As national environmental emission standards continue to tighten, NOx emissions have increasingly drawn attention from both the government and industry. As a result, denitrification technologies centered on selective catalytic reduction (SCR) are becoming a prevailing trend. Whether in the thermal power industry or in non-power industries, the simultaneous installation of SCR denitrification systems or their addition as new equipment has become standard practice. However, due to differences in industry sectors and the varying processes employed, the medium-temperature SCR denitrification catalysts—typically operating at 280–420°C—that are well-suited for the thermal power industry often fail to perform effectively in non-power sectors such as steel coking, sintering machines, waste incineration, glass manufacturing, refractory materials, lime kilns, coal-to-gas power generation, lithium battery production, silicon metallurgy, and alumina refining. On the one hand, the flue gas temperatures in these non-power industries generally fall below the operational range of medium-temperature SCR catalysts, with most flue gases having temperatures between 160 and 280°C. On the other hand, the flue gas composition in non-power industries is far more complex, featuring higher concentrations of alkali metals, moisture, and other harmful substances, thereby placing even stricter demands on the SCR denitrification catalysts—the core component of these systems.

　　Currently in China, denitration catalysts used in SCR denitration systems are classified into three types based on their operating temperatures in different industries: low-temperature catalysts (160–280℃), medium-temperature catalysts (280–420℃), and high-temperature catalysts (≥450℃). Generally, once the operating temperature of an SCR denitration system is determined, the type of catalyst to be used is essentially fixed. Therefore, the operating temperature of the denitration system is the primary criterion for selecting the appropriate type of denitration catalyst. This article focuses on the selection of low-temperature SCR catalysts under specified temperature conditions. After determining the operating temperature of the denitration system, the catalyst should be selected based on the following aspects: 1. Considering the actual flue gas conditions—such as the required denitration efficiency, the NOx concentration at the inlet of the denitration system, and the target NOx emission levels—to estimate the approximate catalyst dosage and determine the initial catalyst volume; 2. Taking into account the dust content and characteristics in the actual flue gas conditions to decide on the appropriate pore size of the catalyst—for example, if the dust content is high, a catalyst with larger pores can be chosen; conversely, a catalyst with smaller pores should be selected; 3. Adjusting the catalyst’s formulation based on the SO2 content, moisture level, and presence of alkali metals or heavy metals in the flue gas, so as to enhance its resistance to sulfur, water, and metal poisoning, thereby ensuring the long-term operational performance of the catalyst; 4. Since the operating temperature range of low-temperature SCR denitration catalysts overlaps with the temperature range for the formation of ammonium bisulfate (ABS) and ammonium sulfate (AS), during the actual catalyst selection process, engineering companies or end-users should be reminded or advised to install corresponding thermal analysis equipment; 5. Based on the designed catalyst dosage, the nature of the industry to which the owner belongs, and the site conditions, further consideration should be given to whether the denitration system needs to be designed with segregated compartments.

　　The coking industry is a typical non-power sector. Due to the inherent characteristics of the coking industry, coke oven designs typically have a service life of 30 years, and the ovens cannot be shut down mid-operation. Moreover, environmental regulations require these ovens to operate continuously for 8,760 hours per year. In regions with particularly stringent environmental standards, SCR systems are required to be divided into separate chambers, enabling online single-chamber regeneration, maintenance of equipment, and catalyst replacement. This places higher demands on environmental protection enterprises. Specifically regarding denitrification, studies have shown that the flue gas emitted from coke ovens varies significantly in both flue gas temperature and pollutant concentrations depending on the type of fuel used. Consequently, when selecting catalysts for denitrification systems, it is essential to differentiate based on the specific properties of the fuel.

　　If the independent coking plant uses coke oven gas as its fuel, which has a relatively high calorific value, the flue gas from the coke oven tends to have a higher temperature—typically ranging from 250 to 310°C—and is significantly influenced by the production load. As a result, the flue gas conditions are more complex and tend to have higher pollutant concentrations: NOx levels generally range from 700 to 1,500 mg/Nm³, while SO₂ levels typically fall between 300 and 1,000 mg/Nm³. According to current standards, SO₂ emissions should be below 30 mg/Nm³ and particulate matter below 15 mg/Nm³. There are two process options available. The first is an established wet desulfurization process: coal tar pretreatment + medium- and low-temperature SCR denitrification + wet desulfurization. This process has the advantage of relatively lower capital costs and offers a wider selection of catalysts. However, its main drawback is that the catalyst’s service life may not reach three years, and after wet desulfurization, the flue gas temperature may fail to meet the minimum temperature requirement for the coke oven chimney’s thermal standby, necessitating heat exchange at the front end. After several years of practical operation, the chemical lifespan of the catalyst typically ranges from 2 to 3 years. Depending on the sulfur content, the operating temperature of the catalyst can be set at ≥230°C, ≥250°C, or ≥270°C. There are many catalyst manufacturers in the market with proven track records to choose from. The second option is a process originally designed without a desulfurization system: SDS dry desulfurization + medium- and low-temperature SCR denitrification. In this process, the catalyst operates under low-sulfur and low-dust conditions, allowing its chemical lifespan to reach up to three years. The operating temperature of the catalyst can be selected as ≥180°C, ≥200°C, or ≥220°C, depending on the actual temperature of the flue gas entering the denitrification system after dust removal and desulfurization. It is advisable to select a catalyst manufacturer with a proven track record based on the specific temperature conditions.

　　The coking plant uses blast furnace gas or mixed gas as fuel, which has a relatively low calorific value. A distinctive feature of this fuel is that the flue gas temperature from the coke oven is relatively low—typically ranging from 200 to 260°C—and is significantly influenced by the production load. Compared with other fuels, the pollutant content is also lower: NOx levels generally do not exceed 500 mg/Nm³, and SO₂ levels typically stay below 300 mg/Nm³. There are two process options available: one is a (semi-)dry desulfurization system combined with baghouse dust removal and low-temperature SCR denitrification; the other is a carbon-based dry desulfurization system paired with a medium-to-low temperature SCR denitrification catalyst. The advantages of these two processes include a temperature reduction of 10–30°C during dry desulfurization (depending on the specific desulfurization method, the inlet SO₂ concentration, and the quality of thermal insulation in the project), ensuring that the flue gas temperature after denitrification meets the requirements for chimney standby operation, and producing neither wastewater nor solid waste. The disadvantages are that there are relatively few manufacturers offering catalysts suitable for temperatures around 180–200°C, and such catalysts tend to be relatively expensive. However, compared to methods involving temperature increase or temperature increase plus heat exchange, using an appropriate low-temperature catalyst can lead to greater energy savings and reduced investment costs. Under conditions of low sulfur and low dust concentrations, the earliest coking plant at Baosteel Zhanjiang Iron and Steel has been operating for more than four years, and its catalysts can last up to 3–4 years, depending on flue gas conditions and maintenance practices. The operating temperature range for the catalyst can be selected between approximately 180 and 220°C; specifically, it’s advisable to carefully choose a catalyst manufacturer with a long track record, based on the temperature achieved after desulfurization and dust removal.

　　In addition, since coking ovens vary in their operational lifespan, flue gas leakage between ovens is also a factor influencing the selection of catalysts for denitrification systems. When designing catalysts, the actual dosage of low-temperature SCR denitrification catalysts should be adjusted based on the leakage rate between ovens. This adjustment ensures not only that the outlet emissions from the denitrification system meet the required standards but also that the monitored environmental indicators comply with regulatory requirements.

　　In summary, when selecting low-temperature SCR denitrification catalysts for the coking industry, it is essential not only to take into account the impact of the fuel but also to comprehensively consider the relevant environmental protection process routes and the leakage conditions in the coke oven flue gas.