Catalytic oxidiser cuts costs and VOCs
Mark Moreton, Project Manager, Anguil Environmental Europe Ltd, explains how regenerative catalytic oxidisation can reduce operating costs and increase VOC destruction efficiency.
Anguil dual-bed regenerative catalytic oxidiser
The Anguil RCO combines the best features of thermal and catalytic oxidation: the highly efficient energy recovery of RTO systems and the low oxidation temperature of catalytic oxidation. This makes it a cost-effective solution for VOC emission abatement in a variety of industries including printing, coating, electronic component manufacturing, wood processing, spray painting and many others.
The Anguil RCO normally operates at about 426oC which is roughly half the operating temperature of an RTO unit. The result is a significant saving in the support energy to run the system, commonly about 50% - 70% less natural gas to oxidise the VOCs.
Electrical power consumption is less because the oxidation temperature is much lower. This reduces the air volume flow rate through the system and as a result, the cost of operating the main system fan can be reduced by 15% - 40% depending upon the design of the equipment.
The Anguil RCO utilises a novel 'reverse flow' design that maximises the use of the exothermic reaction heat energy in a system of alternate inlet and outlet chambers. Initially, the process exhaust stream enters the oxidiser through an inlet manifold and is allowed to enter the first regenerative chamber by the position of air flow control valves. The stream is directed up through a bed of hot ceramic heat-sink thermal transfer material, where it is heated, before passing through the upper layer of catalyst for VOC oxidation.
The stream passes back through an exit layer of catalyst and flows through the next regenerative chamber where the heat is absorbed by the cooler bed of heat-sink material. After the inlet chamber is heated and cooled, and the heat-sink material in the outlet chamber is heated, the airflow control valves reverse so the chambers are functioning alternately in inlet and outlet capacities. The air is then drawn through the outlet manifold and discharged to the atmosphere.
Converting from RTO to RCO
Because RCOs and RTOs are both regenerative VOC abatement systems, they are in many ways structurally similar. For this reason, conversion from RTO to RCO technology is often possible and, depending on the operating and energy consumption conditions of the system, could be highly beneficial.
If space permits, one alternative is to put a layer of monolith catalyst on top of the existing beds in the RTO's regenerative chamber. This will reduce the operating temperature required to oxidise the VOCs to roughly 426oC.
Another method is to remove approximately 0.25m of ceramic heat-sink material and this will be replaced by the same volume of catalysed saddles. The optimum volume of catalyst is determined by computer modelling.
In both these instances, the RTO system will have to be removed from operation but this should not be for more than two days.
There are several important issues that need to be considered before conversion to an RCO is attempted. Each VOC stream needs to be examined to ensure there are no catalyst poisons such as silicones, phosphorus and heavy metals that might deactivate the catalyst. In addition, the catalyst's performance could be affected by masking and/or fouling by particulates entrained in the exhaust stream. However, the catalyst can be recharged relatively easily, first by washing with a chemical solution, then by reheating to 500oC for one to two hours. A new catalyst charge will not normally be needed until after between 5 to 10 years of operation.
RCO provides a number of benefits when compared to RTO including:
less natural gas (up to 70%) is required for fuelling the VOC abatement system due to the lower operating temperature
reduced fan power consumption (up to 70%) is achieved because of the lower air volume flow rate and pressure drop through the system (lower oxidation temperature)
increased life of the system's mechanical structure due to the lower operating temperature and longer cycle switching times
reduced carbon monoxide and nitrogen oxide emissions due to the efficient catalytic oxidation process.