Liquid chemical feed pumps

Most cleaners are available for < 2.20/kg either as a dry blend or as aHquid. Liquid cleaners are usually less expensive than the dry blend type. A trend toward Hquid cleaners is evident as of this writing (ca 1994) because of convenience features such as automatic additions of the cleaner by chemical feed pump. Safety features such as minimized heat generation upon blending with water to make the desired concentration are also important. 

Liquid chemical feed systems consist of storage tanks (with containment for hazardous chemicals), chemical piping, and metering pumps (with calibration equipment). Control systems monitor the level of chemical in the tanks, pressure and flow in the piping, and pump settings. A schematic of a typical liquid chemical feed system is shown in Figure 7-1. 

Determining the chemical feed rates for diluted chemical solutions (c8-7 and c8-8) requires knowing the water flow rate, the strength of the diluted chemical solution, and the chemical feed dosage. Most liquid chemical metering pump feed rates are expressed in mL/min. For inventory control or chemical usage over a protracted period, gallons per day (gpd), or liters per day (L/d), may be a more useful unit of measure. 

These types of liquid chemical feed systems use a second tank (dilution tank). Bulk storage tanks may be distant from the chemical feed pump location, there may be concerns about safety of the bulk chemical, or it may be necessary to dilute the chemical for accurate feed or to aid in mixing with process water. Whatever the reason, feed calculations are the same as those given for chemical feed of solutions calculators (c8-10 through c8-13). The only difference is that the percent solution strength is less than for bulk chemicals. 

A means of adding liquid chemical treatment to a FW tank by means of an overhead dripping container rather than by use of a dosing pump. From a control viewpoint, drip feed is most usually unsatisfactory as the feed rate reduces over time with decrease in treatment head pressure, and ultimately the device tends to gum up. 

STABREX is easier and simpler to use compared to any other oxidant available for industrial water treatment. The product is pumped directly from returnable transporters (PortaFeed Systems)17 with standard chemical feed equipment. Previously, the only practical ways to apply bromine were to oxidize bromide solutions on-site with chlorine in dual liquid feed systems, or with one of the solid organically-stabilized bromine products applied from sidestream erosion feeders. The former is cumbersome and complex, and the latter is prone to dusting and difficult to control. Other oxidants require complex handling and feed of toxic volatile gases, unstable liquids, multiple-component products, or reactive solids. Simplicity in use results in reduced risk to workers and to the environment. 

Fig 18. Experimental trickle-bed system A, tube bundle for liquid flow distribution B, flow distribution packing of glass helices C, activated carbon trickle bed 1, mass flow controllers 2, gas or liquid rotameters, 3, reactor (indicating point of gas phase introduction) 4, overflow tank for the liquid phase feed 5, liquid phase hold-up tank 6, absorber pump 7, packed absorption column for saturation of the liquid phase 8, gas-liquid disengager in the liquid phase saturation circuit. (Figure from Haure et ai, 1989, with permission, 1989 American Institute of Chemical Engineers.)... 

The basic equipment for an ammonia-stripping system includes chemical feed, a stripping tower, a pump and liquid spray system, a forced-air draft, and a recarbonation system. This process requires raising the pH of the wastewater to about 11, the formation of droplets in the stripping tower, and providing air-water... 

Many water treatment operators consider liquid chemicals easy to feed and handle. Chemical suppliers deliver the chemicals in sealed containers, and the feed and delivery systems are contained. Accurate feed is assured when using properly sized, calibrated, and maintained chemical metering pumps and control systems. Liquids also mix easily into the process water stream. Table 7-1 hsts some of the more common liquid chemicals used in water treatment. In addition to these, there are many liquid polyelectrolytes sometimes used in coagulation and filtration. They are not listed in the table because their properties vary depending on the specific product. 

Chemical metering pumps are used to feed most liquid chemicals. Eductors and gravity feed systems are used in some cases, hut a high percentage of the systems use a metering pump. Positive displacement pumps are used for this purpose because they deliver a constant flow to their maximum rated pressure (Figure 7-2). 

Systems for feeding liquid chemicals consist of storage tanks (hazardous chemicals may require containment and neutrahzation facilities), metering pumps (with backflow prevention), and control instrumentation. Many possible system configurations exist. The feed application dictates the best choice for each installation. Two common systems are shown in Figure 7-7. 

Solid (or dry) chemicals are sometimes used to prepare solutions for feeding. Many operators prefer to feed chemicals with metering pumps rather than dry feed equipment. Also, mixing liquid chemicals into the process water stream usually is more efficient. A weighted amount (using a continuous dry chemical feeder or a batch preparation approach) of the dry chemical is mixed with water to prepare the desired solution strength. Then the liquid is metered into the process water in the usual way. 

The difference is that the bulk chemical is first diluted prior to feeding. The percent strength of the liquid bulk chemical must be known to accurately determine the percent strength of the diluted solution. Dilution is accomplished by mixing a known volume of the liquid bulk chemical with a known volume of water. The resultant diluted liquid chemical is then fed to the process water using a chemical metering pump. 

The centrifugal pump is the type most widely used in the chemical industiy for transferring liquids of aU types—raw materials, materials in manufacture, and finished produc ts—as well as for general services of water supply, boiler feed, condenser circulation, condensate return, etc. These pumps are available through avast range of sizes, in capacities from 0.5 mVh to 2 X 10 mVh (2 gal/min to 10 gaJ/min), and for discharge heads (pressures) from a few meters to approximately 48 MPa (7000 Ibf/iu"). The size and type best suited to a particular apphcation can be determined only by an engineering study of the problem. 

Liquid feed was fed by hydrostatic means gas feed was accomplished from a reservoir with the aid of a syringe pump [7]. The gas pressure was held nearly constant by passing a gas stream into a non-absorbing liquid. Analysis was performed both by visual means using a microscope and camera and by chemical analysis of the liquid output solution (Figure 5.33). 

Example 1.3. Our third example illustrates a typical control scheme for an entire simple chemical plant. Figure 1.5 gives a simple schematic sketch of the process configuration and its control system. Two liquid feeds are pumped into a reactor in which they react to form products. The reaction is exothermic, and therefore heat must be removed from the reactor. This is accomplished by adding cooling water to a jacket surrounding the reactor. Reactor elHuent is pumped through a preheater into a distillation column that splits it into two product streams. 

The experimental procedures to establish water treatment plant operational practices have not been without problems. A few of these problems were engineering in nature, such as material compatibility, type of pumps, chemical phase (liquid or solid). Feeding fluoride is like feeding other chemicals experience provides insight in determining the best type of equipment. The feed equipment is in general the same equipment used for feeding alum, soda ash, lime, sulfuric acid, or other chemicals. 

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