Absorption towers bottom-packed

A packed absorption tower is designed to removed SO2 from a coke oven stack. The water flow rate L = 16.64 kgmols/s and the gas flow rate G = 0.39 kgmols/s. The mole fraction of SO2 in the air at the bottom of the tower is 0.03 and its mole fraction in the absorption water at the bottom of the tower is 0.0007. If the mole fraction of SO2 in the air at a point in the tower 7 meters from the bottom is 0.016, what is the corresponding mole fraction of the SO2 in the downward flowing scrubbing water. 

Spray or packed extraction towers, as shown in Figure 5.2, are similar to those used in gas absorption with the exception that two liquids, rather than a gas and a liquid, are flowing countercurrent to each other. The less dense, or lighter, liquid enters the tower bottom through a distributor, which creates small drops flowing upwards. These rise through the... 

Air at 25 °C is used to dry a plastic sheet containing acetone. At the drier exit, the air leaves containing 0.02 mole fraction acetone. The acetone is to be recovered by absorption with water in a packed tower. The gas composition is to be reduced to 5 X10 mole fraction at the colunm exit. The equilibrium relationship is y = 1.8x. The gas enters the bottom of the colunm (Figme 6.12) at a flux of 1000 Ibm/ft - hr, and the water enters the top at a flux of 1400 Ibm/ft hr. The tower is packed with... 

The absorber consists usually of a single stainless-steel tower, although two or more may be necessary for low-pressure plants. Another kind of absorber used is a drum absorber. In general, the cool gases along with additional air are fed to the bottom of the tower, and demineralized water is fed to the top of the tower. Instead of demineralized water, clean condensed steam can be used. Nitric acid is taken out from the bottom, whereas tail gases leave at the top of the tower. The absorption towers can be packed with sieve plates, bubble cap plates, or turbo-grids. 

TEMPERATURE VARIATIONS IN PACKED TOWERS. When rich gas is fed to an absorption tower, the temperature in the tower varies appreciably from bottom to top. The heat of absorption of the solute raises the solution temperature, but evaporation of the solvent tends to lower the temperature. Usually the overall effect is an increase in the liquid temperature, but sometimes the temperature goes through a maximum near the bottom of the column. The shape of the temperature profile depends on the rates of solute absorption, evaporation or condensation of solvent, and heat transfer between the phases. Lengthy computations are needed... 

The 50 per cent acid obtained may be concentrated through the use of strong sulphuric add. A tower similar to the absorption tower is supplied with strong sulphuric acid and the weak nitric add W hich trickles down over the tower packing and is treated with steam introduced at the base of the tower passing counter current to the flow of the acid mixture. The distilled concentrated nitric acid is drawn off near the top of the tower and condensed in the condenser tubes, while the sulphuric acid is drawn ofl at the bottom, coiicentrated and used over again. 

Absorption in a Packed Column. Figure 10.5.4 shows a packed column absorber with unit cross-sectional area and height H. Gas enters the bottom of the tower and liquid absorbent enters the top. Assume that the solute in both gas and liquid is dilute, so that the volumes of carrier gas and solvent are unchanged in passing through the tower. The material balance on a dilferential element is... 

Aim of this paper is to present an innovative and sustainable process based on VOC absorption. An absorption tower is fed on the top by oil which efficiently absorbs at low temperature the VOCs contained by the off-gas which enters the tower at its bottom. The mass ratio between oil and gas is approximately around 1, so that a tray configuration results more efficient than an alternative packed column. Saturated oil from the column is then stripped at high temperature in a vacuum system which condenses VOCs at a temperature slightly below the ambient temperature. Stripped oil is then recycled to the absorption tower. 

Example 13-3 We want to remove alcohol vapor from carbon dioxide using a packed column containing 2.54-cm Raschig rings at 40°C. The vapor (0.01 mole fraction alcohol) needs to have 98 percent recovery of alcohol. The water used for absorption has 0.0001 mole fraction alcohol. The Gm at the tower bottom is 0.0422 kg-mol/sec m. The ratio of L to Gm is 1.5264. Equilibrium is given by T = 1.0682x . Values of He and Hi are 0.54 and 0.30 m, respectively. 

The bottom-packed bed is fed with 450 K, slightly diluted return acid from the steam-from-acid heat boiler. H20( ) in the descending acid reacts with the ascending gas SO3 to form hot H2S04( ) by exothermic reaction (1.2). Input acid composition and flow rate are controlled to give hot ( 500 K) absorption tower product acid. 

The top-packed bed is fed with cool ( 350 K) acid from the acid plant s final absorption tower (Fig. 9.6). Its principal purpose is to absorb SO3, H20(g), and H2S04(g), rising from the hot bottom bed. The vapor pressures of all these gases are all lower with cool acid than with hot acid. 

A reactive absorption is done in a countercurrent packed tower. The material balance is made in terms of solute-free quantities. Inlet conditions are X2 = 0, Yx - 0.5 outlet Xx =0.8, Y2 = 0.1. Bottom is 1, top is 2. 

A common device used in gas absorption and stripping is the packed tower, the elevational section of which is shown in Figure 9.6i. The device consists of a column or tower equipped with a gas inlet and distributor at the bottom and a liquid inlet and distributor at the top. It also consists of a liquid outlet at the bottom and a gas outlet at the top and a supported mass of solid shapes called tower packing or filling. 

The most common applications of this technique in distillation and absorption columns is for liquid level and liquid level interface detection, especially when normal level-measuring techniques suffer from plugging. Neutron backscatter techniques have also been used for froth height measurements on trays and downcomers, and for measuring the top and bottom of packed beds. One case history has been described (71) where downcomer froth height measurements using the neutron backscatter technique led to a detection of downcomer deposits which caused premature flooding of the column. The author is familiar with one case where this technique successfully detected overflow of a packed tower distributor. 

This chapter introduces the use of Aspen HYSYS to model a continuous gas absorption process in a packed column. The only imit operation contained in the Absorber is the Tray Section, and the only streams are the overhead vapor and bottom liquid products. There are no available specifications for the Absorber, which is the base case for all tower configurations. The conditions and composition of the column feed stream, as well as the operating pressure, define the resulting converged solution. The converged solution includes the conditions and composition of the vapor and liquid product streams. 

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