Patent Publication Number: US-6655043-B1

Title: Dryer moisture indicator

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to indicators and more particularly to indicators that display the condition of the contents of containers where knowledge of the condition of the contents of the container is necessary for the performance of supporting activities. 
     2. Related Prior Art 
     In the area of material drying, such as sand drying, the relative moisture content of material to be dried must be known. The relative moisture content is often critical to the speed with which a subsequent dependent process may be accomplished. In some processes, such as drying sand, a high moisture content may prevent the drying process from being accomplished or completed efficiently or satisfactorily. 
     For example, in a sand drying plant where the sand is to be added to aggregates and oil derivatives to form asphalt, the moisture content of sand must be decreased to a predetermined level. Sand is scooped up from an outdoor pile and placed in a large tumbler. The sand is put through a drying procedure where hot gas is circulated over the wet sand, run through a dryer transition stage to a dust collector and then exhausted through the use of a large exhaust fan. The temperature of the exhaust is low when moisture is present in the sand and increases as the moisture content decreases or the sand is dried. When more sand having a significant moisture content is placed in the drying area, the temperature of the exhaust gas drops again, depending on the amount of moisture in the sand. 
     Although all the sand is taken from the same mound, in most cases taking sand from higher on the mound will result in loading sand with a lower moisture content. This is due primarily to the effect of gravity (moisture, i.e. water, is heavier than air and will tend to leach to the lower areas of the mound) and the drying effect of the sun and wind which will be most noticeable on the top and exposed sides of the mound. The drying effect of the sun and wind can be very rapid and significant and can aid in the drying process. In general, dropping the height of the bucket into which sand is loaded by a mere four inches, that is, taking the sand from deeper on the mound where it has a higher moisture content, can produce a significant change in the drying operation. The resulting change can be so significant that it can mean the difference between an efficient successful drying operation and one which operates too slowly and inefficiently, causing costs to increase because of increased man hours and increased gas consumption. 
     Unfortunately, the person who has the most control over the amount of moisture in the sand being loaded, and as a result, the gas consumption, has the least knowledge of the amount of moisture in that sand and the amount of gas being consumed. The dryer operator located in the control room is the only person who has the information concerning the moisture content through the knowledge of the amount of gas being consumed to dry the sand. 
     There are many types of moisture indicators in the art. Some detect the amount of moisture contained in a substance directly by insertion of a probe into the material, measure the moisture content and provide a digital readout of the actual moisture content. One such type is the “AQUA-SPEAR” moisture meter manufactured Mastrad Company. 
     U.S. Pat. No. 4,047,105, titled “Method and Apparatus for Providing an Output Indication Proportional to the Moisture Content of Particulate Material”, issued to Bruce Olen Anderson relates to method and apparatus for providing an output indication proportional to the moisture content of particulate material where a probe drive signal having a predetermined frequency and amplitude is inserted and applied to the particulate material. A current indicator signal proportional to the current applied to the particulate material is provided. The current signal is proportional to the moisture content of the particulate material. 
     U.S. Pat. No. 4,621,229, titled “Instrument for Measuring the Moisture Content of Solids”, issued to Friedrich Hirth, relates to an Instrument for measuring the moisture content of solids that has probes which are placed in contact with the material which is to have its moisture content measured. The probes are used to measure the electrical resistance of the material. A d.c. voltage is connected with the probes and generates the voltage required for measurement of electrical resistance. The characteristic line representing the electrical resistance of the material as a function of its moisture content is logarithmic in nature and, in order to generate a straight characteristic line, the signals from the probes are fed to a logarithmic amplifier. The amplified signals are converted to a moisture content which may be read from an indicator constituting part of the instrument. A calibrating unit is interposed between the logarithmic amplifier and the indicator and functions to adjust the characteristic line of the instrument so that this at least approximates the characteristic line of the material undergoing moisture determination. 
     Other types of moisture indicators may provide a reading by color change. Humidity Indicators manufactured by AGM Container Controls, Inc. are of this type. In general, these indicate the amount of humidity in a specific area. For example, this type of moisture indicator is placed in a closed area such as a room or section of a building. The ambient air humidity is indicated by the color of the indicator. When dealing with a large area such as a room, the color change will be slow to indicate a gradual change in humidity and not an instantaneous change for a small area. 
     SUMMARY OF THE INVENTION 
     The present invention provides a moisture indicator in an air flow drying process where hot gas is circulated over and around a granular material. Typically, this granular material has an undesirable amount of moisture content. In this process, the temperature of the gas after it has been circulated over the wet or damp sand provides an indication of the moisture content of the sand. The greater the moisture content in the sand, the cooler the exhaust gas and conversely, the dryer the sand, the hotter the exhaust gas temperature. The moisture indicator of the present invention includes a detector located in the path of the exhaust gas to determine exhaust flow temperature. A detector is placed in the gas flow process after it has been circulated over the sand to detect temperature of the exhaust gas. A valve control device is either electrically or mechanically associated with the temperature detector. This valve control device is used to control the flow percentage of hydrocarbon gas in the hot gas intake. When the temperature of the gas in the exhaust section drops below a predetermined level, a signal is sent to the valves that control the amount of flammable gas (hydrocarbon heating gas) in the intake flow. This signal causes the valves to open, increasing the percentage of heating gas in the gas flow, increasing the temperature of the hot gas intake. An indicator is connected or linked with the valve control device. The indicator is associated with a display showing the percent of hydrocarbon gas that is currently being fed to the hot gas intake in order to maintain a predetermined temperature in the exhaust gas. This in turn provides an indication of the amount of moisture in the granular material that has just been loaded into the moisture dryer. The percentage of hydrocarbon gas in the intake gas flow is directly proportional to the percentage of moisture in the granular material being dried. The indicator is operated in conjunction with the valve control for the intake hydrocarbon gas and is indicative of the amount of moisture in the granular material as a function of the percentage of gas needed to maintain a predetermined temperature in the exhaust gas. This provides a signal to the loader operator as to whether the granular material loaded has an acceptable amount of moisture for successful, efficient operation of the drying process or whether he should take sand or other granular material from another location. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a granular material drying operation. 
     FIG. 2 is a front view of the display illustrated in connection with the granular drying operation of FIG.  1 . 
     FIG. 3 is a back view of the display of FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, a schematic diagram of a granular material drying operation  12  is illustrated. A container  14  is shown as containing granular material  16  in its lower portion. In this embodiment the granular material used may be sand or other aggregates that require moisture removal. A hot air intake  18  is illustrated as connected to one end of container  14  which provides hot gas for the drying process. A hydrocarbon gas source  20  is connected to hot air intake  18  through a gas line  22 . 
     Intake pipe  18  is preferably approximately thirty inches in diameter with gas line  22  preferably being approximately one inch in diameter. Other sizes may be used as long as it permits adequate intake air flow and proper mixing of hydrocarbon or other flammable gas. 
     Valve assembly  24  with valves  24 A, . . . , etc. is used in gas line  22  to control the amount of hydrocarbon gas which is mixed with outside air within hot gas intake  18 . The hot gas mixture enters container  14  at an opening  26 , which connects to hot gas intake  18 . A hot gas  28  circulates throughout container  14  heating granular material  16  to remove any moisture that it may have. As hot gas  28  contacts moisture laden granular material  16 , it provides heat calories to permit moisture to change states from water to water vapor by absorbing heat. The absorption of heat to vaporize the moisture in granular material  16  causes a reduction in the temperature of hot gas  28 . 
     Hot gas  28  is then withdrawn from container  14  through an exhaust pipe  30 . Exhaust pipe  30  carries hot air  28  through a dust collector  32 . Exhaust pipe  30  is also approximately thirty inches in diameter, but again, any size may be used as long as a proper air flow is permitted. Exhaust pipe  30  has an elbow  38  at point spaced apart from container  14 . The purpose of elbow  38  is to change direction of air flow to direct any dust particles into dust collector  32 . Temperature detector  40  is located outside of container  14  but before elbow  38  in order to obtain the temperature of hot gas  28  as it comes out of container  14  and before it cools further. Any further cooling of hot gas  28  will provide an erroneous reading and cause too high a percentage of hydrocarbon or flammable gas to be mixed with the intake air. 
     An exhaust line  34  is connected to dust collector  32  and contains a fan  36  which pulls hot air  28  from dust collector  32 . Contained within exhaust pipe  30 , near an elbow  38  which turns down to dust collector  32 , is a temperature sensor  40 . 
     Exhaust  34  is also preferably a pipe having a thirty inch diameter with fan  36  mounted therein. Fan  36  may be of any type currently in use in the art, as long as it is sized to fit within exhaust  34  and has the drawing ability to pull hot air out of the drying container. 
     Temperature sensor  40  is used to detect the temperature of hot gas  28  as it is exhausted from container  14 . Sensor  40  sends a signal indicative of the temperature of exhaust hot gas  28  through a line  42 . Line  42  is connected to a valve assembly  24 . Valve assembly  24  is used to control the amount or percentage of hydrocarbon gas being fed to intake line  18 . Valve assembly  24  is connected to an indicator  44  mounted on a display  46  through a mechanical linkage  48 . Indicator  44  is associated with display  48  which indicates the percentage of hydrocarbon gas being fed through intake  18 . 
     In operation hot air enters container  14  through opening  26 . Hot air  28  provides the additional calories to vaporize any moisture which may be contained within granular material  16 . The greater the moisture content in granular material  16 , the greater the number of calories provided by hot air  28  needed to vaporize the moisture in granular material  16 . 
     When hot air  28  is withdrawn from container  14  to dust collector  32  through the pulling action of fan  36 , it passes by temperature detector  40 . Temperature detector  40  compares the temperature of the exhaust gas  28  with a predetermined minimum. When the temperature of exhaust gas  28  is below this predetermined minimum, temperature detector  40  sends a signal to valve assembly  24  to open the valves  24 A, . . . , etc., allowing a greater percentage of hydrocarbon gas from container  20  to travel through gas line  22  to be mixed with intake air within intake pipe  18 . Thus, the lower the temperature of hot gas  28  when it reaches temperature detector  40 , the more hydrocarbon gas that gets mixed with ambient air in air intake  18 . 
     When the temperature drops and valve assembly  24  is told to open valves  24 A, . . . , etc. to permit more hydrocarbon gas to flow, mechanical linkage  48  moves indicator  44  to the right as valves  24 A, . . . , etc. open. Moving indicator  44  to the right indicates a greater percentage of hydrocarbon gas on display  46 . 
     Similarly, if the temperature of hot gas  28  as measured by temperature detector  40  exceeds a predetermined value, a signal is sent through connection  42  to valve assembly  24  to have it close valves  24 A, . . . , etc. and reduce the amount of hydrocarbon gas being fed to intake pipe  18 . As valve assembly  24  closes valves  24 A, . . . , etc., mechanical linkage  48  moves indicator  44  to the left, indicating on display  46  that the intake gas contains a lower percentage of hydrocarbon gas. 
     Referring to FIG. 2, display  46  is illustrated with indicator  44 , showing display  46  as a tractor operator (not shown) would view it from his operating position. As illustrated, display  46  contains a large green area  50 , a white area  52  and a large red area  54 . When the moisture content of granular material  16  is at an acceptable level, indicator  44  points to or is located in green area  50 . As the moisture content increases, indicator  44  will move to through white area  52 . When the moisture content reaches an unacceptable level, indicator  44  points to or is located in the red area  54 . Indicator  44  pointing to the red area  54  is a clear indication to the loader operator that the bucket on the tractor is digging too deep into the mound of sand. The loader operator should either raise his bucket or move to a different location on the sand mound or to a different sand mound. The operation of wind and sun on a sand mound can be such that a mere raising of the bucket four inches can bring the moisture content of granular material  16  down to a level that the moisture level is acceptable. This will move indicator  44  from red area  54  to green area  50 . 
     Referring now to FIG. 3, a back view of display  46  is illustrated. A base  56  of indicator  44  is illustrated as extending through display  46 . Base  56  is fastened to a slip linkage  58 . As mechanical linkage  48  moves to the right indicator  44  will move to the left. And conversely, as mechanical linkage  48  moves to the left moving the lower portion of slip linkage  58  to the left, indicator  44  will move to the right. 
     As can be seen, through the measurement of exhaust hot gas  28  using temperature detector  40 , the opening and closing of valves  24 A, . . . , etc. of valve assembly  24  can be controlled to regulate the flow of hydrocarbon gas from supply  20  through gas line  22 . The opening and closing of valves  24 A of valve assembly  24  will move indicator  44  using mechanical linkage  48  through slip linkage  58  and base  56  to indicate the percentage of hydrocarbon gas in intake gas  28  on display  46 . This percentage of hydrocarbon gas is the percentage which is needed to maintain the temperature of hot intake gas  28  within a predetermined temperature range. The exhaust temperature of hot gas  28  is inversely proportional to the amount of moisture within granular material  16 . As the moisture content of granular material  16  increases, the exhaust temperature of hot gas  28  decreases. Similarly, when the moisture content of granular material  16  decreases, the exhaust of hot gas  28  increases. The inverse proportionality is approximately linear so that an increase in temperature indicates a proportional decrease in moisture and a decrease in the exhaust temperature of hot gas  28  indicates a proportional increase in the moisture content of granular material  16 . 
     While there has been illustrated and described a particular embodiment of the present invention, it will be appreciated that numerous changes and modifications will occur to those skilled in the art, and the present invention should not be limited thereto. It is intended that the present invention cover all those changes and modifications which fall within the true spirit and scope of the appended claims.