| OCR Text |
Show size, and degree of agitation. Furnace temperature directly affects the rate of tire combustion. For most organic reactions, the rate of reaction can be doubled by a temperature increase of 10 degrees centigrade. However, high-temperature combustion has its limitations; an excessively high combustion temperature may lead to the formation of nitrogen oxides. Oxygen levels in the combustion zone are very important, and were referred to in the foregoing discussion of excess air. The size of scrap tire particles is also of importance; it takes a finite length of time to burn through any substance. The minimum dimension of scrap tires is the wall thickness, and it does not take long to burn through a quarter-inch thick piece of scrap tire. It is necessary to reduce the tire size since large pieces have been reported to cause material handling problems in the boiler feed system. In order to make scrap tires compatible with coal-fired boilers, it has been necessary to chop down the scrap tire to a size which fits the boiler and its feeding system; pulverized coal-fired boilers require finely divided scrap tire pieces while stoker fired coal boilers can accomodate large pieces. In one successful fluidized bed combustion test, the size of the scrap tire pieces used was on the order of 6 by 8 inches(10) which was required for compatibility with the solid handling system. Agitation promotes the rate of the reactions which are mandatory for clean and complete combustion by ensuring the transfer of fuels and oxygen to the combustion zone. Agitation is also needed for the removal of combustion products from the combustion zone. Therefore, all incinerators designed for tire combustion must feature good agitation and, as mentioned previously, vigorous mixing is one of the inherent features of fluidized-bed combustion. Uniform Feed A uniform and controllable feed rate is an important capability, particularly when considering charging scrap tires to a tire incinerator. Regardless of the form in which it is fed, tire rubber is a resilient material. Under stress, the rubber will become deformed to accommodat the stress applied and return to its original form when the stress is removed. In solid handling, this resilience can lead to blocking of feed lines and hoppers. Solid handling of coal or hog fuel with some moisture is difficult enough; adding a resilient material like rubber will make matters worse(ll). Once in the incinerator chamber, an unplanned high concentration of tire rubber can lead to two undesirabl conditions. The first potential result of excessive fuel availability is the temperature excursion phenomenon. Temperature excursions can damage the incinerator, and/or cause clinkers to form. The second condition is the development of localized reducing zones, which can cause severe corrosion damage, losses in combustion efficiency, and/ or environmental compliance problems. 11-16 |
