Self-cleaning nozzles of wet scrubber

Details Self-cleaning nozzles of wet scrubber Self-cleaning nozzles of wet scrubber

2001-10-10

2003-11-25

Smith, Duane S. (Department: 1724)

Gas separation: processes

With control responsive to sensed condition

Pressure sensed

C095S149000, C096S244000, C096S253000, C239S107000

Reexamination Certificate

active

06652624

ABSTRACT:

BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to devices that removes dust particles from gases, and more specifically to a particular category of such devices called wet scrubbers, and more specifically to wet scrubbers with nozzles, and even more specifically to wet scrubbers with self-cleaning nozzles.
The concern of this invention is with air pollution resulting from the emission into the atmosphere of particulate matter and other contaminants. As noted in the Federal Register of Dec. 27, 1996 (Vol. 61, No. 25), “[t]he primary goal of the Clean Air Act is to enhance the quality of the Nation's air resources and to promote the public health and welfare and the productive capacity of its population.”
Particulate matter is made up of tiny particles in the atmosphere that can be solid or liquid (except for water or ice) and is produced by a wide variety of natural and manmade sources. Particulate matter includes dust, dirt, soot, smoke and tiny particles of pollutants. Some particles attract and combine with amounts of water so small that they do not fall to the ground as rain. Major sources of particulate pollution are factories, power plants, trash incinerators, motor vehicles, construction activity, fires, and natural windblown dust. Particles below 10 microns in size (about seven times smaller than the width of a human hair) are more likely to travel deep in the respiratory system, and be deposited deep in the lungs where they can be trapped on membranes. If trapped, they can cause excessive growth of fibrous lung tissue, which leads to permanent injury. Children, the elderly, and people suffering from heart or lung disease are especially at risk. Particles of 10 microns or less are also referred to as PM10.
Electrostatic precipitators, which have been used for particulate control since 1923, use electrical fields to remove particulate from boiler flue gas. Inasmuch as precipitators act only on the particulate to be removed, and only minimally hinder flue gas flow, they have very low-pressure drops, and thus low energy requirements and operating costs. The main drawback of a conventional electrostatic precipitator, apart from requiring a high voltage supply, is that the contaminants collected on the collecting electrode tend to adhere thereto. This makes it necessary, on occasion, to shut down the precipitator in order to scale off the accumulated dirt.
Fabric filter collectors are conceptually simple: by passing flue gas through a tightly woven fabric, particulate in the flue gas will be collected on the fabric by sieving and other mechanisms. The dust cake, which forms on the filter from the collected particulate, can contribute significantly to collection efficiency. Practical application of fabric filters requires the use of a large fabric area in order to avoid an unacceptable pressure drop across the fabric.
Cyclones use centrifugal force to separate particulate from gas streams, and belong to the broader family of mechanical collectors, which use a variety of mechanical forces to collect particulate. A multiple cyclone is an array of a large number of small (several inch diameter) cyclones in parallel. Multiple cyclones have overall mass removal efficiencies of 70-90%. However, cyclone collection efficiencies fall off rapidly with particle size, so that control of fine particulate (PM-2.5) is limited.
Wet scrubbers are based on the collection of particles in liquid droplets, and scrubber design therefore is optimized for droplet creation. In venturi scrubbers, which are commonly used for particulate collection, the scrubbing liquid and flue gases accelerate through a converging section of duct into a narrow throat, and then pass through the throat into a diverging section. In the throat, very high gas velocity shears the scrubbing liquid into a cloud of very fine droplets, which collect particles.
The water droplets are thoroughly mixed with the dirty air, and the solid pollutants in gas air are thoroughly wetted. The wet solid pollutants, being relatively heavy, are deflected downward through the action of the baffles and reduced air velocities into the water reservoir. A constant-volume air control means interposed between the chamber and the source of polluted air, such as dirty air from an incinerator or the like, contains a primary air inlet duct and a secondary air inlet duct where the air through each duct is controlled by a damper. The dampers of the two ducts are coupled to operate complementary to each other to provide a constant air flow to the chamber for various flows of polluted air directed to the scrubber through the primary air inlet duct.
Wet Scrubber systems dealing with acid Gas/SO rely on a chemical reaction with a sorbent to remove a wide range of pollutants, including sulfur dioxide (SO
2
), acid gases, and air toxins, from flue gases. When used to remove or “scrub” SO
2
from the flue gas, these devices are commonly called flue gas desulfurization (FGD) or scrubber systems. FGD or scrubber systems are generally classified as either “wet” or “dry”. Wet scrubbers are increasingly recognized as an important part of a multi-pollutant control program. In a wet scrubber, a liquid sorbent is sprayed into the flue gas in an absorber vessel. The gas phase or particulate pollutant comes into direct contact with a sorbent liquid and is dissolved or diffused (scrubbed) into the liquid. The liquid interface for gas and particle absorption include liquid sheets, wetted walls, bubbles and droplets.
In the wet processes, a wet slurry waste or by-product is produced. Most wet FGD systems use alkaline slurries of limestone or slaked lime as sorbents. Sulfur oxides react with the sorbent to form calcium sulfite and calcium sulfate. Uptake of the pollutant by the sorbent results in the formation of a wet solid by-product that may require additional treatment, or when oxidized, results in a gypsum by-product that can be sold. Scrubber technologies for wet scrubbing of gaseous pollutants can achieve extremely high levels of multi-pollutant control, including acid gases, SO
2
, fine particulates and heavy metals (e.g., mercury) from utility and industrial coal-fired boilers, waste-to-energy systems, and other industrial processes.
Wet scrubber technology can be applied to difficult processes such as gas absorption and particle collection, treating combustible particles, and removal of wet, sticky or corrosive particles. Wet scrubbers are used in industrial process mercury removal and to remove ionic forms of mercury from the gas stream of coal-fired power generation facilities. Wet scrubbers generally have relatively small space requirements, low capital cost, and are able to process high temperature, high acidity, and high humidity flue gas streams. Scrubber costs have continued to decrease, largely because of technical innovations. Scrubber energy requirements have also continued to decrease, helping to lower operating costs.
FGD systems are an increasingly significant part of a multi-pollutant control approach, even as the energy requirements of these systems are decreasing to where these systems now consume only about 1% of total boiler output. Where low-cost high-sulfur fuels are available, or where the required reductions are very high, scrubbing is often a viable control option. New wet scrubbers routinely achieve SO
2
removal efficiencies of 95%, with some scrubbers achieving removal efficiencies of up to 99%. Scrubbers have been used in the EPA Acid Rain Program on coal-fired boilers, which are significant sources of hydrochloric acid (HCl) and hydrofluoric acid (HF).
According to the EPA and others sources, both wet and dry scrubbers have been shown to reduce HCl emissions by 95% and more, and wet scrubbers have been shown to reduce HF emissions by more than one-third. Others have reported ranges of 87-94% removal of chlorine and 43-97% removal of fluorine by both wet and dry scrubbers. In addition, wet scrubbers also provide significant removal of arsenic, beryllium, cadmium, chromium, lead, manganese,

Affiliated with

Also associated with

Rating

Self-cleaning nozzles of wet scrubber does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Self-cleaning nozzles of wet scrubber, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Self-cleaning nozzles of wet scrubber will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3151684