Patent Publication Number: US-2011067262-A1

Title: Drieng system with circulating gas

Description:
BACKGROUND 
     The ability of gases and steam to carry water vapor increases by the increasing temperature. The conventional driers working with heated air as drying gas through a bed discharge the vapor in the atmosphere. The air is cooled by evaporation when it is taking over evaporated water and is discharged into the atmosphere at a relatively low temperature. That type of air-dryers need large air flows for the drying and leave emissions from the dried material into the atmosphere. During the drying at low outside temperature the large airflow is heated up to the drying temperature of the dryer, which means a high energy loss. 
     With the device according to this innovation only a small air flow is discharged into the atmosphere in one of the alternatives. In two other alternatives no drying gas is discharged into the atmosphere and main part of the drying energy is reused. 
    
    
     SYSTEM DESCRIPTION 
     1. Figures 
     
       
         
           
               
               
             
               
                   
               
               
                 Pos. 
                 Name 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 1 
                 Filling plate 
               
               
                 2 
                 Container for filling material 
               
               
                 3 
                 Material for next drying cycle 
               
               
                 4 
                 Circulation valve 
               
               
                 5 
                 Inlet channel 
               
               
                 6 
                 Inlet valve 
               
               
                 7 
                 Cleaning system for the air heater 
               
               
                 8 
                 Circulation fan 
               
               
                 9 
                 Air heater 
               
               
                 10 
                 Outlet pipe for the heating fluid from the air heater 
               
               
                 11 
                 Bar feeder for the side wall for discharging the dried material 
               
               
                 12 
                 Mobile side wall for discharging of the dried material 
               
               
                 13 
                 Inlet pipe for the heating fluid to the air heater 
               
               
                 14 
                 Bar feeder with scraper for the drying material fallen from the  
               
               
                   
                 16 to the bottom 
               
               
                 15 
                 Outlet for cleaning water to the cleaning of condensate 
               
               
                 16 
                 Bottom with air openings for the drying material 
               
               
                 17 
                 Bottom for collecting the drying material fallen through the  
               
               
                   
                 air holes in the 16 
               
               
                 18 
                 Conveyer 
               
               
                 19 
                 Dried material during transportation 
               
               
                 20 
                 Mobile sidewall for opening of a discharge channel 
               
               
                 21 
                 Drying material 
               
               
                 22 
                 Bar feeder for the mobile side wall 20 
               
               
                 23 
                 Outlet channel for the air outlet 
               
               
                 24 
                 Outlet valve for the air 
               
               
                 25 
                 Drying device 
               
               
                 26 
                 Air channel to the air condenser 
               
               
                 27 
                 Ionizator 
               
               
                 28 
                 Air condenser 
               
               
                 29 
                 Heating circuit to the preheater 
               
               
                 30 
                 Preheater 
               
               
                 31 
                 Circulation fan for dehumidified air 
               
               
                 32 
                 Droplet separator 
               
               
                 33 
                 Pump for hot water circuit from the economizer 46 
               
               
                 34 
                 Pump for fluid circuit for recovering waste heat from the  
               
               
                   
                 flue gas condenser 58 
               
               
                 35 
                 Return pipe to the economizer 46 
               
               
                 36 
                 Outlet of condensate to the cleaning system from the air  
               
               
                   
                 condenser 28 
               
               
                 37 
                 Pipe for delivering waste heat from the flue gas condenser 58 
               
               
                 38 
                 Pipe for hot water from the economizer 46 
               
               
                 39 
                 Return pipe for recovering heat from the flue gas condenser 58 
               
               
                 40 
                 Pipe with regulation valve for heating of any desired object  
               
               
                   
                 with return water from 9 
               
               
                 41 
                 Desired object for heating with return water from the heater 9,  
               
               
                   
                 e.g. footballs plane with artificial grass 
               
               
                 42 
                 Outlet for condensate from flue gas condenser 58 to a  
               
               
                   
                 cleaning system 
               
               
                 43 
                 Combustion plant 
               
               
                 44 
                 Dust cleaner for flue gas 
               
               
                 45 
                 Flue gas channel from 43 
               
               
                 46 
                 Economizer 
               
               
                 47 
                 Circulation pump for heat recovery from air condenser 28 
               
               
                 48 
                 Receiver of heat from 28 
               
               
                 49 
                 Pipe with control valve for selecting suitable heating for 48 
               
               
                 50 
                 Humidity-and temperature probe 
               
               
                 51 
                 Air/air heat exchanger between ambient air and in the drying  
               
               
                   
                 system circulating air 
               
               
                 52 
                 Outlet of condensate and cleaning water from 51 to water  
               
               
                   
                 cleaning system 
               
               
                 53 
                 Circulation fan for air to be dehumidified 
               
               
                 54 
                 Air fan for cooling air 
               
               
                 55 
                 Preheater for dehumidified cooled air 
               
               
                 56 
                 Inlet pipe to preheater 55 
               
               
                 57 
                 Outlet pipe from preheater 55 
               
               
                 58 
                 Flue gas condenser 
               
               
                 59 
                 Cleaning device for air/air heat exchanger 51 
               
               
                 60 
                 Cleaning device for air condenser 28 
               
               
                 61 
                 Heat circuit between cascade dryers 
               
               
                 62 
                 Cascade condenser 
               
               
                 63 
                 Control valve for the first drying stage 
               
               
                 64 
                 Pipe for economizer connected to return water 
               
               
                 65 
                 Control valve connected to the second drying stage 
               
               
                 66 
                 Drying stage 2 
               
               
                 67 
                 Ionizator 
               
               
                 68 
                 Flue gas outlet to the stack 
               
               
                 69 
                 Cleaning device for the flue gas condenser 
               
               
                 70 
                 Exchange valve 
               
               
                   
               
            
           
         
       
     
     Any type of gas or any type of steam is used as the circulating gas. Air is used as name for the gas. 
     A Drying Cycle Consists of the Following Basic Phases: 
     
         
         
           
             Charging of drying material 
             Heating with circulating air without discharge of air until the air before the air heater has reached desired relative humidity and temperature 
             Discharge of warm humid air with continued heating of circulating air and intake of outside air or returned dehumidified air. The discharged flow is so controlled that the in the dryer circulating air keeps its desired relative humidity and temperature. 
             Discharge of the dried material and at the same time cleaning of all the components whose function can be disturbed by dust. 
             Charging of new material to be dried. 
           
         
       
    
     2. Central Unit 
     In the  FIG. 1  the central unit is shown during the drying period and in the  FIG. 2  when the dried material has discharged from the unit. 
     The drying material is in a container in the drying unit  25  whose two walls  12  and  20  are movable. The wall  12  is pending some centimeters to keep the drying material moving so that the drying air easier comes into contact with all particles. If needed some rotating agitators are pushed through one of both of the stable walls to additionally improve the agitation of the drying material. These agitators (not shown in the  FIGS. 1 and 2 ) draws out when the container is emptied. 
     The bottom  16  of the container is designed to let air come through it. The fan  8  sucks air from the over half of the container. The air is heated in the heater  9  and goes again through the bottom  16  to the bed  21 . No air bypasses the heater  9 , all the air is heated. The dampers  6  and  24  are closed. The probe  50  is used to measure the temperature and the relative humidity of the air. The recirculation of the air continues until the relative humidity comes up to a decided value, e.g. 95% at the same time as the temperature of the air reaches a desired value e.g. 5 C under the fluid temperature which through the pipe  13  heats up the air. 
     When the decided values are reached in the simplest case dampers  6  and  24  are opened to let out a decided air flow which is substituted with incoming outdoor air. If waste energy is available the incoming air is heated with the waste energy in a heat exchanger before the fan  8 . The probe controls the dampers. The drying goes now on with discharge of the evaporated water from the drying material until the probe closes the dampers at a decided position which has experimentally found out to give the desired humidity in the drying material, e.g. 10%. 
     A final drying can be done by high temperature heat from e.g. the economizer  46 , see  FIGS. 6 and 7 . The control valve  63  distributes e.g. fluid at 100 C from the pipe  38  from the economizer  46  in to the fluid inlet  13  and as much cooled fluid goes back to the economizer through the pipe  35 . 
     As the next step the container is emptied, see  FIG. 2 . The bar feeder  22  draws the wall  20  to the left to open a possibility for the dried material to fall down. The bar feeder  11  pushes the wall  12  over the whole bottom  16  of the container and pushes out the dried material to the opening left after the moved wall. The dried material falls through the opening to any desired type of receiver. In the  FIG. 2  the receiver is a conveyer  18  for transportation of the material  19  further. The material  19  can also fall directly in to a wagon or to another transportation device. The bar feeder scrapes then to the opening all the drying material which has fallen to the bottom  17  through the openings in the bottom  16 . 
     The fan  8  is closed down during the discharge cycle and the heater  9  is cleaned by spraying cleaning water through the cleaning devise  7 . The dirty cleaning water is discharged through the outlet  15  for water cleaning. When the cleaning cycle is finalized a new drying cycle is started. 
     When the cycle for discharging is finalized the walls  20  and  12  and the bar feeder  14  return to their original positions after which the feeding plate  1  is opened and the next charge of drying material  3  falls from the magazine  2  into the drying container and a new drying cycle starts. 
     Benefits of the Central Unit Compared with a Conventional Air Dryer. 
     Compared with conventional air dryers this system has the big advantage that the outgoing air is considerably warmer and its relative humidity is higher why the air flow out is considerably lower than from normal air dryers. Example: 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                   
                   
                 Normal air  
                 Circulation dryer,  
               
               
                   
                   
                 dryer 
                 basic system 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 The temperature of the 
                 65 C. 
                 65 C. 
               
               
                   
                 heating media 
                   
                   
               
               
                   
                 The relative humidity of the 
                 75% 
                 95% 
               
               
                   
                 outgoing air 
                   
                   
               
               
                   
                 The temperature of the 
                 30 C. 
                 60 C. 
               
               
                   
                 outgoing air 
                   
                   
               
               
                   
                 Water content g/normal m3 
                 25 
                 150 
               
               
                   
                 air 
                   
                   
               
               
                   
                 Lost air power kW/1000 kg/h  
                 548 kW 
                 160 kW 
               
               
                   
                 evaporated water at −10 C. 
                   
                   
               
               
                   
                 ambient temperature 
                   
                   
               
               
                   
                 Power for evaporation 
                 720 kW 
                 733 kW 
               
               
                   
                 kW/1000 kg/h water 
                   
                   
               
               
                   
                 Power need totally at −10 C. 
                 1268 kW  
                 893 kW 
               
               
                   
                 outdoor + evaporation 
                   
                   
               
               
                   
                 kW/1000 kg/h 
               
               
                   
               
            
           
         
       
     
     The basic system uses only about ⅙ of the air flow as a normal air dryer for the same evaporated water amount. This means a considerable energy saving during the winter, when outdoor air must be heated, although the air must be heated to 60 C instead of to 30 C. 
     The disadvantage of the system is that even in this case humid air with dust comes out into the surroundings. 
     3. System Without Dust Emission in to Atmosphere. 
     Emission of dust from the drying is eliminated through cooling the humid air after the channel  23  with a cooler. The air is dehumidified and the cold saturated air is led back to the central unit through the inlet channel  5 . Examples for the cooling of the humid air are shown in the  FIGS. 3 and 4 . At the same time part of the remaining energy in the humid gas is used for something useful. 
     Cooling with an Out-Air Cooler with Collection of Condensate,  FIG. 3 . 
     The fan  53  sucks the warm humid air from the channel  23  and blows it through the air/air heat exchanger  51  of free design. The fan  54  sucks outdoor air through the other side of the heat exchanger. During the cooling water is condensated and is discharged through the outlet  52  in to a water cleaning system. If waste energy at any temperature is available the cooled saturated gas is preheated in the heat exchanger  55  with the waste energy via inlet  56  and outlet  57 . If necessary the heat exchanger  55  has a cleaning device and a droplet separator with possibly a cleaning device before the heat exchanger. After the drying cycle is finalized the heat exchanger  51  is cleaned with the cleaning device  59 . The heat exchanger  55  is also cleaned if necessary. The heated outdoor air can e.g. be used as a part of the combustion air in the combustion system  43  in the  FIG. 7  or for heating of ventilation air. 
     Several parallel units are connected to the common air/air heat exchanger  51  by large drying need. With the dampers  24  and  6  every unit is disconnected from the system during the discharge and cleaning cycles. 
     Cooling with a Condenser,  FIG. 4 . 
     A condenser  28  takes the warm and humid air from the channel  26 . The pump  47  pumps fluid through the condenser in a fluid circuit  29 . The in the condenser heated fluid is used for heating any desired heat user  48 , e.g. a green house, sport hall or ground with artificial grass as ice—and snow free sport/playing place in the winter. Part of the in the condenser recovered heat is used for preheating of the cold humid returning air to the channel  5  in the heat exchanger  30  after a droplet separator  32 . Both the heat exchanger  30  and the droplet separator  32  have a cleaning device if necessary. The condenser  28  has a cleaning device  60 . The fan  31  circulates the air in the system. All cleanings are done directly after the drying cycle is finalized. 
     Several units are connected in to the condenser  28  at high drying need. With the dampers  24  and  6  every unit is disconnected from the system during discharge and cleaning cycle. 
     Cascade System of Several Units, FIGS. 5 and 6. 
     In the system with cooling with a condenser a large part of the drying energy is recovered in the condenser, but at a lower temperature than the units heating fluid at the inlet  13 . This heat can be used in drying units connected after the first unit into the system, so called cascade dryers. The first dryer is called the mother dryer; the units after it are called cascade dryers. 
     Because the cascade dryer works at a lower air temperature than the mother dryer because the condenser doesn&#39;t deliver as warm heating fluid as the fluid which via the inlet  13  heats the air into the mother dryer the cascade dryer works slower than the mother dryer. The cascade dryer needs also more air to be able to take care of the same water vapor. See the Help figure. 

 
     In the  FIG. 6  a way is shown to get the cascade dryer to work the same way as the mother dryer. See even the  FIG. 7 . Hot fluid e. g. at 100 C from an economizer  46  is blended with in the condenser  28  heated fluid through the control valve  65  to increase the fluid temperature in to the drying stage  66  to the same temperature level as the ingoing heating fluid for the mother dryer  25 . The same amount of fluid is then discharged back to the return pipe of the economizer  35 . Every cascade dryer after the first uses consequently a large part of the waste energy from the cascade dryer before it and gets the rest heat from another heat source with a higher temperature than the ingoing fluid temperature in to the mother dryer. 
     The condensers need cold fluid as cooling fluid. A greenhouse or other profitable user of heat is used to cool the ingoing fluid, preferably protected against freezing, into the condenser. In the summer and during other times when the heat cannot be used it is dumped by an included outdoor- or water cooler. 
     The outgoing temperature of the heating fluid from the dryers varies during the drying cycle. At the beginning when a lot of water is evaporated the heating fluid is cooled strongly and can be used for cooling in the condenser  62 . At the end of the cycle the heating fluid is not cooled at all. Therefore the control valve  70  controls continuously or stepwise the flow to the condenser  62  either directly from the dryer  66  or from the outlet of the heat receiver  48  so that the desired inlet temperature to the condenser  62  is reached. 
     Example of Additional Possibilities for optimizing of the Profitability,  FIG. 7   
     In the  FIG. 7  an example is shown between a boiler and the drying system with heat recovery possibilities. 
     Use of an Economizer in Boilers for Sawmills. 
     Boilers  43  in sawmills don&#39;t have for economical reasons normally an economizer installed after the boiler. Therefore it is profitable to install an economizer at the same time as the drying system is installed. The economizer gives extra high temperature heat at the magnitude of 6 to 8% to the normal sawmill operations. Part of this heat is also used to coordinate the function of the cascade dryers so that their drying capacity and drying time be the same as for the first dryer. It is also possible to get a safety margin for the dryness of the material by ending the drying cycle with a high temperature of the incoming heating water instead of the normally available waste heat. 
     Cleaning of Dust from the Drying System 
     The whole system uses cleaning of the components after the drying cycle to be sure that dust staying in the system is not disturbing its function. One additional way is to install an ionizer  67  before the condenser  58  and an ionizer  27  before the condenser  28 . The dust particles are ionized with high voltage electricity. The condenser has in these cases lamella channels where the cooling fluid is pumped in contra flow in every second channel and the air in every second channel with about 10 mm free channel height for the air. The lamellas are earthed why the dust particles are drawn to the channels where the humidity in the air is condensed and spools down the particles with the water. This system can spool away even very small particles. 
     During the discharge cycle the drying material comes in contact with the outdoor air. A vacuum cleaner is used in the discharge system to separate the dust from the system. 
     Low Temperature Heat to e.g. Football Plan with Artificial Grass. 
     By using the patent 524 363 a part flow  40  from the return fluid to the flue gas condenser  58  can be used to give low temperature heating to any desired object  41  in  FIG. 7 . where the fluid is additionally cooled and recovers extra heat from the outgoing flue gas. 
     The Most Important Benefits of the Innovation According to Point 3. 
     
         
         
           
             No outdoor air must be heated with a high energy loss as result. 
             No dust emissions into the atmosphere during the drying, only during the discharging when dust is leaving the dried material. This dust is sucked in a vacuum cleaner bag. 
             Low temperature heat can be used. 
             A considerable part of the driving heat is recovered and is used several times in cascade dryers coupled after the first unit. 
             The drying result is made sure through a short end drying at high temperature.