Patent Grant
8932458
The present invention relates to the use of a hydrogen sulfide (H2S) scavenger to reduce hydrogen sulfide (H2S) Emission when venting the coke drum in a delayed coker unit.
In a delayed coking process, a heavy liquid hydrocarbon fraction is converted to solid coke, lower boiling hydrocarbon liquids, and gaseous products. The fraction is typically a residual petroleum based oil or a mixture of residual oil with other heavy fractions.
The residual oil is heated with liquid products from the process and is fed into a fractionating tower wherein light end products flashes from the residual oil. The oil is then pumped from the bottom of the fractionating tower through a furnace where it is heated to coking temperature and discharged into a coking drum.
In the coking reaction the residual feedstock is thermally decomposed into solid coke, condensable liquid, and gaseous hydrocarbons. The solid coke remains in the drum while hydrocarbon products are routed to the fractionating tower where they are separated into the desired hydrocarbon fractions.
The delayed coking drums must be vented prior to coke removal. This venting results in emission to the atmosphere. Among the emissions to the atmosphere is hydrogen sulfide which the Environmental Protection Agency has declared must be less than 10 tons per year. It is anticipated that this restriction may be reduced in the foreseeable future.
The coke drum vent gas from the delayed coker unit may contain high levels of hydrogen sulfide (H2S). The invention involves the use of an H2S scavenger to reduce H2S emission when venting the coke drum to atmosphere. The scavenger reacts with H2S to form a non volatile compound.
In a preferred embodiment, the H2S scavenger is an amine hydrogen, preferably triazine. The triazine reacts with H2S to form dithiazine, a non volatile compound. However, any H2S scavenger can be used.
The delayed coking process comprises the steps of: thermally cracking hydrocarbon feedstock in the coke drum thereby converting the feedstock to coke and hydrocarbon products; routing thermally crack hydrocarbon products to downstream fractionators; and periodically removing coke from the drum. Before coke removal, the drum has to be steam stripped, water quench, then vented.
Emissions including hydrogen sulfide (H2S) from the delayed coker depressurization vent were measured. The results showed high levels of H2S in the coker vent gas. Operating conditions and work practices to reduce hydrogen sulfide were adjusted. Specifically, the quenching cycle was adjusted with the direct injection of a scavenger chemical (triazine) into the coke drum. Testing shows that injecting H2S scavenger in the vapor space of the coke drum prior to venting reduces H2S emission to an acceptable level. This practice has been found to control H2S emission. The preferred embodiment uses an amine hydrogen scavenger such as triazine.
Other objects and advantages of the present invention will become apparent to those skilled in the art upon a review of the following detailed description of the preferred embodiments and the accompanying drawings.
Feed to the delayed coker drums 16 is pumped to a process heater where the heavy oil is heated to the desired thermal cracking temperature (>900 F). The vapor-liquid mixture leaving the furnace enters either of the two delayed coke drums 16 where it is converted, via thermal cracking, to lighter hydrocarbon vapors and petroleum coke. The solid petroleum coke is deposited in the coke drum. After the delayed coke drum 16 is full of solidified petroleum coke, its contents are steamed to further recover any remaining volatile hydrocarbon content from the coke, then water—quenched to lower the temperature. Once quenching is complete, the vent line 17 activates and depressures the coke drum to atmosphere.
Emissions were measured including H2S from the delayed coker drums 16 depressurization vent. The result of the testing shows high levels of H2S in the coker vent gas (average 7.1 tons/year). Modification of operating conditions and work practices to reduce hydrogen sulfide were carried out. Specifically, the quenching cycle was altered by the direct injection of an amine-based hydrogen scavenger chemical into the coke drum such as Triazine. Results show that injecting H2S scavenger in the vapor space 19 of a coke drum prior to venting significantly reduces H2S emissions to an acceptable level (average 1.5 tons/year). The H2S scavenger chemical is injected approximately 30 minutes prior to venting the delayed coke drums 16 to provide adequate time for the reaction to occur. A quill (not shown) maybe used to properly disperse the chemical in the vent stream. This practice has been added to reduce H2S emission.
The H2S scavenger is ideally injected into the vapor space 19, at injection point 20, however, it can be injected into the vent line 17, at injection point 22. Note that the hydrogen sulfide scavenger could also be injected into both the vapor space 19 and the vent line 17 at injection points 20 and 22 respectively.
Any H2S scavenger can be used to reduce H2S emissions in a delayed coking drum. Other such H2S scavengers include but are not limited to monoethanolamine (MEN, trialkyl hexahydro triazine, diethanolamine (DEA), methyldiethanolamine (MDEA), Disopropylamine (DIPA), Diglycolamine (DGA), glyoxal and a quanternary ammonium compound.
Testing was done in an attempt to reduce hydrogen sulfide emissions (H2S). Different methods of reducing H2S were attempted, however, it became clear that the most significant and consistent reduction in H2S occurred when 30 gallons of a H2S scavenger was injected at the top of the coke drum approximately 30 minutes prior to venting through the coker steam vents. H2S was reduced from 18.5 tons per year (TPY) to 5.7, 1.1 and 0.1 TPY respectively. When the H2S scavenger is added 30 minutes prior to venting.
The above detailed description of the present invention is given for explanatory purposes. It will be apparent to those skilled in the art that numerous changes and modifications can be made without departing from the scope of the invention. Accordingly, the whole of the foregoing description is to be construed in an illustrative and not a limitative sense, the scope of the invention being defined solely by the appended claims.
The present patent application is based upon and claims the benefit of provisional patent No. 61/616,026, filed Mar. 27, 2012.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4176052 | Bruce | Nov 1979 | A |
| 4302324 | Chen et al. | Nov 1981 | A |
| 4661241 | Dabkowski et al. | Apr 1987 | A |
| 4686027 | Bonilla | Aug 1987 | A |
| 5045177 | Cooper et al. | Sep 1991 | A |
| 5258115 | Heck et al. | Nov 1993 | A |
| 5354453 | Bhatia | Oct 1994 | A |
| 5744024 | Sullivan, III et al. | Apr 1998 | A |
| 7078005 | Smith et al. | Jul 2006 | B2 |
| 20050123466 | Sullivan | Jun 2005 | A1 |
| 20080109107 | Stefani et al. | May 2008 | A1 |
| 20110155646 | Karas et al. | Jun 2011 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 61616026 | Mar 2012 | US |
