Zeolite concentration rotor
The adsorption mechanism of zeolite
Zeolite (also known as molecular sieve) is a silica-aluminate porous silicate or silica-aluminate crystal, which is a system of pores and cavities of molecular size (usually 0.3~2nm) formed by silica-oxygen tetrahedra or aluminum-oxygen tetrahedra connected by oxygen bridge bonds, and has the ability to sieve fluid molecules of different sizes due to the different sizes and shapes of adsorbed molecules.
The adsorption of substances by molecular sieves originates from physical adsorption, and its crystal pores have strong polarity and Coulomb field inside, showing strong adsorption ability for polar molecules (such as water) and unsaturated molecules.
Molecular sieve has a uniform microporous structure, its pore diameter is uniform, these pores can adsorb molecules smaller than its diameter to the interior of the pore cavity, and has a preferential adsorption capacity for polar molecules and unsaturated molecules, so it can separate molecules with different degrees of polarity, different degrees of saturation, different molecular sizes and different boiling points, that is, it has a "sieving "The role of molecules, so called molecular sieve.
Zeolite rotor (VOC concentrator) working principle
The purpose of the zeolite rotor is to concentrate VOC gas from a large air volume to a small air volume. In the small air volume, the VOC gas will be treated more efficiently by the incinerator (TAR/RTO).
Adsorption means that fluid molecules are enriched on a "reactive" substance called an "adsorption medium". Similar to a sponge, the adsorption medium absorbs the VOCs and then "squeezes" them out through high temperature desorption.
The rotor of the VOC concentrator is composed of a honeycomb ceramic fiber sheet impregnated with a water-resistant zeolite (molecular sieve) as the adsorption medium. The concentrator system is a continuous process in which the rotor is always rotating. It is therefore divided into three zones: treatment zone, desorption zone and cooling zone, each separated from the other.
Exhaust gases containing VOCs are collected as they pass through the treatment zone of the rotating rotor. Once the gases have passed the rotor, the VOCs are adsorbed by the adsorption media on the rotor. The purified gas is released into the atmosphere.
In the desorption zone, the VOC attached to the rotor is desorbed from the opposite direction by a continuous high temperature and low flow rate of desorption gas. The highly concentrated VOC gas is removed from the rotor and sent to the thermal oxidation system for final VOC purification.
The hot desorption zone in the rotor is then transferred to the cooling zone where the cooling gas cools it down. a portion of the VOC exhaust gas passes through this cooling zone and goes to the desorption heat exchanger for heat transfer.
In the heat exchanger, the cooling gas is heat exchanged to a high temperature desorption gas by the high temperature purge gas from the high temperature cracking equipment such as TAR/RTO.
Compared to other adsorbent media, zeolite has many advantages: low flammability, long service life due to high desorption temperatures, reduced accumulation of high boiling compounds, and high chemical resistance.
Exhaust gas treatment systems
The purpose of the TAR unit is to oxidize the VOC desorbed gas coming out of the KPR concentrator. Before entering the TAR combustion chamber, the exhaust gas is preheated by a heat exchanger inside the TAR. In the combustion chamber, the burner provides heat to ensure the heat needed for effective VOC oxidation.
VOC oxidation is achieved by heating the gas stream through a natural gas burner to 760°C and maintaining this temperature for at least 1 second to convert the organic matter to harmless CO2 and H2O for emission to the atmosphere.
After passing through the combustion chamber, the purified gas passes through a heat exchanger duct to transfer some of its heat to the incoming exhaust gas. The heat exchanger is at the TAR outlet. The hot purge gas from the combustion chamber passes through the heat exchanger to heat the "cold" desorption gas, which then goes to the concentrator for desorption.