Heat transfer enhancement in tubes is widely applied in various industrial
processes. The traditional method of heat transfer enhancement is to insert
radial fins to expand the internal surface area and destroy the flow.
However, there is a flue gas corridor in the central area of the tube, and
the cost of expanding the inner fin is high. A centrally symmetrical bent
extruded aluminum fin was developed to enhance the heat transfer in the
tube. An experimental platform was constructed to test the performance of
inner finned tubes and explore the process of combining extruded aluminum
inner fin with steel tube. The bent extruded aluminum fins with two side
fins extending to the central axis possesses the best comprehensive heat
transfer performance. The heat transfer correlation of the optimal fin
structure is Nu= 0.8654Re0.4275 Pry0.3818 (Pry/Prw)-0.1004.
With low cost and strong heat transfer performance, the bent
extruded aluminum inner fin tube will gain wide applications in the
engineering field.
A wall-hung gas boiler was innovatively proposed and designed in this paper.
Water-cooling premixed combustion and enhanced condensation heat exchange
technology were adopted in the boiler. The extruded aluminum plate-fin
structure was adopted in the burner and condensing heat exchanger.
Experiment and numerical simulation studies were conducted on the flow,
combustion, and heat exchange characteristics of the boiler. The effect of
the fin structure, excess air coefficient, heat load, and water-cooling
temperature on the thermal performance of the boiler was analyzed. The
results showed that reliable ignition, stable combustion, uniform flame
distribution, and low pollutant emissions can be achieved in the wall-hung
gas boiler. Affected by burning intensity and internal flue gas
recirculation, when the burner plate-fin gap was 1.63 mm, the flame was the
shortest and the NOx emissions were the lowest. Under this fin condition,
ultra-high efficiency and ultra-low emissions can be achieved in the boiler
with a low excess air coefficient. When the excess air coefficient was 1.3,
the NOx emissions were less than 30 mg/m3 at the heat load of 4-14 kW, and
the thermal efficiency can reach up to 102.8% at the rated load of 14 kW.
Within the scope of the experiment, the NOx emissions changed little with
the water-cooling temperature. At the temperature of 333 K, there was still
a great NOx emission reduction effect.
The flue gas after wet desulfurization of coal-fired units still contains a
large amount of particulate matter. Flue gas condensing heat exchangers are
often used to further remove particulate matter. However, current research
focuses on the overall removal effect of the heat exchangers, but ignores
the difference of pollutant removal ability of the inner tube bundle along
the flue gas flow direction. This paper studied the correlation between
pollutant removal and operating parameters of condensation heat exchanger,
so as to make the removed amount of pollutants as large as possible. A field
experimental platform was built on a 3?350 MW supercritical circulating
fluidized bed coal-fired unit. The total amount of pollutants removed
between the 3rd and 6th rows of tube bundles from the inlet of the heat
exchanger was the largest. The removal of particulate matter near the outlet
of the heat exchanger was the smallest. The highest removal rate of
filterable particulate matter (FPM) reached 76 %. The proportion of
condensable particulate matter (CPM) in the total removal of particulate
matter reached around 90 %. The mass ratio of both H2SO4 and SO3 to the
removed CPM were more than 95 %.
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