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Worldwide interest in renewable energy sources is gathering momentum. As a result, biogas production is growing steadily as more manufacturers are setting up plants to produce biogas. By Farah Nazurah

Biogas is a renewable energy source with tremendous potential and is one of the most efficient and effective options among the various other alternative sources of energy currently available, such as wind, geothermal or solar energy. Natural materials that can be used for its production include organic waste, straw, wastewater, liquid manure, and sewage sludge.

The global market for biogas plants is growing as it is an  alternateco-friendlyive source of fossil fuel, and is projected to reach US$10 billion by 2022, according to a report by Global Industry Analysts.

Bioenergy Potential In Southeast Asia

Countries in Southeast Asia have a vast bioenergy potential due to the abundant supply of biomass wastes such as woody biomass, animal wastes, agricultural residues, and municipal solid waste, etc. The region’s industrialisation and fast-growing economies have driven the need adopt the latest waste-to-energy technologies to tap into the full potential of biomass resources.

The region is currently at the forefront of domestic biogas development. China has 42.6 million biogas digester units (or biodigesters), followed by 4.7 million units in India, according to SNV Netherlands Development Organisation. Vietnam has approximately 500,000 installed biodigesters used primarily for pig farms, resulting in biogas access to approximately 2.5 million.

Sugar mills in Indonesia, Philippines, Thailand and Vietnam generate 34 million tonnes of bagasse (residue from sugarcane extraction) annually. Moreover,  Malaysia, Indonesia and Thailand contribute to 90 percent of global palm oil production which results in 27 million tonnes of waste per year in the form of empty fruit bunches, fibres and shells, as well as liquid waste.

With the conversion to liquid biofuels, biomass feedstock has the potential to provide 40 percent of the region’s projected needs for transport fuel if less were diverted to residential heating and cooking, according to International Renewable Energy Association (IRENA). The bioenergy team at IRENA also found that advanced biofuels could provide as much as 7.3 exajoules of primary energy annually in Southeast Asia by 2050, which is half of the region’s total bioenergy potential.

Biogas: A Sustainable And Economical Solution

  • Eco-Friendly Energy Production: Gas generated through biodigestion reduces greenhouse emissions and is non-polluting. As no combustion takes place in the process, greenhouse gases are not emitted to the atmosphere. Biogas plants curb the greenhouse effect significantly as methane emissions are lowered when harmful gases are transformed to biofuel. Biogas generation helps cut reliance on the use of fossil fuels such as oil and coal. The raw materials — such as food and animal waste that are inexhaustible, as well as trees and crops — used in the production of biogas are renewable, making it a sustainable option for energy.
  • Encouraging Economic Sustainability: Biogas can be compressed to achieve  the quality of natural gas and used to power automobiles. Building such plants creates green jobs and requires relatively low capital investment. According to IRENA’s projections, renewable jobs could rise to 24 million by 2030 globally. In Asia, China in particular, 3.6 million people worked in the sector in 2016, which constitutes 21 percent of global renewable energy jobs. Additionally, biogas provides nations with a hedge against fossil fuel price hikes and volatility.
  • Biogas Generation Reduces Soil And Water Pollution: Overflowing landfills enable toxic liquids to drain into underground water sources. Through biogas generation where anaerobic digestion deactivates pathogens and parasites, the incidences of waterborne diseases can be reduced and water quality can be improved. Additionally, one biogas plant is capable of saving 32 litres of kerosene and four tonnes of firewood every year, and an organic chemical plant also contributes indirectly to the protection of soil.
  • Biogas Generation Produces Organic Fertiliser: The main by-product of the biogas generation process is a slurry, a high-quality fertiliser that is higher in nutrients than compost or farmyard manure. Due to the decomposition and breakdown of parts of its organic content, the digested sludge provides fast-acting nutrients that easily enter into the soil solution, thus becoming immediately available to the growing plants. Moreover, they serve as primary nutrients for the development of soil organisms, such as through the replenishment of microorganisms lost through exposure to air in the course of spreading the sludge over the fields.

The main components of the organic content in soil — humic matter and humic acids — present in the sludge contribute to a more rapid decomposition, which in turn help reduce the rate of erosion while increasing the nutrient supply.

Condition Monitoring In Biogas Plants

Biogas is a biofuel produced from a complex biological process where a mixed culture of microorganisms is involved and various consecutive reaction steps take place. Thus, biological process monitoring is necessary to ensure a stable anaerobic digestion — a series of biological processes where one of the end products is biogas.

Biogas manufacturers can reduce critical equipment failure while maximising uptime and profits through condition monitoring, which is essential to implement to stay competitive and to achieve cost-effective plant maintenance.

Condition monitoring is based on trending and it requires that baseline conditions be defined so that there is a reference point for comparing and interpreting the obtained data. There are two different groups among the process monitoring parameters. The first are early indicators of a process imbalance, allowing plant operators to resolve the issue before the process imbalance occurs. The second group consists of parameters which define the process, and they detect and eliminate the cause of the imbalance. Although general guidelines for stability limits of different process parameters can be given, it is necessary to adapt the monitoring strategy to the specific biogas plant and its feedstock.

Overall, plant processes should stay within a standard deviation and if a change occurs in the trend, it should be linked to the affected process or mechanical variable. Plant monitoring creates a better user interface to understand the health of the machines through the gathered data, so it can be easily interpreted and used to make improvements.

Biogas Plant Instrumentation

A line of measurement equipment is necessary to operate a biogas plant, such as for silage delivery, electrical current and heat supply, and feed-in to the natural gas network. There is a continuous need for data on temperatures, flows, levels, pressures and gas composition; the right instrumentation and analytical systems will have a positive impact on plant efficiency.

Thermal meters measure gas mass flow directly without the need for additional pressure, temperature and/or density monitoring, such as the Combimass thermal flow metre by Gas Data. They operate either by introducing a known amount of heat into the flowing stream and measuring an associated temperature change or by maintaining a probe at a constant temperature and measuring the energy required to do so. One sensor measures the process temperature and the other sensor is heated to a specific temperature above this. As the flow rate increases heat gets taken away from the heated sensor.

Similar to thermal flow meters, thermal dispersion devices are based on heat transfer.  One sensor is at the process temperature and the other is being heated by a constant power.  As the flow rate increases, the temperature difference between the sensors decreases. A set point is established so when that specific temperature difference is reached the relay changes state. When used in a level or interface application it is primarily the thermal conductivity of the fluid that will provide the difference in heat transfer. 

Biomass and biogas power generation require significant monitoring and the right measurements and data are needed to ensure renewable power generation plants can be accurately monitored for plant efficiency, fuel and reagent consumption and emission monitoring.

Paving The Way For Renewable Energy

Biogas production is making an increasingly important contribution to waste management and renewable energy production. The promise and appeal of renewable energy have long been clear: clean, inexhaustible, and domestically sourced electricity could lead to significant economic and environmental benefits. Additionally, recent falling renewable energy technology costs could also help renewable energy continue to grow globally.

 

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