustor, this heat is captured by the steam generator through conduction-based thermal energy transfer. The captured heat then boils and vaporizes water in the generator to produce steam.

It must be mentioned that the term 'steam generator' can be used to refer to the entire electricity generation unit of a power plant, which includes the turbine and electric generator. However, these components are essentially different in their functions.

4). Electric Generator

The electric generator in a biomass power plant operates based on the principle of electromagnetic induction, which is the same principle behind most electric generators.

It converts the mechanical energy of a rotating conductor in a magnetic field, to electricity in the form of charges flowing through the conductor.

The mechanical energy itself comes from a turbine, which is made to rotate when steam from the steam generator exerts pressure on its blades.

A biomass generator costs between $4,000 and $200,000 on average as of 2023, and constitutes a significant portion of the total capital cost of a bio power plant.

The amount of electricity which biomass can produce is approximately 4.44 kWh per kilogram (or 16 MJ in energy form). This value is derived from averaging the calorific value per kg of commonly-used biomass fuels.

The performance of the electric generator in a biomass power plant is very crucial as a determinant of overall efficiency. Part of optimization efforts in the field of bioenergy technology is focused on increasing energy efficiency and reducing the rate of energy loss, from the electric generator.

5). Cooling Unit (as one of the Components of Biomass Power Plants)

The design and type of cooling unit that is used in a biomass power plant depends on factors like cost consideration, and scale of operation.

The type of cooling system used in large power plants is a vertical cooling tower that operates based on the principle pressure-temperature proportionality; where temperature of the plant is reduced by allowing vapor from the steam generator to escape (into the tower) and be condensed at low pressure, afterwards of which the water recovered is returned to the system for circulation [4].

For smaller bio power plants, a circulatory recycling cooling unit is used, which works based on heat exchange between a cool circulating fluid and a body of higher temperature. This mechanism is similar to that which is used to cool the reactor core of nuclear power plants.

Pumps represent a secondary component of biomass power plants, which could be used for fluid circulation in the cooling unit.

6). Emissions Control

Five emissions from biomass combustion in bio power plants are; carbon dioxide (CO2), nitrogen oxides (NOx), particulate matter (PM), sulfur dioxide (SO2), and carbon monoxide (CO) [1].

Others toxins like mercury and lead may also be emitted.

These emissions can contribute to global warming and air pollution, especially when released in large volume over extended periods of time.

Biomass contributes to CO2 emissions, accounting for more than 10 percent of global atmospheric carbon dioxide as of 2020.

While this contradicts the claim that biomass is carbon neutral, it only occurs because there are no (or insufficient) measures to replace biomass that is used as fuel or disposed in landfills, through practices like reforestation and afforestation.

The emissions control component of biomass power plants comprises of all equipment used to treat gaseous effluents from the boiler and steam generator units. These equipment include filters, scrubbers and carbon capture sub-units.

Effective functioning of the emissions control unit will result in gaseous emissions that have been mostly stripped of their greenhouse gas and toxin content, and are safe for the ecosystem.

7). Ash Handling Unit (as one of the Components of Biomass Power Plants)

Ash handling system in a power plant is a collection of equipment used to collect, and remove ash derived from combustion of feedstock in the boiler.

Equipment used for ash collection include pneumatic soot-blowers, and ash mixers. Ash is removed from the boiler by physical means, using pressure from the soot blower or any other equipment.

Ash removal is essential for preventing loss of boiler efficiency, and separating useful biomass residue that can be recycled as fuel [3]. Effective ash removal systems can also help reduce the cost of bash disposal [2].

Conclusion

Components of biomass power plants are;

1. Fuel Inlet

2. Furnace/Combustion Chamber/Combustor

3. Steam Generator

4. Electric Generator

5. Cooling Unit

6. Emissions Control

7. Ash Handling Unit

References

1). Aljaafari, A.; Fattah, I. M. R.; Jahirul, M. I.; Gu, Y.; Mahlia, T. M. I.; Islam, A.; Islam, S. (2022). "Biodiesel Emissions: A State-of-the-Art Review on Health and Environmental Impacts." Energies 15(18):6854. Available at: https://doi.org/10.3390/en15186854. (Accessed 13 February 2023).

2). James, A. K.; Thring, R. W.; Helle, S.; Ghuman, H. S. (2012). "Ash Management Review—Applications of Biomass Bottom Ash." Energies 5(12). Available at: https://doi.org/10.3390/en5103856. (Accessed 13 February 2023).

3). Jonghun, L.; Junghwan, K. (2022). "Optimizing Ash Deposit Removal System to Maximize Biomass Recycling as Renewable Energy for Co2 Reduction." Available at: https://ssrn.com/abstract=4002407, http://dx.doi.org/10.2139/ssrn.4002407. (Accessed 13 February 2023).

4). Jovcevski, M.; Lakovic, M.; Baniac, M. (2018). "Improving the energy efficiency of a 110 MW thermal power plant by low-cost modification of the cooling system." Energy & Environment 29(2):0958305X1774742. Available at: https://doi.org/10.1177/0958305X17747428. (Accessed 13 February 2023).

5). Mikielewicz, D.; Kosowski, K.; Stępień, R.; Włodarski, W.; Orynycz, O.; Tucki, K.; Piwowarski, M. (2019). "Gas Turbine Cycle with External Combustion Chamber for Prosumer and Distributed Energy Systems." Energies 12(18):3501. Available at: https://doi.org/10.3390/en12183501. (Accessed 13 February 2023).

6). Srinivas, T.; Reddy, B. V. (2014). "Hybrid solar–biomass power plant without energy storage." Case Studies in Thermal Engineering 2. Available at: https://doi.org/10.1016/j.csite.2013.12.004. (Accessed 13 February 2023).

7). Strzalka, R.; Erhart, T. F.; Eicker, U. (2013). "Analysis and optimization of a cogeneration system based on biomass combustion." Applied Thermal Engineering 50(2):1418–1426. Available at: https://doi.org/10.1016/j.applthermaleng.2011.12.039. (Accessed 13 February 2023).

8). Suik, H.; Pihu, T.; Molodtsov, A. (2008). "Wear of the fuel supply system of CFB boilers." Oil Shale 25(2). Available at: https://doi.org/10.3176/oil.2008.2.03. (Accessed 13 February 2023).

9). Westover, T. L.; Hartley, D. S. (2018). "Biomass Handling and Feeding." Advances in Biofuels and Bioenergy. Available at: https://doi.org/10.5772/intechopen.74606. (Accessed 13 February 2023).