Environmental engineering, plug flow reactor

In summary, the conversation discusses a method for treating acid mine drainage by adding limestone to the stream, and the use of a first-order reaction rate constant to determine the concentration of metals in the stream. The question posed is at what distance the concentration will be 5 ppm, and the solution involves using the equation C(x) = Ce^-kt and the formula t = (distance)(cross-section area)/(flow rate). The final answer is found to be 17.4 feet.
  • #1
hobbyenthusia
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Homework Statement


Another way to treat acid mine drainage is to add limestone to the stream to precipitate the metals. The first order reaction rate constant is 10/day. Assume the stream is 3 feet by 1 foot. If the flow through the stream is 1000 gallons a day and the concentration at the beginning of the stream is 250 ppm. At what distance will the concentration be 5 ppm.


Homework Equations


I'm assuming it is a pfr so the equation, i think, is C(distance) = Ce^-kt and the answer is 17.4 feet, but I keep getting a different answer.
Also used t = (distance)(cross-section area)/(flow rate or Q).
Any ideas?
 
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  • #2
The Attempt at a SolutionC(x) = 250e^-10x 5 = 250e^-10x ln(5/250) = -10x x = ln(5/250)/(-10) = 0.0172737 0.0172737 * 3 (width of stream) = .0518211 17.4 feet
 

1. What is a plug flow reactor in environmental engineering?

A plug flow reactor (PFR) is a type of chemical reactor used in environmental engineering to treat wastewater and other industrial effluents. It is a continuous-flow reactor that operates on the principle of fluid flowing through a tubular or cylindrical vessel. The reactants enter the reactor at one end and flow through the vessel at a constant velocity, while the products are collected at the other end.

2. How does a plug flow reactor work?

In a plug flow reactor, the reactants are introduced at one end of the reactor and flow through the vessel in a narrow, plug-like stream. The reactants are mixed with each other and with any catalysts present as they flow through the vessel, allowing for efficient and uniform reaction. The products are collected at the other end of the reactor, while any unreacted materials are removed from the system.

3. What are the advantages of using a plug flow reactor in environmental engineering?

A plug flow reactor offers several advantages in environmental engineering applications. It allows for a high degree of control over reaction conditions, such as temperature and residence time, which can improve the efficiency of the treatment process. PFRs are also compact and have a small footprint, making them ideal for use in space-limited environments. Additionally, they can handle a wide range of flow rates and are easy to operate and maintain.

4. What are the limitations of using a plug flow reactor in environmental engineering?

While plug flow reactors have many advantages, they also have some limitations. PFRs are not suitable for reactions that require significant mixing or agitation, as they rely on the flow of the reactants for mixing. This can lead to uneven reaction rates and incomplete treatment. Additionally, PFRs may not be suitable for treating highly concentrated or complex wastewater streams, as they may require additional pre-treatment steps or larger reactors to handle these types of effluents.

5. How is a plug flow reactor different from other types of chemical reactors used in environmental engineering?

Plug flow reactors differ from other types of chemical reactors in their design and operation. Unlike batch reactors, which operate in a batch-wise manner, PFRs have a continuous flow of reactants and products. PFRs also differ from other continuous-flow reactors, such as continuous stirred tank reactors (CSTRs), in that they have a more uniform distribution of reactants and products and do not rely on mixing to achieve efficient reaction. PFRs are also different from packed bed reactors, which contain a stationary bed of catalyst material, as PFRs do not have a stationary bed and instead rely on the flow of reactants through the vessel for efficient reaction.

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