Low Density, Ceramic Candle Filter Technology
Local, national and global emissions control regulations have reduced permissible levels of particulate and gaseous exhaust gas pollutants, making compliance expensive and requiring plant and process operators to make significant investments in air pollution control (APC) systems.
High efficiency hot gas particulate matter (PM) filtration – i.e. at temperatures in the range 250-450°C – is necessary to protect the downstream heat exchanger and auxiliary equipment from fouling and erosion in order to meet these new emissions requirements.
Of the range of barrier and non-barrier filtration techniques available – each differing in capture and rejection mechanism, pressure drop, flow capacity and collection efficiency – low density, ceramic candle filter (CF) systems are one of the most promising.
Originally developed in the late 1980s for processes requiring higher temperature capability and insensitivity to sparks (e.g. aluminium industry), today, low density CF elements are produced by vacuum-forming fibres of high-temperature insulation wool (HTIW). On the back of industry trials, the technology – which offers durability and high mechanical strength with higher collection efficiency, higher resistance to fatigue, corrosion and thermal shock – has risen in status to what many now consider to be best available technology (BAT)
Today, CF-based HGF technology is being applied to a broad range of high-dust industrial applications from glass and cement manufacturing plants to waste treatment and power generation.
Typical Industrial Applications
- Glass melting furnaces
- Cement kilns
- Metals processing
- Chemical and petrochemical industry (refineries, FCCU)
- Waste treatment / incineration
- Coal and biomass gasification, pyrolysis , etc
Heat and power generation
Hot gas CF elements are designed to remove particulate matter (PM) with filtration efficiencies exceeding 99% at temperatures between 250-1,000°C, i.e. beyond the point where bag house / fabric filter (BHF/FF) media is able to operate. In conjunction with upstream sorbent injection, capability can also be extended to include control of acid gases (HCl, HF, SO2) as well as particulate matter (PM). Similarly, the upstream injection of powdered activated carbon (PAC) also enables control of dioxin/furan (PCDD/F) and heavy metal emissions.
Performance can be further enhanced with the addition of a DeNOx SCR-coating on the CF. In conjunction with upstream injection of an ammonia-based reductant, so called catalytic candle gas filter (CCF) elements are capable of multi-pollutant control (DeDust, DeSOx and DeNOx), at hot gas temperatures up to 420°C. This “3-in-1” offers inherent CAPEX and OPEX savings and operational benefits (energy savings, extended service life, footprint reduction) associated with “one-stop-shop” system solution.
Key features of hot gas filter element technology
- High temperature operation (>250°C)
- Corrosion resistance
- Compatibility with sorbents and reductants
- Multi-pollutant control (CCF)
- Significant CAPEX and OPEX savings
- Self-supporting elements
CF and CCF hot gas filter elements are manufactured with a “T” or “V”-shaped top flange which allow the filters to hang vertically from the cell plate in a similar fashion to traditional bag/ fabric filter installation but, vitally, without the need for any support cages.
Highly efficient emissions reduction
Achieving almost 100% PM reduction, in conjunction with sorbent injection systems, CF and CCF hot gas filter technology can also achieve enable similar reductions in acid gases such as HCl, HF and SO2 – the injection of powdered activated carbon (PAC) also enabling control of dioxin/furan (PCDD/F) and heavy metal emissions.
Wide operating window
CF and CCF elements are manufactured by vacuum-forming HTIW-fibres that are temperature resistant up to 1,260oC, insensitive to sparks, offering excellent thermal shock resistance and non-flammability, thereby removing the risk of damage and fire associated with the use at high temperatures of conventional FF media. High temperature operation also increases the efficiency of certain sorbents and also enables operation above the de-Novo synthesis temperature window for PCDD/F. CF and CCF elements are also highly resistant to corrosive environments.
Lower power consumption and simpler operation
CF and CCF hot gas filter systems do not require cyclones, dilution air, spark arrestment or other ancillary equipment. For multi-pollutant control (DeDust & DeSOx and/or DeNOx) using CCF, upstream sorbent and/or reductant injection systems are necessary and upper temperatures are limited by the SCR process to 420°C.
Many installations equipped with filter elements can operate routinely for over five (5) years.