Design Specifications for Mixing Tanks

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Questions and Answers

What is the recommended inclination range for the floor of the mixing tank toward the inlet pipe?

15% - 20%

8.5% - 17.5% (correct)

10% - 15%

5% - 12%

What material should the cover of the mixing tank be made from?

Plastic

Fiberglass

Wood

G.I. sheet (correct)

What diameter should the manhole cover be for accessing the digester?

0.75 m

0.5 m

0.85 m

0.65 m (correct)

What is the minimum diameter of reinforcement bars used in a reinforced digester?

10 mm Signup and view all the answers

How should the inlet pipe be sealed for proper functioning?

The inlet pipe shall be sealed Signup and view all the answers

What is the main purpose of PAES 413:2001?

To provide requirements for biogas plant construction Signup and view all the answers

Which term indicates a requirement that must be followed strictly according to the standard?

Shall Signup and view all the answers

Which of the following is NOT a purpose of the references considered in the preparation of this standard?

To offer alternatives to biogas plants Signup and view all the answers

What type of waste does the standard specifically focus on for biogas production?

Animal wastes Signup and view all the answers

Which phrase indicates a recommendation without a strict requirement?

Should Signup and view all the answers

Who initiated the formulation of this national standard?

Agricultural Machinery Testing and Evaluation Center Signup and view all the answers

What is implied by the term 'nonconformance' in the context of this standard?

It means failing to observe stated requirements Signup and view all the answers

What is the recommended maximum tank size for collecting manure in a continuous-fed biogas plant?

Equal to the total slurry volume for 10 days Signup and view all the answers

What ratio of manure to water is used to determine slurry volume?

1:1 Signup and view all the answers

Which type of animal manure has the highest daily production mentioned?

Feedlot cow Signup and view all the answers

What is the minimum diameter required for the inlet pipe in a biogas plant?

0.2 m Signup and view all the answers

Where should the biogas system be located in relation to the animal pen?

Near the pen and lower than the animal pen canal Signup and view all the answers

For batch-fed biogas systems, how is the slurry input rate calculated?

By multiplying slurry input rate by the interval of slurry charging Signup and view all the answers

What should the soil foundation for the biogas system be like?

Stable and away from tree roots Signup and view all the answers

Which type of chicken produces the least amount of manure daily?

Broiler chicken Signup and view all the answers

The optimal dimension for other components of the biogas system should follow the procedure used for which component?

Collecting tank Signup and view all the answers

Which type of plant has the digester and gas chamber as separate units?

Split-type plant Signup and view all the answers

What does the term 'substrate' refer to in the context of biogas plants?

Organic material used to produce biogas Signup and view all the answers

What is the purpose of the baffle board in a digester?

To prevent premature exit of the slurry Signup and view all the answers

What characterizes a floating type biogas plant?

The gasholder floats in the fermenting slurry. Signup and view all the answers

Which factor is NOT included in the classification based on plant set-up?

Single-digester Signup and view all the answers

Which of the following temperature ranges is referred to as mesophilic?

20 °C – 40 °C Signup and view all the answers

What does 'retention time' in a digester refer to?

The average period slurry is held for digestion Signup and view all the answers

What is the primary function of methanogens in a biogas plant?

To produce biogas from organic materials Signup and view all the answers

Which type of plant is characterized by the use of multiple digesters?

Multi-digester plant Signup and view all the answers

What factors determine the digester tank capacity?

Daily slurry volume and retention time Signup and view all the answers

Which substrate has the shortest recommended retention time in the mesophilic temperature range?

Liquid pig manure Signup and view all the answers

In a floating type digester, what is the height/length ratio for a circular design?

0.500 Signup and view all the answers

Which length/width proportion (L/W) results in the lowest height/length ratio for rectangular digesters?

L = 3.5W Signup and view all the answers

What is a prerequisite for a properly designed baffle board in a digester system?

It shall be located midway between the inlet and outlet pipes. Signup and view all the answers

Which combination of ratios applies to integrated floating type plants?

Circular: 1.00, Rectangular L=2.5W: 0.340 Signup and view all the answers

What is the retention time for liquid chicken manure?

20 - 40 days Signup and view all the answers

What is the maximum height/length ratio for a rectangular digester with L = 1.6W?

0.385 Signup and view all the answers

For which substrate mix is the recommended retention time the longest?

Animal manure mixed with plant material Signup and view all the answers

What does the coefficient of W represent in the context of rectangular digesters?

Desired length/width proportion Signup and view all the answers

Study Notes

Philippine Agricultural Engineering Standard - Biogas Plant (PAES 413:2001)

This standard outlines the minimum requirements for designing and constructing biogas plants using animal waste.
The standard was developed by the Agricultural Machinery Testing and Evaluation Center (AMTEC) with funding from the Department of Agriculture.
It adheres to international standards (PNS 01-4:1998, ISO/IEC).
The word "shall" indicates mandatory requirements, while "should" suggests recommended practices.
Several reference documents were consulted during the standard's creation, including reports, training courses, and design manuals.

Definitions and Components

Biogas plant: A system processing animal waste/manure to generate biogas and sludge. Includes inlet/mixing tank, digester, gas chamber, and outlet/sludge tank.
Integrated plant: A biogas plant where the digester and gas chamber are integrated into one unit.
Split-type plant: A biogas plant with separate digester and gas chamber units.
Multi-digester plant: A biogas plant with multiple digesters.
Floating type: Biogas plant with a floating gasholder.
Fixed type: Biogas plant with a fixed gas chamber.
Balloon type: Biogas plant with a plastic balloon acting as both digester and gasholder.
Collecting tank: Holds manure and water, filtering out non-biodegradable waste before entering the digester.
Inlet pipe: Carries manure/water mixture to the digester.
Digester/Biodigester/Bioreactor: The main anaerobic reaction vessel.
Baffle board: Divisions within the digester preventing premature slurry exit.
Stirrer/Mixer/Agitator: Mechanical device for mixing slurry within the digester.
Gas chamber: Collects and stores biogas produced.
Gasholder retainer: Holds the gasholder in place.
Outlet pipe: Carries the effluent/slurry out of the plant.
Backfill: Compacted soil and gravel supporting digester wall.
Loading rate: Amount of slurry processed per unit digester volume per day.
Substrate: Organic material used to produce biogas.
Seeding: Introduction of anaerobic bacteria to the digester.
Slurry: Manure and water mixture.
Freeboard: Difference in height between digester wall and filling line (level of slurry).
Retention time: Period slurry remains in the digester for digestion.
Toxic materials: Substances inhibiting pathogen growth (e.g., minerals, heavy metals, detergents).
Methanization/Digestion: Processes involving methane-producing bacteria.
Methanogens: Anaerobic bacteria producing biogas.
Gas production rate: Amount of biogas produced per unit digester volume per day.
Biogas: Mixture of primarily methane and carbon dioxide, used for fuel.
Scum: Floating material (mainly fibrous) on the slurry.
Sludge: Settled, semi-solid portion of slurry.
Effluent: Residue exiting the digester.
Classification of biogas plant (based on different designs).

Location, Size and Components Details

Biogas plant placement should consider good drainage and elevation below the animal pen.
Collecting tank size dependent on the feeding method (continuous or batch).
Calculation methods for digester and gas chamber volume and dimensions are provided, considering retention time and other factors, using formulas.

Functional Requirements

Collecting tank: Concrete channels, water mixing, and sluice gate for manure and water control.
Inlet pipe: Use of concrete/prefabricated pipes, inclination with digester wall, and appropriate location.
Digester: Various materials used, reinforced components for larger biogas production, and special consideration for finishing, and sealing.
Gas outlet pipe: Materials used (PVC or GI), consideration of underground placement and water traps, dimensions.
Outlet tank: Concrete construction, overflow, height relative to filling line.
Ground water drainage: Blind drainage, water seeps, or deep wells to manage water drainage.
Heating systems: Direct or indirect heating for substrate if temperatures are too low.
Pumps: If gravity feed is not feasible due to topography.
Safety concerns: Visual inspections for cracks, gaps, and tightness, water-holding, gas test to ensure the plant is airtight.

Operational and Maintenance Considerations

Initial loading: Include starter material with high bacteria population (5-10% of volume).
Regular loading: Mixing manure with water to the correct consistency.
Stirring: Daily mixing to ensure uniform temperature.
Periodic cleaning: Regular removal of accumulated sludge.
Damage or cracks repair: Repair procedure.
Emergency guidelines: Provide for the safety of workers and bystanders.

Gas Requirements for Appliances

Provides gas requirements (m³/hr) for different types of appliances like a gas burner, mantle lamp, and refrigerator using standardized types.

Additional Information

Several diagrams/figures show typical biogas plant designs (floating drum, fixed dome, balloon type).
Mathematical formulas and tables aid in calculating plant dimensions for different types of biogas plants.
The standard also includes information regarding the optimization of digestion processes (temperature, pH, and nutrient values), as well as various optional or different possible plant designs.

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Description

This quiz covers essential design specifications for mixing tanks, including the recommended floor inclination range, material for the cover, manhole cover diameter, reinforcement bar diameter, and sealing methods for the inlet pipe. It's crucial for anyone involved in the design and construction of mixing tanks to understand these specifications fully.