Design of Calcination for Aluminum Hydroxide in Aluminum Hydroxide Plant
Introduction
Calcination is an important operation in the manufacturing of aluminum hydroxide, a material with a variety of uses ranging from water purification to fire retardants. It is a process of heating the raw material of aluminum hydroxide (alumina trihydrate) at high temperatures to achieve different desirable characteristics. Calcination is done in rotary kilns, with temperatures ranging from 900°C to 1100°C, and the composition of the product depends on both the kiln temperature and atmosphere. In this paper, we will discuss the design and operation of the calcination process of aluminum hydroxide in an aluminum hydroxide plant.
Calcination Process and Design
Calcination process of aluminum hydroxide is a continuous process which is carried out in a rotary kiln. In this process, alumina trihydrate is heated to temperatures of 900°C - 1000°C in the absence of oxygen. This indicates that, in order to have a successful calcination process at the given temperature, it is important to create a reducing atmosphere in the reactor, which should be sufficiently free from oxygen.
One of the most critical aspects of the design of the calcination process is the design of the kiln. The correct kiln design and kiln operation are necessary to achieve optimal performance of the calcination process. For example, the kiln should be designed with enough volume to receive large volumes of material which needs to be heated. Depending on the kind of rotary kiln used, there are requirements related to the thickness of the lining, height, length and width. The lining should be made of refractory material and adequate insulation should be provided to withstand higher temperatures of calcination and also to reduce the energy losses.
The correct kiln design also helps achieve uniform heating and sufficient retention time of the material in the kiln, which is important for achieving a uniform product of aluminum hydroxide. The kiln should also be equipped with a dust collector system, which is important to prevent against dust escaping into the atmosphere. Additionally, the kiln should be provided with adequate instrumentation for measuring the temperatures inside the reactor, in order to obtain accurate control of the calcination process.
Kiln Operation
The kiln is operated at different temperatures to obtain the desired product of aluminum hydroxide, depending on the process requirements. Generally, an operating temperature of 900°C - 1,050°C is used for the production of aluminum hydroxide. Up to 1,100°C can also be used in certain cases. In order to obtain a uniform product, the temperature profile through the kiln is closely monitored, and it can be adjusted by changing the burner output and/or the feed rate of the material.
The kiln is operated in a continuous mode, with periodic maintenance shut-downs in order to inspect the kiln and replace damaged refractory material. During the shut-downs, cooling of the kiln can be done by inert gas or inert powder injection.
Conclusion
Calcination of aluminum hydroxide is an important process in the manufacturing of aluminum hydroxide. It requires careful design of the kiln and it operation to obtain a uniform product. The kiln design and operation should be tailored to the process requirements and needs to ensure a safe and efficient operation. In addition, appropriate instrumentation should be in place to monitor and control the process.
