a common approach to soften water is to adjust the chemistry of the solution to cause CaCO3(s) to precipitate. As noted previously, such processes often utilize a flow scheme like that shown in the Figure below. New solids are generated in the main reaction tank, and then the solids are separated from solution in a settling tank. However, rather than discarding all of the solids, a fraction of the settled sludge is returned to the reaction tank to provide seed crystals onto which more solid can precipitate. The relevant reaction is:
A proposed water softening process will treat a flow of 5.0 m3 /s. The objective is to induce precipitation of CaCO3(s) to reduce the dissolved Ca2+ concentration from 150 to 20 mg/L. The influent contains no CaCO3(s). The settling step is expected to be very efficient, so the CaCO3(s) concentration in the treated effluent is negligible. The figure below shows some flow streams labeled and some potentially useful control volume (CV) boundaries identified. The flow rates at three points are as follows:
Q1= 5000 L /s
Q4=4910 L / s
Q7=240 L / s
Assuming that the water volumes in the various tanks, the water flow rates, and the concentrations of all the chemicals in the system are steady over time:
A)Determine flow rates of the remaining streams.
B)Determine the concentration of CaCO3(s) solids (mg/L) in the pipe between the main reactor and the settling basin (pipe 3), the pipe leading to the sludge processing facility (pipe 6), and the pipe conveying recycled solids to the main reaction vessel (pipe 7). Assume also that the precipitation reaction occurs only in the reactor, and not in the settling tank.
a common approach to soften water is to adjust the chemistry of the solution to cause CaCO3(s) to precipitate. As noted previously, such processes often utilize a flow scheme like that shown in the Figure below. New solids are generated in the main reaction tank, and then the solids are separated from solution in a settling tank. However, rather than discarding all of the solids, a fraction of the settled sludge is returned to the reaction tank to provide seed crystals onto which more solid can precipitate. The relevant reaction is:
A proposed water softening process will treat a flow of 5.0 m3 /s. The objective is to induce precipitation of CaCO3(s) to reduce the dissolved Ca2+ concentration from 150 to 20 mg/L. The influent contains no CaCO3(s). The settling step is expected to be very efficient, so the CaCO3(s) concentration in the treated effluent is negligible. The figure below shows some flow streams labeled and some potentially useful control volume (CV) boundaries identified. The flow rates at three points are as follows:
Q1= 5000 L /s
Q4=4910 L / s
Q7=240 L / s
Assuming that the water volumes in the various tanks, the water flow rates, and the concentrations of all the chemicals in the system are steady over time:
A)Determine flow rates of the remaining streams.
B)Determine the concentration of CaCO3(s) solids (mg/L) in the pipe between the main reactor and the settling basin (pipe 3), the pipe leading to the sludge processing facility (pipe 6), and the pipe conveying recycled solids to the main reaction vessel (pipe 7). Assume also that the precipitation reaction occurs only in the reactor, and not in the settling tank.
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