Coking industry Solution

Characteristics of Waste Gas

The waste gas emitted from coking processes primarily consists of ammonia (NH₃), hydrogen sulfide (H₂S), and sulfur dioxide (SO₂). These pollutants exhibit relatively stable concentrations throughout the production cycle, which simplifies the design of treatment systems. Depending on specific environmental regulations and operational requirements, downstream processes may require desulfurization and denitration treatments to ensure compliance with stringent emission standards.

Sources of Waste Gas

Waste gas emissions in a coking plant originate from several key sections:
- Desulfurization Section: This section generates waste gas during the removal of sulfur compounds from coal tar and other by-products. The process involves chemical reactions that strip sulfur from the raw materials, resulting in the release of sulfur-containing gases.
- Ammonium Sulfate Section: During the synthesis of ammonium sulfate, various chemical reactions produce waste gas containing ammonia and other volatile compounds. This section is crucial for recovering valuable by-products while managing emissions.
- Salt Extraction Section: Additional waste gas emissions arise from the salt extraction processes, where impurities are removed from the coal tar. This step is essential for producing high-quality coke but also contributes to the overall waste gas stream.

Waste Gas Components

The primary components of the waste gas include:
- Ammonia (NH₃): A pungent gas that can cause respiratory issues if not properly treated.
- Hydrogen sulfide (H₂S): A toxic and corrosive gas known for its rotten egg smell.
- Sulfur dioxide (SO₂): A major contributor to acid rain and air pollution.
- Nitrogen oxides (NOx): Compounds that contribute to smog and respiratory problems.
- Particulate matter (PM): Fine particles that can be harmful when inhaled.
- Volatile organic compounds (VOCs): Organic chemicals that can have adverse health effects and contribute to air pollution.

Process Scheme

To effectively manage and treat the waste gas, a multi-stage treatment process is proposed:
1. Pretreatment: This initial stage conditions the waste gas stream to remove large particulates and adjust temperature and humidity levels. Proper pretreatment ensures optimal conditions for subsequent treatment steps, enhancing the efficiency of pollutant removal.
2. Regenerative Thermal Oxidation (RTO): In this core treatment step, the waste gas is heated to high temperatures, typically between 760°C and 870°C, leading to the oxidation of organic compounds into less harmful substances such as carbon dioxide (CO₂) and water vapor (H₂O). RTO is highly effective in reducing VOCs and other organic pollutants.
3. Optional SCR and Desulfurization: Depending on specific needs and regulatory requirements, selective catalytic reduction (SCR) can be employed to reduce nitrogen oxides (NOx) through a catalytic reaction with ammonia or urea. Following this, desulfurization can be implemented to remove sulfur compounds using limestone or other absorbents. These additional stages significantly enhance the overall efficiency of pollutant removal and help meet strict emission standards.

By implementing this comprehensive treatment scheme, the coking industry can significantly reduce its environmental impact while adhering to stringent emission standards. The multi-stage approach ensures that each pollutant is addressed effectively, contributing to cleaner air and a healthier environment.