The positioning and development path of natural gas power generation in the energy transition period

Comparison of environmental standards between gas-fired and coal-fired power generation

In 2011, China's Ministry of Environmental Protection (now the Ministry of Ecological Environment) and the State Administration of Quality Supervision, Inspection and Quarantine formulated GB13223-2011 "Emission Standards for air pollutants in Thermal Power Plants", which has been implemented since 2012. In the standard, the limits and control requirements of pollutant emission concentration in thermal power plants are specified in detail.

According to GB13223-2011 and the Announcement of the Ministry of Environmental Protection on the Implementation of Special Emission Limits for Air Pollutants, since January 2012, new coal-fired power plants will be implemented in key areas and non-key areas. The emission limits of soot, SO2 and NOx are 30mg/m3, 100mg/m3 and 100mg/m3 respectively (except the southwest region); Since April 2013, new coal-fired units in key control areas have implemented special emission limits for air pollutants, and the emission standards for soot, SO2 and NOx are 20mg/m3, 50mg/m3 and 100mg/m3 respectively. During the "13th Five-Year Plan" period, all thermal power coal-fired units within the municipal area of the key control area shall implement special emission limit requirements.

Coal-fired power plants refer to the emission concentration limits of gas-fired power plants in GB13223-2011 standard, and upgrade the pollutant control facilities of power plants, with the purpose of striving to achieve the concentration of pollutants discharged from the flue gas of coal-fired power plants after transformation to meet the emission limits of gas-fired power plants, that is, the implementation of the "ultra-low emission limits" in Table 1 of conventional pollutant emissions. Call it the "ultra-low emissions" of coal-fired power plants. However, after the "ultra-low emission" transformation of coal-fired power generation, it is only to reach or lower than the emission limit of gas-fired power plants stipulated by the national standard, which is still far higher than the actual emission value of gas-fired power plants. GB13223-2011 increases for the first time the emission concentration limit of air pollutants from gas turbine units, but does not classify gas turbines separately, but is generally classified as "gas-fueled boilers or gas turbine units" with natural gas boilers. The standard stipulates that the emission limits of soot, SO2 and NOx are 5mg/m3, 35mg/m3 and 50mg/m3 respectively. In some economically developed provinces and cities, such as Beijing, Tianjin and Shenzhen, local standards or government regulations have successively issued higher requirements for gas turbine conventional pollutant emissions, especially NOx emissions (Table 1). Local standards are mainly to further strict NOx emission limits from the national requirements of 50mg/m3 to 15 ~ 35mg/m3; Tianjin and Shenzhen have not made more stringent regulations on soot and SO2 emissions of gas turbines, because in actual operation, without taking any post-treatment measures, the emission concentration of these two pollutants of gas turbines is extremely low, and the specification does not need to be required.

Comparison of actual emissions of gas-fired and coal-fired power generation

The emission limits specified in national standards and local standards are the maximum allowable emission limits. During the operation of thermal generating units, there are great differences between the actual emission value and the standard limit value, between coal power and coal power, and between coal power and gas power. Although some experts believe that ultra-low emission coal power can achieve almost the same emission limits as gas power plants in theory, the actual operation of gas power plants is still significantly cleaner than ultra-low emission coal power plants. Xu Jingxin [8] et al. conducted statistics on 99 ultra-low emission coal-fired units in China and 17 gas units in Jiangsu Province (without denitrification devices) through field measurement and literature research. The results showed that: In terms of actual average NOx concentration, there is no significant difference between gas power plants and ultra-low emission coal-fired power plants, but the gas unit can control NOx emission well only by relying on low nitrogen burners. If denitrification devices are installed, the NOx emission concentration can be further reduced [9]. The average soot emission concentration of gas-fired power plants is one order of magnitude lower than that of coal-fired power plants. The average emission concentration of SO2 in coal-fired power plants is about 16mg/m3, which is significantly higher than that in gas-fired units of 2.20mg/m3 (class E) and 0.84 mg/m3 (class F). The average smoke emission concentration of coal-fired units is 1.8 to 2.4 times that of gas-fired units. Many other research results have similar conclusions, that is, at present, the actual emission concentration of soot and SO2 in China's ultra-low emission coal-fired power generation is still higher than that of gas power generation.