Biological Cleanup of Biogas

The most valuable component of biogas is methane (CH4) which typically makes up 60%, with the balance being carbon dioxide (CO2) and small percentages of other gases. However, biogas also contain significant amount of hydrogen sulfide (H2S) gas which needs to be stripped off due to its highly corrosive nature. Hydrogen sulfide is oxidized into sulfur dioxide which dissolves as sulfuric acid. Sulphuric acid, even in trace amounts, can make a solution extremely acidic. Extremely acidic electrolytes dissolve metals rapidly and speed up the corrosion process.

The corrosive nature of H2S has the potential to destroy expensive biogas processing equipment. Even if there is no oxygen present, biogas can corrode metal. Hydrogen sulphide can become its own electrolyte and absorb directly onto the metal to form corrosion. If the hydrogen sulphide concentration is very low, the corrosion will be slow but will still occur due to the presence of carbon dioxide.

The obvious solution is the use of a biogas cleanup process whereby contaminants in the raw biogas stream are absorbed or scrubbed. Desulphurization of biogas can be performed by biological as well as chemical methods. Biological treatment of hydrogen sulphide typically involves passing the biogas through biologically active media. These treatments may include open bed soil filters, biofilters, fixed film bioscrubbers, suspended growth bioscrubbers and fluidized bed bioreactors.

Biological Desulphurization

The simplest method of desulphurization is the addition of oxygen or air directly into the digester or in a storage tank serving at the same time as gas holder. Thiobacilli are ubiquitous and thus systems do not require inoculation. They grow on the surface of the digestate, which offers the necessary micro-aerophilic surface and at the same time the necessary nutrients. They form yellow clusters of sulphur. Depending on the temperature, the reaction time, the amount and place of the air added the hydrogen sulphide concentration can be reduced by 95 % to less than 50 ppm.

Most of the sulphide oxidising micro-organisms belong to the family of Thiobacillus. For the microbiological oxidation of sulphide it is essential to add stoichiometric amounts of oxygen to the biogas. Depending on the concentration of hydrogen sulphide this corresponds to 2 to 6 % air in biogas. Measures of safety have to be taken to avoid overdosing of air in case of pump failures.

Biofiltration

Biofiltration is one of the most promising clean technologies for reducing emissions of malodorous gases and other pollutants into the atmosphere. In a biofiltration system, the gas stream is passed through a packed bed on which pollutant-degrading microbes are immobilized as biofilm. A biological filter combines water scrubbing and biological desulfurization. Biogas and the separated digestate meet in a counter-current flow in a filter bed. The biogas is mixed with 4% to 6% air before entry into the filter bed. The filter media offer the required surface area for scrubbing, as well as for the attachment of the desulphurizing microorganisms. Microorganisms in the biofilm convert the absorbed H2S into elemental sulphur by metabolic activity. Oxygen is the key parameter that controls the level of oxidation.

The capital costs for biological treatment of biogas are moderate and operational costs are low. This technology is widely available worldwide. However, it may be noted that the biological system is capable to remove even very high amounts of hydrogen sulphide from the biogas but its adaptability to fluctuating hydrogen sulphide contents is not yet proven.

How An Increase in Demand of Epoxy Resin Can Fuel the Need for Clean Energy

Epoxy resin is a kind of reactive prepolymer and polymer that contains epoxide groups. It is important to note that epoxy resin is different from other polyester resins in terms of curing. Unlike other resins, instead of using a catalyst as a curing agent, it is cured by an agent known as the hardener. It possesses many desirable properties such as high tensile strength, high adhesive strength, high corrosion resistance, and excellent moisture & chemical resistance. It is also resistant to fatigue, has a long shelf life, and has good electrical and insulating properties. The ability of epoxy resins to be used in various combinations and reinforcements makes it the foundation of a plethora of industries, including clean energy systems.

Applications of Epoxy Resins

Because of the versatile properties of epoxy resins, it is used widely in adhesives, potting, encapsulating electronics, and printed circuit boards. It is also used in the form of matrices for composites in the aerospace industries. Epoxy composite laminates are commonly used for repairing both composite as well as steel structures in marine applications.

Due to its high reactivity, epoxy resin is preferred in repairing boats that have been damaged by impact. Its low shrinking properties and ease of fabrication make it well suited for many tooling applications such as metal-shaping molds, vacuum-forming molds, jigs, patterns etc.

Use of Epoxy Resins in Clean Energy

A variety of industries have been actively trying to find a path that’s moving towards a society that puts less load on the the environment and also contributes towards reducing the carbon footprint. The accelerated use of epoxy resins in generating renewable energy has lead to a rise in its production demand. This is why the epoxy resin market is projected to witness a high demand and growth rate by 2022. Here are some of the sectors contributing to the production of clean energy and how they utilize epoxy resin for their functioning:

  • Solar Energy

The harnessing of solar energy dates back to 700 B.C, when people used a magnifying glass to focus the sun’s rays to produce fire. Today solar power is a vigorously developing energy source around the globe. It not only caters to the rising energy requirements but also the need to protect the environment from the exploitation of exhaustible energy resources.

A piece of average solar equipment endures intense environmental conditions such as scorching heat, UV radiations, bitter cold,  pouring rain, hail, storms, and turbulent winds. To withstand such conditions, the sealing and mounting application of epoxy resins increase the environmental tolerance of the solar equipment.

With their high mechanical strength, impressive dimensional stability and excellent adhesion properties, they are used to protect the solar panels from a wide range of temperatures. Epoxies are cheap, less labor-intensive and easy to apply.

  • Wind Energy

The global wind industry has quickly emerged as one of the largest sources of renewable energy around the world. The wind energy in the U.S. alone grew by 9% in 2017 and today is the largest source for generating clean energy in the country. With such a tremendous demand for wind power, the need for fabricating bigger and better wind turbine blades is also rising. The industry is in a dearth of long-lasting blades, that endure the harsh climatic conditions and wear tear and are able to collect more wind energy at a time.

Sealing and mounting application of epoxy resins increase the environmental tolerance of the solar equipment

Epoxy thermosets are used for making the blades more durable because of their high tensile strength and high creep resistance. Mixing of epoxy resins with various toughening agents and using them on the blades have shown positive results towards making the blades corrosion resistant and fatigue-proof.

  • Hydropower

Hydropower is an essential source of renewable and clean energy. As the hydropower industry is developing rapidly, the solution for protecting the hydropower concrete surfaces against low temperatures and lashing water flow has also been looked into.

As a solution to this issue, epoxy mortar, a mixture of epoxy resins, binder, solvent, mineral fillers, and some additives has proven to be the most effective material used for surface protection. Owing to the properties like non-permeability, adhesive strength, anti-erosive nature, and non-abrasiveness, epoxy mortar paste has been used as a repairing paste in the hydropower industry.

Over the last few decades, epoxy resins have contributed immensely in the maintenance and protection of clean energy sources, helping them to become more efficient and productive.

Final Thoughts

While many argue that factors like a relatively high cost when compared to petroleum-based resins and conventional cement-mortar alternatives has affected the epoxy resin market growth, the fact remains that epoxy resin never fails to deliver top-notch and unmatchable results in the areas of application.