RU2067721C1 - Furnace-and-heat-exchanger assembly - Google Patents

Abstract

FIELD: gas combustion in hot-water flue boilers for heating liquids. SUBSTANCE: assembly has flue tube with burner unit and convective heating surfaces; flue tube length is 3.3-4 of its diameter; burner unit axis is shifted relative to flue tube axis through 1-1.5 of burner outlet diameter; first and second stages of fire tubes have different diameters: first stage along gas flow is made of tubes of greater diameter; quantity of tubes for first and second stages is chosen from definite condition given in description of invention. EFFECT: improved design. 1 dwg

Description

 The invention relates to a furnace technology and can be used for gas combustion in fire tube hot water boilers and heat engineering installations for heating liquids having a furnace, the wall temperature of which is lower than the boiling point of the liquid.

Known furnaces containing a central flame tube with a gas burner installed from one end and exhaust product from the other end through a system of smoke tubes [1]
The disadvantages of the known devices are the low efficiency of the use of gas fuel, the presence of chemical incompleteness due to the low temperature of the walls of the flame tube, the presence of a large number of nitrogen oxides in the combustion products, as well as the low efficiency of thermal work, which leads to an increase in the dimensions and mass of the heat exchanger.

 The essence of the invention lies in the fact that in a firebox-heat exchanger containing a heat pipe with a burner device, convective heating surfaces in the form of smoke pipes combined in two steps, the length of the heat pipe is 3.3-4 times its diameter, the axis of the burner device is offset relative to the axis a flame pipe 1-1.5 times the diameter of the outlet of the burner, and the first and second stages of smoke tubes are made of pipes of different diameters; the first stage along the gases is made of pipes of larger diameter, and the ratio of the number of pipes in ervoy and second stages is selected by equating the flue gas velocities of the first and second stages.

 The present invention will improve the efficiency of thermal work, improve heat transfer in the flame tube and smoke tubes, as well as reduce emissions of harmful gaseous substances into the air pool.

 The drawing shows a firebox-heat exchanger. The furnace contains a fire tube 1, the first stage of the smoke tubes 2, the second stage 3, which are enclosed in a common housing 4. Between the smoke tubes and the flame tube is a heated fluid in a volume of 5.

 The heat pipe 1 ends with box 6, and from the front it is closed by a heat-insulated cover 7, on which the burner 8 and the explosion valve 9 are fixed. The internal cavity of the cover 7 is insulated by packing 10. The heated fluid through the pipe 11 enters the annular volume 5, and is removed through the pipe 12. Cooled combustion products are removed through the flue pipe 13 from the box 14. To impart rigidity to the boxes 6 and 14, thrust pins 15 and 16 are used.

 The device operates as follows. The furnace-heat exchanger is filled with liquid through the nozzle 12. After the furnace is ventilated, the burner 8 is ignited in the established order and tuned to the gas combustion mode, which provides a brightly lit central rod torch, for which gas is supplied to the furnace by two streams in the center for luminosity and at the periphery of the air stream to create primary torch. These conditions correspond to a well-defined relationship between gas flows.

 Due to the fact that the walls of the flame tube have a temperature close to the temperature of the heated fluid, in existing fire tube furnaces, gas and air are intensively mixed in order to reduce carbon oxide emissions and combustion is carried out in a short torch with intense heat in its root part. This creates favorable conditions for the formation of nitrogen oxides.

 Despite this, due to the strong cooling of the combustion products, the flare has a chemical underburning (up to 1% CO by volume). On the other hand, the torch when burning the prepared mixture has a low emissivity, as a result of which the fraction of heat transferred to the walls of the flame tubes is sharply reduced.

 Due to the fact that there is unevenness in the height of the volume occupied by the liquid (the bottom is always colder), which under conditions of poor circulation leads to an increase in the heating time and, accordingly, to an additional gas flow rate, the axis of the burner installation are shifted downward by a distance of 1-1.5 burner diameters . At the same time, the layer of colder gases between the core of the flame and the lower wall of the pipe decreases, which also contributes to a better transfer of heat to the lower part of the flame tube.

где L длина шаровой трубы;
Д диаметр жаровой трубы
По мере остывания дымовых газов изменяются их теплофизические свойства: вязкость, плотность температура. Известно, что с падением температуры газов для поддержания необходимого теплообъема должна возрастать поверхность нагрева. Для этой цели для первой и второй ступени принимаются разные диаметры труб, причем диаметр труб первой ступени больше диаметра труб второй ступени, а скорости движения дыма в рабочих условиях в обеих ступенях равны. Это компенсирует снижение температурного напора развитием поверхности теплообмена при практически незначительном изменении коэффициента теплопередачи
Q = K•FΔt
например, при условии равенства скоростей движения дыма при рабочих условиях имеем:

где V_дг секундный расход дыма в нормальных условиях;
T₁ средняя температура дыма в первой ступени;
ω₁ площадь проходного сечения трубы первой ступени;
n₁ число труб в первой ступени;
T₂ средняя температура дыма второй ступени;
ω₂ площадь проходного сечения второй трубы;
n₂ число труб во второй ступени;
T_o=273 К.Under conditions of forced movement of combustion products, additional fluctuations of the combustion medium appear due to arising acoustic phenomena. Convective heat transfer proceeds most intensively due to induced acoustic phenomena if the diameter of the cylindrical heating surface with respect to its length is 0.25-0.3. Therefore, the length of the flame tube and its diameter must be performed in the ratio

where L is the length of the ball pipe;
D diameter of the flame tube
As the flue gases cool, their thermophysical properties change: viscosity, density, temperature. It is known that with a decrease in the temperature of the gases, the heating surface must increase to maintain the necessary heat volume. For this purpose, different diameters of the pipes are adopted for the first and second stages, the diameter of the pipes of the first stage being larger than the diameter of the pipes of the second stage, and the speeds of the smoke in the working conditions are equal in both stages. This compensates for the decrease in temperature pressure by the development of a heat transfer surface with an almost insignificant change in the heat transfer coefficient
Q = K • FΔt
for example, under the condition that the smoke velocities are equal under operating conditions, we have:

where V _dg second smoke flow under normal conditions;
T ₁ average smoke temperature in the first stage;
ω _{1 is} the flow area of the pipe of the first stage;
n _{1 is the} number of pipes in the first stage;
T _{2 the} average temperature of the smoke of the second stage;
ω _{2 is} the flow area of the second pipe;
n _{2 the} number of pipes in the second stage;
T _o = 273 K.

Так, если температура дымовых газов на выходе из жаровой трубы 900^oC, а после первой ступени 500^oC и температура уходящих газов после второй ступени 180^oC, то взяв для первой ступени трубу ⌀=2'', а для второй ступени o=1'' получим соотношение числа труб:

где n₁ число труб в первом ходе;
n₂ число труб во втором ходе.Then the ratio of the number of pipes is

So, if the temperature of the flue gases at the exit of the flame tube is 900 ^o C, and after the first stage 500 ^o C and the temperature of the exhaust gases after the second stage is 180 ^o C, then taking the pipe ⌀ = 2 '' for the first stage, and o for the second stage = 1 '' we get the ratio of the number of pipes:

where n _{1 is the} number of pipes in the first stroke;
n _{2 the} number of pipes in the second stroke.

One running meter of ⌀2 '' pipes has a side surface of 0.18 m ² , and pipes o1 '' 0.1 m ² , so with almost the same length of smoke pipes, the heating surface in the second stage will be approximately 40% larger
Bench tests of the furnace (without tail surfaces) with the developed gas combustion technology provide heat transfer due to radiation and convection in the amount of 70-75% of full power (i.e., 25-30% of the heat left by the nitrogen oxides remains on the tail surfaces) no more than 30-40 ppm without soot loss on cold surfaces and the practical absence of chemical underburning
(CO <0.012%).

Claims (1)

A heat exchanger furnace containing a heat pipe with a burner device and convective heating surfaces in the form of smoke tubes combined in two steps, characterized in that the length of the heat pipe is 3.3 4.0 and its diameter, the axis of the burner device is offset from the axis of the heat pipe by 1.0 1.5 of the diameter of the outlet of the burner, the first stage along the gas is made of pipes with a diameter greater than the diameter of the pipes of the second stage, and the number of pipes in the first and second stages is chosen from the condition

where n _{1 is the} number of pipes in the first stroke;
n _{2 is the} number of pipes in the second stroke;
W _{1 the} area of the cross section of the pipe of the first stage;
W ₂ the cross-sectional area of the pipe of the second stage;

average smoke temperature in the first stage;

average smoke temperature in the second stage;