Reactor vapor quench

Reactor vapor quench. LCO, naphtha, or other quench streams can be used to quench reactor vapors to minimize thermal cracking. 

As an example, the battery-limits capital cost can be estimated for the production of 10,000 t/yr of ethylene (qv) from ethanol (11). Seven processing blocks, ie, vaporizer, reactor, water quench, compressor, dryer, distillation, and energy recovery, can be identified. The highest temperature is 350°C (reactor), and the highest pressure is about 1.7 MPa (17 atm) (compressor, two towers). If a materials-pressure factor, + of 1.03 is assumed, then for N = 7 0 = 0.87 1/0 = 1 64 and f =0 K = 6.3. This gives the 1981 cost as 4.4 X 10 . The 1991 battery-Hmits investment can be obtained, by updating with the CE Plant Cost Index, as 5.3 x 10 . ... 

The bottom section of the main column provides a heat transfer zone. Shed decks, disk/doughnut trays, and grid packing are among some of the contacting devices used to promote vapor/liquid contact. The overhead reactor vapor is desuperheated and cooled by a pumparound stream. The cooled pumparound also serves as a scrubbing medium to wash down catalyst fines entrained in the vapors. Pool quench can be used to maintain the fractionator bottoms temperature below coking temperature, usually at about 700°F (370°C). 

Since the mid-1980s, FCC technology licensors and a number of oil companies have employed a number of RTD s to reduce non-selective post-riser cracking reactions. Two general approaches have been used to reduce post riser cracking. The most widely used approach is direct connection of the cyclones to the riser and on to the reactor vapor line. The second approach is quenching the reactor vapors downstream of the riser-cyclones (rough-cut cyclones). 

The effluent from the adiabatic reactor is quenched with liquid from the separator. This quenched stream is the hot-side feed to the process-to-process heat exchanger, where the cold stream is the reactor feed stream prior to the furnace. The reactor effluent is then cooled with cooling water, and the vapor (hydrogen, methane) and liquid ( benzene, toluene, diphenyl) are separated. The vapor stream from the separator is split. Part is purged from the process to remove the methane byproduct and the remainder is sent to the compressor for recycle back to the reactor. 

Note that the flash with recycle process is a good representation of a quench vessel, in which hot gases, typically from an exothermic reactor, are quenched by a cold liquid recycle. Quenches are often needed to provide rapid cooling of a reactor effluent by direct-contact heat transfer. Cold liquid is showered over hot, rising gases. As some of the liquid vaporizes, the latent heat of vaporization is absorbed, and cooling occurs. Quenches are particularly... 

Some months later a resourceful technical service engineer decided to use heavy cycle oil (HCO) instead of slurry oil in the vapor-line quench nozzle. I leave it to the reader to explain why the tower began to flood at its former rate, even though the vapor feed was desuperheated by the HCO in the reactor vapor line. The above calculations quantifying the bubble effect partially provide the answer. 

Determine which section initiates flooding Desuperheating reactor vapor Bubble effect in slurry P/A Reactor vapor line quench... 

The reactor effluent might require cooling by direct heat transfer because the reaction needs to be stopped quickly, or a conventional exchanger would foul, or the reactor products are too hot or corrosive to pass to a conventional heat exchanger. The reactor product is mixed with a liquid that can be recycled, cooled product, or an inert material such as water. The liquid vaporizes partially or totally and cools the reactor effluent. Here, the reactor Teed is a cold stream, and the vapor and any liquid from the quench are hot streams. 

Process development of the use of hydrogen as a radical quenching agent for the primary pyrolysis was conducted (37). This process was carried out in a fluidized-bed reactor at pressures from 3.7 to 6.9 MPa (540—1000 psi), and a temperature of 566°C. The pyrolysis reactor was designed to minimize vapor residence time in order to prevent cracking of coal volatiles, thus maximizing yield of tars. Average residence times for gas and soHds were quoted as 25 seconds and 5—10 rninutes. A typical yield stmcture for hydropyrolysis of a subbiturninous coal at 6.9 MPa (1000 psi) total pressure was char 38.4, oil... 

The reactor effluent is rapidly quenched with aqueous mother Hquor in specially designed equipment operating at pressures essentially equal to the reactor pressure. This operation yields an off-gas consisting of ammonia and carbon dioxide vapor and a crystalline melamine slurry saturated with ammonia and carbon dioxide. The slurry is concentrated in a cyclone mill. The mother Hquor overflow is returned to the quenching system. The concentrated slurry is redissolved in the mother Hquor of the crystallization system, and the dissolved ammonia is stripped simultaneously. 

SWEC offers a reactor quench system rather than a closed cyclone system. Their typical RTD is an external, rough-cut cyclone (see Figure 9-7). The vapors from the rough-cut cyclone enter the reactor vessel. 

Effective temperatures. When extracting stream data to represent the heat sources and heat sinks for the heat exchanger network problem, care must be exercised so as to represent the availability of heat at its effective temperature. For example, consider the part of the process represented in Figure 19.8. The feed stream to a reactor is preheated from 20°C to 95°C before entering the reactor. The effluent from the reactor is at 120°C and enters a quench that cools the reactor effluent from 120°C to 100°C. The vapor leaving the quench is at 100°C and needs to be cooled to 40°C. The quenched liquid also leaves at 100°C but needs to be cooled to 30°C. How should the data be extracted ... 

The fundamental question regarding representation of the part of the flowsheet in Figure 19.8 as heat sources and heat sinks is at what temperature the heat becomes available for heat recovery opportunities. Even though the reactor effluent is at 120°C, it is not available at this temperature because the reactor effluent needs to be quenched. The heat only becomes available at 100°C as a vapor stream that needs to be condensed and cooled to 40°C and as a quench liquid at 100°C that needs to be cooled to 30°C. 

Operating pressure There are three modes of operation of a quench tank atmospheric pressure operation, nonvented operation, and controlled venting operation. Atmospheric operation is usually feasible when the effluent Being emitted has a bubble point well above the maximum ambient temperature. A very small quantity of vapor escapes with the air that is displaced as the tank fills with the emergency discharge (typically about 0.2 percent of the reactor contents). Depending on the toxic or flammable properties of the vapor, the vent from the quench tank can be routed to the atmosphere or must be sent to a scrubber or flare. 

Post-riser quench can be used if a reactor vessel has a metallurgical limit and a higher riser outlet temperature is desired. Higher octanes and more alkylation feed may be the result. Improved vaporization of the feed could lower delta coke. 

The sample treatment is executed as follows The sample is located inside the chamber. The SFM scanner is retracted by about 8 mm from the sample. Then the chamber is closed by the lid. In order to anneal the sample successfully, we perform the treatment in a hermetically sealed reactor chamber. The sample is exposed to chloroform vapor while a voltage is applied across the electrodes on the glass substrate. The gas flow rate through the system is controlled by mass flow controllers and additionally checked by a flow meter installed at the outlet of the chamber. After a certain annealing time, the solvent is removed with a flow of pure argon while the voltage is still applied in order to quench the structure in the presence of the electric field. Subsequently the lid is opened, the voltage is switched off, and the SFM scanner is moved towards the sample. This procedure is repeated several times. The accomplishable position stability as a key performance feature of the quasi in situ SFM amounts to almost the same value as reported in [32] (low pressure plasma treatments). The increase in lateral drift is only about 23 nm per process step. The... 

Because of high reactor temperatures, the hydrocarbon volatiles vaporize immediately, and are vented from the reactor to a quench tower (Item 3), where they are sprayed with cooled, recycled, heavy oil, and the larger molecules (molecules containing eight carbon atoms (C8) or more) are condensed. The condensate leaves from the bottom of the quench tower and is collected in the heavy oil receiver (Item 4). Compounds that are not condensed (i.e., light oil, C3-C7) in the quench tower enter a non-contact condenser that uses cold water The light oils, C3 to C7, are condensed and collected in the light oil receiver (Item 6). 

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