Vulcanization is a non-reversible chemical process which greatly improves the useful properties of natural rubber gum or certain synthetic polymers. The process adds sulfur atoms to the elastomer molecules at high temperature, reducing the vulnerability of the elastomer to oxidation and increasing its traction resistance. Vulcanization also generates vapors and gases characterized by complex and variable properties. Those substances need to be removed as much as possible from the exhaust fumes before discharging them in the atmosphere. Nucleation and coagulation phenomena in the exhaust stream produce mostly liquid particles whose concentration and size distribution depends on the stream temperature and concentration of chemical species present. Following the basic vulcanization process, "post-curing" processes, such as further heating or exposure to UV radiation, are also frequently used to treat molded elastomer parts. Such processes can result in release of chemicals remaining in the vulcanized elastomers, and the formation of liquid or solid aerosols. Control and monitoring strategies for these vulcanization processes are necessary to reduce the environmental impact of rubber production and to protect the health of people exposed to their emissions.
We have monitored and analyzed the emission control systems of some post-curing ovens serving a production unit manufacturing small parts containing rubber for the automotive industry. Concentrations and size distributions of particles in the exhaust streams were measured using optical particle spectrometers (size ranges from 300 nm to 10000 nm) and electric particle mobility analyzers (mobility diameter between 10 nm and 420 nm).
We measured the emissions exhausted by two different types of ovens: in-line ovens and batch ovens. In-line ovens work continuously, i.e. they continuously process parts that are post-cured. Batch ovens undergo a cyclic operation lasting about 6 hours, consisting of a temperature ramp-up, followed by a 4-hour phase at a constant 220°C, and a final cool-down.
Each emission control unit is equipped with a heat exchanger cooling the exhaust fume temperature to a value suitable for the operation of the downstream two-stage electrostatic precipitator, while implementing the removal of condensed polluting vapors. Each single pollution control unit collects the fumes exhausted by 3 to 5 ovens, treating a flow rate of almost 1000 m3/h at a duct velocity of 3.8 m/s.
Time evolution of emissions reflects the working schedule of the ovens: Particle number concentration will show...
Session: G11 - Short Oral + Poster Presentations II
Day: 14 March 2018
Time: 14:45 - 16:45 h