Flash tank

The size of a flash tank can be set by one of two possible criteria. The first is to have a liquid holdup time of at least 5 min with the tank half full, based on the liquid leaving the tank. The 

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First we calculate the size of the tank based on a liquid holdup time of 5 min when half fuU. An aspect ratio of 2 is used. 

The simpiest approach to disentraining iiquid is the fiash tank. The velocity is reduced to a vaiue which permits the droplets to settle rather than to be carried by the vapor. Evaporator bodies are generaiiy sized such that particies larger than a certain size will be disentrained. Flash tanks may be either vertical or horizontal. Vertical separators are usually more economical when the diameter is less than 8 feet for larger sizes, horizontal separators may be less expensive. 

Operation of horizontal flash tanks is improved when a distribution pipe is provided. Distributors can be installed normal to the tank axis with perforations directing the flow horizontally. Alternatively, the distributor pipe can be installed parallel to the tank axis with perforations directing the flow perpendicular to the tank axis. The inlet nozzle should always be located well above the maximum liquid level. 

Both vertical and horizontal flash tanks are susceptible to low frequency motion induced by sloshing. Consequently they should be rigidly supported. 

Often it is not practical to provide a vapor body large enough to accomplish the desired disentrainment. Entrainment separators are frequently used to reduce product loss. A number of proprietary designs are available. 

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Fig. 38. Caustic purification system a, 50% caustic feed tank b, 50% caustic feed pumps c, caustic feed preheater d, amonia feed pumps e, ammonia feed preheater f, extractor g, trim heater h, ammonia subcooler i, stripper condenser j, anhydrous ammonia storage tank k, primary flash tank 1, evaporator reboiler m, evaporator n, caustic product transfer pumps o, purified caustic product cooler p, purified caustic storage tank q, ammonia stripper r, purified caustic transfer pumps t, overheads condenser u, evaporator v, evaporator vacuum pump w, aqueous storage ammonia tank x, ammonia scmbber y, scmbber condenser 2, ammonia recirculating pump aa, ammonia recycle pump. CW stands for chilled water.

The rich oil from the absorber is expanded through a hydrauHc turbiae for power recovery. The fluid from the turbiae is flashed ia the rich-oil flash tank to 2.1 MPa (300 psi) and —32°C. The flash vapor is compressed until it equals the inlet pressure before it is recycled to the inlet. The oil phase from the flash passes through another heat exchanger and to the rich-oil deethanizer. The ethane-rich overhead gas produced from the deethanizer is compressed and used for produciag petrochemicals or is added to the residue-gas stream. 

The pressure used in producing gas wells often ranges from 690— 10,300 kPa (100—1500 psi). The temperature of the inlet gas is reduced by heat-exchange cooling with the gas after the expansion. As a result of the cooling, a liquid phase of natural gas liquids that contains some of the LPG components is formed. The liquid is passed to a set of simple distillation columns in which the most volatile components are removed overhead and the residue is natural gasoline. The gas phase from the condensate flash tank is compressed and recycled to the gas producing formation. 

The impact of cold GR-S was quite pronounced. The U.S. government edicted that all of the emulsion SBR plants switch to the cold process. This required addition of refrigeration capacity in these plants as well as other significant changes, such as insulation of reactors, improved vacuum to reduce oxygen that retards polymerization, and the heating of latex in blowdown tanks to aid in the disengagement of butadiene when transferred to the flash tanks. 

The reactivity of ethylene is high, whereas that of propylene is low and the various dienes have different polymerisation reactivities. The viscous mbber solution contains some unpolymerised ethylene, propylene, unpolymerised diene, and about 10% EPDM, all in homogeneous solution. This solution is passed continuously into a flash tank, where reduced pressure causes most of the unpolymerised monomers to escape as gases, which are collected and recycled. 

The mass flow rate at the flash-tank inlet rtij consists of three components rtij = mi + rtisup +... 

When the steam supply to one ejector of a group is closed, some means must be provided to for preventing the pressure in the condenser and flash tank from equ zing through that ejector, A com-partmental flash tank is frequently used for such purposes. With this... 

A float valve is provided to control the supply of makeup water to replace the water vapor that has flashed off, Tne flash tank should be insulated. 

Capacity Control The simplest way to regulate the capacity of most steam vacuum refrigeration systems is to furnish several primary boosters in parallel and operate only those required to handle the heat load. It is not uncommon to have as many as four main boosters on larger units for capacity variation. A simple automatic on-off type of control may be used for this purpose. By sensing the chilled-water temperature leaving the flash tank, a controller can turn steam on and off to each ejector as required. 

Figure 2. Material and energy balance diagram for flash tank.

MEA systems foam rather easily resulting in excessive amine can y over from the absorber. Foaming can be caused by a number of foreign materials such as condensed hydrocarbons, degradation products, solids such as carbon or iron sulfide, excess corrosion inhibitor, valve grease, etc. Solids can be removed with cartridge filters. Hydrocarbon liquids aie usually removed in the flash tank. Degradation products are removed in a reclaimer as previously described. 

Typically the flash tanks are designed for 2 to 3 minutes of retention time for the amine solution while operating half full. 

Pressure-reduction valve and pipe leading to the flash tank... 

There are 79,500 Ibs/hr of 450 psig condensate flowing into a flash tank. The tank is to be held at 250 psig, generating steam at this pressure. Determine the quantity of steam produced. 

Establish condensate receiver (or flash tank) pressure, psig. 

A 450 psig steam system discharges 9,425 lbs,/hr of condensate through traps into a return condensate line. The return header is to discharge into a flash tank held at 90... 

Figure 8-10. Schematic liquid flash tank. Note Feed can be preheated to vaporize feed partially.

Flash Tank Chilled Water Connection - Irtlet, OutI et. Ftonge Ratine. Face... 

Flash Tank Cerr. Allow Barometric Leg Corr. Allow ... 

Blowdown and heat recovery system (BDHR) flash tanks and heat exchangers are potential candidates for sludging, leading to restrictions in the drain line or heat transfer surfaces. Deposits in the BDHR heat exchanger may lead to under-deposit corrosion and leaks. 

Moderate Reactor Productivity. The rhodium catalyst is continuously recycled, but the catalyst is inherently unstable at low CO partial pressures, for example in the post-reactor flash tank. Under these conditions the catalyst may lose CO and eventually form insoluble Rhl3 resulting in an unacceptable loss of expensive catalyst. This reaction is also more likely to occur at low water concentrations, hence in order to run the process satisfactorily catalyst concentrations are kept low and water concentrations relatively high. Hence through a combination of lower than optimum reaction rate (because of low catalyst concentrations) and water taking up valuable reactor volume the overall reactor utilization is less than optimum. 

A typical configuration for a methanol carbonylation plant is shown in Fig. 1. The feedstocks (MeOH and CO) are fed to the reactor vessel on a continuous basis. In the initial product separation step, the reaction mixture is passed from the reactor into a flash-tank where the pressure is reduced to induce vapourisation of most of the volatiles. The catalyst remains dissolved in the liquid phase and is recycled back to the reactor vessel. The vapour from the flash-tank is directed into a distillation train which removes methyl iodide, water and heavier by-products (e.g. propionic acid) from the acetic acid product. 

Exposure of the reaction mixture to reduced carbon monoxide pressure in the flash-tank has implications for catalyst stability. Since the metal catalyst exists principally as iodocarbonyl complexes (e.g. [Rh(CO)2l2] and [Rh(CO)2l4]" for the Rh system), loss of CO ligands and precipitation of insoluble metal species (e.g. Rhl3) can be problematic. It is found that catalyst solubility is enhanced at high water concentrations but this results in a more costly separation process to dry the product. The presence of water also results in occurrence of the water gas shift (WGS) reaction (Eq. 6), which can be catalysed by Rh and Ir iodocarbonyls, in competition with the desired carbonylation process, resulting in a lower utilisation of CO ... 

From the top of the column, the propane that always accompanies the propylene feed emerges, talcing with it some of the benzene. In a flash tank, the propane is vented, and liquid benzene is recycled. From the bottom of the catalytic distillation column come the cumene, the PIPB, and some miscellaneous heavies chat are separated in a fractionator to make cumene, of 99.9% purity. The PIPB is separated in another column and fed to a second reactor with another zeolyte catalyst bed. In there the PIPB reacts catalyti-... 

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