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Home > Textiles and Design > Properties and Performance of Textiles > Acrylic fibre filter bags for power generation plants

Properties and performance of textiles

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Acrylic fibre filter bags for power generation plants

In the area of study: Properties and performance of textiles you will develop knowledge and understanding of the influence and importance of fabric structure, yarn type and fibre properties, in the selection of textiles for functional performance, in a specific industrial end use. One such textile designed for industrial use is woven acrylic bags engineered for filtering fly ash from power generation plants in the production of electricity. This tutorial analyses and evaluates the design and manufacture of an industrial fabric for its functional performance in an industrial end-use application.

Today's modern living means we expect a life with modern appliances, light and power virtually at the flick of a switch.

One of the significant costs of our high reliance on power has been pollution. Coal fired power generation plants have for a number of decades recognised this environmental concern and have been active with scientific research organisations to ensure our skies are left almost spotless. Without filter bags there would be large quantities of fly ash emitted to the atmosphere.

Today power generation plant emission levels operate well below the Government's tight environmental laws. This is partly due to the performance of acrylic fibre filter bags.

When coal is fired in the massive furnaces it leaves behind a very fine residue, called fly ash. The fly ash is drawn to and caught on hundreds of long open ended filter bags that are suspended in the bag house area of a power plant. The bag house operates at a temperature of between 120 to 140 degrees Celsius. Periodically the filter bags are shaken and the ash falls into hoppers where it is collected and taken away to be recycled.

Filter bags are expensive and they are periodically replaced. The latest research involves new innovative developments for fabric surfaces which will make this industrial fabric perform longer and more efficiently.

A modern power generation plant that burns coal to heat water to manufacture electricity. Coal fired power stations create fly ash in the process of burning coal.	Acrylic fibre filter bags trap fly ash and potential pollution dust from entering our skies. This industrial fabric is resistant to high temperatures and chemicals.

Textiles for this industrial end use need to withstand extremely high operational temperatures and be chemically resistant. This tutorial takes you through the process of justifying fabric, yarn and fibre choices for this specialised end use application.

Pre-test

Click to go to Pre-test activity     Flash version     HTML version

The manufacture of woven acrylic filter bags involves a series of manufacturing processes. Textile technologists work with specific industries like power generation plants to engineer a performance fabric to meet an identified end-use.

The functional criteria established for power generation plant filter bag fabric are:

• Temperature resistance: the fabric must withstand an extremely high continuous operational temperature of between 120 to 140 degrees Celsius.
• Dimensional stability: fabric shrinkage is costly to this industry, the fabric must not shrink when in use.
• Air permeability: the fabric must allow air to pass through but trap the fly ash.
• Chemical resistance: the fabric must not deteriorate when in use.

Aesthetically, the fabric does not need to be dyed nor is its shape designed for looks.

Suitable fabrics, yarns, fibres and finishes for this end-use are tested for their functional performance in the textiles testing laboratory. The following are some of the tests completed.

Tensile strength test: a stretch and break test. The fabric needs to be strong but not elastic.	Air permeability test: this test measures the amount of air that passes through the fabric.	Mullens burst test: a test where a rubber membrane is inflated and bursts a sample of the bag fabric.	Water flow test: a pressure test where water is pumped through the fabric sample under pressure.

Fabric structure, yarn type, fibre and fabric finishes required to manufacture power generation plant filter bags

Fabric structure chosen: 2 x 2 twill weave

The 2 x 2 twill weave fabric is made on a rapier loom.

A 2 x 2 twill woven fabric is characterised by the visible diagonal lines. The warp and weft yarns float over two or more yarns from the opposite direction.

2 x 2 twill fabrics are durable, they permeate air and shed soil easily.

Air passes through the bag. The fly ash is drawn to and caught on the surface of hundreds of filter bags where it cakes. After the bags are shaken the coal dust cake falls from the twill surface. This type of twill fabric is chosen for its ability to shed the cake ash and to let air pass through the fabric structure thus acting as a filter. Clean air then passes to the atmosphere.

Yarn chosen: medium S-twist yarn using the woollen spinning system

The acrylic staple fibres are carded, drawn and spun using the ring spinning method to create a medium S-twist yarn with 350 twists per metre. The yarn is characterised as strong, durable and hairy, that is, it has protruding fibre ends.

This type of yarn is excellent for filter bags as the protruding fibre surface allows for greater dust collection on the yarn surface.

Fibre chosen: Acrylic
The synthetic acrylic fibre known as Homoacrylic is composed of 100% polyacrylonitrile. This industrial fibre:

• has a highly oriented polymer structure
• is undyeable
• is highly resistant to chemicals
• has excellent tensile strength.

Homoacrylic is chosen for its excellent inherent properties of thermal and chemical resistance and makes a highly suitable choice for this industrial application. The bag house operates at a temperature from 120 to 140 degrees Celsius and the chemicals that the bag needs to be resistant to include sulfuric acid, nitrogen oxide, carbon monoxide and sulfur dioxide.

Fabric finish required: Dimensional stability achieved through heat setting the fabric

The power station's bag house operates at temperatures between 120 to 140 degrees Celsius. Shrinkage of the bag fabric must be avoided because it's a costly problem to the power industry. The bag fabric must be finished to prevent shrinkage.

The fabric once woven, is wetted then heat set at 180 degrees Celsius under tension. This temperature is higher than the industrial setting. This heat set process will ensure no further shrinkage will occur to the fabric once in use at the industrial site.

Creating a dimensionally stable fabric for filter bags improves bag life, dust release, solid retention and the chemical resistance of the fibre.

New innovations in finishing fabrics for filter bags: Foam coating finish: Primacellž

The coating is applied to the fabric surface and is then air blown dried to create a porous surface.

The porous surface increases the filtration process of the fabric thus filtering more of the fly ash.

Manufacture of the six metre power generation plant filter bags

The bags are laser cut on a four metre wide cutting table that allows for several bags to be cut at once.

The bags are sewn with industrial sewing machines using an acrylic sewing thread. Six metre long fell-lock seams are created using three needles.

This seam type is strong, secure and matches the life of the bag fabric.

Activity

1. Fill in the missing words for a justification of fabric, yarn and fibre usage for this industrial end-use.
   • acrylic
   • fly ash
   • performance
   • designing
   • synthetic
   • high
   • resistant
   • air
   • sheds
   • hairy
   • woollen
   • twill
   • S-twist
     
     
   In ____________________ filter bags for this specific industry end use, a ____________________ fabric has been engineered to perform in intense heat and chemical environments. Because ____________________ Homoacrylic polymers are ____________________ to ____________________ temperatures and chemicals this long chain polymer system is an excellent fibre choice for this industrial end-use. In order for the fabric to filter ____________________ and trap ____________________, a ____________________ weave construction using an ____________________ yarn is required. The ____________________ spun yarn has the ability to collect dust and the twill fabric ____________________ the dust cake easily on shaking. The combination of acrylic properties with twill weave using an S-twist woollen spun system achieves a fabric with superior sustained performance level. Textiles are diverse in their nature and application and the ____________________ fibre is a clear choice in helping prevent pollution as we continue with a high demand for power generated from coal fired power stations.
   
   
2. In your own words justify the use of a heat set, twill weave fabric made from an S-twist acrylic spun yarn for the industrial end-use of filter bags for power generation plants.
   
   
3. Using this web site answer the following questions: 
   1. State the industrial end-uses for fabrics that Albany International manufacture for the global market (page 3).
      
   2. State the fibres that Albany International use for their industrial fabrics and choose one of these fibres and research this fibre further.
      
      
4. With reference to the fibre properties chart, design a functional criteria list for a conveyor belt in a biscuit factory then choose a combination from the following options to create your industrial fabric.
   
   

   Fabric	heat set woven, stabilised knit, singed needled felt from a synthetic.
   Yarn	smooth combed yarn, hairy carded yarn, monofilament, multifilament.
   Fibre	cotton, wool, polyamide, polypropylene, polyester, acrylic copolymer, homopolymer acrylic.

Check your answers

Technology update/Tutorial extension: Visit the following site http://ww3.albint.com/Pages/Companies.aspx to explore the many ways Albany International, Australia leads the way with textile innovation. Click on engineered composites, engineered fabrics and PrimaLoft to view the latest in product development.

Also click on http://www.toyobo.co.jp/e/products/s_sizai.htm#p_4 to view textile information on chemical filters from Toyobo, Japan.