digestate processing

FERTILISER PLANT - DÜNGERWERK

refined, concentrated, separated:

The agriKomp procedure consists of two sub-processes, i.e. concentration and nitrogen separation; they are explained in the following.

1. Concentration

The digestate refinement is preceded by mechanical separation which separates the digestate into a liquid and a solid fraction. The solid digestate is stored intermediately on a suitable area; the liquid fraction is filtered through a fine-mesh sieve and fed to the process of digestate refinement.

This liquid digestate is heated in the plant and subjected to negative pressure. In this step part of the liquid digestate is evaporated. Thus the digestate is concentrated. This step is repeated in another evaporator, where heat recovery allows energy-efficient concentration.

Subsequently, the digestate that has been concentrated in the previous step is removed from the process. The water that evaporated in the process is condensed in heat exchangers and the energy is returned to the drying process. The multiple utilisation of the heat energy and the hermetical sealing of the plant make the procedure an energy-saving, low-emission process.

Evaporation power of the plant:
The max. heat consumption is 400 kW. An amount of 2.5 l condensate is generated per kWh (thermal).

Condensate treatment
Ca. 50 to 60 % of the condensate are evaporated in the wet cooling tower. The condensate that is separated in the evaporation process can be used further depending on the customer's requirements.

  • Use of water for operation purposes 
  • Cold atomisation of the water with an optionally available atomisation unit 
  • Indirect or direct introduction of the water, if applicable, combined with an additional water cleaning unit

2. Nitrogen separation

Vapour scrubbers are used to remove ammonia from the gas phase and by adding H2SO4 this ammonia is converted into ammonium sulphate and concentrated. The negative pressure that is required for the energy-efficient evaporation is generated by a vacuum pump. This pump is connected at the pressure side of the gas compartment of the biogas plant; thus, residual gases emerging from the digestate are safely fed back into the biogas plant. There they are either metabolised microbially (e.g. H2S that could occur is converted into sulphur) or burnt in the CHPS (CH4).

This digestate is highly concentrated now and it contains all nutrients that are also contained in the untreated, not yet concentrated, digestate. The nitrogen contained in the digestate can be stored separately as liquid fertiliser or added to the digestate directly.

2 NH3 + H2SO4  [NH4]2SO4

The information contained herein reflect the current state of development, subject to change. Stated parameters may possibly vary in operation. Designed for use in agricultural biogas plants .