Heat Transfer at a Long Electrically-Simulated Water Wall in a Circulating Fluidised Bed

In fouling, the accumulation of poorly conducting materials on the surface of process equipment, results in an increased resistance to heat transfer and hence reduces heat exchanger effectiveness. Under most conditions fouling is more severe during boiling heat transfer, due to the mechanisms of bubble formation and detachment. Thus, in order to enhance heat transfer and mitigate fouling in boiling processes, a new type of vapour-liquid-solid (three-phase) circulating fluidised bed boiling system has been designed, combining circulating fluidised bed technology with boiling heat transfer. Experiments are conducted in a glass mini-channel of square cross sectional area 21.5 mm × 11mm, height 1000mm, and fitted with an electrically heated cartridge heater rod of 8mm diameter × 730mm length. The set-up uses stainless steel balls to investigate the effect of particle properties (specifically particle size) on three-phase boiling heat transfer enhancement. Experimental results show that overall, compared with two-phase flow boiling, the presence of solid particles in the three-phase boiling system augments the heat transfer coefficient. Results are presented and discussed.

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Bed-To-Wall Heat Transfer in a Supercritical Circulating Fluidised Bed Boiler

Chemical and Process Engineering ◽

10.2478/cpe-2014-0015 ◽

2014 ◽

Vol 35 (2) ◽

pp. 191-204 ◽

Cited By ~ 19

Author(s):

Artur Błaszczuk ◽

Wojciech Nowak ◽

Szymon Jagodzik

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Pressure Measurements ◽

Fluidised Bed ◽

Cfb Boiler ◽

Suspension Density ◽

Bed Temperature ◽

Circulating Fluidised Bed ◽

The Heat Transfer Coefficient

Abstract The purpose of this work is to find a correlation for heat transfer to walls in a 1296 t/h supercritical circulating fluidised bed (CFB) boiler. The effect of bed-to-wall heat transfer coefficient in a long active heat transfer surface was discussed, excluding the radiation component. Experiments for four different unit loads (i.e. 100% MCR, 80% MCR, 60% MCR and 40% MCR) were conducted at a constant excess air ratio and high level of bed pressure (ca. 6 kPa) in each test run. The empirical correlation of the heat transfer coefficient in a large-scale CFB boiler was mainly determined by two key operating parameters, suspension density and bed temperature. Furthermore, data processing was used in order to develop empirical correlation ranges between 3.05 to 5.35 m·s-1 for gas superficial velocity, 0.25 to 0.51 for the ratio of the secondary to the primary air, 1028 to 1137K for bed temperature inside the furnace chamber of a commercial CFB boiler, and 1.20 to 553 kg·m-3 for suspension density. The suspension density was specified on the base of pressure measurements inside the boiler’s combustion chamber using pressure sensors. Pressure measurements were collected at the measuring ports situated on the front wall of the combustion chamber. The obtained correlation of the heat transfer coefficient is in agreement with the data obtained from typical industrial CFB boilers.

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