Venturi systems

A schematic diagram of the entrained flow reactor is shown in Figure 1. At the top of the reactor, a screw feeder and semi-venturi system is used to entrain the ground coal particles in the cold primary gas stream. The coal is then injected into the reactor where it is entrained in, and heated by, the preheated secondary gas. The pyrolyzing coal particles fall in a thin stream through the reactor and are collected by a movable water-cooled collector probe. The time which the particles spend in the reactor is controlled by moving the collector probe up and down the reactor axis. The pyrolysis reactions are rapidly quenched in the collector probe, and the particles are separated from the gas stream by a cyclone in the collection system. 

In these burners gas flow depends on the underpressure created in a venturi system by the air flow. Fuel and air control is not good and a high excess of air is required. The 6% of CO2 contents means that less than double air compared to stechiometric condition is required. Figure 34.8 gives a rough indication of CO and NO, level reached with this technology. Atmospheric burners are premixed burners because air and fuel are mixed before burning, but "premixed burners" for... 

Number of data points bag filter 33 wet scrubber 4 wet venturi system 3... 

Emission levels from the exhaust gas of shot blasting have been eollected in an Italian foundry survey. The results are displayed in Table 3.54. All techniques reach maximum dust emission levels below 30 mg/Nm. The average value is below 15 mg/Nm. The wet Venturi system is the least effeetive system, leaving an emission factor well above those for the other techniques. On the other hand, it also acts as is a safety device to prevent an aluminium-dust-explosion [225, TWO, 2003]. 

Each technique has advantages and disadvantages. Packed columns are flexible as the packing can be easily modified for optimisation of each recovery process, but they are best suited to small scale operations. Tray columns are used for large scale, low to medium flow rate applications involving non-corrosive materials. Spray systems are used almost entirely for applications where pressure drop is critical such as flue gas treatment. Types of equipment classified as spray columns include cyclone and venturi systems. Bubble column equipment is a low cost, low maintenance option however back mixing can occur which reduces the counter-current flows required for optimum absorption. 

Figure 10.36 Experimental study of cavitation corrosion (a) rotating disk in the turbulent-flow regime (b) vibrating device and (c) Venturi system.

The SOLVOX -V process, for example, relies on a venturi system (see Fig. 2.49) and is used for pre-treating and oxygenating waste water. It is very easy to install and can even be lowered into full tanks with no drainage required. 

Venturi scmbbers can be operated at 2.5 kPa (19 mm Hg) to coUect many particles coarser than 1 p.m efficiently. Smaller particles often require a pressure drop of 7.5—10 kPa (56—75 mm Hg). When most of the particulates are smaller than 0.5 p.m and are hydrophobic, venturis have been operated at pressure drops from 25 to 32.5 kPa (187—244 mm Hg). Water injection rate is typicaUy 0.67—1.4 m of Hquid per 1000 m of gas, although rates as high as 2.7 are used. Increasing water rates improves coUection efficiency. Many venturis contain louvers to vary throat cross section and pressure drop with changes in system gas flow. Venturi scmbbers can be made in various shapes with reasonably similar characteristics. Any device that causes contact of Hquid and gas at high velocity and pressure drop across an accelerating orifice wiU act much like a venturi scmbber. A flooded-disk scmbber in which the annular orifice created by the disc is equivalent to a venturi throat has been described (296). An irrigated packed fiber bed with performance similar to a... 

Environmental Protection. Fumes resulting from exposure of anhydrous aluminum chloride to moisture are corrosive and acidic. Collection systems should be provided to conduct aluminum chloride dusts or gases to a scmbbing device. The choice of equipment, usually one of economics, ranges from simple packed-tower scmbbers to sophisticated high energy devices such as those of a Venturi design (11). 

The use of a multiventuri system (in which an inner venturi discharges into the throat of an outer venturi) to increase both the dif-... 

Accuracy Square-edged orifices and venturi tubes have been so extensively studied and standardized that reproducibihties within 1 to 2 percent can be expected between standard meters when new and clean. This is therefore the order of reliabihty to be had, if one assumes (1) accurate measurement of meter differenfial, (2) selection of the coefficient of discharge from recommended published literature, (3) accurate knowledge of fluid density, (4) accurate measurement of critical meter dimensions, (5) smooth upstream face of orifice, and (6) proper location of the meter with respect to other flow-disturbing elements in the system. Care must also be taken to avoid even sh t corrosion or fouliug during use. 

Two-Fluid (Pneumatic) Atomizers This general category includes such diverse apphcations as venturi atomizers and reac tor-effluent quench systems in addition to two-fluid spray nozzles. Depending on the manner in which the two fluids meet, several of the breakup mechanisms may be apphcable, but the final one is high-level turbulent rupture. 

Coke oven charging Hydrocarbons, carbon, coal dust Aspiration systems to draw pollutants into oven, venturi scrubbers... 

Main fuel injector. This unit is designed to deliver a fuel-air mixture to the catalyst that is uniform in composition, temperature, and velocity. A multi-venturi tube (MVT) fuel injection system was developed by GE specifically for this purpose. It consists of 93 individual venturi tubes arrayed across the flow path, with four fuel injection orifices at the throat of each venturi. 

Venturi, product systems, or blow tanks will not be discussed here. 

Since power is a substantial component of the fixed operating cost of a unit, the operating cost would run approximately seven times more on a scrubber installation. The installation costs of a hot-rolled steel precipitator to handle 100,000 cfm would be between 3.50 and 4.50/cfm as opposed to 1.40 to 1.80/cfm for a venturi scrubbing system. Although the initial capital expenditure is high for the precipitator, if the total operating and capital costs are amortized over an acceptable period of time, 8 to 10 years, the precipitator will prove to be the. lore economically feasible choice because of its low operating and maintenance costs. 

Contactor design is important in order to maximize the ozone-transfer efficiency and to minimize the net cost for treatment. The three major obstacles to efficient ozone utilization are ozone s relatively low solubility in water, the low concentrations and amounts of ozone produced from ozone generators, and the instability of ozone. Several contacting devices are currently in use including positive-pressure injectors, diffusers, and venturi units. Specific contact systems must be designed for each different application of ozone to wastewater. Further development in this area of gas-liquid contacting needs to be done despite its importance in waste treatment applications. In order to define the appropriate contactor, the following should be specified ... 

A written list of items or procedures describe prevents chlorine gas flow unievt tin-m ih.-the status of a system. Checklists may vary venturi is sub-atmospheric, u the fu-,i ir-c -considerably in level of detail, depending on the fans, thwnne .,-uua... 

HAZOP focuses on study nodes, process sections, and operating steps. The number of nodes depending on the team leader and study objectives. Conservative studies consider e er line and vessel. An experienced HAZOP leader may combine nodes. For example, the cooling looser . .ater chlorination system may be divided into a) chlorine supply to venturi, b) recirculation loop, and e) to .er water basin. Alternatively, two study nodes may be used a) recirculation loop and tower water basin, and b) chlorine supply to venturi. Or one study node for the entire process. 

This sonic velocity occurs in a pipe system in a restricted area (for example, valve, orifice, venturi) or at the outlet end of pipe (open-ended), as long as the upstream pressure is high enough. The physical properties in the above equations are at the point of maximum velocity. 

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