TREATMENT SYSTEM AND TREATMENT METHOD FOR REMEDIATING CONTAMINANTS, INCLUDING CARBON BASED CONTAMINANTS, IN GASSES

Abstract

A treatment process for removing and/or remediating contaminants in a contaminated gas, includes generating vapor containing hydroxide ions, mixing the vapor containing hydroxide ions with a gas containing carbon dioxide (CO.sub.2), and allowing the mixture of the vapor containing hydroxide ions and the gas to react. The step of generating vapor containing hydroxide ions involves boiling an aqueous solution containing ammonium hydroxide. The aqueous solution containing ammonium hydroxide can be enhanced to a higher hydroxide concentration and a higher pH by dissolving at least one other hydroxide compound in the aqueous solution.

Claims

1. A treatment process for removing and/or remediating contaminants in a contaminated gas, comprising steps of: generating vapor containing hydroxide ions; mixing the vapor containing hydroxide ions with a gas containing carbon dioxide (CO.sub.2); and allowing the mixture of the vapor containing hydroxide ions and the gas to react.

2. The treatment process according to claim 1, wherein the step of generating vapor containing hydroxide ions involves boiling an aqueous solution containing ammonium hydroxide.

3. The treatment process according to claim 2, wherein the aqueous solution containing ammonium hydroxide also contains at least one other hydroxide compound.

4. The treatment process according to claim 1, including a further step of pre-treating the gas to separate a portion of the exhaust gas containing a larger proportion of the carbon dioxide from another portion of the exhaust gas containing a smaller proportion of the carbon dioxide; and the mixing step involves mixing the vapor containing hydroxide ions with exhaust gas with the separated portion of the exhaust gas containing a larger proportion of carbon dioxide.

5. The treatment process according to claim 4, wherein the pre-treatment step involves subjecting the gas to a magnetic field.

6. The treatment process according to claim 1, wherein the gas is exhaust gas generated by combustion of a hydrocarbon based fuel.

Description

DISCLOSURE OF THE INVENTION

[0010] An object of the present invention is to satisfy the discussed need in the art.

[0011] The present inventor has studied at length the treatment of various gasses, including combustion gasses from hydrocarbon based fuels, and has discovered new treatment systems and treatment processes which are far more effective, efficient and economically practical than the conventionally known treatment systems and processes for remediating and/or removing essentially all types of contaminants, including carbon dioxide, in combustion gasses and other gasses down to significantly reduced levels in a very efficient and cost effective manner.

[0012] A first discovery made by the present inventor for treatment of the various gasses to remediate or remove CO.sub.2 and other undesirable contaminants, including carbon monoxide (CO), carbon dioxide (CO.sub.2), nitrogen based oxides (NO.sub.x), sulfur based oxides (SO.sub.x), is that the conventionally known treatment systems and processes are particularly inefficient because they use aqueous liquid solutions for treating the gasses, e.g., the gasses are passed/bubbled up through a quantity of the aqueous solution contained in a reaction tower or column. The inventor has determined that the liquid-gas interaction in such systems and processes is inherently inefficient for a number of reasons, e.g., there is limited amount of contact between the chemical reactants in the liquid aqueous solutions and gaseous contaminants in the contaminated gasses as the gasses bubble up through the aqueous solutions, so that it is particularly challenging to efficiently remove contaminants from the gasses based on liquid to gas reactions.

[0013] Previously, the present inventor has discovered that hydroxide compounds, e.g., sodium hydroxide (NaOH) and potassium hydroxide (KOH), may be added to aqueous water wash solutions for removing various contaminants, including hydrogen sulfide (H.sub.2S) and CO.sub.2, from various gasses, including natural gas and combustion gasses from hydrocarbon based fuels, e.g., see US Patent Pub. 2022/0411701 A1. In comparison to the Solvay process and the other conventionally known processes used to remove CO.sub.2 in gasses, including combustion gasses from hydrocarbon based fuels, the inventor's previously proposed treatment processes involving hydroxide containing water wash solutions are significantly more effective and cost efficient for removing contaminants such as H.sub.2S and CO.sub.2 from such gasses, but the treatment processes involving the water wash solutions still have inefficiencies based on the liquid-gas interactions in such processes.

[0014] The present inventor has further studied this, and has now discovered that it is possible to efficiently generate large volumes of hydroxide containing vapors that can be combined with various gasses for remediating the gasses or components of the gasses. For example, the hydroxide containing vapors generated according to the invention can be combined with the combustion gasses from hydrocarbon based fuels, to achieve a more efficient and cost effective remediation and/or removal of some of the undesirable gasses, including CO, CO.sub.2, NO.sub.x and SO.sub.x, in the combustion gasses because this involves vapor to vapor contact between the undesirable gasses and the hydroxide vapors. Particularly, the inventor has discovered that it is possible to efficiently generate large volumes of hydroxide containing vapors using an ammonium hydroxide (NH.sub.4OH) solution prepared by dissolving ammonia (NH.sub.3) in water. Solutions of ammonium hydroxide come in different concentrations, but a saturated solution of ammonium hydroxide may contain about 25% to 28% wt ammonia and boils at about 98 F. The present inventor has found that by boiling a saturated solution of ammonium hydroxide, the vapors that are released from the boiling solution contain hydroxide and when these vapors are added to the various gasses, e.g., a stream of the hydroxide vapors is added into a flowing stream hydrocarbon combustion gasses, the hydroxide containing vapors quickly and intimately mix into the gasses and quickly remediate the levels of many of the contaminants in the gasses, including CO, CO.sub.2, NO.sub.x and SO.sub.x, down to very low levels, e.g., down to one part per million or less. The CO.sub.2 in the combustion gasses reacts with the hydroxide in the vapors and form ammonium bicarbonate particles, which drop out of the gaseous mixture and can be separated, removed and ultimately sold commercially. Reactions of CO.sub.2 with ammonium hydroxide are as follows:

NH.sub.3+H.sub.2O.fwdarw.NH.sub.4OH

CO.sub.2+H.sub.2O.fwdarw.H.sub.2CO.sub.3

NH.sub.4OH+H.sub.2CO.sub.3.fwdarw.NH.sub.4CO.sub.3+H.sub.2O

[0015] The inventor has determined that one liter of a saturated solution of ammonium hydroxide can generate a much larger volume of the hydroxide containing vapors, e.g., up to eighty two (82) ft.sup.3 of the vapors, although as the ammonium hydroxide solution boils it will contain less and less ammonium hydroxide and the amount of hydroxide in the vapors will be correspondingly reduced. Again, the hydroxide vapors may be easily and quickly combined with the gasses being treated, and because of the gaseous nature of the hydroxide vapors there is much greater contact achieved between the hydroxide in the vapors and the contaminants in the gasses than is possible by bubbling the contaminated gasses through a relatively large amount of a treatment liquid contained in a tower or column as is done in the conventionally known processes. The difference between vapor to vapor contact and liquid to vapor contact for these reactions is very significant. For example, a given amount of combustion gasses from hydrocarbon based fuels can be more efficiently remediated using comparatively small amount of the saturated aqueous solution of ammonium hydroxide, which is boiled an turned into hydroxide containing vapors, as compared to the conventionally known treatment processes which rely on liquid to vapor contact involving a relatively large amount of a treatment liquid disposed in a reactor tower or column. The conventional processes for removing CO.sub.2 involving liquid to vapor contact, such as the Solvay process, may remove the CO.sub.2 at a rate of about 1 mole of key reactant, e.g., ammonia, per mole of CO.sub.2 that is removed. However, in experiments conducted by the present inventor using this new treatment process involving hydroxide containing vapors from a boiled ammonium hydroxide solution he has achieved CO.sub.2 removal rates of up to fifteen (15) moles of CO.sub.2 per mole of the ammonium hydroxide solution.

[0016] While there are many other hydroxide compounds besides ammonium hydroxide, e.g. sodium hydroxide (NaOH) and potassium hydroxide (KOH) are two hydroxides used very extensively everyday in many different commercial processes, ammonium hydroxide is uniquely different from these other hydroxide compounds based on its relatively low boiling point and because it is generated specifically as an aqueous solution using ammonia and water in which the water itself becomes the source of the hydroxide ion. Other hydroxides such as sodium hydroxide and potassium hydroxide come in solid forms containing little or no water at standard temperature and pressure (STP), as well as in an aqueous solutions in various concentrations. Also, these other hydroxide compounds are much stronger bases than ammonium hydroxide and have much higher pKa values than does ammonium hydroxide. However, aqueous solutions of these other hydroxide compounds boil at temperatures much higher than 100 F., such that it would require much more heat and energy to generate hydroxide vapors using these other hydroxide compounds in comparison to ammonium hydroxide.

[0017] An experiment conducted by the inventor provided the following results. In this experiment a saturated solution of ammonium hydroxide was prepared by dissolving ammonia (NH.sub.3) in water at a concentration of about 28 wt % ammonia and this was boiled at about 100 F. or 37.8 C. to generate ammonium hydroxide vapors. The inventor has determined that for treating pure (100%) CO.sub.2 gas with the ammonium hydroxide vapors according to the present invention, an appropriate dosage rate is 1 ml of the saturated solution of ammonium hydroxide which when boiled produces a sufficient amount of ammonium hydroxide vapors to treat one liter of pure (100%) CO.sub.2. Expanding this out to larger volumes, one US gallon of the saturated ammonium hydroxide solution can produce sufficient ammonium hydroxide vapors to treat about 3,220 ft.sup.3 or 91200 liters of pure CO.sub.2 gas, or to treat about 53,660 ft.sup.3 of a gas mixture containing 6% CO.sub.2 gas. Further expanding, twenty US gallons of the saturated ammonium hydroxide solution can produce sufficient ammonium hydroxide vapors to treat about 1,072,000 ft.sup.3 of a gas mixture containing 6% CO.sub.2 gas, which is the equivalent of 5000 lbs or 2.5 tons of CO.sub.2. The reaction of ammonium hydroxide and CO.sub.2 produces ammonium bicarbonate NH.sub.4CO.sub.3 and water. The ammonium bicarbonate can be recovered and sold commercially.

[0018] In summary treatment of CO.sub.2 using a saturated solution of ammonium hydroxide was prepared by dissolving ammonia (NH.sub.3) in water at a concentration of about 28 wt % ammonia and boiled at about 100 F. or 37.8 C. to generate ammonium hydroxide vapors, is as follows: [0019] 1 cubic ft=28,316 liters [0020] Use 1 liter/hr @ 1,000,000 ppm of CO.sub.2 (pure CO.sub.2 gas) [0021] 1/16 of 100 milliliters [0022] Dosing rate: ease of use 1 ml/24 liters of pure CO.sub.2
So everyday 24 liters of gas is mitigated by 1 ml of the saturated ammonium hydroxide solution, And 1 gallon of saturated ammonium hydroxide (NH.sub.4OH) solution mitigates about 91200 liters or 3.22 MCF (1000 ft.sup.3) CO.sub.2 @ 1,000,000 ppm (pure CO.sub.2 gas). [0023] 1 gallon=53.66 MCF @ 60,000 ppm (6 vol % CO.sub.2 gas) [0024] 10 gallons=536.6 MCF @ 60,000 ppm (6 vol % CO.sub.2 gas) [0025] 20 gallons=1,072 MCF @ 60,000 ppm (6 vol % CO.sub.2 gas) [0026] 5,000 lbs CO.sub.2 (2.5 tons) [0027] 1,000,000 ft.sup.3 containing 1 vol % CO.sub.2 (10,000 ppm)=1301 lbs of CO.sub.2 [0028] Currently Ammonium Hydroxide solution costs about $1.45/gallon [0029] 1 gallon of saturated ammonium hydroxide solution remediates17.4 lbs CO.sub.2
Which equates to $0.08 cents/LBS of CO.sub.2 cost, excluding the value of the ammonium bicarbonate produced and recovered.

[0030] Another discovery by the inventor, is that it is possible to enhance an ammonium hydroxide aqueous solution such that it becomes a stronger base with higher pKa and can generate more hydroxide vapors by adding one or more other hydroxide compounds to the ammonium hydroxide solution, and that the enhanced ammonium hydroxide solution can still be readily boiled at relatively low temperatures to generate hydroxide containing vapors for use in treating various gasses such as the combustion gasses from hydrocarbon based fuels. For example, a quantity of one or more other hydroxide compound(s), such as sodium hydroxide and potassium hydroxide, in solid form may be dissolved into the ammonium hydroxide solution, or a quantity of an aqueous solution of such hydroxide compound(s) may be combined with the ammonium hydroxide solution. Also, a chelating agent such as ethylenediaminetetraacetic acid (EDTA) may be added in a small amount, e.g., 0.1 to 2.0 wt %, to help dissociate the hydroxide compound(s) other than ammonium hydroxide. This can result in precipitation of salts from the aqueous solution, while the OH.sup. radicals from the other hydroxide compound(s) enhance the aqueous solution. Generally, all hydroxide compounds may be used provided they can be dissolved or dispersed in the aqueous ammonium hydroxide solution. Some typical hydroxide compounds that may be used in the new treatment compositions include sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), magnesium hydroxide (Mg(OH).sub.2), and manganese hydroxide (Mn(OH).sub.2, Mn(OH).sub.4). However, NaOH and KOH have lower cost than the other hydroxides and if used may make the composition and treatment processes using the composition more economically advantageous. A saturated solution of ammonium hydroxide that has been enhanced with sodium hydroxide and/or potassium hydroxide will produce vapors of these other hydroxides as well as vapors of the ammonium hydroxide, all of which will react with CO.sub.2 and other gasses, such as those contained in the combustion gasses of hydrocarbon based fuels. The reactions of CO.sub.2 with sodium hydroxide and potassium hydroxide are as follows.

2NaOH(s)+CO.sub.2(g).fwdarw.Na.sub.2CO.sub.3(aq)+H.sub.2O(l);

2KOH+CO.sub.2.fwdarw.K.sub.2CO.sub.3(aq)+H.sub.2O(l).

[0031] In an experiment, the inventor combined a saturated aqueous ammonium hydroxide solution containing about 25 wt % ammonia and an aqueous solution containing 45 wt % potassium hydroxide at a ratio of 3:1 ammonium hydroxide solution to potassium hydroxide solution. With this mixture the pH increased to 14.77 from a pH of 10.65 for the saturated solution of ammonium hydroxide. The combined solution boiled at about 112-115 F. and generated hydroxide containing vapors similar to boiling a saturated solution of just ammonium hydroxide. However, the amount of hydroxide ions in the vapor from the combined solution was significantly greater than the amount of hydroxide ions generated by boiling the saturated ammonium hydroxide solution. The hydroxide vapors generated in this manner were used to treat gasses generated by combusting natural gas, i.e., by combining/mixing the hydroxide vapors with the combustion gasses from natural gas. Initially, the combustion gasses contained about 10% volume CO.sub.2, but treatment with the hydroxide vapors according to the present invention reduced the CO.sub.2 content in the combustion gasses to less than 5 ppm. Correspondingly, in the inventor's new vapor to vapor treatment process a given amount of the combined hydroxide solutions was effective for remediating contaminants in a greater volume of the combustion gasses from hydrocarbon based fuels, including CO.sub.2, in comparison to using the same given amount of saturated ammonium hydroxide solution.

[0032] The inventor has also determined that when treating the combustion gasses from hydrocarbon based fuels using his new vapor to vapor treatment process in a continuous manner, e.g., hydroxide containing vapors from a boiled mixed hydroxide solution or a saturated ammonium hydroxide solution are introduced into a pipeline through which the combustion gasses from hydrocarbon based fuels are flowing, it is possible to control and adjust the amount of hydroxide containing vapor being generated and introduced into the pipeline based on the temperature at which the solution is boiled. For example, while a saturated ammonium hydroxide solution may boil at 98 F. and a 3:1 mixed solution of ammonium hydroxide and potassium hydroxide may boil at 112-115 F., the temperatures to which these solutions are heated may be increased above these minimum boiling points. Further, the particular formulation of a mixed hydroxide solution may be adjusted by adding more or less of other hydroxide(s) to the saturated ammonium hydroxide solution to raise or lower the boiling point of the mixed solution. The amount of hydroxide containing vapors may be adjusted based on the levels of contaminants, including CO.sub.2, in the combustion gasses and/or according to a desired level of remediation of the contaminants in the combustion gasses.

[0033] According to another discovery by the present inventor, it is possible to separate or isolate various contaminants in the combustion gasses from hydrocarbon based fuels based on magnetism, which can be advantageous if there is interest in primarily remediating only select contaminants in the combustion gasses, such as CO.sub.2 for which governments give carbon credits. Through research and experimentation the inventor has discovered that CO.sub.2 is a stable diamagnetic molecule with paired electrons and that when CO.sub.2 is exposed to a magnet the CO.sub.2 will be repelled away from the magnet. On the other hand, the inventor has discovered that NO.sub.x, which is a large component of the combustion gasses from hydrocarbon based fuels, is less stable than CO.sub.2 because it is paramagnetic and will be attracted by a magnet. Thus, if there is interest in primarily remediating CO.sub.2 in the combustion gasses from hydrocarbon based fuels, the inventor's new vapor to vapor treatment process can be made more efficient and cost effective by isolating the CO.sub.2 and/or removing the NO.sub.x from the combustion gasses and then treating only the CO.sub.2 which has been isolated or treating the combustion gasses from which the NO.sub.x has been removed. This reduces cost of the treatment process not only because it is possible to treat a much smaller volume of the combustion gas is being treated, and also because none of the hydroxide containing vapor is used to remediate the NO.sub.x. Thus, for example, a flowpath for the combustion gasses from hydrocarbon based fuels may be fitted with magnet(s) and/or electromagnet(s) such that one fraction of the exhaust gas containing a larger proportion of CO.sub.2 may be directed by the magnet(s) to flow into one secondary flowpath and another fraction of the exhaust gas containing a smaller proportion of CO.sub.2 may be directed by the magnet(s) to flow into another secondary flowpath, and only the fraction of the exhaust gas containing the larger proportion of CO.sub.2 may be treated using hydroxide containing vapors according the inventor's new treatment process.

[0034] The foregoing description is given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications within the scope of the invention may be apparent to those having ordinary skill in the art and are encompassed by the claims appended hereto.