The Plant operation supplies a high purity Isobutene stream for various end users.
Plant was constructed in 1981 and has a capacity of 125,000 tons/year
This Isobutylene Plant uses “cold acid extraction” technology for the extraction of isobutylene from a mixed-C4 feed stream. This stream typically comes from a refinery after the butadiene has been extracted. The technology will not have any licensing requirements. This process will work with isobutylene concentrations ranging from 17 - 48% in the mixed-C4 stream with a maximum approx. flow of 34 tons/hr (286,000 tons/yr). This equates to 51,000 – 125,000 tons/yr of isobutylene production depending on the feed-stream composition.
The separation of a mixed-C4 stream is extremely difficult due to the similar boiling points. This technology reacts the isobutylene in the mixed-C4 stream with dilute sulfuric acid (49.5%) to produce tertiary butyl alcohol (TBA). The TBA has a significantly different boiling point which makes it easy to separate from the mixed-C4s. The separated TBA is then “cracked” back to isobutylene using heat in a distillation column. The plant is in excellent condition.
There are significant amounts of Alloy 20, Zirconium, and other alloys in the large-diameter process piping, exchanger tubes, and equipment.
The facility started up in the early 1981, but some of the equipment and piping has been replaced over the years. The plant recently shut down in July, 2014.
Major equipment can be loaded on barges or ships at the plant site which is on a major waterway.
This facility typically operated three years between turnarounds. The turnarounds usually lasted only two or three weeks.
Process Overview - For a complete Report, Click Here
This Isobutylene Plant uses “cold acid extraction” technology for the extraction of isobutylene from a mixed-C4 feed stream (butanes and butenes). This Raffinate I stream typically comes from a refinery after the butadiene has been extracted. The technology will not have any licensing requirements. This process will work with isobutylene concentrations ranging from 17 - 48% in the mixed-C4 stream with a maximum approx. flow of 34 tons/hr (286,000 tons/yr). This equates to 51,000 – 125,000 tons/yr of isobutylene production depending on the feed-stream composition.
The separation of a mixed-C4 stream is extremely difficult due to the similar boiling points. This technology reacts the isobutylene in the mixed-C4 stream with dilute sulfuric acid (49.5 %) to produce tertiary butyl alcohol (TBA) which is soluble in the acid. The mixture of TBA and acid (extract) is purified, heated, and reconverted to recover isobutylene in a pure form.
The TBA has a significantly different boiling point which makes it easy to separate from the mixed-C4s. The separated TBA is then “cracked” back to isobutylene using heat in a distillation column. There is a TBA recovery system for reclaiming the un-converted TBA. The remaining C4s are sold in the market as “Raffinate II” product. The raffinate handling is the current bottleneck in the plant.
The feed (Raffinate I) is pumped in from the feed sphere where it is brought in contact with dilute (49.5%) sulphuric acid and selectively converts the Isobutene into Tertiary Butyl Alcohol (TBA) which is soluble in the acid. There are 3 reactor chains A, B, C, each consisting of a reactor, emulsion pump, cooler and settler. The feed is introduced into the "A" reactor emulsion pump and travels through A,B,C chains becoming leaner in Isobutene. The lean sulfuric acid is introduced at "C" reactor emulsion pump and travels through C, B, A chains becoming richer in TBA before going to Purifying step from the bottom of "A" stage settler. The Spent (Raffinate II) leaves the top of "C" settler and is sent to the Spent C4 wash tower.
In the Purifying substep, recovered TBA is injected into the extract and is heated by low pressure steam on temperature control and passes through a vessel which is maintained in a vacuum. The purified extract is pumped to the Regenerating substep. The material that vaporizes is called “vent butenes”. This vapor is treated and compressed back into a liquid, which is recycled back to the Reacting substep.
In the Regenerating substep, purified extract is heated. The heat converts most of the TBA back into isobutene, and the mixture of vaporized TBA and isobutene, called “crude (or unwashed) isobutene”, continues on to the Isobutene Purifying Step. The sulfuric acid, free of TBA (regenerated), is recycled back to the Reacting substep. Some fresh sulfuric acid is mixed with the regenerated acid to control its quality.
In the isobutene plant, the crude isobutene is mixed with caustic wash, then water washed to clean up any polymer or TBA entrained with the crude isobutene. The isobutene continues on to the Isobutene Compression and Surge Step.
.............Isobutene from here is commonly referred to as product or high purity IC4-.
Isobutene Compression and Surge:
The isobutene enters a knock-out drum and then into the C-1's where it compresses the IC4- vapors. From here it is condensed and put into D-1 surge drum, pumped into T-2 to be rewashed and then into D-23 surge drum. This stream is then analyzed and pumped to the product sphere.
Vent Butene Compression and Surge:
Vent Butene vapors from the flash drum are caustic and water washed, continues on to the Liquid Ring Compressors which create the vacuum. From here the vapors are compressed in the C3's, condensed in E-18, collected in surge drum D-18 and then pumped back into Reactors.
Polymer (C5) is a by product of regenerating TBA into isobutene and needs to be separated from the wash water. D-20 bottoms and T-8 bottoms are pumped into T-9 where it is washed with water to remove the TBA. The Polymer exits the top of the tower and flows into D-21 surge drum and is pumped into D-18 to be pumped into the reactor section. The TBA/Wash water is sent to the TBA recovery section. Spent C4
The overhead of the "C" Reactor is water washed in T-3 to remove TBA from this stream. The spents go overhead to D-8 surge drum where it analyzed and pumped to the spents sphere.
...............This Butene stream is commonly referred to as spent C4’s or Raffinate II.
The TBA Recovery section, recovers the TBA from a combined wash streams (T-3, T-2, T-9 and T-5), by steam stripping in the TBA recovery tower T-10 or T-11. In turn T-10/11 provides us with a clean condensate wash stream that is recycled in the process and a clean recovered TBA stream at 72%, that is returned into the Purifying step. TBA
TK-2 provides storage for the recovered TBA to be re-used in the process.
Water Handling - Cooling water from the river is pumped via from the Steam & Power Plant to the Secondary Cooling Water Loop where it cools the unit cooling water and drains to the 54″ sewer. All process water except the compressor building is drained to the I-Plant Effluent system where it is treated with caustic and pumped directly to Biox. The compressor building drains to the Oily Water Sewer/M.O.S.
Air Distribution - yard air from K-1 East and atmospheric air are compressed and dried to produce instrument air and plant air.
Steam Distribution - 1050 KPA steam from the power plant is distributed to users at 150 KPA and 1050 KPA pressures.
Nitrogen - Nitrogen is used for purging equipment throughout the plant, and is also used for operating the nitrogen blanketing system on the Acid storage tank and Glycol tank.
Condensate System - Condensate is used in the process and any excess condensate is pumped back to the S&PP via D-29 at the I-Plant.
See Report under Process Description for Equipment List
Electricity, steam, water.
Provides Instrument air, Yard air, Process water, 1050 KPA steam, 150 KPA steam, Nitrogen, Condensate distribution for the production of high purity Isobutene.
Documentation is excellent and is primarily electronic. PFDs, P&IDs, process descriptions, and equipment files with maintenance and inspection histories is available.
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