Planning Guide for Biogas Plants

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Overview

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.

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
  
• 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: Address of operator/customer: Place/region/country: Indigenous proj. org./executing org.: Extension officer/advisor: General user data Household structure and number of persons: User's economic situation: Crops: types, areas, manner of cultivation: Non-agricultural activity: Household/farm income: Cultural and social characteristics of user: Problems leading to the "biogas approach" Energy-supply bottlenecks: Workload for prior source of energy: Poor soil structure/yields: Erosion/deforestation: Poor hygiene and other factors: Objectives of the measure "biogas plant" User interests: Project interests: Other interests:

Natural / Agricultural Conditions

	Data	Rating
Natural conditions Mean annual temperature: Seasonal fluctuations: Diurnal variation: Rating:		- o +
Subsoil Type of soil: Groundwater table, potable water catchment area: Rating:		- o +
Water conditions Climatic zone: Annual precipitation: Dry season (months): Distance to source of water: Rating:		- o +
Livestock inventory (useful for biogas production) Animals: kind and quantity: Type of stable: Use of dung: Persons responsible for animals: Rating:		- o +
Vegetable waste (useful for biogas production) Types and quantities: Prior use: Rating:		- o +
Fertilization Customary types and quantities of fertilizer/areas fertilized: Organic fertilizer familiar/in use: Rating:		- o +
Potential sites for biogas plant Combined stable/biogas plant possible: Distance between biogas plant and livestock stable: Distance between biogas plant and place of gas consumption: Rating:		- o +
Overall rating 1		- o +

Balancing the Energy Demand with the Biogas Production

	Data	Rating
Prior energy supply Uses, source of energy, consumption: Anticipated biogas demand (kwh/day or l/d) for cooking: for lighting: for cooling: for engines: Total gas demand a) percentage that must be provided by the biogas plant: b) desired demand coverage: Available biomass (kg/d) and potential gas production (l/d) from animal husbandry pigs: poultry: cattle: Night soil* 1. 2. Totals biomass and potential gas production a) easy to procure: b) less easy to procure:*;Vegetable waste (quantities and potential gas yield) Balancing Gas production clearly greater than gas demand -> positive rating (+) Gas demand larger than gas production -> negative rating (-); but review of results in order regarding: 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: -> qualified positive rating for the plant location (o) If the measures do not take hold: -> site rating remains negative (-)
Overall rating 2		- o +

Plant Design and Construction

	Data	Rating
Selection of plant design Locally customary type of plant: Arguments in favor of floating-drum plant: Arguments in favor of fixe-dome plant: Arguments in favor of other plant(s): Type of plant chosen: Selection of site Availability of building materials Bricks/blocks/stone: Cement: Metal: Sand: Piping/fittings: Miscellaneous: Availability of gas appliances Cookers: Lamps: ... ...
Overall rating 3		- o +

Plant Operation / Maintenance / Repair

	Data	Rating
Assessment of plant operation Incidental work: Work expenditure in h: Persons responsible: Rating with regard to anticipated implementation:		- o +
Plant maintenance Maintenance-intensive components: Maintenance work by user: Maintenance work by external assistance: Rating with regard too anticipated implementation:		- o +
Plant repair Components liable to need repair: Repairs that can be made by the user: Repairs requiring external assistance: Requisite materials and spare parts: Rating with regard to expected repair services:		- o +
Overall rating 4		- o +

Economic Analysis

	Data	Rating
Time-expenditure accounting Time saved with biogas plant Time lost due to biogas plant Rating:		- o +
Microeconomic analysis Initial investment: Cost of operation/maintenance/repair: Return on investment: energy, fertilizer, otherwise: Payback time (static): Productiveness (static): Rating:		- o +
Quality factors, useful socioeconomic effects and costs Useful effects: hygiene, autonomous energy, better lighting, better working conditions, prestige: Drawbacks: need to handle night soil, negative social impact: Rating:		- o +
Overall rating 5		- o +

Social Acceptance and Potential Dissemination

	Data	Rating
Anticipated acceptance Participation in planning and construction Integration into agricultural setting: Integration into household: Sociocultural acceptance: Rating:		- o +
Establishing a dissemination strategy Conditions for and chances of the professional-craftsman approach: Conditions for and chances of the self-help oriented approach:		- o + - o +
General conditions for dissemination Project-executing organization and its staffing: orgnaizational structure: interest and prior experience in biogas technology: Regional infrastructure for transportation: communication: material procurement: Craftsman involvement, i.e. which acitivities: minimum qualifications: tools and machines: Training for engineers, craftsman and users: Proprietary capital, subsidy/credit requirement on the part of user: craftsmen: 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:

1. Calculation of biogas amount
2. Size of digester
3. Size of engine
4. Sitelayout
5. Flow chart
6. 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 biogas plants.
• Acquisition of knowledge about what 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 Engage the services of an experienced and reputable engineering firm/engineering department of an experienced and reputable plant manufacturer.
Get in touch with an 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. Decision on appropriate plant configuration/design and technology with reference to future vision for the site of application and operational restructuring measures necessitated by the biogas plant. Sizing of the plant components according to an analysis of potentials. Question of procedure: How should the project be implemented? Is a turn-key plant possible? What does the plant construction process look like? How high is the available workforce? Can the project be multiplicated to other sites? Which contract works are planned to put out to tender? (e.g. earthworks, electrics…)

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

Step 3: Availability of substrate

Available substrates	Which biomass substrates are available: agricultural residues (e.g. cattle manure, poultry excrement) agroindustrial wastes (e.g. apple mash, POME) wastes from trade and industry (e.g. grease trap waste) wastes from private households (e.g. biowastes) renewable resources, energy crops (e.g.maize silage, grass silage) 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? How high are the land costs? Is the road access suitable for trucks?
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? Does the possibility exist to set up a satellite CHP unit (CHP unit physically separate from the biogas plant and connected to the gas tank by a relatively long gas pipeline)?
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? How wide is the average radius of potential substrate suppliers? How is the seasonal arising of substrates? What are the properties of the envisaged substrates?
Substrate supply chain	What form of substrate delivery is most efficient? What types of long- and short-term storage are available at the site? What forms of treatment and metering are required? 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? Receiving, treatment and loading equipment Digester with internal components and agitator system Type of gas tank Method of digestate storage Biogas utilisation
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? Combined heat and power (CHP) generation (e.g. CHP unit, micro gas turbine, etc.) Cold generation by trigeneration process Upgrading of biogas (dehumidification and desulphurisation) to natural gas quality for feed-in to the public natural gas grid or micro gas grids Processing into fuel for motor vehicles Recovery of heat from biogas

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: costs of individual components substrate costs (delivery 'free to digester') depreciation maintenance and repair interest insurance labour costs financing/permitting costs planning/engineering costs utility costs, grid connection costs transport costs overheads (telephone, rooms, utilities, etc.)

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

• See all Biogas Articles on energypedia