Biogas EnergyRenewable Energy, Sustainable Living

Biogas

We deliver biogas system designs and provide critical components to make your biogas system reliable, easy to maintain, cost-effective with significant positive environmental, social-economic and financial impact! We have on staff one of the best and very experienced biogas experts in Asia Pacific. Our customized biogas generation technology is one of the best high-loading AD system on the market with very reliable and high COD or TS conversion rates. We also have our own H2S scrubbing system. This along with our AD biogas system is all captured in our proprietary biogas control system.

Pretreatment - We understand biological eco-systems and focus on customized pretreatment system design for different substrates. Different substrates need different pretreatment considerations. This is SUPER critical!

Fermentation Digester - We understand anaerobic digester bugs. There are the mesophilic (35C) and the thermophilic (55C) types. Each biological system has its own characteristics. The digester design must be able to allow the bugs or bug types to thrive and at the same time stay in balance and co-exist.

Our specialty is in Continuous Stirred Tank Reactor (CSTR)

  • Capable of high TS concentration from 8~12%
  • Designed with agitator, reflux and discharging device to ensure full mixing
  • Insulated to ensures stable fermentation temperature all year round
  • Can operate more than 8,500 hours per year

Desulfurization - Our proprietary biological desulfurization technology uses patented technology to provide the most stable H2S reduction with performances down to single digit ppm while being extremely cost competitive. Desulfurizing bacteria is a kind of aerobic microbe. The filling elements of scrubber houses the bacteria, which covert H2S into S and H2SO4 under particular conditions. The necessary oxygen is added by means of direct dosing of scrubber and air diffuser of aeration. The recycling liquid provides dissolved oxygen, water and nutrients for the bacteria. The biochemical reaction is as follow:

  • H2S+2O2→H2SO4
  • 2H2S+O2→2S+2H2O

The Asia-Pacific region stands on the threshold of substantial growth in power generation with renewable biogas fuels. Palm oil, cassava, sugar cane, livestock and other agricultural operations, municipal sewage treatment plants, abattoirs and landfills, offer major potential as methane fuel sources. Biogas-to-energy projects can provide electricity for export to the grid or for captive use sustainably by using reciprocating gas engine-generator sets. This effective and efficient use of biogas can mitigate waste management concerns and at the same time destroy a potent greenhouse gas, while delivering strong economic returns.

Green power and heat production from biogas is one of the most reliable and consistent forms of renewable energy. Biogas can be formed from different substrates or raw feedstocks. This paper examines the potential and successful conversion of various raw feedstocks to biogas. Once the biogas is produced, the follow-on conversion to power and heat can provide very efficient utilization of the valuable biogas energy.

Biogas Basics

Biogas fermentation, also known as anaerobic digestion, refers to the process of biogas production through decomposition of organic matter by many varieties of fermentation microorganism under anaerobic conditions. Biogas production is a complex biological process.

The essence of biogas fermentation is a series of microorganism activities. In microbiological terms, biogas fermentation is a process of cultivating anaerobic bacteria that have high activity to obtain high biogas yield. In biogas fermentation, the raw material is the chief link in the process as the substrate of biogas production. The characteristics of the raw material, such as temperature, pH, carbon-to-nitrogen ratio, nourishment, microelements, toxic matter and others, determine the rate of digestion, the fermentation time, and the rate of biogas production.

All kinds of livestock or animal waste, such as pig, cattle and chicken manure, are good raw materials for biogas fermentation. Furthermore, all kinds of crop residue, agricultural castoffs and wastewater from production of alcohol, starch, palm oil and bean products can be used as raw material for fermentation.

Biogas Technology

A typical CSTR biogas plant includes the following major components as shown below

 

 
  • Pretreatment
  • Digester
  • Desulphurisation
  • Gas Storage

No matter what type of biogas technology is selected, pretreatment of substrate is usually the most important precondition to ensure the stable operation of the digester.

Fermentation is the core technology of a biogas plant. Anaerobic digestion has a variety of classification methods. Continuous stirred tank reactor (CSTR) is one of the most successful and popular types.

CSTR is a reactor with stirring device that keeps the fermentation materials and the microorganisms in the state of complete mixing. The efficiency is obviously much higher than in a conventional digester like a covered lagoon. Thus, CSTRs have been commonly used in mid- to large-scale biogas projects, since far more compact than lagoon-based digesters. Additionally, a properly designed, constructed and installed mid- to large-scale steel tank CSTR system is generally much safer than a covered lagoon system, which is prone to tears and leakage.

Operationally, the substrate is periodically or continuously added to the CSTR digestion tank. After mixing and contact with the anaerobic bacteria in the tank via anaerobic microorganism adsorption, digestion and biodegradation, the organic matter is converted into biogas. The biogas is discharged from the top, while the fermented substrate is discharged from the reactor.

Biogas produced through anaerobic digestion mainly contains CH4 and CO2, together with some trace gases, such as H2, N2 and H2S. Usually, the percentage of CH4 is 55-65%, and that of CO2 is 35-40%. Attention must be paid to H2S in the biogas. There are two sources for H2S production: the reaction of removing hydrogen sulfide and deamination after proteolysis, and the deoxidizing of SO4- from sulfates in the substrate. It is essential to note that H2S can become sulfuric acid when it dissolves in water. Sulfuric acid is highly corrosive and can severally damage CHP equipment. H2S is also toxic and as such poses personnel safety concerns. Although both CH4 and CO2 are gases without color, odor and toxicity, biogas has odor and toxicity largely due the presence of H2S.

Bio-desulphurization refers to the process that converts H2S into S through the metabolizing effect of desulphurization bacteria under appropriate temperature, humidity and slight oxygenation. The reaction process is:

H2S + 2O2 → H2SO4
2H2S + O2 → 2S + 2H2O

The key point of the bio-desulphurization method is controlling the concentration of dissolved oxygen in the reaction device based on the changes of the H2S concentration and the redox potential.

In medium to large biogas projects, the output of biogas is sometimes variable due to fluctuating feedstock processing rates. To reasonably and effectively balance biogas production and consumption, gas storage is often adopted. The volume of the gas storage tank used for power projects is typically calculated based on 10% of daily gas production.