Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/46—Removing components of defined structure
  • B01D53/48—Sulfur compounds
  • B01D53/50—Sulfur oxides
  • B01D53/507—Sulfur oxides by treating the gases with other liquids
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/46—Removing components of defined structure
  • B01D53/54—Nitrogen compounds
  • B01D53/56—Nitrogen oxides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/46—Removing components of defined structure
  • B01D53/64—Heavy metals or compounds thereof, e.g. mercury
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/75—Multi-step processes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2251/00—Reactants
  • B01D2251/10—Oxidants
  • B01D2251/106—Peroxides

Definitions

• the present invention relates generally to emission control and in particular to the control of emissions from combustion sources.
• combustion flue gas streams can be treated for the removal of SO ⁇ , NO ⁇ and heavy metals, while isolating useful by-products streams of sulfuric acid and nitric acid as well as solids for the recovery of the heavy metals.
• the apparatus is modular and components can be added or removed depending upon the specific requirements for a given removal operation.
• the invention further includes methods and apparatus of varying scope.
• Figure 1 is a block schematic of an emission control system in accordance with an embodiment of the invention.
• Figure 2 is a schematic of a hydrogen peroxide concentration control system for use in accordance with one embodiment of the invention.
• FIG. 3 is a hydrogen peroxide reaction vessel subsystem for use in accordance with one embodiment of the invention.
• Emission control systems in accordance with the invention address environmental pollutants SO ⁇ , NO ⁇ , and heavy metals. Such systems are designed to control emissions of these environmental pollutants to the levels established by the EPA.
• This emission control system provides a method based on hydrogen peroxide to reduce the SO ⁇ , NO ⁇ , and metal and metal oxide emissions from combustion sources to acceptable levels as established by the Environmental Production Agency.
• useful by-product streams of sulfuric acid, nitric acid, salts of these acids, and feedstock for oxides-of-metal production may be isolated.
• Figure 1 is a block schematic of an emission control system in accordance with an embodiment of the invention. The process starts with a gas stream, such as raw flue gas 150 after the particulates have been removed.
• the first step of the process is to use a cooling and wash chamber 102 to cool and remove some of the particulates in the entering flue gas 150.
• Process water from chamber 103 is provided to chamber 102. Particulates, wash water and heat are sent from chamber 102 to the sedimentation and cooling Pond 104. Water is then re-circulated from pond 104 back to water chamber 103.
• the washed flue gas is fed from wash chamber 102 to a scrubber tower 105 for the removal of SO ⁇ and or heavy metals.
• Scrubber tower 105 uses hydrogen peroxide from hydrogen peroxide storage 112 to oxidize sulfurous acid (H 2 SO 3 ) to sulfuric acid (H 2 SO 4 ) to prevent reemission of SO 2 .
• Hydrogen peroxide storage 112 preferably provides aqueous hydrogen peroxide of approximately 50% to 70% by volume, and more preferably at approximately 70% by volume.
• As the scrubber liquor pH decreases due to the formation of sulfuric acid most of the heavy metal oxides, including Hg, etc., are dispersed as metal oxides and/or dissolved hydroxides are converted to sulfates. The remaining un-dissolved particulates and insoluble sulfates are removed with centrifuge 106, e.g., a solid-bowl centrifuge.
• Centrifuge 106 continuously removes the solids and circulates the scrubber liquor through value 109 back to scrubber tower 105 for continuous scrubbing and cleaning the flue gas.
• the scrubber liquor sulfuric acid
• the cleaned scrubber liquor is discharged from the centrifuge 106 through valve 110 then drained to sulfuric acid storage 111, which can then be utilized for fertilizer or industrial uses.
• the solids from centrifuge 106 are discharged to the recycle solids container 107. Soluble metals and metal oxides present in the cleaned scrubber liquor may further be removed as insoluble solids upon neutralization of the sulfuric acid as may be performed, for example, during the production of fertilizer.
• the concentration of hydrogen peroxide in the first scrubbing mixture is maintained at a predetermined level, e.g., 0.1 to 5 percent by volume. Concentration of the first scrubbing mixture may be maintained using a hydrogen peroxide controller of the type described below. Additional detail of such a controller may be found in U.S. Patent No. 6,039,783 issued March 21, 2000 to Lueck et al. and U.S. Patent No. 6,641,638 issued November 4, 2003 to Lueck et al.
• a hydrogen peroxide controller of the type described below. Additional detail of such a controller may be found in U.S. Patent No. 6,039,783 issued March 21, 2000 to Lueck et al. and U.S. Patent No. 6,641,638 issued November 4, 2003 to Lueck et al.
• Residual acid gases are neutralized with a base in neutralizer 118, and then the cleaned and neutralized flue gas exits through the exhaust stack.
• an exhaust fan could be used in place at the outlet of the neutralizer 118, if desired, to boost the clean and neutralized flue gas out of the exhaust stack as processed flue gas 152.
• the neutralized flue gas from neutralizer 118 flows to NO oxidation tower 113, where nitric oxide (NO) is oxidized to nitrogen dioxide (NO 2 ).
• NO nitric oxide
• NO 2 nitrogen dioxide
• the flue gas may be passed directly from the demister 108 to the NO oxidation tower 113 for later neutralization, eliminating neutralizer 118.
• Hydrogen peroxide (H 2 O 2 ) from the peroxide storage 112 may be concentrated in hydrogen peroxide concentrator 114 or pumped directly into NO oxidation tower 113.
• the concentrator 114 is used to increase the concentration of H 2 O 2 from 70 percent to as high as 85 percent or more as required by the process. While a variety of methods are known for the concentration of hydrogen peroxide, examples particularly suited for use with embodiments of the invention may be found in U.S. Patent Application Serial No. 10/845,607, entitled “CONCENTRATION OF HYDROGEN PEROXIDE” and filed May 11, 2004.
• Oxidation tower 113 decomposes hydrogen peroxide into oxidative species that convert NO into NO 2 .
• the oxidized NO in the flue gas flows from the oxidation tower 113 to the NO ⁇ scrubber tower 115 where it is captured in an acidic hydrogen peroxide scrubber liquor.
• the concentration of hydrogen peroxide in the second scrubbing mixture ranges from 0.1 to 5 percent by volume and is controlled by a second hydrogen peroxide controller.
• the cleaned flue gas that exits from scrubber tower 115 passes into neutralizer 119, where base is added to neutralize any residual acid gases. Once neutralized, the cleaned flue gas exits through the exhaust stack as processed flue gas 152.
• an exhaust fan could be used in place at the outlet of the Neutralizer 119, if desired, to boost the clean and neutralized flue gas out of the exhaust stack as processed flue gas 152.
• ASTM methods D-1608 and D-1609 have been used to measure the concentration of NO ⁇ in the gas streams in early field tests of the emission control system. These methods were later modified to measure the nitrite and nitrate ions directly by ion chromatography. However, these methods required off-line analysis that was not practical to use in a continuous process.
• One optical method Fourier transform infrared, FTIR was used to measure the hydrogen peroxide concentration directly.
• the FTIR analytical method developed to analyze scrubber liquor samples, measured the hydrogen peroxide concentrations continuously with an attenuated total-reflectance (ATR) cell.
• a zinc sulfide ATR crystal was used for the alkaline solutions and an AMER ATR crystal was used for the acid solutions.
• This analytical method was useful for laboratory samples, it was not selected for the hydrogen peroxide controller.
• the analytical system used for the control system contains a unique process that controls the concentration of hydrogen peroxide. The process is controlled by a programmable logic controller (PLC) designed to measure the concentration of hydrogen peroxide and to add additional hydrogen peroxide as required to maintain the preset concentration.
• PLC programmable logic controller
• control system contains two commercial controllers, one for pH and the other to measure the concentration of sulfuric acid, nitric acid, or salts of these acids. These commercial controllers are used to maintain a target pH or concentration and to add reagents as required. Details of the design and operation of the control system are given in the following section.
• the block flow diagram for a hydrogen peroxide controller suited for use with embodiments of the invention is shown in Figure 2.
• the hydrogen peroxide PLC that controls the operations starts the first sequence by pulling a sample into the system from sample point 231 with pump 232 and pumping it through valve 233.
• the pH probe 247 and conductivity probe 248 are exposed to the sample before passing the sample into metallic filter 234 where a portion of the sample passes through the filter 234 and the remainder bypasses the filter 234 and washes the residues back to sample return 245.
• the filtrate that passed through filter 234 continues through valve 235, multiport valve 236, and sample loop 237. From sample loop 237 the sample returns to multiport valve 236, and then exits and returns back to sample return 245.
• the sequence of events described above serves to collect a sample from the sample point 231, filter the sample, fill the sample loop that has a known volume, and returns the unused sample to sample return 245.
• the metering pump 238 While the sample loop 237 is being filled, the metering pump 238 is pulls sodium hypochlorite from container 239 and injects a known volume into reaction cell 240 through multiport valve 236.
• the second sequence is triggered by the PLC, which sends a signal to rotate multiport valve 236 and pump a second quantity of sodium hypochlorite, but this time it is used to displace the sample from the sample loop 237, which is pumped into the reaction cell 240.
• the reaction of sodium hypochlorite with hydrogen peroxide produces water, sodium chloride, and oxygen, which causes an increase in pressure in the reaction cell that is sensed by the pressure transducer 241.
• Calibration data programmed into the PLC for pressure change as a function of hydrogen peroxide concentration is used to control the concentration of hydrogen peroxide in the system. If the measured concentration is below the set concentration, a pump is activated to transfer hydrogen peroxide from storage. The hydrogen peroxide pump stops, when the measured concentration is greater than the set concentration. This cycle is repeated continuously to maintain the set concentration of hydrogen peroxide. While the concentration is being measured, the filter 234 is back-flushed with water 243 through valve 244 to remove particulates captured by the filter 234. When the back-flush starts, valve 233 closes and pump 232 stops and the water 243 pushes through the filter 234 and back to the sample return 245.
• FIG. 3 shows the details of the reaction cell 240.
• the reaction cell body 351 has an internal chamber 352 that is attached to a gauge guard 353 that protects the pressure transducer 241. Sodium hypochlorite and the sample are pulled through sodium hypochlorite inlet 355 by metering pump 238. Once the reaction in the pressure cell is complete, it is discharged through valve 242 to sample waste 246.
• the reaction cell is fabricated preferably from a machinable corrosion-resistant polymer.
• Rosemont's model 0054 ⁇ H/ORP-08 pH controller and a model 306P-02010055 pH probe The pH probe is item 247 in Figure 2 and it is used to continuously measure the pH.
• the pH controller system has proportional algorithms that adjust the pump feed rate as the pH set- point is approached. For one embodiment, the pH is controlled to a level of between 7.0 and ⁇ 0.1 by adding abase, e.g., potassium hydroxide. The concentration of sulfuric acid, nitric acid, or salts of these acids, is controlled with the Rosemont model 1054B%l-99 controller.
• the conductivity probe model 228-02-21-54-61 is item 248 in Figure 2. Once calibrated for the specific ion used in the system, the proportional control algorithms adjust pumping rate for the base used to form the salts.
• the methods utilize hydrogen peroxide to reduce SO ⁇ and mercury (or other oxides-of-metal) emissions. Continuous concentration of hydrogen peroxide to levels approaching or exceeding propellant-grade hydrogen peroxide facilitates increased system efficiency.
• combustion flue gas streams can be treated for the removal of SO ⁇ and oxides-of-metal, while isolating useful byproducts streams of sulfuric acid and as well as solids for the recovery of the heavy metals.
• the methods and apparatus may also be extended to reduce NO ⁇ emissions.
• One of the significant advantages of the present invention is the fact that the process can be run continuously, with measuring and adjustments made in real time while the process is being performed.
• Computer monitoring can initiate flow changes of reagents in response to automatic measurements to maintain desired process conditions.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Environmental & Geological Engineering (AREA)
• Health & Medical Sciences (AREA)
• Biomedical Technology (AREA)
• Analytical Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Treating Waste Gases (AREA)

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• 2005
  • 2005-04-08 WO PCT/US2005/011864 patent/WO2005113116A1/en active Application Filing
  • 2005-04-08 CA CA002565750A patent/CA2565750A1/en not_active Abandoned
  • 2005-04-08 AU AU2005245336A patent/AU2005245336A1/en not_active Abandoned
  • 2005-04-08 MX MXPA06012988A patent/MXPA06012988A/es unknown
  • 2005-04-08 EP EP05734840A patent/EP1761325A1/de not_active Ceased

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