Liquid chemical feed chemicals

Liquid chemical feed calculations are the subject of chapter 8. This chapter includes the calculations for dry chemical feed either directly into process water or first into dissolving or slurry tanks, and to prepare solution batches. All dry chemical feeders are calibrated as needed to ensure accurate delivery of the chemical. 

Figure 7-1 Typical liquid chemical feed system...

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. 

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. 

Chapter 7. Liquid Chemical Feed Equipment and Systems 75... 

Chapter 8. Liquid Chemical Feed-Calculations and Examples 95... 

Figure 2-3 Liquid chemical feed system using dilution water 17...

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. 

Sanitizers. Spa and hot-tub sanitation is dominated by chlorine- and bromine-based disinfectants. Public spas and tubs usually employ automatic feeders, eg, CI2 gas feeders, to maintain a disinfectant residual. Private or residential spas and tubs can use automatic chemical feeding or generating devices, or they can be sanitized manually with granular or liquid products. The most widely used products for private spa and tub sanitation are sodium dichloroisocyanurate and bromochlorodimethylhydantoin. Granular products are normally added before and after use, whereas solids, eg, stick-bromine, are placed in skimmers or feeders. Bromine generating systems can also be used and are based on oxidation of bromide ions (added to the water as sodium bromide) by peroxymonosulfate, chloroisocyanurates, hypochlorites, or ozone to generate the disinfectant HOBr. 

NOTE For fuel oils where the ash content produced is, say, between 1/3 and 1 lb per 250 gallons (approximately 150-450 gram per m3) of fuel oil, the typical feed rate of a liquid chemical treatment to provide 10% CeO in the ash is of the order of 3/4 to 2 pints per 2,500 gallons (approximately 0.33-1 liter per 10m3). The feed rate would be doubled to achieve 20% CeO in the ash. 

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.)... 

As an illustration, let us take a look at a bioreactor (Fig. 1.1). To find out if the bioreactor is operating properly, we monitor variables such as temperature, pH, dissolved oxygen, liquid level, feed flow rate, and the rotation speed of the impeller. In some operations, we may also measure the biomass and the concentration of a specific chemical component in the liquid or the composition of the gas effluent. In addition, we may need to monitor the foam head and make sure it does not become too high. 

Another potential application for zeolite/polymer mixed-matrix membranes is the separation of various liquid chemical mixtures via pervaporation. Pervapora-tion is a promising membrane-based technique for the separation of liquid chemical mixtures, especially in azeotropic or close-boihng solutions. Polydime thy 1-siloxane (PDMS), which is a hydrophobic polymer, has been widely used as the continuous polymer matrix for preparing hydrophobic mixed-matrix membranes. To achieve good compatibility and adhesion between the zeolite particles and the PDMS polymer, ZSM-5 was incorporated into the PDMS polymer matrix, the resulting ZS M -5/ P DM S mixed-matrix membranes showed simultaneous enhancement in selectivity and flux for the separation of isopropyl alcohol from water. It was demonstrated that the separation performance of these membranes was affected by the concentration of the isopropyl alcohol in the feed [96]. 

ABSORPTION is a unit operation in which a gas mixture is contacted with a suitable liquid for the purpose of preferentially dissolving one or more of the constituents of the gas. These constituents are thus removed or partially removed from the gas into the liquid. The dissolved constituents may either form a physical solution with the liquid or react chemically with the liquid. The dissolved constituents are termed solutes, while the dissolving liquid is termed the solvent. When the concentration of solute in the feed gas is low, the process is often called scrubbing. 

Many effective control schemes have been established over the years for individual chemical units (Shinskey, 1988), For example, a tubular reactor usually requires control of inlet temperature. High-temperature endothermic reactions typically have a control system to adjust the fuel flowrate to a furnace supplying energy to the reactor. Crystallizers require manipulation of refrigeration load to control temperatui e. Oxygen concentration in the stack gas from a furnace is controlled to prevent excess fuel usage. Liquid solvent feed flow to an absorber is controlled as some ratio to the gas feed. We deal with the control of various unit operations in Chaps. 4 through 7. 

---