Study on NO Emission in the Oxy-Fuel Combustion of Co-Firing Coal and Biomass in a Bubbling Fluidized Bed Combustor

Abstract

Combustion experiments were performed in a bubbling bed combustor to explore the effects of various oxygen concentrations (21% to 40%), temperatures (850 °C to 950 °C), and mixing ratios (0% to 30%) on the formation of NO gas. In order to correspond to different combustion stages, the generated NO were distinguished as volatile-NO and coke-NO, respectively, and the total amount and the conversion rate of NO were analyzed. The results indicated that NO comes mainly from fixed carbon combustion, and an increased oxygen concentration in the environment could produce more NO during the combustion process, regardless of the blending of biomass. The temperature increase promoted the conversion of nitrogen in the anthracite and accelerated the release of volatiles from the pine powder. During mixed combustion with increasing temperature, the volatiles formed had diluted the environmental oxygen concentration, which led to suppressed NO emissions. In addition, increasing the blending ratio also resulted in decreased NO emissions due to the large amount of intermediates released by the burning pine powder that induced a deoxidation effect on the NO emission.

Part-Load Operation of a Novel Calcium Looping System for Flexible CO2 Capture in Coal-Fired Power Plants

“…Hence, the combustion circumstance tends to be more oxidative to accelerate fuel-N conversion into NO x . 42,43 The concentration of SO 2 in the calciner exhaust gas is significantly reduced under typical operating conditions prevailing in CaL applications (see Figure 9b). The favorable oxy-fuel combustion temperatures, together with the continuous supply of fresh limestone, constitute a favorable framework for efficient flue gas desulfurization.…”

“…As indicated by different authors, it is presumable that when the combustion agent’s oxygen concentration is increased, volatile matters and char are more likely to be oxidized. Hence, the combustion circumstance tends to be more oxidative to accelerate fuel-N conversion into NO x . , …”

Pollutant Emissions during Oxy-Fuel Combustion of Biomass in a Bench Scale CFB Combustor

“…Pu and co-workers [17] studied the influence of oxygen concentration in the oxidizing medium (O 2 /CO 2 mixture with O 2 concentrations in the range 21-40%) on NO emissions in a lab-scale bubbling fluidized-bed combustor at 850-950 • C. Combustion tests were carried out with 2 g samples of anthracite and anthracite blended with 10-30%wt. of pine powder.…”

Oxy-Fuel Combustion of Hard Coal, Wheat Straw, and Solid Recovered Fuel in a 200 kWth Calcium Looping CFB Calciner

“…According to the NDIR results, the specific NO x levels ranged from 359 mg/MJ th during combustion with 100% hard coal down to 203 mg/MJ th with stand-alone biomass firing. As the fuel-NO x formation mechanism is the dominating route under CFB conditions [34], this decrease can be ascribed to the reduced nitrogen content of the wheat straw (1.0 wt% waf ) when compared to the fuel-N contained in the hard coal (1.6 wt% waf ). This explanation is in line with the conclusions drawn by Riaza et al, who evaluated the NO emissions of blends of two distinct coal types with 10 wt% and 20 wt% olive waste under oxy-fuel conditions [35].…”

“…More precisely, an increase in the inlet oxygen volume fraction of about four percentage points caused a marginal increase in the specific NO x NDIR emissions from 310 mg/MJ th up to 335 mg/MJ th . Providing a uniform temperature distribution along the reactor, the promoting effect of the inlet oxygen on NO x emissions can be typically attributed to (i) the increased oxygen concentration intensifying the oxidation of the nitrogen components in the fuel [21,34], and (ii) the reduction in the flue gas recirculation rate causing the reducing zone of the calciner to be decreased [21]. However, within the relatively narrow investigated oxy-fuel range, it cannot be excluded that such deviations were, at least, partly attributable to fuel-N variations other than the aforementioned two reasons.…”