Delayed Coking for Pretreating Vacuum Resids

Delayed coking is being used to pretreat vacuum resids to prepare coker gas oil streams for catalytic cracking and hydrocracking. The coke is used in various applications, including fuel use, anode manufacture for alumina production, and electrode manufacture for steel production. In the early refineries, severe thermal cracking of heavy stocks, including vacuum residues, resulted in coke deposition in the heaters. Heating above the coking temperature is possible without significant coke formation in the furnace by heating so rapidly that little reaction occurs. This is done by operating at high velocities in high heat flux furnaces.

The heater effluent is then sent to the coke drum where it stays to undergo thermal cracking to make coke and vapors which are then condensed. In other words, the coking of the vacuum residue is delayed until it accumulates in the coke drum [1, 2]. Intertek PARC provides delayed coking services using either a small delayed coker pilot plant with a 5 liter coke drum or a large delayed coker pilot plant with three coke drums using either 29 or 81 liter liners.

For more information on Intertek PARC’s delaying coking capabilities, visit: http://www.intertek.com/testing/pilot-plant/thermal-heavy-oil/ . Intertek provides analytical services for coke and coker products analysis. For more information on coke analysis, visit: http://www.intertek.com/petroleum/testing/coke-fly-ash/.


The Petroleum Administration for Defense (PADD) 3 area consists of the following states: Texas, New Mexico, Mississippi, Louisiana, Alabama and Arkansas. 2009 Data indicates that there are 57 operable refineries in the PADD 3 Gulf Coast region. Over the last 15 years, the operable crude oil distillation capacity has increased from ~7.0 MM bbls/day to close to ~8.5 MM bbls/day. To handle the imported, heavier crudes targetted for use in these refineries, delayed coking charge capacity of PADD 3 refineries was increased from 726 M bbl/day to close to 1,350 M bbl/day from 1995 to 2009. Refinery utilization has steadily increased until 2004 when it started to decline. PADD 3 imports have also steadily increased since 1985 until 2004 when it too started to slightly decline [3].



PADD 3 refineries import crude oil from OPEC countries, including Saudi Arabia, Nigeria and Venezuela; and Non-OPEC countries, including Mexico. Developments since 2004 indicate steady declines in Mexican and Venezuelan heavy crude exports to the U.S. Furthermore, Saudi Arabia has reduced exports of high-sulfur crude oil to the U.S. [3, 4]. Mexico’s crude oils consist of a mix of a heavy crude, 22° API Maya, and lighter crudes, 34° API Isthmus and 39° API Olmeca. Most of the lighter crudes are used domestically with the bulk of the Maya being exported to PADD 3 refineries. Venezuela produces four crudes with an average API of less than 20° [3].


Consequently, as Welsch pointed out, heavy crudes are in demand in the PADD 3 region. Only 2.2% of crude refined in the PADD 3 region comes from Canada and producers of crude from Canada’s oilsands are trying to enter the PADD 3 market to take advantage of the increased heavy crude demand [4]. Pilot plant services will be required to quantify yields and product properties upon delayed coker feedstock changes.


References:



1. Gary, J.H., Handwerk, G.E., and Kaiser, M.J., Petroleum Refining: Technology and Economics, Fifth Edition, CRC Press, New York, 2007, pp. 97-105.


2. Hengstebeck, R.J., Petroleum Processing, Principles and Applications, McGraw-Hill Book Company, Inc., New York, 1959, p.136.


3. http://www.eia.doe.gov/


4. Welsch, E., Dow Jones Newswires, March 23, 2010, cited by Downstreamtoday.com.