We found – 8 articles for emission control

Emission Control

Emission Control

Refractory Ceramic Fiber Custom Shape

Emission control is becoming more important everyday. In order to satisfy new regulations, Unifrax Engineered Thermal Components (UETC) has worked with many companies to design insulation solutions for emission control systems.

Applications include:

  • Thermal Oxidizers
  • Catalytic Enclosures
  • Diesel Particulate Filter (DPF) Regenerators
  • Exhaust Systems
  • Secondary Combustion Chambers

Manufacturing capabilities

UETC materials can be formed as boards, sleeves, combustion chambers and any custom shape. In addition, UETC has a wide range of machining capabilities for added details and tight tolerances. Insulation Boards may be surface treated to provide additional erosion or chemical resistance for use in hostile environments. A majority of our materials can have hardware molded or installed into them to provide easy installation.

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Fireplace Equipped with Ceramic Fiber Insulation

Ceramic Fiber Fireplace Logs

Unifrax Engineered Thermal Components’ sister company, Specialty Ceramics, manufactured the first ceramic fiber fireplace log almost 20 years ago. Since then we have been providing hearth products in a multitude of shapes sizes and designs. With a full staff dedicated to providing high end hearth designs, we offer custom designed logs, twigs, coals, rocks and decorative panels. In addition we manufacture emission control products for catalytic and non-catalytic secondary combustion chambers.

Applications include:

  • Logs, Twigs and Log Sets
  • Coals
  • Rocks
  • Decorative Panels
  • Baffle Boards
  • Secondary Combustion chambers

    Hearth Insulation Assembly

    Ceramic Fiber Panels, Boards, Chambers

  • Burner Tops

Manufacturing capabilities

UETC materials can be formed as boards, sleeves, combustion chambers and any custom shape. In addition, UETC has a wide range of machining capabilities for added details and tight tolerances. Insulation Boards may be surface treated to provide additional erosion or chemical resistance for use in hostile environments. A majority of our materials can have hardware molded or installed into them to provide easy installation.

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Ceramic Fiber Products

Unifrax Engineered Thermal Components (UETC) offers a wide range of insulation products and ceramic components in a vast assortment of materials. Our expertise in materials and engineering gives us the advantage to not only provide our customers with thermal insulation products, but insulation solutions.

With a vision toward the future, UETC continues to expand the use of high temperature insulation and refractory products to satisfy new applications in these industries: Appliance, HVAC, hearth, metals, fuel cell, solar energy, fire protection, petrochemicals, industrial process furnaces, food industry, solid fuel appliances and alternative energy. With technology surging ahead, UETC will continue to develop products for any industry where heat needs to be directed or contained. All development, production, finishing and shipping of products is done under stringent quality control procedures according to ISO 9001:2008 standards.

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Product Characteristics

  • Suitable for Temperatures up to 3000ºF
  • Exceptionally Resistant to Thermal Shock
  • Durable and Reduces noise
  • Low Thermal Conductivity
  • Lightweight and Energy Efficient
  • Resistant to Corrosion, Water and Oil Damage
  • Completely Free of Asbestos
  • Reflective
  • Fire Proof
  • Reaches Steady State Quickly
  • Directs and Contains Heat

230 West California Ave.    |    Sebring, OH 44672    |    Tel: 330-938-2101    |    Fax: 330-938-2574    |    Email: bthomas@rsifibre.com

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Hot Gas Filtration Gassification


Unifrax have been supplying PUREFRAX® filter elements in to successful hot gas filtration applications for 20 years. The below article describes a recent case study and outlines how we have built on the success of these products to progress in to new application fields, as well as develop 3 metre length PUREFRAX® filters and the associated extra benefits such a candle can provide.

In 2013, emissions monitoring was undertaken on a gasification system processing Municipal Solid Waste (MSW). Gasification is a well-established process dating from the early 1800s when it was first used to produce town gas from Coal. The gasification system here is integrated with a high temperature air filter, using 1.25 metre long (60mm OD) PUREFRAX® filter candles with a Sodium Bicarbonate (NaHCO3) dry sorbent injection system. The gasification of the MSW produces a combustible synthetic gas (‘syngas’ – typically containing a mix of CO, CO2, H2, CH4 & H2O) which is subsequently combusted in a combustion chamber. The hot exhaust gases from the process are extracted via an induced draft (ID) fan. These are cooled from ≈900oC to >400oC at the filter inlet. By maintaining the temperature at above 400oC, the de-novo synthesis of Dioxins/Furans is prevented. The de-novo synthesis mechanism is the main one by which Dioxins form in the flue gases and involves the formation of Dioxins from organic and inorganic compounds (known as ‘precursors’) at temperatures between 200-400oC (known as the de-novo temperature ‘window’). The filter operates at temperatures above 400oC and by removing these precursors (such as Carbon in fly ash and metal chlorides) as particulate at such temperatures, the main mechanism by which Dioxins are formed is prevented. Dioxins and Furans are poly-chlorinated compounds and it has been shown that major reduction of Dioxin/Furan formation can be brought about with upstream sorbent injection for Hydrogen Chloride (HCl). The filter incorporates Sodium Bicarbonate injection in order to neutralise acid gases such as HCl, HF & SO2. Figure 1 provides a diagrammatic representation of the process.


Figure 1: Process Diagram

As can be seen from figure 1, the combustion gases are cooled through simple radiant heat loss through a suitable length of ducting to achieve the required temperature loss from ≈900oC to >400oC at the filter inlet. However, at other facilities operating the same gasification and Unifrax PUREFRAX® filtration technology principle, this temperature loss is achieved by passing the gases through a waste heat boiler in order to generate steam which is fed to a steam turbine in order to generate electricity or the steam is passed through a heat exchanger to heat water which can then be pumped to any available district heating networks. Typically, a tapping on the Steam Turbine Generator is made in order to provide steam at a suitable pressure for such a purpose – these systems known as CHP (Combined Heat and Power) systems. The interest and development of these systems in the UK is increasing substantially, particularly as gasification technologies can receive government support under the Renewables Obligation Directive through the receipt of Renewable Obligation Credits.

In order to maximise the energy recovery in such systems, the combustion gases are cooled to lower temperatures (≈200oC) and as such will have passed through the de-novo temperature ‘window’ as described above. As such, Powdered Activated Carbon (PAC) is added along with the Sodium Bicarbonate (SB) in order to adsorb Dioxins/Furans. By injecting directly in to the filter, the sorbents create a fully reactive coating on the surface of the filter candles thus maximising contact time between the acid gases and the sorbent particles due to the necessity of the incoming gases to pass through the filter cake that contains the sorbent reagent. The injection of the sorbent as a ‘secondary dust’ also aids this filtration as it enables the particulate to agglomerate. This allows sub-micron particulate to be more easily filtered. Unifrax ceramic filters are almost 100% efficient and allow particulate down to 0.1 micron dia. to be filtered.

Typically, through waste composition analysis i.e. through knowledge of waste Chlorine%, Fluorine% and Sulphur% – estimates of the HCl, HF and SO2 concentrations can be calculated and when coupled with the required Emission Limit Values (ELVs) the required Sodium Bicarbonate additions can be determined. This is further enhanced through pre-abatement flue gas sampling for HCl, HF & SO2. Addition rates are based on the following reactions given below (and a stoichiometric of 1 – 1.5) –

NaHCO3 + HCl -> NaCl + H2O + CO2

2NaHCO3 + SO2 + 1/2 O2 -> Na2SO4 + 2CO2 + H2O

NaHCO3 + HF —–> NaF + H2O + CO2

Furthermore, on many systems – the addition rates are linked to continuous emission monitors (CEMs) that measure the acid gas concentrations and control the addition rates accordingly – thus maximizing efficient use of the sorbent (and thus enabling a financial saving benefit) and optimizing the ability of the system to meet the required ELVs. For example, the system mentioned here has the sorbent injection system coupled controlled to an HCl analyser located in the stack.

Recent emissions testing from the above facility showed that the ELVs for ALL pollutants regulated under the Industrial Emissions Directive (Chapter IV and Annex VI) were being met and therefore demonstrated the efficiency of the filtration system employing Unifrax filtration technology.

Unifrax are now involved in the development of filtration systems incorporating the PUREFRAX® filter candles to filter the syngas rather than the combustion gases as is the case above. The syngas can be cleaned using wet/chemical scrubbers in order to remove particulate, HCl, HF, H2S and NH3. However, waste water treatment from the scrubbers can be very expensive – especially with regards to the removal of metals. By installing a PUREFRAX® filter prior to the wet scrubber, particulate (and thus metals in particulate form) can be removed beforehand thus reducing this expense. Acid gases such as HCl and HF can also be removed using a dry sorbent system as described above – also reducing the expense of having to remove these at the wet scrubber which can now be used to scrub H2S and NH3. By producing a clean syngas, the syngas can be fed to a gas engine or a gas turbine thus increasing electricity production efficiency significantly when compared to the waste heat boiler utilizing combustion gases and the steam turbine route as described previously. These systems are being developed, particularly with the new 3 metre candles that Unifrax have developed in mind.

Space constraints are often a real concern for such developments, particularly because of the size and amount of equipment involved. Therefore, filtration systems employing 3 metre PUREFRAX® candles can significantly reduce the required footprint when compared to systems employing the shorter/smaller diameter candles. Ensuring the equivalent surface area also enables the cleaning systems to be much simplified e.g. reducing the number of reverse jet ‘blast’ valves etc.

Unifrax have been at the forefront of hot gas filtration for 20+ years and it is evident that our success has enabled us to help our customers achieve their objectives – not just in terms of being able to easily meet their environmental responsibilities but also in terms of providing them with equipment capable of allowing them to develop their own technologies to achieve greater financial reward. For more information regarding Unifrax PUREFRAX® filter candles contact your local Unifrax sales office

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Hot Gas Filtration Emmisions


The following are emission levels obtained from air pollution control systems using our PUREFRAX® filter elements. In order to show the levels of air pollution abatement possible, they have been compared to the extremely stringent emission limits specified within the Waste Incineration Directive (WID) – Directive 2000/76/EC.

Example 1: Taken during emissions testing at a gasification facility processing Municipal Solid Waste (MSW). This system utilizes Sodium Bicarbonate sorbent injection.

Pollutant WID limit Emission Level Achieved – % of WID limit
Particulates 10 mg/m3 9.1%
TOC 10 mg/m3 1.6%
HCl 10 mg/m3 12.2%
CO 50 mg/m3 16.0
SO2 50 mg/m3 <1%
NOx 200 mg/m3 38.0%
HF 1 mg/m3 13.1%
Cd and Tl 0.05 mg/m3 3.2%
Hg 0.05 mg/m3 12.2%
Sb, As, Pb, Cr, Co, Cu, Mn, Ni, V 0.5 mg/m3 8.2%


Example 2: Taken during emissions testing at an Aluminum De-coating facility processing heavily contaminated scrap (up to 40% PVC by weight). The system uses Sodium Bicarbonate sorbent injection and operates above the de-Novo synthesis temperature window to prevent the reformation of Dioxins/Furans.

Pollutant WID limit Emission Level Achieved – % of WID limit
Particulates 10 mg/m3 3%
SO2 50 mg/m3 16%
NOx 200 mg/m3 9%
HCl 10 mg/m3 30%
Dioxins/Furans 0.1 ng/m3 14%
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Hot Gas Filtration Benefits


In 2010, Unifrax acquired Brightcross Insulation Ltd and with the acquisition came the sales history and experience of 15 years of manufacturing successful PUREFRAX Hot Gas Filters.

Hundreds of companies have benefitted from and continue to benefit from using these ceramic filter elements. The key benefits include:


Unlike traditional bag/ fabric filters which require cages. PUREFRAX filters are manufactured with a top flange which sits above the cell plate enabling the filters to hang vertically in application.


Elements themselves allow virtually 100% reduction in particulate emissions and through the use of sorbent injection systems enable the same reductions in acid gases such as HCl, HF and SO2 with Powdered Activated Carbon (PAC) injection providing control of Dioxin/Furan and Heavy Metal emissions.


Manufactured from base fibers that are temperature resistance up to 1,260oC, have insensitivity to sparks, excellent thermal shock resistance and non-flammability, PUREFRAX removes the risk of damage and fire associated with the use of conventional fabric filter media at high temperatures.

High temperature operation improves the efficiency of certain sorbents and also enables operation above the de-Novo synthesis temperature window for Dioxins/Furans.

Elements are also highly resistant to corrosive environments.


Excellent dimensional accuracy through full machining of candles and controlled uniform permeability with minimal pressure drop allows both highly efficient filtration efficiency and optimal reverse jet clean-down performance.


Installations with element lives of over 5 years are regularly achieved.


Unifrax is the only company offering Hot Gas Filters that produce both the raw material (Ceramic and LBP Fibers) and finished Hot Gas Filter meaning we have absolute control over production quality and parameters. This can allow us to develop and adapt our filters for a variety of challenging applications


Final filter systems do not require cyclones, dilution air, spark arrestment or other ancillary equipment.


Advice and support is available in all matters relating to air pollution control equipment design, specification and commissioning as well as environmental legislation.

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Purefrax® Hot Gas Filtration

Unifrax PUREFRAX hot gas filter candles

Global regulations have made achieving gas emissions compliance costly and requiring companies to make substantial investments in pollution control technologies. Unifrax offers unique filtration media technology that addresses the problems related to industrial emissions and high temperature filtration. The Unifrax PUREFRAX hot gas filter candles are designed to remove particulate matter with efficiencies exceeding 99%.

PUREFRAX filter elements were developed and commercialized in 1996, for the Aluminum industry to solve an issue of fires happening within the baghouse filter. Sparks were being carried over in the gas stream and setting fire to the fabric filters. PUREFRAX filters were developed using our high temperature fibers and are designed to work in the same way as a traditional fabric filter but with much higher temperature capability and insensitivity to sparks. Since 1996 they have been used in a variety of applications from incineration to product recovery to power generation.

In addition Unifrax has entered into a marketing alliance with Haldor Topsoe to provide the industry with catalytic filter candles. Haldor Topsoe’s Topfrax® Catalytic hot gas filters provide particulate filtration and are engineered to remove NOx, VOC, CO and dioxins that are generated in industrial processes.

Key features of both the Purefrax and Topfrax® hot gas filters include: a high temperature use limit, compatibility with sorbents, non-combustibility, and corrosion resistance.

Designing pollution control equipment around Purefrax and Topfrax® hot gas filtration media saves capital and operation dollars and reduces the footprint of the installation while providing extended service life and energy savings.


  • Industrial Hot Gas Filtration
  • Dedusting of melting furnaces and fluidized bed processes
  • Al2O3– production (dedusting of rotary kiln)
  • Power station processes: gasification of coal, gasification of waste
  • Gasification of bio mass e.g. wood, sewage sludge etc.
  • Cement industry
  • Waste incineration plants
  • Calcium carbide production (dedusting of shaft furnace)
  • Production of nano powders e.g. color pigments
  • Refineries, FCCU: e.g. off-gases from catalytic crackers
  • Thermal processing of foundry sand


  • Purefrax hot gas filter candles
  • Topfrax catalytic hot gas filter candles
  • Additional Product Forms for High Temperature Filtration
  • Automotive Airbag Porosity Controlled Media
  • Provide efficient filtration of effluent gas by removing particulate matter through condensation, adhesion and mechanical entrapment (2000F)

Typical Applications:

  • Automotive airbag
  • Oxygen generators
  • PH Blanket for Liquid Filtration
  • The product chemistry and wet laid structure of Unifrax PH blanket provides superior service life in the filtration of acids in the platinum recovery process


In 2010, Unifrax acquired Brightcross Insulation Ltd and with the...

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The following are emission levels achieved from air pollution control...

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Unifrax have been supplying PUREFRAX® filter elements in to successful...

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