Design of coke oven plant
Background
Coke is a form of nearly pure carbon that is obtained by heating coal in the absence of air, and is primarily used as a fuel. Coke oven plants use a series of ovens to heat coal in the absence of air, resulting in the production of nearly pure carbon (coke). The products of the coke oven plant are coke, by-products (in the form of tar, ammonia, and sulfur), and off-gas.
The coke oven plant process consists of three distinct operations: pre-baking, baking, and post-baking. In the pre-baking stage, coal is conditioned, heated, and impregnated with a coal tar pitch to form coke ovens. The coke ovens are heated by the fuel gases that are produced during the baking stage and the post-baking stage. The baking stage is the actual baking of the coal in the ovens. In the post-baking stage, the coke is cooled and drained of the by-products, then discharged from the ovens.
Scope
This document is designed to provide a comprehensive overview of the design and operation of coke oven plants. This document outlines the major process steps, key equipment, and design considerations for each of the stages of the process.
Pre-baking Stage
The pre-baking stage is the conditioning and heating of the coal in preparation for baking. The pre-baking process begins with the precipitation of some of the sulfur from the coal. This is followed by pitch impregnation, which helps to make the coal more permeable and increases its thermal resistance. After precipitation and impregnation, the coal is heated to drive off volatiles and account for the possible need to switch fuels during the baking stage.
One of the most important considerations in designing a pre-baking system is the choice of fuel. The fuel used to pre-heat the coal must be compatible with the baking process (i.e., the fuel must not cause fouling or other issues in the ovens). Flue gas, fuel oil, and natural gas are generally the preferred fuels for pre-baking applications.
Baking Stage
The baking stage is the actual baking of the coal to produce coke. This process takes place in the coke ovens, which are heated by off-gases and tars. The ovens are typically heated to between 650°C and 850°C, and the baking of the coal takes approximately twenty-four (24) hours. To optimize the efficiency of the process, the ovens are typically divided into three zones – preheat, bake, and cooling.
During the bake cycle, heat from the fuel gases and tars is used to increase the internal temperature of the ovens. The heat is distributed evenly throughout the ovens via baffles, or thick walls, which ensure that the heat enters the ovens uniformly. During the baking process, the coal is transformed into nearly pure carbon (coke).
Post-baking Stage
The post-baking stage is the cooling and draining of the coke in the ovens. The cooling process begins immediately after the baking cycle is completed. Once the ovens reach the desired temperature, the ovens are drained of their residual tars and gases. The off-gases are collected in a gas collection system. The coke is then cooled and discharged from the ovens.
Design Considerations
The design of a coke oven plant must take into consideration many factors, such as the characteristics of the coal, the desired production rate, the type of fuel being used, and the local environmental regulations. Additionally, considerations must be made for the size and layout of the plant, the number of ovens and the fuel management system.
Conclusion
Coke oven plants are an integral part of the process of producing high-quality coke for industrial use. The design of a coke oven plant is a complex process and requires careful consideration of all aspects of the operation, including the pre-baking, baking, and post-baking stages. The availability of reliable fuel management systems and advanced oven designs in recent years has enabled coke oven plants to produce high-quality coke with greater efficiency and lower environmental footprint.
