BIOdry

BIOdry is a drying system, which uses the total heat produced by the CHP unit to reduce the amount of digestate and make organic fertilizer. Thermal energy comes from the engine cooling and from the heat recovery of exhaust gases. The end products obtained are a dry, durable fertilizer and liquid ammonium sulphate.


Function

A belt dryer, which works according to the principle of evaporation, is used. Air is sucked in, heated, and conveyed over and through the dry material. In this way, it absorbs water up to saturation and is then purified after drying.


Air heating

Warm air duct to the dryer
Warm air duct to the dryer

For drying, ambient air must be heated.  The biogas power plant CHP generates the necessary thermal energy in two stages. In the first stage, air is heated through the motor cooling water circuit, and reaches a temperature of about 60°C; in the second stage, heat is recovered from the CHP exhaust gases, thereby heating dry air to a temperature of up to 110°C.
Warm air is then conveyed through a warm air duct to the dryer.


Separation

Separation is not strictly necessary for drying, but helps to reduce the volume of the digestate and provides fluid for dilution in the fermenter. In this processing step, the digestate is divided into a solid fraction and a liquid fraction by means of a separator. The liquid fraction passes through the sieve openings and is collected in a collecting vessel. There, a part of the liquid phase is pumped to be dried while the rest reaches the final repository. At the separator outlet, the solid fraction is collected on a plate.


Belt dryer

Belt dryer
Belt dryer

The belt dryer consists basically of a drying chamber, a mixer, a chain drive, two or four overlapping belts formed by perforated steel plates with optimum air permeability, a tilting device and a discharger.
A portion of the dried material is used for re-mixing, but the larger part is discharged from the dryer and can be stored, transferred or even pelleted in a further step.


Exhaust air purification

Exhaust air purification
Exhaust air purification

Drying air is sucked by fans through the system. Since air is laden with dust, ammonia and other pollutants from the digestate, exhaust air purification is compulsory for compliance with environmental regulations.

Exhaust air purification can be divided into three steps:

  • Acidified spray scrubber used as a dust catcher: Air is largely purified of dust by spray mist.
  • Acidic wash: air passes through a filter body (honeycomb structure) moistened with a sulphuric acid solution.
  • Water wash: the last remaining fine droplets (aerosols) and dust particles are separated by means of water from the air.

Advantages

Advantages of digestate drying at a glance

Digestate
Digestate
  • Use of thermal energy
  • Production of solid fertilizer with high nutrient concentration
  • Use of fertilizer at the right time (permanently available fertilizer)
  • With BIOdry, the generatedd amount of digestate is significantly reduced.
  • The final repository can be made smaller, thus saving construction costs.
  • No nitrogen losses during storage and output
  • Significant area reduction
  • Through drying, transport volumes can be decreased, thereby reducing costs.
  • The dried fraction produced can be profitably sold as fertilizer (export of nutrients)
  • The ammonium sulphate solution can be sold as liquid fertilizer.
  • Generation of a stackable product
  • Increase of the overall efficiency of the plant

Images

  • BIOdry
  • BIOdry
  • BIOdry
  • BIOdry
  • BIOdry


BIOdry

BIOdry

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