Ultrasound systems for biogas

Biogas production

Agriculture and livestock breeding have always utilized agricultural by-products by integrating them in the production cycle, mainly in the form of fertilizers.

Nowadays, a company can also produce biogas from the same by-products with specialized biomass treatment systems: a source which reduces costs for the energy supply which the company needs and generates a new source of income. 

For this reason, biogas production stations are more and more interesting and important for modern society.

The main production phases of biogas are:

Input: By-products and biomasses which come from animal waste or scrap from food plantations and industries are introduced into the digester (fermenter) day-to-day.  An ultrasonic disintegration system enables an increase of the ultimate production yield at this stage.

Biogas production: Bacteria work inside the digester to produce biogas at a temperature of 38-42°. The biomass is then transferred to the storage tank for complete extraction and better desulphurisation.

Electric and thermal energy production: The biogas which has been produced is conveyed to the cogeneration plant which produces electric energy and thermal energy. 

Digestate: The ultimate residual biomass has very high agronomic value and improved characteristics compared to the original biomass and is used as a fertilizer. 

Increase in efficiency through ultrasonic disintegration

From this perspective, Everywave and Unitech have designed and manufactured a special ultrasonic reactor which, integrated with specialized shredding, pumping and process control systems, represents solid and efficient technology for controlling and increasing the production yield of biogas. The most innovative element of the treatment system is the Everywave UDS tubular reactor (Ultrasound Disintegration System), which facilitates maximum continuous flow disintegration of the biomass, along with a sturdy structure which needs no maintenance, for h24 operating without complications.

Operating principle of the reactor

The ultrasonic reactors of the system are loaded by means of a progressing cavity pump (or other type) which draws directly from the biomass storage tank or from a “pre-exchange tank”.

The biomass is swept by the ultrasonic field inside the tubular UDS reactor; the power is adjusted according to the capacity (generally between 1 and 4 tonne/h), so that the ideal supply of energy required for the treatment is reached. 

Use of a shredder at the pump input is advised for biomasses having an approximately 10% or greater solid content and should there be foreign bodies or solid parts of significant size and sturdiness.

Cell disintegration and its possible break-up takes place subsequent to high levels of cavitation induced by ultrasounds in the substratum.

Process control

The ultrasonic reactors system is controlled with a PLC to guarantee steady and efficient operating.  The system is, as a matter of fact, equipped with sensors which control the temperature, pressure, volume flow rate besides the operating parameters of the reactor.

In short, the temperature parameters and delivery pressure of the pump enable to check that the pump itself operates correctly, besides the efficiency of the biomass flow in the treatment circuit. The instantaneous flow, measured at the output of the reactors after the pump, enables adjustment of the optimal sonication power for disintegrating and fluidifying the substratum.

Advantages of the UDS system

The UDS ultrasonic reactor has a sonication chamber with ultrasonic transducers installed externally. This way typical problems of ultrasound disintegration systems with internal sonotrodes (‘Rod type’) are solved.   In fact, as the biomasses with the typical 10% solid (and greater) content have relatively high viscosity, much effort is needed to efficiently couple the ultrasounds to the means.   Building a reactor with a sufficiently small transversal section of the tubes would be needed to obtain the maximum sonication efficiency with an inside sonotrode system and this would increase the risk that the fibrous components typically found in the substratum block and stress the system.  The results would therefore be greater stress and less energy efficiency of the ultrasound system. 

The UDS reactor developed by Everywave specifically for treating biomasses solves this problem. The structure of the reactor, which has no sonotrodes inside, impedes blocking and maintains constant high disintegration efficiency. In addition, the operating life of the UDS reactor is longer compared to classical rod sonotrodes submerged in the biomass.

Increase of the biogas yield

The increase in production of biogas attained with ultrasonic disintegration systems can vary between 10 and 30% and guarantees a general economic benefit in the long term when the system described above is used.

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