Relationship between submicron ash aerosol characteristics and ash deposit compositions and formation rates during air- and oxy-coal combustion

Abstract

Deposition of ash on heat transfer surfaces is a major factor in determining boiler performance. Deposits so formed consist of tightly bound "inside" deposits close to the heat transfer surface and loosely bound "outer" deposits that are easily dislodged. This paper describes research focusing on both the composition of inner and outer deposits, and also on the rate of deposition of the inner deposit layer. Presented are selected results from a wide ranging study concerned with mechanisms governing the formation of fouling deposits during air and oxy-coal combustion in a 100 kW test rig. The primary focus is on establishing a relationship between the size segregated composition of the coal ash aerosol, and the spatially resolved composition of the deposit layer, and this is accomplished by experimentation that addresses the impacts of conversion from air-firing to oxy-firing. Experiments involved three different coals (Powder River Basin or PRB, Illinois and a 60/40 Blend of Illinois and PRB), each burned under air-and oxy-coal combustion conditions. Data for the PRB coal suggested that changes in the composition of the inner deposit layer were caused by variations in sub-micron aerosol compositions, but that these occurred only when there were significant changes in flame temperature. An increase of the latter also led to increasing submicron particle concentrations and deposition rates. Although both aerosol and deposit compositions depended greatly on coal compositions, rates of deposition of the inner deposit layer correlate linearly with the concentration of the submicron aerosol in the flue gas, for all three coals, and under all air-and oxy-firing conditions for which data are available. This result suggests the amount rather than the (variable) composition of the submicron aerosol is important. There was no correlation between deposition rates and total ash concentrations.

Collection of Particles on Cold Surfaces: A Review

“…The fouling of heat exchangers can cause the deterioration of heat transfer and the blockage of the flue gas channel, thereby harming the energy recovery and safe operation, which is given great emphasis. The fouling is caused by many factors, such as fuel type, − elemental composition, − and combustion conditions. − In addition to these factors, thermophoresis also plays a role in the fouling…”

Kinetic Simulation of Fine Particulate Matter Evolution and Deposition in a 25 kW Pulverized Coal Combustor

“…The kinetic approach is also applicable to ash deposition; albeit, the deposited mass is dominated by inertial impaction of bulk ash . Indeed, the deposition propensity is not solely determined by the bulk ash but is also affected by the ultrafine PM formation ability, implying enhanced surface stickiness via condensation and scavenging in the boundary layer. ,,− Considering the possible gas-to-particle route of condensable mineral vapor, it is desirable to quantify the intensity of each pathway and determine a more accurate condensation deposition rate. An analogy is the chemical vapor deposition (CVD), where theories have been explored for condensing rates under a variety of conditions. , However, coagulation was not considered.…”

Particulate Matter Formation and Alkali and Alkaline Earth Metal Partitioning in a Pressurized Oxy-fuel Fluidized-Bed Combustor

“…The advantage of this technology has been validated by many researchers through both simulation methods , and experimental studies. − A variety of research topics have been studied for atmospheric pressure oxy-combustion, such as (1) operating conditions, ignition, and flame stability, − (2) heat transfer, emissivity, and thermal capacity of exhaust gases, − (3) gaseous emissions and effects on pollution formation [NO x , SO 2 , and particulate matter (PM)], − and (4) ash deposition and slagging and fouling on the wall and on the heat transfer surface. − However, to the best knowledge of the authors, the PM formation from a pressurized oxy-fuel combustion process has not yet been reported. Studies concerning PM formation are necessary because it causes ash deposition on the heat transfer surface and may cause serious problems that threaten safety operation of the power plant. , Therefore, the target of this paper is to shed light on PM formation in pressurized oxy-fuel combustion.…”

“…Studies concerning PM formation are necessary because it causes ash deposition on the heat transfer surface and may cause serious problems that threaten safety operation of the power plant. 24,25 Therefore, the target of this paper is to shed light on PM formation in pressurized oxy-fuel combustion.…”