PreMix®: Optimizes solids treatment and increases gas production
Case study: Az. Agr. Ronconi Giacomo, Italy

Problem

High maintenance costs and frequent malfunctions of the mixers

Solution

PreMix: reliably mashes, cuts, homogenizes and conveys solids into the digester

The customer and the problem

Az. Agr. Ronconi is a family-owned Italian agricultural business based in Marmirolo. The livestock farm manages 900 hectares and raises around 130,000 pigs and 2,000 dairy cows. The farm also  operates two biogas plants, each with a capacity of 1 MW. Both plants are fed with the same input materials: slurry, cattle manure, process water from the farm, and a small amount of silage.
The two biogas plants differ fundamentally in their feeding systems. In the first plant, a vertical mixer followed by a screw conveyor feedsd the solids directly into the digester. However, this system led to frequent problems: the digester had to be opened almost monthly and the mixers removed in order to remove ropes, fibers and other long-fiber materials that blocked the mixers. The workload was high and the mixers required a lot of energy to mix the suspension in the digester thoroughly. In addition layers formed, which impaired the gas yield.

Biogas plant Ronconi
Biogas plant Ronconi

The solution

For the second plant, operator Giovanni Ronconi opted for the Vogelsang PreMix; RotaCut RCX-58G and CC66-M1 progressive cavity pump. A screw conveyor feeds the solids directly into the PreMix. There, they are mashed with cattle and pig  slurry from the farm´s own barns and the farm´s wastewater to form a homogeneous suspension, coarse and long-fiber components are crushed, heavy material is separated out in a single process, before being fed into the digester. 

After more than two years of operation, Ronconi was able to compare the two systems in detail. The system with PreMix impresses with less work, fewer malfunctions, and greater process stability. While the digester had to be cleaned regularly with the vertical mixer, this was not necessary at all with PreMix. Maintenance is minimal – so far, only the cutter screen and blades of the cutter have had to be replaced, while the pump itself has continued to run without any problems. In addition, the liquid feeding system prevents the formation of floating and sinking layers and the gas yield has increased. This reduces the amount of silages required daily in the feed ration decreased without affecting daily biogas production. Finally, the PreMix requires less energy than the vertical mixer and reduces the energy requirements of the mixers, which no longer have to struggle with long-fiber components. 
 

“Maintenance requirements at the biogas plant are significantly lower with the PreMix; energy consumption by the solid matter feeding system itself and the mixers has decreased, and the specific gas yield has increased”, Giovanni Ronconi, Itlay.

Advantages of the PreMix®

  • Mashing of the biomass to form a suspension that is optimal for bacteria
  • Cutting of coarse and fibrous solids and separation of heavy materials in front of the pump unit
  • Simple and fast service directly on site

Benefits for the user

  • Significantly lower costs for the maintenance of digesters and mixers
  • Prevention of layers in the digester
  • Lower energy consumption of the feeding system and mixers
  • Less feedstock required while maintaining the same gas production