Patent Application
20160045862
The invention relates to methods and devices for injecting dry material into a gas stream. More specifically the invention relates to injecting dry sorbent into flue gas.
Control of pollution from fossil fueled combustion devices involves limiting and removing objectionable chemical species from the combustion generated flue-gases. Such removal is often accomplished by adsorbing the objectionable gaseous species unto solid particles which themselves can subsequently be removed, thus cleaning the flue-gas.
Dry sorbent injection (DSI) is such a technology whereby a chemical species, which has an affinity to react with the objectionable gaseous pollutant and further to form a solid particle, is injected into the flue-gas stream. An example of this technology is when colloidal slurry of lime or dry lime particles (the sorbent) are sprayed or injected into coal-fired flue-gases to adsorb sulfur oxide gases resulting from the combustion of coal. The absorbed sulfur species are removed from the flue-gas as solid particles of calcium sulfate which is the stable mineral known as gypsum.
The efficiency and therefore the practicality of sorbent injection pollution control processes depends upon how well the sorbent mixes and comes into contact with the gaseous pollutant. The surface area, particle size and such things as surface porosity of the sorbent all affect the probability that the gaseous pollutant will be absorbed by the sorbent particle; but first and foremost for efficient utilization, the sorbent particle must be distributed as uniformly as possible within the flue-gas flow.
Flue-gases are generated by the combustion of fossil fuels for the purpose of releasing heat which is to be used as heat input for such industrial processes as cement, steel and glass making, space heating or conversion of heat to electricity using electric utility boilers to generate steam. This invention applies to not only all such processes which generate flue-gases; but to any process in which it is desired to efficiently and uniformly mix a dry granular component with a gas stream.
The flue-gas is generally conveyed, at higher than ambient temperatures, through large ducts to various pollution control devices (back-end equipment) and thence to a chimney for exhaust to the atmosphere. A diagram of such a large duct is shown in
In order to best distribute the dry sorbent within the flue-gas, numerous methods and devices have been of researched, developed, tested and patented. Often the sorbent is injected through use of a carrying media which may be liquid or gaseous and is meant to distribute or disperse the sorbent particles. However, practicality and costs dictate that there are only a finite number of injection points and that the resulting mixing is not completely uniform. Air is often used as the carrier fluid and the injection point creates a mixing plume which has a sorbent rich center surrounded by gradients of lesser concentrations of sorbent. The temperature of the carrier air is often different and much lower than the hot flue-gas and the viscosity differences of the hot versus cold gases cause them to remain segregated or poorly mixed. Thus many different devices have been developed and patented to improve the sorbent mixing and distribution while minimizing the number of injection points, the volume of carrier fluid and the associated injector equipment costs.
The use of a so called “delta wing” immersed within the hot flue-gas creates a turbulent wake behind the convex satellite shaped delta wing. Such a delta wing device as shown in
When sorbent is injected on the downstream side of the delta wing, the turbulent wake of the wing creates turbulent eddies which essentially use the flue-gas itself to help distribute the sorbent. Since there is much more flue-gas than carrier gas and since the purpose is to mix into this larger volume of gas; this device leads to greatly improved distribution of the sorbent for any finite number of injection points and corresponding delta wings. However, each injection point must be at the center of each delta wing and this may require an array of multiple delta wings and associated injection piping.
Other turbulent wake devices shown in
All of the dry sorbent injection devices known in the art have a region near the output of the dry sorbent where mixing of the sorbent and the flue gas occurs. However, the region is relatively small and localized at the output. Hence, the sorbent absorbs only a small portion of the target material that the sorbent has been injected to remove. One can improve the removal rate by providing one or more additional devices; but that adds costs to the system. Consequently, there is a need for a dry sorbent injection device that provides mixing of dry sorbent with more gas in the gas stream and thereby enables greater absorption and removal of the target material.
We provide a dry material injection device which greatly improves upon the singular injection and centralized wake mixing of these previous mixing devices. We provide an injection tube having a first end configured for attachment to a dry material supply and an open end opposite the first end. The injection tube has an upstream side and a downstream side and at least one opening on the downside side. The opening or openings extend along the axial direction of the injection tube. A wake device is positioned adjacent the upstream side of the injection tube and creates turbulence in the gas stream as the gas stream passes around the wake device.
Our device creates a wake where the dry material is injected that is continuously extended in the axial direction of the injection tube for an arbitrary but carefully designed distance and the dry material is continuously fed or injected into this extended wake zone. We prefer to provide a singular centralized injection zone that extends axially along the injection tube. Hence we increase the region where mixing of the dry sorbent and flue gas occurs from a small localized region near a point source to an arbitrarily longer two dimensional injection zone. And likewise we prefer to use a two dimensionally distributed wake device. The dry material may be injected through a slot or series of slots cut axially in the injection tube or by use of a column or plume of a second carrier fluid such as steam or water or a combination of such.
An alternative embodiment utilizes an injector nozzle in place of the injection tube. The injector nozzle combines a first stream containing dry material in an air stream and a second stream which may be steam or water to form an output stream. A wake device is positioned adjacent the upstream side of the output of the injector nozzle. The wake device creates turbulence in the gas stream as the gas stream passes around the wake device.
Other objects and advantages will become apparent form a description of certain present preferred embodiments thereof which are shown in the drawings.
a is a diagram of a duct through which gas is flowing and into which a dry sorbent is being injected according to another known method that uses a delta wing.
b is a diagram of a duct through which gas is flowing and into which a dry sorbent is being injected according to yet another known method which uses a simple plate.
a is a photograph of the injection plume created when using a single point injector.
b is a photograph of the injection plume created when using our injection device.
Our device builds upon the use of wake mixing, but rather than a singular point of injection into the wake; however formed, we extend the wake device in the axial direction of the injection tube so that the wake device creates a longitudinal turbulence zone of any desired length. In the embodiment shown in
In the embodiment shown in
The continuous sorbent injection and the wake resulting from the extended flat plate 6 interact to fill a vacuum created by the wake with uniformly mixed sorbent. The wake and the flow of dry sorbent through the injection tube subsequently distributes the dry sorbent into a greatly extended two dimensional mixing zone with the rest of the gas.
The continuous injection may be accomplished by a series of injection points along the injection tube or by various slots in the tube along its axial direction. However we have found that it is advantageous to have a single “Vee” cut slot 12 of increasing width in the axial direction along the injection tube 4 as shown in
Use of a “Vee” slot in the axial extension of the injection tube helps prevent dry sorbent bridging and keeps clear with the higher velocity of injection pressure at the beginning of the Vee; while allowing the vacuum of the wake to help draw the dry material at the lower static flow pressure as the Vee opens and the flow velocity decreases in the axial direction. Thus the Vee slot may be designed to have at least the same open area as the cross-section of the tube, but the optimum opening may be determined through trial-and-error experiments, computer modeling or a combination of testing aided by computer fluid-dynamics modeling.
In practice we have found that optimum slots or Vees can be matched with the dimensions of the wake device so that the continuous injection can be extended to lengths of over 4 feet. Photographs were taken during testing and optimization of our device and comparisons of different injection plumes are shown in
The embodiment of our device shown in
The device shown in
A second present preferred embodiment shown in
This distributed injection provided by the devices shown in
The motive fluid may also contain various additives which may improve the operation of specific back-end pollution control equipment. For example, trace amounts of ammonia are known to lower ash resistivity and improve the operation of electrostatic precipitators.
The removal of many pollutants may be enhanced by the presence of increased water or gaseous steam. For example in the removal of acid gases, the moisture content of the flue gas helps to convert the molecule into its acid form; such as when sulfur trioxide is converted to gaseous sulfuric acid the acid more readily adsorbs to the sorbent surface. Thus the motive fluid itself improves the effectiveness of the dry sorbent by adding moisture to the sorbent surface and by enhancing the conversion of sulfate to sulfuric acid in the gas phase.
Use of a wake device will also increase the cross-duct distribution of the dry sorbent by inducing the same wake vacuum downstream of the steam ejector penetrating jet. The wake plate as shown in
Even though we have described our injection device being used to inject dry sorbent into flue gas, the device is not so limited and may be used to inject any dry material into any gas stream that is flowing through a duct or pipe.
Although we have described various present preferred embodiments of our dry sorbent injection device our invention is not limited thereto but may be variously embodied within the scope of the following claims.
The present application claims priority to U.S. Provisional Application Ser. No. 62/036,811, which was filed on Aug. 13, 2014. The entirety of the Provisional Application is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 62036811 | Aug 2014 | US |
