BDS - BIOMASS DRYING SYSTEM

1. Introduction

Liquid manure or fermented residues from biogas systems, also known as digestates; require processing to make easier the storage, reduce transport cost and use them as fertilizer.

2. BDS – Biomass Drying System

BDS operation consist in heat exchangers installed at the outer wall, where warmed air flows through the drying plates from below to upwards. Humid loaded air leaves the dryer through chimneys.

2.1 Substrate pre-treatment:

BDS-Biomass Drying System, can be feed with different kind of substrate and moisture content. The aim of the feeding system is to supply a homogeneous substrate without drops. We offer three options for the feeding system:

*Mixer:Liquid fermented residue is blended in a mixer with part of the substrate dried before. Therefore the mixer will produce a compact substrate that will not drop through the plates holes.

*Trommel Separator:

• Separation of fermented residues. (Volume: liquid ~50% / solid ~50%)
• Concentration of substrate up to 12-14% DM.
• Low energy consumption.
• Avoid surface scum at storage tank and lagoon.
• Relative high P₂O₅ content at the solid separated part. High P₂O₅ content after drying process.

*Press Separator:

Separation of liquid and solid parts of the fermented residue. Liquid manure is used as fertilizer and solid part (>30%DM) is supplied into the dryer. Feeding by a conveyor screw or conveyor belt.

• Separation of substrate by means of pressure
• Liquid separated part (~ 75% of volume), with <5%DM
• Solids separated part (~25% of volume), with 30-35%DM

2.2 Feeding system:

After pre-treatment substrate will be feed homogenously into the upper drying plates by means of a conveyor screw or conveyor belt.

2.3 Arrangement and conveyor plates:

• The length of the facility is around 12-30 m, with a width approximately of 3-5m.
• All running conveyors plates consist in two counter layers of perforated steel plates (0.30 x 2.00m).
• The steel plates have a powder coat and guarantee an optimum air passage from below to upwards.

2.4 Operation:

• Transport speed is variable.
• Continuous movement.
• 7,500 hrs / year
• Substrate throughput depends on the input material, drying aim, available heat, temperature and humidity outdoors.

2.5 Windlass:

• Substrate is placed homogenously on the upper plates layer.
• A windlass avoids formation of scum and compaction.
• Layers high of approximately 5-15 cm

2.6 Conveyor plates;

At the end of the superior drying plates layer, the substrate falls down on the lower drying plates layer . The substrate will be transported again through the dryer on the lower plates layer in opposite direction.

2.7 Air cleaning:

Three stages at exhaust air cleaning:

Dust,Ammonia,Odor

• Automatic conduct of the exhaust air
• Exhaust air before “Air Cleaning” with an ammonia mass concentration approximately: 100 mg / m³
• Exhaust air after “Air Cleaning” respects the limit values of TA (20-30mg/ m ³)
  • At the end of the drying process the substrate reaches a dry matter with ~ 80- >90% DM
  • High nutrient density
  • Dried fermented residues, can be used as fertilizer.
  • Dried fermented residue with: Liquid ammonium sulphate (NH₄)₂SO₄. Sulphur and nitrogen fertilizer.
  • Heating: Heating of the dried fermented residue > 70°C. To be used as bedding material for cattle.
  • Pelletizing: Possible to pelletize substrate after drying process.

 


3. Alternatives:

3.1 Refining of the dry substrate:

Advantages:

• High density (700-750 kg/m³)
• Lower transport cost and better storage conditions
• Homogeneous granulate material
• High nutrient density, pellets can be used as fertilizer.
• High energy density for combustion, similar to wood pellets.
  • Flower fertilizer:Packages of 25-80 kg for domestic use
  

  3.2 Drying of other materials or substrates:

  • Wood chip
  • Corn drying
  • Drying of light products: Sawdust,peat(moor)
  • Dried silo maize, can be used as poultry bedding
  • Grass, herbs, clover, alfalfa drying
  • Sewage sludge