TABLEl. OPERATING CONDITIONSAT THE SELCHP SITE. TABLE 2. GAS COMPOSITION Al THE SELCHP SITE.

Flue gas flow rate 2 x 170,000 Nm3/h Operating temperature 140°C Without flue-gas treatment 220°C Maximum temperature 250°C Filter velocity 1.10 (nominal operation)

1.37 (maximum)

H2O HCl so2 HF pH OF dust Dust load

1.5 - 21 vol% 1500 mg/Nm3 300 mg/Nm3 20 mg/Nm3

il - 12.5 9600 mg/Nm3

with a PTFE coating, at 600 g/m’. The total filtration area is 8294 m2.

The key operating condi- tions at this installation are

shown in Table 1, with the composition of the gas contaminants reported in Table 2.

Imi-Tech Fibres GmbH A-4860 Lenzing, Austria.

Tel: +43 7672 701 2624 Fax: +43 7672 74823

Imi-Tech Fibres PO Box 390

Niverville, NY 12130, USA.

TellFax: + 1 518 784 2247

Lenzing Profilen with extended production capacity

he Profile@ PTFE weaving and sewing yarns produced by

Lenzing AG have been suc- cessful in high-temperature filtration applications. Here Albert Wimmer explains why this material is so successful in its market, and reports on develop- ments within the company.

For a number of years, Lenzing AG has enjoyed success in the market for high-temperature filtration with its PTFE weaving and sewing yarns. Lenzing Pro- filenB is the registered tra- dename of these high- tenacity PTFE yarns and fibres. These products are not only used in filtration, but in other technical areas and in the hygiene sector, for example as dental floss.

An increase in the de- mand for these products has led to the construction of new and modern build- ings, and the installation of new production lines, within the course of the last 12 months. Care was taken with the building de- sign, to create a friendly atmosphere for all the employees.

The new production lines will be started up by the end of August 1996. The com- pany has invested some US$lO million in these new facilities, creating a capa- city of approximately

150 tonnes/annum for pro- ducts for high-temperature filtration. In the future, the aim is to include fibres for the production of nee- dlefelts in the product range, in addition to the weaving and sewing yarns already being produced. Therefore in the future it will be possible to produce needlefelts 100% from Lenzing Profilen products.

WEAVING AND SEWING YARNS

In general, Lenzing has a standard type for both of these applications; thus a 440 dtex yarn with a twist of

300 T/m S is used for the manufacture of supporting scrims (type 204/3008), and triple sewing yarns of 1350 dtex are used for the garment industry.

These materials have been used in high-tempera- ture filtration for many years. They have proven to be successful, where two of this material’s properties have a considerable influ- ence on its success in prac- tice; these are the tenacity and the elongation proper- ties at temperatures higher than room temperature.

Figure 3 shows the de- velopment of tenacity in Profilen yarns. It is clear that at approximately 200°C

a point has been reached at which the tenacity reaches the same value regardless of the tenacity at room temperature. More- over, it is important and interesting to note that the tenacity remains almost stable when the tempera- ture continues to rise, even when the materials are heated to more than 300°C. From this it is clear that a needlefelt made from Profi- len can withstand signifi- cant temperature peaks.

In the same way, the development of elongation at the same temperatures (see Figure 4) is also very interesting. In general, one would expect a thermoplas-

gure 3. Tenacity of yarns with increasing temperature.

Figure 4. Elongation or yarns wttn rncreasmg temperature.

tic material (such as PTFE) to produce a progressively steepening curve. However, it is surprising to note that, at a certain temperature (which is not identical in products from different manufacturers), the elonga- tion begins to reduce. For Lenzing Profilen this means in concrete terms that the same elongation is pro- duced at 300°C as at room temperature. In this re- spect, Profilen differs quite considerably from competi- tive products (see Figure 4).

This property is an im- portant factor when it comes to applications such as filter bags. It would ap- pear that longer filter bags are being used in practice, and are sometimes even placed on the bottom of the filter. Elongation can only influence this if the correct temperature is used.

For example: a filter bag is 400 cm long, the operat- ing temperature is 25O”C, and we assume that the filter bag has to bear a load of up to 25% of its tenacity

as a result of its own weight and the dust load. This produces an elongation of approximately 2% on the curve for Profilen, and results in an 8 cm increase in the length of the filter bag. Other products pro- duce 21 cm or more in the same conditions, depend- ing on which product is being examined. This im- plies that the use of Lenzing Profilen as a supporting scrim has a particular ad- vantage to offer in terms of dimensional stability.

FIBRES

In addition to weaving and sewing yarns, Lenzing AG also produces Profilen fi- bres for the production of needlefelts. These fibres are made from 100% PTFE, and they therefore have the natural white colour of PTFE. This is also con- nected to its anti-adhesion properties, as a character- istic of PTFE, which pro- duces good cleaning behaviour in the filter bags. As a result of this, therefore, they tend not to blind.

Furthermore, the fibre titre is of a lower level than was previously common in PTFE; there is no single titre, and the fibre has a certain proportion of very fine fibres. This in turn results in a much better filtration efficiency tha’n has been previously offered by commercially available PTFE felts, for example. As a result, better cleaning behaviour can be obtained, depending on the require- ments, or alternatively a lighter felt can be used.

Lenzing AG, Films Division A-4860 Lenzing, Austria.

Tel: +43 7672 701 2876 Fax: +43 7672 92572

The KKF viscose filtration system key element in the

production of vis- cose fibre is the

efficient separation of un- dissolved particles from the viscose spinning solu- tion. Here Walter Klein re- ports on a backwash filtration system which was specifically designed to meet the strict require- ments necessary for high quality and for large quan- tities of fibre production.

The efficient separation of undissolved particles from the viscose spinning solution is an essential part of viscose fibre production. The stringent requirements for high quality and for large quantities of fibre

production lead to a de- mand for filtration systems which have been designed specifically to suit this diffi- cult application.

In response to this need, Lenzing has developed the KKF filter plant with all of these requirements in mind. A number of con- siderations with regard to the performance char- acteristics of the KKF filter reveal why the filter is be- lieved to be ideal for fibre manufacture:

l There is optimum adjust- ability of both the quality and output quantity as the main parameters. The automatically ad- justing sealing system gives high operational

efficiency. Automatic filter regen- eration is possible with- out any need for interruption of the filtra- tion process. Thus losses are minimised by the optimised regenera- tion system. The system allows flex- ibility in the modernisa- tion of existing production lines. The combination of filtration plant and spinning pres- sure control system leads to significant im- provements in viscose production plants. Because of low opera- tion and maintenance costs, the system is highly efficient. Also, the plant set-up and

maintenance area is ar- ranged in order to save space, and the closed nature of the system gives better operational safety.

l The air intake into the deaerated spinning solu- tion is eliminated.

l The filter area can be up to 2.1 m* per unit, with a flow rate of up to 22 m3 per unit. The systems can handle mixtures with viscosities in the range from 3 to 35 Pa s.

Lenzing Technik Separation A-4860 Lenzing, Austria.

Tel: +43 7672 701 extn. 2831 Fax: +43 7672 74819