Biogas - Application and Product Development
Planning a biogas plant
Before building a biogas plant, there are different circumstances which should be considered.
For instance, the natural and agricultural conditions in the specific countries are as important
as the social or the economic aspects. To consider the most important factors, we provide a
checklist for the planning procedure, a planning guide and a checklist for construction of a
biogas plant.
Failure or unsatisfactory performance of biogas units occur mostly due to planning mistakes.
The consequences of such mistakes may be immediately evident or may only become
apparent after several years. Thorough and careful planning is, therefore, of utmost
importance to eliminate mistakes before they reach irreversible stages.
As a biogas unit is an expensive investment, it should not be erected as a temporary set-up.
Therefore, determining siting criteria for the stable and the biogas plant are the important
initial steps of planning.
A general problem for the planning engineer is the interference of the customer during
planning. As much as the wishes and expectations of customers have to be taken into
consideration, the most important task of the planner is to lay the foundation for a well
functioning biogas unit. As in most cases the customer has no experience with biogas
technology, the planner has to explain all the reasons for each planning step. Planners
should have the courage to withdraw from the planning process, if the wishes of the
customer will lead to a white elephant on the farm.
Moreover, all extension-service advice concerning agricultural biogas plants must begin with
an estimation of the quantitative and qualitative energy requirements of the interested party.
Then, the biogas-generating potential must be calculated on the basis of the given biomass
production and compared to the energy demand. Both the energy demand and the gas-
generating potential, however, are variables that cannot be accurately determined in the
planning phase. Sizing the plant (digester, gasholder, etc.) is the next step in the planning
process.
In the case of a family-size biogas plant intended primarily as a source of energy,
implementation should only be recommended, if the plant can be expected to cover the
calculated energy demand.
Information about the economic evaluation of a biogas plant can be found in the section on
Costs and Benefits.
Design
Throughout the world, a countless number of designs of biogas plants have been developed
under specific climatic and socio-economic conditions. Chosing a design is essentially part of
the planning process. It is, however, important to familiarize with basic design considerations
before the actual planning process begins. This refers to the planning of a single biogas unit
as well as to the planning of biogas-programs with a regional scope.
Physical conditions
The performance of a biogas plant is dependent on the local conditions in terms of climate,
soil conditions, the substrate for digestion and building material availability. The design must
respond to these conditions. In areas with generally low temperatures, insulation and heating
devices may be important. If bedrock occurs frequently, the design must avoid deep
excavation work. The amount and type of substrate to be digested have a bearing on size
and design of the digester and the inlet and outlet construction. The choice of design will also
be based on the building materials which are available reliably and at reasonable cost.
Skills and labor
High sophistication levels of biogas technology require high levels of skills, from the planner
as well as from the constructor and user. With a high training input, skill gaps can be bridged,
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