In this article we identify the 5 most critical factors in the design of every Biogas Plant.
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Read on for our list and discussion of the 5 most vital design factors which it is essential for every AD Plant designer to get right, for successful stable AD plant operation.
For the benefit of our readers. We recommend that all of our readers note each point carefully.
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If there is one thing for certain about biogas plants it is that the customer's requirements will continuously evolve throughout the life of any biogas plant. It is difficult, if not impossible to anticipate many of those changes, so the flexibility to alter biogas plant configuration to suit feedstocks as needed and in a manner that suits the client's particular site requirements, is essential.
Even though the set-up for each client is carefully customized for each project, the design must incorporate a level of versatility that will ensure that the configuration of the equipment can be changed to maintain efficient operation.
This must allow both for biomass inputs which continually vary, and as the marketable output products also change according to demand and new technological developments come available.
We consider this so important that we recommend that every biogas plant includes an automatic dosing module within their biogas plant that ensures that all the biomass constituents will be adequately controlled, including the feedstock input rate, and pH adjustment dosing and any micronutrient addition, to match the requirements of continually varying feedstock sources and composition.
The module has to be able to provide a high degree of control, in order to achieve a high level of process efficiency, without unnecessarily limiting the plant operator's choice of biomass source/ type.
To keep the digester performing at its best, you must understand the dosing parameters and make timely changes to the feedstock and micronutrient dosing. You will need to be able to show maximum efficiency in the reduction of volatile solids and chemical oxygen demand (COD) in the substrateWhen a gas pressure alert situation is detected, you must implement an interlocked alarm device that causes reactor feeding to halt automatically.
To monitor, record, and display data for continuously monitored parameters, you must employ Supervisory Control and Data Acquisition Equipment (SCADA).
Apply a design philosophy, which involves plants running at the highest feasible process temperature. By doing so, it makes it possible to take the fullest advantage of the natural ability of the micro-oganisms to digest the substrate within their digesters at the highest possible biogas (methane) producing potential.
You'll need to keep an eye on the temperature and gas pressure of the digester at all times. Within your management system, you must identify and establish all operating parameters and constraints.Depending on the environment used and the system architecture, you must determine the optimal operating temperature.
The temperature of the digester must be kept within +/- 2 degrees Celsius of the working temperature.
Reactor design needs to include a stirring and agitation system that gets as close as possible to providing a completely stirred reactor. Nature Biogas, for example, has developed its own technology for this. It is optimized for low energy use to minimize the draw on the plant's own electricity generation. The importance of this lies in keeping operating costs low while producing high gas production rates for the feed material utilized must never be underestimated.
Use a remote-controlled SCADA monitoring and operating system at all their anaerobic digestion plants.
All indications of plant status are viewable, and access to all operating system adjustments are available, via a smartphone app.
This is important to ensure that the gas production process is kept within stable (high efficiency) reactor conditions. And, can be accessed at any time to ensure the smooth running of their plants, which normally run day and night 365 days a year.
Flexibility ensures that the plant can adapt to changing feedstocks, outputs, and evolving client needs, making the system more resilient and future-proof.
Automated dosing provides precise control over feedstock and additives, ensuring efficient digestion and minimizing operational disruptions.
Maintaining an optimal and stable temperature maximizes microbial activity, leading to higher methane yields and process stability.
Energy-efficient mixing and operations reduce costs and improve overall plant sustainability by lowering the energy required for processing.
SCADA systems allow for real-time monitoring, remote control, and precise adjustments, ensuring stable operations and quick response to issues.
Pressure and vacuum relief systems, coupled with SCADA for monitoring and documentation, are critical for handling pressurization and emission events safely.
[First published October . Updated July . Latest update with Key Takeaways and FAQs added: November .]Merriam Webster defines biogas as “a mixture of methane and carbon dioxide produced by the bacterial decomposition of organic wastes and used as a fuel.”
Biogas is a renewable energy source produced from raw materials like food waste, manure, sewage, agricultural waste, and plant material. The process that transforms this organic waste into a mix of gases is called anaerobic digestion and is a natural fermentation process in which bacteria break down the organic matter into its components until all that is left are gases and a residue called digestate.
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The biogas production process is practically natural fermentation in an oxygen-free environment. In nature, it can occur in marshes and swamps, where water helps to seal natural chambers that lack oxygen.
Biogas plants are artificial environments, but the process inside the sealed digesters is 100% natural.
At first, biowaste must be crushed into smaller pieces, and, often, some water is added to accelerate the chemical reactions inside the digester. Then, bacteria decompose organic matter to obtain the right mix of gas.
The process consists of four stages:
This process is optimized when the temperature inside the digester stays between 30 to 38 degrees Celsius (86-100 Fahrenheit). The procedure’s success depends on the chemical composition of the waste fed into the digester. If the raw materials are too acid or have too much nitrogen, you risk disturbing the balance inside the digester, resulting in inconsistent production levels.
Moreover, not all organic wastes have the same fermentation timeline. Bacteria can easily break down food waste, fats, oils, and greases, but livestock waste can be more challenging when fed into the digester. By mixing multiple types of waste inside the digester (co-digestion), you can accelerate the fermentation process and generate consistent amounts of biogas.
Biogas composition consists primarily of methane and carbon dioxide, but the mixture of gases also includes a series of other substances and sometimes traces of water.
The chemical composition of biogas:
[Tabel from: https://www.biogas-renewable-energy.info/biogas_composition.html]
The chemical composition of biogas varies with a series of factors, from the quality of the organic waste put inside the digester to the digester’s feeding rate and the temperature and humidity inside the digester.
As it contains hydrogen sulfide, carbon dioxide, and water, biogas is highly corrosive, so all the systems built for producing, transporting, storing, and using it must be made with specific materials.
Biogas must often be treated to enhance its properties — different chemical reactions remove some components, such as hydrogen sulfide, water, or carbon dioxide, to obtain biomethane. This removal process requires a more complex system for producing biogas, including working with corrosive substances.
Thanks to its similar properties, biogas can substitute natural gas with a significant impact on the environment. Here’s how biogas composition can change its physical characteristics and how they’re different from natural gas: Table
If you use equal amounts of biogas and natural gas, biogas produces twice fewer calories by combustion.
Biogas also helps keep manure from landfills and, therefore, reduces the amount of methane released directly into the atmosphere. Methane is a greenhouse gas with effects 34 times more potent than carbon dioxide’s, so by redirecting it towards biogas production, we get to reduce its impact on climate change.
It’s also important to note that when biogas is combusted (when used as cooking gas, for instance), it still generates carbon dioxide. However, it all comes from plants, which had naturally removed this gas from the atmosphere. Therefore, these emissions are considered carbon-neutral, as the amounts of new CO2 added to the atmosphere are minimum.
Thanks to its physical characteristics, biogas can be used as an alternative to fossil fuels. It can be used similarly to natural gas in water and space heating, drying, absorption cooling, steam and electricity production, and transportation. The more organizations and governments become aware of fossil fuel’s impact on climate change, the more they’re interested in innovating and finding new ways to shift to clean energy sources, including biogas usage.
The most popular applications for biogas are:
1. Cooking gas
Direct combustion is a more straightforward way to use biogas to generate heat and lightning, being an increasingly popular alternative to fossil fuel energy in developing countries. A gas pipe connects the digester to a biogas cooking stove, so you can produce cooking gas and manage waste with minimum impact on the environment.
2. Combined heat and power
A more complex way to use biogas is co-generation or combined heat and power process (CHP), in which case you simultaneously produce electricity and heat with biogas. This application is more suitable for industrial biogas plants that manage large amounts of waste than for domestic use. These systems can supplement energy production in rural areas that otherwise are forced to remain off-grid.
3. Transportation
Biogas can also be used as vehicle fuel if purified and treated to match natural gas quality. The extra effort can pay off, as this shift could significantly impact climate change. By switching to biogas, the transport sector can reduce greenhouse gas emissions by 60 to 80%, compared to gasoline and diesel.
Biogas advantages
Biogas disadvantages:
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