WO2012085926A1

WO2012085926A1 - System for heated ambient air based drying of tea involving ambient psychrometric conditions

Info

Publication number: WO2012085926A1
Application number: PCT/IN2011/000402
Authority: WO
Inventors: Ranjit CHALIHA
Original assignee: Chaliha Ranjit
Priority date: 2010-12-24
Filing date: 2011-06-15
Publication date: 2012-06-28
Also published as: CN103392106B; CN103392106A

Abstract

A system for drying of tea and the like materials is disclosed involving controlled heating of ambient air to predetermined RH to convert it to appropriate inlet air for drying green and wet tea leaves irrespective of initial humidity ratio of the ambient air. An online control of the process parameters is carried out by a system involving i) Electronic Hygrometer-cum- Thermometer, ii) Pre-programmed Micro Controller, iii) Heater Fuel Supply Regulator and iv) Dryer Feed Regulator, such as to achieve predetermined RH of inlet and exhaust air of dryer. The heater fuel supply and dryer feed regulator is monitored and controlled to implement optimum heat addition to inlet air and its utilization for desired drying effect corresponding to a given rate of production and desired quality of dried tea. The present system and method of tea drying thus enable significant savings fuel consumption making use of favourable ambient air condition.

Description

SYSTEM FOR HEATED AMBIENT AIR BASED DRYING OF TEA INVOLVING AMBIENT PSYCHROMETRIC CONDITIONS

FIELD OF THE INVENTION

The present invention relates to a system for heated ambient air based drying of tea and the like materials which would be adapted to take advantage of favourable changes in ambient conditions to make savings in heat energy input required for such drying. More particularly, the present invention is directed to providing a system for drying of tea leaves by controlled heating of ambient air to convert to the inlet air for drying tea leaves depending on the initial humidity ratio of the ambient air. The system is adapted for an online control of the heat input for heating the ambient air for the above drying process involving simple and cost-effective gadgets which further makes the process of drying of such tea and other material simple and user -friendly. The present system and method would thus enable significant savings in heat addition and fuel consumption making use of favourable ambient air condition, making the system and process cost -effective without loss of production or quality of tea products.

BACKGROUND ART It is well known in the process of manufacture of tea, the 'Drying' is an operation in which the wet processed and fermented tea leaves are subjected to a blast of hot dry air inside a Tea Dryer to remove moisture to obtain dried black tea. It is also well known that this drying process is adopted for both Conventional Endless Chain Pressure (ECP) type with Trays and FB (Fluid Bed) type of drying machines.

To implement the conventional drying process, the ambient air is heated to a desired predetermined temperature. The object of heating the ambient air is to increase its moisture holding capacity by lowering the Relative Humidity(RH). In a tea dryer as per normal practice ambient air is heated in the stove or heater of the dryer to a predetermined temperature of the "Inlet Air" between 82.2 to 104.4 °C for Conventional ECP dryer and 120 to 150 °C for FB dryer which require addition of 50 to 150 kilo-Joules of heat per Kg of dry air. This favors satisfactory drying of a given type of tea and results a predetermined "Exhaust Air" temperature of 40 to 60 °C. This is so that the inlet air can pick-up and retain the moisture in vapour form which will be transferred to it from the wet tea leaves as it moves around in case of FB dryers and through the thin layer of tea particles spread on perforated trays inside Conventional ECP dryers. The lower the Relative Humidity of the air the faster is the evaporation of the water and hence the rate of drying of the wet tea leaves. In the case of Conventional tea dryers the recommended overall rate of drying is 2.8 to 3.6% moisture loss per minute. In the case of tea manufacturing, addition of heat to air has another role to play in effecting bio-chemical changes in the constituents of the leaves for formation of the final product. During the process of drying, the moisture on the surface of the wet tea leaves is evaporated into the "Inlet Air" stream due to the difference between the higher vapour pressure of this water and that of the lower pressure of the water-vapour contained in the "Inlet Air". The required latent heat of vaporization of water is supplied by the hot air which as a result cools down and simultaneously becomes progressively more moist due to the increasing quantity of water-vapour it is picking up from the tea leaves. Its Humidity Ratio or the quantity of moisture the air is holding per unit weight of dry air, and therefore the Relative Humidity (RH) is constantly increasing. The cooling of the air mentioned above is termed as 'adiabatic cooling'. No heat is either given to or taken from any outside source, ideally but some heat loss does occur from the body of the dryer to the atmosphere through conduction, convection, radiation and in some cases air leakages. The "Inlet Air" after passing through the dryer and extracting the moisture from the wet tea leaves is allowed to escape into the atmosphere as "Exhaust Air", being considerably cooler and having a much higher Relative Humidity compared to "Inlet Air". It has , however, been a limitation of the existing system and method for such drying process for tea and the like, wherein the ambient air is usually heated to a predetermined temperature to convert it to heated "Inlet Air" for dryer, regardless of the RH or humidity ratio of the ambient air condition. This method of drying and heating of air thus involves waste of heat due to uncontrolled heating of air to a temperature more than what is optimally required for a desired rate of drying of tea leaves which can greatly vary depending upon the constant climatic and weather changes and the resultant variable state of the ambient air and its heating requirements for such purposes of drying. Thus, in a day when the RH of ambient air is very high say 95% at 28°C DBT, the required heating of the ambient air may be to the level of 94°C to reduce the RH to 4.41% for "Inlet Air", while in case of change in the climatic conditions and the ambient air conditions in case of a sunny day with RH of 75% at 28°C DBT may call for heating of the ambient air only up to 88°C to attain the same "Inlet Air" condition and no more. However, under the prevailing practice the heating of the ambient air for the purposes of the heated dry air is usually done irrespective of any monitoring of the ambient conditions and the required conditions for drying. This results in situation where the unutilized heat content is lost through the "Exhaust Air". Further, with the prevailing practice of heating the ambient air to a predetermined temperature it is difficult to have proper control over the drying rate or rate of removal of moisture from the material being dried in the dryer. The drying rate is a function i) RH of the "Inlet Air" ii) RH of the "Exhaust Air" and iii) volume of "Inlet Air". The volume of "Inlet Air" is easily controlled or regulated by means of opening or closing the air damper or adjusting the speed of the fan. However by following the prevailing practice it is not possible to regulate the RH of the "Inlet Air" to any predetermined figure consistent with producing the best quality of the product. In the example given above, if the ambient air in the second case which is drier than the first is heated to the same temperature of 94 *C the RH of the "Inlet Air" would be 3.48 % instead of 4.41 % thereby causing a faster drying rate. If the drying rate is to be maintained at the same level as in the first case the "Inlet Air" volume will have to be altered which in turn will further upset the performance of the dryer. Therefore presently there is no attempt to regulate the drying rate after the dryer controls are set even though this rate may not be the optimum. There has been, therefore, a persistent need in the art to provide for better system and method for heated air drying of tea and the like material in dryer which would favour the desired optimal heat utilization for the drying purposes and save unwanted wastage of unutilized thermal energy as well as reduce fuel consumption in addition to ensuring achieving an optimal rate of drying for consistently uniform and better quality of the product in a simple and cost effective manner for desired rate of production without compromising quality of end products.

OBJECTS OF THE INVENTION

It is thus the basic object of the present invention to provide a system and method for heated ambient air based drying of tea and/or other materials in conventional or FB dryers adapted to ensure automatic online control of air heating commensurate with ambient air condition in order to achieve saving of excess heating than actual requirement and reduce fuel consumption while maintaining desired quality of the dried product.

A further object of the present invention is directed to providing a heated ambient air based drying system and method of air heating for drying of tea and the like material wherein controlled air heating could be carried out to attain predetermined RH of "Inlet Air" and "Exhaust Air" in dryer and thereby favour avoiding unnecessary wastage of heat energy utilized for such drying processes. A further object of the present invention is directed to providing a heated ambient air based drying system and method of air heating for drying of tea and the like material which would be adapted to control the quantum of heat addition to ambient air for generating heated "Inlet Air" for drying with or without further control of the Feed Spreader Height control through feed back control in order to attain predetermined RH of "Inlet" and "Exhaust" air.

A further object of the present invention is directed to providing a heated ambient air based drying system and method of air heating for dryer of tea and the like materials wherein ambient air could be heated in the air heater to a pre-determined RH value, irrespective of the initial Humidity Ratio, so that "Exhaust Air" RH could be maintained at desired level to maintain consistent dried tea quality for a given rate of production.

A further object of the present invention is directed to providing a heated ambient air based drying system and method of air heating for drying of tea and the like materials wherein ambient air could be heated in the air heater to a pre-determined RH value, irrespective of the initial Humidity Ratio, so that rate of removal of moisture from the tea being dried could be maintained at a desired level to maintain consistent dried tea quality for a given rate of production.

A further object of the present invention is directed to providing a heated ambient air based drying system and method of air heating for drying of tea and the like wherein the system would favour a saving in heat of about 7-10% for ECP and FB dryers respectively, to attain predetermined RH values as compared to conventional predetermined temperature based air heating.

A further object of the present invention is directed to providing a air heating system and method for dryer of tea and the like wherein savings in heat energy, and hence fuel is possible when drying substances such as tea and similar materials inside a dryer by taking advantage of the naturally occurring favourable changes in the Humidity Ratio of the Ambient Air.

A further object of the present invention is directed to providing a system and method of air heating for dryer of tea and the like wherein savings in heat energy can be effected by addition of less heat to convert the Ambient Air with higher dryness to "Inlet Air" of predetermined RH, instead of heating the Ambient Air to a predetermined temp. A further object of the present invention is directed to providing an air heating system and method for drying of tea and the like wherein quantity of fuel used per unit weight of dried tea can be reduced by increasing the output of the dryer by feeding larger mass of tea leaves in dryer without increasing the heat input.

SUMMARY OF THE INVENTION

Thus according to the basic aspect of the present invention there is provided a system for heated ambient air based drying of tea and/or other materials involving ambient psychrometric conditions comprising: an ambient air heater with fuel supply regulator either automatically or manually operated ; a dryer having a material feed regulator either automatically or manually operated; electronic hygrometer cum thermometer; a microcontroller means operatively connected and adapted to facilitate the control of the heating of the ambient air for the purposes of drying of the tea or other material in the dryer based on the desired conditions for drying in the dryer.

A further aspect of the present invention directed to said system comprising an electronic hygrometer cum thermometer adapted to measure the ambient air Humidity Ratio and temperature and send relevant data signals to the said microcontroller; said microcontroller processes the said data and computes the correct RH and temperature to which the ambient air need to be heated and sends corresponding signals to the ambient air heater with fuel supply regulator to release proper quantity of fuel for said desired heating of the ambient air in case of automatic operation and sends instructions by way of digital display or sound alert or both for the operator in case of manual operation; a dryer inlet air hygrometer and thermometer adapted to continuously sense and send signals to the microcontroller to thereby update the values of RH and temperature at the air inlet in the microcontroller; said microcontroller adapted to compare the values of the air inlet with values it computed and implemented the burner control mechanism and initiate corrective measures if required to further control the fuel in the burner for desired heating of the ambient air to thereby maintain the desired standard RH and temperature in the dryer . A still further aspect of the present invention is directed to said system comprising a dryer exhaust air hygrometer and thermometer adapted to continuously sense and send signals to the microcontroller to thereby update the values of RH and temperature at the air exhaust in the microcontroller; said microcontroller adapted to compare the values of the air exhaust and actuate based thereon a feed spreader height control mechanism in case of automatic operation and send instructions by way of visual digital display or sound alert or both for the operator in case of manual operation to thereby maintain the desired standard of flow of feed in the dryer. A still further aspect of the present invention is directed to said system wherein said microcontroller adapted to compare the values of the exhaust air and further actuate based thereon inlet air damper and throughput time controller, if required, both in case of automatic or manual operation. According to yet another aspect of the present invention is directed to said system wherein said microcontroller is adapted to heat the ambient air in the air heater to a temperature which will convert its RH to a pre-determined value as required in Conventional dryers or fluidized bed dryers (FBD) irrespective of its initial Humidity Ratio. A still further aspect of the present invention is directed to a system wherein the hygrometer-cum-thermometer is adapted to constantly measure the Humidity Ratio relative humidity and dry bulb temperature of the ambient air and convert the data into electrical signals which in turn is relayed to the micro-controller preferably with further display of the same in LCD or LED digital displays.

A still further aspect of the present invention is directed to said system wherein said heater fuel supply regulator is operatively connected to oil/gas burner or chain grate or other stoker for coal/wood firing and suitable for both automatic and manual operation and adapted to continuously monitor the temperature and RH of the "Inlet Air" and transmit the values to said microcontroller, said microcontroller providing for receiving the same and generating any -corrective commands to the fuel supply regulator based thereon. A still further aspect of the present invention is directed to said system wherein said microcontroller is adapted to compute correct values of temperature and RH of the exhaust air and relay the information to the dryer regulator or manual operator such as to command the same to raise or lower the feed spreader to thereby increase or reduce the quantity of leaf/material being fed into the dryer for further maintaining desired "Exhaust Air" conditions.

According to yet another aspect of the present invention is directed to a method for carrying out heated ambient air based drying of tea and/or other materials involving ambient psychrometric conditions using the system as described above comprising: the step of controlling saving of heat energy and hence fuel by activating said microcontroller based control of the heating of the ambient air based on the desired RH at the inlet of the dryer and the favourable changes in the humidity ratio of the ambient air. Another important aspect of the present invention is directed to said method wherein said saving of heat energy and hence fuel is effected by way of anyone or more of the following : i) by using less heat to convert the ambient air to "Inlet Air" by heating to a predetermined RH instead of heating the ambient air to a predetermined temperature and ii) by increasing the output of the dryer without increasing the heat input such that quantity of fuel used per unit of dried tea/material is reduced.

The objects and advantages of the present invention are described in greater details with reference to the following non limiting illustrative accompanying drawings and examples.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure 1 : is the schematic illustration of the system for ambient air heating control to obtain inlet air for tea dryers according to the present invention showing the different components.

Figure 2: is the schematic illustration of the flow diagram for the process of ambient air heating according to the invention for tea ECP/FB drying machines showing the various inputs and outputs. Figure 3: is the schematic illustration of the installation of ambient air heating control system in a conventional ECP dryer showing the installation of different control mechanisms required.

Figure 4: is the schematic illustration of the implementation of ambient air heating control system in a FB dryer showing the installation of different control mechanisms required.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

The present invention is thus directed to making effective use of the favourable changes in the ambient air, i.e. when it is naturally available with higher dryness in terms of H and humidity ratio at a given temperature, considerable savings in heat can be effected in air heating to attain a desired predetermined RH of inlet air and the exhaust air in the tea drying process, without any additional cost or loss of production or quality.

The system according to the present invention as per an exemplary illustration basically comprises of four different units as per the schematic illustration of the accompanying Figure 1, either by hardwiring or fitted with wireless transmitters and receivers or both, for transmitting signals between them on a continuous basis. These mutually interactive and operatively connected units include i) Electronic Hygrometer-cum-Thermometer, ii) Preprogrammed Micro Controller installed attached to the dryer or separately placed at a convenient location, iii) Heater Fuel Supply Regulator suitable for both automatic and manual operation and iv) Dryer Feed Regulator suitable for both automatic and manual operation.

The working of the control system of the present invention and its components in relation to heated ambient air based controlled air drying for tea dryer are as follows: i) The electronic Hygrometer-cum-Thermometer is adapted to constantly measure the Humidity Ratio Relative Humidity and dry bulb temperature of the ambient air and convert the data into electrical signals which it relays to the Micro-Controller. It also indicates these values by LCD or LED digital display. ii) The Micro-Controller is adapted to receive this data, processing the same and computing the correct temperature to which the ambient air must be heated to attain the predetermined Relative Humidity to convert it into the appropriate "Inlet Air" for the ambient air available at that instant. The micro-controller then relays this information to the Heater Fuel Supply Regulator installed with the oil / gas burner or chain grate or other stoker for coal / wood firing and commands the Regulator or manual operator through visual and/or sound alerts, in case of automatic and manual operation respectively to release the requisite quantity of fuel for combustion for heating the ambient air to reach and maintain the computed values of RH for "Inlet Air". It also indicates the computed values for both "Inlet Air" and "Exhaust Air" through LCD or LED digital display. iii) The Heater Fuel Supply Regulator not only executes these commands but also continuously monitors the temperature and RH of the "Inlet Air" and transmits these values to the Micro-Controller. On receiving this feed back information, if any correction is required the Micro-Controller sends further commands to the Fuel Supply Regulator or manual operator for doing this. It also indicates the current values of temperature and RH of the "Inlet Air" by digital display. iv) The Micro-Controller also computes the correct values of temperature and RH of the "Exhaust Air" and relays this information to the Dryer Feed Regulator or manual operator through visual and/or sound alerts and commands it to raise or lower the height of feed spreader to increase or reduce the quantity of leaf being fed into the dryer for maintaining the required "Exhaust Air" conditions. The Dryer Feed Regulator also transmits to the Micro- Controller feed back information regarding the condition of the "Exhaust Air" for correction, if any. In addition it indicates the "Exhaust Air" temperature and RH by LCD/LED digital display.

The different variable parameters and their effect on the dryer performance are identified as follows:

Variable Effect on the Air

i) Fuel supply - Only on "Inlet Air";Temp. varies directly, & RH inversely;

ii) Feed Control Spreader - Only on "Exhaust Air", Temp, varies inversely with

height & RH of air varies directly with height of spreader.

iii) Inlet Air damper - Only on "Inlet Air"; Temp, varies inversely & RH

(Air volume) varies directly with increase in air volume.

iv) Throughput Time - Only on "Exhaust Air"; Temp, varies directly & RH

varies inversely. The various inputs and outputs to the system for implementing the desired controlled air drying according to the invention are illustrated in the process flow diagram of the accompanying Figure 2.

The ratings and range of operating parameter values sensed by different components of the system as used for conducting experiments may be identified as follows :

Equipment Range of Parameter Values

Amb. Air Hygrometer . Temp. 20 - 40°C RH.- 60%- 97%

Humidity Ratio. 0.01 - 0.031 Kg. Water Vap/Kg.Dry Air

Fuel Regulator Temp. ECP dryer - 80 - 105°C. RH - 1.0 - 5.0%

FBD - 1 10 - 150°C 0.4 - 5.0%

Exhaust Air Thermometer & Hygrometer. Temp. ECP dryer - 40 - 60°C RH - 30 - 60%

FBD - 40 - 60°C - 70 - 95%

Feed Spreader

Height Regulator . . . Temp. ECP dryer - 40 - 60°C RH - 25 - 55%

FBD - 40 - 60°C 25 - 65%

Throughput Time ECP dryer- 10 - 40 minutes

Inlet Air Damper. . . Temp. ECP dryer- 80 - 105°C RH - 1.0 - 5.0%

FBD - 1 10 - 150°C 0.4 - 5.0%

The working of the online air heating control system for tea dryer, based on predetermined RH of the inlet and exhaust air to economize use of heat energy and fuel consumption in air heater shall be more apparent when discussed in relation to following illustrative exemplary embodiments:

Example I:

It has been observed that to evaluate the "Ambient Air" condition, the only relevant data is the value of "Humidity Ratio" which is the absolute weight of moisture per unit weight of dry air. This Humidity Ratio can be measured directly electronically or computed with the aid of other psychrometric properties of the ambient air such as Dry Bulb and Wet Bulb temperatures which are measureable. The Ambient Air is heated in the air heater to a temperature which will convert its RH to a pre-determined value, such as 3.8% in case of conventional ECP Dryers and 1.7% for FBDs at all times irrespective of the initial Humidity Ratio.

The "Inlet Air" so obtained carries out satisfactory drying of the tea fed into the dryer. Following the aforestated it can be confirmed that the psychrometric properties subsisting in this "Inlet Air" would always produce the desired results for drying of similar teas.

In the first instance, Ambient Air of 95% RH at 32°C Dry Bulb temperature, having Humidity Ratio of 0.02935 Kg/Kg is heated to 104.4°C in Conventional ECP Dryer and 130°C in FB Dryer, in order to attain the said desired RH values of the inlet air.

The values of RH benchmarked for Exhaust Air are 48% and 97.4% for ECP and FB dryers when the "Exhaust Air" temperatures were maintained at 54.4°C and 45°C respectively. It is important to note that the values of RH of "Exhaust Air" are never allowed to go higher than 48% and 97.4% as this will have deleterious effect on the quality of the tea being dried due to too slow rate of moisture removal.

Example II:

In this example, the condition of the Ambient Air selected is not as adverse as in the first example. It is drier and hence a lesser quantity of heat will be required to bring this air to the required RH of 3.8% and 1.7% for ECP and FB dryers respectively. Ambient Air having a Dry Bulb temperature of 33°C and 70%RH has a Humidity Ratio 0.0227 Kg moisture/Kg dry air/ is heated to convert it into "Inlet Air" having RH values of 3.8% and 1.7% for ECP and FB dryers as mentioned above, whereby the temperature is raised to 97.5°C and 123°C respectively and the quantum of heat required to be added are 67.48 kj/Kg and 94.16 kj/Kg respectively. Tt is important to note that in the instance the Ambient Air was heated to pre-determined temperatures of 104.4°C and 130°C as per the conventional practice instead of heating it to a pre-determined RH, as proposed herein, then the heat added would have been 74.69 kj/Kg and 101.48 kj/Kg respectively. Thus it can be seen that savings of heat amounting to 7.21 and 7.32 kj/Kg or 9.65% and 7.217% respectively can be effected by adopting the new system.

In the present example, for achieving the same values of H for the "Exhaust Air" i.e. 48% and 97.4%, the temperatures are maintained at 51.12°C and 39.32°C respectively for obtaining the same output from the dryer.

Example III:

In this example the saving of heat is alternatively effected by extracting increased output of dried tea from the same dryer without increasing the heat input.

This is done when Ambient Air condition is favourable, i.e. having low Humidity Ratio. The air is heated to the highest "Inlet Air" temperature as per present practice and then maintaining the "Exhaust Air" RH at the benchmarked values of 48% and 97.4%, instead of the normal predetermined temperatures of 54.4°C and 45°C. Doing this would allow more of the heat present in "Inlet Air" to be utilized in drying of the tea before being released into the atmosphere. But in order to achieve these figures for "Exhaust Air" the intake of leaf into the dryer have to be increased either by raising the Feed Spreader or reducing the throughput time or both. Both operations result in increase in the dryer output. In the present example the Ambient Air with Humidity Ratio of 0.227 Kg/Kg when heated to 104.4°C and 130°C in ECP and FB dryer respectively as per prevalent practice, the RH of the "Inlet Air" becomes 3% and 1.3%. If the RH of the "Exhaust Air" is maintained at 48% and 97.4% then the temperatures of this air will be 52°C and 43.2°C respectively.

If the "Exhaust Air" temperature is maintained at the normal 54.4°C and 45°C then the RH of this air which is released to the atmosphere would be 41.7% and 87.6%. It is thus seen by comparison that these values are drier by 6.3% and 9.8% and so indicate loss of potential drying capacity.

The higher RH of the "Exhaust Air" has resulted in the first case because more moisture has evaporated from a larger mass of leaf fed inside the dryer. This larger mass of leaf has resulted in increased tea output and is proportional to the extra moisture evaporated. In this case the output increase is 6.3*100/41.7 = 15.1% and 9.8* 100/87.6 = 11.2% respectively. Hence, if the heat input as per prevalent drying practice is 100 units and the tea output from the dryer is 'Q' Kg., then the heat input per Kg. tea output from the dryer is 100/'Q' units. When the dryer output goes up by 15.1% and 11.2% as stated above without any increase in the heat input, then the ratio of heat input per Kg. tea output would become 100/1.151'Q' and 100/1.112'Q' which are 86.88% and 89.93% of the original heat input, resulting in a saving in heat of 13.12% and 10.07% for ECP and FB dryer respectively.

In order to achieve the above stated significant advantage in terms of thermal energy saving as well as reducing fuel consumption for air heating in dryer for tea and the like, the online preprogrammed micro-controller based feed back system according to the invention can be implemented in the conventional ECP drier as illustrated in the accompanying Figure 3. Installation of the same control system in relation to the FB dryer is illustrated in the accompanying Figure 4. The modifications which are to be carried out on the existing dryers for incorporating the new system have been shown.

The different control mechanisms used by the system and the different parameter they monitor and control have been shown in respect of ECP and FB type of dryer. The sequence of events for implementation of online control of air heating in dryer using the system of the present invention based on the predetermined RH of inlet and exhaust air are as follows :- ^'

i) The electronic Hygrometer and thermometer(ETH 1) recorder for Ambient Air senses the RH ,Dry Bulb Temperature and Humidity Ratio of ambient air(AA) and sends the signals 'A' to the Micro-Controller(MC) indicating the values of Humidity Ratio, RH and Temperature. ii) On receiving the signals 'A' the Micro-Controller(MC) processes the data and computes what should be the correct RH and Temperature to which the ambient air(AA) must be heated to convert it to appropriate 'Inlet air'(IA) depending on initial humidity ratio of ambient air.

iii) Micro-controller(MC) then sends signals Ά accordingly to the Heater Burner Control mechanism(BCM) of Air Heater(AH) or manual operator to open the burner aperture to release the proper quantity of fuel to reach the computed value of Temperature for 'Inlet Air'(IA) to ensure attaining the predetermined RH.

iv) The 'Inlet Air' hygrometer and thermometer(ETH 2) continuously sends signals 'B' to the Micro-Controller(MC) updating the values of RH and Temperature of inlet air(IA) after ambient air is heated.

v) On receiving these signals 'B' the Micro-Controller(MC) compares the values with the correct values it had computed and commanded the burner mechanism(BCM) to implement. If any variance is found then the Micro-Controller(MC) again sends signals 'Bl' to the burner mechanism(BCM) or manual operator to release greater or lesser quantity of fuel in air heater (AH) in Order to bring back the values to the correct figures. vi) The same sequence of events takes place with "Exhaust Air"(EA) condition monitoring through electronic thermometer and hygrometer(ETH 3) as for "Inlet Air" except that the values are different and the signals in this case are 'C & 'CI'. Also the Feed Spreader Height control mechanism(SHC) located on the leaf path(LP) near the tea leaves intake(TLI) side of the tea drying chamber(TDC), is actuated either automatically or manually in this case to control RH of exhaust air(EA), instead of the Burner Control mechanism(BCM) to attain the desired predetermined RH of the exhaust air(EA). Dried tea discharge (DTD) is obtained at the bottom of the tea drying chamber(TDC).

Similar provisions can also be made for 'Inlet Air Damper' (ADC) to control inlet air(IA) conditions and 'Throughput Time Control ler'(TTC) to control exhaust air(EA) conditions, but these are not considered in the present experiments to avoid complexity of operation.

It is thus possible by way of the present invention to providing an automatic - cum manual online control system for heated ambient air based drying for dryers of tea and like materials adapted to ensure substantial saving of thermal energy and avoid undesired wastage of unutilized heat carried away by exhaust air from the dryer, by selectively controlling the heat input to ambient air to convert it to "Inlet Air" for dryer, based on variable ambient air condition i.e. its initial humidity ratio and to achieve predetermined RH of "Inlet" and "Exhaust" air for dryer favouring consistent satisfactory quality of end product. A dedicated micro-controller is provided to monitor and control the functioning of different control mechanisms to optimize the heat input and tea loading in dryer such as to favour a saving of 7-13% of heat energy and commensurate fuel consumption, as compared to conventional predetermined temperature based control of drying operation.

Claims

I Claim:

1. A system for heated ambient air based drying of tea and/or other materials involving ambient psychrometric conditions comprising: an ambient air heater with fuel supply regulator either automatically or manually operated or both; a dryer having a material feed regulator either automatically or manually operated or both; electronic hygrometer cum thermometer; a microcontroller means operatively connected and adapted to facilitate the control of the heating of the ambient air for the purposes of drying of the tea or other material in the dryer based on the desired conditions for drying in the dryer.

2. A system as claimed in claim 1 comprising an electronic hygrometer cum thermometer adapted to measure the ambient air Humidity Ratio and temperature and send relevant data signals to the said microcontroller; said microcontroller processing the said data and computing the correct RH and temperature to which the ambient air need to be heated and sends corresponding signals to the ambient air heater with fuel supply regulator to release proper quantity of fuel for said desired heating of the ambient air; a dryer inlet air hygrometer and thermometer adapted to continuously sense and send signals to the microcontroller to thereby update the values of RH and temperature at the air inlet in the microcontroller; said microcontroller adapted to compare the values of the air inlet with values it computed and implemented the burner control mechanism either automatically and/or manually and initiate corrective measures if required to further control the fuel in the burner for desired heating of the ambient air to thereby maintain the desired standard RH and temperature in the dryer .

3. A system as claimed in anyone of claims 1 or 2 comprising a dryer exhaust air hygrometer and thermometer adapted to continuously sense and send signals to the microcontroller to thereby update the values of H and temperature at the air inlet in the microcontroller; said microcontroller adapted to compare the values of the air exhaust and actuate based thereon a feed spreader height control mechanism either automatically and/ or manually operated to thereby maintain the desired standard of flow of feed in the dryer.

4. A system as claimed in anyone of claims 1 to 3 wherein said microcontroller adapted to compare the values of the air exhaust and further actuate based thereon inlet air damper and throughput time controller operated automatically and/or manually, if required.

5. A system as claimed in anyone of claims 1 to 4 wherein the microcontroller is adapted to heat the ambient air in the air heater to a temperature which will convert its RH to a pre- determined value as required in conventional dryers or fluidized bed dryers (FBD) irrespective of its initial Humidity Ratio.

6. A system as claimed in anyone of claims 1 to 5 wherein the hygrometer-cum- thermometer is adapted to constantly measure the Humidity Ratio, Relative Humidity and Dry Bulb temperature of the ambient air and convert the data into electrical signals which in turn is relayed to the micro-controller preferably with further display of the same in LCD or LED digital displays.

7. A system as claimed in anyone of claims 1 to 6 wherein said heater fuel supply regulator is operatively connected to oil/gas burner or chain grate or other stoker for coal/wood firing either automatically and/or manually operated and adapted to continuously monitor the temperature and RH of the "Inlet Air" and transmit the values to said microcontroller, said microcontroller providing for receiving the same and generating any corrective commands to the fuel supply regulator based thereon.

8. A system as claimed in anyone of claims 1 to 7 wherein said microcontroller is adapted to compute correct values of temperature and RH of the 'Exhaust Air" and relay the information to the dryer regulator either automatically and/or manually operated such as to command the same to raise or lower the feed spreader to thereby increase or reduce the quantity of leaf/material being fed into the dryer for further maintaining desired "Exhaust Air" conditions!.

9. A method for carrying out heated ambient air based drying of tea and/or other materials involving ambient psychrometric conditions using the system as claimed in anyone of claims 1 to 8 comprising:

the step of controlling saving of heat energy and hence fuel by activating said microcontroller based control of the heating of the ambient air based on the desired RH at the inlet of the dryer and the favourable changes in the Humidity Ratio of the ambient air.

10. A method for carrying out heated ambient air based drying of tea and/or other materials involving ambient psychrometric conditions using the system as claimed in anyone of claims 1 to 8 comprising :

The step of controlling uniform removal of moisture from the tea and/or other materials being dried at a predetermined optimal rate and hence ensuring consistently better quality of the dried product by activating said microcontroller based control of the heating of the ambient air based on desired RH at the inlet of the dryer and the favourable changes in the Humidity Ratio of the ambient air.

11. A method as claimed in claim 9 wherein said saving of heat energy and hence fuel is effected by way of anyone or more of the following: i) by using less heat to convert the ambient air to "Inlet Air" by heating to a predetermined RH instead heating the ambient air to a predetermined temperature and ii) by increasing the output of the dryer without increasing the heat input such that quantity of fuel used per unit of dried tea/material is reduced.

12. A system for heated ambient air based drying of tea and/or other materials involving ambient psychrometric conditions and a method for carrying out heated ambient air based drying of tea and/or other materials involving ambient psychrometric conditions using the same substantially as hereindescribed and illustrated with reference to the accompanying examples and figures.