Abstract:
A method and apparatus for supplying liquid anhydrous ammonia to a pump or other flow control system whereby a separation chamber removes vapor generated by friction in the flow path from a storage tank containing saturated anhydrous ammonia. Additionally, liquid ammonia in the separation chamber creates a static head pressure. The difference in height between the inlet near the top of the separation chamber and the outlet at the bottom causes the static head pressure. The static head assures pure liquid at the bottom since absolute pressure exceeds saturation pressure. As a result, the feed stream to the pump or other flow control system is free of ammonia vapor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of the filing date of U.S. Provisional Application No. 60/462,844, titled “Method and Apparatus for Supplying Liquid Anhydrous Ammonia To A Flow Control System,” filed Apr. 15, 2003. 

   FIELD OF THE INVENTION 
   The present invention relates to a new apparatus and method for providing vapor free liquid to an anhydrous ammonia flow control system. More particularly, the invention relates to a process which removes gaseous ammonia from the liquid stream and provides a static head pressure differential at the inlet of the flow control system. The static head causes anhydrous ammonia at the inlet to have an absolute pressure above its saturation pressure. 
   BACKGROUND OF THE INVENTION 
   Injection of anhydrous ammonia into the soil is a commonly used method of supplying nitrogen fertilizer to grain and other crops using an applicator-vehicle pulled by a tractor. An ammonia storage tank is pulled behind the applicator. A hose connects the storage tank to the distribution system on the applicator. The distribution system splits the ammonia into separate lines which feed several knives. These knives are lowered into the soil several inches and ammonia is injected into the ground at the bottom of the knives as the knives are pulled through the soil. 
   It is normally desired that ammonia be applied uniformly over a field. One of the main problems is achieving this uniformity is difficulty in controlling a stream of mixed liquid and gaseous ammonia. Gaseous ammonia causes many flow sensors to supply incorrect data and causes many pump designs to become vapor locked. Refrigeration of the ammonia and pressurizing with a pump are methods of keeping liquid anhydrous ammonia below its saturation temperature. 
   A typical use of refrigeration is described in U.S. Pat. No. 4,458,609 to Tofte. A part of the liquid ammonia is used as a refrigerant to cool the inlet liquid stream. This is accomplished in a heat exchanger which mechanically separates the stream of inlet liquid ammonia from a stream of coolant ammonia. Typically, the coolant stream taken from the main stream passes through a restriction, losing pressure. The lower pressure, lower temperature stream provides the cooling for the inlet liquid ammonia. 
   Another method of cooling the liquid ammonia stream is the use of an externally powered refrigeration system, described in U.S. Pat. No. 6,269,757 to Kiest. 
   Pressurization of liquid ammonia for agricultural application is typically described in U.S. Pat. No. 5,845,592 to Ridgley and U.S. Pat. No. 6,283,079 to Swanson. 
   This invention relies on separation of gaseous ammonia from the liquid ammonia flow stream. Prior patents cover the separation of the gaseous phase for agricultural use. However, their methods and purposes are quite different from this invention. A typical example is U.S. Pat. No. 4,069,029 to Hudson which discusses the adiabatic expansion of anhydrous ammonia in an expansion chamber. This expansion creates a significant amount of gaseous ammonia. The gas and liquid are separated and utilized at relatively low pressures, generally close to ambient. The resulting liquid remains in a saturated state so that subsequent pressure drops create more gaseous ammonia. This approach is not useful as a method of feeding pumps or other flow control systems. Other similar patents are U.S. Pat. No. 3,978,681 to Kjelgaard et al, U.S. Pat. No. 4,175,394 to Wiesboeck, U.S. Pat. No. 4,169,677 to Luria, U.S. Pat. No. 4,202,283 to Wiesboeck, U.S. Pat. No. 4,310,344 to Kjelgaard et al, U.S. Pat. No. 4,310,555 to Kjelgaard et al, U.S. Pat. No. 4,341,168 to Siebert, U.S. Pat. No. 4,385,500 to Kjelgaard et al, U.S. Pat. No. 4,657,568 to Jones and U.S. Pat. No. 4,900,339 to Ward et al. 
   U.S. Pat. No. 6,117,217 to Jones removes gaseous ammonia from a pumped liquid stream. However, it separates out the gas phase after the pump inlet rather than before the inlet. This method requires a particular pump design. Many pump designs would become vapor locked with a mixed phase feed of gas and liquid as described in the patent. 
   SUMMARY OF THE INVENTION 
   The method and apparatus of the present invention supplies liquid anhydrous ammonia to a pump or other flow control system which is part of a system for application of agricultural ammonia fertilizer. This invention uses a gas separation chamber to remove vapor generated by friction in the flow path from a storage tank containing saturated anhydrous ammonia. Additionally, liquid ammonia in the separation chamber creates a static head pressure. The difference in height between the inlet near the top of the chamber and the outlet at the bottom causes the static head pressure differential. This static head assures pure liquid at the bottom since absolute pressure there exceeds saturation pressure. As a result, the liquid feed stream to the pump or other flow control system is free of ammonia vapor. 
   Liquid anhydrous ammonia in the storage tank is a saturated liquid at its vaporization temperature. As the liquid stream passes through valves, fittings and a connecting hose to the applicator system it experiences a pressure loss due to friction in the hose. Because of the lowered pressure some-liquid ammonia vaporizes to cool the liquid to the saturation temperature associated with that lower pressure. This changes the liquid stream into a mixture of liquid and gaseous phases. The greater the pressure drop, the greater is the ratio of gas to liquid. Anecdotal evidence suggests that application rates near 600 lbs/hr of anhydrous causes temperature drop of less than 1° F. using 1¼″ inside diameter connecting hoses. Smaller hoses and fittings would increase the temperature drop as would higher rates of application. Assuming a 1° F. drop from the storage tank to the separation chamber, approximately 0.2% by weight of ammonia gas would be created. This is about 25% by volume. 
   The gas separation chamber is composed of three sections. Past the feed entry is a quieting section which allows gaseous bubbles to rise out of the liquid stream. This section has a larger diameter to provide increased volume to reduce fluid velocity. Above the quieting section is head space for collection and separation of gaseous ammonia. This space has enough volume to allow liquid level to rise and fall as the gaseous ammonia is metered out of the chamber. Below the quieting section is a reduced diameter stand pipe which creates static head pressure additive to the inlet pressure. The smaller diameter of the stand pipe section reduces the amount of anhydrous liquid stored in the chamber. The diameter need only be big enough to prevent a significant loss of pressure due to fluid friction. 
   Liquid anhydrous ammonia in the storage tank passes through piping, a hose, and several fittings including valves, quick connecting coupling, and break away coupling. Upon entry into the chamber velocity of the incoming liquid stream is reduced such that entrained gas bubbles have time to rise to the top of the chamber. Gaseous ammonia collects above the feed entry to the chamber. A gas eliminator is located at the top of the chamber to vent gaseous ammonia from the container while sealing against flow of liquid. The gaseous ammonia passes through a shut off valve to an exhaust hose which is connected to one of the soil injection knives. Liquid ammonia flows down the stand pipe to the bottom outlet of the chamber. It then enters an elbow and connects to the inlet of the flow control system. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     These and other objects, features and advantages of this invention will become readily apparent in view of the following detailed description of the preferred embodiments and best mode, appended claims and accompanying drawings, in which: 
       FIG. 1  is a side elevation of the apparatus of the present invention being pulled behind a tow vehicle; 
       FIG. 2  is a fragmentary side elevation of the apparatus of the present invention; 
       FIG. 3  is a cutaway view of the separation chamber; and 
       FIG. 4  is an enlarged vertical sectional view of a float controlled gas eliminator valve with a portion of the spool broken away. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring first to  FIG. 1 , the apparatus of the present invention is shown being pulled behind a tow vehicle  100  which could be a tractor, truck, or the like. The apparatus includes a toolbar applicator frame  101  which supports a separation chamber  102 , a flow control system  103  which may include a pump  220 , a hydraulically operated shut off valve  224 , a distribution manifold  225 , flow control orifices  226 , a plurality of soil cutting knives  104 , and a storage tank  105  supported on a plurality of wheels  106  and towed behind the toolbar applicator frame  101 . The toolbar applicator frame  101  itself is supported on a plurality of wheels  107  and has a tongue  116  that is pivotally connected to a hitch  112  on the rear of the tow vehicle  100 . In the preferred embodiment, the toolbar applicator frame  101  is a Progressive series 1300 NH3 Toolbar, manufactured by Progressive Farm Products, Inc. of Hudson, Ill. It is configured by Progressive for “strip till” ammonia application. Multiple knives  104  are suspended from the frame  101 , with there being typically 8, 12, or 16 of the knives  104  attached to a toolbar applicator frame  101 , which is adapted to raise or lower the knives  104  into the soil. Each knife  104  includes at least one injector nozzle  114  through which the ammonia can be emitted into the soil when the knife  104  is lowered into the soil. 
   The storage tank  105  is a pressurized tank that is commercially available and retains a predetermined quantity of fertilizer which may be, by way of illustration, anhydrous ammonia. The storage tank  105  is on a trailer that also has a tongue  120  that is pivotally connected to a hitch  122  on the toolbar applicator frame  101 . 
     FIGS. 1–4  depict the apparatus of the present invention. As shown clearly in  FIG. 1 , a main delivery or exit hose  108  passes from the supply tank after an appropriate manually-operable shutoff valve  109  and a quick connect coupling  110  to a breakaway coupling  111  on the toolbar applicator frame  101 . The main delivery hose  108  would be, by way of example, a 1.25″ internal diameter (“I.D.”) reinforced neoprene-lined hose. The breakaway coupling  111  connects at an entry point  212  (as shown in  FIG. 2 ) to the separation chamber  102  where ammonia vapor is separated in a quieting section  214  from liquid ammonia. 
   Vapor rises to the top of the separation chamber quieting section  214  and exits through a float operated gas vent valve body  215 . Gas vent valves are commercially available. However, the valve described below is a new design. Typically, the float operates on a hinged lever which closes an orifice located part way between the float and the hinge. When the force exerted by the pressure difference across the orifice exceeds the net force caused by the weight of the float acting on its lever arm, the valve will stick in a closed position, allowing no gas to pass. Typically, this problem is solved by the use of a very small orifice. However, a small orifice is typically inadequate to exhaust the total gas generated. This causes gas to build up in the separation chamber until it finally reaches the pump inlet, starving the pump. The valve design described here avoids use of an orifice. With this design there is no pressure differential creating a force to hold the valve in its closed position. The valve consists of a housing  301 , a spool  302 , and a float  303 . When the level of liquid ammonia drops, the float  303  drops also. The spool  302  is rigidly attached to the float  303  and moves as the level of liquid ammonia changes. Travel of the spool  302  is limited by the drive pin  304  through the spool which bottoms at the end of slot  306  in the housing  301 . In this position, the top of the spool  302  is below the gas exit passage  305  so gas flows through the exit passage  305  and out of the separation chamber  214 . As gas leaves the separation chamber  214  the liquid level rises, raising the float  303 . As the float  303  rises, it raises the spool to cover the exit passage  305  stopping flow. This prevents liquid ammonia from exiting the separation chamber. 
   From the exit passage  305  the gas then passes through a hydraulically operated shutoff valve  216 , then through a low pressure hose  217  to a tube  218  on one of the injection knives  104 . This gas has been created by a fluid friction between the storage tank  105  and the separation chamber  214 . 
   Liquid ammonia flows down inside the separation chamber  102  through a static head pipe  219  and exits the chamber to a suitable flow control system  103 . It is possible to create a vortex in the separation chamber  102  whereby ammonia gas can be conveyed to the inlet to the flow control system. To prevent a vortex, a baffle  211  is placed in the quieting zone  214  below the inlet  212  to the separation chamber  102 . An increase in liquid pressure at the exit  229  of the separation chamber  102  is caused by the weight of liquid ammonia in the quieting zone  214  and the static head pipe or standpipe  219 . This pressure increase raises the pressure of the liquid above saturation pressure. The quiet section or quiet zone  214  has an area perpendicular to a flow of liquid ammonia through the quieting section that is at least two times the entry passage  212  area. The standpipe  219  has a standpipe ammonia flow path cross-section area that is smaller than the quieting section area. 
   The flow control system  103  would preferably include a positive displacement pump  220 , such as of the type manufactured under model 1502 or model 7560 by Hypro Corporation of New Brighton, Minn. In the preferred embodiment, the pump  220  is driven by a Char-Lynn hydraulic motor, model 101-1700, using tractor hydraulics. Following the pump  220  is a side stream with a pressure relief valve  221  which limits over pressurization of the system downstream from the pump  220 . Any effluent from the pressure relief valve  221  flows through a hose  228  to the inlet  212  of the separation chamber  102 . Pressure is monitored by a pressure gauge  213 . A flow sensor  222  is connected to a console/controller in the cab of the tow vehicle  100  so that the operator of the tow vehicle  100  can monitor and control the flow of ammonia through a servo valve  223 . Following the servo valve  223  the liquid ammonia flows to one or more hydraulically operated shut off valves  224 . After each shut off valve  224  is a manifold exit, to each knife  104 , that includes an orifice  226 . Each orifice  226  creates a backpressure on the flow controls system  103 , maintaining the ammonia at a pressure above its saturation pressure. The orifices  226  provide equal flow to each knife line. Flexible hoses  227  connect these lines from the manifold  225  to the knives  104 . 
   The hydraulically operated shut off valves,  216  and  224 , are typically operated by the hydraulic circuit which lifts the applicator frame  101  at the end of a row. This reduces escape of ammonia vapor to a minimal amount. At the start of a new row, the system has not been depleted of liquid ammonia. It requires much less time to reach equilibrium at the start of a new row. 
   The ammonia in storage tank  105  is saturated. Liquid ammonia is in the bottom of the tank  105 . Ammonia gas in the top of the tank raises the pressure in the tank until the system is stabilized. If the temperature of the ammonia increases, the quantity of ammonia gas increases and the pressure in the tank  105  increases until the system is stabilized at the higher temperature. If the temperature of ammonia in the tank  105  decreases, some gas becomes liquid, the pressure in the tank decreases and the system stabilized at the decreased temperature. 
   The pressure in the storage tank  105  is sufficient to force liquid ammonia into the open bottom end of a vertical pipe in the storage tank  105  and through the delivery hose  108 . The liquid ammonia enters the separation chamber  102  and any gas that is formed rises to the top of the chamber. Gas forms due to friction as stated above. The friction due to flow of ammonia through the system results in a pressure drop. As the pressure drops, the liquid ammonia boils and cools to a new saturated condition with mixed liquid and gaseous states. The gas vent valve  215  removes ammonia gas to allow continued flow from the tank  105 . 
   Pumps such as the pump  220  reduce pressure on their inlet side. If the pressure on the inlet side of the pump is reduced below the saturation pressure, ammonia gas bubbles will be formed. Such gas bubbles can vapor lock the pump  220 . Any gas passing through the flow sensor  222  will adversely affect the accuracy of the flow sensor  222  and may also result in non-uniform flow from the manifold  225 . The head pipe  219  has sufficient vertical height to create a head and ensure that the pressure of the fluid at the inlet to the pump remains above the saturation pressure. The elevated pressure ensures that no gas passes through the flow sensor  222  or through the orifices  226 . All of the liquid that passes through one orifice  226  is injected through one knife  104 . The vertical distance from the entry point  212  down to the pump inlet at separation chamber exit  229  was 44″ in one test unit that performed well. However, the required static head depends upon ambient temperature, pump capacity, ammonia flow rate, pipe diameters, pipe lengths and obstructions to fluid flow. The required static head will vary from the 44″ depending upon these factors. Other factors, that are not listed above, may also change static head requirements. The 44″ static head is believed to be adequate over a relatively large temperature range with the apparatus tested. 
   The formation of gas in the hoses  227  is generally not a serious problem. The desired quantity of ammonia will be delivered to the crop row. It is understood that the disclosed embodiment is representative of a presently preferred form of the invention and that others that accomplish the same function are incorporated herein within the scope of any ultimately allowed patent claims.