Product drying apparatus and methods

Abstract

The present invention provides improved apparatus and methods for the monitoring and control of apparatus designed to remove moisture from an initially wet product, such as a continuous dryer ( 14 ). The net rate of water removal from the wet product ( 16 ) is determined during drying thereof, preferably on a real-time basis. A control assembly ( 20 ) is operatively coupled with the dryer ( 14 ) and includes sensors ( 24, 26, 28, 34 ), which are operatively coupled with a digital controller ( 38 ). The controller ( 38 ) has a PID controller operable to continuously determine the average net rate of water removal from the product ( 16 ).

We claim: 
     
         1 . Apparatus operable to remove water from product passing through the apparatus by contacting the product with input air to create dried product and moisture-laden exit air, said apparatus including a fan to exhaust said exit air from the apparatus, and structure operable to determine the volumetric flow rate of said exit air from said fan, and to use said volumetric flow rate to determine the net rate of water removal from said product during operation of said apparatus. 
     
     
         2 . The apparatus of  claim 1 , said structure operable to determine at least one operational parameter of said fan, and using said fan parameter to calculate said volumetric flow rate. 
     
     
         3 . The apparatus of  claim 2 , said fan parameter selected from the group consisting of fan motor power, fan rotational speed, and fan pressure, and combinations thereof. 
     
     
         4 . The apparatus of  claim 3 , said structure operable to determine said volumetric flow rate using two operational parameters of said fan selected from the group consisting of: (1) fan motor power and fan rotational speed; (2) fan pressure and fan rotational speed; or (3) fan motor power and fan pressure. 
     
     
         5 . The apparatus of  claim 4 , said structure operable to determine:
 (a) the wet bulb temperature and dry bulb temperature of said exit air;   (b) the rotational speed of said exhaust fan;   (c) the motor power of said exhaust fan;   (d) the wet bulb temperature and dry bulb temperature of said input air; and   operable to calculate said net rate of water removal from said product in real time as the product passes through said apparatus, using the determined values (a)-(d), inclusive.   
     
     
         6 . The apparatus of  claim 2 , said structure operable to calculate said volumetric flow rate using said fan parameter in a Fan Law equation. 
     
     
         7 . The apparatus of  claim 1 , said structure operable to alter the operation of said apparatus in response to said determined net rate of water removal. 
     
     
         8 . The apparatus of  claim 7 , said structure operable to adjust at least one control parameter of said apparatus which will alter said rate of water removal from said product, in response to said determined net rate of water removal. 
     
     
         9 . The apparatus of  claim 8 , said apparatus being a dryer using heated input air to dry said product, said control parameter selected from the group consisting of the temperature of said heated input air, the speed of travel of the product passing through the dryer, the contact time between said product and said heated input air, and combinations thereof. 
     
     
         10 . The apparatus of  claim 7 , said structure operable to determine a set point rate SP which is the desired net rate of water removal from the product during passage thereof through the apparatus, a process variable PV which is the actual net rate of water exiting the product during passage through the apparatus, and to control the operation of the apparatus using said SP and said PV, to cause said PV to approach said SP. 
     
     
         11 . The apparatus of  claim 7 , said structure operable to successively and periodically determine said SP and said PV, and to control the operation of the apparatus using said successive SP and PV determinations. 
     
     
         12 . The apparatus of  claim 11 , said structure including a PLC with a PID controller to carry out said successive determinations of said SP and said PV. 
     
     
         13 . The apparatus of  claim 12 , said PLC controller operable, in each of said successive determinations, to calculate said SP, said PV, the difference between said SP and said PV, and a control variable CV. 
     
     
         14 . The apparatus of  claim 10 , said structure operable to determine said SP as the initial water rate (IWR) minus the final water rate (FWR), where IWR is the rate of water delivered to the apparatus as a part of said wet product input, and FWR is the desired rate of water exiting from the apparatus as a part of said dried product. 
     
     
         15 . The apparatus of  claim 10 , said structure operable to determine said PV as the rate of water leaving said apparatus as a part of the output of said exhaust fan minus the rate of water entering said apparatus as a part of said input air. 
     
     
         16 . The apparatus of  claim 1 , said structure operable to determine the net rate of water removal from said product in real time as the product passes through the apparatus. 
     
     
         17 . The apparatus of  claim 16 , said structure operable to determine the average net rate of water removal from said product. 
     
     
         18 . Apparatus operable to remove water from product passing through the apparatus by contacting the product with input air to create dried product and moisture-laden exit air, said apparatus including a fan to exhaust said exit air from the apparatus, and structure operable to calculate the net rate of water removal from said product in real time during operation of said apparatus. 
     
     
         19 . The apparatus of  claim 18 , said structure operable to determine at least one operational parameter of said exhaust fan, and to use said at least one determined parameter in the calculation of said net rate of water removal from said product during operation of said apparatus. 
     
     
         20 . The apparatus of  claim 19 , said structure operable to determine two operational parameters of said fan selected from the group consisting of: (1) fan motor power and fan rotational speed; (2) fan pressure and fan rotational speed; or (3) fan motor power and fan pressure. 
     
     
         21 . A method of monitoring the operation of apparatus operable to remove water from product passing through the apparatus by contacting the product with input air to create dried product and moisture-laden exit air, said method comprising the steps of employing a fan to exhaust said exit air from the apparatus, determining the volumetric flow rate from said fan, and using said volumetric flow rate to determine the net rate of water removal from said product during operation of said apparatus. 
     
     
         22 . The method of  claim 21 , determining at least one fan parameter, and using said fan parameter to calculate said volumetric flow rate. 
     
     
         23 . The method of  claim 22 , said fan parameter selected from the group consisting of fan motor power, fan rotational speed, and fan pressure, and combinations thereof. 
     
     
         24 . The method of  claim 23 , including the step of determining two operational parameters of said fan selected from the group consisting of: (1) fan motor power and fan rotational speed; (2) fan pressure and fan rotational speed; or (3) fan motor power and fan pressure. 
     
     
         25 . The method of  claim 24 , including the steps of:
 (a) determining the wet bulb temperature and dry bulb temperature of said exit air;   (b) determining the rotational speed of said exhaust fan;   (c) determining the motor power of said exhaust fan;   (d) determining the wet bulb temperature and dry bulb temperature of said input air; and   (e) determining said net rate of water removal from said wet product in real time as the wet product passes through said drying chamber, using the determined values (a)-(d), inclusive.   
     
     
         26 . The method of  claim 22 , including the step of calculating said volumetric flow rate using said fan parameter in a Fan Law equation. 
     
     
         27 . The method of  claim 21 , including the step of controlling the operation of said apparatus in response to said determined net rate of water removal. 
     
     
         28 . The method of  claim 27 , including the step of adjusting at least one control parameter of said apparatus which will alter said rate of water removal from said product, in response to said determined net rate of water removal. 
     
     
         29 . The method of  claim 28 , said apparatus being a dryer using heated input air to dry said product, said control parameter selected from the group consisting of the temperature of said heated input air, the speed of travel of the product passing through the dryer, the contact time between said product and said heated input air, and combinations thereof. 
     
     
         30 . The method of  claim 27 , including the steps of determining a set point rate SP which is the desired net rate of water removal from the product during passage thereof through the apparatus, determining a process variable PV which is the actual net rate of water exiting the product during passage through the apparatus, and controlling the operation of the apparatus using said SP and said PV, to cause said PV to approach said SP. 
     
     
         31 . The method of  claim 27 , including the steps of successively and periodically determining said SP and said PV, and controlling the operation of the apparatus using said successive SP and PV determinations. 
     
     
         32 . The method of  claim 31 , including the step of using a PLC controller with a PID controller to carry out said successive determinations of said SP and said PV. 
     
     
         33 . The method of  claim 32 , said PLC controller operable, in each of said successive determinations, to calculate said SP, said PV, the difference between said SP and said PV, and a control variable CV. 
     
     
         34 . The method of  claim 30 , including the step of determining said SP as the initial water rate (IWR) minus the final water rate (FWR), where IWR is the rate of water delivered to the apparatus as a part of said wet product input, and FWR is the desired rate of water exiting from the apparatus as a part of said dried product. 
     
     
         35 . The method of  claim 30 , including the step of determining said PV as the rate of water leaving said apparatus as a part of the output of said exhaust fan minus the rate of water entering said apparatus as a part of said input air. 
     
     
         36 . The method of  claim 21 , including the step of determining the net rate of water removal from said product in real time as the product passes through the apparatus. 
     
     
         37 . The method of  claim 36 , said net rate of water removal being an average net rate of water removal. 
     
     
         38 . A method of monitoring the operation of apparatus operable to remove water from product passing through the apparatus by contacting the product with input air to create dried product and moisture-laden exit air, said method comprising the steps of employing a fan to exhaust said exit air from the apparatus, and calculating the net rate of water removal from said product in real time during operation of said apparatus. 
     
     
         39 . The method of  claim 38 , including the step of determining at least one operational parameter of said exhaust fan, and using said at least one determined parameter in the calculation of said net rate of water removal from said product during operation of said apparatus. 
     
     
         40 . The method of  claim 39 , said parameter-determining step including the step of determining two operational parameters of said fan selected from the group consisting of: (1) fan motor power and fan rotational speed; (2) fan pressure and fan rotational speed; or (3) fan motor power and fan pressure.