Pump, variable-speed metering

Final control element usually, a control valve or a variable-speed metering pump. This is the device that receives the control signal from the controller and implements it by physically adjusting the value of the manipulated variable. 

Sodium hydroxide or other neutralising agents, water and other solvents if required are normally added to the neutralisation loop using metering pumps. Variable-speed gear pumps controlled by mass-flow meter-based systems can be used. 

In order to ensure that the pH in the SO2 scrubber does not fall excessively, leading to gas emission, it is essential to control the addition of sodium hydroxide to the unit. Cascade control systems can be used, where the pH transducer is used to define a set point for a flow control loop. However, variable-speed metering pumps are more commonly used, the speed of the pump being controlled directly by pH. 

A second requirement of the scrubbing control system is to maintain the total solids level in the effluent below 10% w/w. The single variable-speed metering pump motor can therefore be used to drive a second head for the addition of water, thereby controlling the correct water sodium hydroxide ratio. The temperature and flow-rate of the recirculation liquor should be measured and a low-flow alarm incorporated in the liquor recirculation line. 

After the SO converter has stabilized, the 6—7% SO gas stream can be further diluted with dry air, I, to provide the SO reaction gas at a prescribed concentration, ca 4 vol % for LAB sulfonation and ca 2.5% for alcohol ethoxylate sulfation. The molten sulfur is accurately measured and controlled by mass flow meters. The organic feedstock is also accurately controlled by mass flow meters and a variable speed-driven gear pump. The high velocity SO reaction gas and organic feedstock are introduced into the top of the sulfonation reactor,, in cocurrent downward flow where the reaction product and gas are separated in a cyclone separator, K, then pumped to a cooler, L, and circulated back into a quench cooling reservoir at the base of the reactor, unique to Chemithon concentric reactor systems. The gas stream from the cyclone separator, M, is sent to an electrostatic precipitator (ESP), N, which removes entrained acidic organics, and then sent to the packed tower, H, where SO2 and any SO traces are adsorbed in a dilute NaOH solution and finally vented, O. Even a 99% conversion of SO2 to SO contributes ca 500 ppm SO2 to the effluent gas. 

Agitator Turbine, 3.6 HP, 1750 rpm, XP rated motor, variable speed drive Circulating pump Viking series HL124, 2 HP, 1745 rpm, XP rated motor Micro Motion mass flow meter stainless steel 316L, 0-80 lb/min mass flow range, accuracy of 0.4% of range, XP rated with electronics unit mounted separately in nonhazardous area. 

Fig. 3 shows the experimental apparatus. The feed tank had a 50 gallon capacity and was equipped with a variable speed mixer. The feed pump was a flexible impeller, positive-displacement pump to minimize shearing of the feed emulsion. The pumping rate was regulated by a Graham Variable Speed Transmission. Each flotation tank was 11.5 in. ID with 6.5 in. liquid depth maintained by a CE IN-VAL-CO conductometric level controller with a pneumatically actuated control valve in the effluent line. The fourth cell was not equipped with an air inducer. The outer diameter of the air downcomers was 1.5 in. The rotor in each air inducer was a turbine taken from a 2 in. turbine flow meter. Each rotor was belt driven by a 10,000 rpm, 1/30 hp motor and all three motors were governed by the same variable transformer. Another pulley on each rotor shaft was attached to a non-powered belt connecting all three shafts to ensure that each rotor turned at the same speed. 

Feed tank and metering pump the flow rate through such a pump can be controlled by a stroke adjusting mechanism or a variable speed drive acting on the stoke frequency. Control can be achieved by a fixed adjustment or through a flow meter. 

The preneutralizer slurry is pumped at a controlled rate to a rotary-drum, ammoniator-granulator there it is distributed onto a rolling bed of recycled solids. The most commonly used metering system for the preneutralized slurry is a variable-speed centrifugal pump with automatic control from a magnetic flowmeter. Some plants have had success with a magnetic flowmeter and automatic control valve of a special ball type. 

While formulated for problem liquids, this metering technique can be used for any type of liquid. Greater system flexibility is possible via the use of a variable-speed drive. The cost of such a setup is often less than that of one employing small metering pumps for adding liquids. 

The amounts of materials fed to a chemical reactor are usually sensed by various types of flowmeters (Fig. 1.4). The proportions of raw materials reacting are known from the ratios of the metered flow rates of raw materials moving into the reactor, which may be adjusted if necessary. Today, flow control and many other variables are designed to be proportional, to control a process more readily. Valves may be set to different flow rates, pump speeds... 

Because it is applied as a volatile liquid, anhydrous ammonia must be injected 15 to 30 cm below the surface of the soil this usually is accomplished by an application knife such as those shown in Figure 10.3. Often in sandy, loose soil ammonia is applied by an ammonia chisel, also shown in Figure 10.3. Anhydrous ammonia is usually metered by a variable orifice-type meter or by a piston pump, The rate of application using the orifice meter is determined by the speed of the applicator, the swath width, and the orifice opening. Piston pumps are usually actuated by a drive-chain operated by a sprocket attached to a wheel of the applicator. Application rate is changed by changing the length of stroke of the piston the rate is independent of the applicator s speed. 

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