Patent Application
20150104748
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.
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.
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.
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.
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
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.
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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.
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.
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.
| Number | Date | Country | |
|---|---|---|---|
| 61890668 | Oct 2013 | US |
