Instant Tea Extraction Plant

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 4^oC
• Extraction at 60^o C
• Centrifuge at a temperature 10^oC
• 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