Biomass Energy: Conversion Processes, History, and Fuel Types

Biomass is converted to energy through various processes, including:

• Direct combustion (burning) to produce heat, and pressure
• Thermochemical conversion to produce solid, gaseous, and liquid fuels
• Chemical conversion to produce liquid fuels
• Biological conversion to produce liquid and gaseous fuels

History of…

FIRE!

Man harnessed fire, differentiating us from animals. Our energy system is based on this. Wood was commonly used, but with the discovery of oil, it became more accessible and had higher energy. Biomass is a form of solar energy. Plants convert solar energy to sugars through photosynthesis. Biomass systems use plant-based material as fuel for heat and electricity, such as wood, energy crops, agricultural residues, and waste.

Learn how biomass creates power from waste in this engaging video by the National Renewable Energy Laboratory (NREL).

In 2019, 57 EJ (exajoules) of energy were produced from biomass, compared to 190 EJ from crude oil, 168 EJ from coal, 144 EJ from natural gas, 30 EJ from nuclear, 15 EJ from hydro, and 13 EJ from wind, solar, and geothermal combined – WIKI

The 2020 Global targets for renewable energy (RE) were set at 20%, but we have only achieved 13.8%, falling significantly short. To provide a brief overview of biomass energy generation systems, let’s focus on the main points.

This field is vast, but I believe starting with a brief overview of biomass energy generation systems will help us see the bigger picture.

Biomass energy converting systems.

Fire and ICE!

ICE refers to the Internal Combustion Engine, which utilizes pressure generated by the expansion of combustion gases instead of relying solely on heat. These systems are well-suited for residential applications due to their compact size and proven efficiency over many years. There are conversion kits available that allow generators to run on Dual Fuel options like LPG, NG, or Biogas. Petrol engines can achieve a thermal efficiency of up to 40%, while diesel engines, operating at higher pressures, can reach an impressive 55%. However, in regular passenger cars, these numbers are halved due to varying operating speeds. Typically, heat is considered wasted energy, but in a Co-Generation system, it can be harnessed to increase overall output and efficiency. For instance, hot exhaust gases can be utilized to heat water, driving the efficiency up to 60-70%!

Heat Engines

Scottish engineer and physicist William Rankine made significant contributions to the fields of thermodynamics and engineering. Rankine developed a comprehensive theory for steam engines and all types of heat engines. His groundbreaking work laid the foundation for modern large-scale utility energy power stations, typically powered by coal. In Rankine’s design, water is heated to high pressure steam which drives a turbine, extracting heat energy through steam expansion. The turbine’s condensate is then cooled and pumped back to the boiler under pressure in a closed loop system. All utility power units today operate on what is known as the Rankine Cycle. Rankine’s focus on energy conservation and efficiency led to more effective engine designs and a reduced environmental impact. He worked closely with engineers to bring his ideas to life in practical applications.

Gasification of Biomass

Gasification is a method that transforms carbon-based materials into Synthesis Gas (SynGas) without the use of oxygen. It is essentially a type of chemical reaction that occurs in a combustion zone, converting the raw materials into SynGas. During World War II, the Imbert gasifier was used in Scandinavian countries to power vehicles using wood as a fuel source. SASOL employs the Fischer-Tropsch process to convert SynGas into liquid hydrocarbons. Similar processes are used to produce biochar and charcoal, but the focus is on producing charcoal, with the SynGas being released as a byproduct. The biomass is heated in the absence of oxygen until the temperature reaches the boiling point, at which point the process is halted.

Biomass as Fuel Types

Biodiesel

Transesterification is a chemical process that converts vegetable oils, animal fats, and greases into fatty acid methyl esters (FAME) for biodiesel production. FAME is synthesized by using Methanol and Sodium Methylate as catalysts. Glycerol is subsequently added to remove catalysts and water. Although the process is simple, it raises concerns due to the use of foodstuffs, as demonstrated by the recent increase in Sunflower oil prices in South Africa. Diesel engines ignite fuel through pressure, while petrol engines use ignition/spark. Hybrid Internal Combustion Engines (ICE) utilize both. When diesel engines function as biogas generators, a spark plug is installed to initiate combustion, resembling petrol engines. Producing biodiesel from algae is promising but not yet profitable. However, escalating prices could change this soon. Biodiesel is appealing because it has similar specific energies to diesel and requires minimal modifications to run on current diesel generators.

Biofuel

Biofuel is a renewable fuel derived from organic matter such as plants, particularly Ethanol which is also known as alcohol. Ethanol is used as a substitute for petrol and has a long history of production by humans. Aerobic microbes are used to ferment plant sugars into alcohol. However, converting food into fuel is not sustainable in the long term. Efforts are being made to use cellulose and hemicellulose, which are non-edible fibrous components of plants, for biofuel production. Unlike Biodiesel, ethanol can only be used as a supplement up to 15% (E15) in current internal combustion engines (ICE) due to its lower specific energy and different combustion characteristics.

Biogas

Biogas is a renewable biofuel made from organic waste like agricultural leftovers, food scraps, and sewage. It can be used for heating, making electricity, and fueling vehicles. Biogas is produced through anaerobic digestion, where bacteria break down organic matter in the absence of oxygen to create methane gas.

Biogas has several advantages as an energy source:

• It is a cleaner alternative to fossil fuels.
• It also helps to reduce waste by utilizing organic materials that would otherwise be disposed of in landfills
• Can be used as a source of renewable energy in rural areas where there may be limited access to electricity grids.
• It can be used for cooking, heating, and lighting, providing a reliable and affordable energy source.

Despite its benefits, biogas production also presents some challenges. Variability in the availability and consistency of organic waste materials can impact the efficiency and reliability of biogas production. Furthermore, setting up the necessary infrastructure for biogas production and distribution can be expensive, particularly in remote areas.

Three fundamental types of Biogas Digestors:

According to reports, around 80% of China has adopted Chinese-style fixed dome biogas systems for effluent treatment. These systems are praised for their flow-through design, allowing waste to enter from one side, compost to be produced on the other side, and biogas to be collected from the top.

The Indian or floating drum system enables waste to be fed into the reactor in batches. The dome is weighted to produce pressurized gas.

Taiwan, also known as the bladder system, is a popular choice for biogas commercial projects due to its affordability and convenient installation process. This system is highly effective in treating large quantities of animal waste.

Biogas reactors/digesters are more suitable for Municipal scale due to their lower Specific Energies, as shown in the table below. However, current underground septic tanks can be easily converted into biogas reactors/digesters by combining Chinese dome technology with Taiwan tubular technology, using readily available “bladder tanks” on the market. These tanks already have inlet/outlet and gas supply fittings, making conversion a simple process. A paradigm shift is all that is needed to make this conversion.

Despite the majority of renewable energy projects being biomass-based, it is surprising that none have reached residential level yet. This may be due to NIMBYism, as homeowners may be hesitant to have waste processing in their own yards.

BioChar

Biochar is a carbon-rich material created from biomass using pyrolysis, a process that converts the material through heat. Unlike the production of biogas, pyrolysis takes place at lower temperatures (400-500 °C) to produce more char. Higher temperatures (above 700 °C) are more conducive to creating liquid and gas fuel components (Syngas). Pyrolysis at higher temperatures is quicker, with a process that takes seconds rather than hours. However, the rate of heating can reduce the amount of biochar produced when the temperature falls within the range of 350-600 °C. Typically, the yields are 60% bio-oil, 20% biochar, and 20% syngas. In comparison, slow pyrolysis can generate a significantly higher amount of char (approximately 35%), which can improve soil fertility. Slow pyrolysis, also known as charcoal production, focuses on maximizing charcoal output while minimizing syngas, with the production of liquid bio-oil and ‘wood vinegar’ instead.

Charcoal was only found in the 2000’s to be the reason why the Aztecs could have such large populations in nutrient deficient tropical areas – this is discussed in Blog “Fungi and Plants“.

Biomass Electrical Power Generation

There are numerous categories of biomass and various techniques to extract energy from it, known as the specific energy content.

The energy content of dry biomass fuels typically ranges from 17 to 19 MJ/kg, varying based on density and moisture content. Biomass fuels generally have low levels of nitrogen and sulphur, leading to relatively low emissions of SOx and NOx.

Hydrogen possesses the highest energy content, albeit with the caveat of a comparatively low density. However, the rationale behind utilizing hydrogen power is still valid. The primary concern lies in the storage and, naturally, the safety aspects.

Biodiesel has a high energy content of 42 MJ/kg, but this is currently derived from processed foodstuffs [vegetable oil]. So, there is a concern about food security, which is also applicable to ethanol with its lower specific energy of 30 MJ/kg.

Syngas and biogas are versatile gas mixtures that can be transformed into valuable products, including hydrogen and methane, through efficient processing.

Charcoal deserves more emphasis as it can be utilized on-site in our coal-fired power stations to eradicate extensive areas of ‘Invader Bush’.

Efficiency of Conventional Energy Generation

Rankine cycles in large commercial coal-fired power stations are theoretically limited to an efficiency of 42%. However, most power stations operate at efficiencies of about 30-34%. Medupi, which utilizes newer high-temperature materials and operates at supercritical pressure ranges, achieves an efficiency of 35.6%.

The efficiency of ICE, mainly used for home generation and already installed in numerous locations, varies significantly. Petrol engines operate at an efficiency of approximately 30-35%, while diesel engines exhibit a higher efficiency of 40-45% due to their utilization of less fuel as a result of a higher compression ratio.

Cost of Biomass Generation:

Biomass generation is mainly used by utility companies due to its lower specific energies. However, it can also be utilized by current utilities as a means of converting conventional generation to biomass. As demonstrated earlier, charcoal is a superior alternative to the low-grade coal currently used in South African power stations, making it a relatively straightforward transition. An option for Generation is to incorporate a percentage of charcoal into coal, known as the gasohol route, which would have an immediate impact. Sufficient intruder bush exists in South Africa to supply the smaller units for pilot runs.

Municipal dumps can be modified for landfill gas collection and supplemented with SynGas from waste gasification. On the home front, conversion to gas can be supplemented with biogas from septic tank conversion. It is strange that there are not more products on the market, considering that China has an 80% biogas installation rate.

Biogas can supplement other renewable hybrid energies such as wind and solar by being connected to ICE generators. Biomass is suitable for water and space heating and is made possible through the miracle of photosynthesis and solar energy.

NEXT: Solar Energy

PREVIOUS: Hydroelectricity

Back to Course Intro Table of Contents.

If you have found value in the insights and guidance provided in this course, I kindly request your consideration in making a donation to support the IMBY cause. Your contribution will directly support our Sustainability Test Station (STS), where we relentlessly pursue innovative solutions to pressing challenges in Sustainable Development, to bring out articles like:

•  Free Soda Bottle hydroponic plans
• 5 Essentials for Vermiculture
• 3 ways to make your own Mushroom spawn.