BIOTECHNOLOGY - V. H. Gerasymenko - 2006

Part II. Special Biotechnologies

Chapter 22. BIOTECHNOLOGIES FOR THE UTILIZATION AND BIOCONVERSION OF AGRO-INDUSTRIAL WASTES

22.3. NON-TRADITIONAL METHODS. BIOTECHNOLOGY OF BIOGAS PRODUCTION VIA ANAEROBIC WASTE DIGESTION

22.3.3. Technical and technological aspects of biogas production

22.3.3.1. Composition and global distribution of biogas plants

The process of biogas production through anaerobic Digestion takes place in specialized facilities known as biogas plants or bioenergy units (BGPs or BEUs).

A BGP is an integrated equipment set that includes (depending on its Technical and Technological level): a manure collection and storage tank, a digestion tank (fermenter, Reactor, methane tank, digestion chamber, digester), a biogas storage reservoir (gas holder), heating and mixing devices, pipeline systems, pumps, gas compressors, centrifugal devices, instrumentation and control equipment, and automation tools.

The biogas reactor, where methane Fermentation occurs, is the core element of a biogas plant regardless of its technological level. The mixed biomass is fed from the manure collection tank into the fermentation chamber, where biogas production begins. The fermentation chamber (bioreactor) is a sealed, thermally insulated tank equipped with systems for feeding fresh raw Materials, discharging biogas and sludge, mechanisms for maintaining biomass homogeneity within the chamber (devices for mixing the mass and breaking up scum), as well as systems for maintaining the required fermentation Temperature.

The capacity of gas holders varies and depends on the daily biogas production and consumption rates. However, it should not be less than the maximum daily biogas output. At the same time, the cost of biogas storage reservoirs (gas holders) constitutes a significant portion of overall BGP expenses. Therefore, excessively large reservoirs are rarely built in practice; instead, if necessary, excess biogas is flared or vented into the atmosphere.

The first BGPs appeared even before the scientific foundations of methanogenesis were established. They were introduced in India as early as 1900, using livestock waste and plant residues as raw materials. Similar plants were built in Germany in 1918, in England in 1922, and in the USA in 1930. These resembled simple barrels into which manure flowed from livestock facilities via pipes and troughs. Methane fermentation inside the barrel lasted 40 days or more. Such installations yielded very little biogas and ceased to function altogether during the cold season.

Understanding the fundamentals of methanogenesis made it possible to transition from primitive designs to high-efficiency installations.

The first advanced and productive BGPs, featuring reactor capacities ranging from 300 to 2500 m³ and digestion periods of 10-20 days, were developed in Germany between 1947 and 1950. Following this, mass production of such plants began in many countries worldwide, including China, India, England, the USA, and France.

In Ukraine, research in this field began in 1949, and as early as 1959, the Zaporizhzhia Branch of the Research Institute of Rural Electrification designed a BGP operating in the mesophilic mode. Subsequently, other units were developed, such as the Biogas-301 for Processing pig manure (up to 3,000 heads), installations by UkrNIIAgroperect, Kobos-1, and others.

Today, over 60 varieties of BGPs have been developed and are in operation worldwide, differing in equipment complexity, structural features, operating principles, and capacity—ranging from compact family-scale units to large industrial facilities with reactor volumes from 1 to 6000 m³, respectively.

The total number of industrial biogas plants in the EU currently stands at about 750 units, with the majority located in Germany (500), followed by Austria (120), Italy (70), Switzerland (59), and Denmark (40) (Dubrovin et al., 2004). Today, Denmark has about 20 large centralized Centralised Anaerobic Digestion (CAD) plants serving farms within a 10-15 km radius. Austria operates 3 such facilities, Sweden 8, Italy 5, and Germany 3. Large CAD systems process several hundred tons of agricultural waste supplied annually by agricultural cooperatives. The advantages of centralized systems lie in The ability to employ advanced disinfection technologies and remove large amounts of ballast substances from the raw materials. Such centralized CAD systems feature reactors with capacities of up to 10000 m³, capable of generating energy ranging from several hundred kW to several MW. One of the drawbacks of centralized systems is the long distances over which substrates must be transported.

Fermentation in small-scale reactors without additional system heating, utilizing manure biomass and municipal waste as raw materials, is feasible in countries with high average annual ambient temperatures and agricultural structures different from those of developed countries. Reactors with a capacity of 4-12 m³, serving one or several farms, are most popular in African and Asian countries. Biogas produced in small systems satisfies the energy needs of households, being used for cooking and lighting. The largest number of such installations (8 million fermentation chambers) is located in China.