There are several factors affecting the biogas plant design. Parameters that are related to plant conceptual design are focused on the source of the waste and the desired end-use of the treated material. Parameters that affect the biogas plant size, mass and energy balance, dimensions of different units and power of mixers, pumps and other electrical equipment (i.e. engineering) are related to amount and quality of treated wastes. In Table 2 a selection of these parameters are described.
|Parameter||Conceptual design||Engineering||Design aspect|
|Source of waste(s)||X||Depending of the source, the biogas plant may be required to have e.g. pasteurisation units (high-temperature pre-treatment of wastes) and/or rendering process. Also the plant that receives wastes that are delivered to plant via trucks has to have a closed reception hall, etc.|
|Desired end-use of the treated materials||X||There are several different ways to manage the end-products; field applications, fertiliser products, incineration of the dried end-product, etc. These ways affect to plant design and logistics as well.|
|Volume of treated wastes||X||Dimensioning the tanks, reactors, pumps and agitators are depended on the design flow of the treated waste|
|Quality of treated wastes||X||Quality includes the solid concentration (TS), ratio of organic material in the solids (VS), nutrient levels. These all affect to the process design (loading rates, inhibitor effects, biogas production rate and biogas quality, decanter design).|
The Table 2 indicates several factors that can have also cross-interactions so they all need to be carefully determined before the biogas plant feasibility can be assessed. Therefore the feasibility assessment of the biogas plant has a high significance to the final success or failure of the whole project. Good feasibility study reveals the risks that are connected to specified project and also generally lowers the risk for the investment.
Feasibility study is a way to reduce the risk of the investment and the study should focus not only on technical aspects of the biogas projects (defining the treated materials, mass and energy balance of the biogas plant, possible inhibitors, process solutions, etc.) but also pay attention to the economical side of the project. Economical evaluation includes the investment cost estimation, cost estimation to operate the plant (manpower, use of chemicals, required spare parts, etc.), which together determines the requirement for the annual turn-over that has to be gained from the operation of the plant.
The cost of the feasibility assessment compared to project investment is insignificant, usually project owner should expect that the cost lies somewhere between 1-3 % of the final investment, depending on its size.