Incinerators for treatment of gas with low VOC concentration

Paul Boughton

Tougher regulations and enforcement are encouraging chemical companies to turn to innovative solutions to deal with their VOC emissions. Sean Ottewell reports.

In an effort to meet the ever tightening EU regulations and standards for minimising the release of VOCs, Finnish company Formia has launched a new product series for treating them.

Known as Smart VOC LV, the new products are based on an innovative design, which combines the best robust catalytic technology with efficient heat exchangers for the highly effective treatment of gases with low VOC concentration.

The EU is planning to introduce new, tougher standards to further reduce hydrocarbon emissions and this will also impact less polluting lean VOC sources.

Smart VOC LV is suitable for low VOC emissions of up to 0.5g/Nm3, typical in the paint, printing, pharmaceutical and chemical industries. While Smart VOC LV is particularly suitable for low emissions it can also handle the occasional higher concentrations that often occur during processes.

Incineration of low concentration VOCs usually requires input of additional support energy to maintain incineration and support energy is the major cost item in lean VOC incineration.

The Formia Smart VOC LV uses active carbon or zeolites to adsorb the VOC gas, before burning it in a precious metal catalyst. This enables the processing of low VOC concentrations without the need for supporting energy so offering very low operational cost. Formia's solution needs supporting energy only to start the incineration process.

Other innovative and value-adding features are its small size and low maintenance costs. The Smart VOC LV has been designed to fit into a freight container for easy transportation and rapid installation. It only requires connections to a gas pipeline, compressed air and electricity for operation. Maximum processing capacity in a 20foot standard container installation is 30000m3/h.

The unit's own computer control system allows operating conditions to be set and changed with ease. In addition, it offers the facility for alarms and programming instructions to be transmitted to PCs or mobile phones. Formia Service offers maintenance services of Smart VOC LV systems everywhere in the EU.

The Smart VOC LV's design is very robust and simple, says the company. VOC gases are fed in to the system through a particle filter, which protects the adsorbing materials, either activated carbon or zeolites. In the next phase of the process, these adsorb VOC molecules by surface forces and diffusion. The adsorbent is placed in a rotating cylinder, which is divided into six sectors, four of which are used to adsorb VOCs, one is in regeneration phase and one is in cooling. When one sector emissions reach the limit concentration, the wheel rotates and desorption of the fully loaded sector begins. The desorbing sector emits the concentrated VOCs into a catalytic converter, which burns the VOCs. The catalytic converter using company's proprietary technology is based on a precious metal catalyst with a high geometric and specific surface area. As such, the system is very tolerant to catalyst poisons such as phosphorus, sulphur, calcium and zinc - which adds to the durability of the machine. After this stage the emissions are purified to EU acceptable levels and led to an exhaust pipe.

Another proprietary design is the Smart VOC LV's heat exchanger. It gathers heat from the catalytic process (temperature is 300-350°C), which it transfers to heat the incoming VOC gas. Supporting energy is thus only needed to begin the regeneration cycle.

Regenerative thermal oxidation too

One of the world's largest single stream LDPE production plants is to use a regenerative thermal oxidation system (RTO) supplied by AirProtekt, the Cambridge based air pollution specialist, to remove VOCs in the process gases from the plant's dryer system and six storage silos.

AirProtekt is providing a complete VOC emission control solution for Sabic UK Petrochemicals' 400000t/y LDPE plant at the Wilton site on Teesside in the UK by supplying a five-bed ROXITHERMRTK70RTO systems from Lufttechnik Bayreuth (LTB) of Germany.

AirProtekt is the sole UK distributor of RTOs for LTB. The latter has in-depth experience of European air pollution regulations and has installed more than 200RTO systems across Europe.

The ROXITHERMRTK70 system is being tailored to comply with the LDPE processor's specific emission regulation requirements. The new RTO system is designed to combine very high thermal efficiencies (up to 97 per cent) and while minimising operating costs. The system is capable of treating high volumes of exhaust gases and is able to handle exhaust air flowrates up to 73500Nm3/h at 50°C.

ROXITHERMRTK70's high temperature operation is capable of achieving more than 99 per cent VOC destruction efficiency, says the company. A purge system is featured to prevent emissions of untreated VOCs during the valve operating cycle.

AirProtekt's total package concept embraces process assessment, project design, supply of the air pollution equipment, installation and commissioning. The air pollution specialist also provides a complete after sales service.

Trevor Lawton, AirProtekt's managing director, said: "This application highlights our engineering expertise which enabled us to offer the plant's main contractor, Simon Carves, a competitively priced project solution with a design flexibility that enabled a large RTO system to be efficiently packaged to maximise the potential of the limited available space."

Another new RTO customer is SGL Carbon Fibers in the North of Scotland. This company has also opted for a selective catalytic reduction (SCR) system to remove oxides of nitrogen and other gaseous contaminants, such as hydrogen cyanide (HCN).

SGL Carbon Fibers is a subsidiary of German based SGL Group and the Scottish manufacturing site produces carbon fibre for use in a variety of engineering applications including items such as wind power turbine blades, computer hard disks, aircraft and car brakes which are exported to 27 countries.

As part of a major multi million pound investment SGL Carbon Fibers has upgraded the production capacity of its Scottish carbon fibre manufacturing facility with the addition of two new production lines.

To assist in handling the additional emissions, including fugitives from the upgraded facility, AirProtekt was selected to supply a third RTO system at the site in combination with a new SCR system. The principal purpose of the new combined system is to treat and remove pollutants such as oxides of nitrogen and hydrogen cyanide.

The SGL carbon fibre manufacturing plant is one of a kind in the UK that uses polyacrylonitrile (PAN) as a raw material in the form of long lengths (tows) of carbon fibre.

The tows are heated by passing through a series of electric or gas ovens and furnaces.

The first stage of heating in ovens to 250°C in the presence of air produces oxidised polyacrylonitrile or Panox, which is sold as an oxidised fibre product.

The Panox can be further heated within low temperature and high temperature furnaces to 1500°C, in the absence of air to produce carbon fibres for use in various engineering applications.

The chemical reactions during the heating process generate exhaust gases of oxides of nitrogen, hydrogen cyanide, ammonia, carbon dioxide, carbon monoxide and volatile organic compounds (VOCs).

AirProtekt offered the 4500t/y carbon fibre manufacturing facility a complete solution.