# How Does a Double Effect Evaporator Work in Chemical Concentration?

• Naraneer
In summary: Using this equation, you can calculate the heat transferred and then use that value to determine the overall coefficient of the 2nd effect.
Naraneer

## Homework Statement

A double effect forward feed evaporator is to concentrate a 12.5% solution of a certain chemical compound "YZ". The feed is to be at and is to be 120 F of such an amount as to contain 6250 "YZ" per hour. Saturated steam is available at 250 F (29.7 psi ). The accepted value of the overall coefficient for the first effect is ( 400 Btu/hr ft2 F ). Condensate may be assumed to leave at the saturation temperature of the steam. The evaporator is provided with a barometric counter-current condenser fed with 357500 Ib/hr cooling water entering at 85 F and leaving at 136 F

i) Calculate the values of the concentration of the "YZ" solution leaving the 1st and 2nd effects, respectively. ii) Determine the temperature of the 2nd effect.
iii) What heating surface must be used if all effects are to have the same area?
iv) Compute the value of the overall coefficient of the 2nd effect.

## Homework Equations

[/B]
Cp steam=0.48 Btu/Ib F Latent Heat of steam at 250 F=945.5 Btu/Ib
Feed Enthalpy= 70 Btu/Ib
Evaporation per Ib of Steam = 1.45
Effect I II
T 230 T
t sat 216 141
Lf (latent heat) 967 1011.32
h (enthalpy of liquid) 192 175

## The Attempt at a Solution

(945.5)*m(steam) + 5*10^4(70)=(5*10^4-m(vapor 1)(192)+m(vapor 1)Hv1
Hv1=0.48(230-216)+967 + Enthalpy of Saturated liquid at T=216 F

Effect 2
(0.48(230-216)+967) *m(vapor 1)+(5*10^4-m(vapor 1)(192)=(5*10^-4-m(vapor 1)-m(vapor 2))(175)+m(vapor 2)*Hv2

Hv2=0.48 (T-141)+1013.2 + Enthalpy of Saturated liquid at T=141 F

How can I determine the values of Enthalpy of saturated liquid at 216 F and 141 F?
Secondly, How can I perform an Energy balance over the condenser?

To determine the enthalpy of saturated liquid at 216 F and 141 F, you can use steam tables or thermodynamic property software to find the specific enthalpies at those temperatures. Alternatively, you can use the Clausius-Clapeyron equation to calculate the enthalpies at those temperatures.

To perform an energy balance over the condenser, you can use the following equation:

Q = m_water * Cp_water * (T_out - T_in)

where Q is the heat transferred, m_water is the mass flow rate of cooling water, Cp_water is the specific heat of water, and T_out and T_in are the outlet and inlet temperatures of the cooling water. This equation assumes that there is no change in the enthalpy of the cooling water as it passes through the condenser.

## 1. What is a Double Effect Evaporator?

A Double Effect Evaporator is a type of evaporator used in industrial processes to separate a liquid from a solution. It uses multiple stages of evaporation to increase efficiency and reduce energy consumption.

## 2. How does a Double Effect Evaporator work?

A Double Effect Evaporator works by using a series of heat exchangers and condensers to evaporate a liquid. The first stage uses steam to heat the solution, causing the liquid to evaporate. The resulting vapor is then sent to a second stage, where it is condensed and heated again, further increasing the concentration of the solution. This process can be repeated multiple times to achieve a high level of concentration.

## 3. What are the advantages of using a Double Effect Evaporator?

The main advantage of using a Double Effect Evaporator is its high efficiency. By using multiple stages of evaporation, it can achieve a higher concentration of the solution while using less energy compared to a single-effect evaporator. It also has a smaller footprint and can handle a wider range of solutions, making it a versatile option for industrial processes.

## 4. What are the limitations of a Double Effect Evaporator?

One limitation of a Double Effect Evaporator is its high initial cost. It requires more equipment and a more complex design compared to a single-effect evaporator. It also requires a constant supply of steam, which can be expensive. Additionally, it may not be suitable for solutions with high viscosity or those that are prone to fouling.

## 5. What industries commonly use Double Effect Evaporators?

Double Effect Evaporators are commonly used in industries such as food and beverage, chemical processing, and pharmaceuticals. They are also used in wastewater treatment and desalination plants. Any industry that requires concentration of a solution can benefit from using a Double Effect Evaporator.

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