Liquid chemical feed tanks

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. 

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. 

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. 

Chemical Kinetics, Tank and Tubular Reactor Fundamentals, Residence Time Distributions, Multiphase Reaction Systems, Basic Reactor Types, Batch Reactor Dynamics, Semi-batch Reactors, Control and Stability of Nonisotheimal Reactors. Complex Reactions with Feeding Strategies, Liquid Phase Tubular Reactors, Gas Phase Tubular Reactors, Axial Dispersion, Unsteady State Tubular Reactor Models... 

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.)... 

Nearly complete suspension with filleting. Most of the solid is suspended in the liquid, with a few percent in stationary fillets of solid at the outside periphery of the bottom or at other places in the tank. Having a small amount of solids not in motion may be permissible in a feed tank to a processing unit, as long as the fillets do not grow and the solids do not cake, For crystallization or a chemical reaction, the presence of fillets would be undesirable. 

Pine Bluff. The incineration facility at Pine Bluff provides a technically feasible alternative for destruction of less than 10 percent of the 69,878 non-stockpile items stored there because its design does not include facilities for opening bulk containers of agent and CWM binary components (Appendix C). However, inclusion of such capability in the non-stockpile PBNSF would enable transfer of these liquid chemicals to vessels suitable as feed tanks for the PBCDF liquid incinerator. This modification, plus the addition of DF and QL monitoring systems at the Pine Bluff Chemical Disposal Facility (PBCDF), would allow incineration of the great majority of the PBA non-stockpile inventory. 

ILLUSTRATIVE EXAMPLE 20.16 Consider a chemical reactor that uses two liquid feeds of different densities as provided in Table 20.1. It produces four different liquid chemical products of varying density following chemical reaction and separation, see Table 20.2. The plant storage requirements call for maintaining 4-5 weeks supply of each feed, 4-6 weeks supply of products A, B, and C, and 1-2 weeks supply of product D. The plant operates year round but each tank must be emptied once a year for a week for maintenance. Tanks are normally dedicated to one feed or product and one or two could be used as swing tanks however, one day of cleaning is required between uses with different liquids. 

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. 

Feed systems can be hybrids, combining dry or gas feed with liquid feed components. Dry and liquid systems usually include a dry-to-liquid conversion (using a dissolving tank) that subsequently combines this liquid with another liquid. Gas-liquid hybrid systems can mix the gas with water first or with another liquid chemical in a reaction chamber. Chlorine dioxide generators using chlorine gas are an example of this type of system. The chlorine dioxide formed in the reaction is ultimately mixed with ejector water, and this solution is then mixed with process water at the point of delivery. 

Some liquid chemicals are fed directly from the storage tank to the process water without any dilution. The chemicals may be delivered already diluted or may be 100 percent strength. Calculating the chemical feed rate requires knowing the process water flow rate, the applied dosage, and the solution strength. 

The enthalpy change associated with the mixing of the feed and the liquid in the tank is negligible compared with the enthalpy change for the chemical reaction. In other words, the heat of mixing is negligible compared to the heat of reaction. 

The kinetics of a liquid-phase chemical reaction are investigated in a laboratory-scale continuous stirred-tank reactor. The stoichiometric equation for the reaction is A 2P and it is irreversible. The reactor is a single vessel which contains 3.25 x 10 3 m3 of liquid when it is filled just to the level of the outflow. In operation, the contents of the reactor are well stirred and uniform in composition. The concentration of the reactant A in the feed stream is 0.5 kmol/m3. Results of three steady-state runs are ... 

Two stirred tanks are available at a chemical works, one of volume.100 m3, the other 30 m3. It is suggested that these tanks be used as a two-stage CSTR for carrying out a liquid phase reaction A + B -> product. The two reactants will be present in the feed stream in equimolar proportions, the concentration of each being 1.5 kmol/m3. The volumetric flowrate of the feed stream will be 0.3 x 10"3 m3/s. The reaction is irreversible and is of first order with respect to each of the reactants A and B, i.e. second order overall, with a rate constant 1.8 x I0 4 m3/kmol s. 

Pure component physical property data for the five species in our simulation of the HDA process were obtained from Chemical Engineering (1975) (liquid densities, heat capacities, vapor pressures, etc.). Vapor-liquid equilibrium behavior was assumed to be ideal. Much of the flowsheet and equipment design information was extracted from Douglas (1988). We have also determined certain design and control variables (e.g., column feed locations, temperature control trays, overhead receiver and column base liquid holdups.) that are not specified by Douglas. Tables 10.1 to 10.4 contain data for selected process streams. These data come from our TMODS dynamic simulation and not from a commercial steady-state simulation package. The corresponding stream numbers are shown in Fig. 10.1. In our simulation, the stabilizer column is modeled as a component splitter and tank. A heater is used to raise the temperature of the liquid feed stream to the product column. Table 10.5 presents equipment data and Table 10.6 compiles the heat transfer rates within process equipment. 

A liquid-phase chemical reaction A B takes place in a well-stirred tank. The concentration of A in the feed is Cao (mol/m ), and that in the tank and outlet stream is Ca (mol/m ). Neither concentration varies with time. The volume of the tank contents is K(m ) and the volumetric flow rate of the inlet and outlet streams is v (m /s). The reaction rate (the rate at which A is consumed by reaction in the tank) is given by the expression... 

Figure El-1.1). The product stream, containing sodium acetate and ethanol, together with the unreacted sodium hydroxide and ethyl acetate, is continuously withdrawn from the tank at a rate equal to the total feed rate. The contents of the tank in which this reaction is taking place may be considered to be perfectly mixed. Because the system is operated at steady state, if we were to withdraw liquid samples at some location in the tank at various ttme.s and analyze them chemically, we would find that the concentrations of the individual species in the different samples were idendcai. That is, the concentration of the sample taken at 1 p,m. is the same as that of the sample taken at 3 p.m. Because the species concentrations are constant and therefore do not change with time. 

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