Gas separation: apparatus – With gas and liquid contact apparatus – Fixed gas whirler or rotator for gas separation
Reexamination Certificate
2001-11-28
2003-11-18
Smith, Duane S. (Department: 1724)
Gas separation: apparatus
With gas and liquid contact apparatus
Fixed gas whirler or rotator for gas separation
C096S321000, C435S266000
Reexamination Certificate
active
06648949
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention is a novel stack application related to improved carbon dioxide and particle removal and collection from flue gases produced during coal power-generation processes. More particularly, the invention is related to the direct sequestration of carbon dioxide in pulverized coal fired plants.
b) Description of Related Art
Combustion of carbonaceous materials accounts for the majority of the heat energy generated from fossil fuels. Heat energy is used to generate electrical power and/or for heating applications. Energy produced from combustion of carbonaceous materials constitutes more than 50% of the power and heat production. The final products of the combustion of fossil fuels for power generation are gaseous products, such as carbon oxides, and ash particles. Sulfur and nitrogen compounds in coal may form oxides during the combustion process. Means have been developed by those who are skilled in the art to address the formation, control and post combustion removal of the oxides of sulfur and nitrogen. These gaseous oxides tend to form acids of sulfur and nitrogen, and therefore they are called “acid gases”. Acid gas emission control processes are reported in various technical references and textbooks, and therefore further explanation of such is not necessary.
Traditionally, after the post combustion treatments of the oxides of sulfur, nitrogen, and other particles, the flue gas still contains a minute amount of particles, which may not be feasible for removal by conventional particle or dust removal processes, such as electrostatic precipitation and fabric filtration. Electrostatic precipitation is unable to capture small particles in the near micro or sub-micron size range. This is indicated in most commercially available electrostatic precipitator particle collection units by efficiency curve data. As the particle size approaches a sub-micron size, the collection efficiency drops drastically. Additional improvement of particle capture efficiency can be expected by increasing the residence time for the flue gas inside the electrostatic precipitator train, which can be achieved by adding more electrostatic precipitation units. However, economical, technical, and space or “foot print” considerations may rule out the option of additional residence time being provided by this method. This problem is acute for most of the existing coal-fired power plants.
Electrostatic precipitation (ESP) is an age-proven technology for the capture of fine particles from coal combustion. An electrostatic force is generated by the electrically charged particles and an electrically charged electrode causes the particles to migrate to collecting surfaces possessing an opposing electrical charge. One design consideration is the time for the charged particles to migrate to the collecting surface, which should be shorter than the particle residence time in the ESP confinement. Economic constraints may dictate the optimum design for the ESP dust collector. Variations in the electrical resistivity of the dust particles may also affect the ability of the particles to retain an electric charge. Resistivity of the particles may drastically reduce the intended dust collection efficiency. Industrial field data of electrostatic precipitator performance often show a drop in the collection efficiency for the sub-micron particles. This is mostly due to Brownian or Maxellian motions of small particles.
Alternatively, the use of fabric filtration utilizes the impaction, interception, and random motion of the particles on a fabric target for capture. Because of the low inertia of the small particles, the particles remain within the confinement of the stream lines, or become entrained in the stream lines of the filtering flue gas stream. Therefore, the particles are less likely to wander out of the confinement of these stream lines, and be captured by impaction and/or interception. The chances of random movement of the small particles being captured are even less. As a consequence, even with fabric filters, the likelihood of achieving sub-micron particle capture is not promising. Granted, the retention efficiency can be increased at the expense of deep filtration with a high pressure drop.
Sub-micron particles are a major recent concern for the public. The deposition of respirable particles inside human lungs can lead to the cause of emphysema and many respiratory diseases. The recent promulgation by the U.S. Environmental Protection Agency (EPA) on sub-micron size particle control regulations will add to the aforementioned considerations for design and operation of carbonaceous fuel power generation plants. Small particles and aerosols may elude the capture of thin felt or fabric filters, which have a lower number of fibers for, capture. The use of filtration technology for small particle removal is very similar to that of an ANDERSON IMPACTOR® air sampler for small particle retention. These mechanisms for small particle retention, such as impaction, interception and random motion, are still useful in somewhat limited applications. Emission control of sub-micron size particles needs to be addressed, however.
From an engineering or accounting point of view, the build up of carbon dioxide in the atmosphere is a matter of inventory. Inventory of carbon dioxide is the net result of carbon dioxide input, or generation, minus the carbon dioxide output, or depletion. One must keep in mind that carbon dioxide is formed in a matter of seconds by means of combustion or other related processes. The consumption of carbon dioxide is carried out in terms of bio-chemical or physiological reactions, generally several orders slower than the combustion processes. From an economic point of view, installations other than Mother Nature will be immense in scale and consequently costly in investment.
Addressing the carbon dioxide issue can be cost prohibitive. There is no apparent economical incentive for the developing countries to abide by practices for carbon dioxide sequestration. Many businesses in developed countries are reluctant to reduce their carbon dioxide emissions while developing countries continue to generate carbon dioxide. The production of economically attractive by-products may induce developing countries to adopt the practice of including carbon dioxide sequestration in their fossil fuel power plants. This appears to be logical, and conducive for carbon dioxide sequestration.
Another consideration for the installation of carbon dioxide sequestration facilities in conventional coal or carbonaceous power plants is the space or “foot print” concern. Age-old coal firing power plant design practices leave very little space for an after-thought addition for pollution and carbon dioxide sequestration equipment.
The smoke stack is an ancient solution to the dispersion of flue gas and the products of combustion. The requirement to spread the products of combustion to a wide area or space calls for a tall structure. To facilitate the large volume disposal and dispersing of the gaseous products of combustion and its accompanying fine particles, an induction fan is required to move the gaseous products of combustion up through the stack or chimney. The thermo-siphon effect of the hot flue gas will also propel the gaseous products through the stack. In the past, the chimney or stack served a singular purpose of dispersing the gaseous products of combustion. There are numerous articles and software dealing with stack selection and design in the literature. Therefore, it will be redundant to retell the state of the art in stack design.
A main component of the United States power generation systems is the conventional pulverized coal-fired boiler, which produces high pressure and high temperature steam for electrical power generation in a traditional Rankine cycle. More than half of the U.S. domestic electric power is derived from conventional pulverized coal-fired power generation systems. Eighty-five percent of power generation for transportation and power generation
Der Victor K.
Shang Jer-Yu
Gottlieb Paul A.
Moody Julia Cook
Smith Duane S.
The United States of America as represented by the United States
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