Coal chemical industry

The chemical structure of organic matter in coal consists of macromolecules centred on condensed aromatic rings, linked by bridging bonds and bearing various functional groups (see Coal Chemistry); through thermal and catalytic processing, coal can be converted into various fuels and chemical products.

Among the various chemical processing methods for coal, coking is the oldest and remains the most important to this day. Its primary purpose is the production of metallurgical coke, whilst simultaneously yielding by-products such as coal gas and aromatic hydrocarbons including benzene, toluene, xylene and naphthalene;

Coal gasification also occupies a very important position in the coal chemical industry; it is used to produce town gas and various fuel gases (widely used in industries such as machinery and building materials), as well as to produce synthesis gas (as a raw material for the synthesis of ammonia, methanol, etc.); processes such as low-temperature coal pyrolysis, direct coal liquefaction and indirect coal liquefaction are primarily used to produce liquid fuels.

The new coal chemical industry focuses primarily on the production of clean energy and products that can substitute for petrochemicals, such as diesel, petrol, jet fuel, liquefied petroleum gas (LPG), feedstocks for ethylene and polypropylene, and alternative fuels (methanol, dimethyl ether). By integrating energy and chemical technologies, it can form an emerging integrated industry combining coal with energy and chemical processing.

The coal-based energy and chemical industry will play a vital role in the sustainable utilisation of China’s energy resources and represents a key direction for development over the next 20 years. This is of great significance for China in mitigating environmental pollution caused by coal combustion and reducing the country’s dependence on imported oil. It can be said that the coal chemical industry in China is facing new market demands and development opportunities.

China is rich in coal resources and possesses a comprehensive range of coal types. The development of modern coal conversion technologies, such as coal liquefaction and gasification, holds both immediate and long-term significance for leveraging resource advantages, optimising the end-use energy structure, and bridging the domestic oil supply-demand gap on a large scale. The national ‘Tenth Five-Year Plan’ for energy science and technology and energy infrastructure construction attaches great importance to the development of the coal chemical industry.

Industrial Gas Applications

As an industrial fuel gas, coal gas with a typical calorific value of 1,100–1,350 kcal can be produced using either atmospheric-pressure fixed-bed gasifiers or fluidised-bed gasifiers. It is primarily used in the steel, machinery, sanitation, building materials, light industry, textiles and food sectors to heat various furnaces and kilns, or to directly heat products or semi-finished goods. In practical applications, precise control of heating temperatures is usually required to meet process or quality control objectives; therefore, the stability of the gas’s calorific value is of particular importance.

Online/process mass spectrometers employ measurement compensation technology for the analysis of H₂ and CH₄, ensuring the accuracy of actual calorific value test results and providing effective and robust data support for the combustion monitoring and control of gas.

Applications of Metallurgical Reduction Gas

The CO and H₂ in coal gas possess strong reducing properties. In the metallurgical industry, reducing gases can be used to directly reduce iron ore into sponge iron; in the non-ferrous metals industry, metal oxides such as nickel, copper, tungsten and magnesium can also be smelted using reducing gases. Consequently, metallurgical reducing gases have specific requirements regarding the CO content in the gas. Process gas mass spectrometers can measure CO or H₂ concentrations effectively and in real time, guiding adjustments to the gasification process and ensuring gas production efficiency.

Feed gas for chemical synthesis

With the development of the new coal chemical industry, the process of producing synthesis gas via coal gasification, followed by the direct synthesis of various chemicals, has become the foundation of modern coal chemical production. This primarily includes synthetic ammonia, synthetic methane, synthetic methanol, acetic anhydride and dimethyl ether.

Syngas for chemical synthesis does not have high requirements in terms of calorific value; the main requirements relate to the CO and H₂ content in the gas. Generally, Texaco and Shell gasifiers are considered suitable.

Currently, more than 50 per cent of China’s methanol production for synthetic ammonia comes from coal gasification processes. If the CO₂ concentration in the syngas is too high, it will directly affect the operating efficiency of the compressors in the synthesis process (typically reducing it by around 10 per cent), inevitably leading to increased electricity consumption and compressor maintenance costs.

In recent years, online mass spectrometers have been increasingly utilised in the analysis of gas produced by coal gasification. These instruments analyse the concentrations of CO, CO₂ and CH₄ in the gas stream, whilst using thermal conductivity sensors to measure H₂ concentrations and electrochemical sensors to measure O₂ concentrations. Simultaneously, the theoretical calorific value of the gas is calculated based on the measured concentrations of these components. This replaces the manual sampling and analysis stages associated with the Auster gas analyser, enabling automated measurement and eliminating human error. Compared to combustion-based calorimetric analysers, the pre-treatment system and instruments feature a simpler design and are easier to operate and maintain, making them better suited to the requirements of real-time, online analysis in coal gasification.

In addition to measuring the concentrations of gases such as CO, CO₂ and H₂, the online mass spectrometer also guides the control of the synthesis gas process, ensuring the yield and quality of chemical products whilst achieving energy-saving objectives.

Quantitative analysis using the ProC-TOF online mass spectrometer serves as an effective means of online analysis in industrial processes and possesses inherent advantages over instruments such as chromatographs and infrared analysers. It is used in the production of olefins from synthesis gas, oil from synthesis gas, alkanes from synthesis gas, and olefins from natural gas.

Its analytical characteristics—rapid, multi-flow path, multi-component, high-precision and high-stability—lend even greater significance to its successful application. The successful implementation of mass spectrometry-based quantitative analysis methods has played a positive role in promoting the development and widespread adoption of domestically produced mass spectrometers, whilst also facilitating the optimisation of industrial production processes, leading to more rational resource allocation and improved production efficiency.