Current Situation and Monitoring Suggestions of VOCs Emission in Textile Printing and Dyeing Industry

1 Emission status Industrial source VOCs emissions involved in many industries, the proportion of up to 55.5, industrial sources in the key industries including petroleum refining and storage and transportation, chemical industry, solvent use (including surface coating) and so on. VOCs emissions from solvent use account for 23.3 percent of the total emissions. The textile printing and dyeing industry uses a large number of organic solvents in the production process, which is an important component of industrial source VOCs emissions, and its VOCs emissions account for about 2.8 of the total emissions.

The textile printing and dyeing production process is roughly divided into four stages: cloth preparation and pretreatment, dyeing, printing, finishing and finished product packaging. Due to the differences in the processing of fabrics, the process is slightly different, often requires a variety of raw materials, through a number of combined processes for production, VOCs emissions involve almost all emissions. The finished product setting stage is the largest processing link to prevent and control emissions in the printing and dyeing industry, and its emissions come from the solvent volatilization caused by the use of high-temperature setting machines.

The types and composition of VOCs pollutants emitted by the printing and dyeing industry are complicated, and the composition of pollutants varies greatly in different processing stages, and most of the process air emissions belong to unorganized emissions. Some scholars in China have studied the aspects of emissions and the main pollution factors.

2 Emission standards Internationally, different countries and regions have different constraints on atmospheric emission standards for the textile industry. Among them, the World Bank's "Prevention and Control of Printing and Dyeing Industry Exhaust Emission Level Standards" lists the limits of volatile organic compounds VOCs), chlorine, formaldehyde, particulate matter and other major pollution factors, which are basically the same as the types of exhaust emissions from my country's textile industry. An important technical reference for the textile printing and dyeing industry.

At present, the emission standard of air pollutants in China's printing and dyeing industry is being formulated. Only Zhejiang Province has promulgated the Emission Standard of Air Pollutants for Textile, Dyeing and Finishing Industry in Zhejiang Province (DB33/962-2015). Other provinces and regions are still implementing the Comprehensive Emission Standard of Air Pollutants or the local comprehensive emission standard of air pollution.

At present, there is no air pollutant emission list for the textile printing and dyeing industry in China. In the standards currently implemented in China's textile printing and dyeing industry, there are no prevention and control measures for the processes and equipment that produce pollutants, and the control of process pollutants is weak.

According to national and local environmental protection requirements, textile printing and dyeing enterprises have basically completed the transformation of waste gas treatment. The waste gas treatment of textile printing and dyeing enterprises mainly adopts the treatment technology of water spray activated carbon, and other waste gas treatment technologies, such as incineration, catalytic combustion, adsorption condensation, etc., also have application cases, but due to the comprehensive consideration of the use environment, operating cost and pollutant removal efficiency, it has not been widely used.

4 Monitoring recommendations

(1) Clear monitoring factors

Combined with the characteristics of the industry and the composition analysis of the main pollutants, the main pollutants were selected as the key monitoring objects, and the non-methane total hydrocarbons, benzene series (benzene, toluene, xylene), styrene, chlorobenzene, methanol, formaldehyde, 2-butanone, dichloromethane, vinyl chloride, trichloroethylene, tetrachloroethylene and other pollutants were monitored and analyzed online. Other very visible pollutants, according to the characteristics of pollutants and enterprise environment, specific analysis of the necessity of monitoring projects.

(2) Combination of continuous online monitoring and regular sampling monitoring

As VOCs online monitoring is still in its infancy, the relevant standard requirements and technical specifications are not perfect, limited by monitoring methods and application environment, it is not possible to achieve full component online monitoring of waste gas from textile printing and dyeing enterprises. Therefore, it is recommended to combine online monitoring with regular sampling. In view of the clear limit in the standard, VOCs components that are harmful to the human environment and have suitable detection methods are continuously monitored and analyzed; for special pollutants that have not yet had suitable detection methods and are less harmful to the human body and the environment, regular sampling and monitoring are implemented. Wanwei Yingchuang's VOCs online monitoring products cover continuous online monitoring and portable monitoring series. SmartEM4000 series products include: fixed source TVOC online monitoring system, volatile organic gas VOCs online monitoring instrument, online multi-gas detector, TVOC alarm detector, portable TVOC detector, portable gas chromatograph, etc. The products have environmental protection product certification and measurement certification, and meet the two operating conditions of continuous online monitoring analysis and regular sampling monitoring.

(3) Clear monitoring methods

At present, the main monitoring methods of VOCs are gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), photoionization detection (PID) and optical detection. Because the monitoring method of gas chromatography combined with hydrogen ion flame detector (GC-FID) has the characteristics of wide range, good linearity and wide application range, it has become the main monitoring method of VOCs online monitoring market. Considering the installation cost, use environment, monitoring requirements and other aspects, GC-FID cannot be applied to the monitoring of VOCs of all enterprises in all regions. For areas with no methane, no demand for components and small emissions, PID detection method can be used to monitor the total VOCs online. For environments with complex components and high component requirements, GC-MS monitoring methods are required. The pollution component is single, at the same time, industrial parks with monitoring requirements for other inorganic components can consider using optical monitoring methods.

(4) Clear monitoring points

Reasonable selection of detection points plays an important role in monitoring results and VOCs accounting evaluation. At present, the installation location of fixed sources is selected according to the standard requirements of "Technical Specification for Continuous Monitoring of Flue Gas Emissions from Fixed Pollution Sources (Trial)" (HJ/T75-2007); At present, unorganized emissions at the factory boundary are set up according to the requirements of "Technical Specification for Layout of Ambient Air Quality Monitoring Points (Trial)" (HJ664-2013). For industrial parks composed of multiple enterprises, a three-dimensional monitoring method combining fixed source, plant boundary and park monitoring should be considered. According to the types and emissions of pollutants discharged by the enterprise and the natural environment where the park is located, select reasonable monitoring points, and combine pollutant traceability technology to evaluate the impact of the enterprise on the park and the surrounding environment as a whole.