| At present, coal is the main source of energy in China. However, coal usage in combustion process of industrial systems generates a lot of nitrogen oxides(NOx) and other pollutants. Therefore, to control the impact of NOx on environment, the government of China has formulated strict emission standards and regulations to limit the use of coal in these systems. Similarly, China is a large agricultural country. The huge amount of agricultural waste generated are normally incinerated to provide energy and this also contributes to environmental pollution.Worldwide, biomass fuel use has "zero carbon emissions" thus an ideal alternative renewable fuel. However, biomass fuel characteristics such as low calorific value and high water content render direct incineration technology both difficult and uneconomical in utilizing biomass. Consequently, the advent of biomass gasification technology is gradually increasing to edge out incineration technology. Gasification converts low calorific, high moisture content biomass fuel into a combustible gas with excellent combustion characteristics.In China, corn cob is a typical agricultural waste used for producing furfural. Furfural production entails use of acid hydrolysis process to remove the hemicellulose component in corn cob. The resultant residue referred as furfural residue(FR) is composed of cellulose and lignin components. These makes FR a high calorific value fuel but with high moisture content. In this study, the use of FR in gasification systems at Hebei province and Songjiang, Shanghai were investigated. The system emits high NOx concentration of about 800 mg / Nm3.A series of experiments were therefore designed to aid in understanding formation of NOx from gasification and combustion of FR. This would also help reduce and/or minimize NOx emitted in the investigated systems.A TGA-FTIR set-up investigated release of nitrogen containing gases in FR: NH3 and HCN. FR pyrolysis released HCN as main nitrogen containing gas at pyrolysis peak temperature of about 350 ℃. A summarized reaction pathway of NOx formation mechanism from FR fuel-N up to NOx was developed.Then, SJTU built bench-scale updraft gasifier coupled to flow reactor investigated release of tarN. The tars were collected as per IEA Tar collection protocol and analyzed in GC-MS(tars collected from Hebei were analyzed using the same procedure). Experiments were carried out under different conditions and it was found that tar-N in FR is mainly in form of pyridine& pyrrole ring structure(cyclic compounds). These two compounds undergo subsequent conversion into HCN and thereafter oxidized to form NOx.Finally, the entire gasification and combustion systems at Hebei and Songjiang were investigated. The investigation aimed to understand evolution characteristics of produced gases in gasifier and amount of NOx emitted. It was found that air distribution at the bottom of furnace grate was not uniform. Much more air was supplied in middle section of gasifier thereby reducing the pyrolysis and gasification zones inside the gasifier while broadening the combustion zone. The excess O2 led to high producer gas temperatures, reduced calorific value of produced gases and consequently, high NOx formation. Another aspect was the location of primary air inlet very close to the secondary air inlet in the combustion chamber. This further enhanced NOx formation as more O2 molecules were available to form NO. Based on these findings, this study proposed modification of gasifier furnace grate so as to ensure uniform supply of air across the grate. This would improve calorific value of producer gas, optimize O2 combustion thus effectively reduce NOx emissions. |
