Cement sector is the third largest industrial source of pollution, emitting more than 500,000 tons per year of sulfur dioxide, nitrogen oxide, and carbon monoxide. Nitrogen oxide (NOx) is the third most important greenhouse gas after carbon dioxide and methane, and contributes about 6% to the greenhouse effect. Nitrogen oxide is a minor component of the atmosphere, and it is a thousand times less than carbon dioxide (CO2). Nevertheless, it is much more potent than CO2 and methane, owing to its long stay in the atmosphere of approximately 120 yr and the high global warming potential (GWP) of 298 times that of CO2.
In the cement manufacturing, conditions favorable for formation of NOx (Nitrogen Oxide) are reached routinely because of high process temperatures. Essentially all NOx emissions associated with cement manufacturing are generated in cement kilns. In cement kilns, NOX emissions are formed during fuel combustion by two primary mechanisms:
• Oxidation of molecular nitrogen present in the combustion air, which is termed “thermal NOx” formation, and
• Oxidation of nitrogen compounds present in the fuel, which is termed “fuel NOx” formation.
Often, the raw material feed to the kiln contains a significant amount of nitrogen compounds which may lead to feed NOx formation similar to fuel NOx formation. Because of the high temperatures involved in the burning or clinker formation step, thermal NOx formation provides the dominant mechanism for NOx formation in cement manufacturing.
There are four different types of cement kilns used in the industry: wet kilns, long dry kilns, kilns with a preheater, and kilns with a preheater/precalciner. All cement kiln systems contain a rotary kiln. The wet, long dry, and most preheater kilns have only one fuel combustion zone; whereas, the newer preheater/precalciner kilns and preheater kilns with a riser duct have two fuel combustion zones. Some precalciner kilns have a third combustion zone. Since the typical temperatures in the combustion zones are different, the factors affecting NOx formation are also somewhat different in the different kiln types. In the primary combustion zone at the hot end of a kiln, the high temperatures lead predominantly to thermal NOx formation; whereas, in secondary combustion zones lower gas-phase temperatures suppress thermal NOx formation.
In addition to the specific NOx formation mechanisms, the energy efficiency of the cement making process is also important as it determines the amount of heat input needed to produce a unit quantity of cement. And, a high thermal efficiency would lead to less consumption of heat and fuel, and should produce lower NOx emissions per ton of clinker, the product of the rotary kiln.
Quantum IR Technologies, a technology company for cement manufacturing solutions based in Utah, USA, offer thermal management solutions with predictive analysis for maintenance, captures real-time performance data, and optimizing useful refractory life. It enables customer to see the global view of all plant operations, and have dedicated QIR engineers monitor customer operations 24/7.
QIR Technology also beneficial to improve ROI of client’s company, as the technology itself focusing on kiln refractory optimization, which can help to reduces maintenance costs, extends time between maintenance shutdowns, and increase kiln revenue production days and profits.
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