Patent Application
20150033944
Molten steel is treated under vacuum in the so-called secondary metallurgical processes in steel production, in particular in oxygen blowing processes. The so-called steel degassing and the production of steels with a low C content by so-called top-blowing of oxygen are treatment variants which are known from the prior art and find worldwide application.
The plants for performing the aforementioned method essentially comprise two core components, the so-called vacuum chamber on the one hand, in which foundry ladles with molten steel with a capacity of up to over 300 t are treated under vacuum, and on the other hand the vacuum generator, which is connected via a suction line to the vacuum chamber. In the case of the processes taking place under reduced pressure between 200 mbar and 0.6 mbar absolute, dissolved gases and reaction gases are liberated, which are drawn off by suction from the vacuum generator, whilst maintaining the given absolute working pressure. Entrained metallic and non-metallic dust particles or those arising due to evaporation and condensation are also transported in the waste gas flow. Depending on the process, the dust, with a waste gas temperature of up to 500° C. and a grain size of 0.5 μm to ≧100 μm, can amount to an accumulation by mass of 3 kg to 4 kg dust per tonne of molten steel.
Two different types of vacuum pump systems are used nowadays for high suction volumes at low suction pressure: on the one hand there are the steam jet ejector pumps for the most part insensitive to dust, which have a higher energy requirement, and on the other hand there are the dust-sensitive mechanical vacuum pumps.
In plants in which the vacuum is generated by means of multistage steam jet ejector pumps, the dust load in the waste gas does not represent a direct functional impairment of the ejector pumps. The waste gases are compressed to atmospheric pressure here via multistage ejectors, wherein up to approx. 5% to 10% of the dusts contained in the waste gases is deposited at the walls of the pipelines and ejectors and the remaining 90% to 95% is washed out and carried out by the circuit cooling water into the injection condensers. High outlay on labour-intensive manual cleaning work and on the cleaning of the circuit water contaminated by the dust particles is however considered a drawback here. The vacuum generation by the steam jets, moreover, is further characterised by a high steam consumption, which has to be generated on site in a high-performance steam generator, which gives rise to additional costs.
The operation of mechanical vacuum pumps, which however are sensitive to high temperatures and the dust in the gas sucked in, is on the other hand much more energy-saving. Gas/dust separation and gas cooling between the vacuum chamber and the vacuum pump is therefore always provided in principle for mechanical vacuum pumps. In previously installed plants employing mechanical vacuum pumps, the sucked-in gas is first conveyed through a cyclone before entry into the vacuum pumps, in which cyclone the separation of coarse dust particles takes place. The gas is then conveyed for cooling into a gas cooler and passes from there through a fine dust filter, which is used to separate or segregate the smallest dust particles.
The aforementioned components of a device employing mechanical vacuum pumps are installed one after the other in the vacuum line, which apart from the space requirement leads to a corresponding length of the vacuum line. This is contrary to the requirement for a line as short as possible between the vacuum chamber and the vacuum pump set, in order to achieve maximum efficiency with the vacuum generation in the vacuum chamber.
The problem of the invention is to prevent for the most part the described problems with the use both of steam jet ejector pumps and with mechanical vacuum pumps. This problem is solved with a method having the features disclosed herein.
The core idea of the invention consists in the fact that all the required method steps for the dust separation such as the preliminary dust separation, the fine filtering and the gas cooling are to be carried out in a single, vacuum-tight compact cyclone separator with an installed fine dust filter with a connected gas cooler, wherein the untreated gas entering into the cyclone is forced into a rotary motion by helicoidal baffle plates, as a result of which the coarse dust separation on the one hand is promoted, and on the other hand preliminary cooling of the gas flow is brought about at the outer jacket of the installed heat exchanger. The gas is then conveyed through a fine dust filter equipped with a stainless steel microfilter mat and the connected water-cooled gas cooler and via the gas funnel into the vacuum gas line to the vacuum pumps. It is very particularly advantageous here that, as a result of the compact design of the device, the length of the vacuum line is shortened considerably, as a result of which the pressure loss can be kept low.
Advantageous developments are also stated herein.
The assembled filter/cooling unit is supported loosely on the waste gas funnel of the device, so that the components can easily be removed upwards out of the housing of the device, since the latter merely have to be lifted up.
At the lower funnel-shaped end, the cyclone comprises a vacuum-tight dust cap, via which the occurring coarse and fine dust can be removed.
The fine filter is cleaned pneumatically by means of inert gas. Independently of this, separate flooding of the cyclone interior by means of inert gas is advantageous.
Further advantages, features and details of the invention will emerge from the following description of a preferred example of embodiment of the invention and on the basis of the drawing. In the figures:
The apparatus unit comprises cyclone housing 11 for the preliminary dust separation, gas cooler 14, which is constituted as a water-cooled tube bundle heat exchanger 19, and fine dust filter 13 for the fine filtering of the waste gas.
Fine dust filter 13 and tube bundle heat exchanger 19 are connected to one another and are disposed concentrically in vacuum-tight cyclone housing 11, in such a way that lower part 21 of tube bundle heat exchanger 19 is constituted conical and sits loosely in conical counter-funnel 18 of gas outlet connecting piece 23 of cyclone housing 11. Easy dismantling for maintenance purposes is thus guaranteed after the opening of cover 24 of cyclone housing 11 and after detachment of water inlet and outlet connections 25 and 26. Depending on the requirement, fine dust filter 13 can also be dismantled without gas cooler 14 and tube bundle heat exchanger 19.
A vacuum-tight closure cap 28, preferably with a pneumatic or hydraulic drive, is installed on lower cyclone cone 27 for the dust removal. To assist the dust removal from cyclone separator 12, an agitator 30 with an electric or pneumatic drive is fitted, which is preferably located on cyclone cone 27.
The function of cyclone separator 12 is as follows: the dust-laden hot gas is conveyed by the suction force of vacuum generator 16 into tangentially disposed inlet connecting piece 31 of cyclone separator 12. As a result of the high entry speed and the rotary motion thus occurring, the centrifugal forces act on the larger particles of the hot gas, so that the particles are captured in a known manner in cyclone cone 27. Helicoidally shaped baffle plates 32 at the inner wall of cyclone housing 11 assist the process of separating the particles. As a result of the gas flow initially directed vertically, partial cooling of the gas is already achieved by water-cooled jacket 33 of tube bundle heat exchanger 19.
The total gas volume with the residual dusts is sucked via a fine dust filter 13 and then through tube bundle heat exchanger 19. Fine dust filter 13 preferably comprises close-mesh stainless steel microfilter mats and is adapted to the fine-grained particle size. For the cleaning of fine dust filter 13, pneumatic impulse bursts, preferably by means of inert gas, from the interior of fine dust filter 13 in the direction of cyclone housing 11 are provided during plant downtimes, said impulse bursts conveying the dust downwards into cyclone cone 27.
Water-cooled tube bundle heat exchanger 19 is constituted according to the counter-current principle—gas through the tubes, water around the tubes. The cooled purified gas which has contracted in volume leaves cyclone separator 12 in the direction of vacuum generator 16 through gas outlet connecting piece 23. Depending on the dust grain size distribution, provision can be made to rotate fine dust filter 13 and gas cooler 14 in cyclone housing 18 through 180°.
The flooding of the entire system usually takes place with atmospheric air at the end of the process. On account of an O2 enrichment at the grain surface, the high fine grain proportion can lead to spontaneous ignition or, interlinked with other operating states, e.g. ignition sparks with sufficient capacitance, to explosion. At the end of the process, therefore, the interior of cyclone separator 12 is preferably separated from the remaining volume of the plant and flooded with inert gas.
| Number | Date | Country | Kind |
|---|---|---|---|
| A 71/2012 | Jan 2012 | AT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/051224 | 1/23/2013 | WO | 00 |
