Part of the Complete Polyols Facility, IPP Stock #601057 which includes Propylene Oxide Plant #600894, Polyols Plant #600893 and Polyurethane Plant #601366
The Propylene Oxide Plant has a capacity of 20,000 mt/yr: This chlorohydrin based plant includes titanium reactors and vessels along with two nice propylene storage spheres. There is also a waste water pre-treatment plant incorporated in the PO facility.
This chlorohydrin based plant includes titanium reactors and vessels along with two nice propylene storage spheres. There is also a waste water pre-treatment plant incorporated in the PO facility.
Lime is delivered to the plant by standard railcar. It is unloaded into the lime storage silo and transferred to two slaker vessels where the lime is dissolved in hot water. The lime slurry is then pumped to the slaked lime storage tank located in the PO plant. The lime process equipment is located in another section of the facility.
Propylene is delivered to the plant by standard railcar. This process can operate on propylene with as low as 90% purity as long as the main impurity is propane. It is unloaded with pumps rated for 40 m3/hr each and sent to two spherical storage vessels; each holding 1,220 cubic meters and operating at about 14 bar.
Liquid propylene is pumped from the storage spheres with two pumps rated for 5.0 m3/hr each at 10.3 bar. The pumps are occasionally not necessary depending on the propylene pressure in the storage spheres. The propylene pumped to the vaporizer can contain up to approximately 10% (weight) propane.
Propylene is vaporized with steam in the vaporizer. The steam controls the liquid level in the vessel, which houses 14 square meters of U-tubes for heating. The propylene gas is then superheated with steam from 30°C to 80°C in a 5 square meter superheater operating at less than 11 bar. The heated propylene gas then mixes with the recycle reactor gas stream in a small vessel. The recycle stream contains propylene, propane, propylene dichloride (PDC), ethylene, ethane, and water.
Chlorine gas at 3.5 bar line pressure is injected into the bottom of the chlorohydrin reactor. This important and intricate part of the reactor is explained later.
Process water for cooling (12°C to 20°C) is pumped into the reactor for temperature control of the exothermic reaction. The two pumps are rated for 30 m3/hr each.
In the chlorohydrin reactor, chlorine is dissolved in hot water to form hypochloric acid (HOCl) and hydrochloric acid (HCl). The HOCl then reacts with the propylene to form propylene chlorohydrin and propylene dichloride (PDC) byproduct. Chlorine is injected in the reactor with four horizontal tubes with Kynar jets and Teflon nozzles. The water is also injected in the bottom of the reactor, just below the chlorine. The reactor is packed to a height of 1.8 meters with ceramic saddle packing. The propylene injection nozzle, which is in the form of two concentric rings, is located just above the ceramic packing. About 10% excess propylene is used in this reaction to minimize any residual chlorine. Antifoam additive is injected to reduce foaming in the reactor which can occur with poor water quality.
The chlorohydrin reactor is 2.6 meters diameter at the top and 1.7 meters diameter in the lower section. It is 15.8 meters tall and is constructed of titanium. The lower section uses palladium stabilized (0.15% Pd) titanium for added corrosion resistance. The top of the reactor is designed for the release of the reaction gases. The gases exiting the reactor are routed to a chlorohydrin scrubber to remove any propylene chlorohydrin from the PDC with warm water. The scrubber is constructed of titanium and is filled with ceramic saddle packing.
The recycle reactor gases are then washed in the PDC scrubber with cold water to remove the PDC byproduct. Recycling of PDC with the reactor gases reduces the overall plant yield. The PDC scrubber is 0.9 meters diameter by 13.7 meters tall and is packed with ceramic saddles. It is constructed of carbon steel, but the bottom section is lined with acid brick due to the corrosiveness of this process. Wastewater is pumped from the bottom of the PDC scrubber.
The large diameter piping from the reactor to the scrubbers is constructed of titanium.
The recycle gas is transferred with two blowers which take the pressure from near atmospheric to 2.5 bar. The blowers are Nash model H-7 units.
The recycle gas then flows through a separator for water removal. The separator is 3.7 meters diameter by 1.3 meters tall and is made of carbon steel with stainless steel internal plates. The overheads from this separator flow to another smaller separator where propane is removed overhead and sent to the flare. Recycle gas analyzers are included to analyze the amount of excess propylene in the system for proper reactor control.
In the second step of the reaction, lime is added to the propylene chlorohydrin to produce propylene oxide. Slaked lime slurry is stored in a 150 cubic meter tank with redundant pumps and pipelines in case of plugging. The lime reacts with the propylene chlorohydrin, and it also neutralizes the HCl in the system. A small amount of propylene glycol is produced as a byproduct which leaves with the waste water. The first 2.5 meters of the pipe reactor is constructed out of titanium and the remainder is carbon steel.
The vacuum stripper column concentrates the propylene oxide (PO) from about 2% to 89%. The carbon steel column is 1.4 meters in diameter and 16.2 meters tall with 17 baffle trays. The column overheads, containing the crude PO, are condensed and used as reflux in the column.
Vacuum is pulled on the vacuum stripper column with two Howden Godfrey model MK2/H255 compressors. The gearboxes are Howden model YH8122 with 1470 rpm input and 7078 rpm output. They are driven with 200 kW electric motors. The crude PO at this point contains89% PO, 5.8% water, and 2.8% PDC and other impurities. The stream is then cooled from 90°C to 45°C in a cooling exchanger.
The crude PO stream then enters the dechlorination column which is 0.6 meters diameter by 15.4 meters tall. It has three packed sections of ceramic saddles and is constructed of carbon steel. The product is then cooled and pumped to the 50 cubic meter intermediate storage tank. Crude product is pumped from the intermediate storage tank to the purification column which is 1.7 meters diameter by 47 meters tall. The column is constructed of carbon steel with an acid brick lining in the bottom section. It has 100 sieve trays and a lower packed section with ceramic saddle packing. This column purifies the PO to less than 300 ppm water and only traces of impurities. The PO overheads from the column are cooled to 30°C and some of the liquid is used as reflux on the column. The majority of the condensed PO is sent to storage. Water is removed from the bottom of the column.
PO is stored in three 50 cubic meter carbon steel storage bullets operating at about one bar. There are two pumps used to transfer the PO to the Polyol Plant. The EO comes in by rail and is stored in three larger vessels for use in the Polyol Plant.
There is a large quantity of wastewater generated in the chlorohydrin process for making PO. For this reason, there is a waste water pre-treatment facility integrated into the PO plant. This unit uses distillation and clarification for pre-treating the PO wastewater so it can be sent to a conventional biological treatment plant. The distillation column is packed with ceramic saddle-type packing. The waste water treatment plant (WWTP) is rated for about 200 cubic meters perhour
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