A process for cooling quench effluent includes supplying a quench column effluent into a quench column aftercooler condensate; cooling the quench column effluent to extend a quench column aftercooler condensate; and recirculating at least a section of the quench column aftercooler condensate into the quench column aftercooler at a speed to prevent fouling of the quench column aftercooler.
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BACKGROUND
Various systems and processes for the manufacture of acrylonitrile and methacrylonitrile are known; see for example, U.S. Pat. No. 6,107,509. Normally, recovery and purification of acrylonitrile/methacrylonitrile created by the directreaction of a hydrocarbon selected from the group composed of propane, propylene or isobutylene, oxygen and ammonia in the presence of a catalyst has been accomplished by distributing the reactor effluent containing acrylonitrile/methacrylonitrile to afirst pillar (quench) where the reactor effluent is cooled with a primary aqueous stream, transporting the chilled effluent containing acrylonitrile/methacrylonitrile into another column (absorber) at which the chilled effluent is contacted with a secondaqueous stream to consume the acrylonitrile/methacrylonitrile into the second aqueous stream, transporting the second aqueous stream containing the acrylonitrile/methacrylonitrile in the second column to a first distillation column (recovery column) forseparation of the crude acrylonitrile/methacrylonitrile in the second aqueous stream, and transporting the separated crude acrylonitrile/methacrylonitrile to another distillation column (heads pillar ) to eliminate at least some impurities in the crudeacrylonitrile/methacrylonitrile, and transporting the partly purified acrylonitrile/methacrylonitrile to a third distillation column (product pillar ) to attain product acrylonitrile/methacrylonitrile. U.S. Pat. Nos. 4,234,510; 3,936,360;3,885,928; 3,352,764; 3,198,750 and 3,044,966 are illustrative of typical recovery and purification procedures for acrylonitrile and methacrylonitrile.
Effluent from the quench column may be chilled further before transporting to other downstream equipment. In one aspect, effluent from a quench is chilled in a direct contact cooler, referred to as a quench aftercooler (QAC) prior to going to anabsorber column. The QAC is typically a vertical, shell-and-tube exchanger using the procedure effluent flow through the tube and cooling medium on the other hand. The effluent vapor dissipates as it travels through the tubes and a few organics (primarilyacrylonitrile) and water condense, this is known as process condensate. Uncondensed vapor leaves the bottom of the QAC through a nozzle at the face of the exchanger beneath the tube sheet. The procedure condensate leaves the bottom of the QAC beneath levelcontrol and is pumped to downstream equipment (absorber or recovery column).
The procedure may experience a problem of blockage of the QAC tubes which necessitates regular shutdown of the plant for mechanical cleaning of the QAC. The blockage is a result of gradual buildup of polymer on the inside of the tubes. The polymer isprimarily poly-AN. The main reason behind this polymerization is that some acrylonitrile (AN) condenses on the tubes and this AN monomer isn’t inhibited, which easily allows polymerization to occur. Furthermore, the quench effluent contains some ammonia whichis not eliminated in the quench, and ammonia reacts with AN in liquid phase condensate to form polymer. The AN polymer is tacky and some can stick to the inside tube walls and slowly build up resulting in blockage of the tubes.
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