Three Stage Combustor For Low Quality Fuels

Abstract

A combustor for low quality fuels has a devolatilization chamber receiving the fuel and separating the fuel into char and gases. Char from the devolatilization chamber exits through a first port connected to a char chamber. The char chamber reduced the char to gases and ash. Gases generated in both the devolatilization chamber and char chamber are sent to gas and particulate combustion chamber, such as a fluidized bed. The various stages are operated at the optimum temperatures for the contituents provided to that stage. The resulting process has reduced emissions.

Description

[0001]This application claims benefit of provisional application No. 61 / 522,976, filed on Aug. 12, 2011, the entire contents of which are herein incorporated by reference.BACKGROUND OF THE INVENTION[0002]Low grade fuels, such as coal, burn in three stages including volatile release, char combustion, and gas and residual particulate combustion. Most conventional systems attempt to perform all three stages in a single module, such as the cyclone combustor depicted in FIG. 1, while some advanced systems have a first fuel rich chamber followed by a second fuel lean chamber. The control of the air-fuel mixture reduces NOx emissions by lowering peak temperature.[0003]Coal-fired power plants generate nearly half of the electricity in the United States. The other main energy sources are the fossil fuels natural gas and oil; nuclear power; hydroelectric power; and the renewable sources including solar, wind, geothermal, tidal, and biomass sources.[0004]There are major problems with each of t...

AI Technical Summary

Benefits of technology

The patent describes a method for improving the combustion of coal in a power plant. The method involves using a special technique called "entrained flow" to grind the coal so fine that it flows in the combustion air stream. This is combined with a sudden expansion to slow and mix the air and fuel, which helps to improve combustion. By rotating the incoming air and creating a strong central recirculation zone, the combusting fuel and air mixture produce a strong flame. This method results in more efficient and stable combustion.

Problems solved by technology

There are major problems with each of these sources.

Fossil fuel supplies are being depleted, while concerns about carbon dioxide are rising.

Nuclear technology is expensive, and there are concerns about the safety of both the plants and the spent fuel rods.

Hydroelectric power is limited to areas with adequate water supplies and acceptable environmental impacts.

Green technologies are promising, but these sources are not yet capable of supplying a major portion of the nation's power needs.

Beyond these problems, there is increasing world-wide competition for power, particularly in China and India.

The major objection to coal use is environmental impact: the burning of coal releases large amounts of emissions.

Unfortunately, coal emissions are extremely complex, and are therefore expensive and difficult to control.

The underlying problem is the structure of the coal itself.

This complex structure in turn yields a complicated combustion process.

The loss of the volatiles leaves char, which burns more slowly but quite intensely.

In practical systems, however, the combustion is not complete, leaving unburned fuel, volatile organic compounds, and soot.

Without such a process, it will not be possible to use the nation's plentiful coal reserves.

Unfortunately, advanced coal cleaning processes are expensive and difficult, thereby requiring subsidies or other incentives.

Pre-combustion clean coal technologies are therefore not currently in general use.

Because it is thus not practical to clean the coal before combustion, the only alternative is to burn the coal, and clean the emissions during and / or after the combustion process.

As regulations tighten, the existing technologies must become more and more effective, and thus more and more expensive.

This increasingly complex and expensive piecewise approach to emissions control is simply not sustainable.

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