THE SCIENCE & ENGINEERING BEHIND AD SUCCESS: THE HIGH SOLIDS APPROACH

The technology and equipment that Fitec designs for their facilities are purpose-made for the tough conditions in AD systems. By using feedstock at High Total Solids levels, all aspects of a system can be made more efficient:

• Less water

• Fewer pumps

• Less electricity and heat consumption

• Less trucking costs

These principles are applied to all types of digesters: agricultural, food waste, and mixed waste. Fitec has a high level of expertise in all these areas. Additionally, we offer a Self-Cleaning Digester option that eliminates the need for cleanouts. Read on to learn about all the CAPEX and OPEX advantages of the High Solids Approach.

PROCESS FLOW COMPARISON

In most AD process flows, considerable amounts of water are added ahead of the digestion stage in an effort to support the removal of non-digestible contaminants. Whether for packaged food waste or high sand and grit agricultural wastes, water is used to accentuate density differences in the materials. From 10-15% of volatile solids (gas-producing solids) are lost, translating to an equal reduction in biogas production at the end of the process. Digesters are fed at a TS of approximately 5-10% which works well for conventional pumps, but digester tanks must be very large to accommodate the added non-energy producing volume. The other considered ‘advantage’ of the large tank size is to delay the inevitable cleanout that will be required as the remaining non-digestible contaminants settle inside the tank.

The two main differences in the Fitec system are the total solids at which the system is designed to operate at and the location of the non-digestible contaminant removal in the process flow:

A Fitec system is designed to be fed at 20-25% TS and contaminants are removed in-situ from the tank, during normal daily operation.

Our low wear pumps are designed to handle thick slurries which allows the system to run with up to 77% less water. Once the feedstock begins to decompose, there is a natural separation effect within the tank and the light fraction of contaminants such as plastics or straw will float to the surface, while the heavy fraction such as grit and sand, will sink to the bottom. Our Self-Cleaning Digester technology takes advantage of this naturally occurring phenomenon and deals with this problem inside the tank. A skimming system with a screw press is used to remove the light fraction from the surface and a floor sweeper system and settling tank to remove the heavy fraction from the floor.

As a result, tanks are always operating at full capacity, cleanouts are never required and smaller tanks can be built. As all the volatile solids are preserved, biogas production is optimized.

The end result of operating at a higher TS means a lower OPEX due to:

• More energy being produced per ton of feedstock

• Lower water requirements

• Lower energy use

• Lower disposal costs 

• Lower throughput and therefore slower wear on equipment.

And the CAPEX is lower due to

• smaller tank sizes 

• smaller pumps.

Contact us today to learn how The Fitec High Solids Approach can make your biogas project more profitable and successful.

Stay tuned for a detailed quantitative CAPEX and OPEX comparison page coming soon!