Biogas Technology by Liangwei Deng & Yi Liu & Wenguo Wang

Author:Liangwei Deng & Yi Liu & Wenguo Wang
Language: eng
Format: epub
ISBN: 9789811549403
Publisher: Springer Singapore

The bottom construction of a digester include the following process: building of a groundwater collection and drainage system, settling of the foundation layer and compact soil protection layer, preparation of the bottom exhaust system, and strengthened sealing of connection of the HDPE membrane and pipelines.

Ground water collection and drainage system: Groundwater collection and drainage system must be set up when groundwater level is high, which is harmful to the stability of the foundation layer at the digester bottom, or when the surface water seepage around the digester is harmful to surrounding slope foundation. Such system should be able to collect and drain groundwater and seeped surface water promptly and effectively, and it should have anti-silting capacity and ensure long-term reliability. Underground blind ditch, gravel diversion layer or geotextiles composite drainage network diversion layer should be used for such system.

Foundation layer and compact soil protection layer: Foundation layer should be flat, compact, and free of cracks, loose soil, surface water, stone, tree roots, and other sharp debris. Compactness should be no less than 93%. Structure of a foundation layer of surrounding slope should be stable, and the compactness should be no less than 90%, with a slope gradient more than 1:2.

Bottom gas exhaust system: Underground soil may produce gas (possibly water vapor) due to temperature changes and some other reasons. Underground gas may cause rising and bulge of the bottom membrane, even breaking the impervious layer at the digester bottom. In order to prevent this situation, underground gas drainage facilities should be provided at the foundation layer or the compact soil protection layer. Gas may be exhausted through gravel-based blind ditches or perforated pipe wrapped with permeable materials such as geotextiles.

HDPE anti-seepage membrane layer: Permeability coefficient of compact soil under an HDPE membrane should be no more than 1 × 10−9 m/s, and the thickness should be no less than 750 mm. Thickness of HDPE membrane should be no less than 1.5 mm. Before installation of HDPE membrane, the protective layer under the membrane should be checked. Flatness error per square meter should not exceed 20 mm. The bottom membrane should be settled after getting welded in factory and fully tested based on the size of the digester to be built. Hot melt welding or extrusion welding should be adopted. The lap width of hot melt welding shall be 100 ± 20 mm, and that of extrusion welding shall be 75 ± 20 mm. The membrane laying work should be done in place at one time. Dragging is not allowed after the laying work. It is necessary to leave spaces for any size change caused by thermal expansion and cold contraction of materials. Appropriate waterproofing and drainage measures should be taken for protective layers under the membrane. Measures shall be taken for aboveground membrane to prevent HDPE membranes from wind damages. Constructors should wear protective gloves. Personnel and tool vehicles should not step directly onto HDPE membranes without protective measures. Protective layers (e.g. non-woven geotextiles) shall be provided on the HDPE membrane. After the digester bottom is constructed, water test is required to ensure there is no leakage at digester bottom.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.