Research, Design and Development of
Bio-retting plant
Result
The Cost of 1 KG good quality fibre came down
from INR 1000/- to 250/-
Cost of construction reduced from 40 L to 6 L
Due to price reduction, more businesses can make products in the price range that the market is willing to spend.
Brief
India is the largest exporter of bananas in the world where Tamil Nadu is the major producer.
The banana plant only produces fruit once in its lifespan. It takes approximately 10-12 months to bear fruit.
Once harvested, these plants are chopped and burned, resulting in a negative carbon impact. Rather than burning these plants, high-quality fibres can be harvested from the pseudostems and used as raw materials in a wide range of businesses.
Farmers could earn more money by extracting fibres from harvested plants rather than burning them.
Research Findings
Anatomy of the Plant
Banana is a herb and not a tree. More than 90% of the banana plant's weight is made up of water and only 2% of it is fibre.
Fibres are present in all parts of the plant. Most of the extractable good quality fibres are found in the leaf sheath (false stem which extends to be the leaf).
Selection of Leaf Sheath for Fibres
The outermost fibres have high lignin content. The fibres extracted from them are thicker and do not have much tensile strength.
As we move towards the innermost sheath, the lignin content in the fibres reduces gradually. The fibres become thinner and there is an increase in the tensile strength.
Within a leaf sheath, the fibres at both corners of the sheath are stronger and thinner compared to the center.
Based on the end use of the fibres, these sheaths are separated into multiple grades before extracting fibres.
Selection of Breed
Based on available research papers, it was concluded that the tensile strength of the banana fibres in the native varieties is better than the hybrid ones.
Amongst all the native commercial varieties available, Nendran fibre has the highest tensile strength.
Characters of Banana Fibre
Good moisture absorption
Smooth and lustrous look (like silk)
Good tensile strength (Mercedes uses banana fibres with epoxy to make parts of the car due to its strength to weight ratio compared to synthetic fibres)
Can be dyed easily and has good colour retaining properties.
Historical Significance
The banana silk coat is a renowned and expensive garment that is worn by Indian rulers and aristocrats.
King Krishnadeva Raya used to wear a banana silk coat.
Japanese Kimono is made from banana fibres which are used in traditional ceremonies and are very expensive.
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Fibre Extraction - Different Methods
3 ways to extract banana fibres are hand, machine and bio extraction. A comparative study of all these extraction
methods is given below.
The CAPEX of the bio-extraction is high. It is the best method to get the finest quality fibre on a large scale. This method consumes less energy, labour and is environmentally friendly.
Bio-retting Process
Step 1
Leaf-sheaths are removed from the plant and segregated based on their quality.
Step 2
They are passed through a roller to remove excess moisture content and to damage the pith.
Step 3
They are packed in cages which are then placed into a bio-retting tank.
Step 4
After 5 days of bacterial retting, the fibres have to be removed from the tank. They have to be washed immediately and sun dried.
Step 5
Once dried, it is treated with dilute KOH solution to kill any existing bacteria and to reduce lignin content.
Research Findings
Breed and Variety
Variety: Native than hybrid
Best plant breed: Nendran
Part of the plant: Pseudostem - inner
Subpart: Pseudostem - corner
Process
Best method: Bio-retting
Bacteria type: Anaerobic bacteria
Chemical process: KOH after retting
Cost
CAPEX: Comparatively high
OPEX: Comparatively low
Product cost: Reduces drastically
Requirements and Challenges prior to Execution
Raw Material Availability
In most areas, bananas are harvested only for 2 months/year.
It is expensive to keep the unit idle for 10 months/year. The bacteria in the tank is at risk of dying if not fed during this period
Good quality fibre is extracted from native varieties
Water and Electricity
Continuous water supply is required for the entire process. The water used for cleaning the fibres can be reused for irrigation purposes (natural fertilizers)
Electricity is required to run the motor for 4 hours/day
Labor and Connectivity
Around 5 workers are required to run the unit.
The unit has to be built away from residential areas due to foul smell and safety issues
Finalized Location
Tirunelveli District
Supporting Factors
Major harvests are for 9 months/year
Ample water available
Manpower available nearby
Good road connectivity
Proper temperature for bacteria
Uninterrupted power supply
Design and Redesign
Problem Statement
The initial cost of constructing a bio-retting facility with a capacity of 30 tons was
₹40,00,000/-. The goal was to finish the construction in ₹4,00,000/- with a capacity increase of 35 tons.
This redesign was made in order to make the design economically viable and reproducible in other locations.
Approach
The construction materials used in the new design have to be durable, economically viable and locally sourced.
The construction process should be designed to fit the skillset of local people and should not be time consuming.
The redesign process included ideas and suggestions from Civil-engineers, Architectures and Scientists from NIIST.
Components
The bio-retting plant consists of the following:
Reactor - Increases bacterial culture through hydraulic push and pull.
Tank - Cages of banana barks are placed inside. The bacteria are then passed through it for bacterial retting.
Gas Collection Chamber - Biogas is generated as a residue of the retting process which is then collected through an air-tight pipe.
Motor - A motor is used to pump the bacteria from the reactor to the tank and vice versa.
Reserve tank - This holds the bacteria for a short period of time until the barks are loaded and fibres are unloaded.
Cages or Dividers - Banana barks are placed in cages which are then placed in the tank. Cages are used to ensure that the fibres don't get tangled in the hydraulic push and pull.
The entire process should be air-tight for maximum efficiency.
Working Concept
The motor circulates bacteria from the top of the reactor to the bottom of the tank and vice versa. This ensures that the bacteria reach almost all parts of the leaf sheath with a better hydraulic push.
The tanks have to be air-tight as the bacteria in the tanks are anaerobic (cannot withstand exposure to oxygen). The air-tight lids assist with collecting the residual biogas.
There should be 7000L of bacterial water for every 1000kg of banana bark in the tanks.
The motor has to be used every day for 2 hours in the morning and evening.
The pH value of the bacterial water has to be checked periodically in the reactor. This ensures the good health of the bacteria.
Design Iterations
Final Design
Blueprint
Retting Tank Design
Bio-reactor
Gas Outlet Pipe
The bio-gas produced as a result of the retting process is routed through water so that the pressure created inside allows the bio-gas to escape. Because of the water, outside air will be unable to enter the tank. This procedure is vital because it is necessary to keep the anaerobic bacteria healthy because they perish when exposed to oxygen.
Construction on Site
Many civil engineers refused to take risk constructing it, since it demanded a whole new form of construction that they were unfamiliar with. Finally; one engineer agreed to build the unit according to our specifications and building methods. After signing the MOU and settling on payments, the construction procedure began.
Fibre Extracted
Systems to Run the Unit
Created systems to efficiently run the bio-retting facility. The activity chart below sets a pattern of tasks for the workers, ensuring that they are focused, time-efficient and do not miss any important activities for the day.
The banana bark is placed in the tank the first week. In the following week; barks are retted and the fibres are ready for collection from the tank.
The second week involves removing the fibres from the tank, washing, cleaning and replacing the retted barks with fresh ones. The retting process continues.
RESULT - Costing of the Fibres
The cost of 1 KG of good quality fibre reduced from
1000/- to 250/-.