MX2011000665A

MX2011000665A - System and method for gasification-combustion process using post combustor.

Info

Publication number: MX2011000665A
Application number: MX2011000665A
Authority: MX
Inventors: Hanwei Zhang
Original assignee: Covanta Energy Corp
Priority date: 2008-07-15
Filing date: 2009-07-15
Publication date: 2011-03-25
Also published as: CA2730936A1; WO2010009231A2; WO2010009231A8; WO2010009231A3; CN102144125A; EP2321579A2

Abstract

Systems and methods for effectively combusting municipal waste are disclosed. Aspects of the present invention provide improved techniques for increasing efficiency of combusting municipal waste as well as decreasing emission of harmful gases. In one aspect of the present invention a system is provided which includes a post combustor (10) for combusting gasified waste. In another aspect of the present invention, a method for using the post combustor (10) to gasify the waste is provided.

Description

SYSTEM AND METHOD OF A GASIFICATION PROCEDURE- COMBUSTION USING A POSCOMBUSTER CROSS REFERENCE WITH RELATED REQUESTS This application claims the priority benefit of the Provisional Application of E.U.A. No. 61 / 080,805, filed July 15, 2008 and from the U.S. Patent Application. No. 12 / 467,887, filed on May 18, 2009, whose descriptions are incorporated for reference in their entirety.

TECHNICAL FIELD The present invention relates to a system and method for implementing a gasification-combustion process that converts a waste or solid fuel into energy, while producing a minimum amount of unwanted emissions.

BACKGROUND OF THE INVENTION Municipal solid waste ("MSW") is the gross product collected and processed by municipalities and governments. The MSW includes durable and perishable items, containers and packaging, food and garden waste, as well as inorganic waste miscellaneous from residential, commercial, and industrial sources. Examples include newsprint, household appliances, clothing, food waste, containers and packaging, disposable diapers, plastics of all kinds including disposable tableware and foamed packaging materials, rubber and wood products, potting soil, garden and electronic pruning of consumption, as part of an incomplete list of disposable or thrown away products. A traditional method to dispose of waste is a sanitary landfill, which is still a common practice in some areas. However, many local authorities have found it difficult to establish new landfills. In those areas, solid waste must be transported for disposal, making it more expensive.

As an alternative to landfills, a substantial amount of MSW can be eliminated by combustion in a municipal solid waste combustor ("MWC"), which is also known as a waste-to-waste plant. energy ("WTE" - for its acronym in English). The typical MWC has a mobile grid that allows the movement of the waste through the combustion chamber and therefore allows a complete combustion of the waste. The MWC generally includes a primary air source and a secondary air source. The primary air is supplied from below the grid and is forced through the grid to sequentially dry (release water), devolatilize (release volatile hydrocarbons), and burn (oxidize non-volatile hydrocarbons) the waste bed. The amount of primary air is typically adjusts to maximize the burning of the carbon materials in the waste bed, without having any excess air. The secondary air is supplied through nozzles located above the grid and is used to create a turbulent mixture that destroys the hydrocarbons that are released from the waste bed. The total amount of air (primary and secondary) used in a typical MWC is approximately 60% to 100% more than the amount of air required to achieve the stoichiometric conditions (ie, the theoretical conditions under which a fuel is completely burned) .

One of the problems associated with conventional combustion of MSW and other solid fuels is that it creates unwanted and harmful products, such as NOx, carbon monoxide and dioxins. For example, NOx is formed during combustion through two main mechanisms. First, the NOx of the fuel is formed by the oxidation of the organically bound nitrogen (N) found in the MSW and other fuels. When the amount of O2 in the combustion chamber is low, 2 is the predominant reaction product. However, when a substantial amount of O2 is available, an increased portion of the N bound to the fuel is converted to NOx. Second, thermal NOx is formed by the oxidation of atmospheric N2 at high temperatures. Due to the high activation energy required, thermal NOx formation does not become significant until the flame temperatures reach 1, 100 ° C (2,000 ° F).

There are many technologies to reduce harmful emissions created by the conventional combustion systems of MSW. For example, there are two groups of technologies known to control NOx emissions: combustion controls and afterburners. The combustion controls limit the formation of NOx during the combustion process by reducing the availability of O2 inside the flame and by decreasing the temperatures of the combustion zone. Post-combustion controls involve eliminating the NOx emissions produced during the combustion process (for example, selective non-catalytic reduction (SNCR) systems and selective catalytic reduction (SCR) systems.

Regardless of the improvements made in reducing harmful emissions from conventional combustion systems, there is still a need for alternative methods and systems that efficiently convert MSW or other solid fuels into energy while producing a minimum amount of unwanted emissions.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a gasification-combustion system and the method that converts waste or other solid fuels into energy while producing significantly lower amounts of NOx, carbon monoxide, dioxins, and other unwanted emissions with respect to combustion in conventional mass. Gasification is the partial combustion of a solid fuel that produces a gaseous mixture. The gasifier the present invention operates at lower temperatures and introduces less air than conventional combustion systems, and therefore produces a lower amount of unwanted emissions. In accordance with the present invention, a post-combustion engine uses the gaseous mixture produced by the gasifier to generate thermal energy. The afterburner controls the combustion of the gas mixture using adjustable injection nozzles. The nozzles can be adjusted based on the composition of the specific gas mixture that enters the afterburner, to achieve optimum combustion conditions with minimum emissions. In summary, the gasification-combustion process using the post-combustor of the present invention significantly reduces the amount of unwanted emissions produced by converting waste or solid fuel into energy. The method and system described above are only one example of the present invention, which may vary in other embodiments.

For example, in a configuration of the present invention, a system for gasifying and burning waste is provided. The system may contain a gasifier to mix the syngas with air or recirculated fuel gas; said gasifier may contain an inlet duct and a premix nozzle designed to inject the recirculated fuel gas or air into the gasifier. The system may also contain a post-combustion. The afterburner may contain an inlet duct to receive the syngas from the gasifier; a cyclone-shaped camera placed near the end of the inlet duct designed to collect ashes ruffles or heavy particles; an upper injection nozzle for directing air flow through the afterburner into the cyclone-shaped chamber; tangential nozzles to direct the air or fuel gas recirculated into the afterburner, detectors to measure temperature, humidity, and carbon dioxide; a controller to position and control the nozzles to make the air flow and temperature more uniform in the afterburner, and an outlet duct to allow the gas to exit the afterburner. In some embodiments the upper injection nozzle may be positioned so that the air flowing through the nozzle forces the flying ash or heavy particles into the cyclone-shaped chamber; the tangential nozzles can have a direction and a position; and / or the controller can rely on the information of the detectors to determine the direction and position of the tangential nozzles.

Another configuration of the present invention establishes a method for gasifying and burning a waste. The method may comprise one or more of the following steps: mixing the syngas with recirculated air or fuel gas in a gasifier; receive the syngas from the gasifier to a post-combustion; collect fly ash or heavy particles with a cyclone-shaped camera; direct the flow of air through the afterburner into the cyclone-shaped chamber; direct recirculated air or fuel gas into the afterburner; Using a detector to gather measurements regarding temperature, humidity, and carbon dioxide inside the afterburner, analyze those measurements to determine what direction and position must face the tangential nozzles connected to the afterburner; adjust the tangential nozzles so that they face the determined direction and position; and / or allow the gas to exit the post-combustion.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and which are incorporated as a constituent part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: FIG. 1A is a schematic side view of a post-combustion mode used in the gasification-combustion process of the present invention.

FIG. 1B is a schematic top view of a post-combustion mode used in the gasification-combustion process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Through the drawings, similar reference numbers indicate similar elements.

The present invention relates to a system and method that converts MSW or other solid fuels into energy while producing a reduced amount of unwanted emissions. The first stage of the present invention, gasification, involves the partial combustion of a solid fuel. The second stage, combustion, involves using the gaseous mixture produced during gasification to generate thermal energy. Both stages of the gasification-combustion process, and the apparatus used to carry them out, are described below in detail.

Gasification is the partial combustion of MSW or other solid fuels. It results in the production of a gaseous mixture of hydrogen, carbon monoxide, carbon dioxide, and water vapor, known as singas. The gasification of the solid fuel has many advantages over the conventional method of complete combustion. First, complete combustion generally requires mixing the fuel with air in excess of the amount required to achieve the stoichiometric conditions (ie, ideal conditions in which the fuel is completely burned). The high amount of oxygen present during complete combustion facilitates the production of harmful gases, such as NOx and dioxins. In contrast, gasification involves only partial combustion, and, as a result, requires significantly less air than complete combustion. More specifically, the gasifier of the present invention can perform the gasification of a solid fuel using a sub-stoichiometric amount of air. There are many benefits in air reduction achieved through the use of gasification. The introduction of less oxygen means that less NOx and dioxins are produced by the solid fuel. In addition, nitrogen bound fuel, which normally binds with excess oxygen to form NOx, is more likely to form ammonia or hydrogen cyanide. This is significant because, as described in detail in the following, the singas formed during gasification is subsequently burned using a post-combustion. During this subsequent combustion, ammonia and hydrogen cyanide react and decompose part of the NOx that is generated by the combustion of the syngas. And finally, using less air reduces the costs associated with the operation of a combustion system.

In addition, the gasifier of the present invention is designed to operate at significantly lower temperatures than a conventional combustion system. In a preferred embodiment, the gasifier operates at temperatures lower than the melting temperature of the ash. This is significant because the combustion of solid fuel produces both bottom ash and fly ash. When a combustion system operating at high temperatures, the ash may melt and cause the formation of slag in the components of the mobile grid, which may require substantial maintenance. Therefore, by maintaining an operating temperature lower than the melting point of the ash, the gasifier of the present invention limits the potential slag formation. This reduces the overall maintenance costs associated with converting waste or solid fuel into energy and makes the use of conventional mobile grid technology more practical. The low temperature gasification of solid fuel is also advantageous because it produces less emissions of harmful particles and gases, such as NOx, than conventional high temperature combustion.

According to the present invention, the syngas produced during gasification flows out of the gasifier and into a post-combustor, where the syngas is subjected to combustion. The afterburner subjects the singas to a turbulent air flow having conditions of only a slight stoichiometric excess (and therefore even less than the amount of air used in conventional combustion systems). The afterburner operates at higher temperatures than the gasifier, which has the effect of reducing carbon monoxide emissions and destroying most of the dioxins formed during gasification. In addition, the amount of excess air present in the afterburner is minimal, which, together with the ammonia and hydrogen cyanide formed during gasification, reduce the amount of NOx generated by the combustion of the syngas. In a preferred embodiment of the present invention, the singas reside in the combustion chamber of the afterburner for more than two seconds and the operating temperature is greater than 800 ° C. The thermal energy created by syngas combustion can be used in a variety of ways, such as to produce steam and generate electricity. In summary, the gasification-combustion process of the present invention can convert MSW or other solid fuel into energy while generating significantly lower emissions of carbon monoxide, NOx, and other organic compounds such as dioxins than the conventional method of complete combustion. . 10 FIGS. 1A and 1B show preferred embodiments of the post-combustion 10 used in the gasification-combustion process of the present invention. As can be seen in FIG. 1A, the singas generated by the gasifier flows into the afterburner 10 through an inlet pipe 20. Before entering the combustion chamber 30 of the afterburner 15, singas is premixed with air, recirculating fuel gas (FGR) or another oxidant such as plasma that is injected into the inlet duct 20 via the pre-mix nozzle 44. The premixing of the singas with an oxidant allows combustion to occur. of the singas at a lower temperature than it would without such premixing. This is significant because maintaining a 20 low combustion temperature reduces NOx production.

The afterburner 10 is designed so that there is a cyclone-shaped chamber 50 at the end of the inlet duct 20, where the singas enters the combustion chamber 30. The chamber with I I Cyclone form 50 is used to collect flying ash or heavy particles that are created during gasification or combustion. The cyclone-shaped chamber 50 is assisted by the downward flow of air from the upper injection nozzle 41. The downward air flow forces the fly ash and other heavy particles down into the cyclone-shaped chamber 50, while which allows the syngas to enter the combustion chamber 30. The fly ash and other particles may either concentrate at the center of the cyclone-shaped element 50 and flow downward, or form slag on the walls of the cyclone-shaped element 50 and flow down.

The combustion chamber 30 of the afterburner 10 includes multiple nozzles for injecting air or other oxidant into the combustion chamber 30. As explained above, the upper injection nozzle 41 is designed to inject air or other oxidant into the combustion chamber. 30 in a generally downward direction. The tangential injection nozzles 42 and 43 are configured to inject air or other oxidant tangentially into the combustion chamber 30 from the desired angles. The present invention contemplates that additional nozzles can be provided to achieve the desired injection of air into the combustion chamber 30. The nozzles 41, 42 and 43 can be positioned and controlled by a controller 51 so as to maintain a uniform air flow, as well as a uniform temperature, through the combustion chamber 30 during combustion of the singas. This is important because the variations of temperature, and specifically the bags of higher temperatures, promote the creation of NOx. Therefore, by maintaining a uniform air flow and temperature, the afterburner 10 of the present invention reduces the amount of NOx generated during combustion.

In a preferred embodiment of the present invention, the afterburner 10 measures certain characteristics, such as temperature, humidity, and carbon dioxide content of the syngas as it enters the afterburner 10 of the gasifier. This information is then used to adjust the nozzles 41-44, to obtain an optimum air flow and conditions for the combustion of the specific type of syngas that enters the combustion chamber 30. To obtain optimum conditions, the direction and amount of flow of air from each nozzle 41-44 is adjusted individually and independently of one another. The computational fluid dynamics ("CFD") is used to determine exactly how the nozzles 41-44 should be adjusted in response to the measurements taken as the syngas enters the combustion chamber 30.

The afterburner 10 also includes an outlet duct 60 that allows the fuel gas to leave the combustion chamber 30. As explained above, the fuel gas can be injected back into the combustion chamber 30 via the nozzles 41-44. This is known as fuel gas recirculation ("FGR"). The FGR decreases the amount of O? in the combustion chamber 30 and suppresses the temperature in the combustion chamber 30. As a result, the FGR has the effect of reducing the amount of NOx generated by the combustion of the singas.

Although they have been shown and described in the present exemplary embodiments of the invention, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes and non-substantial substitutions will be apparent to those skilled in the art without departing from the scope of the invention described herein by the Applicants. Accordingly, it is intended that the invention is only limited by the spirit and scope of the claims, as they will be granted.

Claims

NOVELTY OF THE INVENTION CLAIMS

1. - A system to gasify and burn waste that includes: a. a gasifier for mixing singas with air or recirculated fuel gas; said gasifier contains an inlet duct and a premix nozzle designed to inject recirculated fuel gas or air into the gasifier; and b. a post-combustion comprising: i. an inlet duct to receive syngas from the gasifier; ii. a cyclone-shaped chamber placed near the end of the inlet duct designed to collect fly ash or heavy particles; iii. an upper injection nozzle for directing an air flow to the afterburner within the cyclone-shaped chamber; V. a tangential nozzle to direct recirculated air or fuel gas into the afterburner; v. a detector to measure temperature, humidity, or carbon dioxide; and I saw. a controller to position and control the tangential nozzle to make the air flow and temperature more uniform in the afterburner.

2. - The system according to claim 1, further characterized in that the upper injection nozzle is positioned so that the air flowing through the nozzle forces the fly ash or heavy particles into the cyclone-shaped chamber.

3. - The system according to claim 1, further characterized in that said tangential nozzle has a direction and a position; and said controller is based on the detector information to determine the direction and position of the tangential nozzle.

4. - The system according to claim 1, further characterized in that it comprises an outlet duct to allow the gas to exit the post-combustion.

5. - A method to gasify and burn waste that includes the following stages: a. mixing singas with recirculated air or fuel gas in a gasifier; b. receive the syngas from the gasifier to the afterburner; c. collect fly ash or heavy particles with a cyclone-shaped camera; d. direct the flow of air through the afterburner into the cyclone-shaped chamber; and. direct recirculated air or fuel gas into the afterburner; F. use a detector to collect measurements related to temperature, humidity, and carbon dioxide inside the afterburner; g. analyze these measurements to determine in what direction and position a tangential nozzle connected to the afterburner should face; h. Adjust the tangential nozzle so that it faces the determined direction and position.

6. - The method according to claim 5, further characterized in that it comprises a step of allowing the gas to exit the post-combustion.