Liquid bottoms

In a batch process (176), a glass-lined jacketed iron vessel is charged with either sulfur monochloride or sulfur dichloride and about 1% of antimony trichloride as a catalyst. Chlorine is introduced into the reactor near the bottom. Liquid oleum is added to the reactor at such a rate that the temperature of the reaction mass is held at ca 25°C by the use of cooling water in the jacket. 

Liquid reaching the bottom of the column is partially vaporized in a heated r eboiler to provide boil-up, which is sent back up the column. The remainder of the bottom liquid is withdrawn as bottoms, or bottom product. Vapor reaching the top of the column is cooled and condensed to liquid in the over head conden.ser. Part of this liquid is returned to the column as r eflux to provide liquid overflow. The remainder of the overhead stream is withdrawn as distillate, or overhead product . In some cases only part of the vapor is condensed so that a vapor distillate can be withdrawn. 

GLS Fluidized with a Stable Level of Catalyst Only the fluid mixture leaves the vessel. Gas and liquid enter at the bottom. Liquid is continuous, gas is dispersed. Particles are larger than in bubble columns, 0.2 to 1.0 mm (0.008 to 0.04 in). Bed expansion is small. Bed temperatures are uniform within 2°C (3.6°F) in medium-size beds, and neat transfer to embedded surfaces is excellent. Catalyst may be bled off and replenished continuously, or reactivated continuously. Figure 23-40 shows such a unit. 

Effects. Trays can become damaged several ways. A pressure surge can cause damage. A slug of water entering a heavy hydrocarbon fractionator will produce copious amounts of vapor. The author is aware of one example where all the trays were blown out of a crude distillation column. If the bottom liquid level is allowed to reach the reboiler outlet line, the wave action can damage some bottom trays. 

Steam stripping is not adequate for the bottoms purity required. More positive stripping is obtained by charging the tower bottom liquid to the reboiler. In a typical reboiler, 50% of the feed is vaporized and returned to the tower below the bottom plate. A fractionating tower equipped with a steam heated reboiler is shown... 

Distillation Aqueous or non-aqueous solutions high organic concentrations Recovered solvent still bottom liquids, sludge, and tars... 

Assume an initial split of components in the inlet that yields the desired vapor pressure. That is, assume a split of each component between the tower overhead (gas) and bottoms (liquid). There are various rules of thumb that can be used to estimate this split in order to give a desired vapor pressure. Once the split is made, both the assumed composition of the liquid and the assumed composition of the gas lue known. 

Calculate the composition of the inlet liquid falling from Tray 1. Since the composition of the bottom liquid and gas in equilibrium... 

The heat required at the reboiler depends upon the amount of cooling done in the condenser. The colder the condenser, the purer the product and the larger the percentage of the intermediate components that will be recovered in the separator and kept from going out with the gas. The hotter the bottoms, the greater the percentage of light components will be boiled out of the bottoms liquid and the lower the vapor pressure of the bottoms liquid. 

The inherent error between true vapor pressure and RVP means that a stabilizer designed to produce a bottoms liquid with a true vapor pressure equal to the specified RVP will be conservatively designed. The a[>or pressures of various hydrocarbon components at 100°F are given in Table 6-1. 

To estimate the desired composition of the bottom liquid, the vapor pressures of the different components at 100°F can be assumed to be a measure of the volatility of the component. Thus, if a split of n-C4 is assumed, the mole fraction of each component in the liquid can be estimated from ... 

L = total number of moles of component n in the bottom liquid... 

C4 split) = assumed moles of component n-C4 in bottom liquid divided by moles of n-C4 in feed RVn = relative volatility of component n from Table 6-1... 

To determine the compositon of the bottom liquid, assume a split of n-C4 and compute MFn from Equations 6-2 and 6-3. The vapor pressure can then be computed from Equation 6-1. If the vapor pressure is higher than the desired RVP choose a lower number for the 11-C4 split. If the calculated vapor pressure is lower than the desired RVP, choose a higher number for the n-C4 split. Iterate until the calculated vapor pressure equals the desired RVP. 

The tower operates in the same manner as a condensate stabilizer with reflux. The inlet liquid stream is heated by exchange with the gas to approximately 30 F and is injected in the tower at about the point in the tower where the temperature is 30 F. By adjusting the pressure, number of trays, and the amount of reboiler duty, the composition of the bottoms liquid can be determined. 

By decreasing the pressure and increasing the bottoms temperature more methane and ethane can be boiled off the bottoms liquid and the RVP of the liquid stream decreased to meet requirements for sales or further processing. Typical liquid recovery levels are ... 

The de-methanizer is analogous to a cold feed condensate stabilizer As the liquid falls and is heated, the methane is boiled off and the liquid becomes leaner and leaner in methane. Heat is added to the bottom of the tower using the hot discharge residue gas from the compressors to assure that the bottom liquids have an acceptable RVP or methane content. 

The bottoms liquid from any gas plant may be sold as a mixed product. This is common for small, isolated plants where there is insufficient local demand. The mixed product is transported by truck, rail, barge or pipeline to a central location for further processing. Often it is more economical to separate the liquid into its various components and sell it as... 

The temperature at the base of the de-butanizer determines the vapor pressure of the gasoline product. If its vapor pressure is too high, the temperature must be increased or the tower pressure decreased to drive more butanes-minus out of the bottoms liquids. 

Table 5-1 shows that in a cylinder tank, four baffles, each A2 tank diameter above flat bottom, liquid depth is equal to tank diameter, impeller shaft is vertical and at centerline of tank. 

Dimethyl ether is to be separated from methanol. A batch type operation is to be tried to see if an existing coil-in-tank can be used. The pressure of the system will be about 55 psia. How many total mols will remain in the bottoms when the bottoms liquid composition contains 0.5 mol percent dimethyl ether What is the composition of the total overhead collected ... 

The design of a distillation column requires a reboiler operating at 2.23 psia (vapor space above bottom liquid). The heat duty is 1,528,600 Btu/hr. The properties of the acrylonitrile mixture have been calculated to be... 

Example 11.7 Carbon dioxide is sometimes removed from natural gas by reactive absorption in a tray column. The absorbent, typically an amine, is fed to the top of the column and gas is fed at the bottom. Liquid and gas flow patterns are similar to those in a distillation column with gas rising, liquid falling, and gas-liquid contacting occurring on the trays. Develop a model for a multitray CO2 scrubber assuming that individual trays behave as two-phase, stirred tank reactors. 

In this case, both the top and the bottom liquid phases contain the same ion at equilibrium. A micropipette tip is used to deplete concentration of this ion in the top solvent near the ITIES. This depletion results in the ion transfer across the ITIES (Fig. 13), which can produce positive feedback if the bottom phase contains a sufficiently high concentration of M ... 

NGL Column Bottoms Liquid Percentage Concentration from sample analysis ... 

If FLFEES is not zero, the value of jretyp is examined to find which of either the reboiler vapor or bottom liquid has been set in the problem description. If reboiler vapor has been set, the program examines flfees to see if it is less than the fixed amount of reboiler vapor, fixrv. If so, all of FLFEES is taken as reboiler vapor, the bottom liquid is set at zero, KALTER is set to 1, the temperature is determined by a dewpoint calculation on the reboiler vapor, and the calculation returns to the basic program. On the other hand, if flfees is more than large enough to supply FIXRV, the remainder is taken as bottom liquid and the temperature and compositions are obtained by calculation of a flash for which the total vapor and total liquid are known (isovfl). If the bottom liquid is specified, exactly the same procedure is followed except that in the case of a mass input less than the specified bottom liquid, fixbl, all of the input... 

This reactor contains at least two solid phases, two Hquid phases, and a gas phase. The flows are largely driven by gravity caused by the density differences of the soHd and Hquid phases. Taconite and coke are admitted at the top of the reactor and O2 at the bottom. Liquid Fe and slag are withdrawn at the bottom of the reactor. The Hquid iron is either cast into ingots in molds or directly passed from the reactor through rolling mills to process it into sheets. 

Tower-bottom liquid level covering the reboiler vapor return nozzle. 

Increasing the tower bottoms liquid level. However, should this level reach the reboiler return nozzle, thermosyphon flow will be restricted, or even stop. Then, the reboiler heat duty will be reduced, and the tower pressure will drop. 

Note that in a kettle reboiler, the bottoms product level control valve does not control the level in the tower it controls the level on the product side of the reboiler only. The liquid level on the boiling or heat-exchanger side of the kettle is controlled by the internal overflow baffle. But what controls the tower-bottom liquid level ... 

Remember, though, that the increased tower-bottom liquid level will not be reflected on the indicated bottom level seen in the control room, which is actually the level at the end of the kettle reboiler. This is a constant source of confusion to many operators, who have towers that flood, as a result of high liquid levels, yet their indicated liquid level remains normal. 

Three-layered structure. Van Sinderen, Wijn, and Zanting [Trans. IChemE, 81, Part A, p. 94 (January 2003)] postulate a tray dis-ersion consisting of a bottom liquid-rich layer where jets/bub-les form an intermediate liquid-continuous froth layer where bubbles erupt, generating drops and a top gas-continuous layer of drops. The intermediate layer that dampens the bubbles and... 

A schematic process flow sheet is shown in Figure 2. Inlet gas, a mixture of methane, hydrogen and carbon monoxide at 100°F and 500 psia (stream 1) is successively cooled to -140°C by the outlet gas stream from the absorber and some recycle gas. The absorber is a packed column of 1-in. berl saddles with 50% void fraction. The rich liquid from the bottom of the absorber is heat exchanged with the bottom liquid from the stripper. The stripper is also a packed column with 1-in. berl saddles. The dissolved methane, hydrogen, and carbon monoxide is stripped out by heating at the bottom of the stripper. The outlet gas stream from the stripper is heated in a heat exchanger by a recycle gas stream and is further compressed to produce the final methane product at 100°F and 1000 psia. 

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