Pyrophoric iron sulfide treatment using sodium nitrite
Pyrophoric material such as iron sulfide is frequently found in refinery equipment. When the equipment is opened to the atmosphere for maintenance, an exothermic reaction can take place that may cause injury to personnel and catastrophic damage to equipment. A process used to treat pyrophoric material uses sodium nitrite injected into a gaseous carrier stream to oxidize iron sulfides to elemental sulfur and iron oxides. The sodium nitrite solution may be buffered to a pH of about 9 with disodium phosphate or monosodium phosphate. A chemical additive that provides a quantitative measure of reaction completion may be added to the treatment solution.
1. A method for reducing the amount of iron sulfide in chemical process equipment containing deposits of iron sulfide, the method comprising:
injecting a gaseous stream of nitrogen containing a solution of sodium nitrite into the chemical process equipment;
reacting the deposits of iron sulfide with the sodium nitrite;
injecting a solution of lauryl dimethylamine oxide;
monitoring the progress of the method by testing samples withdrawn from the chemical process equipment for the presence of lauryl dimethylamine oxide while continuing the injection of the solution of lauryl dimethylamine oxide; and
continuing the injection of a gaseous stream of nitrogen containing a solution of sodium nitrite and a solution of lauryl dimethylamine oxide into the chemical process equipment until the lauryl dimethylamine oxide is no longer being consumed as indicated by the presence of unreduced lauryl dimethylamine oxide in the test samples.
2. The method recited in claim 1 wherein the sodium nitrite is in a buffered solution.
3. The method recited in claim 2 wherein the sodium nitrite solution is buffered to a pH of about 9.
4. The method recited in claim 3 wherein the buffer is selected from the group consisting of disodium phosphate and monosodium phosphate.
5. The method recited in claim 2 wherein the buffer comprises disodium phosphate or monosodium phosphate.
6. The method recited in claim 2 wherein the buffer comprises disodium phosphate and monosodium phosphate.
7. The method recited in claim 2 wherein the buffer comprises substantially equal concentrations of disodium phosphate and monosodium phosphate.
8. The method recited in claim 1 wherein the sodium nitrite oxidizes iron sulfide to ferric oxide and elemental sulfur.
9. The method recited in claim 1 wherein the solution of lauryl dimethylamine oxide comprises an aqueous solution of about 1.2 percent by weight lauryl dimethylamine oxide.
10. The method recited in claim 1 wherein the solution of lauryl dimethylamine oxide is injected with the solution of sodium nitrite.
11. The method recited in claim 1 wherein the solution of lauryl dimethylamine oxide additionally comprises sodium nitrite.
12. The method recited in claim 1 further comprising:
chemically cleaning hydrocarbons from the chemical process equipment prior to injecting the sodium nitrite solution into the chemical process equipment;
purging the chemical process equipment with a gas selected from the group consisting of steam and nitrogen;
applying steam to the chemical process equipment to heat the equipment to between about 213° F. and about 275° F. at a pressure between about 1 psig and about 20 psig.