MEE are essential equipment in many industries, including food and beverage, pharmaceuticals, dairy, chemicals, and more. They are used to concentrate solutions by removing the solvent, typically water, through the application of heat. One type of evaporator that has gained popularity due to its high efficiency is the triple effect evaporator or multiple effect evaporator (MEE).
A triple effect evaporator, as the name suggests, consists of three separate effects or evaporative stages arranged in series. Each effect operates at a progressively lower pressure and temperature, which maximizes the utilization of heat energy and improves the overall efficiency of the evaporation process.
Let’s dive into the working principle of a typical triple effect evaporator and understand the role of each component:
The feed tank is where the solution to be concentrated is stored. It typically contains a mixture of the desired product and the solvent, with the concentration varying depending on the specific application. The solution is fed into the evaporator system continuously or intermittently.
The feed pump is responsible for supplying the solution from the feed tank to the first effect of the evaporator. It provides the necessary pressure to overcome the pressure drop across the system and maintain a consistent flow rate.
The first effect calandria is a shell and tube heat exchanger located in the first effect of the evaporator. Steam is used as the heating medium in this case. The solution enters the tubes, while steam flows through the shell, causing the solution to boil. Heat is transferred from the steam to the solution, resulting in evaporation and concentration of the solution.
After passing through the first effect calandria, the vapor and liquid mixture enters the first effect vapor separator. Here, the vapor is separated from the concentrated solution, which then flows out of the bottom of the separator, while the vapor rises to the top.
The circulation pump is responsible for recirculating the concentrated solution from the first effect vapor separator back to the first effect calandria. This ensures a continuous flow of the solution and maintains the required concentration gradient.
The vapor from the first effect vapor separator is directed through a vapor line to the calandria of the second effect. This vapor acts as the heating medium in the second effect, providing energy to evaporate the solution.
Similar to the first effect calandria, the second effect calandria is a shell and tube heat exchanger. The vapor from the first effect flows through the shell, while the solution enters the tubes. Heat transfer occurs, leading to further evaporation and concentration of the solution.
Once the vapor and liquid mixture exits the second effect calandria, it enters the second effect vapor separator. Here, the vapor is separated from the concentrated solution, which is then collected and flows out of the bottom.
The circulation pump for the second effect ensures the continuous recirculation of the concentrated solution from the second effect vapor separator back to the second effect calandria, maintaining the concentration gradient.
The vapor separated in the second effect vapor separator is directed through a vapor line to the calandria of the third effect. This vapor serves as the heating medium in the third effect, facilitating further evaporation.
In the third effect calandria, the vapor from the second effect flows through the shell, while the concentrated solution enters the tubes. Heat transfer occurs, causing additional evaporation and concentration of the solution.
After passing through the third effect calandria, the vapor and liquid mixture enters the third effect vapor separator. Here, the vapor is separated from the highly concentrated solution, which is collected and exits from the bottom.
The circulation pump for the third effect ensures the continuous recirculation of the highly concentrated solution from the third effect vapor separator back to the third effect calandria.
The vapor from the third effect is directed to the barometric condenser. In the condenser, the vapor comes into direct contact with cooling water from the cooling tower. This contact causes the vapor to condense, resulting in the removal of heat and the conversion of the vapor back into a liquid form.
The barometric seal tank is used to maintain the barometric condenser in a vacuum. By creating a vacuum, the boiling point of the liquid is lowered, enhancing the condensation process and improving the overall efficiency of the evaporator system.
The vacuum pump is responsible for creating and maintaining the desired vacuum level within the evaporator system. It ensures the proper operation of the evaporator by continuously removing non-condensable gases and maintaining the required pressure differential.
The cooling tower provides a source of cooling water for the barometric condenser. It removes heat from the cooling water by evaporation, thereby facilitating the condensation of the vapor in the condenser.
The control panel contains various control instruments and devices that monitor and regulate the operation of the multiple effect evaporator. It includes temperature controllers, level controllers for each effect, vacuum gauges, and other necessary instrumentation.
Multiple effect evaporators, such as the triple effect evaporator described above, offer significant advantages in terms of energy efficiency and solvent recovery. By utilizing the vapor from one effect as the heating medium for subsequent effects, these evaporators maximize the use of heat energy and reduce energy consumption. Understanding the working principle and the role of each component in the evaporator system helps to appreciate its efficiency and effectiveness in various industrial applications.
