Process Combustion - Thermal and Catalytic Oxidisers

As well as cryogenic vaporisers, fired process heaters, and fire-fighter training systems, Process Combustion Limited (PCL) designs and builds thermal oxidisers and catalytic oxidisers, and can deliver Regenerative Thermal Oxidisers (RTO) to destroy waste gases, waste liquids, and odours.

Clients include leading international chemical, oil and gas operators, multinational engineering companies, government and defence organisations, and manufacturing companies worldwide. Where called for, our plants are designed to meet the requirements of the Solvent Emissions Directive (SED) and the Waste Incineration Directive (WID).

THERMAL OXIDISERS FOR GASES AND LIQUIDS

In some cases, waste gases or liquids may have a high enough heating value to enable them to be burnt as a fuel from which heat can be recovered. If the composition of the wastes is variable, the control system must allow for this.

At a printing ink manufacturing site, a mixture of waste solvents and other organic liquids is used as a fuel to destroy the formaldehyde, phenol and other contaminants in a stream of 12t per day of waste water at temperatures up to 1,200°C.

When a waste material is used as a fuel, the combustion system must now comply with the Waste Incineration Directive and becomes, as a result, a thermal oxidiser. PCL can design and supply the combustion and downstream heat recovery systems, and any further flue gas treatment plant needed.

RECUPERATIVE THERMAL OXIDISERS

If a waste gas stream consists of air containing only small amounts of a combustible pollutant, a considerable heat input may be needed to reach the temperature required in the oxidation chamber.

The auxiliary fuel flow needed for the process can be greatly reduced if the hot, purified flue gas leaving the chamber is used to preheat the cooler, untreated gas entering it.

At a resin impregnation plant in the UK, six gas-fired PCL thermal oxidisers eliminate emissions from curing ovens. On each oxidiser, a first heat exchanger preheats the incoming waste gas to minimise fuel used in the oxidiser, and a second exchanger supplies all of the heat for the drying oven. A third recovery unit in the flue duct recovers heat for a further process step via a glycol / water loop.

DOWNSTREAM OXIDISER HEAT RECOVERY

In some situations, most or all of the heat generated in a thermal oxidiser can be utilised in the factory. This is especially helpful where a cold waste gas stream is likely to foul a recuperative heat exchanger.

PCL have, for example, supplied two 7MW thermal oxidisers to a large food manufacturer where all of the clean, hot flue gas is used in waste heat boilers to generate much of the high pressure steam used in the factory. One of our successes saw the heat from a multi-stream waste gas oxidiser at a chemical plant in Belgium recovered into the large thermal fluid system on site.

CATALYTIC OXIDISERS

Catalysts provide another method for reducing fuel consumption by enabling the oxidation reactions to take place at a lower temperature. Catalytic oxidation systems can incorporate recuperators and downstream heat recovery schemes to further minimise fuel consumption. Catalytic systems are particularly useful for intermittent operation, and can be applied where the waste gas stream is free of smoke, dust, tarry materials, and catalyst poisons.

REGENERATIVE THERMAL OXIDISERS

With its ability to transfer 97.5% or more of the heat in the hot purified gas stream back into the incoming raw gas, the RTO is able to treat waste gas using very little fuel, even when the heat contribution of the contaminants – as in the case of odours - is negligible. Where the heat contribution of the contaminants is significant, the RTO can operate without fuel, and may even make some of the heating value of the VOCs available for recovery. RTOs can treat large volumes of waste gas, and are particularly efficient when used continuously.