PROOF OF PRINCIPAL TEST TO FEED AND METER GRANULAR COAL INTO 450 psig GAS PRESSURE

This research program is concerned with the development of a new form of feeder, known as the Stamet Posimetric O High Pressure Solids Feeder, to feed dry granular solids continuously and controllably into gas pressure. The device is a rotary mechanical feeder, which utilizes the interlocking and internal friction of the granular solids to drive the solids through into the outlet pressure in a continuous and controllable way, using a continuous solids material seal on the feeder outlet to control gas leakage. Earlier work sponsored under previous SBIR grants has successfully demonstrated the potential benefits of the Stamet machine over pressurized lock hopper or paste feeder methods. The objective of this project was to demonstrate proof of principal to feed and meter specified granular coal into 450 psig gas pressure for use with next generation pressurized fluidized bed combustors. This report encompasses the development of material transport properties testers, methods to predict feeder performance by calculation, and the modification and testing of Stamet feeders to feed the material supplied into pressure. Testers were made to measure material compressibility, bulk density, both internal and wall friction coefficients, and permeability under typical conditions experienced inside a Stamet high pressure feeder. This data is then used in support of ongoing efforts to develop calculations to predict the performance of Stamet pressure feeders with different materials and conditions. Three Stamet pressure feeders were modified to handle the fine granular or pulverized coal, and were tested under various conditions using different outlet arrangements. The initial testing identified difficulties in handling the fine materials, but through a series of calculations and tests, the issues were overcome and the material was successfully fed into pressure. In all cases the performance calculated based on the measured material properties and feeder geometry agreed well with the test results, confirming the ability to predict performance and select geometry required to handle different conditions. However, the maximum pressure achieved was limited by an ineffective auger design, which was unable to effectively control the length of the outlet seal at higher pressures without imposing additional mechanical loads on the surface of the coal seal. This prevented steady state conditions being maintained long enough to reach the target pressure. Though the specified coal was successfully pumped into pressures over 200 psi, and the test results clearly indicate the changes required to provide a fixed outlet geometry that would achieve the 450 psi target, time and funding was not available to pursue this goal further under this project