IL103153A - Method for reducing atmospheric pollution caused by CO2 - Google Patents

Description

103,153/2 o^, ->"y DiAjn - ΠΝΪΙ DiiTT muiD-V? ΆΌ->Ϊ> METHOD FOR REDUCING ATMOSPHERIC POLLUTION CAUSED BY C02 The present invention relates to a method for reducing atmospheric pollution caused by C02.

More particularly the present invention relates to a method for reducing atmospheric pollution caused by C02 contained in industrial gases, such as in flue gases produced by combustion powered gas turbines, through the conversion of C02 to CaC03 utilizing commercially available calcium salts .

Carbon dioxide is one of the greenhouse gases , i.e., one of those gases considered to be a major threat to the environment due to the greenhouse effect attributable thereto.

As reported in "Costs of Curbing C02 Emissions Analyzed", C&En 4 (May, 18 1992) the annual damage to the U.S. economy from the doubling of C02 emission (expected to occur between 2025 and 2050), would be about $60 billion, or 1% of the gross domestic product.

Two bills that aim to stabilize carbon dioxide at 1990 levels by 2000 have been introduced in the congress of the U.S. An amendment to the energy bill introduced would stabilize greenhouse emissions.

Reduction in the emissions of C02 has become increasingly more important because of the deteriorating ambient air qualities in many industrial countries. The increasing concern over acid rain, the tightening of emission standards, and the push for the use of more coal to satisfy the energy needs, all point to an urgent need for more efficient and more economic processes. Research and development has been intensified in many countries including the United States, England, Germany, Japan, and Russia as reported e.g. in a) D Bienstock, J.H. Field, S. Katell, and K. D. Plants, "Evaluation of Dry Processes for Removing Sulfur Dioxide from Power Plant Flue Gases." JAPCA 15 459 (1965); and b) J. H. Field, L. W. Brunn, W. P. Haynes and H. E. Benson, "Cost Estimates of Liquid-Scrubbing Processes for Removal of Sulfur Dioxide from Flue Gases" , JAPCA 7 109 (1957). In fiscal year 1992 DOE's Office of Industrial technologies proposed several awards totaling $550,000 for initial R&D work on innovative concepts to utilize waste C02.

In the prior art there are many suggested methods for separating carbon dioxide from gases containing the same.

Thus the following prior art processes have been proposed: a) Mono- and Di-ethanolamine Processes; b) Hot Carbonate Process; c) Sulfinol Process; d) Selexol Process; and e) Modified Selexol-ammonia process; All of these processes are characterized by absorption, desorption, and condensation. Most of them have been developed to deal with situations in which there is a local need for C02 and therefore are designed to utilize locally produced C02 as opposed to bringing C02 to the site where it is required. An example of such a situation is one in which C02 is required for the production of sodium bicarbonate. These processes however were not designed to provide a solution for reducing atmospheric pollution caused by C02 and were not designed to provide a sink for C02 enabling the disposable thereof.

All of these processes involve the use of a recyclable absorber such as Mono- and Di-ethanolamine, Potassium Carbonate, Dimethylether or polyethylene glycol. They further require make up of reagents due to carry over losses which occur during the various stages as well as due - 3 - 103,153/2 to chemical degredation and oxidation. All of these processes suffer from limited absorption capability, since they are based on absorption followed by desorption, and thus a strong absorbant which would otherwise be desirable results in unacceptable energy requirements for effecting the desorption therefrom.

Furthermore, since all of these processes involve several stages, all of which involve gas treatment, the volumes required for effecting these various stages is prohibitive.

It should also be realised that combined processes involving absorption and desorption require energy consumption, at least for the desorption step.

Thus, despite the existence of these various processes, more practical and economical processes are still required, since it is known, e.g., that for lack of a solution for the removal of polluting C02 gas from flue gases produced by the combustion powered gas turbine used in the off-shore drilling rigs in the North Sea fines, in the range of sixty million dollars are paid annually.

In spite of this enormous financial incentive, the prior art has yet to provide a solution for providing a non-hazardous C02 sink applicable to such situations.

With this state of the art in mind, there is now provided according to the present invention a method for reducing atmospheric pollution caused by C02 contained in industrial gases being emitted to the atmosphere, through the conversion of C02 to calcium carbonate using conventionally available calcium salt-containing reactant, said method comprising reacting said pollutant-containing gas, prior to 103,153/3 the venting thereof to the atmosphere, with an alkali base and an aqueous liquor, whereby said pollutant reacts with said base and transfers to said liquor, and the resulting gas vented to the atmosphere has a reduced pollutant content; and reacting a C02-loaded liquor with a calcium salt-containing reactant, said reactant comprising phosphate rock, calcium-containing derived products thereof, calcium nitrate, calcium chloride or gypsum, to form calcium carbonate, with the proviso that said calcium salt-containing reactant is not derived from calcium carbonate or calcium hydroxide; with the co-formation of a commercially utilizable salt containing an anion from said calcium salt reactant and a cation from said alkali base, wherein said alkali base is ammonia or a source thereof , and said commercially utilizable salt is an ammonium salt.

As indicated, CaC03 can provide a sink for large amounts of carbon dioxide. It is formed on contacting C02 with lime milk (suspension of lime in water). However, this is not an option for C02 removal as lime is produced from CaC03 in a process which evolves C02 CaC03 Δ > CaO + C02 and in addition consumes energy.

As indicated hereinbefore, the literature mainly describes processes in which the gas to be removed is separated from the flue gas through absorption in a scrubber. In a second operation, the gas is desorbed and condensed (a third step) and the absorber is regenerated.

In contradistinction, according to the present invention the CO2-containing gas is contacted with an alkali aqueous - 4A - 103,153/1 liquor and then the CO2-loaded liquor is contacted with a calcium containing reactant as defined. Thus, the present invention is based on absorption of C02 as opposed to the prior art processes which involve absorption, desorption and condensation. This fact has practical and commercial ramifications in that the equipment necessary to carry out the present method is simpler, occupies less space and therefore is more applicable to use on off shore drilling rigs .

The method of the present invention is also commercially attractive in that instead of using an absorber which has to - 5 - be recycled it uses a reagent as the absorbent and involves the upgrading of all the components involved to more commercially desirable components while enabling the fixation of the C02 in a product which is environmentally friendly and which is commercially useful.

Since the amounts of C02 which are produced in the industrial waste gases is tremendous any process for dealing therewith is limited by the amount of the reagents available and the by-products produced. As will be realised in the method of the present invention the by-products which are obtained are salts of potassium, ammonia, nitrogen and phosphorous which are used as fertilizers by themselves or in combination with other components and for which there is therefore a tremendous commercial demand. Thus by-products of the present process include ammonium nitrate, phosphate or sulfate or pottassium nitrate, phosphate or sulfate. Thus e.g., in 1991 there were produced 7.3 million tons of ammonium nitrate solution, 2.2 million tons of ammonium sulphate and 0.5 million tons of pottassium nitrate.

Furthermore, in situations in which the source of calcium is phosphate rock C02 in fact serves as an acid source which frees an other more valuable anion such as phosphate or nitrate and in situations in which the source of calcium is a different calcium salt there is produced a product salt which is also more friendly to the environment e.g., CaC03 is preferable over CaS04. Furthermore, calcium carbonate can be used as a filler in the paper industry and as additives to fertilizers for use in acidic soils.

In addition, as will be realised, since the method of the present invention is not based on desorption very strong absorbants effecting maximum aborption can be used such as KOH and ammonia. - 6 - 103,153/2 In a preferred embodiment, the reactant can comprise Ca(N03)2 obtained from the reaction of nitric acid with phosphate rock, or said reactant could comprise acidulated calcium phosphate obtained from the reaction of phosphoric acid with phosphate rock, or phosphogypsum obtained from the reaction of sulfuric acid with phosphate rock.

Thus, e.g., using ammonia or a source thereof the following reactions are envisioned: 2NH40H + C02 = (NH4)2C03 + H20 a) (NH4)2C03 + CaS04 = (NH4)2S04 + CaC03; or b) (NH4)2C03 + CaHP04 = (NH4)2HP04 + CaC03 3(NH4)2C03 + Ca3(P04)2 = 2(NH4)3P04 + 3CaC03; or c) (NH4)2C03 + Ca(N03)2 = 2NH4N03 + CaC03 As will be realised, since the calcium carbonate precipitates out from the aqueous solution said solution can then be further processed to recover therefrom the second product formed by the above reaction whereafter the mother liquor can be recycled for further use in the present method .

Furthermore, since in the vacinity of turbines there is always waste heat available the product can be concentrated by heat evaporation without the need for supplying expensive energy input to produce said heat.

Furthermore, since the absorbant is also a reagent and in fact the reaction therewith is exothermic the overall energy balance of the method is positive and the energy of - 6A - 103,153/1 absorption in fact can enable the concentration of C02 in the absorbant containing aqueous liquor .

While the invention will now be described in connection with certain preferred embodiments in the following examples so - 7 - that aspects thereof may be more fully understood and appreciated, it is not intended to limit the invention to these particular embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the scope of the invention as defined by the appended claims. Thus, the following examples which include preferred embodiments will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purposes of illustrative discussion of preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of formulation procedures as well as of the principles and conceptual aspects of the invention.

EXAMPLE 1 A gaseous mixture of 95% nitrogen and 5% C02 is bubbled through a column filled with a concentrated aqueous solution containing KOH. The C02 content of the gas at the outlet of the column is reduced by more than a half and the resulting solution containing KHC03 is then reacted with Ca3(P04)2 to form insoluble CaC03. The remaining aqueous solution containing potassium phosphate is transferred to an evaporator crystallizer to recover the equivalent amount of potassium phosphate.

EXAMPLE 2 A gaseous mixture of 95% nitrogen and 5% C02 is bubbled through a column filled with a concentrated aqueous solution containing ammonia. The C02 content of the gas at the outlet of the column is reduced by more than a half and the resulting solution containing (NH4)2C03 is reacted with CaS04 to form insoluble CaC03 and (NH)2S04. The remaining aqueous solution containing ammonium sulphate is - 8 - transferred to an evaporator crystallizer to recover the equivalent amount of ammonium sulphate.

EXAMPLE 3 A gaseous mixture of 95% nitrogen and 5% C02 is bubbled through a column filled with a concentrated aqueous solution containing Ca(N03)2 and ammonia. The C02 content of the gas at the outlet of the column is reduced by more than a half and an insoluble CaC03 precipitate is formed in situ in the solution and separated therefrom by filtration. The remaining aqueous solution containing ammonium nitrate is transferred to an evaporator crystallizer to recover the equivalent amounts of ammonium nitrate.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative examples and that the present invention may be embodied in other specific forms without departing from the essential attributes thereof, and it is therefore desired that the present embodiments and examples be considered in all respects as illustrative and not restrictive, reference being made to the appended claims, rather than to the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (6)

- 9 - 103,153/3 WHAT IS CLAIMED IS:

1. A method for reducing atmospheric pollution caused by C02 contained in industrial gases being emitted to the atmosphere, through the conversion of C02 to calcium carbonate using conventionally available calcium salt-containing reactant, said method comprising: reacting said pollutant-containing gas, prior to the venting thereof to the atmosphere, with an alkali base and an aqueous liquor, whereby said pollutant reacts with said base and transfers to said liquor, and the resulting gas vented to the atmosphere has a reduced pollutant content; and reacting a C02-loaded liquor with a calcium salt-containing reactant, said reactant comprising phosphate rock, calcium-containing derived products thereof, calcium nitrate, calcium chloride or gypsum, to form calcium carbonate, with the proviso that said calcium salt-containing reactant is not derived from calcium carbonate or calcium hydroxide; with the co-formation of a commercially utilizable salt containing an anion from said calcium salt reactant and a cation from said alkali base; wherein said alkali base is ammonia or a source thereof, and said commercially utilizable salt is an ammonium salt.

2. A method for reducing atmospheric pollution according to claim 1, wherein said reactant comprises Ca(N03)2 obtained from the reaction of nitric acid with phosphate rock. - 10 - 103,153/3

3. A method for reducing atmospheric pollution according to claim 1, wherein said reactant comprises acidulated phosphate obtained from the reaction of phosphoric acid with phosphate rock.

4. A method for reducing atmospheric pollution according to claim 1, comprising supplying ammonia or a source thereof and a commercially-available, calcium salt-containing reactant; said reactant comprising phosphate rock, calcium-containing derived products thereof, calcium nitrate, calcium chloride and gypsum, to a site of a combustion-powered gas turbine wherein flue gases produced by said combustion are utilised as a source of C02 for the formation of calcium carbonate.

5. A method for reducing atmospheric pollution according to claim 4, wherein said site is an off-shore drilling rig.

6. A method for reducing atmospheric pollution according to claim 1, comprising reacting said industrial gases, prior to emission, with an aqueous liquor containing alkali and a water-soluble calcium salt, whereby C02 transfers to the aqueous liquor, calcium carbonate precipitates, and the gas released to the atmosphere has a lower C02 content. for the Applicant: WOLFF, BREGMAN AND GOLLER