Monday, August 28, 2017

Digester Covers - Digester Cover Design for Biogas Plants

Every digester deepends upon its cover to provide a good air-seal, but are you aware of the digester cover types and the other purposes of these covers?

In this article and in our video below which includes the same content as this page, we talk about digester cover design, and the popularity of membrane digester covers.

Many covers are available from manufacturers/ suppliers like Walker Process Digester Covers.

In fact we think you will find digester gas storage, whether as a floating roof digester cover, double membrane gas holder, to be an interesting subject. See also suppliers/contractors Westech Engineering, and Ovivo for digester cover designs.

To see our other, (more comprehensive) article, visit:
The Video Transcription Text Follows:

Digester Covers. Those Distinctive-Looking Curved, Biogas Tank-Tops

Anaerobic-digestion plant biogas-digesters, are normally covered with a fixed, or floating top, for gas collection.

These tank tops are a very distinctive shape. Once you recognize that shape, an anaerobic-digestion plant is easy to spot from a distance.

There are 3 types:

1.. Floating covers which rise-and-fall according to volume of gas and substrate and their weight provides the gas pressure.
2. Fixed covers which require a separate biogas-holder connected to the space above the digester, that allows the gas to move in both directions.
3. The most popular and easily-recognised distinctive double flexible-membrane covers.

In all but the first type of digester-cover, the pressure of the gas is controlled by an automatic pump.
Digester covers are designed to provide the following:

a) A permanent seal to prevent oxygen entering the digester.
b) A degree of pressurisation to the biogas.
c) In cold countries the cover must provide heat-insulation to keep the digester warm.

Double membrane digester covers are popular, due to their low cost, and when manufactured to high-quality standards they have a remarkably-long service-life.

We hope you found this video interesting.

A Note on Double Membrane Cover Pressurisation

In double membrane cover designs the outer cover, is usually pressurised with the low-oxygen content exhaust from an engine-generator or boiler, etc. The low oxygen level gas between the outer membrane and the inner, reduces the explosion risk.

It also provides a durable and intrinsically safe, warm gas shell over the flexible, inner biogas collection cover and digester cell itself.

The outer cover is maintained at a preset pressure, to hold the outer membrane taught. Taught enough to withstand tornado strength winds.

Snow, sleet and ice is no problem to these roofs because all are rapidly melted off of the outer cover due to its warmth.

The inner digester cover is, as a result, never directly exposed to wind or sunlight. That extends its useful life considerably.

The flexible inner cover is allowed to rise and fall based on the rates of biogas production and biogas fuel demand.

These covers, when fitted over digesters, tend to provide in the region of 48 hours of Biogas storage.

Now you can read the full blog article at:
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