WO2016179824A1

WO2016179824A1 - A system for burning pulverized solid fuel and a method thereof

Info

Publication number: WO2016179824A1
Application number: PCT/CN2015/078948
Authority: WO
Inventors: Zheng Shi
Original assignee: Zheng Shi
Priority date: 2015-05-14
Filing date: 2015-05-14
Publication date: 2016-11-17

Abstract

A system for burning pulverized solid fuel and a method thereof are provided. A high velocity flame jet is projected within a first zone (103) of a combustor (101) where most of combustion occurs and forced to create a powerful turbulent reflux within the first zone (103) of the combustor (101). The pulverized solid fuel entering the reflux consequently spends a prolonged time in the first zone (103) of the combustor (101) before exiting into a second zone (104), thus allowing for more complete combustion given the same volume of combustion space in the first zone (103).

Description

SYSTEM AND METHOD TO IMPROVE EFFICIENCY OF COMBUSTION IN SMALL TO MEDIUM SIZED COMBUSTORS

TECHNICAL FIELD

The present invention relates to the field of combustors for small to medium sized combustors and furnaces using pulverized solid fuel.

BACKGROUND

Combustors wherein a single or a plurality of fuel nozzles are arranged to project a mixture of air and solid fuel, into the combustor are well known. In this type of systems, the powdered solid fuel and pressurized air are blown into a combustor as an air-fuel mixture. Such air-fuel mixture might have been pre-ignited before entering the combustor, or might be entering the combustor to be ignited.

One of the important tasks of the abovementioned systems is to provide the proper conditions for the near-complete combustion of the fuel. This is mainly achieved by projecting the fuel supply fed into the combustor at an appropriate rate, angle and rotation, and keeping the fuel in the combustor for a sufficient time.

In large-scale industrial coal-fired combustors, near-complete combustion of the pulverized solid fuel is always assured as these combustors have large combustors and sophisticated fuel preheating and delivery systems. Typically, in these large combustors, preheating arrangements and the design of the combustor itself is made in such a way that the coal dust thoroughly mixes with combustion air, and spends a protracted amount of time in the combustor and thus assures adequate combustion of the coal dust. For example, elaborate systems such as tangentially-fired combustors are designed in such a way that the coal dust is projected into a virtual vortex flow which protracts the time the fuel spends within the chamber.

Unfortunately, the above is not applicable to small or medium-scale combustors fired by pulverized solid fuel such as powdered coal whereby a small installation is utilized and arrangements for fuel preheating are limited.

Accordingly, there is a need to improve fuel combustion in small to medium-scaled combustors, while simultaneously providing a system that is simple to construct and inexpensive to produce.

SUMMARY OF INVENTION

The present invention discloses a system and method for combustion of solid fuels, such as pulverized coal in small and medium boilers.

In accordance with one embodiment of the present invention, the system includes a combustor having a first zone, a second zone and an exit that connects the two zones, and one or a plurality of pre-combustors where the fuel is heated up, ignited, and/or combusted to a certain extent. A combustion mixture of pulverized solid fuel, combustion air and flame is projected by the pre-combustor (s) , at a high velocity, into the first zone in a first direction that is away from the exit, and then forced to flow in the opposite direction of the first direction in order to enter the second zone, creating a turbulent reflux flow in the first zone.

In accordance with one embodiment of the present invention, the velocity of the combustion mixture is between 50 meters per second and 100 meters per second for a combustor of 10 meters in length along the traveling direction of the combustion mixture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 graphically illustrates the cross-sectional view of one of the embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be better understood and its many objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawing.

FIG. 1 is a cross-sectional view of the combustor according to one of the embodiments of the invention. The combustor 101 is fitted with a pre-combustor (or fuel/air nozzle) 102 that projects a high velocity combustion mixture of pulverized solid fuel, combustion air and flame into the first zone 103 in a first direction that is away from the exit 109. The flue gas is forced to flow in the opposite direction of the first direction in order to move into the second zone 104 of the combustor 101 and then travels into the third zone 105 before exiting at outlet 106. Since the pre-combustor (or fuel/air nozzle) 102 is placed at or near the same side as the exit 109 of the first zone 103, the high power flame jet capable of creating an effective turbulent reflux dynamic occurring within the first zone 103.

For a combustor of around 10 meters in length, the velocity of the combustion mixture is between 50 meters per second and 100 meters per second along the traveling direction of the combustion mixture, and should cover the whole length of the combustor without making direct contact with the opposite wall so as to avoid slag formation.

The method of the present invention can be described as follows. The pre-combustor 102 projects a high velocity combustion mixture of pulverized solid fuel, combustion air and flame against the wall 107 of the first zone 103 (but is designed in such a manner that the flame is not in contact with the wall) . The stream of combustion mixture projected by the pre-combustor 102 is depicted by the arrows labeled 1° in FIG. 1. As the flame steam propagates towards the opposite wall where it consequently reverses back towards to its original direction, forming a turbulent reflux stream. The reflux stream mainly moves backwards in the periphery of the strong stream 1°, depicted by the arrows labeled 2°. A certain portion of the reflux stream 2° gradually loses its backward speed while moving in the opposite direction of the powerful stream 1°, and thus is redirected back and joins stream 1°, which is depicted by the arrows labeled 4°. The remainder of stream 2° will keep on moving towards the opposite wall 108 and then exit into the second zone 104, as labeled by arrow 3°. Steam 3° will go through the second zone 104 and the third zone 105 before eventually exiting the combustor at the outlet 106.

People skilled in the art will recognize the obvious advantage of the system and method described above. Through a simple system of projecting a high-speed combustion mixture inside the confines of the first zone 103 of the combustor 101, a powerful and turbulent reflux effect is created. This turbulent reflux effectively causes the stream of combustion mixture to circulate back and forth from one wall 107 to another wall 108 until it finally exits the first zone 103 at the exit 109. Typically, there is a steep temperature drop from the combustor to the second zone 104 of the combustor 101 due to extensive heat transfer, and consequently, there is little further combustion once the fuel/air/flame has exited the combustor. The fact that the majority of the stream of combustion mixture does not simply pass through the first zone 103 and leave it at the exit 109 as is usually the case in these types of combustor is the premise of the present invention. The powerful turbulent reflux effect within the combustor effectively allows for a much better combustion of the fuel given that the air and fuel mixes well and that the fuel spends a prolonged amount of time within the combustor.

The invention described above effectively enables more thorough mix of the fuel and combustion air, prolongs the amount of time that the fuel stream spends within the combustor, and improves the overall efficiency of combustion of the fuel in a cost effective manner since it allows a smaller combustor to burn a larger amount of fuel.

Claims

A system for burning pulverized solid fuel, comprising:

-a combustor comprising a first zone and a second zone, and an exit that connects the two zones,

-a pre-combustor that is positioned in proximity to the exit,

wherein a combustion mixture of pulverized solid fuel, combustion air and flame is projected by the pre-combustor, at a high velocity, into the first zone in a first direction that is away from the exit, and then forced to flow in the opposite direction of the first direction in order to enter the second zone, creating a turbulent reflux flow in the first zone.
The system of claim 1, wherein the velocity of the combustion mixture is between 50 meters per second and 100 meters per second for a combustor of around 10 meters in length along the traveling direction of the combustion mixture.
A method for burning pulverized solid fuel, comprising:

-projecting, by a pre-combustor and at a high velocity, a combustion mixture of pulverized solid fuel, combustion air and flame into a first zone of a combustor in a first direction, wherein the combustor comprises a first zone and a second zone, and an exit that connects the two zones, and wherein the first direction is moving away from the exit,

-forcing the combustion mixture to flow in the opposite direction of the first direction in order to enter the second zone via the exit, creating a turbulent reflux flow in the first zone.
The method of claim 3, further comprising, wherein the velocity of the combustion mixture is between 50 meters per second and 100 meters per second for a combustor of around 10 meters in length along the traveling direction of the combustion mixture.