PRECISE INJECTION OF NH3 USING PULSE-WIDTH MODULATION METERING

Anhydrous ammonia (NH3), a heavily used nitrogen fertilizer, is a volatile gas which flashes at -40 F. It is handles as pressurized liquid and difficult to meter accurately and dispense. Its low cost, due to inexpensive energy, has encouraged wasteful over-application rather than investment in currently costly and ineffective application control systems. Ammonia costs will increase with energy costs and environmental concerns over nitrates in ground water will motivate growers to more efficiently apply NH3. This project will apply pulse-width modulation, already proven for liquid agrochemicals, to NH3 dispensing. Specifically, PWM control will maintain ammonia as liquid during metering and distribution across the tool bar. Additionally, a thermal recovery manifold will capture the cooling from the expansion downstream of the metering valves and cool the incoming ammonia. A simple electronic system and user interface will control the metering valves and monitor the thermodynamic state of the ammonia to assure accurate dispensing. Based on Phase I results, the system is expected to greatly improve the uniformity of application across the tool bar boom and provide a much faster response and significantly wider range of application rates than existing technology. The system will be easily adapted to GPS and variable rate application.