Furnace control

The feed is normally introduced to the top hearth where the rabble arms and teeth attached to the central shaft rotate and spiral soflds across the hearth to the center, where an opening is provided and the soflds drop to the next hearth. The teeth of the rabble arms on the hearth spiral the soflds toward the outside to ports that let the soflds drop down to the next hearth. Soflds continue downward, traversing each hearth until they reach the bottom and the ash is discharged. The primary advantage of this system is the long residence time in the furnace controlled by the speed of the central shaft and pitch of the teeth. 

Opera.tlon, Because of the long residence time of the materials (8—10 h), the blast furnace process can exhibit considerable inertia, and control is usually appHed where the goal is maintaining smooth, stable input conditions. One of the most important aspects of blast furnace control is supply of consistent quaUty raw materials, which is why there is a strong emphasis on quaUty control at coke plants, peUeti2ing plants, and sinter plants (see Quality ASSURANCE/QUALITY control). 

Case study 4 is based on the updating of information displays for refinery furnace control from traditional pneumatic panels to modem VDU-based display systems. In addition to illustrating the need for worker participation in the introduction of new technology, the case study also shows how task... 

The regulation of the combustion process in a boiler furnace. Control takes place by regulating the access of fuel or air. 

Beryllium is a toxic element, and the reduction operation is therefore carried out in a well-ventilated special double enclosure. The furnace controls are located outside the enclosure. The ball milling of the reduced mass is carried out in walk in-type fume hoods. 

In addition there had to be created a new furnace control device. Now a burner control exists which uses the sensor s signals to adjust the gas-air ratio under various circumstances with a very low emission of polluting gases (CO and NOx). The new appliance is suitable for different gas types without any adjustments, not even at the first start after installation. 

A furnace control system consists of the following loops ... 

CO, reforming reaction was conducted at 500-750°C, reactants mole ratio of CH3 CO, He = 1 1 3, and space velocity = 20000-80000 1/kg/h. Methane oxidation was conducted at 150-550 °C using 1 % CH in air mixture (2 ml/min CH4 198 ml/min air) at space velocity = 60000 1/kg/h, and MIBK (4000 ppm in 150 ml/min air introduced by a syringe pump) combustion at 100-500°C and space velocity of 10000-30000 h 1. Catalytic reactions were conducted in a conventional flow reactor at atmospheric pressure. The catalyst sample, 0.1-0.3g was placed in the middle of a 0.5 inch I.D. quartz reactor and heated in a furnace controlled by a temperature programmer. Reaction products were analyzed by a gas chromatography (TCD/FID) equipped with Molecular Sieves 5A. Porapak Q, and 15m polar C BP 20 capillary column. 

In a typical furnace control system the fuel flow is manipulated to hold temperature or pressure in the process. The air is ratioed to the fuel. This ratio is adjusted to maintain a reasonable oxygen composition in the stack gas. 

Polystyrene capacitors have exceptionally low tan S values (< 10 q, making them well suited for frequency-selective circuits in telecommunications equipment. Polymer capacitors are widely used for power-factor correction in fluorescent lighting units, and in start/run circuitry for medium-type electric motors used in washing machines, tumble-dryers and copying machines for example. They are also used in filter circuits to suppress radio frequencies transmitted along main leads. Such interference noise may originate from mechanical switches, furnace controllers and switch mode power supplies it not only spoils radio and television reception but can also cause serious faults in data-processing and computer equipment. 

Figure 2.16 Proportional-integral-derivative furnace control logic.

A tube furnace drawn over the mullite outer casing is used to heat the contents to a specified temperature, based on a furnace control thermocouple. At the same time, a constant ac voltage2 is applied across the central heater. The microprocessor waits until temperature fluctuations (within 0.1°C, over one minute) at any of the inside or outside thermocouples are eliminated.3 At that point, steady state conditions are assumed to exist. 

Each reactor was heated in an enclosing furnace controlled by an Omega temperature controller. All temperatures were monitored by l/16in Inconel-sheathed thermocouples mounted on the feed side Details regarding sampling and analysis are reported in [2]. The entire reactor/analytial system was configured to operate for long periods of time (lyr) under fixed-conversion variable-temperature conditions. 

We next try a more aggressive heat recovery alternative as shown in Fig. 5.24. The heat input to the furnace is quite small and most of the heat is provided by the large feed-effluent exchanger. With, our choice of measurement lags (two 1-minute lags in series) and the lag in the furnace., this system cannot be stabilized by feedback control around the furnace if the quench controller is in manual. However, it is possible to stabilize the system with just the quench controller in automatic and the furnace controller in manual. Subsequent tuning of the furnace controller is then easy since the new system is open-loop stable. 

An interesting aspect of furnace control is the need to be always on the air-rich side, never on the fuel-rich side. If the furnace became filled with uncombusted fuel and then air was added, the resulting rapid combustion could blow the furnace apart. The same concern makes it important that the start-up of a furnace follow a very carefully thought-out procedure. The control system shown in Fig. 7.1 accomplishes this air-rich operation by the use of several selectors and a lag unit. When the temperature controller calls for more fuel, the air wall increase first before the fuel increases because the low selector on the fuel passes the low signal from the lag to the fuel flow controller while the high selector on the air passes the high signal to the air flow controller. The reverse operation occurs when the temperature controller calls for less fuel The fuel flow decreases first and then the air flow- decreases. 

A fine example of tliis type of work is the determination of Z)q(I2) from vapour density measurements at high temperatures by Perlman and Rollefson 8 8 These workers were interested in obtaining very accurate values of the equilibrium constant to see whether they exhibited any trend which would indicate the presence of 13 and incidentally in obtaining an accurate value of Dq(12) for comparison with the spectroscopically derived result. They introduced highly purified iodine into a silica bulb of known volume contained in a furnace controlled at temperatures between 723° K and 1,274° K, measured the pressure, and then removed the iodine and weighed it. Gas imperfection for molecular iodine was taken into account, but atomic iodine was assumed to be a perfect gas. 

Figure 1. Experimental Set-up of high-temperature metal vapor sorption system I. Flow meter 2. Needle valve 3. Nj 4. O2 5. Steam generator 6. Gas mixer 7. Valve 8. Thermo gravimetric furnace 9. High temperature sorption bed 10. Thermocouple II. Filter 12. Impingers 13. Furnace controller 14. Silicagelbed IS. Vacuum pump 16. Dry gas-meter...

Reactions were carried out under vacuum in silica cells incorporating an optically flat window through which the polymer film could be irradiated. The film, supported on a silica disc, was placed on the bottom of the cell which was placed in a furnace controlled at M.5°. The temperature of the film was measured by a Chromel-Alumel thermocouple placed inside the reaction cell in contact with the film. 

The furnace combustion system contained two air/fuel-type burners firing at 14 x 106 Btu/h (4.1 MW), with air preheated to 500°F (260°C). The existing control system was designed to regulate firing rates to control the roof and bath temperature at desired set point. This system could meter the rate down below 5 x 106 Btu/h (1.5 MW) when the roof or bath temperature was attained. The EZ-Fire controls were incorporated into the existing furnace controls enabling the systems to work... 

To determine the survivability for a TSP, samples were thermally cycled in a Thermoline 46200 high-temperature furnace. The furnace controls were set to raise the temperature to some predetermined value. The sample was then allowed to remain at this high temperature for 1 hr or more, followed by cooling to ambient room conditions. To quantify the fluorescence efficiency of phosphor suspended in the TSP, a Perkin Elmer LS-50B spectrophotometer was used to measure the emission spectrum of the sample after each thermal cycle. For each TSP mixture, two samples were made. The first sample was heated through the curing cycle and used as a control. The second was thermally cycled... 

The ceramic pellet with the porous Ni/SiO2 electrodes was placed in a 316 stainless-steel holder. A glass gasket was used in order to eliminate gas leak through interfaces between the anode and cathode. The anode was supplied with a gas mixture of H2 + H2O or CH4 + H2O. The H2 concentration was 20%. The ( I I, concentration was 10%. Results for other H2 or CH4 concentrations were reported elsewhere [4,5]. H2O was added to the CH4 or H2 gas flow by a bubbler immersed in a constant temperature bath. The cathode was supplied with a mixture of O2 and H2O. The H2O concentration in the cathode was 20%. The concentrations of H2, O. CH4, CO, CO2 and other hydrocarbons at the outlets of the anode and cathode were detected by gas chromatography. The H2O concentration was measured by a dew-point meter. The gas flow rate was controlled to a constant flow rate by mass-flow regulators. The fuel-cell holder was placed in an electric furnace controlled to a constant temperature. Temperature was measured by C-A thermocouples. I-V curves were determined by a two-terminal direct-current method. 

FIG. I—Cross view of the reactor and water pressure reserve. B exhaust vah-e, S specimen, U umbrella D,. D, stainless steel disks P pipe sustaining the sample holder, it is a pipe that contains the temperature measurement thermocouple T cylinder containing a specimen F isolated heating resistor and R furnace control thermocouple. 

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