WO1998009559A1

WO1998009559A1 - Organic waste combustor

Info

Publication number: WO1998009559A1
Application number: PCT/US1997/016659
Authority: WO
Inventors: John W. Crawford; Damon K. I. Kali; Robert A. Gentala
Original assignee: Ems Technologies Corp.
Priority date: 1996-09-05
Filing date: 1997-09-04
Publication date: 1998-03-12
Also published as: AU4426297A

Abstract

An incinerator or organic waste combustor which utilizes a multi-step arrangement. An elongated chamber (16) is positioned substantially vertically and is adapted to receive solid waste via a charging portal (10). A grate (12) within the elongated chamber (16) prevents the solid waste from passing to a lower end (15) of the elongated chamber (16). Using a heating mechanism, the solid waste within said elongated chamber (16) is heated in an oxygen lean environment to create combustible particulates and flammable gasses which are drawn away through a transfer tube (13) which communicates the materials to a cyclone burner (14). Within the cyclone burner (14), the combustible particulates and flammable gasses are burned in an oxygen fed environment.

Description

Organic Waste Combustor

Background:

This invention relates to waste disposal through complete organic combustion by a process known as Pyrolysis. As society has grown, so too have the problems associated with the safe disposal of waste. Waste streams range from relatively benign materials such as raw wood chips, used office paper, and fresh grass clippings, to hazardous materials such as biologically contaminated materials, fuel contaminated soil and pesticide tainted vegetation .

Benign waste streams are typically landfilled at local municipalities. Unfortunately, the sheer volume of waste processed in this manner usually renders the landfill unsuitable for further commercial use. Hazardous waste streams that ar landfilled dramatically increase risk to the environment by leaching into water supplies and emitting harmful volatile components into the atmosphere.

One solution to these problems is incineration or the reduction and destruction of waste streams through heat. Incineration has the advantage of reducing the volume of waste into a landfill by as much as 97% and can render biological and chemical waste streams harmless. However, incineration can also release unacceptable levels of pollution into the atmosphere so incineration reactors must be fitted with expensive and complex post combustion controls to reduce hazardous emissions.

Obviously, an ideal waste disposal system would reduce the volume of the waste stream, introduce no harmful substances into the environment, and be relatively safe and inexpensive.

Summary of Invention:

The present invention uses a dual chamber combustion system. Reference herein is made to figures 1,2, 3, 4, 5, 6, 7A, and 7B. Overvi ew

In the first chamber (gas generator) (16) , waste is decomposed by heat (Pyrolysis) in an oxygen starved environment. This partial combustion generates combustible particulates and flammable gases (lean gas) leaving only a small amount of sterile and generally inorganic ash.

The lean gas is ducted (13) into a second chamber (cyclone oxidizer) (14) where it is mixed with sufficient oxygen and is completely combusted at high temperature. The resulting effluent is only minimally polluting. Methodology

Waste is introduced into the machine through a pneumatically activated sliding charging portal drawer (10) . The drawer (10) has no sliding seals which require precision machining and are prone to mechanical failure. Seal integrity is critical since the pyrolytic process requires precision control of air flow.

In order to allow for continuous feeding for maximum throughput, the drawer (10) must be double sealed or the process will be disrupted and toxic fumes may leak into the immediate environment. .An automated air purging system in the drawer compartment provides an additional level of safety for operators of the equipment .

The size of the drawer (10) is large enough to handle most bagged waste so shredding is not necessary, further reducing the risk to the operator.

After a bag of waste has been loaded (21) into the drawer (10), the machine is sealed (22A-22B) and the drawer delivers the waste (30) into the gas generator (11) . The drawer (10) has sensors to determine its position. When the drawer has returned to its original position (figure 2), it is ready to receive another charge of waste.

Once the waste has entered the gas generator (16), combustion begins. The waste is maintained in a vertical column supported by a heat resistant grate (12) . New waste travels down the column as older waste is consumed in the generator. This process is defined by increasing temperature zones ranging from 100 C at the top to 1000 C at the grate (12) .

Each zone can be characterized in the following way: Zone 1 - Drying and Degassing: Water and light volatiles are vaporized. Zone 2 - Gasification: Solid material begins to gasify under oxygen poor conditions. Zone 3 - Coke Bed: Ungasified materials (mostly carbon) form a high temperature bed of coals . The formation of the coke bed and the production of gas is initiated by a grid of electric heating elements located at the grate (12). Once the process has reached an optimum temperature, the elements are shut off and the process continues unassisted. If the process drops below optimum temperatures, the heating elements are automatically restarted. This is necessary only when the waste stream is laden with non-combustible liquid.

The grate (12) is a heat resistant rod design that allows ash to fall through into a containment compartment (15) . The design of the grate (12) allows for passive control of the size and amount of ash that passes into the compartment (15). A comb of stainless steel fingers (60) is selectively rotated between the rods to clear blockage and to agitate the column of decomposing waste to allow it to settle properly.

Clean-out ports are located above the grate (12) to facilitate the removal of large inorganic objects that may collect on grate 12. The gas generator should be completely cool before this port may be opened. Normal operation renders all the carbon to ash.

However, the grate (12) may be changed to allow more waste to be processed with an accompanying increase in the volume of ash .

If the grate (12) is widened, larger pieces of carbon will fall through before the carbon is completely reduced to ash. Once carbon has left the grate (12) , combustion is essentially stopped. Air is injected into the ash to cool and finish combustion, but the amount is not sufficient to process large pieces.

The ash compartment (15) is accessible through a clean- out port. The gas generator (16) should be completely cool before this port is opened.

Lean gas produced from the waste is forced to pass through the coke bed in order to leave the gas generator (16) . The carbon and the heat react with the lean gas to breakdown or "crack" long-chain hydrocarbons which are the source of extremely hazardous emissions.

The cracked gas is ducted to the cyclone oxidizer (14) through a circular transfer tube (13) . Regulated air (secondary air) is forced through an axial tube that travels through the gas generator (16) into the transfer tube (13) opening where it mixes thoroughly with the lean gas. The mixture spontaneously ignites in the oxygen rich environment and enters the pre-heated cyclone oxidizer (14) .

The mixture remains in the cyclone oxidizer (14) under extremely turbulent conditions until it is completely oxidized rendering it harmless.

The cyclone oxidizer (14) preferably has an octagonal cross section. The shape maintains the mixing efficiency of more traditional circular designs but is easier to construct and insulate. The dimensions of the oxidizer are calculated to insure maximum efficiency based on the volume of gas produced given the capacity of the gas generator . Auxiliary fuel is added to the axial tube (13) for preheating the cyclone oxidizer and for maintaining the proper temperature in the oxidizer (14) . The temperature may fall for two reasons: a) the heat content of the waste stream is too low, and b) the amount of lean gas produced during start up and shut down is too low. Both conditions require that auxiliary fuel be added to sustain the process to keep emissions within acceptable limits.

In order to reduce the need for auxiliary fuel, the transfer tube (13) contains a grid of electric heaters. The grid has the additional benefit of dramatically reducing emissions on start-up.

Under ideal conditions, the process is self-sustaining; that is, once the proper temperature has been attained, no additional auxiliary fuel is needed. This means that the waste provides all of the fuel necessary for its own destruction and the cost of long term operation is very low. Control

The primary method of control is through temperature feedback (figure 7A) . Probes are positioned throughout the machine to provide input for computer control. Secondary control is provided by oxygen and carbon monoxide sensors at the e.xhaust port (Figure 7B) . The temperature in the cyclone oxidizer (14) is controlled by the amount of lean gas and secondary air that is mixed in the transfer tube (13) . The amount of lean gas is controlled by the amount of heat produced in the gas generator (16) . The amount of heat produced in the gas generator (16) is controlled by the amount of primary air that is injected into it.

Precise control of the system is maintained by computer algorithms. The computer uses the temperature and emission data to meter the primary and secondary air flow and to add auxiliary fuel or electric heat to the system. The computer displays continuous numeric and graphic readouts of all the parameters that it monitors and controls.

The goals of the computer control is to reduce harmful emissions and to maximize throughput of the machine.

Harmful emissions are reduced through temperature control . Throughput is maximized by water injection. The capacity of the gas generator is not volume dependent, rather, it is heat capacity dependent . When the heat content of the waste is high, the rate at which the waste passes through the system is low. Conversely, when heat content of the waste is low, the rate at which the waste passes through the system is high. When waste high in heat capacity is added to the system, water is injected to absorb some of the heat content. This has the effect of raising throughput. The exhaust that leaves the system is hot, non- hazardous, and energy laden. The energy can be recovered by a boiler, heat exchanger, or heat pump. Heat recovery may be added to the transfer tube to eliminate the need for water injection.

The present invention provides a means for safe, reliable, and economical disposal of organic waste. It features volume reduction, complete destruction, and minimal handling of waste streams. In addition, it is less expensive to maintain, simpler to operate, easier to adapt to existing systems due to its modular design, and more thermally efficient than current designs.

It is clear that the present invention, due to its unique design, creates a highly improved and energy efficient method of organic waste disposal .

Claims

What is claimed is: 1. An organic waste combustor comprising: a) a first chamber adapted to receive organic waste, said first chamber adapted to heat said organic waste in an oxygen lean environment to produce combustible particulates and flammable gasses from said organic waste; and, b) a second chamber adapted to, 1) withdraw said combustible particulates and flammable gasses from said first chamber, and, 2) burn said combustible particulates and flammable gasses in an oxygen fed environment.

2. The organic waste combustor according to claim 1, wherein said first chamber is an elongated chamber being substantially vertically aligned.

3. The organic waste combustor according to claim 2, further including a waste drawer communicating with an upper end of said first chamber, said waste drawer having, a) an exterior door adapted to allow waste to be deposited into said waste drawer by an operator; and, b) a bottom door adapted to be opened and allow waste within said waste drawer to fall into said first chamber.

4. The organic waste combustor according to claim 2, further including a grate positioned within said first chamber and adapted to prevent solid waste from passing to said second chamber .

5. The organic waste combustor according to claim 4, further including a heating mechanism positioned proximate to said grate, said heating mechanism adapted to heat waste within said first chamber to create said combustible particulates and said flammable gasses.

6. The organic waste combustor according to claim 5, wherein said heating mechanism includes a coke bed.

7. The organic waste combustor according to claim 4, further including an ash collection compartment communicating with a lower end of said first chamber, said ash collection compartment having a door adapted to allow external access to ash collected within said ash collection compartmen .

8. The organic waste combustor according to claim 1, a) wherein said second chamber has a substantially circular cross section, and an exhaust port aligned with a center axis of said second chamber; and, b) further including a transfer tube positioned to communicate said combustible particulates and flammable gasses from said first chamber to said second chamber in such a manner that the combustible gasses and the flammable gasses cyclone within said second chamber.

9. The organic waste combustor according to claim 8, further including a secondary heating mechanism positioned within said transfer tube and adapted to selectively heat combustible particulates and flammable gasses passing therethrough.

10. The organic waste combustor according to claim 9, further including means for selectively introducing oxygen to said second chamber.

11. The organic waste combustor according to claim 10, further including means for selectively introducing auxiliary fuel to said second chamber.

12. The organic waste combustor according to claim 11, a) further including a temperature sensor generating temperature data indicative of a temperature of an interior portion of said second chamber; and, b) further including a computer having, based upon said temperature data, means for adjusting, 1) said means for selectively introducing oxygen to said second chamber, 2) said secondary heating mechanism, and, 3) said means for selectively introducing auxiliary fuel to said second chamber.

13. The organic waste combustor according to claim 12, a) further including an emission sensor positioned at said exhaust port and generating emission data; and, b) wherein said means for adjusting is responsive to said emission data.

14. An incinerator comprising: a) an elongated chamber being substantially vertically aligned and having, l) a waste depository communicating with an upper end of said elongated chamber and adapted to communicate solid waste thereto, 2) a grate adapted to prevent solid waste from passing to a lower end of said elongated chamber, 3) a first heating mechanism positioned proximate to said grate, said first heating mechanism adapted to heat said solid waste within said elongated chamber in an oxygen lean environment to create combustible particulates and flammable gasses; b) a transfer tube having a first end thereof communicating with said elongated chamber below said first heating mechanism, said transfer tube having a second heating mechanism adapted to selectively heat combustible particulates and flammable gasses passing through said transfer tube; and, c) a cyclone burner having an octagonal cross section and an exhaust port aligned substantially along a center axis of said cyclone burner, said cyclone burner communicating with a second end of said transfer tube and adapted to burn combustible particulates and flammable gasses in an oxygen fed environment.

15. The incinerator according to claim 14, wherein said waste depository includes : a) an exterior door adapted to allow waste to be deposited into said waste depository by an operator; and, b) a bottom door adapted to be opened and allow waste within said waste depository to fall into said elongated chamber.

16. The incinerator according to claim 15, further including means for purging sir from said waste depository prior to an opening of said exterior door by the operator.

17. The incinerator according to claim 14, further including a coke bed positioned within said elongated chamber proximate to said first heating mechanism.

18. The incinerator according to claim 14, further including an ash collection compartment communicating with a lower end of said elongated chamber, said ash collection compartment having a door adapted to allow external access to ash collected within said ash collection compartment .

19. The incinerator according to claim 14, a) further including means for selectively introducing oxygen to said cyclone burner; b) further including a temperature sensor generating temperature data indicative of a temperature of an interior portion of said cyclone burner; and, c) further including a computer being responsive to said temperature data and having means for adjusting said means for selectively introducing oxygen to said cyclone burner.

20. The incinerator according to claim 14, a) further including means for selectively introducing auxiliary fuel to said cyclone burner; b) further including a temperature sensor generating temperature data indicative of a temperature of an interior portion of said cyclone burner; and, c) further including a computer being responsive to said temperature data and having means for adjusting said means for selectively introducing auxiliary fuel to said cyclone burner.

21. The incinerator according to claim 14, a) further including means for selectively introducing oxygen to said cyclone burner; a) further including an emission sensor positioned at said exhaust port of said cyclone burner, said emission sensor generating emission data indicative of gas quality proximate to said emission sensor; and, c) further including a computer being responsive to said emission data and having means for adjusting said means for selectively introducing oxygen to said cyclone burner.

22. The incinerator according to claim 14, a) further including means for selectively introducing auxiliary fuel to said cyclone burner; a) further including an emission sensor positioned at said exhaust port of said cyclone burner, said emission sensor generating emission data indicative of gas quality proximate to said emission sensor; and, c) further including a computer being responsive to said emission data and having means for adjusting said means for selectively introducing auxiliary fuel to said cyclone burner.