ELECTRODYNAMIC COMBUSTION CONTROL (ECC) TECHNOLOGY FOR BIOMASS AND COAL SYSTEMS

Abstract

A solid fuel combustion system includes a solid fuel support configured to hold a solid fuel for a combustion reaction. A field electrode is positioned above the solid fuel support. A voltage source supplies a first voltage the solid fuel support and a second voltage to the field electrode.

Description

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority benefit from U.S. Provisional Patent Application No. 61/890,668, entitled “ELECTRODYNAMIC COMBUSTION CONTROL (ECC) TECHNOLOGY FOR BIOMASS AND COAL SYSTEMS”, filed Oct. 14, 2013, (2651-201-02); which, to the extent not inconsistent with the disclosure herein, is incorporated by reference.

BACKGROUND

Heterogeneous combustion systems such as biomass and coal combustion systems are prone to generate particulate matter and oxides of nitrogen (NOx), especially for grate-fired stoker systems that tend to have buoyancy-dominated flames. Poorer mixing of heterogeneous buoyancy-dominated flames (as compared to homogenous combustion with high-momentum gas flames) exacerbates particulate matter, carbon monoxide (CO), and unburned hydrocarbons. However, even in high-momentum flames such as in pulverized coal combustion, the relatively slow speed of char oxidation impedes the overall oxidation process. To reduce unburned hydrocarbons and enhance char oxidation, excess air is increased, but at the expense of higher NOx production. What is needed is a method of enhancing mixing for solid-fuel flames that minimizes required increases in excess oxygen.

SUMMARY

One embodiment is a solid fuel combustion system including a solid fuel support configured to hold a solid fuel for a combustion reaction and a voltage source coupled to the solid fuel support. The solid fuel combustion system further includes a field electrode coupled to the voltage source and disposed in or adjacent to a combustion reaction region above the solid fuel support. The voltage source is configured to output a first voltage signal to the solid fuel support and a second voltage signal to the first field electrode.

The field electrode can apply an electric field to the combustion reaction. The application of an electric field has been found by the inventors to improve characteristics of the combustion reaction. For example, the electric field can cause the combustion reaction to burn more vigorously, to output less oxides of nitrogen (NOx), and/or to output less carbon monoxide.

One embodiment is a method including initiating a combustion reaction of a solid fuel positioned on a solid fuel support and applying a first voltage signal to the solid fuel support. The method further includes applying a second voltage signal to a first field electrode disposed in or adjacent to the combustion reaction above the solid fuel support.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a solid fuel combustion system, according to one embodiment.

FIG. 2 is a diagram of a solid fuel combustion system including two field electrodes according to one embodiment.

FIGS. 3A-3B are diagrams of solid fuel combustion system including a toroidal electrode, according to one embodiment.

FIG. 4 is a diagram of a solid fuel combustion system including an electrode positioned in the combustion reaction, according to one embodiment.

FIG. 5 is a flow diagram of a process for operating a solid fuel combustion system, according to one embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. Other embodiments may be used and/or other changes may be made without departing from the spirit or scope of the disclosure.

FIG. 1 is a block diagram of a solid fuel combustion system 100, according to one embodiment. The solid fuel combustion system 100 includes a solid fuel support 104 configured to support a solid fuel 102. The solid fuel 102 sustains a combustion reaction 106. A voltage source 108 is coupled to the solid fuel support 104 by an electrical connector 115. A field electrode 110 is positioned near the combustion reaction 106. The field electrode 110 is coupled to the voltage source 108 by an electrical connector 113. A control circuit 112 is coupled to the voltage source 108.

The combustion system 100 utilizes the field electrode 110, the voltage source 108, and the solid fuel support 104 to electrically enhance characteristics of the combustion reaction 106. The voltage source 108 is a high voltage source that can apply a high voltage between the solid fuel support 104 and the field electrode 110. In particular, the voltage source 108 applies a first voltage signal to the solid fuel support 104. The voltage source 108 concurrently supplies a second voltage signal to the field electrode 110. There is a high voltage difference between the first voltage signal and the second voltage signal.

With the high voltage applied between the solid fuel support 104 and the field electrode 110, an electric field is generated in a combustion region above the solid fuel support 104. The electric field can have various enhancing effects on the combustion reaction 106.

In one embodiment, the electric field is selected to cause the combustion reaction 106 to burn more vigorously than it would in the absence of the electric field. The more vigorous burning can cause a reduction in harmful or undesirable byproducts of the combustion reaction 106. In particular, the electric field can cause a reduction in the output of oxides of nitrogen (NOx) and carbon monoxide (CO) produced by the combustion reaction 106.

In one embodiment, the first voltage signal is ground, while the second voltage signal is a high voltage with respect to ground. Alternatively, the second voltage signal is ground while the first voltage signal is a high voltage signal with respect to ground. In one embodiment, the first and second voltage signals have opposite polarities from each other.

The first and second voltage signals can be DC signals or time varying signals. For example, the time varying signals can be a chopped DC waveform, an AC waveform, a DC offset AC waveform, or any other suitable voltage signal. In one embodiment the peak-to-peak voltage difference between the first and second voltage signals is greater than or equal to 40,000 V.

In spite of the high voltages, the combustion system 100 requires low power. Less than 0.1% of the thermal output of the combustion reaction 106 is generally sufficient to achieve desirable benefits.

The electric field influences ions generated as a natural byproduct of the combustion process. It is possible that the ion population is enhanced by the presence of a strong electric field. These ions influence bulk mixing through the combustion volume by collision and transfer of momentum to the surrounding neutral species. Benefits include reduced particulate matter, greater luminosity, and improved flame stability. Additional benefits can include enhanced heat transfer with flame and heat transfer surface of opposite polarity, retarded heat transfer with flame and heat transfer surface of like polarity, manipulation of plume direction—thought to be caused by response of H30+ in the flue gas to an electric field. Thermal redistribution over conductive surfaces such as boiler and process tubes can also be improved. Furthermore, manipulation of the combustion reaction 106 by an electric field can promote a qualitative reduction of soot, and quantitative reduction of opacity.

In one embodiment, the field electrode 110 is metal. Alternatively, the field electrode can be metal covered in porcelain. The field electrode 110 can also include silicon carbide.

In one embodiment, the field electrode 110 includes an electrical conductor covered by an electrical insulating material such as fused quartz. Electrically insulating the conductive field electrode 110 can assist in preventing short circuits.

In one embodiment, the solid fuel support 104 is a conductive grate on which the sold fuel 102 rests.

In one embodiment, the combustion system 100 is a combustible substance solid such as biomass, coal, a pulverized coal furnace, resource derived fuel (RDF), municipal solid waste (MSW), etc.

FIG. 2 is a diagram of a solid fuel combustion system 200, according to one embodiment. The solid fuel combustion system 200 includes a combustion reaction 106 of a solid fuel 102 held by a solid fuel support 104. The combustion system 200 further includes two field electrodes 210a, 210b coupled to the voltage source 108. The voltage source 108 is further coupled to the solid fuel support 104 and control circuit 112.

The voltage source 108 applies a first voltage signal to the solid fuel support 104 via an electrical connector 115. The voltage source 108 applies a second voltage signal to the field electrode 210a via an electrical connector 113b. There is a high voltage difference between the first voltage signal and the second voltage signal. As described previously, the high voltage between the field electrode 210a and the solid fuel support 104 generates an electric field in the vicinity of the combustion reaction 106.

In one embodiment, the voltage source 108 applies the second voltage signal to the field electrode 210b via an electrical connector 113a at the same time that the second voltage signal is applied to the field electrode 210a via the electrical connector 113b. Applying the second voltage signal to both the field electrode 210a and the field electrode 210b can have the effect of broadening the combustion reaction 106 toward both the field electrode 210 a and the field electrode 210b. This can help to more fully combust the solid fuel 102.

In one embodiment, the voltage source 108 applies a second voltage to only one of the field electrodes 210a, 210b. This will cause the combustion reaction 106 to be drawn toward the field electrode 210a or 210b to which the second voltage signal has been applied.

In one embodiment charges are introduced into the combustion reaction 106 to enhance manipulation of the combustion reaction by the field electrodes 210a, 210b. Electrons are easily donated to or abstracted from a flame electronically to leave a charged volume amenable to manipulation by electric fields. For example, the flame may be charged by direct contact with an electrode. Alternatively, a charged pilot flame may convey charge to a larger main flame. Additionally or alternatively, flames can be remotely charged through space, for example by applying a voltage to a corona

FIG. 3A is a diagram of a solid fuel combustion system 300, according to one embodiment. The solid fuel combustion system 300 includes a combustion reaction 106 of a solid fuel 102 held by a solid fuel support 104. The combustion system 300 further includes a toroidal field electrode 310 positioned above the combustion reaction 106 and coupled to the voltage source 108. The voltage source 108 is further coupled to the solid fuel support 104 via an electrical connector 115 and control circuit 112.

The voltage source 108 can apply a first voltage signal to the solid fuel support 104 via the electrical connector 115. The voltage source 108 applies a second voltage signal to the toroidal field electrode 310 via an electrical connector 113. There is a high voltage difference between the first voltage signal and the second voltage signal. The high-voltage between the toroidal field electrode 310 and the solid fuel support 104 generates an electric field in the vicinity of the combustion reaction 106.

In FIG. 3A, the first and second voltage signals have not yet been applied to the solid fuel support 102 and the toroidal field electrode 310. Without the high-voltage applied between the toroidal field electrode 310 and a solid fuel support 102, the combustion reaction 106 is comparatively long and extends nearly to the toroidal field electrode 310.

FIG. 3B is a diagram of the solid fuel combustion system 300 in which the first and second voltage signals have been applied to the solid fuel support 104 and the toroidal field electrode 310., according to an embodiment. The high-voltage between the toroidal field electrode 310 and the solid fuel support 104 has the effect of contracting the length of the combustion reaction 106. This can greatly enhance combustion of the solid fuel 102 and can greatly reduce undesirable byproducts of the combustion reaction 106.

FIG. 4 is a diagram of a solid fuel combustion system 400, according to one embodiment. The solid fuel combustion system 400 includes a solid fuel 102 sustaining a combustion reaction 106 and being held by a solid fuel support 104.

The combustion system 400 further includes a charging electrode 410 positioned above the combustion reaction 106 and coupled to the voltage source 108 via an electrical connector 113. The voltage source 108 is further coupled to the solid fuel support 104 via an electrical connector 115 and control circuit 112.

The voltage source 108 can apply a first voltage signal to the solid fuel support 104. The voltage source 108 applies a second voltage signal to the charge electrode 410. There is a high voltage difference between the first voltage signal and the second voltage signal. The charge electrode 410 can impart charges and/or a voltage to the combustion reaction 106.

FIG. 5 is a flow diagram of a process 500 for operating a solid fuel combustion system, according to one embodiment. At 502 a combustion reaction of a solid fuel is initiated. At 504 the first voltage signal is applied to a solid fuel support on which the solid fuel rests. At 506 the second voltage signal is applied to the field electrode positioned in or near the combustion reaction.

In one embodiment, there is a high voltage difference between the first and second voltage signals. Thus, electric field is generated between the solid fuel support and the field electrode. The combustion reaction is therefore subject to the electric field. The electric field serves to enhance the properties of the combustion reaction. In particular, the electric field can cause the combustion reaction to output fewer undesirable byproducts such as nitrous oxide and carbon monoxide.

While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims

1. A solid fuel combustion system, comprising:

a solid fuel support configured to hold a solid fuel for a combustion reaction;

a voltage source coupled to the solid fuel support and configured to output a first voltage signal to the solid fuel support; and

a first field electrode coupled to the voltage source and disposed in or adjacent to a combustion reaction region above the solid fuel support, the voltage source configured to output a second voltage signal to the first field electrode while the first voltage signal is applied to the solid fuel support, the second voltage signal being different than the first voltage signal.

2. The solid fuel combustion system of claim 1, wherein the first field electrode is configured to apply an electric field to the combustion region above the solid fuel support when receiving the second voltage signal.

3. The solid fuel combustion system of claim 2, wherein the electric field is selected to cause the combustion reaction to burn more vigorously than in an absence of the electric field.

4. The solid fuel combustion system of claim 2, wherein the electric field is selected to cause the combustion reaction supported by the solid fuel to output reduced oxides of nitrogen (NOx) than in an absence of the electric field.

5. The solid fuel combustion system of claim 2, wherein the electric field is selected to cause the combustion reaction to evolve reduced carbon monoxide (CO) than in an absence of the electric field.

6. The solid fuel combustion system of claim 1, wherein the second voltage signal is ground.

7. The solid fuel combustion system of claim 1, wherein the second voltage signal has an opposite polarity from the first voltage signal.

8. The solid fuel combustion system of claim 7, wherein the second voltage signal comprises a high voltage opposite in polarity from the first voltage signal.

9. The solid fuel combustion system of claim 1, wherein the voltage signal is a first time-varying voltage signal and the second voltage signal is opposite in polarity from the first time-varying voltage signal.

10. The solid fuel combustion system of claim 9, wherein the first time-varying voltage signal comprises a chopped DC waveform.

11. The solid fuel combustion system of claim 9, wherein the first time-varying voltage signal comprises a DC offset AC waveform.

12. The solid fuel combustion system of claim 9, wherein the first time-varying voltage signal comprises an AC waveform.

13. The solid fuel combustion system of claim 1, wherein the first field electrode includes a metal.

14. The solid fuel combustion system of claim 1, wherein the first field electrode includes porcelain coated metal.

15. The solid fuel combustion system of claim 1, wherein the first field electrode includes silicon carbide (SiC).

16. The solid fuel combustion system of claim 1, comprising a second field electrode coupled to the voltage source, the first and second field electrodes being disposed in or adjacent to walls of a furnace defining the combustion region above the solid fuel support.

17. The solid fuel combustion system of claim 1, wherein the voltage source is configured output the second voltage signal to the second field electrode.

18. The solid fuel combustion system of claim 1, wherein the solid fuel support is a conductive grate.

19. The solid fuel combustion system of claim 1, wherein the first field electrode is a toroidal field electrode positioned above the solid fuel support.

20. A method comprising:

initiating a combustion reaction of a solid fuel positioned on a solid fuel support;

applying a first voltage signal to the solid fuel support; and

applying a second voltage signal to a first field electrode disposed in or adjacent to the combustion reaction above the solid fuel support.

21. The method of claim 20, wherein the first field electrode has a toroid shape and is positioned above the combustion reaction.

22. The method of claim 21, comprising contracting or extending a length of the combustion reaction by applying the second voltage to the first field electrode.

23. The method of claim 20, comprising expanding or contracting a width of the combustion reaction by applying the second voltage signal to a second field electrode positioned adjacent to the combustion reaction.

24. The method of claim 20, comprising generating an electric field in or near the combustion reaction by applying the first and second voltages to the solid fuel support and the first field electrode, respectively.

25. The method of claim 24, wherein generating the electric field causes the combustion reaction to burn more vigorously than in an absence of the electric field.

26. The method of claim 25, comprising reducing oxides of nitrogen (NOx) produced by the combustion reaction by generating the electric field.

27. The method of claim 24, comprising reducing carbon monoxide (CO) produced by the combustion reaction by generating the electric field.

28. The method of claim 20, wherein either the first or the second voltage signal is ground.

29. The method of claim 20, wherein the second voltage signal is a high voltage opposite in polarity from the first voltage.

30. The method of claim 20, wherein the first voltage signal is a time-varying voltage signal.

31. The method of claim 20, wherein the second voltage signal is a time-varying voltage signal.

32. The method of claim 20, wherein one or both of the first and second voltage signals is a chopped DC waveform.

33. The method of claim 20, wherein one or both of the first and second voltage signals is a DC offset AC waveform.

34. The method of claim 20, wherein the solid fuel is a biomass.

35. The method of claim 20, wherein the solid fuel is coal.