Carousel Dryer in The Production of Shrimp Feed

Integrating carousel dryer in shrimp feed pelleting system

During the last 10 years, developments in pellet mill design enable us to pellet material with moisture up to 17%. This development leads to another problem in the shrimp feed production, the existing pelleting system of pellet mill, post conditioner, and cooler are unable to dry the pellets to shelf stable moisture of 9-10%. In order to lower the moisture content, we incorporate the carousel dryer in the pelleting system. From the time period of 2012 until 2020, there has been more than 30 sets of carousel dryer used in shrimp feed pelleting plants.

In many factories, steam heat exchanger is used as the heat source of drying air. There are many types of the steam heat exchanger in the market, one of the most popular is the finned-tube heat exchanger (FTHE). The problem of using this kind of FTHE lies in the accessibility in cleaning, especially when multiple layers is needed. The new design incorporates maintenance door and spacing between every layer of heating tube in order to ease the cleaning process.

Drying and cooling in shrimp feed pelleting

Drying is naturally a highly energy intensive process. Drying process have an unavoidable constraint which is they must supply enough heat or energy to provide the latent heat of evaporation to remove the vapor (around 2000 kJ/kg for water). Many companies view dryer as the main target in application of their energy conservation program because in most cases dryers are operated inefficiently. One way to converse energy is by reusing the exhaust air from the dryer and cooler.

By arranging a carousel cooler directly under a dryer, both components can be connected to one another - without enlarging the installation area and even within existing systems. The warm exhaust air taken from the cooler section is first fed to a filter unit and then pushed back to the dryer section as energy-reducing warm air.

The typical exhaust air temperatures from a cooler are around 45-55 ° C. After the exhaust air has been cleaned using a pocket filter, the energy-rich process air that has been prepared in this way is not released into the atmosphere, but the warm unit is fed into the dryer area. The saving effect on the heat exchanger is obvious: depending on the climatic conditions, between 15 and 20% of primary energy can be saved here.

Use of a carousel dryer in the production line of shrimp feed

The typical production process for shrimp feed in the Far East is shown below. The figure shows schematically the functional processes of a pelletizing system, which comprises five individual components.

• Pre-conditioning system: this is where all the pre-cooking of raw material is done. In this system, heat is provided by both directly and in-directly injecting steam.
• Pellet forming system: specially designed pellet die and roller shell with the right compression ratio is set to produce a compact and tough pellet with higher PDI shrimp feed
• Post-conditioning system: this post conditioning is designed to prolong pellet cooking by providing hot temperature in order to avoid condensation.
• Drying system: dryer is incorporated in this system in order to lower the moisture to around 11%.
• Cooling system: Cooler will ensure the material is cooled to +/- 3 degrees from ambient temperature, in order to avoid condensation of pellets in the packaging.