WO2015069784A1

WO2015069784A1 - Adjusting the flame characteristic within a combustor

Info

Publication number: WO2015069784A1
Application number: PCT/US2014/064152
Authority: WO
Inventors: Zheng Shi
Original assignee: Zheng Shi
Priority date: 2013-11-08
Filing date: 2014-11-05
Publication date: 2015-05-14
Also published as: CN105849464A; CN105849464B

Abstract

The present invention proposes a method and system to improve the operation of a small to medium sized combustor fueled by pulverized solid fuel by changing the aspects of the combustion flame through the adjustment of four major variables. These being: the volume of primary air/fuel mix; the volume of secondary air; the volume of tertiary air and the rotational influence exerted upon the secondary air. Altering these variables can effectively allow for the characteristics of the combustion of the fuel to be significantly adjusted according to user preferences.

Description

ADJUSTING THE FLAME CHARACTERISTIC WITHIN A COMBUSTOR

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.

61/902,073 filed November 8, 2013 entitled "Method System to Improve the Adjustability of the Flame Characteristic Within A Small to Medium Sized Combustor" which is incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to combustion of pulverized solid fuels such as powdered coal within small and medium scale combustors. More particularly, the invention is directed to a system and method that improves the operation of the boiler by allowing for the adjustment of four key variables within the combustion process.

BACKGROUND

The present invention relates to small-scale combustion of pulverized solid fuels and method for operating the said system. However, the invention is not limited for use in this application only. People skilled in the art will recognize that the system and method of the present invention may be used in many other applications whereby a small amount of pulverized solid fuel (e.g., 3.5 tons of coal per hour) is combusted, including but not limited to cement kilns and steam generators.

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 coal 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.

Furthermore, the present invention also enhances the flexibility of operation by allowing for both low and high fuel loads as well as the adjustment of the flame relative to the combustor.

SUMMARY OF INVENTION

The present invention describes a method whereby secondary and tertiary combustion air streams moving significantly in the opposite direction of the primary air/fuel mix stream as well as the rotational influence exerted upon the said secondary air are adjusted so as to significantly transform aspects of the combustion flame. The high range of flame combustion adjustment is effectively enabled through the interplay of four major variables: the volume of primary air/fuel mix stream; the volume of secondary air; the volume of the tertiary air; and the rotational force exerted upon the secondary air.

The present invention has numerous advantages vis-a-vis prior art, notably, an increased turndown ration, an increased efficiency in the combustion process and more operational options during combustion of the fuel.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1A and IB depict two cross-sectional graphical illustration of the present invention according to one embodiment of the invention. Figure 1 A illustrates the system without a rotational influence exerted upon the secondary air whereas Figure IB illustrates the system with a rotational influence upon the secondary air.

Figure 2 is a cross-sectional graphical illustration of the present invention illustrating a scenario where a low fuel load is used and a high proportion of the combustion occurring within the combustor.

Figure 3 is a cross-sectional graphical illustration of the present invention illustrating a scenario where a low fuel load is used and a low proportion of the combustion occurring within the combustor.

Figure 4 is a cross-sectional graphical illustration of the present invention illustrating a scenario where a high fuel load is used and a low proportion of the combustion occurring within the combustor. Figure 5 is a cross-sectional graphical illustration of the present invention illustrating a scenario where a high fuel load is used and a high proportion of the combustion occurring within the combustor.

DETAILED DESCRIPTION OF THE INVENTION

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

Figures 1A and IB are cross-sectional illustration of two of the embodiments of the present invention. Figure 1A graphically depicts a scenario whereby no rotational influence is exerted upon the secondary air whereas Figure IB depicts a scenario whereby a rotational influence is exerted upon the secondary air. The bold arrows numbered 1 to 4 graphically depict the direction of the relevant air streams occurring within the system. Referring to both Figure 1A and Figure IB, the combustor 101 here consists of a combustor whose shape is conically widening. The primary air/fuel mix stream 1 is supplied into the combustor 101 substantially along the central axis of the combustor and in a first direction, via a blow pipe 102 that is fitted at the axis of the outlet of the combustor 101 using a primary air/fuel mix pumping mechanism (not shown in Figure 1). The outlet of the said blow pipe is made to face the inlet of the said combustor 101. At the inlet of the combustor 101, a secondary air pumping mechanism 104 is fitted so that a stream of secondary air 2 is supplied into the combustor 101 in such a way that the direction of the secondary air stream 2 is significantly facing against the stream of primary air/fuel 1. The secondary air stream 2 redirects the primary/air mix stream 1 into a reflux stream 4. In between the secondary air pumping mechanism 104 and the inlet of the combustor 101, an adjustable profiled grid cascade 105 is fitted so that a rotational effect can be applied upon the secondary air 2 arriving into the combustor 101. The adjustable profiled grid cascade 105 is in the direction that is perpendicular to the central axis of the combustor 101. Referring to Fig. la one can see the adjustable profiled grid cascade 105 adjusted so as to provide no rotational influence upon the incoming secondary air 2. In this case, the secondary air 2 is blown directly into the combustor 101 as illustrated by the arrows numbered 2. Referring to Fig. IB one can see the adjustable profiled grid cascade 105 adjusted so as to provide a rotational influence upon the incoming secondary air 2. In this case, the secondary air 2 is blown into the combustor 101 in a rotational manner as illustrated by the arrows numbered 2.

Along the walls of the combustor 101, annular spaces 106 are fitted so that a stream of tertiary air 3 is supplied into the combustor 101 from a tertiary air pump 107 in such a manner that the stream 3 runs substantially along the walls of the combustor 101 roughly in the same direction as that of the stream of secondary air 2. Although not included within the embodiments described in this document, an adjustable profile grid cascade or other mechanism that exerts a rotational influence upon the tertiary air stream in the direction that is perpendicular to the central axis of the combustor 101 can also be envisaged.

As mentioned beforehand, the present invention makes use of 4 key variables to adjust how and where combustion primarily occurs within the system. These are: the volumes of primary air/fuel mix 1, secondary air 2, tertiary air 3 as well as the rotational force R exerted upon the secondary air 2.

The primary air's 1 main purpose is to transport the pulverized solid fuel into the combustor 101 as its volume is too little to contribute significantly to the combustion process of the fuel. The first variable, namely the primary air/fuel mix 1, does not experience significant changes in air volumes. Instead, the volume of pulverized fuel is the determining factor of this variable.

The joint purpose of the secondary 2 and tertiary air 3 is to supply the combustion air into the combustor 101. It is understood that the proportions of combustion air supplied by the secondary air 2 and tertiary air 3 are dependent on the pulverized solid fuel load. Therefore, changing the amount of secondary air volume for a given amount of fuel load must lead to a proportional opposite change in the volume of tertiary air so that the aggregate volume of combustion air supplied into the combustor at anytime must be approximately -/+10% of the molar equivalent volume required for the adequate supply of combustion air for the fuel load (thus, avoiding any potential problems arising from over- or under- supply of combustion air).

Finally, the main function of the fourth variable, the rotational force R exerted upon the secondary air 2, is to allow better mixing of the pulverized solid fuel as well as enable a strong reflux dynamic within the combustor 101 during high fuel load operations.

It is important to point out that the reflux in question is dependent upon the diameter and overall design of the combustor 101 whereby a relatively small diameter will reduce the impact of the rotation of the secondary air stream 2 on the combustor 's internal stream dynamics. On the other hand, a larger diameter will increase the impact of the rotation of secondary air 2 upon the combustor 's internal stream dynamics.

The method and the essence of the invention can best be described by separately describing the operation of the combustor according to 4 distinct operational scenarios: 1. Low fuel load with a high proportion of combustion occurring within the combustor; 2. Low fuel load with a low proportion of the combustion occurring within the combustor; 3. High fuel load with low proportion of the combustion occurring within the combustor; 4. High fuel load with a high proportion of the combustion occurring within the combustor.

It is understood that, for the purpose of simplicity, the abovementioned four operational scenarios have been disclosed. Nevertheless, these are extreme scenarios and the method of the present invention also allows for the progressive transformation of the combustion flame according to various fuel loads which are not described within this document.

1. Low fuel load with a high proportion of combustion occurring within the combustor

Referring to figure 2 one can see how the present invention would operate should a low fuel load with a high proportion of the combustion occurring within the combustor is chosen.

In this scenario, the adjustable profiled grid cascade 205 is made to cause little and preferably no rotational effect upon the incoming secondary air 2. The bold arrows 2 depict the direction of the secondary air 2. It is important to point out that the relative lengths of these arrows represent their volumes relative to other streams and this is the case throughout the other figures as well. In this case, given that there is no rotational effect on the secondary air 2, the secondary air stream 2 is blown straight into the combustor 201. Doing so presents one major advantage during low fuel load scenarios in that the secondary air 2 is blown into the combustor 201 and disperses itself in a fairly homogenous manner (i.e. the amount of air running substantially along the walls and across the central axis is similar). The fuel load within the primary air/fuel mix stream 1 volume is lowered to the desired amount and the reflux effect 4 occurs mainly along the central axis of the combustor 201. This is because, since the central axis of the combustion chamber 201 is supplied with oxygen from the incoming secondary air 2 and that the primary air/fuel mix stream 1 is projected substantially along the axis of the combustor 201 (thus, the pulverized fuel is concentrated in that area), combustion of the fuel largely occurs along this central axis. Therefore, efficient combustion along the axis of the combustor 201 can effectively be achieved at low fuel loads.

At the same time, the relative proportion of secondary air 2 is decreased relative to that of the tertiary air 3. The impact of doing so will cause the reflux 4 to move backwards towards the inlet of the combustor 201 given that the volume of secondary air, and thus the force of the secondary air stream 2, is decreased. This allows for the less-hindered stream of primary air 1 to move further back towards the inlet of the combustor 201. Therefore, the combustion flame settles itself primarily along the central axis and towards the inlet of the combustor 201 as depicted by the flame in figure 2.

2. Low fuel load with a low proportion of the combustion occurring within the combustor

Referring to figure 3 one can see how the present invention would operate during a low fuel load with a low proportion of the combustion occurring within the combustor.

Similar to scenario 1, the adjustable profiled grid cascade 305 is made to cause little and preferably no rotational effect upon the incoming secondary air 2. The secondary air 2 is blown into the combustor 301 and disperses itself in a fairly homogenous manner (i.e. the amount of air running along the walls and across the central axis is similar). The fuel load within the primary air/fuel mix stream 1 volume is lowered to the desired amount and a reflux effect 4 occurs mainly along the central axis of the combustor 301 with the combustion of the fuel largely occurs along the central axis of the combustor 301.

Unlike scenario 1, when one wants to decrease the proportion of combustion occurring within the combustor 301 (and thus increase the proportion of combustion occurring outside the combustor 301) the proportion of the secondary air stream 2 is increased relative to that of the tertiary air stream 3. The impact of doing so will cause the reflux 4 to move forwards towards the outlet of the combustor 301 given that the volume of secondary air, and thus the force of the stream 2, is increased. This allows for more force exerted against the stream of primary air 1 and subsequently pushes the reflux 4 back towards the outlet of the combustor 301. Therefore, the combustion flame settles itself primarily outside the combustor 301 as depicted in figure 3.

3. High fuel load with low proportion of the combustion occurring within the combustor

Referring to figure 4 one can see how the present invention would operate should a high fuel load with a low proportion of the combustion occurring within the combustor is chosen.

As before, the primary air/fuel mix 1 is blown into the combustor 401 through the blow pipe 403 using a primary air pumping mechanism. A secondary air pumping device 405 and a tertiary air pumping mechanism 407 project both the secondary and tertiary air into the combustor 401. Prior to entering the chamber, the secondary air 2 passes through the adjustable profiled grid cascade 406.

As mentioned previously, whenever a high or full fuel load is used, the adjustable profiled grid cascade 406 is adjusted so as to cause a relatively high rotational influence upon the incoming stream of secondary air. Figure 4 graphically depicts the adjustable profiled grid cascade 406 adjusted to cause a high rotational influence upon the secondary air stream 2. The secondary air stream 2 is adjusted in such a way that it is strong enough to cause the reflux stream 4 to be shifted towards the outlet of the combustor 401.

A vortex within the combustor 401 is created whereby the secondary air stream 2 rotates along the walls of the chamber as well as along the axis of the combustor 401. The rotation of the secondary air stream 2 blowing against the stream of primary air 1 allows for adequate mixing of the high fuel load with the combustion air along both the axis and the periphery of the chamber and therefore increases the efficiency of the combustion process.

As with scenario 2, in order to obtain a reduced amount of combustion within the combustor 401, one would increase the proportional volume of secondary air 2 relative to tertiary air 3. Increasing the proportion of secondary air 2 will cause the refiux stream 4 to move forwards towards the outlet of the combustor 401 and outside of the combustor 401 wherein the flame settles as shown in figure 4.

4. High fuel load with a high proportion of the combustion occurring within the combustor

Referring to figure 5 one can see how the present invention would operate should a high fuel load with a high proportion of the combustion occurring within the combustor be chosen.

The adjustable profiled grid cascade 506 is adjusted so as to cause the maximum possible rotational influence upon the incoming stream of secondary air 2.

Similar to scenario 3, as the secondary air rotates around the walls of the combustor 501, a powerful vortex within the combustor 501 is created where the secondary air stream 2 runs along the walls of the chamber and substantially away from the axis of the combustor 501. Figure 5 graphically depicts the adjustable profiled grid cascade 506 adjusted to cause the maximum rotational influence upon the secondary air stream 2. The secondary air stream 2 is adjusted in such a way as to cause the reflux stream 4 to be shifted towards the inlet of the combustor 501. Again, the vortex allows for proper mixing of the high fuel load with the combustion air and therefore increases the efficiency of the combustion process.

Contrary to scenario 3, in order to obtain the maximum amount of combustion within the combustor 501, one would decrease the proportional volume of secondary air relative to tertiary air. Decreasing the proportion of secondary air 2 will cause the reflux stream 4 to move back towards the inlet of the combustion chamber 501 wherein the flame settles as shown in figure 5.

Claims

CLAIMS We claim:

1. A system for improving the characteristics and adjustability of a flame from the combustion of pulverized solid fuel within a combustor, comprising,

- a combustor for initiating and maintaining the flame;

- a first pumping mechanism for injecting a stream of primary air and fuel mix into the flame substantially along a central axis of the combustor in a first direction;

- a second pumping mechanism for injecting a secondary air stream into the flame substantially along the central axis of the combustor in a second direction that is substantially opposite to the first direction;

- a third pumping mechanism for injecting a tertiary air stream into the flame substantially along the wall of the combustor in a third direction that is substantially opposite to the first direction; and

- an adjustment mechanism for adjusting the speed and proportion of the stream of primary air and fuel mix, the secondary air stream, and the tertiary air stream; wherein the confluence of the stream of primary air and fuel mix, the secondary air stream, and the tertiary air stream creates and sustains a flame, and allows the characteristics of the flame to be adjustable.

2. The system of claim 1, wherein a characteristic of the flame is the distribution of the flame along the central axis of the combustor.

3. The system of claim 1, wherein a characteristic of the flame is the rotation of the flame around the central axis of the combustor.

4. The system of claim 1, wherein the adjustment mechanism further comprises an adjustable profiled grid cascade for exerting a rotational influence upon the secondary air stream in a direction that is perpendicular to the central axis of the combustor.

5. The system of claim 1, wherein the adjustment mechanism further comprises an adjustable profiled grid cascade for exerting a rotational influence upon the tertiary air stream in a direction that is perpendicular to the central axis of the combustor.

6. The system of claim 1, wherein the tertiary air stream is configured to be injected into the flame through multiple passages along the wall of the combustor.

7. The system of claim 1, wherein a space of combustion within the combustor is of cylindrical shape.

8. The system of claim 1, wherein a space of combustion within the combustor is of conical shape.

9. The system of claim 1, wherein the second direction and the first direction form an angle that ranges from 120 to 180 degrees.

10. A method for improving the characteristics and adjustability of a flame from the combustion of pulverized solid fuel within a combustor, comprising, injecting a stream of primary air and fuel mix into the flame substantially along a central axis of the combustor in a first direction;

injecting a secondary air stream into the flame substantially along the central axis of the combustor in a second direction that is substantially opposite to the first direction;

injecting a tertiary air stream into the flame substantially along the wall of the combustor in a third direction that is substantially opposite to the first direction;

adjusting the speed and proportion of the stream of primary air and fuel mix, the secondary air stream, and the tertiary air stream; wherein the confluence of the stream of primary air and fuel mix, the secondary air stream, and the tertiary air stream creates and sustains a flame, and allows the characteristics of the flame to be adjustable.

11. The method of claim 10, wherein a characteristic of the flame is the distribution of the flame along the central axis of the combustor.

12. The method of claim 10, wherein a characteristic of the flame is the rotation of the flame around the central axis of the combustor.

13. The method of claim 10, further comprising, exerting a rotational influence upon the secondary air stream in a direction that is perpendicular to the central axis of the combustor by an adjustable profiled grid cascade.

14. The method of claim 10, further comprising, exerting a rotational influence upon the tertiary air stream in a direction that is perpendicular to the central axis of the combustor by an adjustable profiled grid cascade.

15. The method of claim 10, further comprising injecting the tertiary air stream into the flame through multiple passages along the wall of the combustor.

16. The method of claim 10, wherein the space of combustion within the combustor is of cylindrical shape.

17. The method of claim 10, wherein a space of combustion within the combustor is of conical shape. The method of claim 10, wherein the second direction and the first direction an angle that ranges from 120 to 180 degrees.