and our product is made of good quality. The tea extraction plant integrates the process of extraction, separation of waste, evaporation and spray drying. The plants offer a reliable performance at different pressure and temperature conditions and are easy to operate. Available in various specifications, these plants have aroma recovery system which captures the aroma that serves as the essential component in tea.
Pre-Treatment
Tea waste is pre- treated with de- mineralized water
as it contains around 25-28% of soluble solids, out of which around 20% are
extractable as instant tea. There is a paddle mixer into which the DM water
and tea waste are properly mixed through an attached agitator assembly.
After this, the entire mixed solution is conveyed through an elevator to the
extraction section.
Extraction
The extraction process of the soluble solids is carried
out, following a three stage procedure in a counter current extraction
system. The entire system is assembled with 3 extractors, 2 decanters and a
vibroscreen. The unique design of the system ensures that the residual tea
waste mixture that is already twice extracted before comes in contact with
the de- mineralized water. On the other side, after second extraction, the
concentrated solution comes in contact with the fresh freed (teas waste).
There are 3 extractors in the system, all fitted with agitating blades and
rotating shaft that ensure proper mixing of tea waste with the DM water,
resulting into a lighter extract. Tea waste and tea has to be kept at a
temperature of above 60° C and the extractors are jacketed for
protection against low pressure steam. Total retention time for three
extractors comes out to be around 60 minutes, as each extractor takes about
20 minutes. In the first extractor, there will be rich miscella, a solution
of DM water and instant tea along with residual tea waste mixed together in
the form of slurry. In the final stage, this slurry is separated out from
the extract and wet solid residue by processing into super decanter. Then,
the liquid portion is sent to the evaporator section.
After the extraction unit, the wet solid portion is transferred to the
second extractor containing medium concentrated miscella. The entire
extraction process is carried out similarly as above and after about 20
minutes, the slurry is pumped into the super decanter. In the process, the
slurry is sent to vibroscreen and the liquid portion to the third extractor.
The filtrate from the vibroscreen containing 5% concentration is the final.
The residue from this stage is rejected.
Tea waste is fed into the first extractor and fresh DM water to the third
extractor. In this way, the entire system carries out the real counter
current extraction of instant tea solution from tea waste in just about 90
minutes extraction time.
Evaporation
Considered as a double effect falling film plant, the
evaporation plant is fitted with thermocompressor. The feed is pumped to the
pre- heaters from the feed tank through an appropriate pump in which the
vapour elevates the feed temperature to 55 degree Celsius. The feed gets
more heat in the effect calandria for evaporating the water. After the first
effect, the partially concentrated material is fed to the second effect for
concentration. On one side, a thermocompressor reduces the steam
consumption, whereas the vapours from the first effect are used for heating
the second effect. In the continuation, the vapours generated from the
second effect are completely condensed in the surface condenser using
cooling water. For this a vacuum has to be maintained, and for this a two
stage water ring vacuum is installed.
Spray Drying
The feed solution is pumped into the rotary atomizer
through a positive displacement screw pump. There are fast rotating discs in
the atomizer that finely disperses the feed into a spray of droplets,
resulting into a maximized surface area. There is an air distributor through
which the air is sent to the drying chamber after heating in the indirect
oil fired air heater. The spray and the air come in contact with each other
co- currently with mixing of hot air and atomized droplets. Due to the
intense heat and mass transfer, the process of drying gets completed in few
seconds, without degradation of powder. The final separation of the powder
from the exhaust air is carried out in a cyclone separator system.
Salient Features of Instant Tea Extract Plant
Requirement Of Raw Material
A good quality of raw material is necessary for a quality product.
Following are the raw materials that are generally used in the process:
- Tea waste + black tea (proportion will be given later)
- Tea waste (generated from tea producing factory)
- Fresh fermented leaf + tea waste (found near to the tea garden)
- Green tea waste + black tea water (ratio will be 2:8)
- Fresh fermented leaf + made tea (very good quality)
- Fresh fermented leaf (found only near a garden)
Extraction
- Temperature of extraction is set at 60°C
- Three stage counter current extraction is considered as the best
- The continuous process is however a simulated batch process
- Ratio of raw material : DM water = 1:9
- Can be batched or continuous
- Residence time : 20 minutes (low temperature and residence time is
better)
- Recovery from black tea will be: 35%
- Recovery from tea waste will be: 20%
- Recovery from fermented leaf will be : 35% (on dry basis)
Evaporation Or Concentration
- The temperature of evaporation is lowered down through vacuum
evaporation
- Evaporation is done in two stages
- Initial concentration of feed: 5%
- Evaporation rate : 810 kg/hour
- Maximum working temperature: 55°C
- Final concentration of concentrate: 30%
Spray Dryer
- The moisture content in the product: 3% (max.)
- The feed concentration: 30%
- Exhaust air temperature: 96°C or thereabout
- Drying temperature: 180°C to 200°C
- Product temperature: 30°C
- Packing is done in de- humidified room
- Instant tea, being hygroscopic in nature; is also collected in an a/c
dehumidified room
For Cold Water Soluble Tea
- Three stage extraction process
- Chill the liquor to 4oC
- Extraction at 60o C
- Centrifuge at a temperature 10oC
- Post centrifugation, the material is passed through the standard
process of spray drying and evaporation
Additive
- Material is added for pH adjustment as tea is acidic in nature
- Flow improver
- An antioxidant is added at the time of evaporation to prevent any
deterioration to the quality
- Anti foaming agent
USP
- Two plants at Ahimsa Chemicals Limited and Goodricke Group Limited
are already in successful in operation
- The entire infrastructure is planned properly taking into
consideration the flexibility of the process
- The entire infrastructure is planned properly taking into
consideration the flexibility of the process
- The entire process ensures the high standard quality of products