Method for reducing waste oxide gas emissions in industrial processes

Abstract

The method of the present invention reduces the emissions of waste oxide gas produced within a thermal oxidizer by the use of a multizone waste thermal oxidizer, comprising at least one primary combustion zone and at least one downstream waste destruction zone. By performing the primary combustion of fuel prior to the destruction of at least a portion of the waste, it has been discovered that NOx emissions from the waste destruction process can be reduced economically and without significant loss of overall waste destruction efficiency.

Description

[0001] This invention relates to methods for reducing unwanted emissions in industrial processes. More specifically, this invention relates to methods for decreasing the production of waste oxide gases during thermal oxidation.[0002] Thermal oxidizers are often utilized to dispose of waste streams from industrial processes. In a typical thermal oxidizer, a waste stream and an oxidant are combined at high temperature in order to decompose the waste. If the waste stream is well mixed with the oxidant, and the waste is maintained at high temperature within the thermal oxidizer for a sufficient time period, waste destruction will occur through a combination of oxidation reactions. Often, it is also necessary to provide a fuel stream to the thermal oxidizer. The fuel stream is concurrently combusted in the thermal oxidizer to maintain the desired waste destruction temperature. In some instances, waste heat recovery equipment, such as a heat recovery steam boiler (HRSB), may also be incor...

AI Technical Summary

Benefits of technology

[0015] Therefore, one embodiment of the present invention provides novel methods for reducing waste gas oxide emissions in industrial processes. Another embodiment of this invention provides novel waste destruction processes that produce lower waste gas oxide emissions. These and other novel features will be apparent to those skilled in the art after reading the specification and appended claims.

[0016] Accordingly, one embodiment of the present invention provides novel processes for reducing the generation of NOx emissions. These processes comprise the steps of: directing a waste stream to a thermal oxidizer; combusting at least a portion of the waste stream in the primary combustion zone of the thermal oxidizer; and injecting at least a portion of the waste stream in the downstream waste destruction zone of the thermal oxidizer. The waste stream comprises approximately at least 0.5 mole % of reactive waste components and up to approximately 99.5 mole % of inert components. It is preferred that the waste stream comprises approximately at least 2.0 mole % of reactive waste components and up to approximately 98 mole % of inert components.

Problems solved by technology

If the waste stream is well mixed with the oxidant, and the waste is maintained at high temperature within the thermal oxidizer for a sufficient time period, waste destruction will occur through a combination of oxidation reactions.

When introduced to the environment, waste oxide gases can produce undesirable effects.

Sulfur-based oxides are associated with acidification of lakes and streams, accelerated corrosion of buildings and monuments, reduced visibility and adverse health effects.

Carbon-based oxides, most notably carbon monoxide, may present serious health concerns to the public and have been linked to global warming.

Such regulations are expected to become even more restrictive in the coming years.

Unfortunately these methods are of only limited utility.

All industrial boiler emission reduction methods involve substantial capital, operating, or maintenance costs.

Which makes these methods economically unattractive when applied to waste destruction systems.

Moreover, blind application of boiler-related methods to industrial thermal oxidizers may result in reduced waste destruction efficiency and frequently generates byproducts that are as detrimental to the environment as the waste oxide gases themselves.

Consequently staged reduction reduces both flame temperature and oxygen concentration during some phases of combustion, which in turn reduces both thermal NOx and fuel NOx production.

Conventional combustion modification methods, such as those described above, are either very capital intensive or, in the case of operational modifications, detrimental to achieving the required waste destruction efficiencies.

It should be noted that, while conventional post combustion methods are able to achieve some level of reduction in WOG emissions, they are not without undesirable environmental drawbacks.

Released ammonia can lead to adverse impacts downstream of the SNCR system, including air heater fouling, plume formation, and contamination of otherwise noticeable fly ash.

SCR can also have undesirable effects, such as the release of ammonia, enhanced production of undesirable sulfur oxides and high gas-side pressure drops.

Moreover, ammonia handling and storage, necessitated by SNCR and SCR methods, presents serious safety concerns.

Such catalysts are not only expensive to purchase but costly to dispose of when their useful life has ended.

The catalysts are also sensitive to contaminants, such as sulfur-containing compounds, and the system can readily foul (e.g., in-situ formation of ammonium sulfate).

Maintenance costs are also increased with oxide destroying methods and specialized continuous emissions monitoring equipment is often required to monitor the performance of the system.

Accordingly many drawbacks exist with current industrial methods of reducing waste oxide gases associated with thermal oxidizers.

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