OCR Text |
Show A 10-20% caustic solution is injected into the quench sump and into the recirculation water flow of the MX scrubber. The initial and largest percentage of the neutralization occurs in the quench elbow and sump. For that reason the majority of the caustic must be injected at this location. The pH is controlled with Beckman instrumentation operating in slip streams from the recirculation water loops. The injection of caustic directly into the quench system tank from a line controller by a solenoid valve located 25 feet upstream caused large swings in the pH (3-10.5) of the quench sump. The long injection line between the valve and the quench sump causes an initial delay in caustic injection after the valve is activated. The pH continues to decrease during this delay. After the valve is closed the line causes an uncontrolled trail-off of injection. The pH continues to rise during the trail-off. The swings could be controlled for anyone condition of chlorine loading by altering injection timers. However, when chlorine loading changed sharply, the timing required manual changes. Also, under heavy loadings the swings were still excessive. Placing the caustic injection point into the recirculation system instead of directly into the tank greatly reduced the uncontrolled swings. However, after prolonged operation the quench nozzles began to plug with dried caustic. A final solution will require moving the control solenoid adjacent to the quench sump to prevent the control delays. Also, an enlargement of the quench sump would reduce this problem. o WEP Problems It was difficult to establish the required high voltage during initial start-up of the precipitator. The electrodes had to be accurately positioned within each box cell before voltage could be sustained without breakdown. After a hot cycle, the WEP again failed to hold high voltage because of electrode shorting. The electrodes were again adjusted and reinforcing angles were added to the rod suspension system. The unit performed normally for 20 days when all three circuit boards failed in the control panel catastrophically. No conclusive reason could be established for the failure, but metal chips from the initial cabinet assembly were thought to be the cause. After replacing the boards and turning off the fogging sprays, the unit has continued satisfactory operation. It has been necessary to perform a wash cycle daily or more often in heavy feed conditions to maintain high voltage. This wash cycle removes particulate buildup from the surfaces of box cells. o Human Error As mentioned kiln bearings incomplete. stopped the burners and earlier, during one of the trial burn tests the had failed. The failure caused the test to be The system was manually shutdown. This action waste feed, and turned off the kiln and see the induced draft (10) fan. The 10 fan was |