Question

A direct-heat countercurrent rotary hot-air drier is to be chosen for drying an insoluble

crystalline organic solid. The solid will enter at 20°C, containing 20% water. It will be dried by air
entering at 155°C, 0.01 kg water/kg dry air. The solid is expected to leave at l20°C, with a moisture
content 0.3%. Dried product delivered will be 450 kg/h. The heat capacity of the dry solid is 837
J/kg· K, and its average particle size is 0.5 mm. The superficial air velocity should not exceed 1.6
m/s in any part of the drier. The drier will be insulated, and heat losses can be neglected for present
purposes. Choose a drier from the following standard sizes and specify the rate of airflow which
should be used: 1 by 3 m, 1 by 9 m, 1.2 by 12 m, 1.4 by 9 m, 1.5 by 12 m.

Answer 1

To select a suitable rotary hot-air drier, we must calculate the moisture content to be removed, the heat needed to increase the temperature of the solid, and confirm that these requirements can be met within the constraints of the drier sizes and air velocity limits. The chosen drier and airflow rate must facilitate efficient drying, considering the physical properties of the solid and the conditions of the incoming air.

Step-by-step explanation:

Choosing a Rotary Hot-Air Drier for Drying Crystalline Organic Solid

To choose an appropriate drier for the given application, we need to consider several factors, including the drier size, airflow rate, and the thermal properties of the material to be dried.

First, we determine the moisture that needs to be removed from the solid. The initial moisture content is 20%, and the target is 0.3%. The dried product delivery rate is 450 kg/h, which implies that the wet solid has a mass flow rate higher than this value since it contains additional water.

The required mass of water to be removed per hour can be calculated by subtracting the mass of dry solid from the mass of the wet solid. Next, we use the heat capacity of the solid and the required increase in temperature to determine the amount of heat needed to dry the product. This will be conducted by the hot air which has an initial temperature of 155°C. The drying process must be efficient enough to heat the solid from 20°C to 120°C and evaporate the water content.

Given the constraints on superficial air velocity, we choose a drier size that allows for sufficient contact time between the hot air and the crystalline solid while also respecting the air velocity limit. Standard sizes available for driers are listed, and a suitable size must be chosen that enables the process requirements to be met.

Finally, the rate of airflow must be calculated to ensure that it matches the drier's capacity to transfer heat to the solid and remove moisture while adhering to the velocity constraints.

The detailed calculations and considerations would enable the selection of an appropriate drier from the standard sizes provided and the specification of an airflow rate that ensures efficient drying of the crystalline organic solid.

Answer 2

To select the appropriate drier, you must consider the solid's entry and exit conditions, moisture content, heat capacity, particle size, airflow rate, and standard drier sizes. Without additional specific drying rate data and drier dimensions, an accurate selection cannot be made.

Step-by-step explanation:

Choosing the Appropriate Direct-Heat Countercurrent Rotary Hot-Air Drier

To select a suitable direct-heat countercurrent rotary hot-air drier for drying a crystalline organic solid, several factors need to be taken into consideration. These factors include the entry and exit temperatures of the solid, the moisture content in the solid, the heat capacity, particle size, the desired airflow rate, and the drier dimensions. Given the specified conditions of the solid entering at 20°C and exiting at 120°C, with an initial moisture content of 20% and a final moisture content of 0.3%, along with a dried product output of 450 kg/h, determining the appropriate drier size among the standard sizes provided is essential.

The calculations would require balancing the mass and energy flow rates to ensure the drier chosen is capable of both accomplishing the necessary moisture removal and accommodating the specified airflow rate without exceeding the superficial air velocity limit of 1.6 m/s. This process involves the use of engineering formulas considering heat and mass transfer principles alongside empirical data related to similar drying processes.

Unfortunately, without additional details such as the specific drying rate, latent heat of vaporization of water, the required air humidity after the drying process, and the complete dimensions of the driers (including diameter and length), it's not possible to accurately select a drier or specify the airflow rate. In practice, one would use the product's drying characteristics and the drier's performance curves to match the process needs with the drier's capabilities. If necessary, a detailed engineering analysis and consultation with drier manufacturers would be the next step.