CA2053939A1

CA2053939A1 - In-situ removal of effluents from a gaseous stream by injection of an effluent sorbent nitrate into the gaseous stream downstream of the combustion zone

Info

Publication number: CA2053939A1
Application number: CA002053939A
Authority: CA
Inventors: Domingo Rodriguez; Roy Payne; Cebers O. Gomez; Peter Maly; Maria T. Terrer
Original assignee: Intevep SA
Current assignee: Intevep SA
Priority date: 1991-02-19
Filing date: 1991-10-22
Publication date: 1992-08-20
Also published as: IT1250359B; FR2672821A1; DE4204770A1; KR940006398B1; ITTO910957A0; GB9121476D0; GB2252965A; ITTO910957A1; DE4204770C2; BR9104515A; ES2034898B1; ES2034898A1; DK170991D0; DK170991A; NL9200311A; KR920016130A

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention is drawn to a process for removing effluents from off-gases generated by the combustion of a hydrocarbon fuel and, more particularly, a process as aforesaid wherein an effluent sorbent nitrate is injected into the off-gas stream downstream of the combustion zone at a controlled off-gas stream temperature.

Description

~ ~0~3~39 BACKGROUND OF THE INVENTION
The present invention relates to a process for removing effluents froJn off-gases generated by the combustion of a hydrocarbon fuel and, more particularly, a process for removing the effluents wherein an effluent sorbent nitrate is injected into the off-gases downstream of the combustion zone.
Co-pending Application Serial Number 498,952, filed March 26, 1990, of which the instant application is a continuation-in-part, discloses a process for the in-situ production of a sorbent-oxide aerosol used for removing effluents from a gaseous combustion stream. In accordance with the process of U.S. Patent Application Serial No. 498,952 an aqueous solution compxising an effluent sorbent compound dissolved in water is admixed ~ith a hydrocarbon containing fuel so as to form a combustible fuel mixture. The hydrocarbon fuel may be fuel oil, crude oil, an oil-in-water emulsion, coal or bitumen or any other suitable fossil fuel. The combustible fuel mixture is atomized and fed to a combustion zone wherein the atomized fuel mixture is combusted under controlled conditions to a temperature of greater than or equal to 1400K in the presence of an oxidant. During the combustion of the atomized fuel mixture at the temperature indicated above, a ', , ' ~ ~ ' - ', : ' ;' 2~3939 sorbent-oxide aerosol is produced which comprises ultra-fine sorbent-oxide particles having a mean diameter of submicron size in the gaseous combustion stream. The gaseous combustion stream is thereafter cooled to a temperature of between 700K to about 1350~K
so that the sorbent-oxide particleg absorb the effluents from the gaseous combustion stream. The process of U.S.
Patent Application Serial Number 498,952 has proved to be particularly useful for removing sulfur from combustion gas streams.
Co-pending application Serial No. , filed concurrently herewith on , 1990 (Attorney's -Docket No. 90-181) is drawn to a process for removing effluents from off-gases generated by the combustion of a hydrocarbon fuel. The process of the present invention comprises combusting a hydrocarbon fuel in a combustion zone at a preferred temperature and thereafter transporting the off-gases generated from the combustion of the fuel away from the combustion zone.
During the transportation of the off-gases, the off-gases are cooled to a controlled temperature range ~hich is less than the combustion temperature. An effluent sorbent is injected into the off-gas stream at the controlled temperature downstream of the combustion zone. During the injection of the effluent sorbent at . . ,:

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, ' ,. ' ,' the controlled off-gas stream temperature, the sorbent absorbs effluents from the off-gases.
Naturally, it would be highly desirable to develop new and improved processes for removing effluent~ from hydrocarbon fuel combustion gas strea~s which are economic to use and efficient in effluent reduction.
Accordingly, it is a principle object of the present invention to provide a process for removing environmental harmful effluents from a gaseous stream, It is a particular object of the present invention to provide a process for the removal of e~fluents from a gaseous combustion stream wherein an effluent sorbent nitrate is injected into the combustion gas stream downstream of the combustion zone.
Further objects and advantages of the present invention will appear hereinbelow.

SUMMARY OF THE INVENTION
In accordance with the present invention, the foregoing objects and advantages are readily obtained.
The present invention is drawn to a process for removing effluents from off-ga~es generated by the combustion of a hydrocarbon fuel. The process of the present invention co~prises combusting a hydrocarbon fuel in a combustion zone at a preferred temperature and :

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- , ~ `: , , ' , ~,, ` , ' 2~3~39 , thereafter transporting the off-gases generated from the combustion of the fuel away from the comhustion zone.
During the transportation of the off-gases, the off-gases are cooled to a controlled temperature range which is less than the combustion temperature. An effluent sorbent nitrate is injected into the off-gas stream at the controlled temperature downstream of the combustion zone. During the injection of the effluent sorbent nitrate at the controlled off-gas stream temperature, the sorbent absorbs effluents from the off-gases.
In a preferred embodiment of the present invention the effluent sorbent nitrate is spiked with a promoter which enhances the effect of the effluent sorbent on removing effluents from the off-gases. In accordance with the present invention the effluent sorbent nitrate may be mixed with water and the promoter to form an aqueous mixture which is injected into the off-gas stream. In this embodiment of the present invention the effluent sorbent nitrate mixture is injected in a manner so as to produce a fine spray wherein the average particle size is less than 100 microns.
In an alternative embodiment of ~he present invention, the sorbent nitrate may be spiked with the promoter and fed in a dry manner into the off-gas , ',: ,, . ' ' ~,. :

2~3939 , stream. In ~his embodiment of the present invention the average particle size of the spiked sorbent nitrate should be less than 50 microns, preferably less than 20 microns.
The most desired sorbent nitrate used in the process of the present invention includes nitrate salts with the nitrate salts of magnesium and calcium being most preferred. Suitable pro~oters include iron, copper, manganese, boron, aluminum~ sodium, potassium, zinc, nickel and mixtures thereof ~ith iron, copper, manganese and boron being preferred and iron and copper being ideal. In accordance with the preferred features of the present invention the molar ratio of sorbent nitrate to effluent is 0.05 to 2.0 and preferably 0.1 to 1.0 while the molar ratio of promoter to sorbent is 0.001 to 0.1, preferably equal to or below 0.05.
The process of the present invention offers an effective and economic mechanism for removing effluents from a combustion gas stream. The effectiveness of the process of the present invention will be made clear hereinbelow from a reading of the detailed description.

DETAILED DESCRIPTION
The present invention is drawn to a process for removing effluents from off-gases generated by the .: ' ,! ~ ' ' ' ' : ~ ' ~ , ' ' '' ' ,' .
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, , ' , , , .:, 2~3939 combustion of a hydrocarbon fuel and, more particularly, a process as aforesaid wherein an effluent sorbent nitrate is injected into the off~gas stream downstream of the combustion zone at a controlled off-gas stream temperature.
As noted above, the process of the present invention comprises the steps of injecting an effluent sorbent nitrate into an off~gas stream downstream of a combustion zone when the off-gas stream i5 at a critical temperature range. In accordance with a preferred embodiment of the present invention, the effluent sorbent nitrate is mixed with a promoter and injected into the off-gas stream. In one embodiment of the process of the present invention the effluent sorbent nitrate is mixed with water and the promoter so as to form an aqueous effluent sorbent nitrate mixtureO The mixture is thereafter injected into the off-gas stream under controlled conditions at a desired off-gas stream temperature. The effluent sorbent mixture is injected in a controlled manner so as to produce a fine spray having an average droplet size of less than 100 microns preferably less than 50 microns. In an alternative embodiment of the present invention the effluent sorbent nitrate is spiked with the promoter and injected into the off-gas stream in dry form. The particular way to ., . . .. ;...... . ~ . .~. :
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2 053~39 spike a water insoluble solid sorbent with the promoter depends in part on the nature of both the sorben~ and the promoter. For example calcium hydroxide (CatOH)2), also kno~n as hydrated lime, is a solid prepared by the addition of water to calcium oxide.
Hydrated lime is a well known ~2 sorbent. Hydrated lime could be easily spiked ~ith the promoter according to the following procedure: A promoter compound is solubilized in the required proportion in the water ~hat is going to be used to hydrate the lime. Then the lime is hydrated with such solution, effectively incorporating the promoter into the solid. The hydration reaction is quite exothermic, thus a dry spiked solid sorbent could be produced if the right conditions are met. Otherwise, drying of the wet solid is required. The promoted sorbent could then be injected into the furnace off-gases as a finely divided dry solid. In this embodiment of the present invention the average partlcle size of the effluent sorbent nitrate is less than or equal to 10 microns.
As noted above, the effluent sorbent nitrate with or without promoter is injected into the off-gas stream when the off-gas stream is at a desired temperature. It has been found in accordance ~ith the present invention that when the effluent sorbent nitrate is in]ected into .

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2~3~39 the gas stream without emplo~ing a promoter the desired temperature o~ the off-gas ætream when injection takes place is between 2000 and 2400 F. When a promoter is incorporated with the effluent sorbent, the temperature window for injection into the off-gas stream is increased up to 2800 F. In accordance with the present invention, the molar ratio of sor~ent nitrate to effluent should be 0.05 to 2.0, and preferably between 0.1 to 1.0 and the molar ratio of promoter to sorbent nitrate is 0.001 to 0.1, and preferably equal to or below 0.05. The effluent sorbent nitrate compound may be any nitrate such as HN03 and the like with the preferred being nitrate metal salts. The most preferred effluent sorbents a}e nitrates of calcium and magnesium. The promoter employed in the process of the present invention includes metals selected from the group consisting of iron, copper, manganese, boron, aluminum, sodium, potassium, zinc, nickel and mixtures thereof Preferred promoters are iron, copper, manganese and boron with iron and copper being the most preferred.

In accordance with the present invention the effluent sorbent nitrate with or without promoter may be injected into the off-gas stream in the presence of an oxidant. As noted above, the injection should take .. .. . . . ..

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2V~3939 place when the gas stream is at a temperature of between 2000 to 2800 F in the case of whe~ a promoter is employed and at a temperature of between 2000 to 2400F when no promoter is employed. When the e~1uent sorbant nitrate is injected into the off-gas stream with an oxidant, it is preferred that oxidant be present in such amount as to provide a fine sorbent nitrate spray.

The following examples illustrate specific features of the process of the present invention but are in no way are intended to be limiting.

EXAMPLE I
.
In order to demonstrate and quantify the existence of unwanted effluents, particularly, sulf~r, in a hydrocarbon combustion stream a liquid hydrocarbon having a sulfur content of 3.8% by weight was mixed with water so as to obtain a mixture of 55~ by volume hydrocarbon fuel and 45% by volume water. The mixture was thereafter combusted to completion. The fuel mixture was fed to the furnace through a commercial nozæle. The fuel was atomized with air using a mass of about l.l the stoichiometric requirement The hydrocarbon fuel was combusted at a firing rate of about one million BTU per hour until completely combusted.
The concentration of S02 in the dry emission gases ., , : ..

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were measured and the concentration of S02 was found to be 2700 ppm. By dry emission gases is meant all the gases produced durirlg the combustion process, with the exception of H20, corrected to 0~ oxygen.

EXAMPLE II
In order to demonstrate the effectiveness of nitrates as an effluent sorbent in the process of the present invention the liquid hydrocarbon employed in Example I was combusted under the same conditions set forth in Example I. The off-gases from the combustion zone were carried off and cooled to a temperature of 2100 F. An aqueous solution of calcium nitrate was injected into the off-gases at the temperature of 2100 F. The molar ratio of calcium nitrate injected into the off-gas stream to sulfur in the fuel was 0.7.
After injection of the aqueous solution of calcium nitrate into the off-gas stream the SO2 concentration of the dry emission gases were measured and were found to be 1301 ppm. This level of S02 represents a 52%

reduction in S02 when compared to Example I where calcium nitrate was not employed as an effluent sorbent. The amount of the nitrate sorbent utilized was found to be 40~. Sorbent utilization is defined as follows:

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2~3~39 % sorbent ~[effluent~baseline - [effluent~sorbent~
utilized = 100 x _ ~ [effluent]baseline 1 moles sorbent ~ moles effluent Where is the stoichiometric coefficient in the sorbent and effluent chemical reaction and [effluent] baseline is the concentration of effluent in the dry emission gases in the absence of a sorbent. Thus, the process of the present invention is effective in reducing SO2 levels in the off-gases of the combustion stream when an aqueous solution of an effluent sorbent nitrate is injected into the off-gas stream downstrea~ of the combustion zone.

EXAMPLE III
In order to demonstrate the superior performance obtained by the process of the present invention which employs nitrates as the effluent sorbent, a similar experiment was conducted employing the methodology described above with regard to Example II. In this case instead of injecting an aqueous solution of calcium nitrate an aqueous solution of calcium formate was injected into the combustion stream. The temperature of tne off-gases at the point of injection was 2100 F and the molar ratio of calcium formate to sulfur was 0.7.
The SO2 concentration of the off-gases was again 2~3939 measured after injection and was found to be equal to 1944 ppm which represents a 28~ reduction in S0 emissions when compared to Example I and a 40~ sorbent~
utilization. When comparing the results of the inatant example to that obtained in Example II, it is clear tha~, ti~ 4 ~'.
calcium nitrate is a far better effluent sorbent~that calcium formate.

EXAMPLE IV
In order to demonstrate the effectiveness of a preferred embodiment of the present invention t~o additional tests were run under the same conditions set forth above with regard to Example II.
In the first ~est a promoter in the form of iron gluconate was dissolved in the aqueous solution of water and calcium nitrate prior to the injection of the aqueous solution into the off-gas stream. The iron to calcium molar ratio in the solution was 0.05. The calcium to sulfur molar ratio was maintained at 0.70 After injection the level of S02 in the flue gas was measured and was found to be 810 ppm which represents a 70~ reduction in S02 levels wi~h respect the base line test of Example I. This 70~ reduction in S02 levels corresponds to a sorbent utilization of 100%.

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The second test performed was identical to the first test except that the promoter was dissolved in water and mixed with the fuel and combusted therewith.
The calcium nitrate solution was injected into the off-gases in the same manner as discussed above With regard to Example II. Again, the S02 emissions level was measured and found to be 810 ppm representing a 70%
reduction in SO2 levels and a 100~ sorbent utilization.
The results of these tests show that the introduction of small amounts of an iron salt in the furnace while injecting a nitrate solution into the flue gas stream substantially enhances the removal of SO2 when compared with those levels obtained without a promoter as in Example II. The example further shows that similar results may be obtained when the iron salt is injected together with the nitrate solution or with the fuel being combusted.

EXAMPLE V
In order to demonstrate the effectiveness of the process of the present invention when employed with the combustion of other fossil fuels, a bituminous coal with a sulfur content of 4.3 wt.~ was combusted under controlled conditions and the level of SO2 concentration in the flue gases on a dry basis ~as found to be 3000 ppm.

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- ~0~3939 In order to demonstrate the effectiveness of the process of the present invention a first test was run wherein an aqueous solution of calcium nitrate was injected into the flue gas stream at a temperature of 2100 F. The molar ratio of calcium nitrate to sulfur in the coal combusted was 0.7. After injection, the S2 concentration in the flue gas was measured and found to be less than 10 ppm. The surprising result represents a 100% reduction in S02 levels when compared to Example I and a sorbent utilization of 143%.
As a result of the surprising results obtained in the first test aescribed above, a second test was conducted under the same conditions with the only change being a reduction in calcium nitrate so as to provide a molar ratio of calcium to sulfur of 0.33 rather than 0.7 as done in the first test a~ove. The S02 levels were again measured and found to be 120 ppm which represents a 96~ S02 reduction with a sorbent utilization of 290~.
As a result of this further surprising result, a third test was run wherein the molar ratio of calcium to sulfur was 0.1, all other conditions remained the same.
Upon measurement of S02 concentration in the flue gases the concentration was found to be 2370 ppm representing only a 21~ reduction in S02 emissions while still having a sorbent utilization of 210~. The '''' ' '' ' ,' " "' ', ': ' ' ' ~; ',' , ' :''' ' ' . : ' ' ., ,' ' ' ; ~ , : ' 20~3.~39 tests in this Example V demonstrate that the process of the present invention is extremely effectiv~ in removing S2 from flue gases generated from the combustion of coal and is more effective when employed with the combustion of coal than in the case of low ash liquid fuels. The ash composition of the coal employed in the instant example was as follows:

Percentage of ash - 9.42~
Ash composition (as oxides) SiO2 50.35~
A123 17.61%
Tio2 0.64 Fe23 18.0 MgO 0.95 Na20 0.67 K20 1.81 P205 0.1%
SO3 3~77 EXAMPLE VI
In order to demonstrate the effectiveness of other nitrates in the process of the present invention a further test was run identical to Test 1 of Exa~ple V

with the exception that magnesium nitrate was injected . ' ' '~
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20~3939 into the furnace instead of calcium nitrate. All of the parameters of Test 1 of the instant example were identical to those employed in Test 1 of Example V. The S2 concentration in the flue gases was again measured and found to be less than 10 ppm which again represents a 100~ reduction in S02 and a sorbent utilization of 143%. This example clearly demonstrates the effectiveness of nitrates on sulfur removal in accordance with the process of the present inventionO
This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

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Claims

1. A process for removing effluents from off-gases generated by the combustion of a hydrocarbon fuel comprising combusting said hydrocarbon fuel in a combustion zone at a temperature T1 so as to generate off-gases containing effluents; transporting said off-gases from said combustion zone and cooling said off-gases to a temperature T2 where T2 is less than T1; providing an effluent sorbent selected from the group consisting of nitrate; and injecting said effluent sorbent into said off-gases downstream of said combustion zone at a point where the temperature of said off-gases is T2 wherein said sorbent absorbs said effluents from said off-gases.

2. A process according to claim 1 including mixing said effluent sorbent with water so as to form an aqueous effluent sorbent mixture prior to injecting.

3. A process according to claim 2 including injecting said effluent sorbent mixture into said off-gases so as to produce a fine spray having an average droplet size of less than 100 microns.

4. A process according to claim 2 including injecting said effluent sorbent mixture into said off-gases so as to produce a fine spray having an average droplet size of less than 50 microns.

5. A process according to claim 3 including providing nitrate salts as said effluent sorbent.

6. A process according to claim 5 wherein said nitrate salts are selected from the group consisting of calcium, magnesium and mixtures thereof.

7. A process according to claim 2 including preparing an aqueous solution of a sorbent promoter and mixing said aqueous solution with said hydrocarbon fuel prior to combusting said fuel.

8. A process according to claim 2 including mixing a sorbent promoter with said aqueous effluent sorbent mixture prior to injection.

9. A process according to claim 7 wherein said promoter is selected from the group consisting of salts of iron, copper, manganese, boron, aluminum, sodium, potassium, zinc, nickel and mixtures thereof.

10. A process according to claim 8 wherein said promoter is selected from the group consisting of salts of iron, copper, manganese, boron, aluminum, sodium, potassium, zinc, nickel and mixtures thereof.

11. A process according to claim 7 wherein said promoter is selected from the group consisting of salts of iron, copper, manganese, boron and mixtures thereof.

12. A process according to claim 8 wherein said promoter is selected from the group consisting of salts of iron, copper, manganese, boron and mixtures thereof.

13. A process according to claim 7 wherein said promoter is selected from the group consisting of salts of iron, copper and mixtures thereof.

14. A process according to claim 8 wherein said promoter is selected from the group consisting of salts of iron, copper and mixtures thereof.

15. A process according to claim 2 wherein the molar ratio of sorbent to effluent is 0.05 to 2Ø

16. A process according to claim 2 wherein the molar ratio of sorbent to effluent is 0.1 to 1Ø

17. A process according to claim 7 wherein the molar ratio of promoter to sorbent is 0.005 to 0.1.

18. A process according to claim 7 wherein the molar ratio of promoter to sorbent is preferably equal to or below 0.05.

19, A process according to claim 8 wherein the molar ratio of promoter to sorbent is 0.005 to 0.1.

20. A process according to claim 8 wherein the molar ratio of promoter to sorbent is preferably equal to or below 0.05.

21. A process according to claim 2 wherein T2 is between 2000° and 2400° F.

22. A process according to claim 7 wherein T2 is between 2000° and 2800° F.

23. A process according to claim 8 wherein T2 is between 2000° and 2800° F.

24. A process according to claim 1 including forming said hydrocarbon fuel by preparing an oil-in-water emulsion.

25. A process according to claim 1 wherein said hydrocarbon fuel is coal.