DESCRIPTION OF THE PREFERRED EMBODIMENT

[0034] The invention is a device and method of separating and collecting low density fly ash particles from the overall and unprocessed raw fly ash stream produced by coal burning in a coal fired, steam generating, electric power plant by setting out such low density fly ash particles from the raw coal ash stream using the de-energized inlet portion of an electrostatic precipitator as a separating device. This is specifically accomplished using a method and device that utilizes velocity deceleration to separate and collect the low density fly ash from the raw coal fly ash which will be collected by energized fields of the electrostatic precipitator.

[0035] The invention includes an electrostatic precipitator 10 as shown in one embodiment in FIG. 1 . The electrostatic precipitator 10 generally includes an inlet or expansion nozzle 11 , an outlet or outlet nozzle 12 , and an enlarged hollow body 13 therebetween which is divided into multiple fields 14 A, 14 B, 14 C, etc. that are energizable as described below. Many different varieties and constructions of electrostatic precipitators have been or are available on the market, all of which may incorporate this invention as described herein. The variety of precipitators available is large and includes, for example, models such as those described in the following U.S. Pat. Nos. : 1,298,409, 1,381,660, 3,898,060, 4,308,036, 4,374,652, and 5,160,510, as well as any other commercially available electrostatic precipitator.

[0036] In more detail, the electrostatic precipitator 10 is fluidly connected within an exhaust duct on a coal fired power plant that is between a combustor 21 , or other combustion chamber, and a stack 23 which releases exhaust to the atmosphere 22 . The exhaust duct is thus broken into an inlet duct 20 , the precipitator 10 , and an outlet duct 25 . This is typically accomplished by cutting the exhaust duct into two pieces, namely a first section or inlet duct 20 and a second section or outlet duct 25 , with the electrostatic precipitator 10 attached therebetween whereby the inlet duct 20 separates the combustor 21 from the electrostatic precipitator 10 while the outlet duct 25 separates the electrostatic precipitator 10 from the stack 23 and subsequently the atmosphere 22 . An exhaust gas-to-air heat exchanger is typically used to preheat the air for combustion, and can be either on the inlet or outlet side of the precipitator, such as within the inlet duct 20 or the outlet duct 25 .

[0037] The inlet and outlet ducts 20 and 25 are generally of a similar diameter and cross sectional area, while the diameter and cross-sectional area of the hollow body 13 is larger so as to substantially slow down the fluid flow therein due to an overall increase in volume. More particularly, the cross sectional area of hollow body 13 is in the range of from six to twenty-five times larger than the duct. More particularly, the large diameter of expansion nozzle 11 and hollow body 13 has an area at least ten times larger than the area associated with inlet duct 20 . Basically, the flow or velocity of fluid, in the form of gas with particulate suspended therein, must be sufficiently slowed for the electrostatic precipitator to properly charge the particles, and this is accomplished by a significant increase in volume in the expansion nozzle 11 to the body 13 . Thereafter, the flow is increased in the outlet nozzle 12 by decreasing the exhaust cross section. In one embodiment, the gas flow in the inlet duct 20 is approximately 60 ft./sec. while it falls to 2.5 to 5 ft./sec. in the precipitator body 13 .

[0038] The electrostatic precipitator 10 is longitudinally subdivided into the fields between expansion nozzle 11 and outlet nozzle 12 . As is standard for electrostatic precipitator, each field 14 A, 14 B, 14 C, etc. includes one or more power supplies and each power supply is connected to one or more independently energizable portions known as bus sections. The number of fields is not important as the precipitator may only have a few or may have in excess of a dozen, while most standard precipitators have six or eight.

[0039] Per this longitudinal subdivision, the fields are aligned one after another from the expansion nozzle 11 to the outlet nozzle 12 with the first field 14 A being adjacent or nearest the expansion nozzle 11 , the second field 14 B being next to the first field, and so on across the hollow body 13 to the outlet nozzle 12 . Each field 14 A, 14 B, 14 C, etc. is an arrangement of collecting surfaces and discharge electrodes as is well known in the art.

[0040] In use, the fields 14 A, 14 B, 14 C, etc. are energized with high voltage by a transformer-rectifier combination that is electrically attached to a variety of controls and other electrical components. The energizing of the fields as the products of coal combustion in the form of exhaust gases with suspended particles pass through electrostatic precipitator 10 basically imparts a charge on the particles within the gas stream to separate out particles. This is well known in the industry as it has been in use for years, and ash separation from exhaust gas is required by environmental regulations. For these reasons, a large percentage of coal fired power plants have electrostatic precipitators on each exhaust duct after the combustor.

[0041] The electrostatic precipitator is positioned in a horizontal manner such that the gases must travel horizontally or approximately horizontally through it. This allows for particle fallout. Below or at the bottom of each field, or a collection of fields, is a hopper or collection chamber, namely hopper 30 A for field 14 A, hopper 30 B for field 14 B, etc. These hoppers are separated by walls 31 . Each hopper basically collects any fall out that occurs above it as gases and particles pass through the precipitator and the specific field above it.

[0042] Electrostatic fields are created when the precipitator's charging wires are energized. Particles passing these charged wires are imparted with electrostatic charge. As a result, the charged particles are collected and later dislodged from grounded plates and the particles fall into the hoppers while the gaseous components of the flue gas pass through and are exhausted to the atmosphere 22 . Basically, only non-particulate matter passes all the way through the precipitator 10 to the outlet 12 and thus is exhausted to the atmosphere 22 .

[0043] In accordance with one of the features of the invention, the electrostatic precipitator 10 is oversized. Oversized being defined as having excess capacity in that either lesser capacity or lesser number of fields are needed to fully remove the particles from the exhaust gases of the coal combustion process in order to meet environmental regulations. An oversized electrostatic precipitator 10 has fields that may be de-energized while still performing all of its particulate removal objectives.

[0044] In accordance with yet another feature of the invention, the first field 14 A is de-energized by turning off the electric power to section 14 A by operating breaker A or other similar device. As a result, a first area is provided in the precipitator body 13 that does not impart charges on the particles but is of a significantly increased cross sectional dimension, thus decelerating the exhaust gases containing the particles. In this first field when de-energized, a large portion of the low density ash 40 falls out into hopper 30 A and accumulates as captured low density ash 45 while almost all of the higher density ash particles 41 , due to greater momentum and less drag, pass into the next fields where they are charged and fall out into the hoppers 30 B, 30 C, etc. as captured higher density ash 46 . The first hopper 30 A may then be evacuated using a conveying system and the contents packaged as low density mineral material.

[0045] Referring specifically to the fly ash, it is, as stated, the dust-like material collected from the gas stream to be passed out of the stack, leaving the furnace of power plants which consume coal, and specifically powdered and pulverized coal. Chemically, fly ash is essentially a mixture of silica, aluminum oxide and other metal oxides containing minor proportions of alkalis and carbon. The carbon content of the fly ash represents that portion of the carbon of the original total that did not burn during the combustion in the furnace due to the short time of exposure of the coal to combustion temperatures and to inconsistencies in operation. Hence, depending on these and other factors, the fly ash may contain from as little as less than 1% to as high as even 40% by weigh of carbon in isolated instances. A typical fly ash analysis is as follows: 1

[0046] Additionally, this mixture contains an available alkali equivalent Na2O of 0.33, and an Iron Oxide of Fe3O ₄ of 2.0. The low density ash of the present invention includes a major amount of frothy, solid particles with both internal and external porosity or interstitial cavities such as those shown on attached FIG. 2 , and a minor amount of thick wall hollow particles as shown in FIG. 3 having both internal and external pores. Still further, a minor amount of cenospheres, such as those shown in FIG. 4 are also collected in the low density ash of the present invention. More particularly, the present invention includes from 10% to 70% of the total mixture by weight of frothy, solid particles such as those shown in FIG. 2 , from 10% to 70% of thick walled hollow particles such as those shown in FIG. 3 , and less than 1% of cenospheres such as those shown in FIG. 4 . More particularly, and in one embodiment of the invention, the mixture of low density fly ash includes from 20% to 60% of frothy, solid particles and from 10% to 50% of thick walled hollow particles such as those shown in FIG. 3 .

[0047] It has been found that the low density ash particles from the first hopper are of a significantly lower density than the other ash particles which tend to fall out in hoppers 30 B, 30 C, etc. The accumulation of material in the first hopper 30 A is of a good quality and is of a high percentage, if not all, low density ash. The density of this accumulation in hopper 30 A is at least 10% lower in density than raw fly ash normally produced by electrostatic precipitation, and it has been found to be 35% or more lower in density.

[0048] In experiments, the accumulation of material had a specific gravity of less than 2 and often is in the range of 1.6 to 1.99, which is a very good grade low density filler material. The vast majority of particles collected in hopper 30 A were also about between 30 microns to 400 microns in size. It is also noted that the cost of collection of such low density ash from the first hoppers 30 A is very low, far less than the costs associated with other processes to separate ash by particle size or density. Chemically, the composition of the low density ash particles is similar to the composition of the overall ash population passing in the gas stream, and is lower in density as a result of its frothy form and structure which has both internal and external porosity, which ensures that there is a relatively low density associated with the product.

[0049] In an alternative embodiment, the first and second fields 14 A and 14 B, or first three fields 14 A- 14 C may be de-energized. In this case, low density fly ash is deposited in all three respective hoppers although a gradual increase in the density generally occurs in each successive field. Still further, the present invention may be operated by ensuring that expansion nozzle 11 has a cross sectional configuration large enough to decelerate the gas stream efficiently to ensure that lower density particles will fall out of the gas stream and into hopper 30 A. In this manner, de-energizing the electrostatic precipitator is not necessary as the large diameter expansion nozzle 11 is sufficient to slow the gas stream and allow low density air entrained particles to fall out as a result of the drastic reduction in momentum. Expansion nozzle 11 may not be positioned adjacent an electrostatic precipitator, and simply decelerate the gas stream to allow low density particles to fall out of the stream. However, if expansion nozzle 11 is positioned adjacent a precipitator, then the collector plates must be de-energized to allow low density particles to fall.

[0050] Accordingly, the improved low density ash separation and collection method and device achieves all the enumerated objectives, does so with great cost efficiency and generates an entirely new low density fly ash material with unique properties and characteristics as a result of this new art.

[0051] In the foregoing description, certain terms have been used for brevity, clearness and understanding; but no unnecessary limitations are to be implied therefrom beyond the requirement of the prior art, because such terms are used for descriptive purposes and are intended to be broadly construed.

[0052] Moreover, the description and illustration of the invention is by way of example, and the scope of the invention is not limited to the exact details shown or described.

[0053] Having now described the features, discoveries and principles of the invention, the manner in which the improved low density ash separation and collection method and device is constructed and used, the characteristics of the construction, and the advantageous, new and useful results obtained; the new and useful structures, devices, elements, arrangements, parts and combinations, are set forth in the appended Claims.