Investigation On Photocatalytic Purification Of Gaseous Pollutants In Paper Mill And Its Automatic Monitoring System

Nowadays, the focus of paper industrial pollution is still waste water and waste residue. The research and treatment of gaseous pollutants in paper mill is often ignored by researchers and the public which will hinder the benign sustainable development of paper-making industry. Many kinds of gaseous pollutants, such as benzene, toluene, sulfur dioxide, hydrogen sulphide will be produced in pulp and paper process. These toxic gases do great harm to human body. Some gaseous pollutants are even more dangerous than those of water pollution.In order to solve the problem of gaseous pollutants in paper mill, the gaseous pollutants in a Guangzhou paper mill were analyzed by means of Activated carbon adsorption/Dichloromethane desorption GC-MS and Acetylacetone spectrophotometry, and a set of photocatalytic purification automatic monitoring system was designed. The optimal value for the process parameters of purification system were searched for and its degradation of performance testing under the optimal value was also tested to compare the differences of degradability while handling different pollution load and different pollutants.First, in order to determine the gas component of paper mill, the gaseous pollutants of four sampling points(office area, vacuum pump outlet, papermaking workshop, waste paper sorting room) were analyzed by means of Activated carbon adsorption/Dichloromethane desorption GC-MS and Acetylacetone spectrophotometry. The results showed that: BTEX that had complicated structure were detected in all sampling points; all the sampling points have dangerous levels of formaldehyde comparing with the IAQ standard(GB/T18883-2002, China). The formaldehyde concentration of vacuum pump outlet exceeds the limit 1.7 multiplies.Then, the photocatalytic purification system adopting the photocatalytic oxidation technology was designed. Using nanosized-titanium dioxide as catalyst, adopting the structure of multistage photo-catalytic oxidation, installation a double strainer at the entrance of the reactor for the removal of solid particles in the air, illuminating under 253.7nm ultraviolet light, series of 2mm honeycomb aluminum meshes coated with nanosized- titanium dioxide on played an important role in the degradation of gaseous pollutants in the air.Moreover, the automatic monitoring system of the photocatalytic purification was designed. It uses the microcontrollers STM32F103RBT6 as the core. The formaldehyde sensor EC803-CH2 O is used to detect the formaldehyde concentration of the environment. The digital temperature and humidity sensor DHT11 detects the temperature and humidity. The automatic monitoring system can automatically adjust the flow rate and light intensity to fit into the pollution load and the concentration value will be real-time displayed on the LCD screen.Finally, the paper also explores the optimal process parameters of the photocatalytic purification system taking formaldehyde as a target pollutant. The experiment result shows the optimal value of flow rate, photocatalytic component number, and physical dimension for the photocatalytic purification system were 97.2m3/h, 3, and 2mm. Its degradation of performance testing under the optimal value was also tested to compare the differences of degradability while handling different pollution load and different pollutants. It shows that both degradation rate of formaldehyde and benzene were 100%, the complete degrading time of formaldehyde and benzene were 45 minutes and 165 minutes, the photocatalytic oxidation reaction of formaldehyde follows the first order reaction kinetics model, the benzene reaction rate of photocatalytic oxidation decreased with the increase of the benzene concentration, and the main reason lead to the decrease of the rate of benzene reaction is the competitive adsorption of intermediate.