Drum

Figure 3.1a shows a flash drum used to separate by gravity a vapor-liquid mixture. The velocity of the vapor through the flash drum must be less than the settling velocity of the liquid drops. Figure 3.11) shows a simple gravity settler for removing a... 

Drum dryers are shown in Fig. 3.15c. his consists of a heated metal roll. As the roll rotates, a layer of liquid or slurry is dried. The final dry solid is scraped off the roll. The product comes ofiF in flaked form. Drum dryers are suitable for handling slurries or pastes of solids in fine suspension and are limited to low and moderate throughput. 

The reactants dissolve and immediately begin to react to form further dichloroethane. The reaction is essentially complete at a point only two-thirds up the rising leg. As the liquid continues to rise, boiling begins, and finally, the vapor-liquid mixture enters the disengagement drum. A very slight excess of ethylene ensures essentially 100 percent conversion of chlorine. 

The storage of chemicals, lubricants, aviation fuel and diesel fuel is normally on the platforms, with chemicals kept in bulk storage or in drums depending on the quantities. A typical diesel storage would be adequate to run back-up power generators for around a week, but the appropriate storage for each item would need to be specified in the FDR... 

New Inspection Method of Steam Drums in Paper Mills. 

In Austria, as well as all over Europe, the first and repetition tests of all pressure equipments including steam drums are required for security reasons within fixed time intervals. These repetitive inspections are done differently in the most European countries, but most time these inspections include, according to the European Pressure Equipment Directive" and the specific national law any kind of over-pressurisation (e.g. hydrotest) and visual inside inspection. 

One production line of a paper mill consists according the size and the quality of the produced paper sometimes from more than 50 steam drums to dry and flatten the produced paper. These drums (cylinders with flat bottoms, see figure 1) will be used with a steam pressure up to 500 kPa (5 bar) and additionally with a rotation speed up 1200 m.min the material is mainly grey cast iron (with lamellar graphite). The diameters can reach up to 2.2 m and the cylindrical lengths up to 10 m. For the specific flattening drums the cyhndrical diameters can be up to 5 m and more. 

For the repetitive inspections the required hydrotest can only be performed for a limited number of the small cylinders, and even then the drums have to be removed from the line and the cylinders will be supported in defined distances for the weight of the water and the pressurisation. For the new and long cylinders even this is impossible, because they loose due to the additional weight of the water and the over-pressurisation their roundness and balances. Therefore the law in the most countries within and outside of the EU accept as a replacement of the hydrotest an additional application of different NDT methods, which were often done by an ultrasonic measurement of the wall thickness of the cylindrical part and a MT of the flat covers. 

A fatal accident and some other disasters, which were caused by small cracks, lead to a more strict consideration of the security of these steam drums. Parallel to these the economical pressure, due to the globalisation of the today s industry, lead to the increase of the pressure and the rotation speed of the paper production machines for a higher output of the production, which means, that all safety aspects from the design and the material will be exploited totally. On the other hand cast iron is also not a ductile and comfortable material, like the most steels for the pressure equipment. 

Based on our practical experiences in the applieation of AE on pressure equipments since 1979, we started in the year 1994 to apply AE on steam drums in combination with pneumatic tests. Before we are able to do this, we have to perform extensive lab tests with the specific material (grey cast iron and cast steel) from which these drums are produced. 

Beside all technical reasons the big advantage of a pneumatic test is, that the steam drums can remain within the line because first we have no additional load for the bearing and only small adjustments (for the connection with the pressurisation unit and the tightening of the man ways for the applied low temperature gas test) have to be done to make the drum ready for a pneumatic loading. The pressurised air is available in every paper mill and even if the maximum pressure does not fit, the use of a compressor or pressure bottles produce no problems. 

Before the performance of the loading we have to apply 5 up to 12 sensors, according their size, on the cylindrical part of the drums and after a short check of the required sensitivity and the wave propagation the pneumatic pressure test monitored by AE can be performed. The selection of the sensors and their positions was performed earlier in pre-tests under the postulate, that the complete cylinder can be tested with the same sensitivity, reliability and that furthermore the localisation accuracy of defects in the on-line- and the post analysis is sufficient for the required purpose. For the flat eovers, which will be tested by specific sensors, the geometrical shape is so complicated, that we perform in this case only a defect determination with a kind of zone-location. 

The vessels will be pressurised up to 1,1 - 1,25 fold of the normal service pressure of the drums, within stress increments of 50 kPa (0,5 bar) and a constant and smooth slope of less than 10 kPa.min . During the complete test the data will be acquired, stored and analysed. 

How it was declared, the new steam drums cannot undergo a hydrotest, because they loose their roundness and balance due to the additional weight of the water, even if the cylindrical part will be supported. 

The older steam drums, which can sustain these additional effects better, have to be removed of their position in the production line because of the bearing and this would be expensive and time consuming. 

Since 1994 when the test method was implemented in the inspection program of many paper mills, we test now regularly the steam drums in the most paper mills in Austria (see table 1). 

Table 1 Steam drums, which undergo a pneumatic test monitored with AE...

An additional benefit was the detection of big cracks in the balance weights. These weights were hold together only with the fixation screws, (picture 2) This defect can result in big damages of the drums in the following operational period. 

Beside all these safety reasons, we are able to test 2 or 3 drums at the same time and by some improvements of the application we are able to reduce the test-period down to 4 hours, which results in an also for the production sufficient number of tested drums during the short shut down periods. These increase the availability and the production output of a plant and result therefore in a gain of safety an economical competitiveness of the European industry. 

It was pointed out, that the periodical inspection of the steam drums has been become an absolute must especially under the circumstance, that the economical pressure results in smaller wall thickness, higher steam pressure and higher rotation speed. The conventional periodical inspection (hydrotest and visual inside inspection) is on one hand time consuming and therefore expensive and on the other hand the results of the hydrotest are doubtful and can result in a seriously damage of the roundness and balance of the steam drum. 

Even the replacement of the hydrotest by a NDT method is only sufficient, if you perform much more than it is usual today e.g. a complete ET of the cylindrical part, which requires the possibility to rotate the drum during the shut down and is therefore much more time consuming and expensive. 

The only meaningful solution is a pneumatic test in conjunction with an AE. Beside the high sensitivity of an AE and its reliability in combination with an established and proven data base, the method can be performed by experienced testing agencies easily and within short shut down period. A lot of 4 up to 9 drums can be tested within one day. 

In future we will increase our data base also for the newest types of drums and are also convinced, that by the application of pattern recognition AE becomes beside its detection ability more and more also a valuation technique. 

Near Drum Corrosion Inspection of Boiler Tubes. 

The near drum corrosion problem is relatively newly identified in Scandinavia. This paper presents the experience from many years of inspections in North America. 

Through the use of lab tests implemented by the pulp and paper companies in the United States and Canada it was determined that all but one manual technique were both unrepeatable and inaccurate. During some years ago the operators of black liquor recovery boilers have been able to take advantage of the latest teehnology to inspect the wall thickness of the near drum generator tubes. The technology utilises immersion ultrasound and automated computer... 

After inspecting a bank of near drum generator tubes using full coverage scans, the following information can be obtained ... 

When a tube is rolled or expanded into the tube sheet three different wall thicknesses are created on the tube in the near drum region. They are the thickness of the tube within the tube sheet, the thickness of the tube from the tube sheet to the roll mark, and the thickness of the tube above the roll mark. 

Near drum wastage is the most prevalent type of wastage documented. It cart be found anywhere in the generating bank but is most common on the wall tubes, in tlic row immediately next to soot blower lanes and in the hot and cold row s. Three types of near drum w astagc have been documented. 

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