Method and apparatus for drying solid fuels

Abstract

A method for drying solid fuels prior to injection and burning in solid fuel boilers is described. High moisture content solid fuels such as bark, sludge, wet coal, etc. must be dried before they can burn. Embodiments of the present invention incorporates a fuel delivery chute integrated with the boiler wall using a flow of combustion gasses and radiant heating to partially dry the solid fuel before it reaches the combustion zone of the boiler. The combustion gasses are drawn through the delivery chute by means of the flowing fuel and air jet inductors that then blows the combustion gasses back into the boiler. A refractory wall separates the fuel chute from the boiler proper, is heated by the combustion in the boiler, and radiates heat to the fuel falling through the fuel chute.

Description

[0001]The present application is a continuation of International Patent Application No. PCT / US12 / 50610 filed Aug. 13, 2012, which claims priority from U.S. Provisional Application 61 / 522,939, filed Aug. 12, 2011, which are hereby incorporated by reference.TECHNICAL FIELD OF THE INVENTION[0002]The present invention relates to solid fuel boilers, and in particular, to a fuel chute that removed moisture from the solid fuel before the fuel enters the boiler.BACKGROUND OF THE INVENTION[0003]Solid fuel boilers are commonly used by industry and utilities to generate steam for process requirements and to generate electricity. These boilers burn bark, coal, sludge, wood waste, refuse, tires, and other organic materials, often in combinations, and with fossil fuels. Generally the organic materials have high moisture contents and are stored outdoors where they are often wet from rain water or, in the case of sludge, reclaimed from wastewater treatment facilities. In some cases some of the mois...

AI Technical Summary

Benefits of technology

The present invention relates to a fuel chute for solid fuel boilers that removes moisture from the fuel before it enters the boiler. The problem is that high moisture content in the fuel can cause unstable combustion and inefficient operation of the boiler. Current methods of removing moisture from the fuel are expensive, troublesome, and not efficient. The invention aims to provide a more efficient and cost-effective solution for removing moisture from the fuel to improve the combustion process and operational efficiency of the boiler.

Problems solved by technology

These practices are often troublesome, expensive, risky, and not particularly efficient.

For these reasons these methods are not universally employed.

Even with these methods the fuels still contain significant moisture content.

In any case all of the water in the fuel must be removed during the combustion process and when the fuels are wet the combustion process can be unstable and inefficient.

The situation is further exacerbated by changing moisture contents of the fuel (e.g., from rain) that introduces variations into the combustion process and make it more difficult to operate the boilers.

In all of these arrangements if the fuel is not properly dried poor combustion can result leading to poor operational efficiencies and high environmental emissions.

Grate type boilers generally require some type of fuel distribution whereas fluidized bed boilers can be run without them as the fluidized bed can distribute the fuel, albeit inefficiently.

Inconsistent and high moisture content of the fuels makes it difficult for the boiler to respond effectively to the required load changes.

Fossil fuels are typically used to start these boilers but continual use of fossil fuels is extremely expensive.

Fluidized beds can help to compensate for varying moisture contents and load rates because they act as heat sinks, but they are limited in their heat release rate and can have significant operational and mechanical problems such as sand sintering and sand erosion and they require a sand reclamation system.

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