Foundation, Concrete and Earthquake Engineering

Component Comprising Biogas System

Biogas production is most suitable for farms that handle large amount of manure as liquid, slurry, or semi-solid with little or no bedding added. To produce a cost effective system, it should be designed by an experienced animal waste digester designer. A typical biogas system consists of the following components:

A) Manure Collection
B) Anaerobic Digester
C) Effluent Storage
D) Gas Handling
E) Gas Use

All of these components are discussed briefly:

A) Manure Collection:
A manure management system is developed in livestock farms to consider environmental, sanitary and farm operational facilities which includes collection and storage of manure. This can be collected and stored as liquid, slurries, semi-solids, or solids.

a) Raw Manure
The solid content of 8-25% is excreted as raw manure. It can be diluted by various processes.

b) Liquid Manure
Such manure is diluted to a solid content of less than 5%.

c) Slurry Manure
Manure handled as slurry is diluted to a solids contents of about 5-10%.

d) Semi Solid Manure
Manure handled as a semi-solid has a solid content of 10-20%. Water is not added to such manure and it is typically stored until it is spread on local fields.

e) Solid Manure
Manure having a solids content of greater than 20% is handled as a solid by a scoop leader.

B) Anaerobic Digester
Naturally occurring anaerobic bacteria is decomposed in a digester and manure is also treated in it during the process of biogas generation. An air-tight impermeable cover is used to trap the gas for on –farm energy use.the manure handling system defines which type of digester can be used.

Different types of digester are listed below:
a) Cover Lagoon Digester

It is used to treat and produce biogas from liquid manure( solids <>b) Complete Mix Digester

It is used to treat slurry manure with a solid content of 3-10%.
Component Comprising Biogas System

c) Plug Flow Digester

It can treat scraped dairy manure having a solid concentration of 11-13%.

d) Fixed Film Digester
It is best suited for dilute waste streams typically associated with flush manure handling.

C) Effluent Storage

The anaerobic digestion of manure produces biogas and effluent. The effluent is a organic solution having a quality to be used as fertilizer and other potential uses.
The size of storage facility and storage period depends on farm requirements during non-growing season. The longer storage facility provides flexible management of the waste to account for weather changes, equipment availability or break down or other operational management.

D) Gas Handling

The expected biogas is received from the digester and transport to the final use i.e., an engine or a plant through as a gas or a plant through a gas handling system which includes: piping, gas pump or blower, gas meter, pressure regulator, and condensate drain.

The trapped gas under an air-tight cover over the digester, is collected by pulling a slight vacuum on the collection pipe using a gas pump or blower to the end of pipe. A gas meter is provided to monitor gas flow rate. Sometimes a gas scrubber is used to purify the gas to remove corrosive compounds ( e.g., hydrogen sulfide). When warm gas is cooled during traveling through pipe system and water vapor in the gas condenses. The condensate product is removed using a condensate drain(s).

E) Gas Use

Methane content in biogas is about 60-80% which have a heating value of approximately 600-800 Btu/ft3. Such gas can generate electricity, can be used as fuel for a boiler, space heater, or refrigeration equipment, or it may be directly combusted as a cooking and lighting fuel.

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