Stripper/scrubber

Figure 20.2 Different types of membrane contactors, (a) stripper/ scrubber, driving force difference of concentration (b) liquid-liquid extractors, driving force difference of concentration (c) removal of volatiles/gases from liquids, driving force difference of partial pressures (d) direct contact membrane distillation, driving force difference of partial pressures (e) supported liquid membranes, driving force difference of concentrations.

When compared to conventional systems (such as strippers, scrubbers, distillation columns, packed towers, bubble columns, evaporators, etc.), membrane contactors present several advantages, as reported in Figure 20.3. However, some drawbacks have also to be taken into account, as shown in Figure 20.4. 

Figure 7-3. The Scientific Design Co. Ethylene Oxide process (1) reactor, (2) scrubber, (3,4) C02 removal, (5) stripper, (6,7) fractionators.

The stream from the reactor consisting of a mixture of urea, unconverted ammonium carbamate, excess water, and NH, is fed into the top of the stripper. The ACES stripper utilizes a ferrite—austenite stainless steel, as do the carbamate condensers. The reactor and scrubber are constructed with 316 L urea-grade stainless steel. 

The cooled process gas that leaves the Syngas Scrubber is fed to the Amine unit. The amine unit consists of an absorption-stripping system plus associated equipment. In this system a circulating amine stream (activated MDEA - or Methyl Diethanolamine) absorbs the C02 in the C02 Absorber. The amine is regenerated in the C02 Stripper with the C02 being recycled to the compressor. 

The ACES stripper uses a ferrite-austenite stainless steel as do the carbamate condensers. The reactor and scrubber are constructed with 316L urea-grade stainless steel110. 

A multistage compressor, driven by a steam turbine, compresses the cooled gas. LP and HP condensates are stripped in two separate strippers where medium gasoline is produced and part of the C3+ cut is recovered respectively. A caustic scrubber removes acid gases. 

Fig. 38. Caustic purification system, a, 50% caustic feed tank b, 50% caustic feed pumps c, caustic feed preheater d, amonia feedpumps 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 scrubber y, scrubber condenser z, ammonia recirculating pump aa, ammonia recycle pump. CW stands for chilled water.

Figure 116. Ammonia production based on heavy fuel oil (l.inde flow scheme with Texaco gasification) a) Air separation unit h) Soot extraction c) C02 absorption d) Methanol/H,() distillation e) Stripper f) Mol regenerator g) Refrigerant h) Dryer i) liquid N2 scrubber j) Syngas compressor k) Nil, reactor Material Balance...

Deodorization. The neutralized/bleached oil is pumped into a deaerator operated under a pressure of 500 Pa to evacuate entrained air. From the deaerator, the oil passes through a shell and tube economizer and is heated to a temperature of 240°C by means of a thermal oil heater. The stripper and deodorizing column operates under a pressure of 600-1000 Pa volatile components such as low-molecular-weight fatty acids, ketones, aldehydes, and other odoriferous substances are stripped off by live steam. The rising vapors laden with volatile components pass through a cyclone scrubber where fresh fatty acid oil is sprayed on top of the vessel to recover outgoing fatty acids. 

The other method, extraction, passes the air-solvent vapor mixture through a miniature solvent-extraction system using mineral oil as a solvent to absorb, or extract, the solvent vapor from the airstream. The mineral oil then goes to a steam stripper to strip out the solvent. The steam-solvent vapors are condensed and go to the solvent-water separator. The hot mineral oil from the stripper is chilled and goes back to the absorber where it picks up more solvent. Called mineral oil scrubber, the mineral oil is continuously recirculated through the absorber, the stripper, and the chiller. 

Membrane crystallizers, membrane emulsifiers, membrane strippers and scrubbers, membrane distillation systems, membrane extractors, etc. can be devised and integrated in the production lines together with the other existing membranes operations for advanced molecular separation, and chemical transformations conducted using selective membranes and membrane reactors, overcoming existing limits of the more traditional membrane processes (e.g., the osmotic effect of concentration by reverse osmosis). 

A portion of the heat obtained from this reaction is also recovered as steam which, together with that produced by the sulfur-burning boiler, is frequently sufficient to heat the stripper of the associated Girbotol (amine scrubber) plant. The net overall Claus chemistry, thus, involves oxidation of hydrogen sulfide with air to yield sulfur and water (Eq. 9.20). 

Carbon dioxide removal in ammonia plants is usually accomplished by organic or inorganic solvents with suitable activators and corrosion inhibitors. In a few circumstances, C02 is removed by pressure swing adsorption (PSA) (see Chapter 3). The removed C02 is sometimes vented to the atmosphere, but in many instances it is recovered for the production of urea and dry ice. Urea is the primary use of carbon dioxide and, in case of a natural gas feed, all of the C02 is consumed by the urea plant. This practice is especially significant since C02 is a proven greenhouse gas. Typically, 1.3 tons of C02/ton of NH3 is produced in a natural gas-based ammonia plant. The C02 vented to the atmosphere usually contains water vapor, dissolved gases from the absorber (e.g., H2, N2, CH4, CO, Ar), traces of hydrocarbons, and traces of solvent. Water wash trays in the top of the stripper and double condensation of the overhead help to minimize the amount of entrained solvent. The solvent reclaimer contents are neutralized with caustic before disposal. Waste may be burned in an incinerator with an afterburner and a scrubber to control NOx emissions. 

Distillation columns, absorbers, scrubber, strippers, flash drums, etc. 

Caustic Scrubbers and Sour-Water Strippers. Caustic scrubbers and sour-water strippers are used to remove sulfur from a variety of products, gases, and waste streams. Foaming is a fairly common occurrence in these systems because of contaminants found in the streams. 

A plant manufacturing dry ice will bum coke in air to produce a flue gas which when cleaned and cooled will contain 15% C02, 6% 02, and 79% N2. The gas will be blown into a bubble-cap tower scrubber at 1.2 atm and 298 K, to be scrubbed countercurrently with a 30 wt% monoethanolamine (C2H ON) aqueous solution entering at 298 K. The scrubbing liquid, which is recycled from a stripper, will contain 0.058 mol C02/mol solution. The gas leaving the scrubber is to contain 2% C02. A liquid-to-gas ratio of 1.2 times the minimum is specified. Assume isothermal operation. At 298 K and 1.2 atm, the equilibrium mole fraction of carbon dioxide over aqueous solutions of monoethanolamine (30 wt%) is given by... 

The remaining uncondensed NH3 and CO leaving the shell side of the evaporator are sent to a MP carbamate condenser. The heat released by condensation in this condenser is dissipated into a tempered cooling water system. This process forms MP carbamate that contains only 20 wt%-22 wt% water. The carbamate is transferred via a HP carbamate pump to the HP scrubber in the urea synthesis section. The urea solution leaving the adiabatic CO stripper and the HP stripper are expanded together in the LP recirculation section. 

FIGURE 4.2 (a) Hydrophobic membrane contactors as strippers, (b) Hydrophobic membrane contactors as scrubbers. 

Fig. 5.2. LURGI phaiosolvan process, (a) Mixer/settler extractor (ft) distillation (c) scrubber, (d) solvent stripper, (e) blower... 

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