Sulfatreat now well established for odour control
SulfaTreat systems have been providing exceptionally cost effective H2S removal from air and gas streams for many years. The Water Industry has proved to be an ideal market place by providing high challenges and requiring trouble free operation. H&H would like Odour Control Contractors to offer SulfaTreat media in their hardware so that they can benefit from the attractive performance and commercial advantages.Properties
SulfaTreat is a patented process for H2S removal. It uses proprietary chemistry to selectively remove hydrogen sulphide and light mercaptans from either air or gas streams. It works best when the feed stream is water saturated.
SulfaTreat is a dry granular material. It is non toxic, non hazardous, non pyrophoric and environmentally safe in both its unreacted and ready for disposal condition. Its active ingredient is a unique combination of iron oxides which react as follows:-
The ingredients of SulfaTreat are heavy compared to activated carbon or activated alumina giving an overall specific gravity at 1.0. The active chemicals are securely bonded to the base material which is a very stable and impervious clay. The adhesives are fully water resistant which enables SulfaTreat media to operate in saturated conditions without the risk of the active chemicals being washed out. The active ingredients are stable under all ambient conditions thus ensuring an indefinite shelf life without reduction in performance and activity levels.
Reaction times are relatively slow in comparison to conventional carbon or alumina systems. This has the benefit for many odour control applications in that breakthrough of odours is not rapid but progressive thus giving early warning of the need for change out. A simple life analysis to determine media replacement dates is possible and this service is offered by Higgins & Hewins.
SulfaTreat will remove all hydrogen sulphide and light mercaptans (methyl and ethyl). 50% of the light mercaptans are however converted to dimethyl disulphide. That is 2ppm of light mercaptans will result in 1ppm of DMDS. For odour control applications therefore final polishing is required to remove the higher mercaptans, the dimethyl disulphide and any other compounds present. The take up by weight for hydrogen sulphide at low concentrations is broadly similar to impregnated carbons at 20%. Due to the high density of SulfaTreat however the hydrogen sulphide removal capacity by volume is quite exceptional and significantly exceeds that for all other conventional forms of dry scrubbing. This outstanding feature of SulfaTreat systems is clearly demonstrated below:-
|Media||H2S Removal Capacity, by wt||Density kg/m³||H2S Removal Capacity by volume, kg/m³||Typical Price/per kg of media||Cost for H2S Removal £/kg H2S|
|Caustic Impregnated Carbon||20%||550||110||£1.35||£6.75|
The figures above show that for dry scrubbing systems that use replaceable media, SulfaTreat has the lowest unit cost by weight for removing hydrogen sulphide and it also has the best removal capacity for hydrogen sulphide for a given size of housing. SulfaTreat systems will therefore normally take up much less floor space against comparable designs using carbon or alumina.
There is no limit for the H2S concentration that can be treated. This can vary from low ppm levels through to 100% H2S. For application areas at the high percentage level of H2S additional precautions such as water irrigation are necessary to dissipate the exothermic heat created through the chemical reactions. With SulfaTreat no acclimatisation or initiation time delay is required before rapid fluctuations in incoming H2S challenge. The design performance of the media is therefore always available for any challenge at any time provided the air stream is water saturated.
For the water industry the ideal application areas for SulfaTreat centre around sludge treatment processes.
Ductwork collection systems typically would include:-
· Sludge Holding Tanks.
· Dewatering chambers.
· Belt Thickeners and Centrifuges.
· Picket Fence Thickeners
· Sludge Screens and Skips
· Sludge Tanker Vacuum Pump Discharges
Another important SulfaTreat application area in the water treatment industry is treating digester, biogas or landfill gas prior to use in gas engines for power generation. Typically maximum H2S levels are specified by the engine manufacturers at 500mg/m³ to prevent damage to the valve gear and contamination of the engine oil. The simplicity of the SulfaTreat process is ideal for this application. In particular since it is ideally suited to the water saturated condition which is typical for digester gas. Even if H2S treatment is not required by the engine supplier there may still need to scrub the exhaust gases since the sulphur dioxide which is formed from hydrogen sulphide is also very odorous and there will still be unconverted H2S and mercaptans in the chimney discharge.
A version of SulfaTreat is available for treating water streams that have absorbed hydrogen sulphide. Its chemistry is identical to that of SulfaTreat and it is available for either treating potable streams or non potable streams. A typical application could be for treating sour bore hole water that is required for irrigation or washing down purposes.
The following important recommendations should be followed when designing SulfaTreat systems.
· Down flow is always preferred since it prevents the accumulation of water within the bed.
· Velocities are typically less than 0.07m/s for odour control applications. Combined with bed depths which typically vary between 1000 and 1500mm this ensures that the pressure drop through the system is suitable for normal industrial centrifugal fans.
· Dust filtration is required as normal to prevent blinding of the media. Demisting is only required if the air stream has high loadings of aerosol droplets.
· SulfaTreat media is normally available in 900kg sling bags with tie cord sealed flexible outlets. This enables simple gravity emptying by forklifts or hiab lorries. Beds are normally designed to hold multiples of full bags.
· Spent media is normally free flowing enabling low level gravity emptying. Vacuum emptying from above however is preferred for media changes.
· A lead/lag arrangement with two vessels in series provides the optimum running costs. The lead vessel is retained until the inlet and outlet concentrations are equal. The lag vessel then becomes the lead vessel and media is changed in the original lead vessel. Ideal arrangement for very high challenges.
SulfaTreat lead / lag vessel arrangement for H2S removal - Biogas
A final polishing section is normally required to remove heavy mercaptans, dimethyl disulphide and other residual odorous compounds. This section will typically contain combinations of plain activated carbon, caustic impregnated activated carbon and potassium permanganate impregnated alumina.
The proportions and quantities of these residual gases will be very site specific. In particular the requirement to treat ammonia and hydrocarbons appears to be on the increase and these compounds in particular have there own special requirements.
To optimise the performance of the polishing section humidity control is good practise. Though SulfaTreat requires high relative humidity the same humidity levels in the polishing bed reduce the adsorption capacity of the media and can result in the chemical impregnates being leeched out. Heating to give a 5°C temperature rise is recommended for humidity control for the polishing section.
The illustration shows key features of a composite design, which allows for an economical combination of SulfaTreat and final polishing sections within the same vessel.
SulfaTreat media and process design information is now available from Higgins & Hewins for all customers to design and install their own systems. . Large stocks of SulfaTreat media are held at the Higgins & Hewins works in Stourbridge. Following submittal of a completed fact sheet providing data on the process flow Higgins & Hewins can produce an estimated performance specification (EPS). This indicates vessel sizes, H2S removal capacity, media life and pressure drop.
For schemes which have process conditions which are largely unknown, pilot testing can be a useful option to ensure a realistic design and reduce the chance of failure. Higgins & Hewins stocks a wide range of hire units which are available for short or long term hire. Most units are available with process fan, discharge chimney and simple motor starters. Flexible ducting can be provided to suit the installation. Pilot testing enables the optimum selection of media and contact time to be established.
For further information please email Higgins & Hewins Air and Gas Purifications Systems