Process for producing sulfuric acid with low levels of nitrogen oxides
A process for producing sulfuric acid with reduced levels of nitrogen oxides (NO x ) within a typical sulfuric acid production line. A hydrazine source material can be mixed with a sulfuric acid effluent at a temperature of at least about 90° C. for a period of at least 1 minute to reduce the level of NO x is the sulfuric acid effluent.
1. A process for producing sulfuric acid with reduced levels of niter or nitrogen oxides (NO x ) comprising:
a) providing an absorption tower wherein sulfur trioxide is absorbed in a sulfuric acid feed having a first sulfuric acid solution to produce a sulfuric acid effluent having i) a second sulfuric acid solution which has a higher concentration than the first sulfuric acid solution, ii) a NO x concentration greater than about 5 ppm by weight (as NO 3 ) and iii) an effluent temperature greater than or equal to about 90° C.; and
b) admixing a hydrazine source selected from the group consisting of hydrazine sulfate, dihydrazine sulfate and hydrazine hydrate with the sulfuric acid effluent to form a hydrazine-treated sulfuric acid effluent, the treated sulfuric acid effluent being maintained at a temperature of greater than or equal to 90° C. for a maintenance period of at least 1 minute.
2. The process of claim 1 wherein the first sulfuric acid has a concentration of at least about 93%.
3. The process of claim 1 wherein the second sulfuric acid has a concentration of at least about 99%.
4. The process of claim 1 wherein the treated sulfuric acid effluent is maintained at a temperature of at least about 95° C.
5. The process of claim 1 wherein the treated sulfuric acid effluent is maintained at a temperature of at least about 98° C.
6. The process of claim 1 wherein the treated sulfuric acid effluent is maintained at a temperature of at least about 100° C.
7. The process of claim 1 wherein the treated sulfuric acid effluent has a NO x concentration (as NO 3 ) of about 5 ppm or less on a weight basis of sulfuric acid.
8. The process of claim 7 wherein the treated sulfuric acid effluent has a NO x concentration (as NO 3 ) of about 1 ppm or less on a weight basis of sulfuric acid.
9. The process of claim 1 wherein the hydrazine comprises hydrazine hydrate.
10. The process of claim 1 further comprising the step of diluting the sulfuric acid effluent with water wherein the dilution is performed before, after, or at the same time as the admixing of the hydrazine.
11. The process of claim 1 wherein the hydrazine is admixed with the sulfuric acid effluent at a rate of between about 0.001 and 0.1 gram of the hydrazine per liter of the sulfuric acid effluent.
12. The process of claim 1 wherein the hydrazine is admixed with the sulfuric acid effluent at a rate of between about 1 to 1.5 moles of the hydrazine per mole of NO x (as NO 3 ) in the sulfuric acid effluent.
13. The process of claim 1 wherein the hydrazine is in the form of an aqueous solution.
14. The process of claim 1 wherein the maintenance temperature of the treated effluent is maintained for a maintenance period of between about 1 minute and 30 minutes, after which maintenance period the treated effluent is cooled to a temperature below the minimum maintenance temperature.
15. The process of claim 10 further comprising the steps of: cooling the treated, diluted effluent to a temperature below about 90° C.; splitting the treated, diluted effluent into a first treated, diluted effluent stream and a second treated, diluted effluent stream; recycling the first treated, diluted effluent stream to become all or part of the sulfuric acid feed to the absorption tower; and collecting the second treated, diluted effluent stream as sulfuric acid product.
16. The process of claim 15 wherein hydrogen peroxide is added to the second diluted, treated effluent stream in an amount suitable to consume residual hydrazine.
17. The process of claim 15 wherein the sulfuric acid product has a NO x content (as NO 3 ) of less than about 5 ppm on a weight basis of sulfuric acid.
18. Sulfuric acid produced by the process of claim 1 wherein the sulfuric acid concentration is in the range of about 93% to 99% and the NO x concentration (as NO 3 ) is less than about 5 ppm on a weight basis of sulfuric acid.
19. Sulfuric acid produced by the process of claim 15 wherein the sulfuric acid concentration is in the range of about 93% to 99% and the NO x concentration (as NO 3 ) is less than about 5 ppm on a weight basis of sulfuric acid.