Abstract

      All high-temperature processes passing in the furnace perniciously influence on elements liner, external fixture (a beam, suspension, armature of the furnace and other). Cooling is very important to prevent this influence.
     To maintain the normal temperature in the top layer to the martin furnace is necessary the system of regulation which will operatively read out and process data about current temperature, will automatically make a decision on necessity of cooling or heating of a layer, and automatically take corresponding measures on achievement of result. For this purpose it is necessary to use components of system meeting the requirements systems on modes of operation, time of reaction, sensitivity, thermodurability and other parameters. And also to be optimal from the economic point of view.
     Except from the basic function of the given system – functions of cooling of the arch by regulation of speed (productivity) of a current of water, the system should supervise and regulate adjacent questions of work of system, such, as: the control of the top and bottom water levels over a catchment basin, regulation of water delivery from a network in a catchment basin. As the signal system about a current condition of system of cooling of the arch (temperature (maximal, minimal, normal), a water level (minimal, maximal, normal)) is indispensable [1].
     During development of the project it is necessary to give much attention to questions of mathematical modelling of process of cooling to have precise rated data on temperature for different points of the arch, speed of cooling, gradients of temperatures, etc. It is necessary to create the hardware of system in view of modern needs: with application of modern microcontrollers, connection of system to the computer for diagnostics, regulation by software, and also for visualization of process of work of system.

      For measurement of temperature it is necessary to choose from all means in what bottom border of a range of measurements below 90°C, and top above 190°C, thus it should be analog instead of discrete, for continuous reception of the information and the cheapest. These parameters are answered with thermoelectric thermometers and resistive gauges of temperature. We shall consider their advantages and lacks to choice of concrete type of the device having lead the comparative analysis.

Figure 2 - the function chart of system of cooling of the arch of the martin furnace

     Approximately 50 % of all measurements of temperature in the industry are carried out by thermocouples, 30-40 % resistive gauges of temperature (RGT), and other measurements — other gauges, for example, optical pyrometers. RGT it is possible to use for measurements of heats (approximately up to 1000 °C), but practically it appears to provide difficultly accuracy of measurement if the temperature exceeds 400 °C. In the same way thermocouples can be used for measurement of temperatures down to 3000 °C, but obtain authentic data at temperatures above 1000 °C extremely difficultly. RGT and thermocouples work well enough in a range of temperatures up to 400 °C [2].
      As is known, RGT — the active gauge. To measure its resistance, it is necessary to pass through it a small electric current (usually no more than 1 мА) [4]. The current forces platinum element RGT to heat up above temperature of environment in which it is placed. The size of heating is proportional to a square of a proceeding current and factor of a heat transfer between sensitive element RGT and environment. Emission of heat on a sensitive element — one of principal causes of occurrence of an error at carrying out of measurement of temperature by means of RGT. These mistakes named by mistakes of a self-warming up, are peculiar absolutely to all RGT. Because of self-warming up RGT not always will be the best gauge at carrying out of measurements in environments with a bad heat transfer. In these cases it is better to use thermocouples provided that other parameters of process allow the use of them. The thermocouple in free space can have faster time of the response, than RGT.
     But when gauges are used in isolating thermobox, time of the response in the big degree depends on an air interval between a sensitive element of the gauge and a wall of the case. In this case time of the response at them approximately equal.
     As it is known, RGT are more exact, than thermocouples. But it is exact calibrate the thermocouple it can be so exact, as well as RGT. However RGT the thermocouple holds the calibration is better and longer. Besides RGT can be removed from technological process and it is repeated calibrate while calibration of the thermocouple usually cannot be made after its use [8].
     So from all described above it is possible to draw conclusions, that in interesting us a range of well show also thermocouples and RGT, but in our measuring system we shall use the closed execution of the case of a sensitive element, and it in turn influences on error RGT caused by a self-warming up. As on error RGT essential influence renders differences of external temperatures (on connecting wires). And close furnaces take place significant differences of temperatures. Due to low cost of thermocouples in comparison with RGT we can make is more often replacement of thermocouples, instead of calibrate them. Lack of thermocouples is weak value EMF that demands short communication lines (up to 8 meters) which should be shield.
     Indemnification of the cold ends is a challenge, especially in conditions of the martin furnace. Use for this purpose a bath with a thawing ice, in the majority of practical cases is unacceptable. Use active thermoresistors, supporting cold connections at raised (the order 60°C) temperature, raises power consumption the measuring equipment, leads to occurrence of additional handicapes and necessity regraduation. Therefore in practice indemnification of temperature cold connections is usually made by hardware or hardware-software means. In this case inclusion in a measuring circuit consistently with the thermocouple of the bridge scheme fig.2 is used.

      In this course project was developed structure of the automatic temperature regulation of arch of the martin furnace. It keeps temperature in the set limits, adjusting a current of cooling water an automatic latch, as well as adjusts a water level in a catchment basin in the set limits. It has to be noted merits and demerits of the developed arrangement.
     To dignity concern:
     -low cost of arrangement in manufacture;
     -opportunity of flexible adjustment of arrangement on the certain conditions of operation, and a possibility of variation of algorithm of work without intervention in the hardware (changing only the program), simple synchronization of arrangement with a computer.
     -opportunity of gauging of temperature in several seats on the arch at the same time. To lacks I could carry only the limited length of communication lines (wires) from thermocouples to arrangement.
     For the further improvement of the given arrangement to it it would be possible will add all spectrum of functions under the control and management of water cooling of the arch of the martin furnace, such as:
     -control of pressure over system and delivery of a signal to the dispatcher (about accident) at pressure drop;
     -visualization of the given process on a computer in actual time.
     The given arrangement, from the economic point of view, will reduce expenses for production due to savings of fuel, as well as prolongation of service life of constructive elements of the martin furnace ( beams, suspension the arch) to reduce terms of repair idle time (the limited work).
     To sum up rough market prices for components of the given arrangement a condition for April 2009, has received a total cost which is equal 2300 ± 300 grivnes. Without taking into account cost of connecting wires. Considering cost of power resources for given time and dynamics of price increase for them, it is necessary to use all possibilities on savings of fuel that will in turn be reflected in a net cost and consequently and on competitiveness of a product of martin manufacture in the market.

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