World Class Filtration Solutions
Porvair Filtration Group has a well-established portfolio of porous bronze and stainless steel materials for use in a wide range of industrial applications. Many form part of manufacturing processes for chemicals and polymers etc which are under extreme price pressure from emerging markets. Our standard porous metal products faced intense competition from low cost countries in applications that are prepared to compromise quality to achieve face-value low cost. We have therefore found that our greatest opportunities are in applications that are technically challenging and not addressable by unsophisticated competitors.
One of our core competencies is the ability to fabricate porous metal materials and structures from finely divided metal powders such as stainless steel. They are used in filtration applications that demand high strength, corrosion resistance and high temperature resistance. They have an intrinsic range of pore sizes that can be as low as 5 microns. However, there are applications such as blowback, crossflow, gasification and HEPAs that demand much smaller pore sizes, but these are not achievable using the basic technology without inducing significantly increased pressure drops in the resulting systems.
In recent years, Porvair has developed a new metal membrane technology that extends the range of filtration down to much finer, previously unobtainable ratings. This has opened up new markets for the materials where filters are chosen on technical performance rather than on low cost, hence we now have access to new industries that can justify further technology development to meet our new customer demands.
Porvair has developed a way of producing thin porous metal membranes on the very outer surfaces of their conventional porous structures. The composites have the combined benefits of strength of the underlying porous materials coupled with the finer pore rating of the outer membrane. Such composites lend themselves to applications that require physical or chemical regeneration can survive high temperature and corrosive environments like those found in the emerging coal gasification technologies. The implementation and development of this new proprietary technology is underway and to date we have achieved pore ratings down to sub micron sizes, with acceptable pressure drop characteristics, based on stainless steel and other more exotic alloys. It is hoped that in time the pore rating could be further reduced to 0.1mm to allow it's use in microfiltration applications. This technology is particularly well suited for blow-back or cross-flow applications where the filter cake is either periodically removed by temporarily reversing the flow or cleared off the surface by a cross-flow current.
Further, we have developed technologies for coating and protecting the porous metals in high temperature and extremely corrosive environments. These modified filters are allowing us to address applications in the new gasification technologies that are emerging as the future of energy generation.
A diverse range of advanced power generation systems is being developed that are based on the gasification of coal, biomass and associated fuels. Integrated Combined Cycle IGCC systems have reached the demonstration stage in Europe and USA. The filters currently employed are based on the designs developed for pressurised fluidised bed combustion applications in the 1980s using ceramic filter elements. The unreliability of the ceramic filter elements in demonstration trials and the high capital cost of these systems have hindered their application and are factors restricting the uptake of gasification power plants in general. The key limitations of the existing ceramic technology are low permeability leading to large costly installations and poor regenerability/low service life, embrittlement and fragility resulting in plant shutdowns.
Historically attempts have been made to develop metallic based filter technology to overcome the embrittlement and fragility characteristics of ceramics, these have been largely unsuccessful due to continued embrittlement, low permeability, poor regenerability and corrosion and thus have not found their way into commercial operation.
Our research and development team, developed an inert coated metallic filter element overcoming the limitations of the existing ceramic technology defined above. In addition the developments overcame the limitations of metallic filtration resulting from fuel gas driven sulphidation, erosion and fouling and down-time corrosion, resulting from deposits of particles and condensates developed during operation, leading to severe pitting damage and stress corrosion cracking.
Our research and development approach used a combination of corrosion resistant alloys in a composite structure with a highly permeable metal fibre filtration layer. The complete structure was then coated with a fused silica coating to provide additional corrosion resistance and resistance to embrittlement. The coating technology had to meet the challenge of providing uniformity and thickness to provide corrosion resistance, but maintain the pore size and therefore permeability and filtration properties of the filter media. Numerous materials and processes were evaluated. Extensive in-house laboratory test work, external analysis and trials in a major US coal gasification facility to validate the technology. The work conducted led to the application and granting of a UK patent.
Porous stainless steel filters have also been endowed with super hydrophobic coatings that can survive up to 250ºC and find uses in applications such as water resistant vents, breathers and barriers.
One of our core competencies is its depth of knowledge in the area of filtration. This has been augmented in recent years in collaboration with the University of Plymouth. We sponsored a project that studied and quantified the physical properties of Sinterflo and correlated it with Plymouths Pore-Cor computer model (AIChE Journal, Dec 2009, Vol.55, Nº 12, 3134). The project investigated ways of developing computer modelling techniques to mimic and make predictions of the way their porous materials behave in the real world. This work has resulted in significant insights to their materials that will help us improve features such as porosity and filtration properties and better match materials with customer's application requirements.