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Two-stage static dryer for converting organic waste to solid fuel

  • US 8,151,482 B2
  • Filed: 11/25/2008
  • Issued: 04/10/2012
  • Est. Priority Date: 11/25/2008
  • Status: Expired due to Fees
First Claim
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1. A method for drying organic waste material comprising the steps of:

  • (a) hot-air convection drying, with wet solid organic material entering through the top inlet of the hot-air temperature unit and hot air entering through the bottom inlet of the hot-air temperature drying unit, said hot-air temperature drying unit further comprising the following operating conditions;

    i) hot-air convective drying with heated air having a temperature between 150°

    F. (66°

    C.) and 350°

    F. (177°

    C.);

    ii) short residence time of solid organic material between 30-300 seconds;

    iii) ratio of volumetric airflow-to-solid organic material between 25-75 scf (standard ft3)/lbmass (1.6-4.7 standard m3/kg);

    iv) air velocity of 300-600 ft/min (1.5-3.0 m/s) moving upward counter-currently to the downward flow of moist wet solid organic material;

    (b) warm-air convection drying, with moist, partially dried solid organic material produced in the hot-air temperature drying unit entering at the top inlet to the warm-air temperature drying unit and warm air entering through the bottom inlet of the warm-air temperature drying unit, said warm-air temperature drying unit further comprising the following operating conditions;

    i) warm-air convective drying with warm from a mixture of cooler ambient air and hotter air from the hot-air temperature unit exhaust gas, said mixture having a temperature between 90°

    F. (32°

    C.) and 150°

    F. (66°

    C.);

    ii) long residence time of solid organic material between 2-12 hr (7,200-43,200 s);

    iv) ratio of volumetric airflow-to-solid organic material between 40-100 scf (standard ft3)/lbmass (2.5-6.3 standard m3/kg);

    iv) air velocity of 60-300 ft/min (0.3-1.5 m/s) moving upward counter-currently to the downward flow of partially dried solid organic material(c) gas recirculation of hot-air temperature unit exhaust gas that is mixed with ambient air to make warm inlet air for the warm-air temperature unit gas supply, said mixing of hot-air temperature unit exhaust gas with ambient air acting as means of increasing the thermal efficiency of the dryer.

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