Liquid particle

Impingement demister systems are designed to intercept liquid particles before the gas outlet. They are usually constructed from wire mesh or metal plates and liquid droplets impinge on the internal surfaces of the mist mats or plate labyrinth as the gas weaves through the system. The intercepted droplets coalesce and move downward under gravity into the liquid phase. The plate type devices or vane packs are used where the inlet stream is dirty as they are much less vulnerable to clogging than the mist mat. 

Centrifugal demister or cyclone) devices rely on high velocities to remove liquid particles and substantial pressure drops are required in cyclone design to generate these velocities. Cyclones have a limited range over which they operate efficiently this is a disadvantage if the input stream flowrate is very variable. 

Because of the diverse appHcatioas involving Hquid atomizers, a large vocabulary of terms has evolved ia the spray community. The American Society for Testing and Materials, ASTM Subcommittee E29.04 on Liquid Particle Characterization, has attempted to standardize the terminology relating to atomizing devices (1). The definitions adopted by ASTM are used herein. 

ASTM E1620-96, Terminology Relating to Liquid Particles and Atomization, ASTM, Philadelphia, Pa., 1996. 

Practical separation techniques for hquid particles in gases are discussed. Since gas-borne particulates include both hquid and sohd particles, many devices used for dry-dust collection (discussed in Sec. 17 under Gas-Sohds Separation ) can be adapted to liquid-particle separation. Also, the basic subject of particle mechanics is covered in Sec. 6. Separation of liquid particulates is frequently desirable in chemical processes such as in countercurrent-stage contacting because hquid entrainment with the gas partially reduces true countercurrency. Separation before entering another process step may be needed to prevent corrosion, to prevent yield loss, or to prevent equipment damage or malfunc tion. Separation before the atmospheric release of gases may be necessaiy to prevent environmental problems and for regula-toiy compliance. 

Albertsson (Paiiition of Cell Paiiicle.s and Macromolecules, 3d ed., Wiley, New York, 1986) has extensively used particle distribution to fractionate mixtures of biological products. In order to demonstrate the versatility of particle distribution, he has cited the example shown in Table 22-14. The feed mixture consisted of polystyrene particles, red blood cells, starch, and cellulose. Liquid-liquid particle distribution has also been studied by using mineral-matter particles (average diameter = 5.5 Im) extracted from a coal liquid as the solid in a xylene-water system [Prudich and Heniy, Am. Inst. Chem. Eng. J., 24(5), 788 (1978)]. By using surface-active agents in order to enhance the water wettability of the solid particles, recoveries of better than 95 percent of the particles to the water phase were obsei ved. All particles remained in the xylene when no surfactant was added. 

Another advantage is that wet ESPs can collect sticky particles and mists, as well as highly resistive or explosive dusts. The continuous or intermittent washing with a liquid eliminates the reentrainment of particles due to rapping which dry ESPs are subject to. The humid atmosphere that results from the washing in a wet ESP enables them to collect high resistivity particles, absorb gases or cause pollutants to condense, and cools and conditions the gas stream. Liquid particles or aerosols... 

Aerosol a mixture of microscopic solid or liquid particles in a gaseous medium. Smoke, haze, and fog are aerosol examples. 

Scott Wells. .. processes. Research includes modeling the dynamics of cake filtration and the dynamics of liquid/particle flow in water and wastewater... 

The dryers make use of warm air, flue gases, and direct radiant heat to the liquid-particle mixture. This method allows complete extraction of the solid through removal of the liquid by vaporization. Due to the energy input required with this method, it is the most costly. 

Aerosols are also a form of a mist characterized by highly respirable, minute liquid particles. They can be formed by atomizing, spraying, or mixing, or by violent chemical reactions, evolution of gas from a liquid, or escape of a dissolved gas when pressure is released. 

Electrostatic precipitation is one of the fundamental means of separating solid or liquid particles from gas streams. This technique has been utilized in numerous applications, including industrial gas-cleaning systems, air cleaning in general ventilation systems, and household room air cleaners. 

A very important parr of the gas-deatimg process is the removal of the collected particles from the cleaning system. This should be as controlled as possible in order to avoid particle reenrrainmenr to the gas flow. This can be accomplished in the case of liquid particles such as acid fume or tar or oil smoke. olid particles are normally removed by periodic rapping of discharge and collection electrodes. Solid particles can also be removed with the aid of water, as is done in wet electrostatic precipitators. 

Coarse solid particles Any solid particle larger than 50 xm, and solid particles contained in or on any liquid particle. 

Smoke Aerosols formed from minute solid or liquid particles, most less than 1 xm in diameter, generated by the incomplete combustion of a fuel or by sublimation. 

It is worth noting that the extractive process can be performed continuously. Thus, the separation of ( )-mandelic acid into its enantiomers was achieved with a liquid particle extractor described by Abe et al. [190-192] using A-docecyl-L-proline as chiral selector. 

Regardless of their density, all liquid particles moving at the same velocity in a pipe have the same velocity head [ 11 ]. The velocity head may vary across a medium to large diameter pipe. However, the average velocity of flow, that is, dividing the total flow as cu ft/sec by the cross-sectional area of the pipe is usually accurate enough for most design purposes. 

Table 4-7 summarizes liquid particle separators as to the general process-qqte application. 

A stationary separator element of knitted small diameter wire or plastic material is formed of wire 0.003 in. to 0.016 in. (or larger) diameter into a pad of 4 inches, 6 inches or 12 inches thick and serves as the impingement surface for liquid particle separation. Solid particles can be separated, but they must be flushed from the mesh to prevent plugging. Although several trade name units are available they basically perform on the same principle, and have very close physical characteristics. Carpenter [4] presented basic perform.ance data for mesh units. Figure 4-15 shows a qpical eliminator pad. 

To allow for surges, variations in liquid load and peculiarities in liquid particle size and physical properties, use ... 

The concept of removal of entrained liquid particle is essendally the same as for ware mesh designs, except the... 

For corrosive gases/liquid particles, corrosion resistant metals can be used for construction. 

The performance of the unit involves the gas characteristics, analysis, velocity, flow rate, dust or liquid particle size and analysis, resistixdty and required final particle efficiency of removal. Some particle materials of high electrical resistivity prevent proper electrical operation. 

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