Experimental Investigation On NO_x Emission Characteristics Of The Sludge-Coal Combined Fuel

As a kind of harmless, minimizing, resourceful, volume reducing sludge treatment, sludge combustion was widely favored. Co-combustion of sludge and coal is an effective method for sludge disposal. Because of the high ash content of sludge,containing toxic and harmful substances, producing secondary pollution for emission of nitrogen oxides, polycyclic aromatic hydrocarbons, etc during drying and combustion, co-combustion of sludge and coal is still under research. Related research mostly concentrated on the combustion and emission characteristics of pollutants, while the studies on emissions reduction during co-combustion of sludge and coal are few. In this study, we provided a new briquette fuel(SC) which was produced by the mixture of coal fines, sewage sludge, lignin, tannin and elemental silicon, investigated effects of addictives on the compressive strength and emissions of NO_x(NO and NO2) of mixture fuel of sludge and coal(SC0) and analysized the effects of different heating rates, air flow rates, combustion temperatures on emissions of NO_x of SC.The proximate and ultimate analysis, thermogravimetric analysis, calorific values of sewage sludge, coal and their mixtures were investigated. The results showed that sewage sludge mixed with coal fines increased the content of fixed carbon and calorific value of the fuel and made the combustion more durable;combustion of sludge is mainly composed of separation of free water and bound water, evolution and combustion of volatile matter, combustion of fixed carbon,while combustion of coal is mainly the combustion process of fixed carbon; and the TG-DTG curve of sludge and coal was different, and that of their mixture was between the two and the combustion process of the mixture components was relatively independent.The self-reconstructive WDW-10 electronic universal testing machine was used to prepare fuel granule of sludge and coal with an array of recipes of lignin, tannin,elemental silicon. And the Meyer hardness of sample granule was measured to assess the compressive strength. The results showed that lignin and tannin were effective binders,but silicon had some negative effect on the binding effect of the lignin and tannin; the Meyer hardness of sample granule increased with the adding of lignin ratio and increased with the adding of tannin first and then decreased; compared tothe characteristics of briquette fuel produced only by the mixture of coal and sewage sludge(the ratio of coal to sewage sludge was the same as that of SC), the Meyer hardness of SC was 12.6% higher than that of SC0.Lastly, the combustion experiments of fuel sample were conducted with a mono pipe high temperature carbon furnace and X-ray photoelectron spectroscopy of fuel sample and its residua were carried out to investigate the action mechanism of additive. The results showed the NO_x emissions of SC were 27.83% less than that of SC0 under the same combustion conditions; the XPS results suggested that the possible mechanism for the reduction of NO_x emissions was that nitrogen and silicon in SC formed the oxides of silicon and nitrogen at high temperatures; within the experiment condition, the NO_x emissions of SC decreased with the adding of heating rate and increased with the rise of air flow rate. When the temperature was below1000°C, the emissions of NO_x increased with the elevated temperature, however,further temperature extension will result in a decreasing in emissions of NO_x.