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

• US 20100126037A1
• Filed: 11/25/2008
• Published: 05/27/2010
• Est. Priority Date: 11/25/2008
• Status: Active Grant

• Current Assignee: Richard J. Romanek Jr, William H. Moss
• Original Assignee: Richard J. Romanek Jr, William H. Moss
• Inventors: Romanek, Richard J. JR., Moss, William H.
• Granted Patent: US 8,151,482 B2
• Time in Patent Office: Days
• US Class Current: 34/471
• CPC Class Codes: F26B 17/001 the material moving down superimposed floors superimposed belts F26B17/08
• CPC Class Codes: F26B 21/06 Controlling, e.g. regulating, parameters of gas supply F26B21/14 takes precedence; control in general G05
• CPC Class Codes: F26B 2200/02 Biomass, e.g. waste vegetative matter, straw
• CPC Class Codes: F26B 2200/18 Sludges, e.g. sewage, waste, industrial processes, cooling towers
• CPC Class Codes: F26B 3/06 the gas or vapour flowing through the materials or objects to be dried F26B3/14 takes precedence

Abstract

An energy-efficient method and apparatus for drying pelletized, moist organic material is described. The method consists of a rapid, high temperature static drying process in a shallow bed, followed by traditional vertical static drying in a deep bed. Hot exhaust gas from the shallow-bed, hot-temperature static dryer is then recirculated to provide thermal energy to the deep-bed, warn-temperature static dryer. This invention can be used to convert wet, organic waste materials such as animal and poultry waste, municipal wastewater sludge, urban post-consumer food waste, or manufactured food byproducts and residuals into solid fuel.

Claims

1. A method for drying organic waste material consisting of both high-temperature and low-temperature drying, said high temperature drying method consisting of:

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

F. (66°

C.) and 350°

F. (177°

C.);

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

(c) ratio of volumetric airflow-to-solid organic material between 25-75 scfm (standard ft³ )/lb_mass (1.6-4.7 standard m³/kg).

(d) air velocity of 300-600 ft/min (1.5-3.0 m/s) moving upward counter-currently to the downward flow of moist pellets

2. The method as recited in claim 1, said low temperature drying method consisting of:

(a) warm-air convective drying with heated air having a temperature between 90°

F. (32°

C.) and 150°

F. (66°

C.);

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

(c) ratio of volumetric airflow-to-solid organic material between 40-100 scfm (standard ft³ )/lb_mass (2.5-6.3 standard m³/kg).

(d) air velocity of 60-300 ft/min (0.3-1.5 m/s) moving upward counter-currently to the downward flow of partially dried pellets

3. The method as recited in claim 2, wherein hot exhaust gas from high-temperature drying is recirculated to blend with ambient air to make warm inlet air for warm-temperature drying.

4. A two-stage, vertical static dryer apparatus consisting of:

(a) an upper hot-temperature stage with wet solid organic material entering at the top inlet, hot air entering the bottom below an inverted diffusion cone to distribute hot air across the horizontal cross section of the upper hot-temperature unit, and an exhaust gas outlet at the top of the hot-temperature upper stage;

(b) a lower warm-temperature stage with moist, partially-dried solid material that has developed a dry, crusted exterior in the upper hot-temperature stage entering at the top inlet of the lower warm-temperature stage, warm air entering the bottom below an inverted diffusion cone to distribute warm air across the horizontal cross section of the lower warm-temperature unit, and an exhaust gas outlet at the top of the warm-temperature lower stage;

(c) a hot exhaust gas recirculation duct that routes hot exhaust gas from the upper hot-temperature dryer to a mixing venturi inlet to mix hot exhaust gas with ambient air upstream of the inlet to the lower warm-temperature stage.

5. The apparatus as recited in claim 4, wherein temperature controllers are used to control the thermal energy inputs to a) the hot inlet air in the upper hot-temperature stage and b) the warm inlet air in the lower warm-temperature stage.

6. The apparatus as recited in claim 5, wherein diffusion cones are used to distribute the volumetric flowrate of hot inlet air evenly across the cross-sectional area of the upper hot-temperature stage dryer and warm inlet air evenly across the cross-sectional area of the lower warm-temperature stage dryer.

7. The apparatus as recited in claim 6, wherein pellet baffles are used to distribute the mass flow of solid organic material evenly across the cross-sectional area of the dryer as material flows downward.