MXPA06012988A - Method and apparatus utilising hydrogen peroxyde to reduce sox, nox and heavy metal emissions. - Google Patents

Abstract

Methods and apparatus utilizing hydrogen peroxide are useful to reduce SOx and mercury (or other heavy metal) emissions from combustion flue gas streams. The methods and apparatus may further be modified to reduce NOx emissions. Continuous concentration of hydrogen peroxide to levels approaching or exceeding propellant-grade hydrogen peroxide facilitates increased system efficiency. In this manner, combustion flue gas streams can be treated for the removal of SOx and heavy metals, while isolating useful by-products streams of sulfuric acid as well as solids for the recovery of the heavy metals. Where removal of NOx emissions is included, nitric acid may also be isolated for use in fertilizer or other industrial applications.

Description

treat combustion gas streams. Brief Description of the Invention Methods and apparatus that use hydrogen peroxide to reduce SOx, NOx, and mercury or other metal oxide emissions are described herein. The continuous concentration of hydrogen peroxide (H202) at levels that approximate or exceed the propellant-grade hydrogen peroxide facilitates the higher efficiency of the system. By using methods and apparatuses according to the invention, combustion smoke streams can be treated to remove SOx, NOx and heavy metals, while currents of useful by-products of sulfuric acid and nitric acid are isolated as well as solids for the recovery of the heavy metals. The apparatus is modular and components can be added or removed depending on the specific requirements during a given recall operation. The invention also includes methods and apparatus for different purposes. Brief Description of the Drawings Figure 1 is a block diagram of an emission control system according to one 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. Figure 3 is a subsystem of a reaction vessel for hydrogen peroxide for use in accordance with one embodiment of the invention.

Detailed Description of the Invention In the following detailed description of the present embodiment, reference is made to the appended drawings that form a part thereof, and which is shown by way of illustration of the specific preferred embodiments in which the invention may be embodied. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is understood that other embodiments may be utilized and that logical, mechanical and chemical changes may be made without departing from the spirit and scope of the present invention. . It is noted that the drawings are not to scale unless a scale is indicated therein. The following detailed description, therefore, has not been taken in a limiting system and the scope of the present invention is defined only by means of the appended claims and their equivalents. The emission control systems according to the invention refer to environmental pollutants SOx, NOx, and heavy metals. These systems are designed to control the emissions of these environmental pollutants to levels established by the EPA. This emission control system provides a method based on hydrogen peroxide to reduce SOx, NOx and metal oxide and metal oxide emissions from combustion sources to acceptable levels as established by the Environmental Protection Agency. . In addition, the useful by-product streams of sulfuric acid, nitric acid, salts of these acids and raw materials for the production of metal oxides. Figure 1 is a block diagram of an emission control system according to an embodiment of the invention. The process begins with a gas stream, such as the raw smoke 150 after the particles have been removed. There are several options for this design and the stages can be omitted or alternated and the unit operations can be substituted for the overall process depending on the requirements of the installation. These alternate stages are mentioned during the description of the process. The first step of the process is to use a cooling and washing chamber 102 to cool and remove some of the particles in the incoming smoke 150. The water from the processing of the chamber 103 is provided to the chamber 102. The particles, the water Washings are sent from the chamber 102 to the settling and cooling pond 104. The water is then recirculated from the pond 104 back to the water chamber 103. The washed smoke is fed from the washing chamber 102 to a water tower. purification 105 to remove SOx and / or heavy metals. The purification tower 105 uses hydrogen peroxide from the storage of peroxide 112 to oxidize the sulfurous acid (H2S03) to sulfuric acids (H2SO4) to prevent the re-emission of SO2. The storage of hydrogen peroxide 112 preferably provides an aqueous hydrogen peroxide of about 50% to 70% by volume, and more preferably at about 70% by volume. As the pH of the scrubber liquor is reduced due to the formation of sulfuric acid, most of the heavy metal oxides, including Hg, etc. disperse as metal oxides and / or dissolved hydroxides are converted to sulfates. The particles are dissolved remnants and the insoluble sulfates are removed with a centrifuge 106, for example a centrifuge with a solid container. The centrifuge 106 continuously removes the solids and circulates the refining liquor through a valve 109 back to the scrubbing tower 105 for continuous purification and cleaning of the smoke, when the scrubber liquor (sulfuric acid) reaches the desired concentration , the clean waste liquor is discharged from the centrifuge through the valve 110 then drained to the sulfuric acid store 111, which can then be used as fertilizer or for industrial uses. The solids of the centrifuge 106 are discharged from the container of recycled solids 107. The soluble metals and the metal oxides present in the liquor of the clean scrubber can be removed as insoluble solids after the neutralization of the sulfuric acid which can be carried out for example during the production of the fertilizer. The concentration of hydrogen peroxide in the first purification mixture is maintained at a predetermined level, for example 0.1 to 5 volume percent. The concentration of the first purification mixture can be maintained using a hydrogen peroxide controller of the type described below. Additional detail of that controller can be found in U.S. Pat. No. 6,039,783 published March 21, 2000 by Lueck et al. and U.S. Patent No. 6,641,638 published November 4, 2003 by Lueck et al. When the smoke comes out of the scrubber 105 it contacts the denebulizer 108, in which the mist containing sulfuric acid is unified. The unified mist is returned to the scrubber 105 and the sulfur-free smoke flows to the neutralizer 118. The waste gas is neutralized with a base in the neutralizer 118, and then the clean and neutralized smoke exits through the exhaust pipe. Alternatively, the exhaust fan could be used in place at the outlet of the neutralizer 118, if desired to expel the clean and neutralized smoke out of the exhaust pipe in the form of processed smoke 152. When or if the removal of the NOx emissions, the neutralized smoke of the neutralizer 118 flows to an oxidation tower 113, where the nitric oxide NO) is oxidized to form nitrogen dioxide (N02). Alternatively, the smoke can be passed directly from the denebulizer 108 to the oxidation tower of NO 113 for subsequent neutralization, removed to the neutralizer 118. Hydrogen oxide (H202) from the storage of peroxide 112 can be concentrated in the hydrogen peroxide concentrator 114 or pumping directly into the oxidation tower of NO 113. The concentrator 114 is used to increase the concentration of H202 from 70 percent and up to 85 percent or more as the process requires. Although a variety of methods are known for the concentration of hydrogen peroxide, examples particularly suitable for use with the embodiments of the invention can be found in U.S. patent application no. 10 / 845,607, entitled "CONCENTRATION OF HYDROGEN PEROXIDE" filed on May 11, 2004. Oxidation tower 113 decomposes hydrogen peroxide into oxidative classes that convert NO to N02. An example of this process, the catalytic decomposition of hydrogen peroxide, is described in US Patent no. 6,793,903. The NO oxidized in the smoke flows from the oxidation tower 113 to the NOx purification tower 115 where it is captured in the liquor of the acid hydrogen peroxide scavenger. The concentration of hydrogen peroxide in the second blending mixture varies from 0.1 to 5 volume percent and is controlled by a second hydrogen peroxide controller. The clean smoke leaving the purifying tower 115 passes to the neutralizer 119, where base is added to neutralize any residual gas. Once neutralized, clean smoke exits through the exhaust in the form of processed smoke 152. Alternatively, an exhaust fan may be used in its place at the outlet of neutralizer 119, if desired to expel the smoke out of the exhaust in the form of Processed smoke 152. ASTM methods D-1608 and D-1609 have been used to measure NOx concentration in gas streams in previous field tests of the emission control system. These methods were then modified to measure the nitrite and nitrate ions directly by means of ion chromatography. However, those methods required for offline analysis are not practical for use in a continuous process. An optical method (infrared Fourier transform, FTIR) was used to directly measure the concentration of hydrogen peroxide. The FTIR analytical method was developed to analyze the liquor samples from the scrubber, the concentrations of hydrogen peroxide were measured continuously with a cell of attenuated total reflectance (ATR). An ATR zinc sulfide crystal was used for the alkaline solutions and a AMTIR ATR crystal is used for the acid solutions. Although 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 is initially described in US Patent no. 6,039,783, contains a unique process that controls the concentration of hydrogen peroxide. The process is controlled by means of a programmable logic controller (PLC) designed to measure the concentration of hydrogen peroxide and add additional hydrogen peroxide required to maintain the predetermined concentration. In addition to the hydrogen peroxide controller, the control system contains two commercial controllers, one for the pH and the other for measuring the concentration of sulfuric acid, nitric acid, or salts of those acids. These commercial controllers are used to maintain an objective pH or concentration and add the required reagents. Details of the design and operation of the system or control are given in the next section. The block flow diagram for a hydrogen peroxide controller suitable for use with the embodiments of the invention is shown in Figure 2. The hydrogen peroxide PLC which controls the operations initiates the first sequence by introducing a sample into the system from the same point 231 with the pump 232 and pump it through the valve 233. The pH probe 247 and the conductivity probe 248 are exposed to the sample before passing the sample to a metal filter 234 in which a portion of the sample passes through the filter 234 and the remainder avoids the filter 234 and drags the waste back to the return of the sample 245. The filtrate passing through the filter 234 continues through the valve 235, of the multiport valve 236, a sample circuit 237. From the sample circuit 237 the sample returns to the multi-port valve 236, and then exits and returns to the return of the sample 245. The sequence of events described above serves to recollect Eject a sample from sample point 231, filter the sample, fill the sample circuit that has a known volume, and return the unused sample to the return of sample 245. While the sample 237 circuit is being filled, the pump dosing station 238 extracts sodium hypochlorite from content 239 and injects a known volume into reaction cell 240 through a multiport valve 236. The second sequence is triggered by the PLV, which transmits a signal to rotate the multiport valve 236 and pumps a second quantity of sodium hypochlorite, but this time it is used to displace the sample from the sample circuit 237, which is pumped into the reaction cell 240. The reaction of sodium hypochlorite with hydrogen peroxide produces water, sodium chloride and oxygen causing an increase in pressure in the reaction cell that is being recorded by the pressure transducer 241. The calibration data programmed in the PLC for the pressure changes as a function of the peroxide concentration of the Hydrogen are 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 the hydrogen peroxide from the store. The hydrogen peroxide pump stops, when the measured concentration is greater than the set concentration. This cycle is repeated continuously to maintain the fixed concentration of hydrogen peroxide. While the concentration is being measured, the filter 234 is rinsed from the back with water 243 through the valve 244 to remove the particles captured by the filter 234. When the rinsing starts from behind, the valve 233 is closed and the pump 232 stops and the water is pushed 243 through the filter 234 and back to the sample return 245. In addition, the contents of the reaction cell can be expelled through the valve 242 to the sample waste 246 at that time. Once the back rinse has finished, the PLC returns the process to the first sequence and the sampling process starts again. Figure 3 shows the details of the reaction cell 240. The body of the reaction cell 351 has an internal chamber 352 which is attached to a calibration shield 353 which protects the pressure transducer 241. Sodium hypochlorite and sample they are extracted through the inlet for sodium hypochlorite 355 by means of the dosing pump 238. Once the reaction in the pressure cell has been completed, it is discharged through the valve 242 to sample disposal 246. The The reaction is preferably manufactured from a corrosion-resistant polymer that can be processed mechanically. While the above brief description of hydrogen peroxide concentration control is included to assist the reader, a more detailed description is provided in U.S. Pat. No. 6,039,783 and 6,641,638 as previously indicated. The pH can be controlled with commercially recognized devices, such as the Rosemont model 0054pH / ORP-08 pH controller and a model pH probe 306P-02010055. The pH probe is article 247 in Figure 2 and is used to continuously measure the pH. The pH controller system has proportional algorithms that adjust the feed rate of the pump when it approaches the pH reference value. For a modality, the pH is controlled at a level between 7.0 and >; 0.1 adding a base, for example potassium hydroxide. The concentration of sulfuric acid, nitric acid, or salts of these acids, is controlled with the model controller 1054N% 1-99 of Rosemont. The conductivity probe model 228-02-21-54-61 is the article 248 in figure 2. Once calibrated for the specific ion used in the system, the proportional control algorithms adjust the pump rate for the base used for form the salts. CONCLUSION Methods and devices to control emissions. The methods use hydrogen peroxide to reduce SOx emissions and mercury (or other metal oxides). The continuous concentration of hydrogen peroxide at levels that approximate or exceed the propellant-grade hydrogen peroxide facilitates the system's highest efficiency. By using methods and apparatus according to the invention, combustion smoke streams can be treated to remove SOx and metal oxides, while currents of useful sulfuric acid by-products are isolated as well as solids for the recovery of heavy metals. The methods and apparatus can also be extended to reduce NOx emissions. One of the important advantages of the present invention is the fact that the processes can be performed continuously, while measurements and adjustments are made in real time while the process is being carried out. Computer monitoring can initiate changes in the flow of reagents in response to automatic measurements to maintain the desired process conditions.

Although specific embodiments have been illustrated and described, those skilled in the art will appreciate that any arrangement which is calculated to obtain the same purpose can substitute for the specific embodiment shown. This application is intended to cover those adaptations or variations of the present invention. It is therefore manifestly intended that this invention be limited only by the claims and their equivalents.

Claims (24)

1. A method for treating a gas stream to remove at least sulfur oxides, the method consists in: purifying a gas stream with a first hydrogen peroxide solution, producing a first purification liquor; regulate a flow of the first hydrogen peroxide solution, and remove a stream of by-products containing sulfuric acid after achieving a desired concentration of sulfuric acid in the first liquor of the scrubber. The method of claim 1, further comprising: after debugging the gas stream with the first hydrogen peroxide solution, oxidizing the gas stream using a second hydrogen peroxide solution in an oxidation process adapted to convert nitric oxide to nitrogen dioxide; and after oxidizing the gas stream, purging the gas stream with a third hydrogen peroxide solution and removing a stream of by-product containing nitric acid; wherein the second hydrogen peroxide solution is concentrated to a level of about 75% or more by volume before being used in the oxidation of the gas stream. The method of claim 1, wherein the purging of the gas stream with the first hydrogen peroxide solution further comprising: feeding a gas stream in a scrubber; feed the first hydrogen peroxide solution in the scrubber; remove solids from the first liquor of the scrubber; and recycling the first scrubber liquor in the scrubber with the first hydrogen peroxide solution. The method of claim 3, further comprising: taking a sample of the first hydrogen peroxide solution and the first scrubber liquor to search for a level of hydrogen peroxide; and controlling the level of hydrogen peroxide in the mixture so that it is at least at a predetermined level. The method of claim 3, wherein the removal of the solids consists in centrifuging the resulting scrubber liquor. The method of claim 2, wherein the purging of the gas stream with the third hydrogen peroxide solution further comprises: feeding the gas stream to a scrubber; feed a third hydrogen peroxide solution to the scrubber; removing the solids from the second scrubber liquor; and recycling the second scrubber liquor in the scrubber with the third hydrogen peroxide solution. The method of claim 6, further comprising: taking a sample of the third hydrogen peroxide solution and the first scrubber liquor to search for a level of hydrogen peroxide; and controlling the level of hydrogen peroxide in the mixture so that it is at least at a predetermined level. The method of claim 7, wherein the predetermined level of hydrogen peroxide is an amount necessary to provide a stoichiometric excess of hydrogen peroxide for reaction with the gas stream. 9. A process for converting vapor streams containing at least one sulfur oxide to a liquid sulfur oxy acid (s) composition, which consists of directing a vapor stream containing a sulfur oxide to a first sulfur oxide zone. Contact; contacting the steam stream with water to form sulfur oxy-acid (s) of at least one sulfur oxide; directing the acid (s) to a second stream to a second contact zone; exposing the second stream to hydrogen peroxide which is present within the second contact zone to convert at least some of the sulfuric acid oxides (s) other than the sulfuric acids present within the second stream to a sulfate ion; taking samples of the current within the second contact zone to determine the relative amount of hydrogen peroxide within the second contact zone; and adding hydrogen peroxide to the second contact zone when the sampling determines that it is less than the excess hydrogen peroxide in the second stream. The process of claim 9, wherein the samples are removed from the second contact zone, the pH of the samples is determined, and the pH of the materials within the second contact zone is adjusted to the range of 7.0 a >; 0.1. The process of claim 9, wherein the predetermined excess of hydrogen peroxide is at least 0.1% by weight of the second stream. 1

2. A process for converting an aqueous stream containing sulfur oxide products into a useful liquid chemical composition consisting of: directing the current to a first contact zone; exposing the stream to hydrogen peroxide which is present within the first contact zone to convert at least some of the sulfuric acid oxides (s) other than those in the form of sulfuric acid present to sulfate ions; add hydrogen peroxide to the first contact zone when the sampling determines that it is less than an excess of hydrogen peroxide in the solution; and adding a solution containing potassium hydroxide or other base to the first contact zone to maintain a pH between 7.0 and < 0.1 within the first contact zone to form a solution of a sulfuric acid salt. 1

3. A process for converting vapor streams containing at least one sulfur oxide to a useful liquid chemical composition, which consists of: directing a vapor stream containing at least one sulfur oxide to a first contact zone; contacting the steam stream with water to form sulfur oxides (s) of at least one sulfur oxide; directing the acid (s) to a second stream to a second contact zone; exposing the second stream to the hydrogen peroxide that is present within the second contact zone to convert at least some of the sulfuric acid oxides (s) differently from the sulfuric acid present within the second stream to a sulfate ion; add hydrogen peroxide to the second contact zone when the sampling determines that it is less than an excess of hydrogen peroxide in the second stream; and adding a solution containing potassium hydroxide or another base to the second stream to maintain a pH between 7.0 and < 0.1 within the second stream within the second contact zone to form a solution of a sulfuric acid salt. 1

4. A system for removing at least sulfur oxides from a combustion smoke to a system consisting of: a coupled water wash to receive a stream of raw smoke; a first scrubber coupled to receive an outlet gas stream from the water wash and coupled to receive a first hydrogen peroxide solution; a centrifuge coupled to receive a first scrubber liquor from the first scrubber and provide a recycled scrubber liquor to the first scrubber after removing solids from the first scrubber liquor; a control system for maintaining a desired concentration of hydrogen peroxide in the recycled scrubber liquor and maintaining a desired concentration of sulfuric acid in the recycled scrubber liquor; a demister coupled to receive an outlet gas stream from the first scrubber: and a neutralizer coupled to receive an offgas stream from the de-nebulizer. The system of claim 14, further comprising: an oxidation tower coupled to receive a gas stream from the de-aerator or neutralizer, and to receive a second hydrogen peroxide solution from the hydrogen peroxide concentrator; a second scrubber coupled to receive an off-gas stream from the oxidation tower and coupled to receive a third hydrogen peroxide solution and a recycled liquor from the second scrubber; and a neutralizer coupled to receive an output gas stream from the second scrubber. 16. A method to treat a gas stream to remove the heavy metal components and at least sulfur oxides, the method consists of: feeding the gas stream to the scrubber; feed a first hydrogen peroxide solution to the scrubber; debugging the gas stream with the first hydrogen peroxide solution, producing a first scrubber liquor containing sulfuric acid and insoluble oxides of the heavy metal components; recycle the first scrubber liquor to the scrubber to obtain the desired concentration of sulfuric acid; and removing the solids from the first scrubber liquor, wherein the solids contain at least a portion of the insoluble oxides of the heavy metal components. The method of claim 16, further comprising: neutralizing a position of the first scrubber liquor after removing the solids, wherein the first scrubber liquor further contains soluble forms of the heavy metal components and / or soluble oxides of heavy metal components and wherein the neutralization of the portion of the first scrubber liquor forms second solids of the soluble forms of the heavy metal components and / or the soluble oxides of the heavy metal components; and removing the second solids from the first neutralized scrubber liquor. The method of claim 16, further comprising: maintaining the desired concentration of hydrogen peroxide in the first scrubber liquor by regulating the flow of the first hydrogen peroxide solution; and removing a stream of by-products containing sulfuric acid after obtaining the desired concentration of sulfuric acids in the first scrubber liquor. The method of claim 18, further comprising: taking a sample of the first hydrogen peroxide solution and the first recycled scrubber liquor to search for a level of hydrogen peroxide; and controlling the level of hydrogen peroxide in the mixture so that it is at least at a predetermined level. The method of claim 16, wherein the removal of the solids consists in centrifuging the resulting scrubber liquor. 21. A method to treat a gas stream to remove mercury and at least sulfur oxides, the method consists of: feeding the gas stream to a scrubber; feeding a first hydrogen peroxide solution to the scrubber; purify the gas stream with the first hydrogen peroxide solution, thereby producing a first scrubber liquor containing sulfuric acid and insoluble mercury oxides; recycle the first scrubber liquor to the scrubber to obtain a desired concentration of sulfuric acid; and centrifuging the first scrubber liquor to remove at least a portion of the insoluble mercury oxides. 22. The method of claim 21, further comprising: neutralizing a portion of the first scrubber liquor after centrifugation, the first scrubber liquor containing the soluble forms of mercury and / or soluble oxides of mercury and in which the neutralization of the portion of the first liquor of depurated forms second solids of the soluble forms of mercury and / or soluble oxides of mercury; and removing the second solids from the first neutralized scrub liquor. The method of claim 21, further comprising: maintaining a desired level of concentration of hydrogen peroxide in the first scrubber liquor by regulating the flow of the first hydrogen peroxide solution; and removing a stream of by-products containing sulfuric acid after reaching the desired concentration of sulfuric acid in the first scrubber liquor. The method of claim 23, further comprising: taking a sample of the first hydrogen peroxide solution and the first recycled scrubber liquor to search for a level of hydrogen peroxide; and controlling the level of hydrogen peroxide in the mixture so that it is at least at a predetermined level.