Overheat

Allowing DRI to become wet does not necessatily cause it to overheat. When large pdes of DRI are wetted with rain, the corrosion reactions are limited to the outer surface area of the pde and the resultant heat from the corrosion reactions is dissipated into the atmosphere. However, if water penetrates into the pde from the bottom, or if wet DRI is covered with dry DRI, the heat from corrosion reactions can budd up inside the pde to the point where rapid reoxidation begins. Corrosion occurs significantly faster with salt water than with fresh water. DRI saturated with water can cause steam explosions if it is batch charged into an electric arc furnace. 

Transportation. For short distances from the mine, transportation (qv) is by tmck or conveyor belt. Rail transportation is generally used for greater distances. Slurry pipelines (qv) ate being considered as an alternative. Rail transport over hundreds of kilometers results in loss of surface material in uncovered cats and a tendency to overheat in bottom-dumping tail cats owing to air infiltration around the cracks (31). Proper sealing and covets permit shipping over hundreds of kilometers. 

The second class of grinding equipment is used to prepare dispersions. Typical of this class are baU and pebble mills, ultrasonic mills, and attrition mills. SoHds, eg, sulfur, antioxidants, accelerators, and zinc oxide, are generaUy ground on this equipment (see Size reduction). BaU mill action is assisted in some mills by a combination of dispersion circulation by an external pump and mechanical osciUation of an otherwise fixed nonrotary mill chamber. Where baU mill chambers are rotated it is necessary to experimentally estabHsh an optimum speed of rotation, the size and weight of the baU charge, and ensure the mills do not overheat during the grinding period. 

Large quantities of fines in the furnace charge cause furnace blows that are hazardous to operator and equipment. Blows result when the steady flow of mix to part of the melt zone is stopped by a fines bridge the calcium carbide Hquid overheats and then dissociates at 2250°C. 

When the motor overheats, the thermostat opens, interrupting motorline current. Pilot thermostats mounted on the windings of larger motors trip the motor starter rather than interrupt line current. This method gives good protection for sustained overloads, but because of the thermal time lag between the copper winding and the thermostat it may not provide adequate protec tion for stalled conditions or severe overloads. 

Since the resistive loss would vary in a square proportion of the current, the motor will overheat on lower voltages (drawing higher currents). At higher voltages, while the stator current may decrease, the core losses will be higher. 

The life of the insulation will also be affected by an excessive operating temperature. It is halved for every 11°C rise in temperature over its rated value and occurs when a machine is occasionally overloaded. Sometimes the size of the machine may be only marginal when it was initially chosen and with the passage of time, it may be required to perform duties that are too arduous. Every time the machine overheats, the insulation deteriorates, and this is called thermal ageing of insulation. Figure 9.1 illustrates an approximate reduction in life expectancy with a rise in operating temperature. 

Bearings make a churning noise or overheat Check condition and level of grease as well as any skin effects or watermarks on the races, balls or rollers. If there are watermarks, the bearings should be replaced. Otherwise wash and regrease them, as explained earlier. 

The motor makes rumbling noise and the stator eurrent fluctuates. The rotor circuit may be broken and should be repaired. If the motor also overheats, there may be an inter-turn fault or a short-circuit between the phases. Detect these and rectify if possible, otherwise rewind the motor. 

If the field excitation is also lost, the generator will run as an induction motor again driving the primer mover as above. As an induction motor, it will now operate at less than the synchronous speed and cause slip frequency current and slip losses in the rotor circuit, which may overheat the rotor and damage it, see also Section. 1.3 and equation (1.9). A reverse power relay under such a condition will disconnect the generator from the mains and protect the machine. 

After the addition of the last of the /)-nitroaniline, the stream of phosgene is continued for five minutes and then shut off. The flame under the flask is then turned up and the ethyl acetate distilled. Care must be taken at the end not to overheat the residue. The brown residue (Note 5) is treated with 800 cc. of hot dry carbon tetrachloride, and the insoluble residue (the di-substituted urea) is removed by filtration. 

Double seals require some type of support system. The reason is simple. With two seals mounted onto the same shaft, one seal is the principal or primary seal and the other becomes the secondary or back up seal already installed. If the primary seal is performing its function and sealing the pumped liquid, the. secondary. seal would be running dry, overheat, burn and self-destruct. Then when the crucial moment comes, we won t have a second seal to assume the ftinctions, which was the original reason to consider a dual seal. 

One of the major funetions of the eombined eontrol-proteetion system is to perform the startup sequenee. This sequenee ensures that all subsystems of the gas turbine perform satisfaetorily, and the turbine does not heat too rapidly or overheat during startup. The exaet sequenee will vary for eaeh manufaeturer s engine, and the owner s and operator s manual should be eonsulted for details. 

The patient may suffer from shock, in proportion to the extent of the injury. Give small drinks and keep warm do not overheat. In all cases, speed of treatment is crucial to limit the effects of burns. Flowcharts which summarize the initial procedures for electrical, thermal and chemical burns respectively are shown in Figure 13.5. 

While great public protection is provided by these barriers, accidents can happen. Regardless of the cause of an accident, the core cannot overheat while in contact with liquid water. Furthermore it cannot be critical in the absence of water (because of the low enrichment of the fuel) thus, any accident involves a subcritical core that is heal by decaying radionuclides with inadequate cooling. Figure 8.1-1 shows the rate of heat evolution as a function of time after shutting down a 3,0(K3-MW reactor (Cohen, 1982). Even after an hour, th leat production is about 40 MW. 

In Europe, the gas safety controls must meet the requirements of CEN standards, including flame failure devices, solenoid control valve, pilot con trols, ignition and governor. Overheat-type thermostats and either a pressure switch or an airflow-proving device are fitted to ensure that the burner will cut off in the event of no air flowing through the heater, such as occurs with fan failure. 

For safe operation, the heater should have an overheat thermostat and either a pressure switch or airflow-proving device. This control device ensures that tlie burner will isolate in the event of restricted or no airflow through the heater. 

Fire tubes, especially in heater treaters, where they can be immersed in crude oil, can become a source of ignition if the tube develops a leak, allowing crude oil to come in direct contact with the flame. Fire tubes can also be a source of ignition if the burner controls fail and the tube overheats or if the pilot is out and the burner turns on when there is a combustible mixture in the tubes. 

Pumps can overheat if they run with the delivery valve almost closed. In one incident a pump designed to deliver 10 tons/hr was required to deliver only 14 ton/hr. The delivery valve was gagged, the pump got too hot, the casing joint sprang, and the contents leaked out and caught fire. 

Hot spot formation witliin tlie reactor can result in catalyst breakdown or physical deterioration of tlie reactor vessel." If tlie endothermic cyanide reaction has ceased (e.g., because of poor catalyst performance), the reactor is likely to overheat. Iron is a decomposition catalyst for hydrogen cyanide and ammonia under the conditions present in the cyanide reactor, and e. posed iron surfaces in the reactor or reactor feed system can result in uncontrolled decomposition, which could in turn lead to an accidaital release by overheating and overpressure. 

Uber-heben, v.t. pull over exempt, excuse. — V.T. overstrain be conceited, boast, -heizen, v.t. overheat superheat. tJberhitze,/. excess heat waste heat superheat. 

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