Planning Guide for Biogas Plants
Introduction
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.
Overview
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.
Considering Biogas
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.
Excluding Factors
If only one of the following criteria is evident, then the widespread dissemination of simple household biogas plants is not possible. As an exception, suitable farms in the region could allow individual measures that make biogas a feasible technology.
- too cold or too dry region
- very irregular or no gas demand
- less than 20 kg dung/day available to fill the plant or less than 1,000 kg live weight of animals per household in indoor stabling or 2,000 kg in night stabling
- no stabling or livestock in large pens where the dung cannot be collected
- no building materials available locally
- no or very little water available
- integration of the biogas plant into the household and farm routines not possible
- no suitable institution can be found for dissemination
Critical Factors
Each of the following factors will lead to severe problems in biogas dissemination. Accompanying measures, particularly modified technical developments, high financial promotion or additional organizational structures within the dissemination program are necessary to guarantee project success.
- low income or unstable economic situation of the target group
- unfavorable macro- and micro-economic conditions
- gas appliances not available regionally or nationally
- irregular gas demand
- very good supply of energy throughout the year, therefore only moderate economic incentives for the biogas plant
- high building costs
- low qualification of artisans
- counterpart organization has only limited access to the target group
- weak structure of the counterpart
- no substantial interest of the government is evident
Ideal Conditions
If each of the following conditions is fulfilled then household biogas plants will definitely be a success. A dissemination program is then strongly recommended.
- even, daily temperatures over 20ºC throughout the year
- regular gas demand approximately corresponding to gas production
- full stabling of animals (zero-grazing) on concrete floors
- at least 30 kg/day dung available per plant
- dairy farming is the main source of income
- use of organic fertilizer is traditionally practiced
- farmers are owners of the farm and live primarily on the farm. Farm products are their main source of income.
- plants can be located in favorable positions to the stables and to the point of gas consumption
- operating the biogas plant can be integrated into the normal working routine of the house and the farm
- gas utilization and attendance of the plant can be clearly regulated within the household
- moderate price of plant in relation to the income of the target group
- insufficient and expensive supply of fossil sources of energy
- building materials and gas appliances available locally
- counterpart organization has access to and experience in contact with the target group
- efficient counterpart organizations with the experience in cooperating with the private sector
- counterpart organization has experience in programs comparable to biogas dissemination
- political will of the government to support biogas technology and other small and medium-scale farm technologies
- secured financing of the dissemination structure
Standardization
For larger biogas programs, especially when aiming at a self-supporting dissemination process, standards in dimensions, quality and pricing are essential. Standard procedures, standard drawings and forms and standardized contracts between the constructor, the planner, the provider of material and the customer avoid mistakes and misunderstandings and save time. There is, however a trade-off between the benefits of standardization and the necessity of individual, appropriate solutions.
Selection of Appropriate Design
The design selection is determined largely be the prevailing design in the region, which, in turn takes the climatic, economic and substrate specific conditions into consideration. Large plants are designed on a case-to-case basis.
Typical design criteria are:
Space: determines mainly the decision if the fermenter is above-ground or underground, if it is to be constructed as an upright cylinder or as a horizontal plant.
Existing structures may be used like a liquid manure tank, an empty hall or a steel container. To reduce costs, the planner may need to adjust the design to theses existing structures.
Minimizing costs can be an important design parameter, especially when the monetary benefits are expected to be low. In this case a flexible cover of the digester is usually the cheapest solution. Minimizing costs is often opposed to maximizing gas yield.
Available substrate determines not only the size and shape of mixing pit but the digester volume (retention time!), the heating and agitation devices. Agitation through gas injection is only feasible with homogenous substrate and a dry matter content below 5%. Mechanical agitation becomes problematic above 10% dry matter.
Planning Guide for Domestic Biogas
This guide to planning is intended to serve agricultural extension officers as a comprehensive tool for arriving at decisions concerning the suitability of locations for family-sized biogas plants. The detailed planning outline has a data column for entering the gathered information and a rating column for noting the results of evaluation.
Evaluation criteria are:
- Siting condition are favorable
- o Siting condition are unfavorable, but
- a) compensable by project activities
- b) not serious enough to cause ultimate failure
- - Siting condition are not satisfactory
Despite its detailed nature, this planning guide is only a framework within which the extension officer should proceed to conduct a careful investigation and give due consideration, however subjectively, to the individual conditions in order to arrive at a locally practical solution. By no means is this planning guide intended to relieve the agricultural extension officer of the responsibility to thoroughly familiarize himself with the on-the-spot situation and to judge the overall value of a given location on the basis of the knowledge thus gained.
Initial Situation
| Data | Rating | |
| Addresses/project characterization
Plant acronym: General user data Household structure and number of persons: Problems leading to the "biogas approach" Energy-supply bottlenecks: Objectives of the measure "biogas plant" User interests: |
Natural / Agricultural Conditions
| Data | Rating | |
| Natural conditions
Mean annual temperature: Rating: |
- o + | |
| Subsoil
Type of soil: Rating: |
- o + | |
| Water conditions
Climatic zone: Rating: |
- o + | |
| Livestock inventory (useful for biogas production)
Animals: kind and quantity: Rating: |
- o + | |
| Vegetable waste (useful for biogas production)
Types and quantities: Rating: |
- o + | |
| Fertilization
Customary types and quantities of fertilizer/areas fertilized: Rating: |
- o + | |
| Potential sites for biogas plant
Combined stable/biogas plant possible: Rating: |
- o + | |
| Overall rating 1 | - o + |
Balancing the Energy Demand with the Biogas Production
| Data | Rating | |
| Prior energy supply
Uses, source of energy, consumption:
Available biomass (kg/d) and potential gas production (l/d) from animal husbandry
Balancing Gas production clearly greater than gas demand Gas demand larger than gas production a) possible reduction of gas demand by the following measures b) possible increase in biogas production by the following measures If the measures take hold: If the measures do not take hold: |
||
| Overall rating 2 | - o + |
Plant Design and Construction
| Data | Rating | |
| Selection of plant design
Locally customary type of plant: Type of plant chosen: Selection of site Availability of building materials Bricks/blocks/stone: Availability of gas appliances Cookers: |
||
| Overall rating 3 | - o + |
Plant Operation / Maintenance / Repair
| Data | Rating | |
| Assessment of plant operation
Incidental work: Rating with regard to anticipated implementation: |
- o + | |
| Plant maintenance
Maintenance-intensive components: Rating with regard too anticipated implementation: |
- o + | |
| Plant repair
Components liable to need repair: Rating with regard to expected repair services: |
- o + | |
| Overall rating 4 | - o + |
Economic Analysis
| Data | Rating | |
| Time-expenditure accounting
Time saved with biogas plant Rating: |
- o + | |
| Microeconomic analysis
Initial investment: Rating: |
- o + | |
| Quality factors, useful socioeconomic effects and costs
Useful effects: hygiene, autonomous energy, better lighting, better working conditions, prestige: Rating: |
- o + | |
| Overall rating 5 | - o + |
Social Acceptance and Potential Dissemination
| Data | Rating | |
| Anticipated acceptance
Participation in planning and construction Rating: |
- o + | |
| Establishing a dissemination strategy
Conditions for and chances of the professional-craftsman approach: |
- o + - o + | |
| General conditions for dissemination
Project-executing organization and its staffing: Regional infrastructure for Craftsman involvement, i.e. Training for engineers, craftsman and users: Proprietary capital, subsidy/credit requirement on the part of Rating: |
- o + | |
| Overall rating 6 | - o + |
Planning Guide for Industrial Biogas
Steps of planning
The following steps serve as a step by step guideline to reach a decision whether a biogas project is technically and economically feasible.
Basic steps in planning a biogas plant according to Krieg & Fischer:
- Calculation of biogas amount
- Size of digester
- Size of engine
- Sitelayout
- Flow chart
- Estimate of costs
Basic Steps according to the "Guide to Biogas" from FNR:
Step 1: Preparing the project outline
| Long-term availability of substrates | Which substrates will be available on a long-term basis? What impact/changes in the medium- and long-term are possible at the specific site? How will this affect the planned biogas plant? (biology/materials, process, energy) Is the supply of substrates guaranteed on the long term? Is the use of these substrates worthwhile in view of the statutory requirements? (question of proportionality) |
| Concepts of exemplary biogas plants | Go and visit some existing plants as a way of acquiring experience and information. What structural options are available on the market? Where are there structural/process-related problems? How were those problems solved? What has been the experience of existing plant operators with various components and substrate combinations? |
Goals
- Initial assessment of the possibilities
- Gathering of experience from other programms related to Biogas biogas plants
- Acquisition of knowledge about what of a biogas plant plants/components are available on the market
Step 2: Developing the feasibility study
| Availability of substrates |
Check whether it makes sense to have a feasibility study carried out by using the study template pre-feasibility study template Engage the services of an experienced and reputable engineering firm/engineering department of an experienced |
| Get in touch with an is who in Biogas agricultural adviser / professional consultancy | An agricultural adviser or biogas consultant experienced in the building and operation of biogas plants should be approached for site selection and plant design through, construction and commissioning. |
| Decision on the type of plant and construction procedure as well as on the size of plant. |
Definition of the site characteristics, e.g. ordering of a soil report. Site selection (with reference to a general plan of the farm, buildings, silo areas). Location of the nearest power or gas feed-in point. Sizing of the plant components according to an analysis of potentials.
How should the project be implemented? Is a turn-key plant possible? Can the project be multiplicated to other sites? |
Goals
- Involvement of an experienced engineering firm or adviser for preparation of a feasibility study.
- Determination of the preferred size of plant and type of plant/procedure with possible feedin points for power, heat or processed biogas
Engineering firms and companies that we have experience with take a look at the Pack Biogas Who is Who in Biogas.
Step 3: Availability of substrate
| Available substrates
|
Which biomass substrates are available:
At what times will the substrates be available? In what quality will the substrates be supplied? |
| Biomass suppliers | Who are the potential long-term suppliers of substrates? |
| Costs of supply | How much will the substrates cost to supply (price of substrate, transport, workforce)? |
| Storage area | How much storage area will be needed at the planned site of the plant? |
| Pretreatment | How much pretreatment (e.g. mixing, comminution) will the envisaged substrates require? |
Goals
- Selection of substrates with a view to a workable digestion process.
- Definition of measures for pretreatment and processing of substrates. Selection of potential biomass suppliers.
Step 4: Selecting the site
It must first of all be clarified whether the preferred site is of the necessary size, whether the subsoil is suitable and, if possible, free from contamination, whether any existing buildings and storage areas are in a usable condition and whether grid connection points and heat offtakers are available. The purpose of such an assessment is to keep down the construction costs. The relatively low capacitiesinvolved in agricultural biogas production and the associated substrate streams allow the supply of substrate and the disposal of digestate to be effected by road transport. Many substrates scarcely merit the cost of transport on account of their relatively low energy density. Consequently, the search for substrates with which to supply the biogas plant will focus on biomass that is available from the immediate regional vicinity. It will be advantageous to select a site that has access to roads of average transport capacity (such as country roads/B-roads.)
| The site | What is the site like? Is the subsoil suitable? |
| The infrastructure |
Is the site in an industrial zone (on the periphery) or on a farm in the outer zone? |
| Options for heat utilisation |
Can the waste heat from the CHP process be used at the site or nearby? Are the associated conversion works/costs in proportion to the benefit? How much heat needs to be supplied every month? |
| Options for power feed-in | Which utilities (power, water, sewage, telecoms, natural gas) are available at the site? How far away is the nearest power feed-in point? |
| Local acceptance | Which local residents and businesses will be affected? Which local residents and businesses need to be informed about the project at an early stage and, where appropriate, involved in the project? Are there potential heat offtakers? Which public institutions need to be included at an early stage? What nature conservation interests need to be addressed? |
Goals
- Selection of the site
- Selection of form of biogas utilisation (CHP unit at the site, setting-up of a satellite CHP unit or processing of biogas for feed-in to the natural gas grid)
- Building-up of local acceptance through campaign and Human Capacity Development
Find another detailed site evaluation procedure in energypedia.
Step 5: Material stream logistics
| Material stream volumes |
What volumes of substrates are included? What are the properties of the envisaged substrates? |
| Substrate supply chain |
What form of substrate delivery is most efficient? What degree of price uncertainty exists in relation to the purchase of substrates? |
| Biomass suppliers and digestate offtakers | What substrate delivery terms and quality standards exist? (e.g. billing of the delivered biomass quantity/volume) Are there offtakers for the digestate? |
| Substrate transport inside the plant | What handling/transport equipment is needed? What conveying/pumping equipment will I need inside the plant? |
| Storage of digestate | What quantities of digestate will be produced? What method of digestate storage is structurally possible? What method of digestate transport and what digestate field spreading intervals are possible? |
Goals
- Determination of transport and handling technologies
- Definition of available area for substrate and digestate storage at the site of the biogas plant
- Selection of biomass suppliers and digestate offtakers
- Definition of supply agreements and, if possible, long-term supply contracts
Step 6: Selecting the technology
| Selection of digestion process | Will the plant use wet or dry digestion? What process stages will the plant use? And at what process temperature? |
| Select the plant components | What components will the plant use?
|
| Involved parties | Which farms and enterprises will be involved as network partners? experience do the involved parties have? What installation and maintenance firms are available in the immediate vicinity? How much do my staff and partners know about substrate treatment/loading or about transport/silage equipment? |
Goals
- Selection of state-of-the-art plant components of high-grade, maintenance-friendly materials with automated operation.
Step 7: Recovering the energy from the biogas
| Type of biogas utilisation | How can the produced biogas be efficiently used at the site?
|
Goals
- Selection of method of energy recovery from biogas
Step 8: Evaluation and decision-making
| Detailed cost budget |
A detailed cost budget can be drawn up based on the selected procedure. The cost budget should allow budgetary control at all times. The cost items should be broken down into the following blocks:
|
| Possibilities of subsidies and international fundings |
Which possible mechanisms of funding can be used for the project? |
Goals
- Preparation of a profitability analysis, taking account of the assessment of other advantages
- Profitability analysis as a decision-making basis
Further Information
Biogas Box
and operative information/02_Construction of a Biogas Plant Literature and templates for planning
