SELF CLEANING DIGESTER

Not at all, actually! The floor sweeper uses only a 1hp motor located on the digester roof. It moves slowly and only as needed, depending on the contamination level of the feedstock. Grit is collected before it has a chance to accumulate so only a small force is required to overcome the weight of accumulated sediments. In reality, you will find that Fitec systems have a very low energy demand compared to other biogas plants. Check out our blog posts to learn more about how the Fitec architecture makes a difference.

The design of the SCD locates all maintenance points in easily accessible locations on the outside of the digester. On the inside, anything in the liquid level is made of a heavy gauge mild steel and anything coming into contact with biogas is made of stainless steel. This means the internal components do not require any maintenance whatsoever. This fact is confirmed in all of our 20+ systems in operation worldwide, the oldest of which is 20 years and counting.

We have never had a situation where the floor sweeper has needed repair. As a worst case scenario, if it did stop working, you could continue to operate the digester without it, just as most digesters operate. All other components are accessed from their roof mounted ports or tank side-entry door.

Currently, the maximum tank diameter that can be serviced by the floor sweeper arm is 60 ft (18 m). Technically there is no minimum diameter, but the smallest we’ve constructed has been 20 ft (6 m). There is also no maximum height, but the tallest we’ve constructed to date is 66 ft (20 m).

The only additional components required to build a Fitec Self-Cleaning Digester are

·         the column and floor sweeper

·         a grit pump

·         a sediment trap

·         and (for food waste facilities) a screw press.

Exact prices will vary based on the specifics of each individual project, but these components typically account only for 5-15% of the total for all digester process equipment, excluding upgrading. When looking at total project costs including development, this often amounts to less than 1%.

In addition to this small cost, it is important to take other variables into consideration. For example:

1.      The reduction in volume and throughput achieved in a Fitec High Solids System significantly reduces the CAPEX (smaller tanks, smaller/fewer pumps, etc.)

2.      The OPEX savings on energy efficiency and avoidance of tank cleanouts (see blog post)

3.      The increased revenue from producing biogas at 100% capacity for the lifetime of the facility

Taken together, these savings add up to much more than the cost of the few additional components required to build a Self-Cleaning Digester.

The system presently uses a 1mm screen to capture contaminants, which has resulted in digestate that passes the test of the world’s strictest standards set by the United Kingdom. The Fitec Self-Cleaning Digester achieves this in a few ways:

• The floor sweeper and grit removal system removes sinking contaminants like sand and grit

• The skimming system and screw press remove floating contaminants like plastic

• All digestate passes through a 1 mm filter screen

Independent 3rd party analysis completed in the United Kingdom and in Canada confirms that digestate from the Fitec Self-Cleaning Digester surpasses all laboratory standards for clean digestate. Results from 3rd party analysis of our digestate using Ontario standards show that Total Foreign Matter and Total Plastics both have results of BDL (Below Detectable Levels).