RTO Process Heat Recovery

The Regenerative Thermal Oxidiser (RTO) is an extremely efficient thermal oxidiser that uses a number of ceramic beds, either loose saddles or honeycomb blocks, to absorb heat from its exhaust gases. It then uses this captured heat to preheat the incoming process air stream and destroy air pollutants contained in this air stream, at temperatures ranging up to 1000oC.

The primary advantage of this technique is very high VOC destruction efficiencies, often in excess of 99%, and a high thermal efficiency providing low, or near zero, gas consumption. It is used throughout industry to destroy air toxins, odours, VOC’s and hazardous air pollutants discharged from industrial processes.

The ceramic beds provide primary heat recovery of up to 95% thermal efficiency enabling auto-thermal or self-sustaining operation (with no additional heating from a gas burner) of the oxidiser with very low VOC concentrations of approximately 2 g/m3, ie. less than 5% of the Lower Explosive Limit (LEL).

On the occasions when the inlet VOC concentration exceeds approximately 2 g/m3 then the energy present in the VOC’s, which is released during the high temperature oxidation process and destruction of the VOC, will exceed the energy losses in the system. At even higher concentrations the combustion temperature within the RTO will rise and this excess energy has the potential then to be recovered.

This excess energy would be in the form of air at very high temperatures of up to 1000oC and will require the use of specialist heat exchangers, designed and constructed to withstand these temperatures, and active control systems. This energy can be captured in various fluids including thermal oil, water and steam in order to allow the recovered waste energy to be re-utilised elsewhere in the process. A medium sized RTO could have in excess of 500kW of excess energy available for re-use.

Operational has the experience and engineering expertise to evaluate the quantity of energy available and determine the best approach for re-use of the energy elsewhere in the process.

Following this, our process & project teams will take full ‘turn-key’ responsibility for the design, manufacture and installation of the heat recovery system including heat exchangers, ductwork systems, fans, pipework, pumps, expansion tanks and necessary controls and instrumentation.

The following selection of case studies illustrate the increased environmental and thermal efficiencies which can often be achieved with return on investments of less than 2 years:-

Coated Alloy Automotive Products – RTO Process Heat Recovery

Our client produces coated products for the automotive industry and uses ovens to dry coat these component parts. Their existing RTO was installed to remove VOC’s from the process exhaust air stream and was using excessive quantities of gas as support fuel and increasingly expensive to operate.

Operational carried out a comprehensive survey to identify the problems and were able to propose an oven heat recovery solution. The RTO was extensively modified and the existing ceramic media was replaced with a high surface area, high efficiency porcelain media.

The RTO capacity was increased from 46,000Nm3/h to 55,000Nm3/h and thermal efficiency to 99%. Energy cost savings of €125,000 per annum were made and an overall return on investment of less than 12 months achieved.

Security Tapes and Threads – RTO Process Heat Recovery

A coating process producing security tapes and threads uses an RTO for environmental abatement.

Operational carried out a detailed survey of the oxidiser and the requirement for space heating in a storage and production area. It was found that 300kWh of waste heat from the RTO exhaust was available for re-use as space heating.

We installed a fully welded, stainless steel, counter-flow air to air heat exchanger designed to recover over 300kWh of energy. A sophisticated temperature control and air mixing system was utilised to achieve the maximum use of the recovered energy and replacement of the existing gas-fired space-heating system.

Total energy savings of £36,000 per annum were achieved with a payback period of 1.6 years.

Decor Coating of Thermoplastic Films – RTO Process Heat Recovery

One of our clients manufactures décor printed thermoplastic films for use with furniture, window frame laminates and general building products. Their process involved evaporating VOC which requires an abatement system to meet legislation. The clients’ existing abatement system was based on RTO technology, meaning, operating costs were proving to be very expensive. They requested Operational to reduce energy costs and improve process control.

Operational replaced the RTO existing ceramic saddles with a 5 layer honeycomb ceramic design, thereby, significantly reducing the pressure drop across the ceramic beds and increasing thermal efficiency from 87% to 97%. The RTO internal support structure was replaced and modified with incorporation of bed temperature monitoring and control system.

Total gas and electricity savings of €75,000 per annum were made and an overall return on investment of 12 months achieved.

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