Filtration of amines in Gas Treating Units
Many cartridges cause operating problems in amine units. Cartridges made with paper and fabrics that have been chemically treated can cause foaming in the amine solution. Cartridges that have a glue or binder can be destroyed in amine service. Oils in the virgin cotton and the bleaches that are used to remove the oil and whiten the cotton can cause amine foaming if the cartridge manufacturer does not know how to prepare the cartridges before use. Some cartridges do not have the thermal stability required for amine service. Arbitrarily choosing a type of cartridge and a flow rate per cartridge can be very costly. The flow rate is dependent on
the type of cartridge, micron rating, fluid viscosity, length and diameter of the cartridge and other factors.
A better knowledge of filtration can help lower the filtration costs and solve unit problems. The cost for filter cartridges in some amine units is higher than the annual amine cost. This is a ridiculous waste of cartridges and manpower. Part of the confusion is due to a lack of industry standards on cartridges. For example, nominal micron ratings can be very confusing and misleading. A cartridge with a nominal rating of five microns may capture only 50 percent of the five micron particles while other cartridges with the same five micron rating may remove 76 to 99+ percent of the five micron particles. Until the filter cartridge manufacturers develop common performance standards to show both micron ratings and the percent capture of the rated particle size, confusion will continue. On the other hand, in most amine unit the filtration is on slip stream basis only, so need for absolute filtration is there. Other important information that is needed to compare cartridges is the chemical resistance, the sludge holding capacity, the optimum flow rate through the cartridge and the maximum pressure differential the cartridge can tolerate before change outs are made. Some cartridges start releasing the sludge back into the system at a low pressure differential and thus the filtration costs are much higher. Cost can play a major role in the cartridge selection. The real cost of a filter cartridge is determined by the cost per volume filtered, including the labour and disposal costs, not the cost per cartridge. The real cost can only be determined by actual plant test. Users should focus more on cartridge life and filtering capability rather than the first cost of the cartridge. A cartridge that lasts longer in service minimizes the labour costs needed to replace cartridges and reduces the cost of disposal of the dirty cartridges. It will also probably improve filtration because many operators will bypass the filters if change outs are too frequent and they do not have the time to constantly change cartridges. With rising labor, disposal and cartridge costs, the overall filtration efficiency should become more important in the cost equation and, hopefully, the first cost of the cartridge will become less important than performance. Royal Dahlman offers the industry a proven filter, the Terraced Filter® with extremely high dirt loading capacity and efficiency in amine filtration service.
The Dahlman Terraced Filter has found its roots originally in the filtration of gel particles in the production process of Vinyl Chloride Resin (PVC), Polyol and Rubber. Originally a conical pleated type of filter element design with 2,5 m2 filtration area was used which used a resin bonded sealing.
The new generation has led to an element which uses a special needlefelt fabric, has a sewn construction instead of resin bonded and holds a filter surface area of 5,4 m2 (more than two times than its precursor).
The name Terraced Filter, abbreviated T-Filter, derives its name of the radial pleated construction of the filter media. The filtration direction is from inside to the outside. Between each terrace drainage material is foreseen to provide some space between each layer. This ensures a proper flow distribution and makes a high DHC possible.
The latest development is doubling the length of the element. It still has the same diameter as the standard filter, but by increasing the length it has now a filter surface area of 9,5 m2. Typically this double length element is used for excessive dirt loadings.
The nature of solids present in amine systems
Iron sulphides (FeS) are mainly formed in the amine system due to the reaction between the sulphur present in the amine and the carbon steel piping and towers. Also corrosion products like scaling and other degradation products foul the system. In particular the FeS is a main problem causer for filters due to its natural characteristics. Iron sulphide in concentrated forms can be best compared to black shoe polish. It is sticky, fatty like and not permeable at all. These are almost the worst ingredients for designing a good filter system.
Before Filtration After filtration
The Terraced Filters are available with 1, 3, 5, and maximum 7 elements installed with single or double length elements, depending on the flow rate, dirt load and requested overall system pressure drop.
Advantages Dahlman Terraced Filters
- Large filter area per element, surface and depth filtration combined in one element,
- Filter area 5,4 m2 up to 9,5 m2 per single element.
- Very high dirt holding capacity (DHC), up to 35 kgs per element, therefor low element consumption.
- Significant reduction of operation involvement for change outs.
- Depth filtration combined with a large surface.
- Very easy change out;
- Quick sealing system design allows for super fast change out time.
- No risk of bypasses; sealing material is filter fabric.
- No more environmental pollution;
- The filter is completely drainable. The element can be drained using suitable gas e.g N2 / air or steam before replacement; product loss reduced to a minimum.
- No more operator exposure to the pollution, solids captured inside the element, which results in a minimum contact between the product and the operator.
- Elements are incinerable, the element is supported by a metal basket, therefore only the filter media is waste.
- Elements available in various micron ratings, materials and efficiencies, depending on the requested chemical resistance;
- Materials: Polyamide / Polypropylene / Ryton / Nylon / PTFE.
- Micron ratings: 1 / 5/ 10 / 25 / 50 / 100 / 200.
Proven performance in the following applications:
- MEA (2-amino-ethanol or ethanolamine)
- DEA (Di-ethanolamine)
- MDEA (Methyl diethanolamine)
- ADIP (Di-Iso-Propanol Amine)
- Sulfolane ((CH2)4SO2)
- Ucarsol (UCARSOL AP 814 Solvent)