Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Waste gas purifier
Reexamination Certificate
1995-05-23
2001-10-16
Tran, Hien (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Waste gas purifier
C422S170000, C422S172000
Reexamination Certificate
active
06303083
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates, in general, to the removal of particulates and other contaminants from flue gas produced by the buming of a fossil fuel and, in particular, to a new and useful method and system which simultaneously removes sulfur trioxide (SO
3
) from the flue gas by injecting dry sorbent downstream of a particulate collection device, capturing reacted and unreacted dry sorbent in a wet scrubber, and removing sulfur dioxide (SO
2
) in the wet scrubber.
In the pollution control field, several approaches are used to remove sulfur oxides and other contaminants from a flue gas produced by the burning of a fossil fuel in order to comply with Federal and State emissions requirements. One approach involves locating and utilizing fossil fuels lower in sulfur content and/or other contaminants. A second approach involves removing or reducing the suffur content and/or other contaminants in the fuel, prior to combustion, via mechanical and/or chemical processes. A major disadvantage to the second approach is the limited cost effectiveness of the mechanical and/or chemical processing required to achieve the mandated reduction levels of sulfur oxides and/or other contaminants.
By and large, the most widely used approaches to removing sulfur oxides and/or other contaminants from flue gas involves post-combustion clean-up of the flue gas. Several methods have been developed to remove the SO
2
species from flue gases.
A first method for removing SO
2
from flue gas involves either mixing dry alkali material with the fuel prior to combustion, or injection of pulverized alkali material directly into the hot combustion gases to remove sulfur oxides and other contaminants via absorption or absorption followed by oxidation. Major disadvantages of this first method include: fouling of heat transfer surfaces (which then requires more frequent soot blowing of these heat transfer surfaces), low to moderate removal efficiencies, poor reagent utilization, and increased particulate loadings in the combustion gases which may require additional conditioning (i.e. humidification or sulfur trioxide injection) of the gas if an electrostatic precipitator is used for downstream particulate collection.
A second method for removing SO
2
from flue gas, collectively referred to as wet chemical absorption processes and also known as wet scrubbing, involves “washing” the hot flue gases with an aqueous alkaline solution or slurry in an upflow, gas-liquid contact device to remove sulfur oxides and other contaminants. Major disadvantages associated with these wet scrubbing processes include: the loss of liquid both to the atmosphere (i.e., due to saturation of the flue gas and mist carry-over) and to the sludge produced in the process, and the economics associated with the construction materials for the absorber module itself and all related auxiliary downstream equipment (i.e., primary/secondary dewatering and waste water treatment subsystems).
A third method, collectively referred to as spray drying chemical absorption processes and also known as dry scrubbing, involves spraying an aqueous alkuline solution or slurry which has been finely atomized via mechanical, dual-fluid or rotary cup-type atomizers, into the hot flue gases to remove sulfur oxdes and other contaminants. Major disadvantages associated with these dry scrubbing processes include: moderate to high gas-side pressure drop across the spray dryer gas inlet disribution device, and limitations on the spray down temperature (i.e., the approach to flue gas saturation temperature) required to maintain controlled operations.
Several methods have been developed to remove SO
3
from flue gas. One method is known as dry sorbent injection, which involves injecting a sorbent (generally lime, limestone, promoted lime, sodium bicarbonate or other alkali sodium salts, or other alkali metal salts such as silica, aluminum, iron, etc.) into the flue gas at temperatures above the adiabatic saturation temperature of the flue gas. The amount of sorbent required is highly dependent upon the sorbent properties (i.e., the composition, particle size, surface area, etc.), flue gas temperature, and method of injecting.
Spray drying chemical absorption processes, such as described above in connection with SO
2
removal, are also used for SO
3
control.
Wet precipitators have also been used to remove SO
3
from wet flue gas streams. In these systems, the SO
3
forms an aerosol of H
2
SO
4
by reaction with water. The aerosol behaves much like a solid particle in that it is removed when an electrical charge is applied. The aerosol is then collected by impaction on wetted plates or tubes for removal from the flue gas stream.
SO
3
can also be removed via condensation. One known process is the WSA-SNOX process in which SO
2
is catalytically converted to SO
3
. The SO
3
is then removed by condensation, forming a dilute sulfuric acid. Other known methods for SO
3
removal include activated carbon, and packed, moving, or fluidized bed processes. Also, combined processes which utilize a hot catalytic baghouse are known to remove SO
3
. Moreover, SO
3
can also be removed by adding a sorbent or reagent such as MgO to the fuel.
One known system for removing SO
3
from flue gas produced by a combustion process is schematically illustrated in
FIG. 1. A
fossil fuel
2
, such as coal, is burned in a boiler
4
and the resulting flue gas
6
is passed through a heat exchanger
8
to cool the gas. SO
3
from the flue gas
6
is removed in a dry scrubber
10
by contacting the flue gas
6
with an atomized reagent slurry
12
in an evaporating mode. The reagent slurry
12
used in the dry scrubber
10
is provided by a reagent preparation system
14
. After dry scrubbing, the partially cleaned but particle-laden flue gas
16
is channeled to a particulate collector
18
, such as a baghouse or precipitator, to remove particles from the flue gas
16
. After particles are removed from the flue gas
16
, the cleaned flue gas
20
exits the system through a stack
22
. Reaction product
24
, and collected particles and other material
26
collected in the dry scrubber
10
and particulate collector
18
are then channeled to a waste disposal device
28
, while any reusable reagent from the reaction product
24
is provided back into the reagent preparation system
14
. Dry scrubber systems such as shown in
FIG. 1
have high operating costs due to both the power requirements to atomize the reagent slurry and the cost of the reagent itself. In addition, reagent utilization is poor compared to other systems such as wet scrubber systems.
FIG. 2
schematically illustrates another known system for removing SO
3
from flue gas produced by the combustion of a fossil fuel. In this system, a dry injection process injects a sorbent
30
at one or more of a plurality of locations in the system. A first location
32
involves injection of the sorbent
30
directly along with the fuel
2
. A second location
34
involves injection of the sorbent into the boiler
4
so that it mixes with the flue gas
6
at a location downstream of the fuel
2
injection point. A third location
36
involves injection of the sorbent
30
into the flue gas
6
just upstream or prior to its entry into the heat exchanger
8
, while a fourth location
38
involves injection of the sorbent
30
into the flue gas after it exits the heat exchanger
8
. The sorbent
30
is provided by a sorbent receiving and preparation station
40
, while the collected particles and other materials
42
are collected in a waste disposal device
44
. These dry injection processes, similar to dry scrubbers, typically require high cost reagents and are known to have poor reagent utilization, resulting in increased operating costs and quantities of waste product Additionally, the presence of unused reagent in the waste product limits its the use as a product and detrimentally affects the properties of the waste, which impacts landfill operations. Finally, since both the reaction products and unused sorbe
Bhat Pervaje Ananda
Goots Thomas Robert
Johnson Dennis Wayne
Baraona R. C.
Marich Eric
The Babcock & Wilcox Company
Tran Hien
LandOfFree
Method and system for SO2 and SO3 control by dry... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and system for SO2 and SO3 control by dry..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and system for SO2 and SO3 control by dry... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2591797