Coke oven

Coal coking, also known as high-temperature dry distillation of coal, is a coal conversion process in which coal is used as the raw material and heated to approximately 950 °C in an oxygen-free environment. Through high-temperature dry distillation, coke is produced whilst simultaneously yielding coal gas, coal tar and other chemical products.

To ensure the quality of the coke, the most fundamental requirements for selecting coking coal are its volatile matter content, caking properties and coking properties; The vast majority of coking coal must undergo washing and beneficiation to ensure the lowest possible ash, sulphur and phosphorus content.

When selecting coking coal, attention must also be paid to the expansion pressure generated during the coking process. Coking with low-volatile coal, due to its high gel viscosity, tends to produce high actual expansion pressure, which can cause damage to the coke oven lining; this requires resolution through coal blending.

The typical yields of the main products obtained from coking dry coal are generally as follows:

Coke 70%–80%, crude tar 2.5%–4%, crude benzene 0.7%–1.3%, ammonia 0.2%–0.35%, hydrogen sulphide 0.1%–0.5%,

pyridine 0.015%–0.025%, coke oven gas 300–380 m^³/t of coal.

In particular, coke oven gas has a high calorific value of 16,720–18,810 kJ/m^³, with a high proportion of combustible components (approximately 90 per cent). Given its high calorific value, it must be fully recovered and utilised, and the gas content must be precisely monitored.

In coking plants, the by-product of coal cracking is high-calorific-value raw gas (coke products are used for iron reduction in blast furnaces). After purification, coke oven gas is used as fuel in other steel smelting processes.

Purification plants are essential for removing interferents (tar and naphthalene blockages) and environmental pollutants (H₂S, NH₃, benzene). In coking plants, H_₂S and O_₂ are typically monitored effectively.

Measurements of ammonia, naphthalene and benzene using traditional wet chemical methods are limited to a single sampling point per day, which presents significant constraints.

Gas monitoring is required in all of the above processes; the ProC-TOF online mass spectrometer is used for online monitoring in coke oven gas purification plants, expanding the range of gas components that can be measured.

This is because the gas is not only used as fuel in other processes but also for heating the coke oven itself. These characteristics include: calorific value, density, specific gravity, air-to-fuel ratio, and the air requirement based on stoichiometric composition.

Online monitoring enables the optimisation of the gas purification process. Furthermore, mass spectrometric analysis of all gas components allows the combustion characteristics of the gas to be derived.

Derivative calculations for the gas enable more efficient utilisation of the fuel gas and result in significant cost savings.